--- /dev/null
- The format of a hist trigger is as follows::
-
- hist:keys=<field1[,field2,...]>[:values=<field1[,field2,...]>]
- [:sort=<field1[,field2,...]>][:size=#entries][:pause][:continue]
- [:clear][:name=histname1] [if <filter>]
-
- When a matching event is hit, an entry is added to a hash table
- using the key(s) and value(s) named. Keys and values correspond to
- fields in the event's format description. Values must correspond to
- numeric fields - on an event hit, the value(s) will be added to a
- sum kept for that field. The special string 'hitcount' can be used
- in place of an explicit value field - this is simply a count of
- event hits. If 'values' isn't specified, an implicit 'hitcount'
- value will be automatically created and used as the only value.
- Keys can be any field, or the special string 'stacktrace', which
- will use the event's kernel stacktrace as the key. The keywords
- 'keys' or 'key' can be used to specify keys, and the keywords
- 'values', 'vals', or 'val' can be used to specify values. Compound
- keys consisting of up to two fields can be specified by the 'keys'
- keyword. Hashing a compound key produces a unique entry in the
- table for each unique combination of component keys, and can be
- useful for providing more fine-grained summaries of event data.
- Additionally, sort keys consisting of up to two fields can be
- specified by the 'sort' keyword. If more than one field is
- specified, the result will be a 'sort within a sort': the first key
- is taken to be the primary sort key and the second the secondary
- key. If a hist trigger is given a name using the 'name' parameter,
- its histogram data will be shared with other triggers of the same
- name, and trigger hits will update this common data. Only triggers
- with 'compatible' fields can be combined in this way; triggers are
- 'compatible' if the fields named in the trigger share the same
- number and type of fields and those fields also have the same names.
- Note that any two events always share the compatible 'hitcount' and
- 'stacktrace' fields and can therefore be combined using those
- fields, however pointless that may be.
-
- 'hist' triggers add a 'hist' file to each event's subdirectory.
- Reading the 'hist' file for the event will dump the hash table in
- its entirety to stdout. If there are multiple hist triggers
- attached to an event, there will be a table for each trigger in the
- output. The table displayed for a named trigger will be the same as
- any other instance having the same name. Each printed hash table
- entry is a simple list of the keys and values comprising the entry;
- keys are printed first and are delineated by curly braces, and are
- followed by the set of value fields for the entry. By default,
- numeric fields are displayed as base-10 integers. This can be
- modified by appending any of the following modifiers to the field
- name:
-
- - .hex display a number as a hex value
- - .sym display an address as a symbol
- - .sym-offset display an address as a symbol and offset
- - .syscall display a syscall id as a system call name
- - .execname display a common_pid as a program name
-
- Note that in general the semantics of a given field aren't
- interpreted when applying a modifier to it, but there are some
- restrictions to be aware of in this regard:
-
- - only the 'hex' modifier can be used for values (because values
- are essentially sums, and the other modifiers don't make sense
- in that context).
- - the 'execname' modifier can only be used on a 'common_pid'. The
- reason for this is that the execname is simply the 'comm' value
- saved for the 'current' process when an event was triggered,
- which is the same as the common_pid value saved by the event
- tracing code. Trying to apply that comm value to other pid
- values wouldn't be correct, and typically events that care save
- pid-specific comm fields in the event itself.
-
- A typical usage scenario would be the following to enable a hist
- trigger, read its current contents, and then turn it off::
-
- # echo 'hist:keys=skbaddr.hex:vals=len' > \
- /sys/kernel/debug/tracing/events/net/netif_rx/trigger
-
- # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
-
- # echo '!hist:keys=skbaddr.hex:vals=len' > \
- /sys/kernel/debug/tracing/events/net/netif_rx/trigger
-
- The trigger file itself can be read to show the details of the
- currently attached hist trigger. This information is also displayed
- at the top of the 'hist' file when read.
-
- By default, the size of the hash table is 2048 entries. The 'size'
- parameter can be used to specify more or fewer than that. The units
- are in terms of hashtable entries - if a run uses more entries than
- specified, the results will show the number of 'drops', the number
- of hits that were ignored. The size should be a power of 2 between
- 128 and 131072 (any non- power-of-2 number specified will be rounded
- up).
-
- The 'sort' parameter can be used to specify a value field to sort
- on. The default if unspecified is 'hitcount' and the default sort
- order is 'ascending'. To sort in the opposite direction, append
- .descending' to the sort key.
-
- The 'pause' parameter can be used to pause an existing hist trigger
- or to start a hist trigger but not log any events until told to do
- so. 'continue' or 'cont' can be used to start or restart a paused
- hist trigger.
-
- The 'clear' parameter will clear the contents of a running hist
- trigger and leave its current paused/active state.
-
- Note that the 'pause', 'cont', and 'clear' parameters should be
- applied using 'append' shell operator ('>>') if applied to an
- existing trigger, rather than via the '>' operator, which will cause
- the trigger to be removed through truncation.
-
- - enable_hist/disable_hist
-
- The enable_hist and disable_hist triggers can be used to have one
- event conditionally start and stop another event's already-attached
- hist trigger. Any number of enable_hist and disable_hist triggers
- can be attached to a given event, allowing that event to kick off
- and stop aggregations on a host of other events.
-
- The format is very similar to the enable/disable_event triggers::
-
- enable_hist:<system>:<event>[:count]
- disable_hist:<system>:<event>[:count]
-
- Instead of enabling or disabling the tracing of the target event
- into the trace buffer as the enable/disable_event triggers do, the
- enable/disable_hist triggers enable or disable the aggregation of
- the target event into a hash table.
-
- A typical usage scenario for the enable_hist/disable_hist triggers
- would be to first set up a paused hist trigger on some event,
- followed by an enable_hist/disable_hist pair that turns the hist
- aggregation on and off when conditions of interest are hit::
-
- # echo 'hist:keys=skbaddr.hex:vals=len:pause' > \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-
- # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
-
- # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
-
- The above sets up an initially paused hist trigger which is unpaused
- and starts aggregating events when a given program is executed, and
- which stops aggregating when the process exits and the hist trigger
- is paused again.
-
- The examples below provide a more concrete illustration of the
- concepts and typical usage patterns discussed above.
-
-
- 6.2 'hist' trigger examples
- ---------------------------
-
- The first set of examples creates aggregations using the kmalloc
- event. The fields that can be used for the hist trigger are listed
- in the kmalloc event's format file::
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/format
- name: kmalloc
- ID: 374
- format:
- field:unsigned short common_type; offset:0; size:2; signed:0;
- field:unsigned char common_flags; offset:2; size:1; signed:0;
- field:unsigned char common_preempt_count; offset:3; size:1; signed:0;
- field:int common_pid; offset:4; size:4; signed:1;
-
- field:unsigned long call_site; offset:8; size:8; signed:0;
- field:const void * ptr; offset:16; size:8; signed:0;
- field:size_t bytes_req; offset:24; size:8; signed:0;
- field:size_t bytes_alloc; offset:32; size:8; signed:0;
- field:gfp_t gfp_flags; offset:40; size:4; signed:0;
-
- We'll start by creating a hist trigger that generates a simple table
- that lists the total number of bytes requested for each function in
- the kernel that made one or more calls to kmalloc::
-
- # echo 'hist:key=call_site:val=bytes_req' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- This tells the tracing system to create a 'hist' trigger using the
- call_site field of the kmalloc event as the key for the table, which
- just means that each unique call_site address will have an entry
- created for it in the table. The 'val=bytes_req' parameter tells
- the hist trigger that for each unique entry (call_site) in the
- table, it should keep a running total of the number of bytes
- requested by that call_site.
-
- We'll let it run for awhile and then dump the contents of the 'hist'
- file in the kmalloc event's subdirectory (for readability, a number
- of entries have been omitted)::
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
- # trigger info: hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
-
- { call_site: 18446744072106379007 } hitcount: 1 bytes_req: 176
- { call_site: 18446744071579557049 } hitcount: 1 bytes_req: 1024
- { call_site: 18446744071580608289 } hitcount: 1 bytes_req: 16384
- { call_site: 18446744071581827654 } hitcount: 1 bytes_req: 24
- { call_site: 18446744071580700980 } hitcount: 1 bytes_req: 8
- { call_site: 18446744071579359876 } hitcount: 1 bytes_req: 152
- { call_site: 18446744071580795365 } hitcount: 3 bytes_req: 144
- { call_site: 18446744071581303129 } hitcount: 3 bytes_req: 144
- { call_site: 18446744071580713234 } hitcount: 4 bytes_req: 2560
- { call_site: 18446744071580933750 } hitcount: 4 bytes_req: 736
- .
- .
- .
- { call_site: 18446744072106047046 } hitcount: 69 bytes_req: 5576
- { call_site: 18446744071582116407 } hitcount: 73 bytes_req: 2336
- { call_site: 18446744072106054684 } hitcount: 136 bytes_req: 140504
- { call_site: 18446744072106224230 } hitcount: 136 bytes_req: 19584
- { call_site: 18446744072106078074 } hitcount: 153 bytes_req: 2448
- { call_site: 18446744072106062406 } hitcount: 153 bytes_req: 36720
- { call_site: 18446744071582507929 } hitcount: 153 bytes_req: 37088
- { call_site: 18446744072102520590 } hitcount: 273 bytes_req: 10920
- { call_site: 18446744071582143559 } hitcount: 358 bytes_req: 716
- { call_site: 18446744072106465852 } hitcount: 417 bytes_req: 56712
- { call_site: 18446744072102523378 } hitcount: 485 bytes_req: 27160
- { call_site: 18446744072099568646 } hitcount: 1676 bytes_req: 33520
-
- Totals:
- Hits: 4610
- Entries: 45
- Dropped: 0
-
- The output displays a line for each entry, beginning with the key
- specified in the trigger, followed by the value(s) also specified in
- the trigger. At the beginning of the output is a line that displays
- the trigger info, which can also be displayed by reading the
- 'trigger' file::
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
- hist:keys=call_site:vals=bytes_req:sort=hitcount:size=2048 [active]
-
- At the end of the output are a few lines that display the overall
- totals for the run. The 'Hits' field shows the total number of
- times the event trigger was hit, the 'Entries' field shows the total
- number of used entries in the hash table, and the 'Dropped' field
- shows the number of hits that were dropped because the number of
- used entries for the run exceeded the maximum number of entries
- allowed for the table (normally 0, but if not a hint that you may
- want to increase the size of the table using the 'size' parameter).
-
- Notice in the above output that there's an extra field, 'hitcount',
- which wasn't specified in the trigger. Also notice that in the
- trigger info output, there's a parameter, 'sort=hitcount', which
- wasn't specified in the trigger either. The reason for that is that
- every trigger implicitly keeps a count of the total number of hits
- attributed to a given entry, called the 'hitcount'. That hitcount
- information is explicitly displayed in the output, and in the
- absence of a user-specified sort parameter, is used as the default
- sort field.
-
- The value 'hitcount' can be used in place of an explicit value in
- the 'values' parameter if you don't really need to have any
- particular field summed and are mainly interested in hit
- frequencies.
-
- To turn the hist trigger off, simply call up the trigger in the
- command history and re-execute it with a '!' prepended::
-
- # echo '!hist:key=call_site:val=bytes_req' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- Finally, notice that the call_site as displayed in the output above
- isn't really very useful. It's an address, but normally addresses
- are displayed in hex. To have a numeric field displayed as a hex
- value, simply append '.hex' to the field name in the trigger::
-
- # echo 'hist:key=call_site.hex:val=bytes_req' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
- # trigger info: hist:keys=call_site.hex:vals=bytes_req:sort=hitcount:size=2048 [active]
-
- { call_site: ffffffffa026b291 } hitcount: 1 bytes_req: 433
- { call_site: ffffffffa07186ff } hitcount: 1 bytes_req: 176
- { call_site: ffffffff811ae721 } hitcount: 1 bytes_req: 16384
- { call_site: ffffffff811c5134 } hitcount: 1 bytes_req: 8
- { call_site: ffffffffa04a9ebb } hitcount: 1 bytes_req: 511
- { call_site: ffffffff8122e0a6 } hitcount: 1 bytes_req: 12
- { call_site: ffffffff8107da84 } hitcount: 1 bytes_req: 152
- { call_site: ffffffff812d8246 } hitcount: 1 bytes_req: 24
- { call_site: ffffffff811dc1e5 } hitcount: 3 bytes_req: 144
- { call_site: ffffffffa02515e8 } hitcount: 3 bytes_req: 648
- { call_site: ffffffff81258159 } hitcount: 3 bytes_req: 144
- { call_site: ffffffff811c80f4 } hitcount: 4 bytes_req: 544
- .
- .
- .
- { call_site: ffffffffa06c7646 } hitcount: 106 bytes_req: 8024
- { call_site: ffffffffa06cb246 } hitcount: 132 bytes_req: 31680
- { call_site: ffffffffa06cef7a } hitcount: 132 bytes_req: 2112
- { call_site: ffffffff8137e399 } hitcount: 132 bytes_req: 23232
- { call_site: ffffffffa06c941c } hitcount: 185 bytes_req: 171360
- { call_site: ffffffffa06f2a66 } hitcount: 185 bytes_req: 26640
- { call_site: ffffffffa036a70e } hitcount: 265 bytes_req: 10600
- { call_site: ffffffff81325447 } hitcount: 292 bytes_req: 584
- { call_site: ffffffffa072da3c } hitcount: 446 bytes_req: 60656
- { call_site: ffffffffa036b1f2 } hitcount: 526 bytes_req: 29456
- { call_site: ffffffffa0099c06 } hitcount: 1780 bytes_req: 35600
-
- Totals:
- Hits: 4775
- Entries: 46
- Dropped: 0
-
- Even that's only marginally more useful - while hex values do look
- more like addresses, what users are typically more interested in
- when looking at text addresses are the corresponding symbols
- instead. To have an address displayed as symbolic value instead,
- simply append '.sym' or '.sym-offset' to the field name in the
- trigger::
-
- # echo 'hist:key=call_site.sym:val=bytes_req' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
- # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=hitcount:size=2048 [active]
-
- { call_site: [ffffffff810adcb9] syslog_print_all } hitcount: 1 bytes_req: 1024
- { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8
- { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7
- { call_site: [ffffffff8154acbe] usb_alloc_urb } hitcount: 1 bytes_req: 192
- { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7
- { call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40
- { call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128
- { call_site: [ffffffff811febd5] fsnotify_alloc_group } hitcount: 2 bytes_req: 528
- { call_site: [ffffffff81440f58] __tty_buffer_request_room } hitcount: 2 bytes_req: 2624
- { call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 2 bytes_req: 96
- { call_site: [ffffffffa05e19af] ieee80211_start_tx_ba_session [mac80211] } hitcount: 2 bytes_req: 464
- { call_site: [ffffffff81672406] tcp_get_metrics } hitcount: 2 bytes_req: 304
- { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128
- { call_site: [ffffffff81089b05] sched_create_group } hitcount: 2 bytes_req: 1424
- .
- .
- .
- { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1185 bytes_req: 123240
- { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 1185 bytes_req: 104280
- { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 1402 bytes_req: 190672
- { call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 1518 bytes_req: 146208
- { call_site: [ffffffffa029070e] drm_vma_node_allow [drm] } hitcount: 1746 bytes_req: 69840
- { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 2021 bytes_req: 792312
- { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 2592 bytes_req: 145152
- { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2629 bytes_req: 378576
- { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2629 bytes_req: 3783248
- { call_site: [ffffffff81325607] apparmor_file_alloc_security } hitcount: 5192 bytes_req: 10384
- { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 5529 bytes_req: 110584
- { call_site: [ffffffff8131ebf7] aa_alloc_task_context } hitcount: 21943 bytes_req: 702176
- { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 55759 bytes_req: 5074265
-
- Totals:
- Hits: 109928
- Entries: 71
- Dropped: 0
-
- Because the default sort key above is 'hitcount', the above shows a
- the list of call_sites by increasing hitcount, so that at the bottom
- we see the functions that made the most kmalloc calls during the
- run. If instead we we wanted to see the top kmalloc callers in
- terms of the number of bytes requested rather than the number of
- calls, and we wanted the top caller to appear at the top, we can use
- the 'sort' parameter, along with the 'descending' modifier::
-
- # echo 'hist:key=call_site.sym:val=bytes_req:sort=bytes_req.descending' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
- # trigger info: hist:keys=call_site.sym:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
-
- { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 2186 bytes_req: 3397464
- { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1790 bytes_req: 712176
- { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 8132 bytes_req: 513135
- { call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 106 bytes_req: 440128
- { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 2186 bytes_req: 314784
- { call_site: [ffffffff812891ca] ext4_find_extent } hitcount: 2174 bytes_req: 208992
- { call_site: [ffffffff811ae8e1] __kmalloc } hitcount: 8 bytes_req: 131072
- { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 859 bytes_req: 116824
- { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 1834 bytes_req: 102704
- { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 972 bytes_req: 101088
- { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl [drm] } hitcount: 972 bytes_req: 85536
- { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 3333 bytes_req: 66664
- { call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 209 bytes_req: 61632
- .
- .
- .
- { call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128
- { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128
- { call_site: [ffffffff812d8406] copy_semundo } hitcount: 2 bytes_req: 48
- { call_site: [ffffffff81200ba6] inotify_new_group } hitcount: 1 bytes_req: 48
- { call_site: [ffffffffa027121a] drm_getmagic [drm] } hitcount: 1 bytes_req: 48
- { call_site: [ffffffff811e3a25] __seq_open_private } hitcount: 1 bytes_req: 40
- { call_site: [ffffffff811c52f4] bprm_change_interp } hitcount: 2 bytes_req: 16
- { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8
- { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7
- { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7
-
- Totals:
- Hits: 32133
- Entries: 81
- Dropped: 0
-
- To display the offset and size information in addition to the symbol
- name, just use 'sym-offset' instead::
-
- # echo 'hist:key=call_site.sym-offset:val=bytes_req:sort=bytes_req.descending' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
- # trigger info: hist:keys=call_site.sym-offset:vals=bytes_req:sort=bytes_req.descending:size=2048 [active]
-
- { call_site: [ffffffffa046041c] i915_gem_execbuffer2+0x6c/0x2c0 [i915] } hitcount: 4569 bytes_req: 3163720
- { call_site: [ffffffffa0489a66] intel_ring_begin+0xc6/0x1f0 [i915] } hitcount: 4569 bytes_req: 657936
- { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23+0x694/0x1020 [i915] } hitcount: 1519 bytes_req: 472936
- { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23+0x516/0x1020 [i915] } hitcount: 3050 bytes_req: 211832
- { call_site: [ffffffff811e2a1b] seq_buf_alloc+0x1b/0x50 } hitcount: 34 bytes_req: 148384
- { call_site: [ffffffffa04a580c] intel_crtc_page_flip+0xbc/0x870 [i915] } hitcount: 1385 bytes_req: 144040
- { call_site: [ffffffff811ae8e1] __kmalloc+0x191/0x1b0 } hitcount: 8 bytes_req: 131072
- { call_site: [ffffffffa0287592] drm_mode_page_flip_ioctl+0x282/0x360 [drm] } hitcount: 1385 bytes_req: 121880
- { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc+0x32/0x100 [drm] } hitcount: 1848 bytes_req: 103488
- { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state+0x2c/0xa0 [i915] } hitcount: 461 bytes_req: 62696
- { call_site: [ffffffffa029070e] drm_vma_node_allow+0x2e/0xd0 [drm] } hitcount: 1541 bytes_req: 61640
- { call_site: [ffffffff815f8d7b] sk_prot_alloc+0xcb/0x1b0 } hitcount: 57 bytes_req: 57456
- .
- .
- .
- { call_site: [ffffffff8109524a] alloc_fair_sched_group+0x5a/0x1a0 } hitcount: 2 bytes_req: 128
- { call_site: [ffffffffa027b921] drm_vm_open_locked+0x31/0xa0 [drm] } hitcount: 3 bytes_req: 96
- { call_site: [ffffffff8122e266] proc_self_follow_link+0x76/0xb0 } hitcount: 8 bytes_req: 96
- { call_site: [ffffffff81213e80] load_elf_binary+0x240/0x1650 } hitcount: 3 bytes_req: 84
- { call_site: [ffffffff8154bc62] usb_control_msg+0x42/0x110 } hitcount: 1 bytes_req: 8
- { call_site: [ffffffffa00bf6fe] hidraw_send_report+0x7e/0x1a0 [hid] } hitcount: 1 bytes_req: 7
- { call_site: [ffffffffa00bf1ca] hidraw_report_event+0x8a/0x120 [hid] } hitcount: 1 bytes_req: 7
-
- Totals:
- Hits: 26098
- Entries: 64
- Dropped: 0
-
- We can also add multiple fields to the 'values' parameter. For
- example, we might want to see the total number of bytes allocated
- alongside bytes requested, and display the result sorted by bytes
- allocated in a descending order::
-
- # echo 'hist:keys=call_site.sym:values=bytes_req,bytes_alloc:sort=bytes_alloc.descending' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
- # trigger info: hist:keys=call_site.sym:vals=bytes_req,bytes_alloc:sort=bytes_alloc.descending:size=2048 [active]
-
- { call_site: [ffffffffa046041c] i915_gem_execbuffer2 [i915] } hitcount: 7403 bytes_req: 4084360 bytes_alloc: 5958016
- { call_site: [ffffffff811e2a1b] seq_buf_alloc } hitcount: 541 bytes_req: 2213968 bytes_alloc: 2228224
- { call_site: [ffffffffa0489a66] intel_ring_begin [i915] } hitcount: 7404 bytes_req: 1066176 bytes_alloc: 1421568
- { call_site: [ffffffffa045e7c4] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 1565 bytes_req: 557368 bytes_alloc: 1037760
- { call_site: [ffffffff8125847d] ext4_htree_store_dirent } hitcount: 9557 bytes_req: 595778 bytes_alloc: 695744
- { call_site: [ffffffffa045e646] i915_gem_do_execbuffer.isra.23 [i915] } hitcount: 5839 bytes_req: 430680 bytes_alloc: 470400
- { call_site: [ffffffffa04c4a3c] intel_plane_duplicate_state [i915] } hitcount: 2388 bytes_req: 324768 bytes_alloc: 458496
- { call_site: [ffffffffa02911f2] drm_modeset_lock_crtc [drm] } hitcount: 3911 bytes_req: 219016 bytes_alloc: 250304
- { call_site: [ffffffff815f8d7b] sk_prot_alloc } hitcount: 235 bytes_req: 236880 bytes_alloc: 240640
- { call_site: [ffffffff8137e559] sg_kmalloc } hitcount: 557 bytes_req: 169024 bytes_alloc: 221760
- { call_site: [ffffffffa00b7c06] hid_report_raw_event [hid] } hitcount: 9378 bytes_req: 187548 bytes_alloc: 206312
- { call_site: [ffffffffa04a580c] intel_crtc_page_flip [i915] } hitcount: 1519 bytes_req: 157976 bytes_alloc: 194432
- .
- .
- .
- { call_site: [ffffffff8109bd3b] sched_autogroup_create_attach } hitcount: 2 bytes_req: 144 bytes_alloc: 192
- { call_site: [ffffffff81097ee8] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
- { call_site: [ffffffff8109524a] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
- { call_site: [ffffffff81095225] alloc_fair_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
- { call_site: [ffffffff81097ec2] alloc_rt_sched_group } hitcount: 2 bytes_req: 128 bytes_alloc: 128
- { call_site: [ffffffff81213e80] load_elf_binary } hitcount: 3 bytes_req: 84 bytes_alloc: 96
- { call_site: [ffffffff81079a2e] kthread_create_on_node } hitcount: 1 bytes_req: 56 bytes_alloc: 64
- { call_site: [ffffffffa00bf6fe] hidraw_send_report [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8
- { call_site: [ffffffff8154bc62] usb_control_msg } hitcount: 1 bytes_req: 8 bytes_alloc: 8
- { call_site: [ffffffffa00bf1ca] hidraw_report_event [hid] } hitcount: 1 bytes_req: 7 bytes_alloc: 8
-
- Totals:
- Hits: 66598
- Entries: 65
- Dropped: 0
-
- Finally, to finish off our kmalloc example, instead of simply having
- the hist trigger display symbolic call_sites, we can have the hist
- trigger additionally display the complete set of kernel stack traces
- that led to each call_site. To do that, we simply use the special
- value 'stacktrace' for the key parameter::
-
- # echo 'hist:keys=stacktrace:values=bytes_req,bytes_alloc:sort=bytes_alloc' > \
- /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
-
- The above trigger will use the kernel stack trace in effect when an
- event is triggered as the key for the hash table. This allows the
- enumeration of every kernel callpath that led up to a particular
- event, along with a running total of any of the event fields for
- that event. Here we tally bytes requested and bytes allocated for
- every callpath in the system that led up to a kmalloc (in this case
- every callpath to a kmalloc for a kernel compile)::
-
- # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/hist
- # trigger info: hist:keys=stacktrace:vals=bytes_req,bytes_alloc:sort=bytes_alloc:size=2048 [active]
-
- { stacktrace:
- __kmalloc_track_caller+0x10b/0x1a0
- kmemdup+0x20/0x50
- hidraw_report_event+0x8a/0x120 [hid]
- hid_report_raw_event+0x3ea/0x440 [hid]
- hid_input_report+0x112/0x190 [hid]
- hid_irq_in+0xc2/0x260 [usbhid]
- __usb_hcd_giveback_urb+0x72/0x120
- usb_giveback_urb_bh+0x9e/0xe0
- tasklet_hi_action+0xf8/0x100
- __do_softirq+0x114/0x2c0
- irq_exit+0xa5/0xb0
- do_IRQ+0x5a/0xf0
- ret_from_intr+0x0/0x30
- cpuidle_enter+0x17/0x20
- cpu_startup_entry+0x315/0x3e0
- rest_init+0x7c/0x80
- } hitcount: 3 bytes_req: 21 bytes_alloc: 24
- { stacktrace:
- __kmalloc_track_caller+0x10b/0x1a0
- kmemdup+0x20/0x50
- hidraw_report_event+0x8a/0x120 [hid]
- hid_report_raw_event+0x3ea/0x440 [hid]
- hid_input_report+0x112/0x190 [hid]
- hid_irq_in+0xc2/0x260 [usbhid]
- __usb_hcd_giveback_urb+0x72/0x120
- usb_giveback_urb_bh+0x9e/0xe0
- tasklet_hi_action+0xf8/0x100
- __do_softirq+0x114/0x2c0
- irq_exit+0xa5/0xb0
- do_IRQ+0x5a/0xf0
- ret_from_intr+0x0/0x30
- } hitcount: 3 bytes_req: 21 bytes_alloc: 24
- { stacktrace:
- kmem_cache_alloc_trace+0xeb/0x150
- aa_alloc_task_context+0x27/0x40
- apparmor_cred_prepare+0x1f/0x50
- security_prepare_creds+0x16/0x20
- prepare_creds+0xdf/0x1a0
- SyS_capset+0xb5/0x200
- system_call_fastpath+0x12/0x6a
- } hitcount: 1 bytes_req: 32 bytes_alloc: 32
- .
- .
- .
- { stacktrace:
- __kmalloc+0x11b/0x1b0
- i915_gem_execbuffer2+0x6c/0x2c0 [i915]
- drm_ioctl+0x349/0x670 [drm]
- do_vfs_ioctl+0x2f0/0x4f0
- SyS_ioctl+0x81/0xa0
- system_call_fastpath+0x12/0x6a
- } hitcount: 17726 bytes_req: 13944120 bytes_alloc: 19593808
- { stacktrace:
- __kmalloc+0x11b/0x1b0
- load_elf_phdrs+0x76/0xa0
- load_elf_binary+0x102/0x1650
- search_binary_handler+0x97/0x1d0
- do_execveat_common.isra.34+0x551/0x6e0
- SyS_execve+0x3a/0x50
- return_from_execve+0x0/0x23
- } hitcount: 33348 bytes_req: 17152128 bytes_alloc: 20226048
- { stacktrace:
- kmem_cache_alloc_trace+0xeb/0x150
- apparmor_file_alloc_security+0x27/0x40
- security_file_alloc+0x16/0x20
- get_empty_filp+0x93/0x1c0
- path_openat+0x31/0x5f0
- do_filp_open+0x3a/0x90
- do_sys_open+0x128/0x220
- SyS_open+0x1e/0x20
- system_call_fastpath+0x12/0x6a
- } hitcount: 4766422 bytes_req: 9532844 bytes_alloc: 38131376
- { stacktrace:
- __kmalloc+0x11b/0x1b0
- seq_buf_alloc+0x1b/0x50
- seq_read+0x2cc/0x370
- proc_reg_read+0x3d/0x80
- __vfs_read+0x28/0xe0
- vfs_read+0x86/0x140
- SyS_read+0x46/0xb0
- system_call_fastpath+0x12/0x6a
- } hitcount: 19133 bytes_req: 78368768 bytes_alloc: 78368768
-
- Totals:
- Hits: 6085872
- Entries: 253
- Dropped: 0
-
- If you key a hist trigger on common_pid, in order for example to
- gather and display sorted totals for each process, you can use the
- special .execname modifier to display the executable names for the
- processes in the table rather than raw pids. The example below
- keeps a per-process sum of total bytes read::
-
- # echo 'hist:key=common_pid.execname:val=count:sort=count.descending' > \
- /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
-
- # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/hist
- # trigger info: hist:keys=common_pid.execname:vals=count:sort=count.descending:size=2048 [active]
-
- { common_pid: gnome-terminal [ 3196] } hitcount: 280 count: 1093512
- { common_pid: Xorg [ 1309] } hitcount: 525 count: 256640
- { common_pid: compiz [ 2889] } hitcount: 59 count: 254400
- { common_pid: bash [ 8710] } hitcount: 3 count: 66369
- { common_pid: dbus-daemon-lau [ 8703] } hitcount: 49 count: 47739
- { common_pid: irqbalance [ 1252] } hitcount: 27 count: 27648
- { common_pid: 01ifupdown [ 8705] } hitcount: 3 count: 17216
- { common_pid: dbus-daemon [ 772] } hitcount: 10 count: 12396
- { common_pid: Socket Thread [ 8342] } hitcount: 11 count: 11264
- { common_pid: nm-dhcp-client. [ 8701] } hitcount: 6 count: 7424
- { common_pid: gmain [ 1315] } hitcount: 18 count: 6336
- .
- .
- .
- { common_pid: postgres [ 1892] } hitcount: 2 count: 32
- { common_pid: postgres [ 1891] } hitcount: 2 count: 32
- { common_pid: gmain [ 8704] } hitcount: 2 count: 32
- { common_pid: upstart-dbus-br [ 2740] } hitcount: 21 count: 21
- { common_pid: nm-dispatcher.a [ 8696] } hitcount: 1 count: 16
- { common_pid: indicator-datet [ 2904] } hitcount: 1 count: 16
- { common_pid: gdbus [ 2998] } hitcount: 1 count: 16
- { common_pid: rtkit-daemon [ 2052] } hitcount: 1 count: 8
- { common_pid: init [ 1] } hitcount: 2 count: 2
-
- Totals:
- Hits: 2116
- Entries: 51
- Dropped: 0
-
- Similarly, if you key a hist trigger on syscall id, for example to
- gather and display a list of systemwide syscall hits, you can use
- the special .syscall modifier to display the syscall names rather
- than raw ids. The example below keeps a running total of syscall
- counts for the system during the run::
-
- # echo 'hist:key=id.syscall:val=hitcount' > \
- /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
-
- # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
- # trigger info: hist:keys=id.syscall:vals=hitcount:sort=hitcount:size=2048 [active]
-
- { id: sys_fsync [ 74] } hitcount: 1
- { id: sys_newuname [ 63] } hitcount: 1
- { id: sys_prctl [157] } hitcount: 1
- { id: sys_statfs [137] } hitcount: 1
- { id: sys_symlink [ 88] } hitcount: 1
- { id: sys_sendmmsg [307] } hitcount: 1
- { id: sys_semctl [ 66] } hitcount: 1
- { id: sys_readlink [ 89] } hitcount: 3
- { id: sys_bind [ 49] } hitcount: 3
- { id: sys_getsockname [ 51] } hitcount: 3
- { id: sys_unlink [ 87] } hitcount: 3
- { id: sys_rename [ 82] } hitcount: 4
- { id: unknown_syscall [ 58] } hitcount: 4
- { id: sys_connect [ 42] } hitcount: 4
- { id: sys_getpid [ 39] } hitcount: 4
- .
- .
- .
- { id: sys_rt_sigprocmask [ 14] } hitcount: 952
- { id: sys_futex [202] } hitcount: 1534
- { id: sys_write [ 1] } hitcount: 2689
- { id: sys_setitimer [ 38] } hitcount: 2797
- { id: sys_read [ 0] } hitcount: 3202
- { id: sys_select [ 23] } hitcount: 3773
- { id: sys_writev [ 20] } hitcount: 4531
- { id: sys_poll [ 7] } hitcount: 8314
- { id: sys_recvmsg [ 47] } hitcount: 13738
- { id: sys_ioctl [ 16] } hitcount: 21843
-
- Totals:
- Hits: 67612
- Entries: 72
- Dropped: 0
-
- The syscall counts above provide a rough overall picture of system
- call activity on the system; we can see for example that the most
- popular system call on this system was the 'sys_ioctl' system call.
-
- We can use 'compound' keys to refine that number and provide some
- further insight as to which processes exactly contribute to the
- overall ioctl count.
-
- The command below keeps a hitcount for every unique combination of
- system call id and pid - the end result is essentially a table
- that keeps a per-pid sum of system call hits. The results are
- sorted using the system call id as the primary key, and the
- hitcount sum as the secondary key::
-
- # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount' > \
- /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
-
- # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
- # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 [active]
-
- { id: sys_read [ 0], common_pid: rtkit-daemon [ 1877] } hitcount: 1
- { id: sys_read [ 0], common_pid: gdbus [ 2976] } hitcount: 1
- { id: sys_read [ 0], common_pid: console-kit-dae [ 3400] } hitcount: 1
- { id: sys_read [ 0], common_pid: postgres [ 1865] } hitcount: 1
- { id: sys_read [ 0], common_pid: deja-dup-monito [ 3543] } hitcount: 2
- { id: sys_read [ 0], common_pid: NetworkManager [ 890] } hitcount: 2
- { id: sys_read [ 0], common_pid: evolution-calen [ 3048] } hitcount: 2
- { id: sys_read [ 0], common_pid: postgres [ 1864] } hitcount: 2
- { id: sys_read [ 0], common_pid: nm-applet [ 3022] } hitcount: 2
- { id: sys_read [ 0], common_pid: whoopsie [ 1212] } hitcount: 2
- .
- .
- .
- { id: sys_ioctl [ 16], common_pid: bash [ 8479] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: bash [ 3472] } hitcount: 12
- { id: sys_ioctl [ 16], common_pid: gnome-terminal [ 3199] } hitcount: 16
- { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 1808
- { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 5580
- .
- .
- .
- { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2690] } hitcount: 3
- { id: sys_waitid [247], common_pid: upstart-dbus-br [ 2688] } hitcount: 16
- { id: sys_inotify_add_watch [254], common_pid: gmain [ 975] } hitcount: 2
- { id: sys_inotify_add_watch [254], common_pid: gmain [ 3204] } hitcount: 4
- { id: sys_inotify_add_watch [254], common_pid: gmain [ 2888] } hitcount: 4
- { id: sys_inotify_add_watch [254], common_pid: gmain [ 3003] } hitcount: 4
- { id: sys_inotify_add_watch [254], common_pid: gmain [ 2873] } hitcount: 4
- { id: sys_inotify_add_watch [254], common_pid: gmain [ 3196] } hitcount: 6
- { id: sys_openat [257], common_pid: java [ 2623] } hitcount: 2
- { id: sys_eventfd2 [290], common_pid: ibus-ui-gtk3 [ 2760] } hitcount: 4
- { id: sys_eventfd2 [290], common_pid: compiz [ 2994] } hitcount: 6
-
- Totals:
- Hits: 31536
- Entries: 323
- Dropped: 0
-
- The above list does give us a breakdown of the ioctl syscall by
- pid, but it also gives us quite a bit more than that, which we
- don't really care about at the moment. Since we know the syscall
- id for sys_ioctl (16, displayed next to the sys_ioctl name), we
- can use that to filter out all the other syscalls::
-
- # echo 'hist:key=id.syscall,common_pid.execname:val=hitcount:sort=id,hitcount if id == 16' > \
- /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger
-
- # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist
- # trigger info: hist:keys=id.syscall,common_pid.execname:vals=hitcount:sort=id.syscall,hitcount:size=2048 if id == 16 [active]
-
- { id: sys_ioctl [ 16], common_pid: gmain [ 2769] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: evolution-addre [ 8571] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: gmain [ 3003] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: gmain [ 2781] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: gmain [ 2829] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: bash [ 8726] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: bash [ 8508] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: gmain [ 2970] } hitcount: 1
- { id: sys_ioctl [ 16], common_pid: gmain [ 2768] } hitcount: 1
- .
- .
- .
- { id: sys_ioctl [ 16], common_pid: pool [ 8559] } hitcount: 45
- { id: sys_ioctl [ 16], common_pid: pool [ 8555] } hitcount: 48
- { id: sys_ioctl [ 16], common_pid: pool [ 8551] } hitcount: 48
- { id: sys_ioctl [ 16], common_pid: avahi-daemon [ 896] } hitcount: 66
- { id: sys_ioctl [ 16], common_pid: Xorg [ 1267] } hitcount: 26674
- { id: sys_ioctl [ 16], common_pid: compiz [ 2994] } hitcount: 73443
-
- Totals:
- Hits: 101162
- Entries: 103
- Dropped: 0
-
- The above output shows that 'compiz' and 'Xorg' are far and away
- the heaviest ioctl callers (which might lead to questions about
- whether they really need to be making all those calls and to
- possible avenues for further investigation.)
-
- The compound key examples used a key and a sum value (hitcount) to
- sort the output, but we can just as easily use two keys instead.
- Here's an example where we use a compound key composed of the the
- common_pid and size event fields. Sorting with pid as the primary
- key and 'size' as the secondary key allows us to display an
- ordered summary of the recvfrom sizes, with counts, received by
- each process::
-
- # echo 'hist:key=common_pid.execname,size:val=hitcount:sort=common_pid,size' > \
- /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/trigger
-
- # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_recvfrom/hist
- # trigger info: hist:keys=common_pid.execname,size:vals=hitcount:sort=common_pid.execname,size:size=2048 [active]
-
- { common_pid: smbd [ 784], size: 4 } hitcount: 1
- { common_pid: dnsmasq [ 1412], size: 4096 } hitcount: 672
- { common_pid: postgres [ 1796], size: 1000 } hitcount: 6
- { common_pid: postgres [ 1867], size: 1000 } hitcount: 10
- { common_pid: bamfdaemon [ 2787], size: 28 } hitcount: 2
- { common_pid: bamfdaemon [ 2787], size: 14360 } hitcount: 1
- { common_pid: compiz [ 2994], size: 8 } hitcount: 1
- { common_pid: compiz [ 2994], size: 20 } hitcount: 11
- { common_pid: gnome-terminal [ 3199], size: 4 } hitcount: 2
- { common_pid: firefox [ 8817], size: 4 } hitcount: 1
- { common_pid: firefox [ 8817], size: 8 } hitcount: 5
- { common_pid: firefox [ 8817], size: 588 } hitcount: 2
- { common_pid: firefox [ 8817], size: 628 } hitcount: 1
- { common_pid: firefox [ 8817], size: 6944 } hitcount: 1
- { common_pid: firefox [ 8817], size: 408880 } hitcount: 2
- { common_pid: firefox [ 8822], size: 8 } hitcount: 2
- { common_pid: firefox [ 8822], size: 160 } hitcount: 2
- { common_pid: firefox [ 8822], size: 320 } hitcount: 2
- { common_pid: firefox [ 8822], size: 352 } hitcount: 1
- .
- .
- .
- { common_pid: pool [ 8923], size: 1960 } hitcount: 10
- { common_pid: pool [ 8923], size: 2048 } hitcount: 10
- { common_pid: pool [ 8924], size: 1960 } hitcount: 10
- { common_pid: pool [ 8924], size: 2048 } hitcount: 10
- { common_pid: pool [ 8928], size: 1964 } hitcount: 4
- { common_pid: pool [ 8928], size: 1965 } hitcount: 2
- { common_pid: pool [ 8928], size: 2048 } hitcount: 6
- { common_pid: pool [ 8929], size: 1982 } hitcount: 1
- { common_pid: pool [ 8929], size: 2048 } hitcount: 1
-
- Totals:
- Hits: 2016
- Entries: 224
- Dropped: 0
-
- The above example also illustrates the fact that although a compound
- key is treated as a single entity for hashing purposes, the sub-keys
- it's composed of can be accessed independently.
-
- The next example uses a string field as the hash key and
- demonstrates how you can manually pause and continue a hist trigger.
- In this example, we'll aggregate fork counts and don't expect a
- large number of entries in the hash table, so we'll drop it to a
- much smaller number, say 256::
-
- # echo 'hist:key=child_comm:val=hitcount:size=256' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
- # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
-
- { child_comm: dconf worker } hitcount: 1
- { child_comm: ibus-daemon } hitcount: 1
- { child_comm: whoopsie } hitcount: 1
- { child_comm: smbd } hitcount: 1
- { child_comm: gdbus } hitcount: 1
- { child_comm: kthreadd } hitcount: 1
- { child_comm: dconf worker } hitcount: 1
- { child_comm: evolution-alarm } hitcount: 2
- { child_comm: Socket Thread } hitcount: 2
- { child_comm: postgres } hitcount: 2
- { child_comm: bash } hitcount: 3
- { child_comm: compiz } hitcount: 3
- { child_comm: evolution-sourc } hitcount: 4
- { child_comm: dhclient } hitcount: 4
- { child_comm: pool } hitcount: 5
- { child_comm: nm-dispatcher.a } hitcount: 8
- { child_comm: firefox } hitcount: 8
- { child_comm: dbus-daemon } hitcount: 8
- { child_comm: glib-pacrunner } hitcount: 10
- { child_comm: evolution } hitcount: 23
-
- Totals:
- Hits: 89
- Entries: 20
- Dropped: 0
-
- If we want to pause the hist trigger, we can simply append :pause to
- the command that started the trigger. Notice that the trigger info
- displays as [paused]::
-
- # echo 'hist:key=child_comm:val=hitcount:size=256:pause' >> \
- /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
- # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [paused]
-
- { child_comm: dconf worker } hitcount: 1
- { child_comm: kthreadd } hitcount: 1
- { child_comm: dconf worker } hitcount: 1
- { child_comm: gdbus } hitcount: 1
- { child_comm: ibus-daemon } hitcount: 1
- { child_comm: Socket Thread } hitcount: 2
- { child_comm: evolution-alarm } hitcount: 2
- { child_comm: smbd } hitcount: 2
- { child_comm: bash } hitcount: 3
- { child_comm: whoopsie } hitcount: 3
- { child_comm: compiz } hitcount: 3
- { child_comm: evolution-sourc } hitcount: 4
- { child_comm: pool } hitcount: 5
- { child_comm: postgres } hitcount: 6
- { child_comm: firefox } hitcount: 8
- { child_comm: dhclient } hitcount: 10
- { child_comm: emacs } hitcount: 12
- { child_comm: dbus-daemon } hitcount: 20
- { child_comm: nm-dispatcher.a } hitcount: 20
- { child_comm: evolution } hitcount: 35
- { child_comm: glib-pacrunner } hitcount: 59
-
- Totals:
- Hits: 199
- Entries: 21
- Dropped: 0
-
- To manually continue having the trigger aggregate events, append
- :cont instead. Notice that the trigger info displays as [active]
- again, and the data has changed::
-
- # echo 'hist:key=child_comm:val=hitcount:size=256:cont' >> \
- /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
- # trigger info: hist:keys=child_comm:vals=hitcount:sort=hitcount:size=256 [active]
-
- { child_comm: dconf worker } hitcount: 1
- { child_comm: dconf worker } hitcount: 1
- { child_comm: kthreadd } hitcount: 1
- { child_comm: gdbus } hitcount: 1
- { child_comm: ibus-daemon } hitcount: 1
- { child_comm: Socket Thread } hitcount: 2
- { child_comm: evolution-alarm } hitcount: 2
- { child_comm: smbd } hitcount: 2
- { child_comm: whoopsie } hitcount: 3
- { child_comm: compiz } hitcount: 3
- { child_comm: evolution-sourc } hitcount: 4
- { child_comm: bash } hitcount: 5
- { child_comm: pool } hitcount: 5
- { child_comm: postgres } hitcount: 6
- { child_comm: firefox } hitcount: 8
- { child_comm: dhclient } hitcount: 11
- { child_comm: emacs } hitcount: 12
- { child_comm: dbus-daemon } hitcount: 22
- { child_comm: nm-dispatcher.a } hitcount: 22
- { child_comm: evolution } hitcount: 35
- { child_comm: glib-pacrunner } hitcount: 59
-
- Totals:
- Hits: 206
- Entries: 21
- Dropped: 0
-
- The previous example showed how to start and stop a hist trigger by
- appending 'pause' and 'continue' to the hist trigger command. A
- hist trigger can also be started in a paused state by initially
- starting the trigger with ':pause' appended. This allows you to
- start the trigger only when you're ready to start collecting data
- and not before. For example, you could start the trigger in a
- paused state, then unpause it and do something you want to measure,
- then pause the trigger again when done.
-
- Of course, doing this manually can be difficult and error-prone, but
- it is possible to automatically start and stop a hist trigger based
- on some condition, via the enable_hist and disable_hist triggers.
-
- For example, suppose we wanted to take a look at the relative
- weights in terms of skb length for each callpath that leads to a
- netif_receieve_skb event when downloading a decent-sized file using
- wget.
-
- First we set up an initially paused stacktrace trigger on the
- netif_receive_skb event::
-
- # echo 'hist:key=stacktrace:vals=len:pause' > \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-
- Next, we set up an 'enable_hist' trigger on the sched_process_exec
- event, with an 'if filename==/usr/bin/wget' filter. The effect of
- this new trigger is that it will 'unpause' the hist trigger we just
- set up on netif_receive_skb if and only if it sees a
- sched_process_exec event with a filename of '/usr/bin/wget'. When
- that happens, all netif_receive_skb events are aggregated into a
- hash table keyed on stacktrace::
-
- # echo 'enable_hist:net:netif_receive_skb if filename==/usr/bin/wget' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
-
- The aggregation continues until the netif_receive_skb is paused
- again, which is what the following disable_hist event does by
- creating a similar setup on the sched_process_exit event, using the
- filter 'comm==wget'::
-
- # echo 'disable_hist:net:netif_receive_skb if comm==wget' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
-
- Whenever a process exits and the comm field of the disable_hist
- trigger filter matches 'comm==wget', the netif_receive_skb hist
- trigger is disabled.
-
- The overall effect is that netif_receive_skb events are aggregated
- into the hash table for only the duration of the wget. Executing a
- wget command and then listing the 'hist' file will display the
- output generated by the wget command::
-
- $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
-
- # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
- # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
-
- { stacktrace:
- __netif_receive_skb_core+0x46d/0x990
- __netif_receive_skb+0x18/0x60
- netif_receive_skb_internal+0x23/0x90
- napi_gro_receive+0xc8/0x100
- ieee80211_deliver_skb+0xd6/0x270 [mac80211]
- ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
- ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
- ieee80211_rx+0x31d/0x900 [mac80211]
- iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
- iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
- iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
- irq_thread_fn+0x20/0x50
- irq_thread+0x11f/0x150
- kthread+0xd2/0xf0
- ret_from_fork+0x42/0x70
- } hitcount: 85 len: 28884
- { stacktrace:
- __netif_receive_skb_core+0x46d/0x990
- __netif_receive_skb+0x18/0x60
- netif_receive_skb_internal+0x23/0x90
- napi_gro_complete+0xa4/0xe0
- dev_gro_receive+0x23a/0x360
- napi_gro_receive+0x30/0x100
- ieee80211_deliver_skb+0xd6/0x270 [mac80211]
- ieee80211_rx_handlers+0xccf/0x22f0 [mac80211]
- ieee80211_prepare_and_rx_handle+0x4e7/0xc40 [mac80211]
- ieee80211_rx+0x31d/0x900 [mac80211]
- iwlagn_rx_reply_rx+0x3db/0x6f0 [iwldvm]
- iwl_rx_dispatch+0x8e/0xf0 [iwldvm]
- iwl_pcie_irq_handler+0xe3c/0x12f0 [iwlwifi]
- irq_thread_fn+0x20/0x50
- irq_thread+0x11f/0x150
- kthread+0xd2/0xf0
- } hitcount: 98 len: 664329
- { stacktrace:
- __netif_receive_skb_core+0x46d/0x990
- __netif_receive_skb+0x18/0x60
- process_backlog+0xa8/0x150
- net_rx_action+0x15d/0x340
- __do_softirq+0x114/0x2c0
- do_softirq_own_stack+0x1c/0x30
- do_softirq+0x65/0x70
- __local_bh_enable_ip+0xb5/0xc0
- ip_finish_output+0x1f4/0x840
- ip_output+0x6b/0xc0
- ip_local_out_sk+0x31/0x40
- ip_send_skb+0x1a/0x50
- udp_send_skb+0x173/0x2a0
- udp_sendmsg+0x2bf/0x9f0
- inet_sendmsg+0x64/0xa0
- sock_sendmsg+0x3d/0x50
- } hitcount: 115 len: 13030
- { stacktrace:
- __netif_receive_skb_core+0x46d/0x990
- __netif_receive_skb+0x18/0x60
- netif_receive_skb_internal+0x23/0x90
- napi_gro_complete+0xa4/0xe0
- napi_gro_flush+0x6d/0x90
- iwl_pcie_irq_handler+0x92a/0x12f0 [iwlwifi]
- irq_thread_fn+0x20/0x50
- irq_thread+0x11f/0x150
- kthread+0xd2/0xf0
- ret_from_fork+0x42/0x70
- } hitcount: 934 len: 5512212
-
- Totals:
- Hits: 1232
- Entries: 4
- Dropped: 0
-
- The above shows all the netif_receive_skb callpaths and their total
- lengths for the duration of the wget command.
-
- The 'clear' hist trigger param can be used to clear the hash table.
- Suppose we wanted to try another run of the previous example but
- this time also wanted to see the complete list of events that went
- into the histogram. In order to avoid having to set everything up
- again, we can just clear the histogram first::
-
- # echo 'hist:key=stacktrace:vals=len:clear' >> \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-
- Just to verify that it is in fact cleared, here's what we now see in
- the hist file::
-
- # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
- # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
-
- Totals:
- Hits: 0
- Entries: 0
- Dropped: 0
-
- Since we want to see the detailed list of every netif_receive_skb
- event occurring during the new run, which are in fact the same
- events being aggregated into the hash table, we add some additional
- 'enable_event' events to the triggering sched_process_exec and
- sched_process_exit events as such::
-
- # echo 'enable_event:net:netif_receive_skb if filename==/usr/bin/wget' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
-
- # echo 'disable_event:net:netif_receive_skb if comm==wget' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
-
- If you read the trigger files for the sched_process_exec and
- sched_process_exit triggers, you should see two triggers for each:
- one enabling/disabling the hist aggregation and the other
- enabling/disabling the logging of events::
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_process_exec/trigger
- enable_event:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
- enable_hist:net:netif_receive_skb:unlimited if filename==/usr/bin/wget
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_process_exit/trigger
- enable_event:net:netif_receive_skb:unlimited if comm==wget
- disable_hist:net:netif_receive_skb:unlimited if comm==wget
-
- In other words, whenever either of the sched_process_exec or
- sched_process_exit events is hit and matches 'wget', it enables or
- disables both the histogram and the event log, and what you end up
- with is a hash table and set of events just covering the specified
- duration. Run the wget command again::
-
- $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
-
- Displaying the 'hist' file should show something similar to what you
- saw in the last run, but this time you should also see the
- individual events in the trace file::
-
- # cat /sys/kernel/debug/tracing/trace
-
- # tracer: nop
- #
- # entries-in-buffer/entries-written: 183/1426 #P:4
- #
- # _-----=> irqs-off
- # / _----=> need-resched
- # | / _---=> hardirq/softirq
- # || / _--=> preempt-depth
- # ||| / delay
- # TASK-PID CPU# |||| TIMESTAMP FUNCTION
- # | | | |||| | |
- wget-15108 [000] ..s1 31769.606929: netif_receive_skb: dev=lo skbaddr=ffff88009c353100 len=60
- wget-15108 [000] ..s1 31769.606999: netif_receive_skb: dev=lo skbaddr=ffff88009c353200 len=60
- dnsmasq-1382 [000] ..s1 31769.677652: netif_receive_skb: dev=lo skbaddr=ffff88009c352b00 len=130
- dnsmasq-1382 [000] ..s1 31769.685917: netif_receive_skb: dev=lo skbaddr=ffff88009c352200 len=138
- ##### CPU 2 buffer started ####
- irq/29-iwlwifi-559 [002] ..s. 31772.031529: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433d00 len=2948
- irq/29-iwlwifi-559 [002] ..s. 31772.031572: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432200 len=1500
- irq/29-iwlwifi-559 [002] ..s. 31772.032196: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433100 len=2948
- irq/29-iwlwifi-559 [002] ..s. 31772.032761: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d433000 len=2948
- irq/29-iwlwifi-559 [002] ..s. 31772.033220: netif_receive_skb: dev=wlan0 skbaddr=ffff88009d432e00 len=1500
- ....
-
-
- The following example demonstrates how multiple hist triggers can be
- attached to a given event. This capability can be useful for
- creating a set of different summaries derived from the same set of
- events, or for comparing the effects of different filters, among
- other things.
- ::
-
- # echo 'hist:keys=skbaddr.hex:vals=len if len < 0' >> \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
- # echo 'hist:keys=skbaddr.hex:vals=len if len > 4096' >> \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
- # echo 'hist:keys=skbaddr.hex:vals=len if len == 256' >> \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
- # echo 'hist:keys=skbaddr.hex:vals=len' >> \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
- # echo 'hist:keys=len:vals=common_preempt_count' >> \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
-
- The above set of commands create four triggers differing only in
- their filters, along with a completely different though fairly
- nonsensical trigger. Note that in order to append multiple hist
- triggers to the same file, you should use the '>>' operator to
- append them ('>' will also add the new hist trigger, but will remove
- any existing hist triggers beforehand).
-
- Displaying the contents of the 'hist' file for the event shows the
- contents of all five histograms::
-
- # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist
-
- # event histogram
- #
- # trigger info: hist:keys=len:vals=hitcount,common_preempt_count:sort=hitcount:size=2048 [active]
- #
-
- { len: 176 } hitcount: 1 common_preempt_count: 0
- { len: 223 } hitcount: 1 common_preempt_count: 0
- { len: 4854 } hitcount: 1 common_preempt_count: 0
- { len: 395 } hitcount: 1 common_preempt_count: 0
- { len: 177 } hitcount: 1 common_preempt_count: 0
- { len: 446 } hitcount: 1 common_preempt_count: 0
- { len: 1601 } hitcount: 1 common_preempt_count: 0
- .
- .
- .
- { len: 1280 } hitcount: 66 common_preempt_count: 0
- { len: 116 } hitcount: 81 common_preempt_count: 40
- { len: 708 } hitcount: 112 common_preempt_count: 0
- { len: 46 } hitcount: 221 common_preempt_count: 0
- { len: 1264 } hitcount: 458 common_preempt_count: 0
-
- Totals:
- Hits: 1428
- Entries: 147
- Dropped: 0
-
-
- # event histogram
- #
- # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
- #
-
- { skbaddr: ffff8800baee5e00 } hitcount: 1 len: 130
- { skbaddr: ffff88005f3d5600 } hitcount: 1 len: 1280
- { skbaddr: ffff88005f3d4900 } hitcount: 1 len: 1280
- { skbaddr: ffff88009fed6300 } hitcount: 1 len: 115
- { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 115
- { skbaddr: ffff88008cdb1900 } hitcount: 1 len: 46
- { skbaddr: ffff880064b5ef00 } hitcount: 1 len: 118
- { skbaddr: ffff880044e3c700 } hitcount: 1 len: 60
- { skbaddr: ffff880100065900 } hitcount: 1 len: 46
- { skbaddr: ffff8800d46bd500 } hitcount: 1 len: 116
- { skbaddr: ffff88005f3d5f00 } hitcount: 1 len: 1280
- { skbaddr: ffff880100064700 } hitcount: 1 len: 365
- { skbaddr: ffff8800badb6f00 } hitcount: 1 len: 60
- .
- .
- .
- { skbaddr: ffff88009fe0be00 } hitcount: 27 len: 24677
- { skbaddr: ffff88009fe0a400 } hitcount: 27 len: 23052
- { skbaddr: ffff88009fe0b700 } hitcount: 31 len: 25589
- { skbaddr: ffff88009fe0b600 } hitcount: 32 len: 27326
- { skbaddr: ffff88006a462800 } hitcount: 68 len: 71678
- { skbaddr: ffff88006a463700 } hitcount: 70 len: 72678
- { skbaddr: ffff88006a462b00 } hitcount: 71 len: 77589
- { skbaddr: ffff88006a463600 } hitcount: 73 len: 71307
- { skbaddr: ffff88006a462200 } hitcount: 81 len: 81032
-
- Totals:
- Hits: 1451
- Entries: 318
- Dropped: 0
-
-
- # event histogram
- #
- # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len == 256 [active]
- #
-
-
- Totals:
- Hits: 0
- Entries: 0
- Dropped: 0
-
-
- # event histogram
- #
- # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len > 4096 [active]
- #
-
- { skbaddr: ffff88009fd2c300 } hitcount: 1 len: 7212
- { skbaddr: ffff8800d2bcce00 } hitcount: 1 len: 7212
- { skbaddr: ffff8800d2bcd700 } hitcount: 1 len: 7212
- { skbaddr: ffff8800d2bcda00 } hitcount: 1 len: 21492
- { skbaddr: ffff8800ae2e2d00 } hitcount: 1 len: 7212
- { skbaddr: ffff8800d2bcdb00 } hitcount: 1 len: 7212
- { skbaddr: ffff88006a4df500 } hitcount: 1 len: 4854
- { skbaddr: ffff88008ce47b00 } hitcount: 1 len: 18636
- { skbaddr: ffff8800ae2e2200 } hitcount: 1 len: 12924
- { skbaddr: ffff88005f3e1000 } hitcount: 1 len: 4356
- { skbaddr: ffff8800d2bcdc00 } hitcount: 2 len: 24420
- { skbaddr: ffff8800d2bcc200 } hitcount: 2 len: 12996
-
- Totals:
- Hits: 14
- Entries: 12
- Dropped: 0
-
-
- # event histogram
- #
- # trigger info: hist:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 if len < 0 [active]
- #
-
-
- Totals:
- Hits: 0
- Entries: 0
- Dropped: 0
-
- Named triggers can be used to have triggers share a common set of
- histogram data. This capability is mostly useful for combining the
- output of events generated by tracepoints contained inside inline
- functions, but names can be used in a hist trigger on any event.
- For example, these two triggers when hit will update the same 'len'
- field in the shared 'foo' histogram data::
-
- # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \
- /sys/kernel/debug/tracing/events/net/netif_receive_skb/trigger
- # echo 'hist:name=foo:keys=skbaddr.hex:vals=len' > \
- /sys/kernel/debug/tracing/events/net/netif_rx/trigger
-
- You can see that they're updating common histogram data by reading
- each event's hist files at the same time::
-
- # cat /sys/kernel/debug/tracing/events/net/netif_receive_skb/hist;
- cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
-
- # event histogram
- #
- # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
- #
-
- { skbaddr: ffff88000ad53500 } hitcount: 1 len: 46
- { skbaddr: ffff8800af5a1500 } hitcount: 1 len: 76
- { skbaddr: ffff8800d62a1900 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bccb00 } hitcount: 1 len: 468
- { skbaddr: ffff8800d3c69900 } hitcount: 1 len: 46
- { skbaddr: ffff88009ff09100 } hitcount: 1 len: 52
- { skbaddr: ffff88010f13ab00 } hitcount: 1 len: 168
- { skbaddr: ffff88006a54f400 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bcc500 } hitcount: 1 len: 260
- { skbaddr: ffff880064505000 } hitcount: 1 len: 46
- { skbaddr: ffff8800baf24e00 } hitcount: 1 len: 32
- { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 46
- { skbaddr: ffff8800d3edff00 } hitcount: 1 len: 44
- { skbaddr: ffff88009fe0b400 } hitcount: 1 len: 168
- { skbaddr: ffff8800a1c55a00 } hitcount: 1 len: 40
- { skbaddr: ffff8800d2bcd100 } hitcount: 1 len: 40
- { skbaddr: ffff880064505f00 } hitcount: 1 len: 174
- { skbaddr: ffff8800a8bff200 } hitcount: 1 len: 160
- { skbaddr: ffff880044e3cc00 } hitcount: 1 len: 76
- { skbaddr: ffff8800a8bfe700 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bcdc00 } hitcount: 1 len: 32
- { skbaddr: ffff8800a1f64800 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bcde00 } hitcount: 1 len: 988
- { skbaddr: ffff88006a5dea00 } hitcount: 1 len: 46
- { skbaddr: ffff88002e37a200 } hitcount: 1 len: 44
- { skbaddr: ffff8800a1f32c00 } hitcount: 2 len: 676
- { skbaddr: ffff88000ad52600 } hitcount: 2 len: 107
- { skbaddr: ffff8800a1f91e00 } hitcount: 2 len: 92
- { skbaddr: ffff8800af5a0200 } hitcount: 2 len: 142
- { skbaddr: ffff8800d2bcc600 } hitcount: 2 len: 220
- { skbaddr: ffff8800ba36f500 } hitcount: 2 len: 92
- { skbaddr: ffff8800d021f800 } hitcount: 2 len: 92
- { skbaddr: ffff8800a1f33600 } hitcount: 2 len: 675
- { skbaddr: ffff8800a8bfff00 } hitcount: 3 len: 138
- { skbaddr: ffff8800d62a1300 } hitcount: 3 len: 138
- { skbaddr: ffff88002e37a100 } hitcount: 4 len: 184
- { skbaddr: ffff880064504400 } hitcount: 4 len: 184
- { skbaddr: ffff8800a8bfec00 } hitcount: 4 len: 184
- { skbaddr: ffff88000ad53700 } hitcount: 5 len: 230
- { skbaddr: ffff8800d2bcdb00 } hitcount: 5 len: 196
- { skbaddr: ffff8800a1f90000 } hitcount: 6 len: 276
- { skbaddr: ffff88006a54f900 } hitcount: 6 len: 276
-
- Totals:
- Hits: 81
- Entries: 42
- Dropped: 0
- # event histogram
- #
- # trigger info: hist:name=foo:keys=skbaddr.hex:vals=hitcount,len:sort=hitcount:size=2048 [active]
- #
-
- { skbaddr: ffff88000ad53500 } hitcount: 1 len: 46
- { skbaddr: ffff8800af5a1500 } hitcount: 1 len: 76
- { skbaddr: ffff8800d62a1900 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bccb00 } hitcount: 1 len: 468
- { skbaddr: ffff8800d3c69900 } hitcount: 1 len: 46
- { skbaddr: ffff88009ff09100 } hitcount: 1 len: 52
- { skbaddr: ffff88010f13ab00 } hitcount: 1 len: 168
- { skbaddr: ffff88006a54f400 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bcc500 } hitcount: 1 len: 260
- { skbaddr: ffff880064505000 } hitcount: 1 len: 46
- { skbaddr: ffff8800baf24e00 } hitcount: 1 len: 32
- { skbaddr: ffff88009fe0ad00 } hitcount: 1 len: 46
- { skbaddr: ffff8800d3edff00 } hitcount: 1 len: 44
- { skbaddr: ffff88009fe0b400 } hitcount: 1 len: 168
- { skbaddr: ffff8800a1c55a00 } hitcount: 1 len: 40
- { skbaddr: ffff8800d2bcd100 } hitcount: 1 len: 40
- { skbaddr: ffff880064505f00 } hitcount: 1 len: 174
- { skbaddr: ffff8800a8bff200 } hitcount: 1 len: 160
- { skbaddr: ffff880044e3cc00 } hitcount: 1 len: 76
- { skbaddr: ffff8800a8bfe700 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bcdc00 } hitcount: 1 len: 32
- { skbaddr: ffff8800a1f64800 } hitcount: 1 len: 46
- { skbaddr: ffff8800d2bcde00 } hitcount: 1 len: 988
- { skbaddr: ffff88006a5dea00 } hitcount: 1 len: 46
- { skbaddr: ffff88002e37a200 } hitcount: 1 len: 44
- { skbaddr: ffff8800a1f32c00 } hitcount: 2 len: 676
- { skbaddr: ffff88000ad52600 } hitcount: 2 len: 107
- { skbaddr: ffff8800a1f91e00 } hitcount: 2 len: 92
- { skbaddr: ffff8800af5a0200 } hitcount: 2 len: 142
- { skbaddr: ffff8800d2bcc600 } hitcount: 2 len: 220
- { skbaddr: ffff8800ba36f500 } hitcount: 2 len: 92
- { skbaddr: ffff8800d021f800 } hitcount: 2 len: 92
- { skbaddr: ffff8800a1f33600 } hitcount: 2 len: 675
- { skbaddr: ffff8800a8bfff00 } hitcount: 3 len: 138
- { skbaddr: ffff8800d62a1300 } hitcount: 3 len: 138
- { skbaddr: ffff88002e37a100 } hitcount: 4 len: 184
- { skbaddr: ffff880064504400 } hitcount: 4 len: 184
- { skbaddr: ffff8800a8bfec00 } hitcount: 4 len: 184
- { skbaddr: ffff88000ad53700 } hitcount: 5 len: 230
- { skbaddr: ffff8800d2bcdb00 } hitcount: 5 len: 196
- { skbaddr: ffff8800a1f90000 } hitcount: 6 len: 276
- { skbaddr: ffff88006a54f900 } hitcount: 6 len: 276
-
- Totals:
- Hits: 81
- Entries: 42
- Dropped: 0
-
- And here's an example that shows how to combine histogram data from
- any two events even if they don't share any 'compatible' fields
- other than 'hitcount' and 'stacktrace'. These commands create a
- couple of triggers named 'bar' using those fields::
-
- # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
- /sys/kernel/debug/tracing/events/sched/sched_process_fork/trigger
- # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
- /sys/kernel/debug/tracing/events/net/netif_rx/trigger
-
- And displaying the output of either shows some interesting if
- somewhat confusing output::
-
- # cat /sys/kernel/debug/tracing/events/sched/sched_process_fork/hist
- # cat /sys/kernel/debug/tracing/events/net/netif_rx/hist
-
- # event histogram
- #
- # trigger info: hist:name=bar:keys=stacktrace:vals=hitcount:sort=hitcount:size=2048 [active]
- #
-
- { stacktrace:
- _do_fork+0x18e/0x330
- kernel_thread+0x29/0x30
- kthreadd+0x154/0x1b0
- ret_from_fork+0x3f/0x70
- } hitcount: 1
- { stacktrace:
- netif_rx_internal+0xb2/0xd0
- netif_rx_ni+0x20/0x70
- dev_loopback_xmit+0xaa/0xd0
- ip_mc_output+0x126/0x240
- ip_local_out_sk+0x31/0x40
- igmp_send_report+0x1e9/0x230
- igmp_timer_expire+0xe9/0x120
- call_timer_fn+0x39/0xf0
- run_timer_softirq+0x1e1/0x290
- __do_softirq+0xfd/0x290
- irq_exit+0x98/0xb0
- smp_apic_timer_interrupt+0x4a/0x60
- apic_timer_interrupt+0x6d/0x80
- cpuidle_enter+0x17/0x20
- call_cpuidle+0x3b/0x60
- cpu_startup_entry+0x22d/0x310
- } hitcount: 1
- { stacktrace:
- netif_rx_internal+0xb2/0xd0
- netif_rx_ni+0x20/0x70
- dev_loopback_xmit+0xaa/0xd0
- ip_mc_output+0x17f/0x240
- ip_local_out_sk+0x31/0x40
- ip_send_skb+0x1a/0x50
- udp_send_skb+0x13e/0x270
- udp_sendmsg+0x2bf/0x980
- inet_sendmsg+0x67/0xa0
- sock_sendmsg+0x38/0x50
- SYSC_sendto+0xef/0x170
- SyS_sendto+0xe/0x10
- entry_SYSCALL_64_fastpath+0x12/0x6a
- } hitcount: 2
- { stacktrace:
- netif_rx_internal+0xb2/0xd0
- netif_rx+0x1c/0x60
- loopback_xmit+0x6c/0xb0
- dev_hard_start_xmit+0x219/0x3a0
- __dev_queue_xmit+0x415/0x4f0
- dev_queue_xmit_sk+0x13/0x20
- ip_finish_output2+0x237/0x340
- ip_finish_output+0x113/0x1d0
- ip_output+0x66/0xc0
- ip_local_out_sk+0x31/0x40
- ip_send_skb+0x1a/0x50
- udp_send_skb+0x16d/0x270
- udp_sendmsg+0x2bf/0x980
- inet_sendmsg+0x67/0xa0
- sock_sendmsg+0x38/0x50
- ___sys_sendmsg+0x14e/0x270
- } hitcount: 76
- { stacktrace:
- netif_rx_internal+0xb2/0xd0
- netif_rx+0x1c/0x60
- loopback_xmit+0x6c/0xb0
- dev_hard_start_xmit+0x219/0x3a0
- __dev_queue_xmit+0x415/0x4f0
- dev_queue_xmit_sk+0x13/0x20
- ip_finish_output2+0x237/0x340
- ip_finish_output+0x113/0x1d0
- ip_output+0x66/0xc0
- ip_local_out_sk+0x31/0x40
- ip_send_skb+0x1a/0x50
- udp_send_skb+0x16d/0x270
- udp_sendmsg+0x2bf/0x980
- inet_sendmsg+0x67/0xa0
- sock_sendmsg+0x38/0x50
- ___sys_sendmsg+0x269/0x270
- } hitcount: 77
- { stacktrace:
- netif_rx_internal+0xb2/0xd0
- netif_rx+0x1c/0x60
- loopback_xmit+0x6c/0xb0
- dev_hard_start_xmit+0x219/0x3a0
- __dev_queue_xmit+0x415/0x4f0
- dev_queue_xmit_sk+0x13/0x20
- ip_finish_output2+0x237/0x340
- ip_finish_output+0x113/0x1d0
- ip_output+0x66/0xc0
- ip_local_out_sk+0x31/0x40
- ip_send_skb+0x1a/0x50
- udp_send_skb+0x16d/0x270
- udp_sendmsg+0x2bf/0x980
- inet_sendmsg+0x67/0xa0
- sock_sendmsg+0x38/0x50
- SYSC_sendto+0xef/0x170
- } hitcount: 88
- { stacktrace:
- _do_fork+0x18e/0x330
- SyS_clone+0x19/0x20
- entry_SYSCALL_64_fastpath+0x12/0x6a
- } hitcount: 244
-
- Totals:
- Hits: 489
- Entries: 7
- Dropped: 0
+=============
+Event Tracing
+=============
+
+:Author: Theodore Ts'o
+:Updated: Li Zefan and Tom Zanussi
+
+1. Introduction
+===============
+
+Tracepoints (see Documentation/trace/tracepoints.txt) can be used
+without creating custom kernel modules to register probe functions
+using the event tracing infrastructure.
+
+Not all tracepoints can be traced using the event tracing system;
+the kernel developer must provide code snippets which define how the
+tracing information is saved into the tracing buffer, and how the
+tracing information should be printed.
+
+2. Using Event Tracing
+======================
+
+2.1 Via the 'set_event' interface
+---------------------------------
+
+The events which are available for tracing can be found in the file
+/sys/kernel/debug/tracing/available_events.
+
+To enable a particular event, such as 'sched_wakeup', simply echo it
+to /sys/kernel/debug/tracing/set_event. For example::
+
+ # echo sched_wakeup >> /sys/kernel/debug/tracing/set_event
+
+.. Note:: '>>' is necessary, otherwise it will firstly disable all the events.
+
+To disable an event, echo the event name to the set_event file prefixed
+with an exclamation point::
+
+ # echo '!sched_wakeup' >> /sys/kernel/debug/tracing/set_event
+
+To disable all events, echo an empty line to the set_event file::
+
+ # echo > /sys/kernel/debug/tracing/set_event
+
+To enable all events, echo ``*:*`` or ``*:`` to the set_event file::
+
+ # echo *:* > /sys/kernel/debug/tracing/set_event
+
+The events are organized into subsystems, such as ext4, irq, sched,
+etc., and a full event name looks like this: <subsystem>:<event>. The
+subsystem name is optional, but it is displayed in the available_events
+file. All of the events in a subsystem can be specified via the syntax
+``<subsystem>:*``; for example, to enable all irq events, you can use the
+command::
+
+ # echo 'irq:*' > /sys/kernel/debug/tracing/set_event
+
+2.2 Via the 'enable' toggle
+---------------------------
+
+The events available are also listed in /sys/kernel/debug/tracing/events/ hierarchy
+of directories.
+
+To enable event 'sched_wakeup'::
+
+ # echo 1 > /sys/kernel/debug/tracing/events/sched/sched_wakeup/enable
+
+To disable it::
+
+ # echo 0 > /sys/kernel/debug/tracing/events/sched/sched_wakeup/enable
+
+To enable all events in sched subsystem::
+
+ # echo 1 > /sys/kernel/debug/tracing/events/sched/enable
+
+To enable all events::
+
+ # echo 1 > /sys/kernel/debug/tracing/events/enable
+
+When reading one of these enable files, there are four results:
+
+ - 0 - all events this file affects are disabled
+ - 1 - all events this file affects are enabled
+ - X - there is a mixture of events enabled and disabled
+ - ? - this file does not affect any event
+
+2.3 Boot option
+---------------
+
+In order to facilitate early boot debugging, use boot option::
+
+ trace_event=[event-list]
+
+event-list is a comma separated list of events. See section 2.1 for event
+format.
+
+3. Defining an event-enabled tracepoint
+=======================================
+
+See The example provided in samples/trace_events
+
+4. Event formats
+================
+
+Each trace event has a 'format' file associated with it that contains
+a description of each field in a logged event. This information can
+be used to parse the binary trace stream, and is also the place to
+find the field names that can be used in event filters (see section 5).
+
+It also displays the format string that will be used to print the
+event in text mode, along with the event name and ID used for
+profiling.
+
+Every event has a set of ``common`` fields associated with it; these are
+the fields prefixed with ``common_``. The other fields vary between
+events and correspond to the fields defined in the TRACE_EVENT
+definition for that event.
+
+Each field in the format has the form::
+
+ field:field-type field-name; offset:N; size:N;
+
+where offset is the offset of the field in the trace record and size
+is the size of the data item, in bytes.
+
+For example, here's the information displayed for the 'sched_wakeup'
+event::
+
+ # cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/format
+
+ name: sched_wakeup
+ ID: 60
+ format:
+ field:unsigned short common_type; offset:0; size:2;
+ field:unsigned char common_flags; offset:2; size:1;
+ field:unsigned char common_preempt_count; offset:3; size:1;
+ field:int common_pid; offset:4; size:4;
+ field:int common_tgid; offset:8; size:4;
+
+ field:char comm[TASK_COMM_LEN]; offset:12; size:16;
+ field:pid_t pid; offset:28; size:4;
+ field:int prio; offset:32; size:4;
+ field:int success; offset:36; size:4;
+ field:int cpu; offset:40; size:4;
+
+ print fmt: "task %s:%d [%d] success=%d [%03d]", REC->comm, REC->pid,
+ REC->prio, REC->success, REC->cpu
+
+This event contains 10 fields, the first 5 common and the remaining 5
+event-specific. All the fields for this event are numeric, except for
+'comm' which is a string, a distinction important for event filtering.
+
+5. Event filtering
+==================
+
+Trace events can be filtered in the kernel by associating boolean
+'filter expressions' with them. As soon as an event is logged into
+the trace buffer, its fields are checked against the filter expression
+associated with that event type. An event with field values that
+'match' the filter will appear in the trace output, and an event whose
+values don't match will be discarded. An event with no filter
+associated with it matches everything, and is the default when no
+filter has been set for an event.
+
+5.1 Expression syntax
+---------------------
+
+A filter expression consists of one or more 'predicates' that can be
+combined using the logical operators '&&' and '||'. A predicate is
+simply a clause that compares the value of a field contained within a
+logged event with a constant value and returns either 0 or 1 depending
+on whether the field value matched (1) or didn't match (0)::
+
+ field-name relational-operator value
+
+Parentheses can be used to provide arbitrary logical groupings and
+double-quotes can be used to prevent the shell from interpreting
+operators as shell metacharacters.
+
+The field-names available for use in filters can be found in the
+'format' files for trace events (see section 4).
+
+The relational-operators depend on the type of the field being tested:
+
+The operators available for numeric fields are:
+
+==, !=, <, <=, >, >=, &
+
+And for string fields they are:
+
+==, !=, ~
+
+The glob (~) accepts a wild card character (\*,?) and character classes
+([). For example::
+
+ prev_comm ~ "*sh"
+ prev_comm ~ "sh*"
+ prev_comm ~ "*sh*"
+ prev_comm ~ "ba*sh"
+
+5.2 Setting filters
+-------------------
+
+A filter for an individual event is set by writing a filter expression
+to the 'filter' file for the given event.
+
+For example::
+
+ # cd /sys/kernel/debug/tracing/events/sched/sched_wakeup
+ # echo "common_preempt_count > 4" > filter
+
+A slightly more involved example::
+
+ # cd /sys/kernel/debug/tracing/events/signal/signal_generate
+ # echo "((sig >= 10 && sig < 15) || sig == 17) && comm != bash" > filter
+
+If there is an error in the expression, you'll get an 'Invalid
+argument' error when setting it, and the erroneous string along with
+an error message can be seen by looking at the filter e.g.::
+
+ # cd /sys/kernel/debug/tracing/events/signal/signal_generate
+ # echo "((sig >= 10 && sig < 15) || dsig == 17) && comm != bash" > filter
+ -bash: echo: write error: Invalid argument
+ # cat filter
+ ((sig >= 10 && sig < 15) || dsig == 17) && comm != bash
+ ^
+ parse_error: Field not found
+
+Currently the caret ('^') for an error always appears at the beginning of
+the filter string; the error message should still be useful though
+even without more accurate position info.
+
+5.3 Clearing filters
+--------------------
+
+To clear the filter for an event, write a '0' to the event's filter
+file.
+
+To clear the filters for all events in a subsystem, write a '0' to the
+subsystem's filter file.
+
+5.3 Subsystem filters
+---------------------
+
+For convenience, filters for every event in a subsystem can be set or
+cleared as a group by writing a filter expression into the filter file
+at the root of the subsystem. Note however, that if a filter for any
+event within the subsystem lacks a field specified in the subsystem
+filter, or if the filter can't be applied for any other reason, the
+filter for that event will retain its previous setting. This can
+result in an unintended mixture of filters which could lead to
+confusing (to the user who might think different filters are in
+effect) trace output. Only filters that reference just the common
+fields can be guaranteed to propagate successfully to all events.
+
+Here are a few subsystem filter examples that also illustrate the
+above points:
+
+Clear the filters on all events in the sched subsystem::
+
+ # cd /sys/kernel/debug/tracing/events/sched
+ # echo 0 > filter
+ # cat sched_switch/filter
+ none
+ # cat sched_wakeup/filter
+ none
+
+Set a filter using only common fields for all events in the sched
+subsystem (all events end up with the same filter)::
+
+ # cd /sys/kernel/debug/tracing/events/sched
+ # echo common_pid == 0 > filter
+ # cat sched_switch/filter
+ common_pid == 0
+ # cat sched_wakeup/filter
+ common_pid == 0
+
+Attempt to set a filter using a non-common field for all events in the
+sched subsystem (all events but those that have a prev_pid field retain
+their old filters)::
+
+ # cd /sys/kernel/debug/tracing/events/sched
+ # echo prev_pid == 0 > filter
+ # cat sched_switch/filter
+ prev_pid == 0
+ # cat sched_wakeup/filter
+ common_pid == 0
+
+5.4 PID filtering
+-----------------
+
+The set_event_pid file in the same directory as the top events directory
+exists, will filter all events from tracing any task that does not have the
+PID listed in the set_event_pid file.
+::
+
+ # cd /sys/kernel/debug/tracing
+ # echo $$ > set_event_pid
+ # echo 1 > events/enable
+
+Will only trace events for the current task.
+
+To add more PIDs without losing the PIDs already included, use '>>'.
+::
+
+ # echo 123 244 1 >> set_event_pid
+
+
+6. Event triggers
+=================
+
+Trace events can be made to conditionally invoke trigger 'commands'
+which can take various forms and are described in detail below;
+examples would be enabling or disabling other trace events or invoking
+a stack trace whenever the trace event is hit. Whenever a trace event
+with attached triggers is invoked, the set of trigger commands
+associated with that event is invoked. Any given trigger can
+additionally have an event filter of the same form as described in
+section 5 (Event filtering) associated with it - the command will only
+be invoked if the event being invoked passes the associated filter.
+If no filter is associated with the trigger, it always passes.
+
+Triggers are added to and removed from a particular event by writing
+trigger expressions to the 'trigger' file for the given event.
+
+A given event can have any number of triggers associated with it,
+subject to any restrictions that individual commands may have in that
+regard.
+
+Event triggers are implemented on top of "soft" mode, which means that
+whenever a trace event has one or more triggers associated with it,
+the event is activated even if it isn't actually enabled, but is
+disabled in a "soft" mode. That is, the tracepoint will be called,
+but just will not be traced, unless of course it's actually enabled.
+This scheme allows triggers to be invoked even for events that aren't
+enabled, and also allows the current event filter implementation to be
+used for conditionally invoking triggers.
+
+The syntax for event triggers is roughly based on the syntax for
+set_ftrace_filter 'ftrace filter commands' (see the 'Filter commands'
+section of Documentation/trace/ftrace.txt), but there are major
+differences and the implementation isn't currently tied to it in any
+way, so beware about making generalizations between the two.
+
+6.1 Expression syntax
+---------------------
+
+Triggers are added by echoing the command to the 'trigger' file::
+
+ # echo 'command[:count] [if filter]' > trigger
+
+Triggers are removed by echoing the same command but starting with '!'
+to the 'trigger' file::
+
+ # echo '!command[:count] [if filter]' > trigger
+
+The [if filter] part isn't used in matching commands when removing, so
+leaving that off in a '!' command will accomplish the same thing as
+having it in.
+
+The filter syntax is the same as that described in the 'Event
+filtering' section above.
+
+For ease of use, writing to the trigger file using '>' currently just
+adds or removes a single trigger and there's no explicit '>>' support
+('>' actually behaves like '>>') or truncation support to remove all
+triggers (you have to use '!' for each one added.)
+
+6.2 Supported trigger commands
+------------------------------
+
+The following commands are supported:
+
+- enable_event/disable_event
+
+ These commands can enable or disable another trace event whenever
+ the triggering event is hit. When these commands are registered,
+ the other trace event is activated, but disabled in a "soft" mode.
+ That is, the tracepoint will be called, but just will not be traced.
+ The event tracepoint stays in this mode as long as there's a trigger
+ in effect that can trigger it.
+
+ For example, the following trigger causes kmalloc events to be
+ traced when a read system call is entered, and the :1 at the end
+ specifies that this enablement happens only once::
+
+ # echo 'enable_event:kmem:kmalloc:1' > \
+ /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
+
+ The following trigger causes kmalloc events to stop being traced
+ when a read system call exits. This disablement happens on every
+ read system call exit::
+
+ # echo 'disable_event:kmem:kmalloc' > \
+ /sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger
+
+ The format is::
+
+ enable_event:<system>:<event>[:count]
+ disable_event:<system>:<event>[:count]
+
+ To remove the above commands::
+
+ # echo '!enable_event:kmem:kmalloc:1' > \
+ /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
+
+ # echo '!disable_event:kmem:kmalloc' > \
+ /sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger
+
+ Note that there can be any number of enable/disable_event triggers
+ per triggering event, but there can only be one trigger per
+ triggered event. e.g. sys_enter_read can have triggers enabling both
+ kmem:kmalloc and sched:sched_switch, but can't have two kmem:kmalloc
+ versions such as kmem:kmalloc and kmem:kmalloc:1 or 'kmem:kmalloc if
+ bytes_req == 256' and 'kmem:kmalloc if bytes_alloc == 256' (they
+ could be combined into a single filter on kmem:kmalloc though).
+
+- stacktrace
+
+ This command dumps a stacktrace in the trace buffer whenever the
+ triggering event occurs.
+
+ For example, the following trigger dumps a stacktrace every time the
+ kmalloc tracepoint is hit::
+
+ # echo 'stacktrace' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ The following trigger dumps a stacktrace the first 5 times a kmalloc
+ request happens with a size >= 64K::
+
+ # echo 'stacktrace:5 if bytes_req >= 65536' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ The format is::
+
+ stacktrace[:count]
+
+ To remove the above commands::
+
+ # echo '!stacktrace' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ # echo '!stacktrace:5 if bytes_req >= 65536' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ The latter can also be removed more simply by the following (without
+ the filter)::
+
+ # echo '!stacktrace:5' > \
+ /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
+
+ Note that there can be only one stacktrace trigger per triggering
+ event.
+
+- snapshot
+
+ This command causes a snapshot to be triggered whenever the
+ triggering event occurs.
+
+ The following command creates a snapshot every time a block request
+ queue is unplugged with a depth > 1. If you were tracing a set of
+ events or functions at the time, the snapshot trace buffer would
+ capture those events when the trigger event occurred::
+
+ # echo 'snapshot if nr_rq > 1' > \
+ /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+ To only snapshot once::
+
+ # echo 'snapshot:1 if nr_rq > 1' > \
+ /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+ To remove the above commands::
+
+ # echo '!snapshot if nr_rq > 1' > \
+ /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+ # echo '!snapshot:1 if nr_rq > 1' > \
+ /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+ Note that there can be only one snapshot trigger per triggering
+ event.
+
+- traceon/traceoff
+
+ These commands turn tracing on and off when the specified events are
+ hit. The parameter determines how many times the tracing system is
+ turned on and off. If unspecified, there is no limit.
+
+ The following command turns tracing off the first time a block
+ request queue is unplugged with a depth > 1. If you were tracing a
+ set of events or functions at the time, you could then examine the
+ trace buffer to see the sequence of events that led up to the
+ trigger event::
+
+ # echo 'traceoff:1 if nr_rq > 1' > \
+ /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+ To always disable tracing when nr_rq > 1::
+
+ # echo 'traceoff if nr_rq > 1' > \
+ /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+ To remove the above commands::
+
+ # echo '!traceoff:1 if nr_rq > 1' > \
+ /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+ # echo '!traceoff if nr_rq > 1' > \
+ /sys/kernel/debug/tracing/events/block/block_unplug/trigger
+
+ Note that there can be only one traceon or traceoff trigger per
+ triggering event.
+
+- hist
+
+ This command aggregates event hits into a hash table keyed on one or
+ more trace event format fields (or stacktrace) and a set of running
+ totals derived from one or more trace event format fields and/or
+ event counts (hitcount).
+
++ See Documentation/trace/histogram.txt for details and examples.
--- /dev/null
+========================
+ftrace - Function Tracer
+========================
+
+Copyright 2008 Red Hat Inc.
+
+:Author: Steven Rostedt <srostedt@redhat.com>
+:License: The GNU Free Documentation License, Version 1.2
+ (dual licensed under the GPL v2)
+:Original Reviewers: Elias Oltmanns, Randy Dunlap, Andrew Morton,
+ John Kacur, and David Teigland.
+
+- Written for: 2.6.28-rc2
+- Updated for: 3.10
+- Updated for: 4.13 - Copyright 2017 VMware Inc. Steven Rostedt
+- Converted to rst format - Changbin Du <changbin.du@intel.com>
+
+Introduction
+------------
+
+Ftrace is an internal tracer designed to help out developers and
+designers of systems to find what is going on inside the kernel.
+It can be used for debugging or analyzing latencies and
+performance issues that take place outside of user-space.
+
+Although ftrace is typically considered the function tracer, it
+is really a frame work of several assorted tracing utilities.
+There's latency tracing to examine what occurs between interrupts
+disabled and enabled, as well as for preemption and from a time
+a task is woken to the task is actually scheduled in.
+
+One of the most common uses of ftrace is the event tracing.
+Through out the kernel is hundreds of static event points that
+can be enabled via the tracefs file system to see what is
+going on in certain parts of the kernel.
+
+See events.txt for more information.
+
+
+Implementation Details
+----------------------
+
+See :doc:`ftrace-design` for details for arch porters and such.
+
+
+The File System
+---------------
+
+Ftrace uses the tracefs file system to hold the control files as
+well as the files to display output.
+
+When tracefs is configured into the kernel (which selecting any ftrace
+option will do) the directory /sys/kernel/tracing will be created. To mount
+this directory, you can add to your /etc/fstab file::
+
+ tracefs /sys/kernel/tracing tracefs defaults 0 0
+
+Or you can mount it at run time with::
+
+ mount -t tracefs nodev /sys/kernel/tracing
+
+For quicker access to that directory you may want to make a soft link to
+it::
+
+ ln -s /sys/kernel/tracing /tracing
+
+.. attention::
+
+ Before 4.1, all ftrace tracing control files were within the debugfs
+ file system, which is typically located at /sys/kernel/debug/tracing.
+ For backward compatibility, when mounting the debugfs file system,
+ the tracefs file system will be automatically mounted at:
+
+ /sys/kernel/debug/tracing
+
+ All files located in the tracefs file system will be located in that
+ debugfs file system directory as well.
+
+.. attention::
+
+ Any selected ftrace option will also create the tracefs file system.
+ The rest of the document will assume that you are in the ftrace directory
+ (cd /sys/kernel/tracing) and will only concentrate on the files within that
+ directory and not distract from the content with the extended
+ "/sys/kernel/tracing" path name.
+
+That's it! (assuming that you have ftrace configured into your kernel)
+
+After mounting tracefs you will have access to the control and output files
+of ftrace. Here is a list of some of the key files:
+
+
+ Note: all time values are in microseconds.
+
+ current_tracer:
+
+ This is used to set or display the current tracer
+ that is configured.
+
+ available_tracers:
+
+ This holds the different types of tracers that
+ have been compiled into the kernel. The
+ tracers listed here can be configured by
+ echoing their name into current_tracer.
+
+ tracing_on:
+
+ This sets or displays whether writing to the trace
+ ring buffer is enabled. Echo 0 into this file to disable
+ the tracer or 1 to enable it. Note, this only disables
+ writing to the ring buffer, the tracing overhead may
+ still be occurring.
+
+ The kernel function tracing_off() can be used within the
+ kernel to disable writing to the ring buffer, which will
+ set this file to "0". User space can re-enable tracing by
+ echoing "1" into the file.
+
+ Note, the function and event trigger "traceoff" will also
+ set this file to zero and stop tracing. Which can also
+ be re-enabled by user space using this file.
+
+ trace:
+
+ This file holds the output of the trace in a human
+ readable format (described below). Note, tracing is temporarily
+ disabled while this file is being read (opened).
+
+ trace_pipe:
+
+ The output is the same as the "trace" file but this
+ file is meant to be streamed with live tracing.
+ Reads from this file will block until new data is
+ retrieved. Unlike the "trace" file, this file is a
+ consumer. This means reading from this file causes
+ sequential reads to display more current data. Once
+ data is read from this file, it is consumed, and
+ will not be read again with a sequential read. The
+ "trace" file is static, and if the tracer is not
+ adding more data, it will display the same
+ information every time it is read. This file will not
+ disable tracing while being read.
+
+ trace_options:
+
+ This file lets the user control the amount of data
+ that is displayed in one of the above output
+ files. Options also exist to modify how a tracer
+ or events work (stack traces, timestamps, etc).
+
+ options:
+
+ This is a directory that has a file for every available
+ trace option (also in trace_options). Options may also be set
+ or cleared by writing a "1" or "0" respectively into the
+ corresponding file with the option name.
+
+ tracing_max_latency:
+
+ Some of the tracers record the max latency.
+ For example, the maximum time that interrupts are disabled.
+ The maximum time is saved in this file. The max trace will also be
+ stored, and displayed by "trace". A new max trace will only be
+ recorded if the latency is greater than the value in this file
+ (in microseconds).
+
+ By echoing in a time into this file, no latency will be recorded
+ unless it is greater than the time in this file.
+
+ tracing_thresh:
+
+ Some latency tracers will record a trace whenever the
+ latency is greater than the number in this file.
+ Only active when the file contains a number greater than 0.
+ (in microseconds)
+
+ buffer_size_kb:
+
+ This sets or displays the number of kilobytes each CPU
+ buffer holds. By default, the trace buffers are the same size
+ for each CPU. The displayed number is the size of the
+ CPU buffer and not total size of all buffers. The
+ trace buffers are allocated in pages (blocks of memory
+ that the kernel uses for allocation, usually 4 KB in size).
+ If the last page allocated has room for more bytes
+ than requested, the rest of the page will be used,
+ making the actual allocation bigger than requested or shown.
+ ( Note, the size may not be a multiple of the page size
+ due to buffer management meta-data. )
+
+ Buffer sizes for individual CPUs may vary
+ (see "per_cpu/cpu0/buffer_size_kb" below), and if they do
+ this file will show "X".
+
+ buffer_total_size_kb:
+
+ This displays the total combined size of all the trace buffers.
+
+ free_buffer:
+
+ If a process is performing tracing, and the ring buffer should be
+ shrunk "freed" when the process is finished, even if it were to be
+ killed by a signal, this file can be used for that purpose. On close
+ of this file, the ring buffer will be resized to its minimum size.
+ Having a process that is tracing also open this file, when the process
+ exits its file descriptor for this file will be closed, and in doing so,
+ the ring buffer will be "freed".
+
+ It may also stop tracing if disable_on_free option is set.
+
+ tracing_cpumask:
+
+ This is a mask that lets the user only trace on specified CPUs.
+ The format is a hex string representing the CPUs.
+
+ set_ftrace_filter:
+
+ When dynamic ftrace is configured in (see the
+ section below "dynamic ftrace"), the code is dynamically
+ modified (code text rewrite) to disable calling of the
+ function profiler (mcount). This lets tracing be configured
+ in with practically no overhead in performance. This also
+ has a side effect of enabling or disabling specific functions
+ to be traced. Echoing names of functions into this file
+ will limit the trace to only those functions.
+
+ The functions listed in "available_filter_functions" are what
+ can be written into this file.
+
+ This interface also allows for commands to be used. See the
+ "Filter commands" section for more details.
+
+ set_ftrace_notrace:
+
+ This has an effect opposite to that of
+ set_ftrace_filter. Any function that is added here will not
+ be traced. If a function exists in both set_ftrace_filter
+ and set_ftrace_notrace, the function will _not_ be traced.
+
+ set_ftrace_pid:
+
+ Have the function tracer only trace the threads whose PID are
+ listed in this file.
+
+ If the "function-fork" option is set, then when a task whose
+ PID is listed in this file forks, the child's PID will
+ automatically be added to this file, and the child will be
+ traced by the function tracer as well. This option will also
+ cause PIDs of tasks that exit to be removed from the file.
+
+ set_event_pid:
+
+ Have the events only trace a task with a PID listed in this file.
+ Note, sched_switch and sched_wake_up will also trace events
+ listed in this file.
+
+ To have the PIDs of children of tasks with their PID in this file
+ added on fork, enable the "event-fork" option. That option will also
+ cause the PIDs of tasks to be removed from this file when the task
+ exits.
+
+ set_graph_function:
+
+ Functions listed in this file will cause the function graph
+ tracer to only trace these functions and the functions that
+ they call. (See the section "dynamic ftrace" for more details).
+
+ set_graph_notrace:
+
+ Similar to set_graph_function, but will disable function graph
+ tracing when the function is hit until it exits the function.
+ This makes it possible to ignore tracing functions that are called
+ by a specific function.
+
+ available_filter_functions:
+
+ This lists the functions that ftrace has processed and can trace.
+ These are the function names that you can pass to
+ "set_ftrace_filter" or "set_ftrace_notrace".
+ (See the section "dynamic ftrace" below for more details.)
+
+ dyn_ftrace_total_info:
+
+ This file is for debugging purposes. The number of functions that
+ have been converted to nops and are available to be traced.
+
+ enabled_functions:
+
+ This file is more for debugging ftrace, but can also be useful
+ in seeing if any function has a callback attached to it.
+ Not only does the trace infrastructure use ftrace function
+ trace utility, but other subsystems might too. This file
+ displays all functions that have a callback attached to them
+ as well as the number of callbacks that have been attached.
+ Note, a callback may also call multiple functions which will
+ not be listed in this count.
+
+ If the callback registered to be traced by a function with
+ the "save regs" attribute (thus even more overhead), a 'R'
+ will be displayed on the same line as the function that
+ is returning registers.
+
+ If the callback registered to be traced by a function with
+ the "ip modify" attribute (thus the regs->ip can be changed),
+ an 'I' will be displayed on the same line as the function that
+ can be overridden.
+
+ If the architecture supports it, it will also show what callback
+ is being directly called by the function. If the count is greater
+ than 1 it most likely will be ftrace_ops_list_func().
+
+ If the callback of the function jumps to a trampoline that is
+ specific to a the callback and not the standard trampoline,
+ its address will be printed as well as the function that the
+ trampoline calls.
+
+ function_profile_enabled:
+
+ When set it will enable all functions with either the function
+ tracer, or if configured, the function graph tracer. It will
+ keep a histogram of the number of functions that were called
+ and if the function graph tracer was configured, it will also keep
+ track of the time spent in those functions. The histogram
+ content can be displayed in the files:
+
+ trace_stats/function<cpu> ( function0, function1, etc).
+
+ trace_stats:
+
+ A directory that holds different tracing stats.
+
+ kprobe_events:
+
+ Enable dynamic trace points. See kprobetrace.txt.
+
+ kprobe_profile:
+
+ Dynamic trace points stats. See kprobetrace.txt.
+
+ max_graph_depth:
+
+ Used with the function graph tracer. This is the max depth
+ it will trace into a function. Setting this to a value of
+ one will show only the first kernel function that is called
+ from user space.
+
+ printk_formats:
+
+ This is for tools that read the raw format files. If an event in
+ the ring buffer references a string, only a pointer to the string
+ is recorded into the buffer and not the string itself. This prevents
+ tools from knowing what that string was. This file displays the string
+ and address for the string allowing tools to map the pointers to what
+ the strings were.
+
+ saved_cmdlines:
+
+ Only the pid of the task is recorded in a trace event unless
+ the event specifically saves the task comm as well. Ftrace
+ makes a cache of pid mappings to comms to try to display
+ comms for events. If a pid for a comm is not listed, then
+ "<...>" is displayed in the output.
+
+ If the option "record-cmd" is set to "0", then comms of tasks
+ will not be saved during recording. By default, it is enabled.
+
+ saved_cmdlines_size:
+
+ By default, 128 comms are saved (see "saved_cmdlines" above). To
+ increase or decrease the amount of comms that are cached, echo
+ in a the number of comms to cache, into this file.
+
+ saved_tgids:
+
+ If the option "record-tgid" is set, on each scheduling context switch
+ the Task Group ID of a task is saved in a table mapping the PID of
+ the thread to its TGID. By default, the "record-tgid" option is
+ disabled.
+
+ snapshot:
+
+ This displays the "snapshot" buffer and also lets the user
+ take a snapshot of the current running trace.
+ See the "Snapshot" section below for more details.
+
+ stack_max_size:
+
+ When the stack tracer is activated, this will display the
+ maximum stack size it has encountered.
+ See the "Stack Trace" section below.
+
+ stack_trace:
+
+ This displays the stack back trace of the largest stack
+ that was encountered when the stack tracer is activated.
+ See the "Stack Trace" section below.
+
+ stack_trace_filter:
+
+ This is similar to "set_ftrace_filter" but it limits what
+ functions the stack tracer will check.
+
+ trace_clock:
+
+ Whenever an event is recorded into the ring buffer, a
+ "timestamp" is added. This stamp comes from a specified
+ clock. By default, ftrace uses the "local" clock. This
+ clock is very fast and strictly per cpu, but on some
+ systems it may not be monotonic with respect to other
+ CPUs. In other words, the local clocks may not be in sync
+ with local clocks on other CPUs.
+
+ Usual clocks for tracing::
+
+ # cat trace_clock
+ [local] global counter x86-tsc
+
+ The clock with the square brackets around it is the one in effect.
+
+ local:
+ Default clock, but may not be in sync across CPUs
+
+ global:
+ This clock is in sync with all CPUs but may
+ be a bit slower than the local clock.
+
+ counter:
+ This is not a clock at all, but literally an atomic
+ counter. It counts up one by one, but is in sync
+ with all CPUs. This is useful when you need to
+ know exactly the order events occurred with respect to
+ each other on different CPUs.
+
+ uptime:
+ This uses the jiffies counter and the time stamp
+ is relative to the time since boot up.
+
+ perf:
+ This makes ftrace use the same clock that perf uses.
+ Eventually perf will be able to read ftrace buffers
+ and this will help out in interleaving the data.
+
+ x86-tsc:
+ Architectures may define their own clocks. For
+ example, x86 uses its own TSC cycle clock here.
+
+ ppc-tb:
+ This uses the powerpc timebase register value.
+ This is in sync across CPUs and can also be used
+ to correlate events across hypervisor/guest if
+ tb_offset is known.
+
+ mono:
+ This uses the fast monotonic clock (CLOCK_MONOTONIC)
+ which is monotonic and is subject to NTP rate adjustments.
+
+ mono_raw:
+ This is the raw monotonic clock (CLOCK_MONOTONIC_RAW)
+ which is montonic but is not subject to any rate adjustments
+ and ticks at the same rate as the hardware clocksource.
+
+ boot:
+ Same as mono. Used to be a separate clock which accounted
+ for the time spent in suspend while CLOCK_MONOTONIC did
+ not.
+
+ To set a clock, simply echo the clock name into this file::
+
+ # echo global > trace_clock
+
+ trace_marker:
+
+ This is a very useful file for synchronizing user space
+ with events happening in the kernel. Writing strings into
+ this file will be written into the ftrace buffer.
+
+ It is useful in applications to open this file at the start
+ of the application and just reference the file descriptor
+ for the file::
+
+ void trace_write(const char *fmt, ...)
+ {
+ va_list ap;
+ char buf[256];
+ int n;
+
+ if (trace_fd < 0)
+ return;
+
+ va_start(ap, fmt);
+ n = vsnprintf(buf, 256, fmt, ap);
+ va_end(ap);
+
+ write(trace_fd, buf, n);
+ }
+
+ start::
+
+ trace_fd = open("trace_marker", WR_ONLY);
+
+ trace_marker_raw:
+
+ This is similar to trace_marker above, but is meant for for binary data
+ to be written to it, where a tool can be used to parse the data
+ from trace_pipe_raw.
+
+ uprobe_events:
+
+ Add dynamic tracepoints in programs.
+ See uprobetracer.txt
+
+ uprobe_profile:
+
+ Uprobe statistics. See uprobetrace.txt
+
+ instances:
+
+ This is a way to make multiple trace buffers where different
+ events can be recorded in different buffers.
+ See "Instances" section below.
+
+ events:
+
+ This is the trace event directory. It holds event tracepoints
+ (also known as static tracepoints) that have been compiled
+ into the kernel. It shows what event tracepoints exist
+ and how they are grouped by system. There are "enable"
+ files at various levels that can enable the tracepoints
+ when a "1" is written to them.
+
+ See events.txt for more information.
+
+ set_event:
+
+ By echoing in the event into this file, will enable that event.
+
+ See events.txt for more information.
+
+ available_events:
+
+ A list of events that can be enabled in tracing.
+
+ See events.txt for more information.
+
++ timestamp_mode:
++
++ Certain tracers may change the timestamp mode used when
++ logging trace events into the event buffer. Events with
++ different modes can coexist within a buffer but the mode in
++ effect when an event is logged determines which timestamp mode
++ is used for that event. The default timestamp mode is
++ 'delta'.
++
++ Usual timestamp modes for tracing:
++
++ # cat timestamp_mode
++ [delta] absolute
++
++ The timestamp mode with the square brackets around it is the
++ one in effect.
++
++ delta: Default timestamp mode - timestamp is a delta against
++ a per-buffer timestamp.
++
++ absolute: The timestamp is a full timestamp, not a delta
++ against some other value. As such it takes up more
++ space and is less efficient.
++
+ hwlat_detector:
+
+ Directory for the Hardware Latency Detector.
+ See "Hardware Latency Detector" section below.
+
+ per_cpu:
+
+ This is a directory that contains the trace per_cpu information.
+
+ per_cpu/cpu0/buffer_size_kb:
+
+ The ftrace buffer is defined per_cpu. That is, there's a separate
+ buffer for each CPU to allow writes to be done atomically,
+ and free from cache bouncing. These buffers may have different
+ size buffers. This file is similar to the buffer_size_kb
+ file, but it only displays or sets the buffer size for the
+ specific CPU. (here cpu0).
+
+ per_cpu/cpu0/trace:
+
+ This is similar to the "trace" file, but it will only display
+ the data specific for the CPU. If written to, it only clears
+ the specific CPU buffer.
+
+ per_cpu/cpu0/trace_pipe
+
+ This is similar to the "trace_pipe" file, and is a consuming
+ read, but it will only display (and consume) the data specific
+ for the CPU.
+
+ per_cpu/cpu0/trace_pipe_raw
+
+ For tools that can parse the ftrace ring buffer binary format,
+ the trace_pipe_raw file can be used to extract the data
+ from the ring buffer directly. With the use of the splice()
+ system call, the buffer data can be quickly transferred to
+ a file or to the network where a server is collecting the
+ data.
+
+ Like trace_pipe, this is a consuming reader, where multiple
+ reads will always produce different data.
+
+ per_cpu/cpu0/snapshot:
+
+ This is similar to the main "snapshot" file, but will only
+ snapshot the current CPU (if supported). It only displays
+ the content of the snapshot for a given CPU, and if
+ written to, only clears this CPU buffer.
+
+ per_cpu/cpu0/snapshot_raw:
+
+ Similar to the trace_pipe_raw, but will read the binary format
+ from the snapshot buffer for the given CPU.
+
+ per_cpu/cpu0/stats:
+
+ This displays certain stats about the ring buffer:
+
+ entries:
+ The number of events that are still in the buffer.
+
+ overrun:
+ The number of lost events due to overwriting when
+ the buffer was full.
+
+ commit overrun:
+ Should always be zero.
+ This gets set if so many events happened within a nested
+ event (ring buffer is re-entrant), that it fills the
+ buffer and starts dropping events.
+
+ bytes:
+ Bytes actually read (not overwritten).
+
+ oldest event ts:
+ The oldest timestamp in the buffer
+
+ now ts:
+ The current timestamp
+
+ dropped events:
+ Events lost due to overwrite option being off.
+
+ read events:
+ The number of events read.
+
+The Tracers
+-----------
+
+Here is the list of current tracers that may be configured.
+
+ "function"
+
+ Function call tracer to trace all kernel functions.
+
+ "function_graph"
+
+ Similar to the function tracer except that the
+ function tracer probes the functions on their entry
+ whereas the function graph tracer traces on both entry
+ and exit of the functions. It then provides the ability
+ to draw a graph of function calls similar to C code
+ source.
+
+ "blk"
+
+ The block tracer. The tracer used by the blktrace user
+ application.
+
+ "hwlat"
+
+ The Hardware Latency tracer is used to detect if the hardware
+ produces any latency. See "Hardware Latency Detector" section
+ below.
+
+ "irqsoff"
+
+ Traces the areas that disable interrupts and saves
+ the trace with the longest max latency.
+ See tracing_max_latency. When a new max is recorded,
+ it replaces the old trace. It is best to view this
+ trace with the latency-format option enabled, which
+ happens automatically when the tracer is selected.
+
+ "preemptoff"
+
+ Similar to irqsoff but traces and records the amount of
+ time for which preemption is disabled.
+
+ "preemptirqsoff"
+
+ Similar to irqsoff and preemptoff, but traces and
+ records the largest time for which irqs and/or preemption
+ is disabled.
+
+ "wakeup"
+
+ Traces and records the max latency that it takes for
+ the highest priority task to get scheduled after
+ it has been woken up.
+ Traces all tasks as an average developer would expect.
+
+ "wakeup_rt"
+
+ Traces and records the max latency that it takes for just
+ RT tasks (as the current "wakeup" does). This is useful
+ for those interested in wake up timings of RT tasks.
+
+ "wakeup_dl"
+
+ Traces and records the max latency that it takes for
+ a SCHED_DEADLINE task to be woken (as the "wakeup" and
+ "wakeup_rt" does).
+
+ "mmiotrace"
+
+ A special tracer that is used to trace binary module.
+ It will trace all the calls that a module makes to the
+ hardware. Everything it writes and reads from the I/O
+ as well.
+
+ "branch"
+
+ This tracer can be configured when tracing likely/unlikely
+ calls within the kernel. It will trace when a likely and
+ unlikely branch is hit and if it was correct in its prediction
+ of being correct.
+
+ "nop"
+
+ This is the "trace nothing" tracer. To remove all
+ tracers from tracing simply echo "nop" into
+ current_tracer.
+
+
+Examples of using the tracer
+----------------------------
+
+Here are typical examples of using the tracers when controlling
+them only with the tracefs interface (without using any
+user-land utilities).
+
+Output format:
+--------------
+
+Here is an example of the output format of the file "trace"::
+
+ # tracer: function
+ #
+ # entries-in-buffer/entries-written: 140080/250280 #P:4
+ #
+ # _-----=> irqs-off
+ # / _----=> need-resched
+ # | / _---=> hardirq/softirq
+ # || / _--=> preempt-depth
+ # ||| / delay
+ # TASK-PID CPU# |||| TIMESTAMP FUNCTION
+ # | | | |||| | |
+ bash-1977 [000] .... 17284.993652: sys_close <-system_call_fastpath
+ bash-1977 [000] .... 17284.993653: __close_fd <-sys_close
+ bash-1977 [000] .... 17284.993653: _raw_spin_lock <-__close_fd
+ sshd-1974 [003] .... 17284.993653: __srcu_read_unlock <-fsnotify
+ bash-1977 [000] .... 17284.993654: add_preempt_count <-_raw_spin_lock
+ bash-1977 [000] ...1 17284.993655: _raw_spin_unlock <-__close_fd
+ bash-1977 [000] ...1 17284.993656: sub_preempt_count <-_raw_spin_unlock
+ bash-1977 [000] .... 17284.993657: filp_close <-__close_fd
+ bash-1977 [000] .... 17284.993657: dnotify_flush <-filp_close
+ sshd-1974 [003] .... 17284.993658: sys_select <-system_call_fastpath
+ ....
+
+A header is printed with the tracer name that is represented by
+the trace. In this case the tracer is "function". Then it shows the
+number of events in the buffer as well as the total number of entries
+that were written. The difference is the number of entries that were
+lost due to the buffer filling up (250280 - 140080 = 110200 events
+lost).
+
+The header explains the content of the events. Task name "bash", the task
+PID "1977", the CPU that it was running on "000", the latency format
+(explained below), the timestamp in <secs>.<usecs> format, the
+function name that was traced "sys_close" and the parent function that
+called this function "system_call_fastpath". The timestamp is the time
+at which the function was entered.
+
+Latency trace format
+--------------------
+
+When the latency-format option is enabled or when one of the latency
+tracers is set, the trace file gives somewhat more information to see
+why a latency happened. Here is a typical trace::
+
+ # tracer: irqsoff
+ #
+ # irqsoff latency trace v1.1.5 on 3.8.0-test+
+ # --------------------------------------------------------------------
+ # latency: 259 us, #4/4, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+ # -----------------
+ # | task: ps-6143 (uid:0 nice:0 policy:0 rt_prio:0)
+ # -----------------
+ # => started at: __lock_task_sighand
+ # => ended at: _raw_spin_unlock_irqrestore
+ #
+ #
+ # _------=> CPU#
+ # / _-----=> irqs-off
+ # | / _----=> need-resched
+ # || / _---=> hardirq/softirq
+ # ||| / _--=> preempt-depth
+ # |||| / delay
+ # cmd pid ||||| time | caller
+ # \ / ||||| \ | /
+ ps-6143 2d... 0us!: trace_hardirqs_off <-__lock_task_sighand
+ ps-6143 2d..1 259us+: trace_hardirqs_on <-_raw_spin_unlock_irqrestore
+ ps-6143 2d..1 263us+: time_hardirqs_on <-_raw_spin_unlock_irqrestore
+ ps-6143 2d..1 306us : <stack trace>
+ => trace_hardirqs_on_caller
+ => trace_hardirqs_on
+ => _raw_spin_unlock_irqrestore
+ => do_task_stat
+ => proc_tgid_stat
+ => proc_single_show
+ => seq_read
+ => vfs_read
+ => sys_read
+ => system_call_fastpath
+
+
+This shows that the current tracer is "irqsoff" tracing the time
+for which interrupts were disabled. It gives the trace version (which
+never changes) and the version of the kernel upon which this was executed on
+(3.8). Then it displays the max latency in microseconds (259 us). The number
+of trace entries displayed and the total number (both are four: #4/4).
+VP, KP, SP, and HP are always zero and are reserved for later use.
+#P is the number of online CPUs (#P:4).
+
+The task is the process that was running when the latency
+occurred. (ps pid: 6143).
+
+The start and stop (the functions in which the interrupts were
+disabled and enabled respectively) that caused the latencies:
+
+ - __lock_task_sighand is where the interrupts were disabled.
+ - _raw_spin_unlock_irqrestore is where they were enabled again.
+
+The next lines after the header are the trace itself. The header
+explains which is which.
+
+ cmd: The name of the process in the trace.
+
+ pid: The PID of that process.
+
+ CPU#: The CPU which the process was running on.
+
+ irqs-off: 'd' interrupts are disabled. '.' otherwise.
+ .. caution:: If the architecture does not support a way to
+ read the irq flags variable, an 'X' will always
+ be printed here.
+
+ need-resched:
+ - 'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set,
+ - 'n' only TIF_NEED_RESCHED is set,
+ - 'p' only PREEMPT_NEED_RESCHED is set,
+ - '.' otherwise.
+
+ hardirq/softirq:
+ - 'Z' - NMI occurred inside a hardirq
+ - 'z' - NMI is running
+ - 'H' - hard irq occurred inside a softirq.
+ - 'h' - hard irq is running
+ - 's' - soft irq is running
+ - '.' - normal context.
+
+ preempt-depth: The level of preempt_disabled
+
+The above is mostly meaningful for kernel developers.
+
+ time:
+ When the latency-format option is enabled, the trace file
+ output includes a timestamp relative to the start of the
+ trace. This differs from the output when latency-format
+ is disabled, which includes an absolute timestamp.
+
+ delay:
+ This is just to help catch your eye a bit better. And
+ needs to be fixed to be only relative to the same CPU.
+ The marks are determined by the difference between this
+ current trace and the next trace.
+
+ - '$' - greater than 1 second
+ - '@' - greater than 100 milisecond
+ - '*' - greater than 10 milisecond
+ - '#' - greater than 1000 microsecond
+ - '!' - greater than 100 microsecond
+ - '+' - greater than 10 microsecond
+ - ' ' - less than or equal to 10 microsecond.
+
+ The rest is the same as the 'trace' file.
+
+ Note, the latency tracers will usually end with a back trace
+ to easily find where the latency occurred.
+
+trace_options
+-------------
+
+The trace_options file (or the options directory) is used to control
+what gets printed in the trace output, or manipulate the tracers.
+To see what is available, simply cat the file::
+
+ cat trace_options
+ print-parent
+ nosym-offset
+ nosym-addr
+ noverbose
+ noraw
+ nohex
+ nobin
+ noblock
+ trace_printk
+ annotate
+ nouserstacktrace
+ nosym-userobj
+ noprintk-msg-only
+ context-info
+ nolatency-format
+ record-cmd
+ norecord-tgid
+ overwrite
+ nodisable_on_free
+ irq-info
+ markers
+ noevent-fork
+ function-trace
+ nofunction-fork
+ nodisplay-graph
+ nostacktrace
+ nobranch
+
+To disable one of the options, echo in the option prepended with
+"no"::
+
+ echo noprint-parent > trace_options
+
+To enable an option, leave off the "no"::
+
+ echo sym-offset > trace_options
+
+Here are the available options:
+
+ print-parent
+ On function traces, display the calling (parent)
+ function as well as the function being traced.
+ ::
+
+ print-parent:
+ bash-4000 [01] 1477.606694: simple_strtoul <-kstrtoul
+
+ noprint-parent:
+ bash-4000 [01] 1477.606694: simple_strtoul
+
+
+ sym-offset
+ Display not only the function name, but also the
+ offset in the function. For example, instead of
+ seeing just "ktime_get", you will see
+ "ktime_get+0xb/0x20".
+ ::
+
+ sym-offset:
+ bash-4000 [01] 1477.606694: simple_strtoul+0x6/0xa0
+
+ sym-addr
+ This will also display the function address as well
+ as the function name.
+ ::
+
+ sym-addr:
+ bash-4000 [01] 1477.606694: simple_strtoul <c0339346>
+
+ verbose
+ This deals with the trace file when the
+ latency-format option is enabled.
+ ::
+
+ bash 4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \
+ (+0.000ms): simple_strtoul (kstrtoul)
+
+ raw
+ This will display raw numbers. This option is best for
+ use with user applications that can translate the raw
+ numbers better than having it done in the kernel.
+
+ hex
+ Similar to raw, but the numbers will be in a hexadecimal format.
+
+ bin
+ This will print out the formats in raw binary.
+
+ block
+ When set, reading trace_pipe will not block when polled.
+
+ trace_printk
+ Can disable trace_printk() from writing into the buffer.
+
+ annotate
+ It is sometimes confusing when the CPU buffers are full
+ and one CPU buffer had a lot of events recently, thus
+ a shorter time frame, were another CPU may have only had
+ a few events, which lets it have older events. When
+ the trace is reported, it shows the oldest events first,
+ and it may look like only one CPU ran (the one with the
+ oldest events). When the annotate option is set, it will
+ display when a new CPU buffer started::
+
+ <idle>-0 [001] dNs4 21169.031481: wake_up_idle_cpu <-add_timer_on
+ <idle>-0 [001] dNs4 21169.031482: _raw_spin_unlock_irqrestore <-add_timer_on
+ <idle>-0 [001] .Ns4 21169.031484: sub_preempt_count <-_raw_spin_unlock_irqrestore
+ ##### CPU 2 buffer started ####
+ <idle>-0 [002] .N.1 21169.031484: rcu_idle_exit <-cpu_idle
+ <idle>-0 [001] .Ns3 21169.031484: _raw_spin_unlock <-clocksource_watchdog
+ <idle>-0 [001] .Ns3 21169.031485: sub_preempt_count <-_raw_spin_unlock
+
+ userstacktrace
+ This option changes the trace. It records a
+ stacktrace of the current user space thread after
+ each trace event.
+
+ sym-userobj
+ when user stacktrace are enabled, look up which
+ object the address belongs to, and print a
+ relative address. This is especially useful when
+ ASLR is on, otherwise you don't get a chance to
+ resolve the address to object/file/line after
+ the app is no longer running
+
+ The lookup is performed when you read
+ trace,trace_pipe. Example::
+
+ a.out-1623 [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0
+ x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
+
+
+ printk-msg-only
+ When set, trace_printk()s will only show the format
+ and not their parameters (if trace_bprintk() or
+ trace_bputs() was used to save the trace_printk()).
+
+ context-info
+ Show only the event data. Hides the comm, PID,
+ timestamp, CPU, and other useful data.
+
+ latency-format
+ This option changes the trace output. When it is enabled,
+ the trace displays additional information about the
+ latency, as described in "Latency trace format".
+
+ record-cmd
+ When any event or tracer is enabled, a hook is enabled
+ in the sched_switch trace point to fill comm cache
+ with mapped pids and comms. But this may cause some
+ overhead, and if you only care about pids, and not the
+ name of the task, disabling this option can lower the
+ impact of tracing. See "saved_cmdlines".
+
+ record-tgid
+ When any event or tracer is enabled, a hook is enabled
+ in the sched_switch trace point to fill the cache of
+ mapped Thread Group IDs (TGID) mapping to pids. See
+ "saved_tgids".
+
+ overwrite
+ This controls what happens when the trace buffer is
+ full. If "1" (default), the oldest events are
+ discarded and overwritten. If "0", then the newest
+ events are discarded.
+ (see per_cpu/cpu0/stats for overrun and dropped)
+
+ disable_on_free
+ When the free_buffer is closed, tracing will
+ stop (tracing_on set to 0).
+
+ irq-info
+ Shows the interrupt, preempt count, need resched data.
+ When disabled, the trace looks like::
+
+ # tracer: function
+ #
+ # entries-in-buffer/entries-written: 144405/9452052 #P:4
+ #
+ # TASK-PID CPU# TIMESTAMP FUNCTION
+ # | | | | |
+ <idle>-0 [002] 23636.756054: ttwu_do_activate.constprop.89 <-try_to_wake_up
+ <idle>-0 [002] 23636.756054: activate_task <-ttwu_do_activate.constprop.89
+ <idle>-0 [002] 23636.756055: enqueue_task <-activate_task
+
+
+ markers
+ When set, the trace_marker is writable (only by root).
+ When disabled, the trace_marker will error with EINVAL
+ on write.
+
+ event-fork
+ When set, tasks with PIDs listed in set_event_pid will have
+ the PIDs of their children added to set_event_pid when those
+ tasks fork. Also, when tasks with PIDs in set_event_pid exit,
+ their PIDs will be removed from the file.
+
+ function-trace
+ The latency tracers will enable function tracing
+ if this option is enabled (default it is). When
+ it is disabled, the latency tracers do not trace
+ functions. This keeps the overhead of the tracer down
+ when performing latency tests.
+
+ function-fork
+ When set, tasks with PIDs listed in set_ftrace_pid will
+ have the PIDs of their children added to set_ftrace_pid
+ when those tasks fork. Also, when tasks with PIDs in
+ set_ftrace_pid exit, their PIDs will be removed from the
+ file.
+
+ display-graph
+ When set, the latency tracers (irqsoff, wakeup, etc) will
+ use function graph tracing instead of function tracing.
+
+ stacktrace
+ When set, a stack trace is recorded after any trace event
+ is recorded.
+
+ branch
+ Enable branch tracing with the tracer. This enables branch
+ tracer along with the currently set tracer. Enabling this
+ with the "nop" tracer is the same as just enabling the
+ "branch" tracer.
+
+.. tip:: Some tracers have their own options. They only appear in this
+ file when the tracer is active. They always appear in the
+ options directory.
+
+
+Here are the per tracer options:
+
+Options for function tracer:
+
+ func_stack_trace
+ When set, a stack trace is recorded after every
+ function that is recorded. NOTE! Limit the functions
+ that are recorded before enabling this, with
+ "set_ftrace_filter" otherwise the system performance
+ will be critically degraded. Remember to disable
+ this option before clearing the function filter.
+
+Options for function_graph tracer:
+
+ Since the function_graph tracer has a slightly different output
+ it has its own options to control what is displayed.
+
+ funcgraph-overrun
+ When set, the "overrun" of the graph stack is
+ displayed after each function traced. The
+ overrun, is when the stack depth of the calls
+ is greater than what is reserved for each task.
+ Each task has a fixed array of functions to
+ trace in the call graph. If the depth of the
+ calls exceeds that, the function is not traced.
+ The overrun is the number of functions missed
+ due to exceeding this array.
+
+ funcgraph-cpu
+ When set, the CPU number of the CPU where the trace
+ occurred is displayed.
+
+ funcgraph-overhead
+ When set, if the function takes longer than
+ A certain amount, then a delay marker is
+ displayed. See "delay" above, under the
+ header description.
+
+ funcgraph-proc
+ Unlike other tracers, the process' command line
+ is not displayed by default, but instead only
+ when a task is traced in and out during a context
+ switch. Enabling this options has the command
+ of each process displayed at every line.
+
+ funcgraph-duration
+ At the end of each function (the return)
+ the duration of the amount of time in the
+ function is displayed in microseconds.
+
+ funcgraph-abstime
+ When set, the timestamp is displayed at each line.
+
+ funcgraph-irqs
+ When disabled, functions that happen inside an
+ interrupt will not be traced.
+
+ funcgraph-tail
+ When set, the return event will include the function
+ that it represents. By default this is off, and
+ only a closing curly bracket "}" is displayed for
+ the return of a function.
+
+ sleep-time
+ When running function graph tracer, to include
+ the time a task schedules out in its function.
+ When enabled, it will account time the task has been
+ scheduled out as part of the function call.
+
+ graph-time
+ When running function profiler with function graph tracer,
+ to include the time to call nested functions. When this is
+ not set, the time reported for the function will only
+ include the time the function itself executed for, not the
+ time for functions that it called.
+
+Options for blk tracer:
+
+ blk_classic
+ Shows a more minimalistic output.
+
+
+irqsoff
+-------
+
+When interrupts are disabled, the CPU can not react to any other
+external event (besides NMIs and SMIs). This prevents the timer
+interrupt from triggering or the mouse interrupt from letting
+the kernel know of a new mouse event. The result is a latency
+with the reaction time.
+
+The irqsoff tracer tracks the time for which interrupts are
+disabled. When a new maximum latency is hit, the tracer saves
+the trace leading up to that latency point so that every time a
+new maximum is reached, the old saved trace is discarded and the
+new trace is saved.
+
+To reset the maximum, echo 0 into tracing_max_latency. Here is
+an example::
+
+ # echo 0 > options/function-trace
+ # echo irqsoff > current_tracer
+ # echo 1 > tracing_on
+ # echo 0 > tracing_max_latency
+ # ls -ltr
+ [...]
+ # echo 0 > tracing_on
+ # cat trace
+ # tracer: irqsoff
+ #
+ # irqsoff latency trace v1.1.5 on 3.8.0-test+
+ # --------------------------------------------------------------------
+ # latency: 16 us, #4/4, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+ # -----------------
+ # | task: swapper/0-0 (uid:0 nice:0 policy:0 rt_prio:0)
+ # -----------------
+ # => started at: run_timer_softirq
+ # => ended at: run_timer_softirq
+ #
+ #
+ # _------=> CPU#
+ # / _-----=> irqs-off
+ # | / _----=> need-resched
+ # || / _---=> hardirq/softirq
+ # ||| / _--=> preempt-depth
+ # |||| / delay
+ # cmd pid ||||| time | caller
+ # \ / ||||| \ | /
+ <idle>-0 0d.s2 0us+: _raw_spin_lock_irq <-run_timer_softirq
+ <idle>-0 0dNs3 17us : _raw_spin_unlock_irq <-run_timer_softirq
+ <idle>-0 0dNs3 17us+: trace_hardirqs_on <-run_timer_softirq
+ <idle>-0 0dNs3 25us : <stack trace>
+ => _raw_spin_unlock_irq
+ => run_timer_softirq
+ => __do_softirq
+ => call_softirq
+ => do_softirq
+ => irq_exit
+ => smp_apic_timer_interrupt
+ => apic_timer_interrupt
+ => rcu_idle_exit
+ => cpu_idle
+ => rest_init
+ => start_kernel
+ => x86_64_start_reservations
+ => x86_64_start_kernel
+
+Here we see that that we had a latency of 16 microseconds (which is
+very good). The _raw_spin_lock_irq in run_timer_softirq disabled
+interrupts. The difference between the 16 and the displayed
+timestamp 25us occurred because the clock was incremented
+between the time of recording the max latency and the time of
+recording the function that had that latency.
+
+Note the above example had function-trace not set. If we set
+function-trace, we get a much larger output::
+
+ with echo 1 > options/function-trace
+
+ # tracer: irqsoff
+ #
+ # irqsoff latency trace v1.1.5 on 3.8.0-test+
+ # --------------------------------------------------------------------
+ # latency: 71 us, #168/168, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+ # -----------------
+ # | task: bash-2042 (uid:0 nice:0 policy:0 rt_prio:0)
+ # -----------------
+ # => started at: ata_scsi_queuecmd
+ # => ended at: ata_scsi_queuecmd
+ #
+ #
+ # _------=> CPU#
+ # / _-----=> irqs-off
+ # | / _----=> need-resched
+ # || / _---=> hardirq/softirq
+ # ||| / _--=> preempt-depth
+ # |||| / delay
+ # cmd pid ||||| time | caller
+ # \ / ||||| \ | /
+ bash-2042 3d... 0us : _raw_spin_lock_irqsave <-ata_scsi_queuecmd
+ bash-2042 3d... 0us : add_preempt_count <-_raw_spin_lock_irqsave
+ bash-2042 3d..1 1us : ata_scsi_find_dev <-ata_scsi_queuecmd
+ bash-2042 3d..1 1us : __ata_scsi_find_dev <-ata_scsi_find_dev
+ bash-2042 3d..1 2us : ata_find_dev.part.14 <-__ata_scsi_find_dev
+ bash-2042 3d..1 2us : ata_qc_new_init <-__ata_scsi_queuecmd
+ bash-2042 3d..1 3us : ata_sg_init <-__ata_scsi_queuecmd
+ bash-2042 3d..1 4us : ata_scsi_rw_xlat <-__ata_scsi_queuecmd
+ bash-2042 3d..1 4us : ata_build_rw_tf <-ata_scsi_rw_xlat
+ [...]
+ bash-2042 3d..1 67us : delay_tsc <-__delay
+ bash-2042 3d..1 67us : add_preempt_count <-delay_tsc
+ bash-2042 3d..2 67us : sub_preempt_count <-delay_tsc
+ bash-2042 3d..1 67us : add_preempt_count <-delay_tsc
+ bash-2042 3d..2 68us : sub_preempt_count <-delay_tsc
+ bash-2042 3d..1 68us+: ata_bmdma_start <-ata_bmdma_qc_issue
+ bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
+ bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
+ bash-2042 3d..1 72us+: trace_hardirqs_on <-ata_scsi_queuecmd
+ bash-2042 3d..1 120us : <stack trace>
+ => _raw_spin_unlock_irqrestore
+ => ata_scsi_queuecmd
+ => scsi_dispatch_cmd
+ => scsi_request_fn
+ => __blk_run_queue_uncond
+ => __blk_run_queue
+ => blk_queue_bio
+ => generic_make_request
+ => submit_bio
+ => submit_bh
+ => __ext3_get_inode_loc
+ => ext3_iget
+ => ext3_lookup
+ => lookup_real
+ => __lookup_hash
+ => walk_component
+ => lookup_last
+ => path_lookupat
+ => filename_lookup
+ => user_path_at_empty
+ => user_path_at
+ => vfs_fstatat
+ => vfs_stat
+ => sys_newstat
+ => system_call_fastpath
+
+
+Here we traced a 71 microsecond latency. But we also see all the
+functions that were called during that time. Note that by
+enabling function tracing, we incur an added overhead. This
+overhead may extend the latency times. But nevertheless, this
+trace has provided some very helpful debugging information.
+
+
+preemptoff
+----------
+
+When preemption is disabled, we may be able to receive
+interrupts but the task cannot be preempted and a higher
+priority task must wait for preemption to be enabled again
+before it can preempt a lower priority task.
+
+The preemptoff tracer traces the places that disable preemption.
+Like the irqsoff tracer, it records the maximum latency for
+which preemption was disabled. The control of preemptoff tracer
+is much like the irqsoff tracer.
+::
+
+ # echo 0 > options/function-trace
+ # echo preemptoff > current_tracer
+ # echo 1 > tracing_on
+ # echo 0 > tracing_max_latency
+ # ls -ltr
+ [...]
+ # echo 0 > tracing_on
+ # cat trace
+ # tracer: preemptoff
+ #
+ # preemptoff latency trace v1.1.5 on 3.8.0-test+
+ # --------------------------------------------------------------------
+ # latency: 46 us, #4/4, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+ # -----------------
+ # | task: sshd-1991 (uid:0 nice:0 policy:0 rt_prio:0)
+ # -----------------
+ # => started at: do_IRQ
+ # => ended at: do_IRQ
+ #
+ #
+ # _------=> CPU#
+ # / _-----=> irqs-off
+ # | / _----=> need-resched
+ # || / _---=> hardirq/softirq
+ # ||| / _--=> preempt-depth
+ # |||| / delay
+ # cmd pid ||||| time | caller
+ # \ / ||||| \ | /
+ sshd-1991 1d.h. 0us+: irq_enter <-do_IRQ
+ sshd-1991 1d..1 46us : irq_exit <-do_IRQ
+ sshd-1991 1d..1 47us+: trace_preempt_on <-do_IRQ
+ sshd-1991 1d..1 52us : <stack trace>
+ => sub_preempt_count
+ => irq_exit
+ => do_IRQ
+ => ret_from_intr
+
+
+This has some more changes. Preemption was disabled when an
+interrupt came in (notice the 'h'), and was enabled on exit.
+But we also see that interrupts have been disabled when entering
+the preempt off section and leaving it (the 'd'). We do not know if
+interrupts were enabled in the mean time or shortly after this
+was over.
+::
+
+ # tracer: preemptoff
+ #
+ # preemptoff latency trace v1.1.5 on 3.8.0-test+
+ # --------------------------------------------------------------------
+ # latency: 83 us, #241/241, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+ # -----------------
+ # | task: bash-1994 (uid:0 nice:0 policy:0 rt_prio:0)
+ # -----------------
+ # => started at: wake_up_new_task
+ # => ended at: task_rq_unlock
+ #
+ #
+ # _------=> CPU#
+ # / _-----=> irqs-off
+ # | / _----=> need-resched
+ # || / _---=> hardirq/softirq
+ # ||| / _--=> preempt-depth
+ # |||| / delay
+ # cmd pid ||||| time | caller
+ # \ / ||||| \ | /
+ bash-1994 1d..1 0us : _raw_spin_lock_irqsave <-wake_up_new_task
+ bash-1994 1d..1 0us : select_task_rq_fair <-select_task_rq
+ bash-1994 1d..1 1us : __rcu_read_lock <-select_task_rq_fair
+ bash-1994 1d..1 1us : source_load <-select_task_rq_fair
+ bash-1994 1d..1 1us : source_load <-select_task_rq_fair
+ [...]
+ bash-1994 1d..1 12us : irq_enter <-smp_apic_timer_interrupt
+ bash-1994 1d..1 12us : rcu_irq_enter <-irq_enter
+ bash-1994 1d..1 13us : add_preempt_count <-irq_enter
+ bash-1994 1d.h1 13us : exit_idle <-smp_apic_timer_interrupt
+ bash-1994 1d.h1 13us : hrtimer_interrupt <-smp_apic_timer_interrupt
+ bash-1994 1d.h1 13us : _raw_spin_lock <-hrtimer_interrupt
+ bash-1994 1d.h1 14us : add_preempt_count <-_raw_spin_lock
+ bash-1994 1d.h2 14us : ktime_get_update_offsets <-hrtimer_interrupt
+ [...]
+ bash-1994 1d.h1 35us : lapic_next_event <-clockevents_program_event
+ bash-1994 1d.h1 35us : irq_exit <-smp_apic_timer_interrupt
+ bash-1994 1d.h1 36us : sub_preempt_count <-irq_exit
+ bash-1994 1d..2 36us : do_softirq <-irq_exit
+ bash-1994 1d..2 36us : __do_softirq <-call_softirq
+ bash-1994 1d..2 36us : __local_bh_disable <-__do_softirq
+ bash-1994 1d.s2 37us : add_preempt_count <-_raw_spin_lock_irq
+ bash-1994 1d.s3 38us : _raw_spin_unlock <-run_timer_softirq
+ bash-1994 1d.s3 39us : sub_preempt_count <-_raw_spin_unlock
+ bash-1994 1d.s2 39us : call_timer_fn <-run_timer_softirq
+ [...]
+ bash-1994 1dNs2 81us : cpu_needs_another_gp <-rcu_process_callbacks
+ bash-1994 1dNs2 82us : __local_bh_enable <-__do_softirq
+ bash-1994 1dNs2 82us : sub_preempt_count <-__local_bh_enable
+ bash-1994 1dN.2 82us : idle_cpu <-irq_exit
+ bash-1994 1dN.2 83us : rcu_irq_exit <-irq_exit
+ bash-1994 1dN.2 83us : sub_preempt_count <-irq_exit
+ bash-1994 1.N.1 84us : _raw_spin_unlock_irqrestore <-task_rq_unlock
+ bash-1994 1.N.1 84us+: trace_preempt_on <-task_rq_unlock
+ bash-1994 1.N.1 104us : <stack trace>
+ => sub_preempt_count
+ => _raw_spin_unlock_irqrestore
+ => task_rq_unlock
+ => wake_up_new_task
+ => do_fork
+ => sys_clone
+ => stub_clone
+
+
+The above is an example of the preemptoff trace with
+function-trace set. Here we see that interrupts were not disabled
+the entire time. The irq_enter code lets us know that we entered
+an interrupt 'h'. Before that, the functions being traced still
+show that it is not in an interrupt, but we can see from the
+functions themselves that this is not the case.
+
+preemptirqsoff
+--------------
+
+Knowing the locations that have interrupts disabled or
+preemption disabled for the longest times is helpful. But
+sometimes we would like to know when either preemption and/or
+interrupts are disabled.
+
+Consider the following code::
+
+ local_irq_disable();
+ call_function_with_irqs_off();
+ preempt_disable();
+ call_function_with_irqs_and_preemption_off();
+ local_irq_enable();
+ call_function_with_preemption_off();
+ preempt_enable();
+
+The irqsoff tracer will record the total length of
+call_function_with_irqs_off() and
+call_function_with_irqs_and_preemption_off().
+
+The preemptoff tracer will record the total length of
+call_function_with_irqs_and_preemption_off() and
+call_function_with_preemption_off().
+
+But neither will trace the time that interrupts and/or
+preemption is disabled. This total time is the time that we can
+not schedule. To record this time, use the preemptirqsoff
+tracer.
+
+Again, using this trace is much like the irqsoff and preemptoff
+tracers.
+::
+
+ # echo 0 > options/function-trace
+ # echo preemptirqsoff > current_tracer
+ # echo 1 > tracing_on
+ # echo 0 > tracing_max_latency
+ # ls -ltr
+ [...]
+ # echo 0 > tracing_on
+ # cat trace
+ # tracer: preemptirqsoff
+ #
+ # preemptirqsoff latency trace v1.1.5 on 3.8.0-test+
+ # --------------------------------------------------------------------
+ # latency: 100 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+ # -----------------
+ # | task: ls-2230 (uid:0 nice:0 policy:0 rt_prio:0)
+ # -----------------
+ # => started at: ata_scsi_queuecmd
+ # => ended at: ata_scsi_queuecmd
+ #
+ #
+ # _------=> CPU#
+ # / _-----=> irqs-off
+ # | / _----=> need-resched
+ # || / _---=> hardirq/softirq
+ # ||| / _--=> preempt-depth
+ # |||| / delay
+ # cmd pid ||||| time | caller
+ # \ / ||||| \ | /
+ ls-2230 3d... 0us+: _raw_spin_lock_irqsave <-ata_scsi_queuecmd
+ ls-2230 3...1 100us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
+ ls-2230 3...1 101us+: trace_preempt_on <-ata_scsi_queuecmd
+ ls-2230 3...1 111us : <stack trace>
+ => sub_preempt_count
+ => _raw_spin_unlock_irqrestore
+ => ata_scsi_queuecmd
+ => scsi_dispatch_cmd
+ => scsi_request_fn
+ => __blk_run_queue_uncond
+ => __blk_run_queue
+ => blk_queue_bio
+ => generic_make_request
+ => submit_bio
+ => submit_bh
+ => ext3_bread
+ => ext3_dir_bread
+ => htree_dirblock_to_tree
+ => ext3_htree_fill_tree
+ => ext3_readdir
+ => vfs_readdir
+ => sys_getdents
+ => system_call_fastpath
+
+
+The trace_hardirqs_off_thunk is called from assembly on x86 when
+interrupts are disabled in the assembly code. Without the
+function tracing, we do not know if interrupts were enabled
+within the preemption points. We do see that it started with
+preemption enabled.
+
+Here is a trace with function-trace set::
+
+ # tracer: preemptirqsoff
+ #
+ # preemptirqsoff latency trace v1.1.5 on 3.8.0-test+
+ # --------------------------------------------------------------------
+ # latency: 161 us, #339/339, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+ # -----------------
+ # | task: ls-2269 (uid:0 nice:0 policy:0 rt_prio:0)
+ # -----------------
+ # => started at: schedule
+ # => ended at: mutex_unlock
+ #
+ #
+ # _------=> CPU#
+ # / _-----=> irqs-off
+ # | / _----=> need-resched
+ # || / _---=> hardirq/softirq
+ # ||| / _--=> preempt-depth
+ # |||| / delay
+ # cmd pid ||||| time | caller
+ # \ / ||||| \ | /
+ kworker/-59 3...1 0us : __schedule <-schedule
+ kworker/-59 3d..1 0us : rcu_preempt_qs <-rcu_note_context_switch
+ kworker/-59 3d..1 1us : add_preempt_count <-_raw_spin_lock_irq
+ kworker/-59 3d..2 1us : deactivate_task <-__schedule
+ kworker/-59 3d..2 1us : dequeue_task <-deactivate_task
+ kworker/-59 3d..2 2us : update_rq_clock <-dequeue_task
+ kworker/-59 3d..2 2us : dequeue_task_fair <-dequeue_task
+ kworker/-59 3d..2 2us : update_curr <-dequeue_task_fair
+ kworker/-59 3d..2 2us : update_min_vruntime <-update_curr
+ kworker/-59 3d..2 3us : cpuacct_charge <-update_curr
+ kworker/-59 3d..2 3us : __rcu_read_lock <-cpuacct_charge
+ kworker/-59 3d..2 3us : __rcu_read_unlock <-cpuacct_charge
+ kworker/-59 3d..2 3us : update_cfs_rq_blocked_load <-dequeue_task_fair
+ kworker/-59 3d..2 4us : clear_buddies <-dequeue_task_fair
+ kworker/-59 3d..2 4us : account_entity_dequeue <-dequeue_task_fair
+ kworker/-59 3d..2 4us : update_min_vruntime <-dequeue_task_fair
+ kworker/-59 3d..2 4us : update_cfs_shares <-dequeue_task_fair
+ kworker/-59 3d..2 5us : hrtick_update <-dequeue_task_fair
+ kworker/-59 3d..2 5us : wq_worker_sleeping <-__schedule
+ kworker/-59 3d..2 5us : kthread_data <-wq_worker_sleeping
+ kworker/-59 3d..2 5us : put_prev_task_fair <-__schedule
+ kworker/-59 3d..2 6us : pick_next_task_fair <-pick_next_task
+ kworker/-59 3d..2 6us : clear_buddies <-pick_next_task_fair
+ kworker/-59 3d..2 6us : set_next_entity <-pick_next_task_fair
+ kworker/-59 3d..2 6us : update_stats_wait_end <-set_next_entity
+ ls-2269 3d..2 7us : finish_task_switch <-__schedule
+ ls-2269 3d..2 7us : _raw_spin_unlock_irq <-finish_task_switch
+ ls-2269 3d..2 8us : do_IRQ <-ret_from_intr
+ ls-2269 3d..2 8us : irq_enter <-do_IRQ
+ ls-2269 3d..2 8us : rcu_irq_enter <-irq_enter
+ ls-2269 3d..2 9us : add_preempt_count <-irq_enter
+ ls-2269 3d.h2 9us : exit_idle <-do_IRQ
+ [...]
+ ls-2269 3d.h3 20us : sub_preempt_count <-_raw_spin_unlock
+ ls-2269 3d.h2 20us : irq_exit <-do_IRQ
+ ls-2269 3d.h2 21us : sub_preempt_count <-irq_exit
+ ls-2269 3d..3 21us : do_softirq <-irq_exit
+ ls-2269 3d..3 21us : __do_softirq <-call_softirq
+ ls-2269 3d..3 21us+: __local_bh_disable <-__do_softirq
+ ls-2269 3d.s4 29us : sub_preempt_count <-_local_bh_enable_ip
+ ls-2269 3d.s5 29us : sub_preempt_count <-_local_bh_enable_ip
+ ls-2269 3d.s5 31us : do_IRQ <-ret_from_intr
+ ls-2269 3d.s5 31us : irq_enter <-do_IRQ
+ ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter
+ [...]
+ ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter
+ ls-2269 3d.s5 32us : add_preempt_count <-irq_enter
+ ls-2269 3d.H5 32us : exit_idle <-do_IRQ
+ ls-2269 3d.H5 32us : handle_irq <-do_IRQ
+ ls-2269 3d.H5 32us : irq_to_desc <-handle_irq
+ ls-2269 3d.H5 33us : handle_fasteoi_irq <-handle_irq
+ [...]
+ ls-2269 3d.s5 158us : _raw_spin_unlock_irqrestore <-rtl8139_poll
+ ls-2269 3d.s3 158us : net_rps_action_and_irq_enable.isra.65 <-net_rx_action
+ ls-2269 3d.s3 159us : __local_bh_enable <-__do_softirq
+ ls-2269 3d.s3 159us : sub_preempt_count <-__local_bh_enable
+ ls-2269 3d..3 159us : idle_cpu <-irq_exit
+ ls-2269 3d..3 159us : rcu_irq_exit <-irq_exit
+ ls-2269 3d..3 160us : sub_preempt_count <-irq_exit
+ ls-2269 3d... 161us : __mutex_unlock_slowpath <-mutex_unlock
+ ls-2269 3d... 162us+: trace_hardirqs_on <-mutex_unlock
+ ls-2269 3d... 186us : <stack trace>
+ => __mutex_unlock_slowpath
+ => mutex_unlock
+ => process_output
+ => n_tty_write
+ => tty_write
+ => vfs_write
+ => sys_write
+ => system_call_fastpath
+
+This is an interesting trace. It started with kworker running and
+scheduling out and ls taking over. But as soon as ls released the
+rq lock and enabled interrupts (but not preemption) an interrupt
+triggered. When the interrupt finished, it started running softirqs.
+But while the softirq was running, another interrupt triggered.
+When an interrupt is running inside a softirq, the annotation is 'H'.
+
+
+wakeup
+------
+
+One common case that people are interested in tracing is the
+time it takes for a task that is woken to actually wake up.
+Now for non Real-Time tasks, this can be arbitrary. But tracing
+it none the less can be interesting.
+
+Without function tracing::
+
+ # echo 0 > options/function-trace
+ # echo wakeup > current_tracer
+ # echo 1 > tracing_on
+ # echo 0 > tracing_max_latency
+ # chrt -f 5 sleep 1
+ # echo 0 > tracing_on
+ # cat trace
+ # tracer: wakeup
+ #
+ # wakeup latency trace v1.1.5 on 3.8.0-test+
+ # --------------------------------------------------------------------
+ # latency: 15 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+ # -----------------
+ # | task: kworker/3:1H-312 (uid:0 nice:-20 policy:0 rt_prio:0)
+ # -----------------
+ #
+ # _------=> CPU#
+ # / _-----=> irqs-off
+ # | / _----=> need-resched
+ # || / _---=> hardirq/softirq
+ # ||| / _--=> preempt-depth
+ # |||| / delay
+ # cmd pid ||||| time | caller
+ # \ / ||||| \ | /
+ <idle>-0 3dNs7 0us : 0:120:R + [003] 312:100:R kworker/3:1H
+ <idle>-0 3dNs7 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up
+ <idle>-0 3d..3 15us : __schedule <-schedule
+ <idle>-0 3d..3 15us : 0:120:R ==> [003] 312:100:R kworker/3:1H
+
+The tracer only traces the highest priority task in the system
+to avoid tracing the normal circumstances. Here we see that
+the kworker with a nice priority of -20 (not very nice), took
+just 15 microseconds from the time it woke up, to the time it
+ran.
+
+Non Real-Time tasks are not that interesting. A more interesting
+trace is to concentrate only on Real-Time tasks.
+
+wakeup_rt
+---------
+
+In a Real-Time environment it is very important to know the
+wakeup time it takes for the highest priority task that is woken
+up to the time that it executes. This is also known as "schedule
+latency". I stress the point that this is about RT tasks. It is
+also important to know the scheduling latency of non-RT tasks,
+but the average schedule latency is better for non-RT tasks.
+Tools like LatencyTop are more appropriate for such
+measurements.
+
+Real-Time environments are interested in the worst case latency.
+That is the longest latency it takes for something to happen,
+and not the average. We can have a very fast scheduler that may
+only have a large latency once in a while, but that would not
+work well with Real-Time tasks. The wakeup_rt tracer was designed
+to record the worst case wakeups of RT tasks. Non-RT tasks are
+not recorded because the tracer only records one worst case and
+tracing non-RT tasks that are unpredictable will overwrite the
+worst case latency of RT tasks (just run the normal wakeup
+tracer for a while to see that effect).
+
+Since this tracer only deals with RT tasks, we will run this
+slightly differently than we did with the previous tracers.
+Instead of performing an 'ls', we will run 'sleep 1' under
+'chrt' which changes the priority of the task.
+::
+
+ # echo 0 > options/function-trace
+ # echo wakeup_rt > current_tracer
+ # echo 1 > tracing_on
+ # echo 0 > tracing_max_latency
+ # chrt -f 5 sleep 1
+ # echo 0 > tracing_on
+ # cat trace
+ # tracer: wakeup
+ #
+ # tracer: wakeup_rt
+ #
+ # wakeup_rt latency trace v1.1.5 on 3.8.0-test+
+ # --------------------------------------------------------------------
+ # latency: 5 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+ # -----------------
+ # | task: sleep-2389 (uid:0 nice:0 policy:1 rt_prio:5)
+ # -----------------
+ #
+ # _------=> CPU#
+ # / _-----=> irqs-off
+ # | / _----=> need-resched
+ # || / _---=> hardirq/softirq
+ # ||| / _--=> preempt-depth
+ # |||| / delay
+ # cmd pid ||||| time | caller
+ # \ / ||||| \ | /
+ <idle>-0 3d.h4 0us : 0:120:R + [003] 2389: 94:R sleep
+ <idle>-0 3d.h4 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up
+ <idle>-0 3d..3 5us : __schedule <-schedule
+ <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep
+
+
+Running this on an idle system, we see that it only took 5 microseconds
+to perform the task switch. Note, since the trace point in the schedule
+is before the actual "switch", we stop the tracing when the recorded task
+is about to schedule in. This may change if we add a new marker at the
+end of the scheduler.
+
+Notice that the recorded task is 'sleep' with the PID of 2389
+and it has an rt_prio of 5. This priority is user-space priority
+and not the internal kernel priority. The policy is 1 for
+SCHED_FIFO and 2 for SCHED_RR.
+
+Note, that the trace data shows the internal priority (99 - rtprio).
+::
+
+ <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep
+
+The 0:120:R means idle was running with a nice priority of 0 (120 - 120)
+and in the running state 'R'. The sleep task was scheduled in with
+2389: 94:R. That is the priority is the kernel rtprio (99 - 5 = 94)
+and it too is in the running state.
+
+Doing the same with chrt -r 5 and function-trace set.
+::
+
+ echo 1 > options/function-trace
+
+ # tracer: wakeup_rt
+ #
+ # wakeup_rt latency trace v1.1.5 on 3.8.0-test+
+ # --------------------------------------------------------------------
+ # latency: 29 us, #85/85, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+ # -----------------
+ # | task: sleep-2448 (uid:0 nice:0 policy:1 rt_prio:5)
+ # -----------------
+ #
+ # _------=> CPU#
+ # / _-----=> irqs-off
+ # | / _----=> need-resched
+ # || / _---=> hardirq/softirq
+ # ||| / _--=> preempt-depth
+ # |||| / delay
+ # cmd pid ||||| time | caller
+ # \ / ||||| \ | /
+ <idle>-0 3d.h4 1us+: 0:120:R + [003] 2448: 94:R sleep
+ <idle>-0 3d.h4 2us : ttwu_do_activate.constprop.87 <-try_to_wake_up
+ <idle>-0 3d.h3 3us : check_preempt_curr <-ttwu_do_wakeup
+ <idle>-0 3d.h3 3us : resched_curr <-check_preempt_curr
+ <idle>-0 3dNh3 4us : task_woken_rt <-ttwu_do_wakeup
+ <idle>-0 3dNh3 4us : _raw_spin_unlock <-try_to_wake_up
+ <idle>-0 3dNh3 4us : sub_preempt_count <-_raw_spin_unlock
+ <idle>-0 3dNh2 5us : ttwu_stat <-try_to_wake_up
+ <idle>-0 3dNh2 5us : _raw_spin_unlock_irqrestore <-try_to_wake_up
+ <idle>-0 3dNh2 6us : sub_preempt_count <-_raw_spin_unlock_irqrestore
+ <idle>-0 3dNh1 6us : _raw_spin_lock <-__run_hrtimer
+ <idle>-0 3dNh1 6us : add_preempt_count <-_raw_spin_lock
+ <idle>-0 3dNh2 7us : _raw_spin_unlock <-hrtimer_interrupt
+ <idle>-0 3dNh2 7us : sub_preempt_count <-_raw_spin_unlock
+ <idle>-0 3dNh1 7us : tick_program_event <-hrtimer_interrupt
+ <idle>-0 3dNh1 7us : clockevents_program_event <-tick_program_event
+ <idle>-0 3dNh1 8us : ktime_get <-clockevents_program_event
+ <idle>-0 3dNh1 8us : lapic_next_event <-clockevents_program_event
+ <idle>-0 3dNh1 8us : irq_exit <-smp_apic_timer_interrupt
+ <idle>-0 3dNh1 9us : sub_preempt_count <-irq_exit
+ <idle>-0 3dN.2 9us : idle_cpu <-irq_exit
+ <idle>-0 3dN.2 9us : rcu_irq_exit <-irq_exit
+ <idle>-0 3dN.2 10us : rcu_eqs_enter_common.isra.45 <-rcu_irq_exit
+ <idle>-0 3dN.2 10us : sub_preempt_count <-irq_exit
+ <idle>-0 3.N.1 11us : rcu_idle_exit <-cpu_idle
+ <idle>-0 3dN.1 11us : rcu_eqs_exit_common.isra.43 <-rcu_idle_exit
+ <idle>-0 3.N.1 11us : tick_nohz_idle_exit <-cpu_idle
+ <idle>-0 3dN.1 12us : menu_hrtimer_cancel <-tick_nohz_idle_exit
+ <idle>-0 3dN.1 12us : ktime_get <-tick_nohz_idle_exit
+ <idle>-0 3dN.1 12us : tick_do_update_jiffies64 <-tick_nohz_idle_exit
+ <idle>-0 3dN.1 13us : cpu_load_update_nohz <-tick_nohz_idle_exit
+ <idle>-0 3dN.1 13us : _raw_spin_lock <-cpu_load_update_nohz
+ <idle>-0 3dN.1 13us : add_preempt_count <-_raw_spin_lock
+ <idle>-0 3dN.2 13us : __cpu_load_update <-cpu_load_update_nohz
+ <idle>-0 3dN.2 14us : sched_avg_update <-__cpu_load_update
+ <idle>-0 3dN.2 14us : _raw_spin_unlock <-cpu_load_update_nohz
+ <idle>-0 3dN.2 14us : sub_preempt_count <-_raw_spin_unlock
+ <idle>-0 3dN.1 15us : calc_load_nohz_stop <-tick_nohz_idle_exit
+ <idle>-0 3dN.1 15us : touch_softlockup_watchdog <-tick_nohz_idle_exit
+ <idle>-0 3dN.1 15us : hrtimer_cancel <-tick_nohz_idle_exit
+ <idle>-0 3dN.1 15us : hrtimer_try_to_cancel <-hrtimer_cancel
+ <idle>-0 3dN.1 16us : lock_hrtimer_base.isra.18 <-hrtimer_try_to_cancel
+ <idle>-0 3dN.1 16us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18
+ <idle>-0 3dN.1 16us : add_preempt_count <-_raw_spin_lock_irqsave
+ <idle>-0 3dN.2 17us : __remove_hrtimer <-remove_hrtimer.part.16
+ <idle>-0 3dN.2 17us : hrtimer_force_reprogram <-__remove_hrtimer
+ <idle>-0 3dN.2 17us : tick_program_event <-hrtimer_force_reprogram
+ <idle>-0 3dN.2 18us : clockevents_program_event <-tick_program_event
+ <idle>-0 3dN.2 18us : ktime_get <-clockevents_program_event
+ <idle>-0 3dN.2 18us : lapic_next_event <-clockevents_program_event
+ <idle>-0 3dN.2 19us : _raw_spin_unlock_irqrestore <-hrtimer_try_to_cancel
+ <idle>-0 3dN.2 19us : sub_preempt_count <-_raw_spin_unlock_irqrestore
+ <idle>-0 3dN.1 19us : hrtimer_forward <-tick_nohz_idle_exit
+ <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward
+ <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward
+ <idle>-0 3dN.1 20us : hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11
+ <idle>-0 3dN.1 20us : __hrtimer_start_range_ns <-hrtimer_start_range_ns
+ <idle>-0 3dN.1 21us : lock_hrtimer_base.isra.18 <-__hrtimer_start_range_ns
+ <idle>-0 3dN.1 21us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18
+ <idle>-0 3dN.1 21us : add_preempt_count <-_raw_spin_lock_irqsave
+ <idle>-0 3dN.2 22us : ktime_add_safe <-__hrtimer_start_range_ns
+ <idle>-0 3dN.2 22us : enqueue_hrtimer <-__hrtimer_start_range_ns
+ <idle>-0 3dN.2 22us : tick_program_event <-__hrtimer_start_range_ns
+ <idle>-0 3dN.2 23us : clockevents_program_event <-tick_program_event
+ <idle>-0 3dN.2 23us : ktime_get <-clockevents_program_event
+ <idle>-0 3dN.2 23us : lapic_next_event <-clockevents_program_event
+ <idle>-0 3dN.2 24us : _raw_spin_unlock_irqrestore <-__hrtimer_start_range_ns
+ <idle>-0 3dN.2 24us : sub_preempt_count <-_raw_spin_unlock_irqrestore
+ <idle>-0 3dN.1 24us : account_idle_ticks <-tick_nohz_idle_exit
+ <idle>-0 3dN.1 24us : account_idle_time <-account_idle_ticks
+ <idle>-0 3.N.1 25us : sub_preempt_count <-cpu_idle
+ <idle>-0 3.N.. 25us : schedule <-cpu_idle
+ <idle>-0 3.N.. 25us : __schedule <-preempt_schedule
+ <idle>-0 3.N.. 26us : add_preempt_count <-__schedule
+ <idle>-0 3.N.1 26us : rcu_note_context_switch <-__schedule
+ <idle>-0 3.N.1 26us : rcu_sched_qs <-rcu_note_context_switch
+ <idle>-0 3dN.1 27us : rcu_preempt_qs <-rcu_note_context_switch
+ <idle>-0 3.N.1 27us : _raw_spin_lock_irq <-__schedule
+ <idle>-0 3dN.1 27us : add_preempt_count <-_raw_spin_lock_irq
+ <idle>-0 3dN.2 28us : put_prev_task_idle <-__schedule
+ <idle>-0 3dN.2 28us : pick_next_task_stop <-pick_next_task
+ <idle>-0 3dN.2 28us : pick_next_task_rt <-pick_next_task
+ <idle>-0 3dN.2 29us : dequeue_pushable_task <-pick_next_task_rt
+ <idle>-0 3d..3 29us : __schedule <-preempt_schedule
+ <idle>-0 3d..3 30us : 0:120:R ==> [003] 2448: 94:R sleep
+
+This isn't that big of a trace, even with function tracing enabled,
+so I included the entire trace.
+
+The interrupt went off while when the system was idle. Somewhere
+before task_woken_rt() was called, the NEED_RESCHED flag was set,
+this is indicated by the first occurrence of the 'N' flag.
+
+Latency tracing and events
+--------------------------
+As function tracing can induce a much larger latency, but without
+seeing what happens within the latency it is hard to know what
+caused it. There is a middle ground, and that is with enabling
+events.
+::
+
+ # echo 0 > options/function-trace
+ # echo wakeup_rt > current_tracer
+ # echo 1 > events/enable
+ # echo 1 > tracing_on
+ # echo 0 > tracing_max_latency
+ # chrt -f 5 sleep 1
+ # echo 0 > tracing_on
+ # cat trace
+ # tracer: wakeup_rt
+ #
+ # wakeup_rt latency trace v1.1.5 on 3.8.0-test+
+ # --------------------------------------------------------------------
+ # latency: 6 us, #12/12, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
+ # -----------------
+ # | task: sleep-5882 (uid:0 nice:0 policy:1 rt_prio:5)
+ # -----------------
+ #
+ # _------=> CPU#
+ # / _-----=> irqs-off
+ # | / _----=> need-resched
+ # || / _---=> hardirq/softirq
+ # ||| / _--=> preempt-depth
+ # |||| / delay
+ # cmd pid ||||| time | caller
+ # \ / ||||| \ | /
+ <idle>-0 2d.h4 0us : 0:120:R + [002] 5882: 94:R sleep
+ <idle>-0 2d.h4 0us : ttwu_do_activate.constprop.87 <-try_to_wake_up
+ <idle>-0 2d.h4 1us : sched_wakeup: comm=sleep pid=5882 prio=94 success=1 target_cpu=002
+ <idle>-0 2dNh2 1us : hrtimer_expire_exit: hrtimer=ffff88007796feb8
+ <idle>-0 2.N.2 2us : power_end: cpu_id=2
+ <idle>-0 2.N.2 3us : cpu_idle: state=4294967295 cpu_id=2
+ <idle>-0 2dN.3 4us : hrtimer_cancel: hrtimer=ffff88007d50d5e0
+ <idle>-0 2dN.3 4us : hrtimer_start: hrtimer=ffff88007d50d5e0 function=tick_sched_timer expires=34311211000000 softexpires=34311211000000
+ <idle>-0 2.N.2 5us : rcu_utilization: Start context switch
+ <idle>-0 2.N.2 5us : rcu_utilization: End context switch
+ <idle>-0 2d..3 6us : __schedule <-schedule
+ <idle>-0 2d..3 6us : 0:120:R ==> [002] 5882: 94:R sleep
+
+
+Hardware Latency Detector
+-------------------------
+
+The hardware latency detector is executed by enabling the "hwlat" tracer.
+
+NOTE, this tracer will affect the performance of the system as it will
+periodically make a CPU constantly busy with interrupts disabled.
+::
+
+ # echo hwlat > current_tracer
+ # sleep 100
+ # cat trace
+ # tracer: hwlat
+ #
+ # _-----=> irqs-off
+ # / _----=> need-resched
+ # | / _---=> hardirq/softirq
+ # || / _--=> preempt-depth
+ # ||| / delay
+ # TASK-PID CPU# |||| TIMESTAMP FUNCTION
+ # | | | |||| | |
+ <...>-3638 [001] d... 19452.055471: #1 inner/outer(us): 12/14 ts:1499801089.066141940
+ <...>-3638 [003] d... 19454.071354: #2 inner/outer(us): 11/9 ts:1499801091.082164365
+ <...>-3638 [002] dn.. 19461.126852: #3 inner/outer(us): 12/9 ts:1499801098.138150062
+ <...>-3638 [001] d... 19488.340960: #4 inner/outer(us): 8/12 ts:1499801125.354139633
+ <...>-3638 [003] d... 19494.388553: #5 inner/outer(us): 8/12 ts:1499801131.402150961
+ <...>-3638 [003] d... 19501.283419: #6 inner/outer(us): 0/12 ts:1499801138.297435289 nmi-total:4 nmi-count:1
+
+
+The above output is somewhat the same in the header. All events will have
+interrupts disabled 'd'. Under the FUNCTION title there is:
+
+ #1
+ This is the count of events recorded that were greater than the
+ tracing_threshold (See below).
+
+ inner/outer(us): 12/14
+
+ This shows two numbers as "inner latency" and "outer latency". The test
+ runs in a loop checking a timestamp twice. The latency detected within
+ the two timestamps is the "inner latency" and the latency detected
+ after the previous timestamp and the next timestamp in the loop is
+ the "outer latency".
+
+ ts:1499801089.066141940
+
+ The absolute timestamp that the event happened.
+
+ nmi-total:4 nmi-count:1
+
+ On architectures that support it, if an NMI comes in during the
+ test, the time spent in NMI is reported in "nmi-total" (in
+ microseconds).
+
+ All architectures that have NMIs will show the "nmi-count" if an
+ NMI comes in during the test.
+
+hwlat files:
+
+ tracing_threshold
+ This gets automatically set to "10" to represent 10
+ microseconds. This is the threshold of latency that
+ needs to be detected before the trace will be recorded.
+
+ Note, when hwlat tracer is finished (another tracer is
+ written into "current_tracer"), the original value for
+ tracing_threshold is placed back into this file.
+
+ hwlat_detector/width
+ The length of time the test runs with interrupts disabled.
+
+ hwlat_detector/window
+ The length of time of the window which the test
+ runs. That is, the test will run for "width"
+ microseconds per "window" microseconds
+
+ tracing_cpumask
+ When the test is started. A kernel thread is created that
+ runs the test. This thread will alternate between CPUs
+ listed in the tracing_cpumask between each period
+ (one "window"). To limit the test to specific CPUs
+ set the mask in this file to only the CPUs that the test
+ should run on.
+
+function
+--------
+
+This tracer is the function tracer. Enabling the function tracer
+can be done from the debug file system. Make sure the
+ftrace_enabled is set; otherwise this tracer is a nop.
+See the "ftrace_enabled" section below.
+::
+
+ # sysctl kernel.ftrace_enabled=1
+ # echo function > current_tracer
+ # echo 1 > tracing_on
+ # usleep 1
+ # echo 0 > tracing_on
+ # cat trace
+ # tracer: function
+ #
+ # entries-in-buffer/entries-written: 24799/24799 #P:4
+ #
+ # _-----=> irqs-off
+ # / _----=> need-resched
+ # | / _---=> hardirq/softirq
+ # || / _--=> preempt-depth
+ # ||| / delay
+ # TASK-PID CPU# |||| TIMESTAMP FUNCTION
+ # | | | |||| | |
+ bash-1994 [002] .... 3082.063030: mutex_unlock <-rb_simple_write
+ bash-1994 [002] .... 3082.063031: __mutex_unlock_slowpath <-mutex_unlock
+ bash-1994 [002] .... 3082.063031: __fsnotify_parent <-fsnotify_modify
+ bash-1994 [002] .... 3082.063032: fsnotify <-fsnotify_modify
+ bash-1994 [002] .... 3082.063032: __srcu_read_lock <-fsnotify
+ bash-1994 [002] .... 3082.063032: add_preempt_count <-__srcu_read_lock
+ bash-1994 [002] ...1 3082.063032: sub_preempt_count <-__srcu_read_lock
+ bash-1994 [002] .... 3082.063033: __srcu_read_unlock <-fsnotify
+ [...]
+
+
+Note: function tracer uses ring buffers to store the above
+entries. The newest data may overwrite the oldest data.
+Sometimes using echo to stop the trace is not sufficient because
+the tracing could have overwritten the data that you wanted to
+record. For this reason, it is sometimes better to disable
+tracing directly from a program. This allows you to stop the
+tracing at the point that you hit the part that you are
+interested in. To disable the tracing directly from a C program,
+something like following code snippet can be used::
+
+ int trace_fd;
+ [...]
+ int main(int argc, char *argv[]) {
+ [...]
+ trace_fd = open(tracing_file("tracing_on"), O_WRONLY);
+ [...]
+ if (condition_hit()) {
+ write(trace_fd, "0", 1);
+ }
+ [...]
+ }
+
+
+Single thread tracing
+---------------------
+
+By writing into set_ftrace_pid you can trace a
+single thread. For example::
+
+ # cat set_ftrace_pid
+ no pid
+ # echo 3111 > set_ftrace_pid
+ # cat set_ftrace_pid
+ 3111
+ # echo function > current_tracer
+ # cat trace | head
+ # tracer: function
+ #
+ # TASK-PID CPU# TIMESTAMP FUNCTION
+ # | | | | |
+ yum-updatesd-3111 [003] 1637.254676: finish_task_switch <-thread_return
+ yum-updatesd-3111 [003] 1637.254681: hrtimer_cancel <-schedule_hrtimeout_range
+ yum-updatesd-3111 [003] 1637.254682: hrtimer_try_to_cancel <-hrtimer_cancel
+ yum-updatesd-3111 [003] 1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel
+ yum-updatesd-3111 [003] 1637.254685: fget_light <-do_sys_poll
+ yum-updatesd-3111 [003] 1637.254686: pipe_poll <-do_sys_poll
+ # echo > set_ftrace_pid
+ # cat trace |head
+ # tracer: function
+ #
+ # TASK-PID CPU# TIMESTAMP FUNCTION
+ # | | | | |
+ ##### CPU 3 buffer started ####
+ yum-updatesd-3111 [003] 1701.957688: free_poll_entry <-poll_freewait
+ yum-updatesd-3111 [003] 1701.957689: remove_wait_queue <-free_poll_entry
+ yum-updatesd-3111 [003] 1701.957691: fput <-free_poll_entry
+ yum-updatesd-3111 [003] 1701.957692: audit_syscall_exit <-sysret_audit
+ yum-updatesd-3111 [003] 1701.957693: path_put <-audit_syscall_exit
+
+If you want to trace a function when executing, you could use
+something like this simple program.
+::
+
+ #include <stdio.h>
+ #include <stdlib.h>
+ #include <sys/types.h>
+ #include <sys/stat.h>
+ #include <fcntl.h>
+ #include <unistd.h>
+ #include <string.h>
+
+ #define _STR(x) #x
+ #define STR(x) _STR(x)
+ #define MAX_PATH 256
+
+ const char *find_tracefs(void)
+ {
+ static char tracefs[MAX_PATH+1];
+ static int tracefs_found;
+ char type[100];
+ FILE *fp;
+
+ if (tracefs_found)
+ return tracefs;
+
+ if ((fp = fopen("/proc/mounts","r")) == NULL) {
+ perror("/proc/mounts");
+ return NULL;
+ }
+
+ while (fscanf(fp, "%*s %"
+ STR(MAX_PATH)
+ "s %99s %*s %*d %*d\n",
+ tracefs, type) == 2) {
+ if (strcmp(type, "tracefs") == 0)
+ break;
+ }
+ fclose(fp);
+
+ if (strcmp(type, "tracefs") != 0) {
+ fprintf(stderr, "tracefs not mounted");
+ return NULL;
+ }
+
+ strcat(tracefs, "/tracing/");
+ tracefs_found = 1;
+
+ return tracefs;
+ }
+
+ const char *tracing_file(const char *file_name)
+ {
+ static char trace_file[MAX_PATH+1];
+ snprintf(trace_file, MAX_PATH, "%s/%s", find_tracefs(), file_name);
+ return trace_file;
+ }
+
+ int main (int argc, char **argv)
+ {
+ if (argc < 1)
+ exit(-1);
+
+ if (fork() > 0) {
+ int fd, ffd;
+ char line[64];
+ int s;
+
+ ffd = open(tracing_file("current_tracer"), O_WRONLY);
+ if (ffd < 0)
+ exit(-1);
+ write(ffd, "nop", 3);
+
+ fd = open(tracing_file("set_ftrace_pid"), O_WRONLY);
+ s = sprintf(line, "%d\n", getpid());
+ write(fd, line, s);
+
+ write(ffd, "function", 8);
+
+ close(fd);
+ close(ffd);
+
+ execvp(argv[1], argv+1);
+ }
+
+ return 0;
+ }
+
+Or this simple script!
+::
+
+ #!/bin/bash
+
+ tracefs=`sed -ne 's/^tracefs \(.*\) tracefs.*/\1/p' /proc/mounts`
+ echo nop > $tracefs/tracing/current_tracer
+ echo 0 > $tracefs/tracing/tracing_on
+ echo $$ > $tracefs/tracing/set_ftrace_pid
+ echo function > $tracefs/tracing/current_tracer
+ echo 1 > $tracefs/tracing/tracing_on
+ exec "$@"
+
+
+function graph tracer
+---------------------------
+
+This tracer is similar to the function tracer except that it
+probes a function on its entry and its exit. This is done by
+using a dynamically allocated stack of return addresses in each
+task_struct. On function entry the tracer overwrites the return
+address of each function traced to set a custom probe. Thus the
+original return address is stored on the stack of return address
+in the task_struct.
+
+Probing on both ends of a function leads to special features
+such as:
+
+- measure of a function's time execution
+- having a reliable call stack to draw function calls graph
+
+This tracer is useful in several situations:
+
+- you want to find the reason of a strange kernel behavior and
+ need to see what happens in detail on any areas (or specific
+ ones).
+
+- you are experiencing weird latencies but it's difficult to
+ find its origin.
+
+- you want to find quickly which path is taken by a specific
+ function
+
+- you just want to peek inside a working kernel and want to see
+ what happens there.
+
+::
+
+ # tracer: function_graph
+ #
+ # CPU DURATION FUNCTION CALLS
+ # | | | | | | |
+
+ 0) | sys_open() {
+ 0) | do_sys_open() {
+ 0) | getname() {
+ 0) | kmem_cache_alloc() {
+ 0) 1.382 us | __might_sleep();
+ 0) 2.478 us | }
+ 0) | strncpy_from_user() {
+ 0) | might_fault() {
+ 0) 1.389 us | __might_sleep();
+ 0) 2.553 us | }
+ 0) 3.807 us | }
+ 0) 7.876 us | }
+ 0) | alloc_fd() {
+ 0) 0.668 us | _spin_lock();
+ 0) 0.570 us | expand_files();
+ 0) 0.586 us | _spin_unlock();
+
+
+There are several columns that can be dynamically
+enabled/disabled. You can use every combination of options you
+want, depending on your needs.
+
+- The cpu number on which the function executed is default
+ enabled. It is sometimes better to only trace one cpu (see
+ tracing_cpu_mask file) or you might sometimes see unordered
+ function calls while cpu tracing switch.
+
+ - hide: echo nofuncgraph-cpu > trace_options
+ - show: echo funcgraph-cpu > trace_options
+
+- The duration (function's time of execution) is displayed on
+ the closing bracket line of a function or on the same line
+ than the current function in case of a leaf one. It is default
+ enabled.
+
+ - hide: echo nofuncgraph-duration > trace_options
+ - show: echo funcgraph-duration > trace_options
+
+- The overhead field precedes the duration field in case of
+ reached duration thresholds.
+
+ - hide: echo nofuncgraph-overhead > trace_options
+ - show: echo funcgraph-overhead > trace_options
+ - depends on: funcgraph-duration
+
+ ie::
+
+ 3) # 1837.709 us | } /* __switch_to */
+ 3) | finish_task_switch() {
+ 3) 0.313 us | _raw_spin_unlock_irq();
+ 3) 3.177 us | }
+ 3) # 1889.063 us | } /* __schedule */
+ 3) ! 140.417 us | } /* __schedule */
+ 3) # 2034.948 us | } /* schedule */
+ 3) * 33998.59 us | } /* schedule_preempt_disabled */
+
+ [...]
+
+ 1) 0.260 us | msecs_to_jiffies();
+ 1) 0.313 us | __rcu_read_unlock();
+ 1) + 61.770 us | }
+ 1) + 64.479 us | }
+ 1) 0.313 us | rcu_bh_qs();
+ 1) 0.313 us | __local_bh_enable();
+ 1) ! 217.240 us | }
+ 1) 0.365 us | idle_cpu();
+ 1) | rcu_irq_exit() {
+ 1) 0.417 us | rcu_eqs_enter_common.isra.47();
+ 1) 3.125 us | }
+ 1) ! 227.812 us | }
+ 1) ! 457.395 us | }
+ 1) @ 119760.2 us | }
+
+ [...]
+
+ 2) | handle_IPI() {
+ 1) 6.979 us | }
+ 2) 0.417 us | scheduler_ipi();
+ 1) 9.791 us | }
+ 1) + 12.917 us | }
+ 2) 3.490 us | }
+ 1) + 15.729 us | }
+ 1) + 18.542 us | }
+ 2) $ 3594274 us | }
+
+Flags::
+
+ + means that the function exceeded 10 usecs.
+ ! means that the function exceeded 100 usecs.
+ # means that the function exceeded 1000 usecs.
+ * means that the function exceeded 10 msecs.
+ @ means that the function exceeded 100 msecs.
+ $ means that the function exceeded 1 sec.
+
+
+- The task/pid field displays the thread cmdline and pid which
+ executed the function. It is default disabled.
+
+ - hide: echo nofuncgraph-proc > trace_options
+ - show: echo funcgraph-proc > trace_options
+
+ ie::
+
+ # tracer: function_graph
+ #
+ # CPU TASK/PID DURATION FUNCTION CALLS
+ # | | | | | | | | |
+ 0) sh-4802 | | d_free() {
+ 0) sh-4802 | | call_rcu() {
+ 0) sh-4802 | | __call_rcu() {
+ 0) sh-4802 | 0.616 us | rcu_process_gp_end();
+ 0) sh-4802 | 0.586 us | check_for_new_grace_period();
+ 0) sh-4802 | 2.899 us | }
+ 0) sh-4802 | 4.040 us | }
+ 0) sh-4802 | 5.151 us | }
+ 0) sh-4802 | + 49.370 us | }
+
+
+- The absolute time field is an absolute timestamp given by the
+ system clock since it started. A snapshot of this time is
+ given on each entry/exit of functions
+
+ - hide: echo nofuncgraph-abstime > trace_options
+ - show: echo funcgraph-abstime > trace_options
+
+ ie::
+
+ #
+ # TIME CPU DURATION FUNCTION CALLS
+ # | | | | | | | |
+ 360.774522 | 1) 0.541 us | }
+ 360.774522 | 1) 4.663 us | }
+ 360.774523 | 1) 0.541 us | __wake_up_bit();
+ 360.774524 | 1) 6.796 us | }
+ 360.774524 | 1) 7.952 us | }
+ 360.774525 | 1) 9.063 us | }
+ 360.774525 | 1) 0.615 us | journal_mark_dirty();
+ 360.774527 | 1) 0.578 us | __brelse();
+ 360.774528 | 1) | reiserfs_prepare_for_journal() {
+ 360.774528 | 1) | unlock_buffer() {
+ 360.774529 | 1) | wake_up_bit() {
+ 360.774529 | 1) | bit_waitqueue() {
+ 360.774530 | 1) 0.594 us | __phys_addr();
+
+
+The function name is always displayed after the closing bracket
+for a function if the start of that function is not in the
+trace buffer.
+
+Display of the function name after the closing bracket may be
+enabled for functions whose start is in the trace buffer,
+allowing easier searching with grep for function durations.
+It is default disabled.
+
+ - hide: echo nofuncgraph-tail > trace_options
+ - show: echo funcgraph-tail > trace_options
+
+ Example with nofuncgraph-tail (default)::
+
+ 0) | putname() {
+ 0) | kmem_cache_free() {
+ 0) 0.518 us | __phys_addr();
+ 0) 1.757 us | }
+ 0) 2.861 us | }
+
+ Example with funcgraph-tail::
+
+ 0) | putname() {
+ 0) | kmem_cache_free() {
+ 0) 0.518 us | __phys_addr();
+ 0) 1.757 us | } /* kmem_cache_free() */
+ 0) 2.861 us | } /* putname() */
+
+You can put some comments on specific functions by using
+trace_printk() For example, if you want to put a comment inside
+the __might_sleep() function, you just have to include
+<linux/ftrace.h> and call trace_printk() inside __might_sleep()::
+
+ trace_printk("I'm a comment!\n")
+
+will produce::
+
+ 1) | __might_sleep() {
+ 1) | /* I'm a comment! */
+ 1) 1.449 us | }
+
+
+You might find other useful features for this tracer in the
+following "dynamic ftrace" section such as tracing only specific
+functions or tasks.
+
+dynamic ftrace
+--------------
+
+If CONFIG_DYNAMIC_FTRACE is set, the system will run with
+virtually no overhead when function tracing is disabled. The way
+this works is the mcount function call (placed at the start of
+every kernel function, produced by the -pg switch in gcc),
+starts of pointing to a simple return. (Enabling FTRACE will
+include the -pg switch in the compiling of the kernel.)
+
+At compile time every C file object is run through the
+recordmcount program (located in the scripts directory). This
+program will parse the ELF headers in the C object to find all
+the locations in the .text section that call mcount. Starting
+with gcc verson 4.6, the -mfentry has been added for x86, which
+calls "__fentry__" instead of "mcount". Which is called before
+the creation of the stack frame.
+
+Note, not all sections are traced. They may be prevented by either
+a notrace, or blocked another way and all inline functions are not
+traced. Check the "available_filter_functions" file to see what functions
+can be traced.
+
+A section called "__mcount_loc" is created that holds
+references to all the mcount/fentry call sites in the .text section.
+The recordmcount program re-links this section back into the
+original object. The final linking stage of the kernel will add all these
+references into a single table.
+
+On boot up, before SMP is initialized, the dynamic ftrace code
+scans this table and updates all the locations into nops. It
+also records the locations, which are added to the
+available_filter_functions list. Modules are processed as they
+are loaded and before they are executed. When a module is
+unloaded, it also removes its functions from the ftrace function
+list. This is automatic in the module unload code, and the
+module author does not need to worry about it.
+
+When tracing is enabled, the process of modifying the function
+tracepoints is dependent on architecture. The old method is to use
+kstop_machine to prevent races with the CPUs executing code being
+modified (which can cause the CPU to do undesirable things, especially
+if the modified code crosses cache (or page) boundaries), and the nops are
+patched back to calls. But this time, they do not call mcount
+(which is just a function stub). They now call into the ftrace
+infrastructure.
+
+The new method of modifying the function tracepoints is to place
+a breakpoint at the location to be modified, sync all CPUs, modify
+the rest of the instruction not covered by the breakpoint. Sync
+all CPUs again, and then remove the breakpoint with the finished
+version to the ftrace call site.
+
+Some archs do not even need to monkey around with the synchronization,
+and can just slap the new code on top of the old without any
+problems with other CPUs executing it at the same time.
+
+One special side-effect to the recording of the functions being
+traced is that we can now selectively choose which functions we
+wish to trace and which ones we want the mcount calls to remain
+as nops.
+
+Two files are used, one for enabling and one for disabling the
+tracing of specified functions. They are:
+
+ set_ftrace_filter
+
+and
+
+ set_ftrace_notrace
+
+A list of available functions that you can add to these files is
+listed in:
+
+ available_filter_functions
+
+::
+
+ # cat available_filter_functions
+ put_prev_task_idle
+ kmem_cache_create
+ pick_next_task_rt
+ get_online_cpus
+ pick_next_task_fair
+ mutex_lock
+ [...]
+
+If I am only interested in sys_nanosleep and hrtimer_interrupt::
+
+ # echo sys_nanosleep hrtimer_interrupt > set_ftrace_filter
+ # echo function > current_tracer
+ # echo 1 > tracing_on
+ # usleep 1
+ # echo 0 > tracing_on
+ # cat trace
+ # tracer: function
+ #
+ # entries-in-buffer/entries-written: 5/5 #P:4
+ #
+ # _-----=> irqs-off
+ # / _----=> need-resched
+ # | / _---=> hardirq/softirq
+ # || / _--=> preempt-depth
+ # ||| / delay
+ # TASK-PID CPU# |||| TIMESTAMP FUNCTION
+ # | | | |||| | |
+ usleep-2665 [001] .... 4186.475355: sys_nanosleep <-system_call_fastpath
+ <idle>-0 [001] d.h1 4186.475409: hrtimer_interrupt <-smp_apic_timer_interrupt
+ usleep-2665 [001] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt
+ <idle>-0 [003] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt
+ <idle>-0 [002] d.h1 4186.475427: hrtimer_interrupt <-smp_apic_timer_interrupt
+
+To see which functions are being traced, you can cat the file:
+::
+
+ # cat set_ftrace_filter
+ hrtimer_interrupt
+ sys_nanosleep
+
+
+Perhaps this is not enough. The filters also allow glob(7) matching.
+
+ ``<match>*``
+ will match functions that begin with <match>
+ ``*<match>``
+ will match functions that end with <match>
+ ``*<match>*``
+ will match functions that have <match> in it
+ ``<match1>*<match2>``
+ will match functions that begin with <match1> and end with <match2>
+
+.. note::
+ It is better to use quotes to enclose the wild cards,
+ otherwise the shell may expand the parameters into names
+ of files in the local directory.
+
+::
+
+ # echo 'hrtimer_*' > set_ftrace_filter
+
+Produces::
+
+ # tracer: function
+ #
+ # entries-in-buffer/entries-written: 897/897 #P:4
+ #
+ # _-----=> irqs-off
+ # / _----=> need-resched
+ # | / _---=> hardirq/softirq
+ # || / _--=> preempt-depth
+ # ||| / delay
+ # TASK-PID CPU# |||| TIMESTAMP FUNCTION
+ # | | | |||| | |
+ <idle>-0 [003] dN.1 4228.547803: hrtimer_cancel <-tick_nohz_idle_exit
+ <idle>-0 [003] dN.1 4228.547804: hrtimer_try_to_cancel <-hrtimer_cancel
+ <idle>-0 [003] dN.2 4228.547805: hrtimer_force_reprogram <-__remove_hrtimer
+ <idle>-0 [003] dN.1 4228.547805: hrtimer_forward <-tick_nohz_idle_exit
+ <idle>-0 [003] dN.1 4228.547805: hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11
+ <idle>-0 [003] d..1 4228.547858: hrtimer_get_next_event <-get_next_timer_interrupt
+ <idle>-0 [003] d..1 4228.547859: hrtimer_start <-__tick_nohz_idle_enter
+ <idle>-0 [003] d..2 4228.547860: hrtimer_force_reprogram <-__rem
+
+Notice that we lost the sys_nanosleep.
+::
+
+ # cat set_ftrace_filter
+ hrtimer_run_queues
+ hrtimer_run_pending
+ hrtimer_init
+ hrtimer_cancel
+ hrtimer_try_to_cancel
+ hrtimer_forward
+ hrtimer_start
+ hrtimer_reprogram
+ hrtimer_force_reprogram
+ hrtimer_get_next_event
+ hrtimer_interrupt
+ hrtimer_nanosleep
+ hrtimer_wakeup
+ hrtimer_get_remaining
+ hrtimer_get_res
+ hrtimer_init_sleeper
+
+
+This is because the '>' and '>>' act just like they do in bash.
+To rewrite the filters, use '>'
+To append to the filters, use '>>'
+
+To clear out a filter so that all functions will be recorded
+again::
+
+ # echo > set_ftrace_filter
+ # cat set_ftrace_filter
+ #
+
+Again, now we want to append.
+
+::
+
+ # echo sys_nanosleep > set_ftrace_filter
+ # cat set_ftrace_filter
+ sys_nanosleep
+ # echo 'hrtimer_*' >> set_ftrace_filter
+ # cat set_ftrace_filter
+ hrtimer_run_queues
+ hrtimer_run_pending
+ hrtimer_init
+ hrtimer_cancel
+ hrtimer_try_to_cancel
+ hrtimer_forward
+ hrtimer_start
+ hrtimer_reprogram
+ hrtimer_force_reprogram
+ hrtimer_get_next_event
+ hrtimer_interrupt
+ sys_nanosleep
+ hrtimer_nanosleep
+ hrtimer_wakeup
+ hrtimer_get_remaining
+ hrtimer_get_res
+ hrtimer_init_sleeper
+
+
+The set_ftrace_notrace prevents those functions from being
+traced.
+::
+
+ # echo '*preempt*' '*lock*' > set_ftrace_notrace
+
+Produces::
+
+ # tracer: function
+ #
+ # entries-in-buffer/entries-written: 39608/39608 #P:4
+ #
+ # _-----=> irqs-off
+ # / _----=> need-resched
+ # | / _---=> hardirq/softirq
+ # || / _--=> preempt-depth
+ # ||| / delay
+ # TASK-PID CPU# |||| TIMESTAMP FUNCTION
+ # | | | |||| | |
+ bash-1994 [000] .... 4342.324896: file_ra_state_init <-do_dentry_open
+ bash-1994 [000] .... 4342.324897: open_check_o_direct <-do_last
+ bash-1994 [000] .... 4342.324897: ima_file_check <-do_last
+ bash-1994 [000] .... 4342.324898: process_measurement <-ima_file_check
+ bash-1994 [000] .... 4342.324898: ima_get_action <-process_measurement
+ bash-1994 [000] .... 4342.324898: ima_match_policy <-ima_get_action
+ bash-1994 [000] .... 4342.324899: do_truncate <-do_last
+ bash-1994 [000] .... 4342.324899: should_remove_suid <-do_truncate
+ bash-1994 [000] .... 4342.324899: notify_change <-do_truncate
+ bash-1994 [000] .... 4342.324900: current_fs_time <-notify_change
+ bash-1994 [000] .... 4342.324900: current_kernel_time <-current_fs_time
+ bash-1994 [000] .... 4342.324900: timespec_trunc <-current_fs_time
+
+We can see that there's no more lock or preempt tracing.
+
+
+Dynamic ftrace with the function graph tracer
+---------------------------------------------
+
+Although what has been explained above concerns both the
+function tracer and the function-graph-tracer, there are some
+special features only available in the function-graph tracer.
+
+If you want to trace only one function and all of its children,
+you just have to echo its name into set_graph_function::
+
+ echo __do_fault > set_graph_function
+
+will produce the following "expanded" trace of the __do_fault()
+function::
+
+ 0) | __do_fault() {
+ 0) | filemap_fault() {
+ 0) | find_lock_page() {
+ 0) 0.804 us | find_get_page();
+ 0) | __might_sleep() {
+ 0) 1.329 us | }
+ 0) 3.904 us | }
+ 0) 4.979 us | }
+ 0) 0.653 us | _spin_lock();
+ 0) 0.578 us | page_add_file_rmap();
+ 0) 0.525 us | native_set_pte_at();
+ 0) 0.585 us | _spin_unlock();
+ 0) | unlock_page() {
+ 0) 0.541 us | page_waitqueue();
+ 0) 0.639 us | __wake_up_bit();
+ 0) 2.786 us | }
+ 0) + 14.237 us | }
+ 0) | __do_fault() {
+ 0) | filemap_fault() {
+ 0) | find_lock_page() {
+ 0) 0.698 us | find_get_page();
+ 0) | __might_sleep() {
+ 0) 1.412 us | }
+ 0) 3.950 us | }
+ 0) 5.098 us | }
+ 0) 0.631 us | _spin_lock();
+ 0) 0.571 us | page_add_file_rmap();
+ 0) 0.526 us | native_set_pte_at();
+ 0) 0.586 us | _spin_unlock();
+ 0) | unlock_page() {
+ 0) 0.533 us | page_waitqueue();
+ 0) 0.638 us | __wake_up_bit();
+ 0) 2.793 us | }
+ 0) + 14.012 us | }
+
+You can also expand several functions at once::
+
+ echo sys_open > set_graph_function
+ echo sys_close >> set_graph_function
+
+Now if you want to go back to trace all functions you can clear
+this special filter via::
+
+ echo > set_graph_function
+
+
+ftrace_enabled
+--------------
+
+Note, the proc sysctl ftrace_enable is a big on/off switch for the
+function tracer. By default it is enabled (when function tracing is
+enabled in the kernel). If it is disabled, all function tracing is
+disabled. This includes not only the function tracers for ftrace, but
+also for any other uses (perf, kprobes, stack tracing, profiling, etc).
+
+Please disable this with care.
+
+This can be disable (and enabled) with::
+
+ sysctl kernel.ftrace_enabled=0
+ sysctl kernel.ftrace_enabled=1
+
+ or
+
+ echo 0 > /proc/sys/kernel/ftrace_enabled
+ echo 1 > /proc/sys/kernel/ftrace_enabled
+
+
+Filter commands
+---------------
+
+A few commands are supported by the set_ftrace_filter interface.
+Trace commands have the following format::
+
+ <function>:<command>:<parameter>
+
+The following commands are supported:
+
+- mod:
+ This command enables function filtering per module. The
+ parameter defines the module. For example, if only the write*
+ functions in the ext3 module are desired, run:
+
+ echo 'write*:mod:ext3' > set_ftrace_filter
+
+ This command interacts with the filter in the same way as
+ filtering based on function names. Thus, adding more functions
+ in a different module is accomplished by appending (>>) to the
+ filter file. Remove specific module functions by prepending
+ '!'::
+
+ echo '!writeback*:mod:ext3' >> set_ftrace_filter
+
+ Mod command supports module globbing. Disable tracing for all
+ functions except a specific module::
+
+ echo '!*:mod:!ext3' >> set_ftrace_filter
+
+ Disable tracing for all modules, but still trace kernel::
+
+ echo '!*:mod:*' >> set_ftrace_filter
+
+ Enable filter only for kernel::
+
+ echo '*write*:mod:!*' >> set_ftrace_filter
+
+ Enable filter for module globbing::
+
+ echo '*write*:mod:*snd*' >> set_ftrace_filter
+
+- traceon/traceoff:
+ These commands turn tracing on and off when the specified
+ functions are hit. The parameter determines how many times the
+ tracing system is turned on and off. If unspecified, there is
+ no limit. For example, to disable tracing when a schedule bug
+ is hit the first 5 times, run::
+
+ echo '__schedule_bug:traceoff:5' > set_ftrace_filter
+
+ To always disable tracing when __schedule_bug is hit::
+
+ echo '__schedule_bug:traceoff' > set_ftrace_filter
+
+ These commands are cumulative whether or not they are appended
+ to set_ftrace_filter. To remove a command, prepend it by '!'
+ and drop the parameter::
+
+ echo '!__schedule_bug:traceoff:0' > set_ftrace_filter
+
+ The above removes the traceoff command for __schedule_bug
+ that have a counter. To remove commands without counters::
+
+ echo '!__schedule_bug:traceoff' > set_ftrace_filter
+
+- snapshot:
+ Will cause a snapshot to be triggered when the function is hit.
+ ::
+
+ echo 'native_flush_tlb_others:snapshot' > set_ftrace_filter
+
+ To only snapshot once:
+ ::
+
+ echo 'native_flush_tlb_others:snapshot:1' > set_ftrace_filter
+
+ To remove the above commands::
+
+ echo '!native_flush_tlb_others:snapshot' > set_ftrace_filter
+ echo '!native_flush_tlb_others:snapshot:0' > set_ftrace_filter
+
+- enable_event/disable_event:
+ These commands can enable or disable a trace event. Note, because
+ function tracing callbacks are very sensitive, when these commands
+ are registered, the trace point is activated, but disabled in
+ a "soft" mode. That is, the tracepoint will be called, but
+ just will not be traced. The event tracepoint stays in this mode
+ as long as there's a command that triggers it.
+ ::
+
+ echo 'try_to_wake_up:enable_event:sched:sched_switch:2' > \
+ set_ftrace_filter
+
+ The format is::
+
+ <function>:enable_event:<system>:<event>[:count]
+ <function>:disable_event:<system>:<event>[:count]
+
+ To remove the events commands::
+
+ echo '!try_to_wake_up:enable_event:sched:sched_switch:0' > \
+ set_ftrace_filter
+ echo '!schedule:disable_event:sched:sched_switch' > \
+ set_ftrace_filter
+
+- dump:
+ When the function is hit, it will dump the contents of the ftrace
+ ring buffer to the console. This is useful if you need to debug
+ something, and want to dump the trace when a certain function
+ is hit. Perhaps its a function that is called before a tripple
+ fault happens and does not allow you to get a regular dump.
+
+- cpudump:
+ When the function is hit, it will dump the contents of the ftrace
+ ring buffer for the current CPU to the console. Unlike the "dump"
+ command, it only prints out the contents of the ring buffer for the
+ CPU that executed the function that triggered the dump.
+
+trace_pipe
+----------
+
+The trace_pipe outputs the same content as the trace file, but
+the effect on the tracing is different. Every read from
+trace_pipe is consumed. This means that subsequent reads will be
+different. The trace is live.
+::
+
+ # echo function > current_tracer
+ # cat trace_pipe > /tmp/trace.out &
+ [1] 4153
+ # echo 1 > tracing_on
+ # usleep 1
+ # echo 0 > tracing_on
+ # cat trace
+ # tracer: function
+ #
+ # entries-in-buffer/entries-written: 0/0 #P:4
+ #
+ # _-----=> irqs-off
+ # / _----=> need-resched
+ # | / _---=> hardirq/softirq
+ # || / _--=> preempt-depth
+ # ||| / delay
+ # TASK-PID CPU# |||| TIMESTAMP FUNCTION
+ # | | | |||| | |
+
+ #
+ # cat /tmp/trace.out
+ bash-1994 [000] .... 5281.568961: mutex_unlock <-rb_simple_write
+ bash-1994 [000] .... 5281.568963: __mutex_unlock_slowpath <-mutex_unlock
+ bash-1994 [000] .... 5281.568963: __fsnotify_parent <-fsnotify_modify
+ bash-1994 [000] .... 5281.568964: fsnotify <-fsnotify_modify
+ bash-1994 [000] .... 5281.568964: __srcu_read_lock <-fsnotify
+ bash-1994 [000] .... 5281.568964: add_preempt_count <-__srcu_read_lock
+ bash-1994 [000] ...1 5281.568965: sub_preempt_count <-__srcu_read_lock
+ bash-1994 [000] .... 5281.568965: __srcu_read_unlock <-fsnotify
+ bash-1994 [000] .... 5281.568967: sys_dup2 <-system_call_fastpath
+
+
+Note, reading the trace_pipe file will block until more input is
+added.
+
+trace entries
+-------------
+
+Having too much or not enough data can be troublesome in
+diagnosing an issue in the kernel. The file buffer_size_kb is
+used to modify the size of the internal trace buffers. The
+number listed is the number of entries that can be recorded per
+CPU. To know the full size, multiply the number of possible CPUs
+with the number of entries.
+::
+
+ # cat buffer_size_kb
+ 1408 (units kilobytes)
+
+Or simply read buffer_total_size_kb
+::
+
+ # cat buffer_total_size_kb
+ 5632
+
+To modify the buffer, simple echo in a number (in 1024 byte segments).
+::
+
+ # echo 10000 > buffer_size_kb
+ # cat buffer_size_kb
+ 10000 (units kilobytes)
+
+It will try to allocate as much as possible. If you allocate too
+much, it can cause Out-Of-Memory to trigger.
+::
+
+ # echo 1000000000000 > buffer_size_kb
+ -bash: echo: write error: Cannot allocate memory
+ # cat buffer_size_kb
+ 85
+
+The per_cpu buffers can be changed individually as well:
+::
+
+ # echo 10000 > per_cpu/cpu0/buffer_size_kb
+ # echo 100 > per_cpu/cpu1/buffer_size_kb
+
+When the per_cpu buffers are not the same, the buffer_size_kb
+at the top level will just show an X
+::
+
+ # cat buffer_size_kb
+ X
+
+This is where the buffer_total_size_kb is useful:
+::
+
+ # cat buffer_total_size_kb
+ 12916
+
+Writing to the top level buffer_size_kb will reset all the buffers
+to be the same again.
+
+Snapshot
+--------
+CONFIG_TRACER_SNAPSHOT makes a generic snapshot feature
+available to all non latency tracers. (Latency tracers which
+record max latency, such as "irqsoff" or "wakeup", can't use
+this feature, since those are already using the snapshot
+mechanism internally.)
+
+Snapshot preserves a current trace buffer at a particular point
+in time without stopping tracing. Ftrace swaps the current
+buffer with a spare buffer, and tracing continues in the new
+current (=previous spare) buffer.
+
+The following tracefs files in "tracing" are related to this
+feature:
+
+ snapshot:
+
+ This is used to take a snapshot and to read the output
+ of the snapshot. Echo 1 into this file to allocate a
+ spare buffer and to take a snapshot (swap), then read
+ the snapshot from this file in the same format as
+ "trace" (described above in the section "The File
+ System"). Both reads snapshot and tracing are executable
+ in parallel. When the spare buffer is allocated, echoing
+ 0 frees it, and echoing else (positive) values clear the
+ snapshot contents.
+ More details are shown in the table below.
+
+ +--------------+------------+------------+------------+
+ |status\\input | 0 | 1 | else |
+ +==============+============+============+============+
+ |not allocated |(do nothing)| alloc+swap |(do nothing)|
+ +--------------+------------+------------+------------+
+ |allocated | free | swap | clear |
+ +--------------+------------+------------+------------+
+
+Here is an example of using the snapshot feature.
+::
+
+ # echo 1 > events/sched/enable
+ # echo 1 > snapshot
+ # cat snapshot
+ # tracer: nop
+ #
+ # entries-in-buffer/entries-written: 71/71 #P:8
+ #
+ # _-----=> irqs-off
+ # / _----=> need-resched
+ # | / _---=> hardirq/softirq
+ # || / _--=> preempt-depth
+ # ||| / delay
+ # TASK-PID CPU# |||| TIMESTAMP FUNCTION
+ # | | | |||| | |
+ <idle>-0 [005] d... 2440.603828: sched_switch: prev_comm=swapper/5 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2242 next_prio=120
+ sleep-2242 [005] d... 2440.603846: sched_switch: prev_comm=snapshot-test-2 prev_pid=2242 prev_prio=120 prev_state=R ==> next_comm=kworker/5:1 next_pid=60 next_prio=120
+ [...]
+ <idle>-0 [002] d... 2440.707230: sched_switch: prev_comm=swapper/2 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2229 next_prio=120
+
+ # cat trace
+ # tracer: nop
+ #
+ # entries-in-buffer/entries-written: 77/77 #P:8
+ #
+ # _-----=> irqs-off
+ # / _----=> need-resched
+ # | / _---=> hardirq/softirq
+ # || / _--=> preempt-depth
+ # ||| / delay
+ # TASK-PID CPU# |||| TIMESTAMP FUNCTION
+ # | | | |||| | |
+ <idle>-0 [007] d... 2440.707395: sched_switch: prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2243 next_prio=120
+ snapshot-test-2-2229 [002] d... 2440.707438: sched_switch: prev_comm=snapshot-test-2 prev_pid=2229 prev_prio=120 prev_state=S ==> next_comm=swapper/2 next_pid=0 next_prio=120
+ [...]
+
+
+If you try to use this snapshot feature when current tracer is
+one of the latency tracers, you will get the following results.
+::
+
+ # echo wakeup > current_tracer
+ # echo 1 > snapshot
+ bash: echo: write error: Device or resource busy
+ # cat snapshot
+ cat: snapshot: Device or resource busy
+
+
+Instances
+---------
+In the tracefs tracing directory is a directory called "instances".
+This directory can have new directories created inside of it using
+mkdir, and removing directories with rmdir. The directory created
+with mkdir in this directory will already contain files and other
+directories after it is created.
+::
+
+ # mkdir instances/foo
+ # ls instances/foo
+ buffer_size_kb buffer_total_size_kb events free_buffer per_cpu
+ set_event snapshot trace trace_clock trace_marker trace_options
+ trace_pipe tracing_on
+
+As you can see, the new directory looks similar to the tracing directory
+itself. In fact, it is very similar, except that the buffer and
+events are agnostic from the main director, or from any other
+instances that are created.
+
+The files in the new directory work just like the files with the
+same name in the tracing directory except the buffer that is used
+is a separate and new buffer. The files affect that buffer but do not
+affect the main buffer with the exception of trace_options. Currently,
+the trace_options affect all instances and the top level buffer
+the same, but this may change in future releases. That is, options
+may become specific to the instance they reside in.
+
+Notice that none of the function tracer files are there, nor is
+current_tracer and available_tracers. This is because the buffers
+can currently only have events enabled for them.
+::
+
+ # mkdir instances/foo
+ # mkdir instances/bar
+ # mkdir instances/zoot
+ # echo 100000 > buffer_size_kb
+ # echo 1000 > instances/foo/buffer_size_kb
+ # echo 5000 > instances/bar/per_cpu/cpu1/buffer_size_kb
+ # echo function > current_trace
+ # echo 1 > instances/foo/events/sched/sched_wakeup/enable
+ # echo 1 > instances/foo/events/sched/sched_wakeup_new/enable
+ # echo 1 > instances/foo/events/sched/sched_switch/enable
+ # echo 1 > instances/bar/events/irq/enable
+ # echo 1 > instances/zoot/events/syscalls/enable
+ # cat trace_pipe
+ CPU:2 [LOST 11745 EVENTS]
+ bash-2044 [002] .... 10594.481032: _raw_spin_lock_irqsave <-get_page_from_freelist
+ bash-2044 [002] d... 10594.481032: add_preempt_count <-_raw_spin_lock_irqsave
+ bash-2044 [002] d..1 10594.481032: __rmqueue <-get_page_from_freelist
+ bash-2044 [002] d..1 10594.481033: _raw_spin_unlock <-get_page_from_freelist
+ bash-2044 [002] d..1 10594.481033: sub_preempt_count <-_raw_spin_unlock
+ bash-2044 [002] d... 10594.481033: get_pageblock_flags_group <-get_pageblock_migratetype
+ bash-2044 [002] d... 10594.481034: __mod_zone_page_state <-get_page_from_freelist
+ bash-2044 [002] d... 10594.481034: zone_statistics <-get_page_from_freelist
+ bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics
+ bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics
+ bash-2044 [002] .... 10594.481035: arch_dup_task_struct <-copy_process
+ [...]
+
+ # cat instances/foo/trace_pipe
+ bash-1998 [000] d..4 136.676759: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000
+ bash-1998 [000] dN.4 136.676760: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000
+ <idle>-0 [003] d.h3 136.676906: sched_wakeup: comm=rcu_preempt pid=9 prio=120 success=1 target_cpu=003
+ <idle>-0 [003] d..3 136.676909: sched_switch: prev_comm=swapper/3 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=rcu_preempt next_pid=9 next_prio=120
+ rcu_preempt-9 [003] d..3 136.676916: sched_switch: prev_comm=rcu_preempt prev_pid=9 prev_prio=120 prev_state=S ==> next_comm=swapper/3 next_pid=0 next_prio=120
+ bash-1998 [000] d..4 136.677014: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000
+ bash-1998 [000] dN.4 136.677016: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000
+ bash-1998 [000] d..3 136.677018: sched_switch: prev_comm=bash prev_pid=1998 prev_prio=120 prev_state=R+ ==> next_comm=kworker/0:1 next_pid=59 next_prio=120
+ kworker/0:1-59 [000] d..4 136.677022: sched_wakeup: comm=sshd pid=1995 prio=120 success=1 target_cpu=001
+ kworker/0:1-59 [000] d..3 136.677025: sched_switch: prev_comm=kworker/0:1 prev_pid=59 prev_prio=120 prev_state=S ==> next_comm=bash next_pid=1998 next_prio=120
+ [...]
+
+ # cat instances/bar/trace_pipe
+ migration/1-14 [001] d.h3 138.732674: softirq_raise: vec=3 [action=NET_RX]
+ <idle>-0 [001] dNh3 138.732725: softirq_raise: vec=3 [action=NET_RX]
+ bash-1998 [000] d.h1 138.733101: softirq_raise: vec=1 [action=TIMER]
+ bash-1998 [000] d.h1 138.733102: softirq_raise: vec=9 [action=RCU]
+ bash-1998 [000] ..s2 138.733105: softirq_entry: vec=1 [action=TIMER]
+ bash-1998 [000] ..s2 138.733106: softirq_exit: vec=1 [action=TIMER]
+ bash-1998 [000] ..s2 138.733106: softirq_entry: vec=9 [action=RCU]
+ bash-1998 [000] ..s2 138.733109: softirq_exit: vec=9 [action=RCU]
+ sshd-1995 [001] d.h1 138.733278: irq_handler_entry: irq=21 name=uhci_hcd:usb4
+ sshd-1995 [001] d.h1 138.733280: irq_handler_exit: irq=21 ret=unhandled
+ sshd-1995 [001] d.h1 138.733281: irq_handler_entry: irq=21 name=eth0
+ sshd-1995 [001] d.h1 138.733283: irq_handler_exit: irq=21 ret=handled
+ [...]
+
+ # cat instances/zoot/trace
+ # tracer: nop
+ #
+ # entries-in-buffer/entries-written: 18996/18996 #P:4
+ #
+ # _-----=> irqs-off
+ # / _----=> need-resched
+ # | / _---=> hardirq/softirq
+ # || / _--=> preempt-depth
+ # ||| / delay
+ # TASK-PID CPU# |||| TIMESTAMP FUNCTION
+ # | | | |||| | |
+ bash-1998 [000] d... 140.733501: sys_write -> 0x2
+ bash-1998 [000] d... 140.733504: sys_dup2(oldfd: a, newfd: 1)
+ bash-1998 [000] d... 140.733506: sys_dup2 -> 0x1
+ bash-1998 [000] d... 140.733508: sys_fcntl(fd: a, cmd: 1, arg: 0)
+ bash-1998 [000] d... 140.733509: sys_fcntl -> 0x1
+ bash-1998 [000] d... 140.733510: sys_close(fd: a)
+ bash-1998 [000] d... 140.733510: sys_close -> 0x0
+ bash-1998 [000] d... 140.733514: sys_rt_sigprocmask(how: 0, nset: 0, oset: 6e2768, sigsetsize: 8)
+ bash-1998 [000] d... 140.733515: sys_rt_sigprocmask -> 0x0
+ bash-1998 [000] d... 140.733516: sys_rt_sigaction(sig: 2, act: 7fff718846f0, oact: 7fff71884650, sigsetsize: 8)
+ bash-1998 [000] d... 140.733516: sys_rt_sigaction -> 0x0
+
+You can see that the trace of the top most trace buffer shows only
+the function tracing. The foo instance displays wakeups and task
+switches.
+
+To remove the instances, simply delete their directories:
+::
+
+ # rmdir instances/foo
+ # rmdir instances/bar
+ # rmdir instances/zoot
+
+Note, if a process has a trace file open in one of the instance
+directories, the rmdir will fail with EBUSY.
+
+
+Stack trace
+-----------
+Since the kernel has a fixed sized stack, it is important not to
+waste it in functions. A kernel developer must be conscience of
+what they allocate on the stack. If they add too much, the system
+can be in danger of a stack overflow, and corruption will occur,
+usually leading to a system panic.
+
+There are some tools that check this, usually with interrupts
+periodically checking usage. But if you can perform a check
+at every function call that will become very useful. As ftrace provides
+a function tracer, it makes it convenient to check the stack size
+at every function call. This is enabled via the stack tracer.
+
+CONFIG_STACK_TRACER enables the ftrace stack tracing functionality.
+To enable it, write a '1' into /proc/sys/kernel/stack_tracer_enabled.
+::
+
+ # echo 1 > /proc/sys/kernel/stack_tracer_enabled
+
+You can also enable it from the kernel command line to trace
+the stack size of the kernel during boot up, by adding "stacktrace"
+to the kernel command line parameter.
+
+After running it for a few minutes, the output looks like:
+::
+
+ # cat stack_max_size
+ 2928
+
+ # cat stack_trace
+ Depth Size Location (18 entries)
+ ----- ---- --------
+ 0) 2928 224 update_sd_lb_stats+0xbc/0x4ac
+ 1) 2704 160 find_busiest_group+0x31/0x1f1
+ 2) 2544 256 load_balance+0xd9/0x662
+ 3) 2288 80 idle_balance+0xbb/0x130
+ 4) 2208 128 __schedule+0x26e/0x5b9
+ 5) 2080 16 schedule+0x64/0x66
+ 6) 2064 128 schedule_timeout+0x34/0xe0
+ 7) 1936 112 wait_for_common+0x97/0xf1
+ 8) 1824 16 wait_for_completion+0x1d/0x1f
+ 9) 1808 128 flush_work+0xfe/0x119
+ 10) 1680 16 tty_flush_to_ldisc+0x1e/0x20
+ 11) 1664 48 input_available_p+0x1d/0x5c
+ 12) 1616 48 n_tty_poll+0x6d/0x134
+ 13) 1568 64 tty_poll+0x64/0x7f
+ 14) 1504 880 do_select+0x31e/0x511
+ 15) 624 400 core_sys_select+0x177/0x216
+ 16) 224 96 sys_select+0x91/0xb9
+ 17) 128 128 system_call_fastpath+0x16/0x1b
+
+Note, if -mfentry is being used by gcc, functions get traced before
+they set up the stack frame. This means that leaf level functions
+are not tested by the stack tracer when -mfentry is used.
+
+Currently, -mfentry is used by gcc 4.6.0 and above on x86 only.
+
+More
+----
+More details can be found in the source code, in the `kernel/trace/*.c` files.
projects / linux-2.6-block.git / commitdiff