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1 | ======================== |
2 | ftrace - Function Tracer | |
3 | ======================== | |
4 | ||
5 | Copyright 2008 Red Hat Inc. | |
6 | ||
7 | :Author: Steven Rostedt <srostedt@redhat.com> | |
8 | :License: The GNU Free Documentation License, Version 1.2 | |
9 | (dual licensed under the GPL v2) | |
10 | :Original Reviewers: Elias Oltmanns, Randy Dunlap, Andrew Morton, | |
11 | John Kacur, and David Teigland. | |
12 | ||
13 | - Written for: 2.6.28-rc2 | |
14 | - Updated for: 3.10 | |
15 | - Updated for: 4.13 - Copyright 2017 VMware Inc. Steven Rostedt | |
16 | - Converted to rst format - Changbin Du <changbin.du@intel.com> | |
17 | ||
18 | Introduction | |
19 | ------------ | |
20 | ||
21 | Ftrace is an internal tracer designed to help out developers and | |
22 | designers of systems to find what is going on inside the kernel. | |
23 | It can be used for debugging or analyzing latencies and | |
24 | performance issues that take place outside of user-space. | |
25 | ||
26 | Although ftrace is typically considered the function tracer, it | |
2a1e03ca | 27 | is really a framework of several assorted tracing utilities. |
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28 | There's latency tracing to examine what occurs between interrupts |
29 | disabled and enabled, as well as for preemption and from a time | |
30 | a task is woken to the task is actually scheduled in. | |
31 | ||
32 | One of the most common uses of ftrace is the event tracing. | |
2a1e03ca | 33 | Throughout the kernel is hundreds of static event points that |
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34 | can be enabled via the tracefs file system to see what is |
35 | going on in certain parts of the kernel. | |
36 | ||
37 | See events.txt for more information. | |
38 | ||
39 | ||
40 | Implementation Details | |
41 | ---------------------- | |
42 | ||
43 | See :doc:`ftrace-design` for details for arch porters and such. | |
44 | ||
45 | ||
46 | The File System | |
47 | --------------- | |
48 | ||
49 | Ftrace uses the tracefs file system to hold the control files as | |
50 | well as the files to display output. | |
51 | ||
52 | When tracefs is configured into the kernel (which selecting any ftrace | |
53 | option will do) the directory /sys/kernel/tracing will be created. To mount | |
54 | this directory, you can add to your /etc/fstab file:: | |
55 | ||
56 | tracefs /sys/kernel/tracing tracefs defaults 0 0 | |
57 | ||
58 | Or you can mount it at run time with:: | |
59 | ||
60 | mount -t tracefs nodev /sys/kernel/tracing | |
61 | ||
62 | For quicker access to that directory you may want to make a soft link to | |
63 | it:: | |
64 | ||
65 | ln -s /sys/kernel/tracing /tracing | |
66 | ||
67 | .. attention:: | |
68 | ||
69 | Before 4.1, all ftrace tracing control files were within the debugfs | |
70 | file system, which is typically located at /sys/kernel/debug/tracing. | |
71 | For backward compatibility, when mounting the debugfs file system, | |
72 | the tracefs file system will be automatically mounted at: | |
73 | ||
74 | /sys/kernel/debug/tracing | |
75 | ||
76 | All files located in the tracefs file system will be located in that | |
77 | debugfs file system directory as well. | |
78 | ||
79 | .. attention:: | |
80 | ||
81 | Any selected ftrace option will also create the tracefs file system. | |
82 | The rest of the document will assume that you are in the ftrace directory | |
83 | (cd /sys/kernel/tracing) and will only concentrate on the files within that | |
84 | directory and not distract from the content with the extended | |
85 | "/sys/kernel/tracing" path name. | |
86 | ||
87 | That's it! (assuming that you have ftrace configured into your kernel) | |
88 | ||
89 | After mounting tracefs you will have access to the control and output files | |
90 | of ftrace. Here is a list of some of the key files: | |
91 | ||
92 | ||
93 | Note: all time values are in microseconds. | |
94 | ||
95 | current_tracer: | |
96 | ||
97 | This is used to set or display the current tracer | |
98 | that is configured. | |
99 | ||
100 | available_tracers: | |
101 | ||
102 | This holds the different types of tracers that | |
103 | have been compiled into the kernel. The | |
104 | tracers listed here can be configured by | |
105 | echoing their name into current_tracer. | |
106 | ||
107 | tracing_on: | |
108 | ||
109 | This sets or displays whether writing to the trace | |
110 | ring buffer is enabled. Echo 0 into this file to disable | |
111 | the tracer or 1 to enable it. Note, this only disables | |
112 | writing to the ring buffer, the tracing overhead may | |
113 | still be occurring. | |
114 | ||
115 | The kernel function tracing_off() can be used within the | |
116 | kernel to disable writing to the ring buffer, which will | |
117 | set this file to "0". User space can re-enable tracing by | |
118 | echoing "1" into the file. | |
119 | ||
120 | Note, the function and event trigger "traceoff" will also | |
121 | set this file to zero and stop tracing. Which can also | |
122 | be re-enabled by user space using this file. | |
123 | ||
124 | trace: | |
125 | ||
126 | This file holds the output of the trace in a human | |
127 | readable format (described below). Note, tracing is temporarily | |
128 | disabled while this file is being read (opened). | |
129 | ||
130 | trace_pipe: | |
131 | ||
132 | The output is the same as the "trace" file but this | |
133 | file is meant to be streamed with live tracing. | |
134 | Reads from this file will block until new data is | |
135 | retrieved. Unlike the "trace" file, this file is a | |
136 | consumer. This means reading from this file causes | |
137 | sequential reads to display more current data. Once | |
138 | data is read from this file, it is consumed, and | |
139 | will not be read again with a sequential read. The | |
140 | "trace" file is static, and if the tracer is not | |
141 | adding more data, it will display the same | |
142 | information every time it is read. This file will not | |
143 | disable tracing while being read. | |
144 | ||
145 | trace_options: | |
146 | ||
147 | This file lets the user control the amount of data | |
148 | that is displayed in one of the above output | |
149 | files. Options also exist to modify how a tracer | |
150 | or events work (stack traces, timestamps, etc). | |
151 | ||
152 | options: | |
153 | ||
154 | This is a directory that has a file for every available | |
155 | trace option (also in trace_options). Options may also be set | |
156 | or cleared by writing a "1" or "0" respectively into the | |
157 | corresponding file with the option name. | |
158 | ||
159 | tracing_max_latency: | |
160 | ||
161 | Some of the tracers record the max latency. | |
162 | For example, the maximum time that interrupts are disabled. | |
163 | The maximum time is saved in this file. The max trace will also be | |
164 | stored, and displayed by "trace". A new max trace will only be | |
165 | recorded if the latency is greater than the value in this file | |
166 | (in microseconds). | |
167 | ||
168 | By echoing in a time into this file, no latency will be recorded | |
169 | unless it is greater than the time in this file. | |
170 | ||
171 | tracing_thresh: | |
172 | ||
173 | Some latency tracers will record a trace whenever the | |
174 | latency is greater than the number in this file. | |
175 | Only active when the file contains a number greater than 0. | |
176 | (in microseconds) | |
177 | ||
178 | buffer_size_kb: | |
179 | ||
180 | This sets or displays the number of kilobytes each CPU | |
181 | buffer holds. By default, the trace buffers are the same size | |
182 | for each CPU. The displayed number is the size of the | |
183 | CPU buffer and not total size of all buffers. The | |
184 | trace buffers are allocated in pages (blocks of memory | |
185 | that the kernel uses for allocation, usually 4 KB in size). | |
186 | If the last page allocated has room for more bytes | |
187 | than requested, the rest of the page will be used, | |
188 | making the actual allocation bigger than requested or shown. | |
189 | ( Note, the size may not be a multiple of the page size | |
190 | due to buffer management meta-data. ) | |
191 | ||
192 | Buffer sizes for individual CPUs may vary | |
193 | (see "per_cpu/cpu0/buffer_size_kb" below), and if they do | |
194 | this file will show "X". | |
195 | ||
196 | buffer_total_size_kb: | |
197 | ||
198 | This displays the total combined size of all the trace buffers. | |
199 | ||
200 | free_buffer: | |
201 | ||
202 | If a process is performing tracing, and the ring buffer should be | |
203 | shrunk "freed" when the process is finished, even if it were to be | |
204 | killed by a signal, this file can be used for that purpose. On close | |
205 | of this file, the ring buffer will be resized to its minimum size. | |
206 | Having a process that is tracing also open this file, when the process | |
207 | exits its file descriptor for this file will be closed, and in doing so, | |
208 | the ring buffer will be "freed". | |
209 | ||
210 | It may also stop tracing if disable_on_free option is set. | |
211 | ||
212 | tracing_cpumask: | |
213 | ||
214 | This is a mask that lets the user only trace on specified CPUs. | |
215 | The format is a hex string representing the CPUs. | |
216 | ||
217 | set_ftrace_filter: | |
218 | ||
219 | When dynamic ftrace is configured in (see the | |
220 | section below "dynamic ftrace"), the code is dynamically | |
221 | modified (code text rewrite) to disable calling of the | |
222 | function profiler (mcount). This lets tracing be configured | |
223 | in with practically no overhead in performance. This also | |
224 | has a side effect of enabling or disabling specific functions | |
225 | to be traced. Echoing names of functions into this file | |
226 | will limit the trace to only those functions. | |
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227 | This influences the tracers "function" and "function_graph" |
228 | and thus also function profiling (see "function_profile_enabled"). | |
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229 | |
230 | The functions listed in "available_filter_functions" are what | |
231 | can be written into this file. | |
232 | ||
233 | This interface also allows for commands to be used. See the | |
234 | "Filter commands" section for more details. | |
235 | ||
236 | set_ftrace_notrace: | |
237 | ||
238 | This has an effect opposite to that of | |
239 | set_ftrace_filter. Any function that is added here will not | |
240 | be traced. If a function exists in both set_ftrace_filter | |
241 | and set_ftrace_notrace, the function will _not_ be traced. | |
242 | ||
243 | set_ftrace_pid: | |
244 | ||
245 | Have the function tracer only trace the threads whose PID are | |
246 | listed in this file. | |
247 | ||
248 | If the "function-fork" option is set, then when a task whose | |
249 | PID is listed in this file forks, the child's PID will | |
250 | automatically be added to this file, and the child will be | |
251 | traced by the function tracer as well. This option will also | |
252 | cause PIDs of tasks that exit to be removed from the file. | |
253 | ||
254 | set_event_pid: | |
255 | ||
256 | Have the events only trace a task with a PID listed in this file. | |
257 | Note, sched_switch and sched_wake_up will also trace events | |
258 | listed in this file. | |
259 | ||
260 | To have the PIDs of children of tasks with their PID in this file | |
261 | added on fork, enable the "event-fork" option. That option will also | |
262 | cause the PIDs of tasks to be removed from this file when the task | |
263 | exits. | |
264 | ||
265 | set_graph_function: | |
266 | ||
267 | Functions listed in this file will cause the function graph | |
268 | tracer to only trace these functions and the functions that | |
269 | they call. (See the section "dynamic ftrace" for more details). | |
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270 | Note, set_ftrace_filter and set_ftrace_notrace still affects |
271 | what functions are being traced. | |
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272 | |
273 | set_graph_notrace: | |
274 | ||
275 | Similar to set_graph_function, but will disable function graph | |
276 | tracing when the function is hit until it exits the function. | |
277 | This makes it possible to ignore tracing functions that are called | |
278 | by a specific function. | |
279 | ||
280 | available_filter_functions: | |
281 | ||
282 | This lists the functions that ftrace has processed and can trace. | |
283 | These are the function names that you can pass to | |
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284 | "set_ftrace_filter", "set_ftrace_notrace", |
285 | "set_graph_function", or "set_graph_notrace". | |
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286 | (See the section "dynamic ftrace" below for more details.) |
287 | ||
288 | dyn_ftrace_total_info: | |
289 | ||
290 | This file is for debugging purposes. The number of functions that | |
291 | have been converted to nops and are available to be traced. | |
292 | ||
293 | enabled_functions: | |
294 | ||
295 | This file is more for debugging ftrace, but can also be useful | |
296 | in seeing if any function has a callback attached to it. | |
297 | Not only does the trace infrastructure use ftrace function | |
298 | trace utility, but other subsystems might too. This file | |
299 | displays all functions that have a callback attached to them | |
300 | as well as the number of callbacks that have been attached. | |
301 | Note, a callback may also call multiple functions which will | |
302 | not be listed in this count. | |
303 | ||
304 | If the callback registered to be traced by a function with | |
305 | the "save regs" attribute (thus even more overhead), a 'R' | |
306 | will be displayed on the same line as the function that | |
307 | is returning registers. | |
308 | ||
309 | If the callback registered to be traced by a function with | |
310 | the "ip modify" attribute (thus the regs->ip can be changed), | |
311 | an 'I' will be displayed on the same line as the function that | |
312 | can be overridden. | |
313 | ||
314 | If the architecture supports it, it will also show what callback | |
315 | is being directly called by the function. If the count is greater | |
316 | than 1 it most likely will be ftrace_ops_list_func(). | |
317 | ||
318 | If the callback of the function jumps to a trampoline that is | |
319 | specific to a the callback and not the standard trampoline, | |
320 | its address will be printed as well as the function that the | |
321 | trampoline calls. | |
322 | ||
323 | function_profile_enabled: | |
324 | ||
325 | When set it will enable all functions with either the function | |
326 | tracer, or if configured, the function graph tracer. It will | |
327 | keep a histogram of the number of functions that were called | |
328 | and if the function graph tracer was configured, it will also keep | |
329 | track of the time spent in those functions. The histogram | |
330 | content can be displayed in the files: | |
331 | ||
1fee4f77 | 332 | trace_stat/function<cpu> ( function0, function1, etc). |
1f198e22 | 333 | |
1fee4f77 | 334 | trace_stat: |
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335 | |
336 | A directory that holds different tracing stats. | |
337 | ||
338 | kprobe_events: | |
339 | ||
340 | Enable dynamic trace points. See kprobetrace.txt. | |
341 | ||
342 | kprobe_profile: | |
343 | ||
344 | Dynamic trace points stats. See kprobetrace.txt. | |
345 | ||
346 | max_graph_depth: | |
347 | ||
348 | Used with the function graph tracer. This is the max depth | |
349 | it will trace into a function. Setting this to a value of | |
350 | one will show only the first kernel function that is called | |
351 | from user space. | |
352 | ||
353 | printk_formats: | |
354 | ||
355 | This is for tools that read the raw format files. If an event in | |
356 | the ring buffer references a string, only a pointer to the string | |
357 | is recorded into the buffer and not the string itself. This prevents | |
358 | tools from knowing what that string was. This file displays the string | |
359 | and address for the string allowing tools to map the pointers to what | |
360 | the strings were. | |
361 | ||
362 | saved_cmdlines: | |
363 | ||
364 | Only the pid of the task is recorded in a trace event unless | |
365 | the event specifically saves the task comm as well. Ftrace | |
366 | makes a cache of pid mappings to comms to try to display | |
367 | comms for events. If a pid for a comm is not listed, then | |
368 | "<...>" is displayed in the output. | |
369 | ||
370 | If the option "record-cmd" is set to "0", then comms of tasks | |
371 | will not be saved during recording. By default, it is enabled. | |
372 | ||
373 | saved_cmdlines_size: | |
374 | ||
375 | By default, 128 comms are saved (see "saved_cmdlines" above). To | |
376 | increase or decrease the amount of comms that are cached, echo | |
377 | in a the number of comms to cache, into this file. | |
378 | ||
379 | saved_tgids: | |
380 | ||
381 | If the option "record-tgid" is set, on each scheduling context switch | |
382 | the Task Group ID of a task is saved in a table mapping the PID of | |
383 | the thread to its TGID. By default, the "record-tgid" option is | |
384 | disabled. | |
385 | ||
386 | snapshot: | |
387 | ||
388 | This displays the "snapshot" buffer and also lets the user | |
389 | take a snapshot of the current running trace. | |
390 | See the "Snapshot" section below for more details. | |
391 | ||
392 | stack_max_size: | |
393 | ||
394 | When the stack tracer is activated, this will display the | |
395 | maximum stack size it has encountered. | |
396 | See the "Stack Trace" section below. | |
397 | ||
398 | stack_trace: | |
399 | ||
400 | This displays the stack back trace of the largest stack | |
401 | that was encountered when the stack tracer is activated. | |
402 | See the "Stack Trace" section below. | |
403 | ||
404 | stack_trace_filter: | |
405 | ||
406 | This is similar to "set_ftrace_filter" but it limits what | |
407 | functions the stack tracer will check. | |
408 | ||
409 | trace_clock: | |
410 | ||
411 | Whenever an event is recorded into the ring buffer, a | |
412 | "timestamp" is added. This stamp comes from a specified | |
413 | clock. By default, ftrace uses the "local" clock. This | |
414 | clock is very fast and strictly per cpu, but on some | |
415 | systems it may not be monotonic with respect to other | |
416 | CPUs. In other words, the local clocks may not be in sync | |
417 | with local clocks on other CPUs. | |
418 | ||
419 | Usual clocks for tracing:: | |
420 | ||
421 | # cat trace_clock | |
422 | [local] global counter x86-tsc | |
423 | ||
424 | The clock with the square brackets around it is the one in effect. | |
425 | ||
426 | local: | |
427 | Default clock, but may not be in sync across CPUs | |
428 | ||
429 | global: | |
430 | This clock is in sync with all CPUs but may | |
431 | be a bit slower than the local clock. | |
432 | ||
433 | counter: | |
434 | This is not a clock at all, but literally an atomic | |
435 | counter. It counts up one by one, but is in sync | |
436 | with all CPUs. This is useful when you need to | |
437 | know exactly the order events occurred with respect to | |
438 | each other on different CPUs. | |
439 | ||
440 | uptime: | |
441 | This uses the jiffies counter and the time stamp | |
442 | is relative to the time since boot up. | |
443 | ||
444 | perf: | |
445 | This makes ftrace use the same clock that perf uses. | |
446 | Eventually perf will be able to read ftrace buffers | |
447 | and this will help out in interleaving the data. | |
448 | ||
449 | x86-tsc: | |
450 | Architectures may define their own clocks. For | |
451 | example, x86 uses its own TSC cycle clock here. | |
452 | ||
453 | ppc-tb: | |
454 | This uses the powerpc timebase register value. | |
455 | This is in sync across CPUs and can also be used | |
456 | to correlate events across hypervisor/guest if | |
457 | tb_offset is known. | |
458 | ||
459 | mono: | |
460 | This uses the fast monotonic clock (CLOCK_MONOTONIC) | |
461 | which is monotonic and is subject to NTP rate adjustments. | |
462 | ||
463 | mono_raw: | |
464 | This is the raw monotonic clock (CLOCK_MONOTONIC_RAW) | |
2a1e03ca | 465 | which is monotonic but is not subject to any rate adjustments |
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466 | and ticks at the same rate as the hardware clocksource. |
467 | ||
468 | boot: | |
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469 | This is the boot clock (CLOCK_BOOTTIME) and is based on the |
470 | fast monotonic clock, but also accounts for time spent in | |
471 | suspend. Since the clock access is designed for use in | |
472 | tracing in the suspend path, some side effects are possible | |
473 | if clock is accessed after the suspend time is accounted before | |
474 | the fast mono clock is updated. In this case, the clock update | |
475 | appears to happen slightly sooner than it normally would have. | |
476 | Also on 32-bit systems, it's possible that the 64-bit boot offset | |
477 | sees a partial update. These effects are rare and post | |
478 | processing should be able to handle them. See comments in the | |
479 | ktime_get_boot_fast_ns() function for more information. | |
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480 | |
481 | To set a clock, simply echo the clock name into this file:: | |
482 | ||
483 | # echo global > trace_clock | |
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484 | |
485 | trace_marker: | |
486 | ||
487 | This is a very useful file for synchronizing user space | |
488 | with events happening in the kernel. Writing strings into | |
489 | this file will be written into the ftrace buffer. | |
490 | ||
491 | It is useful in applications to open this file at the start | |
492 | of the application and just reference the file descriptor | |
493 | for the file:: | |
494 | ||
495 | void trace_write(const char *fmt, ...) | |
496 | { | |
497 | va_list ap; | |
498 | char buf[256]; | |
499 | int n; | |
500 | ||
501 | if (trace_fd < 0) | |
502 | return; | |
503 | ||
504 | va_start(ap, fmt); | |
505 | n = vsnprintf(buf, 256, fmt, ap); | |
506 | va_end(ap); | |
507 | ||
508 | write(trace_fd, buf, n); | |
509 | } | |
510 | ||
511 | start:: | |
512 | ||
513 | trace_fd = open("trace_marker", WR_ONLY); | |
514 | ||
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515 | Note: Writing into the trace_marker file can also initiate triggers |
516 | that are written into /sys/kernel/tracing/events/ftrace/print/trigger | |
517 | See "Event triggers" in Documentation/trace/events.rst and an | |
518 | example in Documentation/trace/histogram.rst (Section 3.) | |
519 | ||
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520 | trace_marker_raw: |
521 | ||
522 | This is similar to trace_marker above, but is meant for for binary data | |
523 | to be written to it, where a tool can be used to parse the data | |
524 | from trace_pipe_raw. | |
525 | ||
526 | uprobe_events: | |
527 | ||
528 | Add dynamic tracepoints in programs. | |
529 | See uprobetracer.txt | |
530 | ||
531 | uprobe_profile: | |
532 | ||
533 | Uprobe statistics. See uprobetrace.txt | |
534 | ||
535 | instances: | |
536 | ||
537 | This is a way to make multiple trace buffers where different | |
538 | events can be recorded in different buffers. | |
539 | See "Instances" section below. | |
540 | ||
541 | events: | |
542 | ||
543 | This is the trace event directory. It holds event tracepoints | |
544 | (also known as static tracepoints) that have been compiled | |
545 | into the kernel. It shows what event tracepoints exist | |
546 | and how they are grouped by system. There are "enable" | |
547 | files at various levels that can enable the tracepoints | |
548 | when a "1" is written to them. | |
549 | ||
550 | See events.txt for more information. | |
551 | ||
552 | set_event: | |
553 | ||
554 | By echoing in the event into this file, will enable that event. | |
555 | ||
556 | See events.txt for more information. | |
557 | ||
558 | available_events: | |
559 | ||
560 | A list of events that can be enabled in tracing. | |
561 | ||
562 | See events.txt for more information. | |
563 | ||
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564 | timestamp_mode: |
565 | ||
566 | Certain tracers may change the timestamp mode used when | |
567 | logging trace events into the event buffer. Events with | |
568 | different modes can coexist within a buffer but the mode in | |
569 | effect when an event is logged determines which timestamp mode | |
570 | is used for that event. The default timestamp mode is | |
571 | 'delta'. | |
572 | ||
573 | Usual timestamp modes for tracing: | |
574 | ||
575 | # cat timestamp_mode | |
576 | [delta] absolute | |
577 | ||
578 | The timestamp mode with the square brackets around it is the | |
579 | one in effect. | |
580 | ||
581 | delta: Default timestamp mode - timestamp is a delta against | |
582 | a per-buffer timestamp. | |
583 | ||
584 | absolute: The timestamp is a full timestamp, not a delta | |
585 | against some other value. As such it takes up more | |
586 | space and is less efficient. | |
587 | ||
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588 | hwlat_detector: |
589 | ||
590 | Directory for the Hardware Latency Detector. | |
591 | See "Hardware Latency Detector" section below. | |
592 | ||
593 | per_cpu: | |
594 | ||
595 | This is a directory that contains the trace per_cpu information. | |
596 | ||
597 | per_cpu/cpu0/buffer_size_kb: | |
598 | ||
599 | The ftrace buffer is defined per_cpu. That is, there's a separate | |
600 | buffer for each CPU to allow writes to be done atomically, | |
601 | and free from cache bouncing. These buffers may have different | |
602 | size buffers. This file is similar to the buffer_size_kb | |
603 | file, but it only displays or sets the buffer size for the | |
604 | specific CPU. (here cpu0). | |
605 | ||
606 | per_cpu/cpu0/trace: | |
607 | ||
608 | This is similar to the "trace" file, but it will only display | |
609 | the data specific for the CPU. If written to, it only clears | |
610 | the specific CPU buffer. | |
611 | ||
612 | per_cpu/cpu0/trace_pipe | |
613 | ||
614 | This is similar to the "trace_pipe" file, and is a consuming | |
615 | read, but it will only display (and consume) the data specific | |
616 | for the CPU. | |
617 | ||
618 | per_cpu/cpu0/trace_pipe_raw | |
619 | ||
620 | For tools that can parse the ftrace ring buffer binary format, | |
621 | the trace_pipe_raw file can be used to extract the data | |
622 | from the ring buffer directly. With the use of the splice() | |
623 | system call, the buffer data can be quickly transferred to | |
624 | a file or to the network where a server is collecting the | |
625 | data. | |
626 | ||
627 | Like trace_pipe, this is a consuming reader, where multiple | |
628 | reads will always produce different data. | |
629 | ||
630 | per_cpu/cpu0/snapshot: | |
631 | ||
632 | This is similar to the main "snapshot" file, but will only | |
633 | snapshot the current CPU (if supported). It only displays | |
634 | the content of the snapshot for a given CPU, and if | |
635 | written to, only clears this CPU buffer. | |
636 | ||
637 | per_cpu/cpu0/snapshot_raw: | |
638 | ||
639 | Similar to the trace_pipe_raw, but will read the binary format | |
640 | from the snapshot buffer for the given CPU. | |
641 | ||
642 | per_cpu/cpu0/stats: | |
643 | ||
644 | This displays certain stats about the ring buffer: | |
645 | ||
646 | entries: | |
647 | The number of events that are still in the buffer. | |
648 | ||
649 | overrun: | |
650 | The number of lost events due to overwriting when | |
651 | the buffer was full. | |
652 | ||
653 | commit overrun: | |
654 | Should always be zero. | |
655 | This gets set if so many events happened within a nested | |
656 | event (ring buffer is re-entrant), that it fills the | |
657 | buffer and starts dropping events. | |
658 | ||
659 | bytes: | |
660 | Bytes actually read (not overwritten). | |
661 | ||
662 | oldest event ts: | |
663 | The oldest timestamp in the buffer | |
664 | ||
665 | now ts: | |
666 | The current timestamp | |
667 | ||
668 | dropped events: | |
669 | Events lost due to overwrite option being off. | |
670 | ||
671 | read events: | |
672 | The number of events read. | |
673 | ||
674 | The Tracers | |
675 | ----------- | |
676 | ||
677 | Here is the list of current tracers that may be configured. | |
678 | ||
679 | "function" | |
680 | ||
681 | Function call tracer to trace all kernel functions. | |
682 | ||
683 | "function_graph" | |
684 | ||
685 | Similar to the function tracer except that the | |
686 | function tracer probes the functions on their entry | |
687 | whereas the function graph tracer traces on both entry | |
688 | and exit of the functions. It then provides the ability | |
689 | to draw a graph of function calls similar to C code | |
690 | source. | |
691 | ||
692 | "blk" | |
693 | ||
694 | The block tracer. The tracer used by the blktrace user | |
695 | application. | |
696 | ||
697 | "hwlat" | |
698 | ||
699 | The Hardware Latency tracer is used to detect if the hardware | |
700 | produces any latency. See "Hardware Latency Detector" section | |
701 | below. | |
702 | ||
703 | "irqsoff" | |
704 | ||
705 | Traces the areas that disable interrupts and saves | |
706 | the trace with the longest max latency. | |
707 | See tracing_max_latency. When a new max is recorded, | |
708 | it replaces the old trace. It is best to view this | |
709 | trace with the latency-format option enabled, which | |
710 | happens automatically when the tracer is selected. | |
711 | ||
712 | "preemptoff" | |
713 | ||
714 | Similar to irqsoff but traces and records the amount of | |
715 | time for which preemption is disabled. | |
716 | ||
717 | "preemptirqsoff" | |
718 | ||
719 | Similar to irqsoff and preemptoff, but traces and | |
720 | records the largest time for which irqs and/or preemption | |
721 | is disabled. | |
722 | ||
723 | "wakeup" | |
724 | ||
725 | Traces and records the max latency that it takes for | |
726 | the highest priority task to get scheduled after | |
727 | it has been woken up. | |
728 | Traces all tasks as an average developer would expect. | |
729 | ||
730 | "wakeup_rt" | |
731 | ||
732 | Traces and records the max latency that it takes for just | |
733 | RT tasks (as the current "wakeup" does). This is useful | |
734 | for those interested in wake up timings of RT tasks. | |
735 | ||
736 | "wakeup_dl" | |
737 | ||
738 | Traces and records the max latency that it takes for | |
739 | a SCHED_DEADLINE task to be woken (as the "wakeup" and | |
740 | "wakeup_rt" does). | |
741 | ||
742 | "mmiotrace" | |
743 | ||
744 | A special tracer that is used to trace binary module. | |
745 | It will trace all the calls that a module makes to the | |
746 | hardware. Everything it writes and reads from the I/O | |
747 | as well. | |
748 | ||
749 | "branch" | |
750 | ||
751 | This tracer can be configured when tracing likely/unlikely | |
752 | calls within the kernel. It will trace when a likely and | |
753 | unlikely branch is hit and if it was correct in its prediction | |
754 | of being correct. | |
755 | ||
756 | "nop" | |
757 | ||
758 | This is the "trace nothing" tracer. To remove all | |
759 | tracers from tracing simply echo "nop" into | |
760 | current_tracer. | |
761 | ||
762 | ||
763 | Examples of using the tracer | |
764 | ---------------------------- | |
765 | ||
766 | Here are typical examples of using the tracers when controlling | |
767 | them only with the tracefs interface (without using any | |
768 | user-land utilities). | |
769 | ||
770 | Output format: | |
771 | -------------- | |
772 | ||
773 | Here is an example of the output format of the file "trace":: | |
774 | ||
775 | # tracer: function | |
776 | # | |
777 | # entries-in-buffer/entries-written: 140080/250280 #P:4 | |
778 | # | |
779 | # _-----=> irqs-off | |
780 | # / _----=> need-resched | |
781 | # | / _---=> hardirq/softirq | |
782 | # || / _--=> preempt-depth | |
783 | # ||| / delay | |
784 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
785 | # | | | |||| | | | |
786 | bash-1977 [000] .... 17284.993652: sys_close <-system_call_fastpath | |
787 | bash-1977 [000] .... 17284.993653: __close_fd <-sys_close | |
788 | bash-1977 [000] .... 17284.993653: _raw_spin_lock <-__close_fd | |
789 | sshd-1974 [003] .... 17284.993653: __srcu_read_unlock <-fsnotify | |
790 | bash-1977 [000] .... 17284.993654: add_preempt_count <-_raw_spin_lock | |
791 | bash-1977 [000] ...1 17284.993655: _raw_spin_unlock <-__close_fd | |
792 | bash-1977 [000] ...1 17284.993656: sub_preempt_count <-_raw_spin_unlock | |
793 | bash-1977 [000] .... 17284.993657: filp_close <-__close_fd | |
794 | bash-1977 [000] .... 17284.993657: dnotify_flush <-filp_close | |
795 | sshd-1974 [003] .... 17284.993658: sys_select <-system_call_fastpath | |
796 | .... | |
797 | ||
798 | A header is printed with the tracer name that is represented by | |
799 | the trace. In this case the tracer is "function". Then it shows the | |
800 | number of events in the buffer as well as the total number of entries | |
801 | that were written. The difference is the number of entries that were | |
802 | lost due to the buffer filling up (250280 - 140080 = 110200 events | |
803 | lost). | |
804 | ||
805 | The header explains the content of the events. Task name "bash", the task | |
806 | PID "1977", the CPU that it was running on "000", the latency format | |
807 | (explained below), the timestamp in <secs>.<usecs> format, the | |
808 | function name that was traced "sys_close" and the parent function that | |
809 | called this function "system_call_fastpath". The timestamp is the time | |
810 | at which the function was entered. | |
811 | ||
812 | Latency trace format | |
813 | -------------------- | |
814 | ||
815 | When the latency-format option is enabled or when one of the latency | |
816 | tracers is set, the trace file gives somewhat more information to see | |
817 | why a latency happened. Here is a typical trace:: | |
818 | ||
819 | # tracer: irqsoff | |
820 | # | |
821 | # irqsoff latency trace v1.1.5 on 3.8.0-test+ | |
822 | # -------------------------------------------------------------------- | |
823 | # latency: 259 us, #4/4, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
824 | # ----------------- | |
825 | # | task: ps-6143 (uid:0 nice:0 policy:0 rt_prio:0) | |
826 | # ----------------- | |
827 | # => started at: __lock_task_sighand | |
828 | # => ended at: _raw_spin_unlock_irqrestore | |
829 | # | |
830 | # | |
831 | # _------=> CPU# | |
832 | # / _-----=> irqs-off | |
833 | # | / _----=> need-resched | |
834 | # || / _---=> hardirq/softirq | |
835 | # ||| / _--=> preempt-depth | |
836 | # |||| / delay | |
837 | # cmd pid ||||| time | caller | |
838 | # \ / ||||| \ | / | |
839 | ps-6143 2d... 0us!: trace_hardirqs_off <-__lock_task_sighand | |
840 | ps-6143 2d..1 259us+: trace_hardirqs_on <-_raw_spin_unlock_irqrestore | |
841 | ps-6143 2d..1 263us+: time_hardirqs_on <-_raw_spin_unlock_irqrestore | |
842 | ps-6143 2d..1 306us : <stack trace> | |
843 | => trace_hardirqs_on_caller | |
844 | => trace_hardirqs_on | |
845 | => _raw_spin_unlock_irqrestore | |
846 | => do_task_stat | |
847 | => proc_tgid_stat | |
848 | => proc_single_show | |
849 | => seq_read | |
850 | => vfs_read | |
851 | => sys_read | |
852 | => system_call_fastpath | |
853 | ||
854 | ||
855 | This shows that the current tracer is "irqsoff" tracing the time | |
856 | for which interrupts were disabled. It gives the trace version (which | |
857 | never changes) and the version of the kernel upon which this was executed on | |
858 | (3.8). Then it displays the max latency in microseconds (259 us). The number | |
859 | of trace entries displayed and the total number (both are four: #4/4). | |
860 | VP, KP, SP, and HP are always zero and are reserved for later use. | |
861 | #P is the number of online CPUs (#P:4). | |
862 | ||
863 | The task is the process that was running when the latency | |
864 | occurred. (ps pid: 6143). | |
865 | ||
866 | The start and stop (the functions in which the interrupts were | |
867 | disabled and enabled respectively) that caused the latencies: | |
868 | ||
869 | - __lock_task_sighand is where the interrupts were disabled. | |
870 | - _raw_spin_unlock_irqrestore is where they were enabled again. | |
871 | ||
872 | The next lines after the header are the trace itself. The header | |
873 | explains which is which. | |
874 | ||
875 | cmd: The name of the process in the trace. | |
876 | ||
877 | pid: The PID of that process. | |
878 | ||
879 | CPU#: The CPU which the process was running on. | |
880 | ||
881 | irqs-off: 'd' interrupts are disabled. '.' otherwise. | |
882 | .. caution:: If the architecture does not support a way to | |
883 | read the irq flags variable, an 'X' will always | |
884 | be printed here. | |
885 | ||
886 | need-resched: | |
887 | - 'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set, | |
888 | - 'n' only TIF_NEED_RESCHED is set, | |
889 | - 'p' only PREEMPT_NEED_RESCHED is set, | |
890 | - '.' otherwise. | |
891 | ||
892 | hardirq/softirq: | |
893 | - 'Z' - NMI occurred inside a hardirq | |
894 | - 'z' - NMI is running | |
895 | - 'H' - hard irq occurred inside a softirq. | |
896 | - 'h' - hard irq is running | |
897 | - 's' - soft irq is running | |
898 | - '.' - normal context. | |
899 | ||
900 | preempt-depth: The level of preempt_disabled | |
901 | ||
902 | The above is mostly meaningful for kernel developers. | |
903 | ||
904 | time: | |
905 | When the latency-format option is enabled, the trace file | |
906 | output includes a timestamp relative to the start of the | |
907 | trace. This differs from the output when latency-format | |
908 | is disabled, which includes an absolute timestamp. | |
909 | ||
910 | delay: | |
911 | This is just to help catch your eye a bit better. And | |
912 | needs to be fixed to be only relative to the same CPU. | |
913 | The marks are determined by the difference between this | |
914 | current trace and the next trace. | |
915 | ||
916 | - '$' - greater than 1 second | |
2a1e03ca AL |
917 | - '@' - greater than 100 millisecond |
918 | - '*' - greater than 10 millisecond | |
1f198e22 CD |
919 | - '#' - greater than 1000 microsecond |
920 | - '!' - greater than 100 microsecond | |
921 | - '+' - greater than 10 microsecond | |
922 | - ' ' - less than or equal to 10 microsecond. | |
923 | ||
924 | The rest is the same as the 'trace' file. | |
925 | ||
926 | Note, the latency tracers will usually end with a back trace | |
927 | to easily find where the latency occurred. | |
928 | ||
929 | trace_options | |
930 | ------------- | |
931 | ||
932 | The trace_options file (or the options directory) is used to control | |
933 | what gets printed in the trace output, or manipulate the tracers. | |
934 | To see what is available, simply cat the file:: | |
935 | ||
936 | cat trace_options | |
937 | print-parent | |
938 | nosym-offset | |
939 | nosym-addr | |
940 | noverbose | |
941 | noraw | |
942 | nohex | |
943 | nobin | |
944 | noblock | |
945 | trace_printk | |
946 | annotate | |
947 | nouserstacktrace | |
948 | nosym-userobj | |
949 | noprintk-msg-only | |
950 | context-info | |
951 | nolatency-format | |
952 | record-cmd | |
953 | norecord-tgid | |
954 | overwrite | |
955 | nodisable_on_free | |
956 | irq-info | |
957 | markers | |
958 | noevent-fork | |
959 | function-trace | |
960 | nofunction-fork | |
961 | nodisplay-graph | |
962 | nostacktrace | |
963 | nobranch | |
964 | ||
965 | To disable one of the options, echo in the option prepended with | |
966 | "no":: | |
967 | ||
968 | echo noprint-parent > trace_options | |
969 | ||
970 | To enable an option, leave off the "no":: | |
971 | ||
972 | echo sym-offset > trace_options | |
973 | ||
974 | Here are the available options: | |
975 | ||
976 | print-parent | |
977 | On function traces, display the calling (parent) | |
978 | function as well as the function being traced. | |
979 | :: | |
980 | ||
981 | print-parent: | |
982 | bash-4000 [01] 1477.606694: simple_strtoul <-kstrtoul | |
983 | ||
984 | noprint-parent: | |
985 | bash-4000 [01] 1477.606694: simple_strtoul | |
986 | ||
987 | ||
988 | sym-offset | |
989 | Display not only the function name, but also the | |
990 | offset in the function. For example, instead of | |
991 | seeing just "ktime_get", you will see | |
992 | "ktime_get+0xb/0x20". | |
993 | :: | |
994 | ||
995 | sym-offset: | |
996 | bash-4000 [01] 1477.606694: simple_strtoul+0x6/0xa0 | |
997 | ||
998 | sym-addr | |
999 | This will also display the function address as well | |
1000 | as the function name. | |
1001 | :: | |
1002 | ||
1003 | sym-addr: | |
1004 | bash-4000 [01] 1477.606694: simple_strtoul <c0339346> | |
1005 | ||
1006 | verbose | |
1007 | This deals with the trace file when the | |
1008 | latency-format option is enabled. | |
1009 | :: | |
1010 | ||
1011 | bash 4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \ | |
1012 | (+0.000ms): simple_strtoul (kstrtoul) | |
1013 | ||
1014 | raw | |
1015 | This will display raw numbers. This option is best for | |
1016 | use with user applications that can translate the raw | |
1017 | numbers better than having it done in the kernel. | |
1018 | ||
1019 | hex | |
1020 | Similar to raw, but the numbers will be in a hexadecimal format. | |
1021 | ||
1022 | bin | |
1023 | This will print out the formats in raw binary. | |
1024 | ||
1025 | block | |
1026 | When set, reading trace_pipe will not block when polled. | |
1027 | ||
1028 | trace_printk | |
1029 | Can disable trace_printk() from writing into the buffer. | |
1030 | ||
1031 | annotate | |
1032 | It is sometimes confusing when the CPU buffers are full | |
1033 | and one CPU buffer had a lot of events recently, thus | |
1034 | a shorter time frame, were another CPU may have only had | |
1035 | a few events, which lets it have older events. When | |
1036 | the trace is reported, it shows the oldest events first, | |
1037 | and it may look like only one CPU ran (the one with the | |
1038 | oldest events). When the annotate option is set, it will | |
1039 | display when a new CPU buffer started:: | |
1040 | ||
1041 | <idle>-0 [001] dNs4 21169.031481: wake_up_idle_cpu <-add_timer_on | |
1042 | <idle>-0 [001] dNs4 21169.031482: _raw_spin_unlock_irqrestore <-add_timer_on | |
1043 | <idle>-0 [001] .Ns4 21169.031484: sub_preempt_count <-_raw_spin_unlock_irqrestore | |
1044 | ##### CPU 2 buffer started #### | |
1045 | <idle>-0 [002] .N.1 21169.031484: rcu_idle_exit <-cpu_idle | |
1046 | <idle>-0 [001] .Ns3 21169.031484: _raw_spin_unlock <-clocksource_watchdog | |
1047 | <idle>-0 [001] .Ns3 21169.031485: sub_preempt_count <-_raw_spin_unlock | |
1048 | ||
1049 | userstacktrace | |
1050 | This option changes the trace. It records a | |
1051 | stacktrace of the current user space thread after | |
1052 | each trace event. | |
1053 | ||
1054 | sym-userobj | |
1055 | when user stacktrace are enabled, look up which | |
1056 | object the address belongs to, and print a | |
1057 | relative address. This is especially useful when | |
1058 | ASLR is on, otherwise you don't get a chance to | |
1059 | resolve the address to object/file/line after | |
1060 | the app is no longer running | |
1061 | ||
1062 | The lookup is performed when you read | |
1063 | trace,trace_pipe. Example:: | |
1064 | ||
1065 | a.out-1623 [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0 | |
1066 | x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6] | |
1067 | ||
1068 | ||
1069 | printk-msg-only | |
1070 | When set, trace_printk()s will only show the format | |
1071 | and not their parameters (if trace_bprintk() or | |
1072 | trace_bputs() was used to save the trace_printk()). | |
1073 | ||
1074 | context-info | |
1075 | Show only the event data. Hides the comm, PID, | |
1076 | timestamp, CPU, and other useful data. | |
1077 | ||
1078 | latency-format | |
1079 | This option changes the trace output. When it is enabled, | |
1080 | the trace displays additional information about the | |
1081 | latency, as described in "Latency trace format". | |
1082 | ||
1083 | record-cmd | |
1084 | When any event or tracer is enabled, a hook is enabled | |
1085 | in the sched_switch trace point to fill comm cache | |
1086 | with mapped pids and comms. But this may cause some | |
1087 | overhead, and if you only care about pids, and not the | |
1088 | name of the task, disabling this option can lower the | |
1089 | impact of tracing. See "saved_cmdlines". | |
1090 | ||
1091 | record-tgid | |
1092 | When any event or tracer is enabled, a hook is enabled | |
1093 | in the sched_switch trace point to fill the cache of | |
1094 | mapped Thread Group IDs (TGID) mapping to pids. See | |
1095 | "saved_tgids". | |
1096 | ||
1097 | overwrite | |
1098 | This controls what happens when the trace buffer is | |
1099 | full. If "1" (default), the oldest events are | |
1100 | discarded and overwritten. If "0", then the newest | |
1101 | events are discarded. | |
1102 | (see per_cpu/cpu0/stats for overrun and dropped) | |
1103 | ||
1104 | disable_on_free | |
1105 | When the free_buffer is closed, tracing will | |
1106 | stop (tracing_on set to 0). | |
1107 | ||
1108 | irq-info | |
1109 | Shows the interrupt, preempt count, need resched data. | |
1110 | When disabled, the trace looks like:: | |
1111 | ||
1112 | # tracer: function | |
1113 | # | |
1114 | # entries-in-buffer/entries-written: 144405/9452052 #P:4 | |
1115 | # | |
1116 | # TASK-PID CPU# TIMESTAMP FUNCTION | |
1117 | # | | | | | | |
1118 | <idle>-0 [002] 23636.756054: ttwu_do_activate.constprop.89 <-try_to_wake_up | |
1119 | <idle>-0 [002] 23636.756054: activate_task <-ttwu_do_activate.constprop.89 | |
1120 | <idle>-0 [002] 23636.756055: enqueue_task <-activate_task | |
1121 | ||
1122 | ||
1123 | markers | |
1124 | When set, the trace_marker is writable (only by root). | |
1125 | When disabled, the trace_marker will error with EINVAL | |
1126 | on write. | |
1127 | ||
1128 | event-fork | |
1129 | When set, tasks with PIDs listed in set_event_pid will have | |
1130 | the PIDs of their children added to set_event_pid when those | |
1131 | tasks fork. Also, when tasks with PIDs in set_event_pid exit, | |
1132 | their PIDs will be removed from the file. | |
1133 | ||
1134 | function-trace | |
1135 | The latency tracers will enable function tracing | |
1136 | if this option is enabled (default it is). When | |
1137 | it is disabled, the latency tracers do not trace | |
1138 | functions. This keeps the overhead of the tracer down | |
1139 | when performing latency tests. | |
1140 | ||
1141 | function-fork | |
1142 | When set, tasks with PIDs listed in set_ftrace_pid will | |
1143 | have the PIDs of their children added to set_ftrace_pid | |
1144 | when those tasks fork. Also, when tasks with PIDs in | |
1145 | set_ftrace_pid exit, their PIDs will be removed from the | |
1146 | file. | |
1147 | ||
1148 | display-graph | |
1149 | When set, the latency tracers (irqsoff, wakeup, etc) will | |
1150 | use function graph tracing instead of function tracing. | |
1151 | ||
1152 | stacktrace | |
1153 | When set, a stack trace is recorded after any trace event | |
1154 | is recorded. | |
1155 | ||
1156 | branch | |
1157 | Enable branch tracing with the tracer. This enables branch | |
1158 | tracer along with the currently set tracer. Enabling this | |
1159 | with the "nop" tracer is the same as just enabling the | |
1160 | "branch" tracer. | |
1161 | ||
1162 | .. tip:: Some tracers have their own options. They only appear in this | |
1163 | file when the tracer is active. They always appear in the | |
1164 | options directory. | |
1165 | ||
1166 | ||
1167 | Here are the per tracer options: | |
1168 | ||
1169 | Options for function tracer: | |
1170 | ||
1171 | func_stack_trace | |
1172 | When set, a stack trace is recorded after every | |
1173 | function that is recorded. NOTE! Limit the functions | |
1174 | that are recorded before enabling this, with | |
1175 | "set_ftrace_filter" otherwise the system performance | |
1176 | will be critically degraded. Remember to disable | |
1177 | this option before clearing the function filter. | |
1178 | ||
1179 | Options for function_graph tracer: | |
1180 | ||
1181 | Since the function_graph tracer has a slightly different output | |
1182 | it has its own options to control what is displayed. | |
1183 | ||
1184 | funcgraph-overrun | |
1185 | When set, the "overrun" of the graph stack is | |
1186 | displayed after each function traced. The | |
1187 | overrun, is when the stack depth of the calls | |
1188 | is greater than what is reserved for each task. | |
1189 | Each task has a fixed array of functions to | |
1190 | trace in the call graph. If the depth of the | |
1191 | calls exceeds that, the function is not traced. | |
1192 | The overrun is the number of functions missed | |
1193 | due to exceeding this array. | |
1194 | ||
1195 | funcgraph-cpu | |
1196 | When set, the CPU number of the CPU where the trace | |
1197 | occurred is displayed. | |
1198 | ||
1199 | funcgraph-overhead | |
1200 | When set, if the function takes longer than | |
1201 | A certain amount, then a delay marker is | |
1202 | displayed. See "delay" above, under the | |
1203 | header description. | |
1204 | ||
1205 | funcgraph-proc | |
1206 | Unlike other tracers, the process' command line | |
1207 | is not displayed by default, but instead only | |
1208 | when a task is traced in and out during a context | |
1209 | switch. Enabling this options has the command | |
1210 | of each process displayed at every line. | |
1211 | ||
1212 | funcgraph-duration | |
1213 | At the end of each function (the return) | |
1214 | the duration of the amount of time in the | |
1215 | function is displayed in microseconds. | |
1216 | ||
1217 | funcgraph-abstime | |
1218 | When set, the timestamp is displayed at each line. | |
1219 | ||
1220 | funcgraph-irqs | |
1221 | When disabled, functions that happen inside an | |
1222 | interrupt will not be traced. | |
1223 | ||
1224 | funcgraph-tail | |
1225 | When set, the return event will include the function | |
1226 | that it represents. By default this is off, and | |
1227 | only a closing curly bracket "}" is displayed for | |
1228 | the return of a function. | |
1229 | ||
1230 | sleep-time | |
1231 | When running function graph tracer, to include | |
1232 | the time a task schedules out in its function. | |
1233 | When enabled, it will account time the task has been | |
1234 | scheduled out as part of the function call. | |
1235 | ||
1236 | graph-time | |
1237 | When running function profiler with function graph tracer, | |
1238 | to include the time to call nested functions. When this is | |
1239 | not set, the time reported for the function will only | |
1240 | include the time the function itself executed for, not the | |
1241 | time for functions that it called. | |
1242 | ||
1243 | Options for blk tracer: | |
1244 | ||
1245 | blk_classic | |
1246 | Shows a more minimalistic output. | |
1247 | ||
1248 | ||
1249 | irqsoff | |
1250 | ------- | |
1251 | ||
1252 | When interrupts are disabled, the CPU can not react to any other | |
1253 | external event (besides NMIs and SMIs). This prevents the timer | |
1254 | interrupt from triggering or the mouse interrupt from letting | |
1255 | the kernel know of a new mouse event. The result is a latency | |
1256 | with the reaction time. | |
1257 | ||
1258 | The irqsoff tracer tracks the time for which interrupts are | |
1259 | disabled. When a new maximum latency is hit, the tracer saves | |
1260 | the trace leading up to that latency point so that every time a | |
1261 | new maximum is reached, the old saved trace is discarded and the | |
1262 | new trace is saved. | |
1263 | ||
1264 | To reset the maximum, echo 0 into tracing_max_latency. Here is | |
1265 | an example:: | |
1266 | ||
1267 | # echo 0 > options/function-trace | |
1268 | # echo irqsoff > current_tracer | |
1269 | # echo 1 > tracing_on | |
1270 | # echo 0 > tracing_max_latency | |
1271 | # ls -ltr | |
1272 | [...] | |
1273 | # echo 0 > tracing_on | |
1274 | # cat trace | |
1275 | # tracer: irqsoff | |
1276 | # | |
1277 | # irqsoff latency trace v1.1.5 on 3.8.0-test+ | |
1278 | # -------------------------------------------------------------------- | |
1279 | # latency: 16 us, #4/4, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1280 | # ----------------- | |
1281 | # | task: swapper/0-0 (uid:0 nice:0 policy:0 rt_prio:0) | |
1282 | # ----------------- | |
1283 | # => started at: run_timer_softirq | |
1284 | # => ended at: run_timer_softirq | |
1285 | # | |
1286 | # | |
1287 | # _------=> CPU# | |
1288 | # / _-----=> irqs-off | |
1289 | # | / _----=> need-resched | |
1290 | # || / _---=> hardirq/softirq | |
1291 | # ||| / _--=> preempt-depth | |
1292 | # |||| / delay | |
1293 | # cmd pid ||||| time | caller | |
1294 | # \ / ||||| \ | / | |
1295 | <idle>-0 0d.s2 0us+: _raw_spin_lock_irq <-run_timer_softirq | |
1296 | <idle>-0 0dNs3 17us : _raw_spin_unlock_irq <-run_timer_softirq | |
1297 | <idle>-0 0dNs3 17us+: trace_hardirqs_on <-run_timer_softirq | |
1298 | <idle>-0 0dNs3 25us : <stack trace> | |
1299 | => _raw_spin_unlock_irq | |
1300 | => run_timer_softirq | |
1301 | => __do_softirq | |
1302 | => call_softirq | |
1303 | => do_softirq | |
1304 | => irq_exit | |
1305 | => smp_apic_timer_interrupt | |
1306 | => apic_timer_interrupt | |
1307 | => rcu_idle_exit | |
1308 | => cpu_idle | |
1309 | => rest_init | |
1310 | => start_kernel | |
1311 | => x86_64_start_reservations | |
1312 | => x86_64_start_kernel | |
1313 | ||
1314 | Here we see that that we had a latency of 16 microseconds (which is | |
1315 | very good). The _raw_spin_lock_irq in run_timer_softirq disabled | |
1316 | interrupts. The difference between the 16 and the displayed | |
1317 | timestamp 25us occurred because the clock was incremented | |
1318 | between the time of recording the max latency and the time of | |
1319 | recording the function that had that latency. | |
1320 | ||
1321 | Note the above example had function-trace not set. If we set | |
1322 | function-trace, we get a much larger output:: | |
1323 | ||
1324 | with echo 1 > options/function-trace | |
1325 | ||
1326 | # tracer: irqsoff | |
1327 | # | |
1328 | # irqsoff latency trace v1.1.5 on 3.8.0-test+ | |
1329 | # -------------------------------------------------------------------- | |
1330 | # latency: 71 us, #168/168, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1331 | # ----------------- | |
1332 | # | task: bash-2042 (uid:0 nice:0 policy:0 rt_prio:0) | |
1333 | # ----------------- | |
1334 | # => started at: ata_scsi_queuecmd | |
1335 | # => ended at: ata_scsi_queuecmd | |
1336 | # | |
1337 | # | |
1338 | # _------=> CPU# | |
1339 | # / _-----=> irqs-off | |
1340 | # | / _----=> need-resched | |
1341 | # || / _---=> hardirq/softirq | |
1342 | # ||| / _--=> preempt-depth | |
1343 | # |||| / delay | |
1344 | # cmd pid ||||| time | caller | |
1345 | # \ / ||||| \ | / | |
1346 | bash-2042 3d... 0us : _raw_spin_lock_irqsave <-ata_scsi_queuecmd | |
1347 | bash-2042 3d... 0us : add_preempt_count <-_raw_spin_lock_irqsave | |
1348 | bash-2042 3d..1 1us : ata_scsi_find_dev <-ata_scsi_queuecmd | |
1349 | bash-2042 3d..1 1us : __ata_scsi_find_dev <-ata_scsi_find_dev | |
1350 | bash-2042 3d..1 2us : ata_find_dev.part.14 <-__ata_scsi_find_dev | |
1351 | bash-2042 3d..1 2us : ata_qc_new_init <-__ata_scsi_queuecmd | |
1352 | bash-2042 3d..1 3us : ata_sg_init <-__ata_scsi_queuecmd | |
1353 | bash-2042 3d..1 4us : ata_scsi_rw_xlat <-__ata_scsi_queuecmd | |
1354 | bash-2042 3d..1 4us : ata_build_rw_tf <-ata_scsi_rw_xlat | |
1355 | [...] | |
1356 | bash-2042 3d..1 67us : delay_tsc <-__delay | |
1357 | bash-2042 3d..1 67us : add_preempt_count <-delay_tsc | |
1358 | bash-2042 3d..2 67us : sub_preempt_count <-delay_tsc | |
1359 | bash-2042 3d..1 67us : add_preempt_count <-delay_tsc | |
1360 | bash-2042 3d..2 68us : sub_preempt_count <-delay_tsc | |
1361 | bash-2042 3d..1 68us+: ata_bmdma_start <-ata_bmdma_qc_issue | |
1362 | bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd | |
1363 | bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd | |
1364 | bash-2042 3d..1 72us+: trace_hardirqs_on <-ata_scsi_queuecmd | |
1365 | bash-2042 3d..1 120us : <stack trace> | |
1366 | => _raw_spin_unlock_irqrestore | |
1367 | => ata_scsi_queuecmd | |
1368 | => scsi_dispatch_cmd | |
1369 | => scsi_request_fn | |
1370 | => __blk_run_queue_uncond | |
1371 | => __blk_run_queue | |
1372 | => blk_queue_bio | |
1373 | => generic_make_request | |
1374 | => submit_bio | |
1375 | => submit_bh | |
1376 | => __ext3_get_inode_loc | |
1377 | => ext3_iget | |
1378 | => ext3_lookup | |
1379 | => lookup_real | |
1380 | => __lookup_hash | |
1381 | => walk_component | |
1382 | => lookup_last | |
1383 | => path_lookupat | |
1384 | => filename_lookup | |
1385 | => user_path_at_empty | |
1386 | => user_path_at | |
1387 | => vfs_fstatat | |
1388 | => vfs_stat | |
1389 | => sys_newstat | |
1390 | => system_call_fastpath | |
1391 | ||
1392 | ||
1393 | Here we traced a 71 microsecond latency. But we also see all the | |
1394 | functions that were called during that time. Note that by | |
1395 | enabling function tracing, we incur an added overhead. This | |
1396 | overhead may extend the latency times. But nevertheless, this | |
1397 | trace has provided some very helpful debugging information. | |
1398 | ||
88d380eb CD |
1399 | If we prefer function graph output instead of function, we can set |
1400 | display-graph option:: | |
1401 | with echo 1 > options/display-graph | |
1402 | ||
1403 | # tracer: irqsoff | |
1404 | # | |
1405 | # irqsoff latency trace v1.1.5 on 4.20.0-rc6+ | |
1406 | # -------------------------------------------------------------------- | |
1407 | # latency: 3751 us, #274/274, CPU#0 | (M:desktop VP:0, KP:0, SP:0 HP:0 #P:4) | |
1408 | # ----------------- | |
1409 | # | task: bash-1507 (uid:0 nice:0 policy:0 rt_prio:0) | |
1410 | # ----------------- | |
1411 | # => started at: free_debug_processing | |
1412 | # => ended at: return_to_handler | |
1413 | # | |
1414 | # | |
1415 | # _-----=> irqs-off | |
1416 | # / _----=> need-resched | |
1417 | # | / _---=> hardirq/softirq | |
1418 | # || / _--=> preempt-depth | |
1419 | # ||| / | |
1420 | # REL TIME CPU TASK/PID |||| DURATION FUNCTION CALLS | |
1421 | # | | | | |||| | | | | | | | |
1422 | 0 us | 0) bash-1507 | d... | 0.000 us | _raw_spin_lock_irqsave(); | |
1423 | 0 us | 0) bash-1507 | d..1 | 0.378 us | do_raw_spin_trylock(); | |
1424 | 1 us | 0) bash-1507 | d..2 | | set_track() { | |
1425 | 2 us | 0) bash-1507 | d..2 | | save_stack_trace() { | |
1426 | 2 us | 0) bash-1507 | d..2 | | __save_stack_trace() { | |
1427 | 3 us | 0) bash-1507 | d..2 | | __unwind_start() { | |
1428 | 3 us | 0) bash-1507 | d..2 | | get_stack_info() { | |
1429 | 3 us | 0) bash-1507 | d..2 | 0.351 us | in_task_stack(); | |
1430 | 4 us | 0) bash-1507 | d..2 | 1.107 us | } | |
1431 | [...] | |
1432 | 3750 us | 0) bash-1507 | d..1 | 0.516 us | do_raw_spin_unlock(); | |
1433 | 3750 us | 0) bash-1507 | d..1 | 0.000 us | _raw_spin_unlock_irqrestore(); | |
1434 | 3764 us | 0) bash-1507 | d..1 | 0.000 us | tracer_hardirqs_on(); | |
1435 | bash-1507 0d..1 3792us : <stack trace> | |
1436 | => free_debug_processing | |
1437 | => __slab_free | |
1438 | => kmem_cache_free | |
1439 | => vm_area_free | |
1440 | => remove_vma | |
1441 | => exit_mmap | |
1442 | => mmput | |
1443 | => flush_old_exec | |
1444 | => load_elf_binary | |
1445 | => search_binary_handler | |
1446 | => __do_execve_file.isra.32 | |
1447 | => __x64_sys_execve | |
1448 | => do_syscall_64 | |
1449 | => entry_SYSCALL_64_after_hwframe | |
1f198e22 CD |
1450 | |
1451 | preemptoff | |
1452 | ---------- | |
1453 | ||
1454 | When preemption is disabled, we may be able to receive | |
1455 | interrupts but the task cannot be preempted and a higher | |
1456 | priority task must wait for preemption to be enabled again | |
1457 | before it can preempt a lower priority task. | |
1458 | ||
1459 | The preemptoff tracer traces the places that disable preemption. | |
1460 | Like the irqsoff tracer, it records the maximum latency for | |
1461 | which preemption was disabled. The control of preemptoff tracer | |
1462 | is much like the irqsoff tracer. | |
1463 | :: | |
1464 | ||
1465 | # echo 0 > options/function-trace | |
1466 | # echo preemptoff > current_tracer | |
1467 | # echo 1 > tracing_on | |
1468 | # echo 0 > tracing_max_latency | |
1469 | # ls -ltr | |
1470 | [...] | |
1471 | # echo 0 > tracing_on | |
1472 | # cat trace | |
1473 | # tracer: preemptoff | |
1474 | # | |
1475 | # preemptoff latency trace v1.1.5 on 3.8.0-test+ | |
1476 | # -------------------------------------------------------------------- | |
1477 | # latency: 46 us, #4/4, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1478 | # ----------------- | |
1479 | # | task: sshd-1991 (uid:0 nice:0 policy:0 rt_prio:0) | |
1480 | # ----------------- | |
1481 | # => started at: do_IRQ | |
1482 | # => ended at: do_IRQ | |
1483 | # | |
1484 | # | |
1485 | # _------=> CPU# | |
1486 | # / _-----=> irqs-off | |
1487 | # | / _----=> need-resched | |
1488 | # || / _---=> hardirq/softirq | |
1489 | # ||| / _--=> preempt-depth | |
1490 | # |||| / delay | |
1491 | # cmd pid ||||| time | caller | |
1492 | # \ / ||||| \ | / | |
1493 | sshd-1991 1d.h. 0us+: irq_enter <-do_IRQ | |
1494 | sshd-1991 1d..1 46us : irq_exit <-do_IRQ | |
1495 | sshd-1991 1d..1 47us+: trace_preempt_on <-do_IRQ | |
1496 | sshd-1991 1d..1 52us : <stack trace> | |
1497 | => sub_preempt_count | |
1498 | => irq_exit | |
1499 | => do_IRQ | |
1500 | => ret_from_intr | |
1501 | ||
1502 | ||
1503 | This has some more changes. Preemption was disabled when an | |
1504 | interrupt came in (notice the 'h'), and was enabled on exit. | |
1505 | But we also see that interrupts have been disabled when entering | |
1506 | the preempt off section and leaving it (the 'd'). We do not know if | |
1507 | interrupts were enabled in the mean time or shortly after this | |
1508 | was over. | |
1509 | :: | |
1510 | ||
1511 | # tracer: preemptoff | |
1512 | # | |
1513 | # preemptoff latency trace v1.1.5 on 3.8.0-test+ | |
1514 | # -------------------------------------------------------------------- | |
1515 | # latency: 83 us, #241/241, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1516 | # ----------------- | |
1517 | # | task: bash-1994 (uid:0 nice:0 policy:0 rt_prio:0) | |
1518 | # ----------------- | |
1519 | # => started at: wake_up_new_task | |
1520 | # => ended at: task_rq_unlock | |
1521 | # | |
1522 | # | |
1523 | # _------=> CPU# | |
1524 | # / _-----=> irqs-off | |
1525 | # | / _----=> need-resched | |
1526 | # || / _---=> hardirq/softirq | |
1527 | # ||| / _--=> preempt-depth | |
1528 | # |||| / delay | |
1529 | # cmd pid ||||| time | caller | |
1530 | # \ / ||||| \ | / | |
1531 | bash-1994 1d..1 0us : _raw_spin_lock_irqsave <-wake_up_new_task | |
1532 | bash-1994 1d..1 0us : select_task_rq_fair <-select_task_rq | |
1533 | bash-1994 1d..1 1us : __rcu_read_lock <-select_task_rq_fair | |
1534 | bash-1994 1d..1 1us : source_load <-select_task_rq_fair | |
1535 | bash-1994 1d..1 1us : source_load <-select_task_rq_fair | |
1536 | [...] | |
1537 | bash-1994 1d..1 12us : irq_enter <-smp_apic_timer_interrupt | |
1538 | bash-1994 1d..1 12us : rcu_irq_enter <-irq_enter | |
1539 | bash-1994 1d..1 13us : add_preempt_count <-irq_enter | |
1540 | bash-1994 1d.h1 13us : exit_idle <-smp_apic_timer_interrupt | |
1541 | bash-1994 1d.h1 13us : hrtimer_interrupt <-smp_apic_timer_interrupt | |
1542 | bash-1994 1d.h1 13us : _raw_spin_lock <-hrtimer_interrupt | |
1543 | bash-1994 1d.h1 14us : add_preempt_count <-_raw_spin_lock | |
1544 | bash-1994 1d.h2 14us : ktime_get_update_offsets <-hrtimer_interrupt | |
1545 | [...] | |
1546 | bash-1994 1d.h1 35us : lapic_next_event <-clockevents_program_event | |
1547 | bash-1994 1d.h1 35us : irq_exit <-smp_apic_timer_interrupt | |
1548 | bash-1994 1d.h1 36us : sub_preempt_count <-irq_exit | |
1549 | bash-1994 1d..2 36us : do_softirq <-irq_exit | |
1550 | bash-1994 1d..2 36us : __do_softirq <-call_softirq | |
1551 | bash-1994 1d..2 36us : __local_bh_disable <-__do_softirq | |
1552 | bash-1994 1d.s2 37us : add_preempt_count <-_raw_spin_lock_irq | |
1553 | bash-1994 1d.s3 38us : _raw_spin_unlock <-run_timer_softirq | |
1554 | bash-1994 1d.s3 39us : sub_preempt_count <-_raw_spin_unlock | |
1555 | bash-1994 1d.s2 39us : call_timer_fn <-run_timer_softirq | |
1556 | [...] | |
1557 | bash-1994 1dNs2 81us : cpu_needs_another_gp <-rcu_process_callbacks | |
1558 | bash-1994 1dNs2 82us : __local_bh_enable <-__do_softirq | |
1559 | bash-1994 1dNs2 82us : sub_preempt_count <-__local_bh_enable | |
1560 | bash-1994 1dN.2 82us : idle_cpu <-irq_exit | |
1561 | bash-1994 1dN.2 83us : rcu_irq_exit <-irq_exit | |
1562 | bash-1994 1dN.2 83us : sub_preempt_count <-irq_exit | |
1563 | bash-1994 1.N.1 84us : _raw_spin_unlock_irqrestore <-task_rq_unlock | |
1564 | bash-1994 1.N.1 84us+: trace_preempt_on <-task_rq_unlock | |
1565 | bash-1994 1.N.1 104us : <stack trace> | |
1566 | => sub_preempt_count | |
1567 | => _raw_spin_unlock_irqrestore | |
1568 | => task_rq_unlock | |
1569 | => wake_up_new_task | |
1570 | => do_fork | |
1571 | => sys_clone | |
1572 | => stub_clone | |
1573 | ||
1574 | ||
1575 | The above is an example of the preemptoff trace with | |
1576 | function-trace set. Here we see that interrupts were not disabled | |
1577 | the entire time. The irq_enter code lets us know that we entered | |
1578 | an interrupt 'h'. Before that, the functions being traced still | |
1579 | show that it is not in an interrupt, but we can see from the | |
1580 | functions themselves that this is not the case. | |
1581 | ||
1582 | preemptirqsoff | |
1583 | -------------- | |
1584 | ||
1585 | Knowing the locations that have interrupts disabled or | |
1586 | preemption disabled for the longest times is helpful. But | |
1587 | sometimes we would like to know when either preemption and/or | |
1588 | interrupts are disabled. | |
1589 | ||
1590 | Consider the following code:: | |
1591 | ||
1592 | local_irq_disable(); | |
1593 | call_function_with_irqs_off(); | |
1594 | preempt_disable(); | |
1595 | call_function_with_irqs_and_preemption_off(); | |
1596 | local_irq_enable(); | |
1597 | call_function_with_preemption_off(); | |
1598 | preempt_enable(); | |
1599 | ||
1600 | The irqsoff tracer will record the total length of | |
1601 | call_function_with_irqs_off() and | |
1602 | call_function_with_irqs_and_preemption_off(). | |
1603 | ||
1604 | The preemptoff tracer will record the total length of | |
1605 | call_function_with_irqs_and_preemption_off() and | |
1606 | call_function_with_preemption_off(). | |
1607 | ||
1608 | But neither will trace the time that interrupts and/or | |
1609 | preemption is disabled. This total time is the time that we can | |
1610 | not schedule. To record this time, use the preemptirqsoff | |
1611 | tracer. | |
1612 | ||
1613 | Again, using this trace is much like the irqsoff and preemptoff | |
1614 | tracers. | |
1615 | :: | |
1616 | ||
1617 | # echo 0 > options/function-trace | |
1618 | # echo preemptirqsoff > current_tracer | |
1619 | # echo 1 > tracing_on | |
1620 | # echo 0 > tracing_max_latency | |
1621 | # ls -ltr | |
1622 | [...] | |
1623 | # echo 0 > tracing_on | |
1624 | # cat trace | |
1625 | # tracer: preemptirqsoff | |
1626 | # | |
1627 | # preemptirqsoff latency trace v1.1.5 on 3.8.0-test+ | |
1628 | # -------------------------------------------------------------------- | |
1629 | # latency: 100 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1630 | # ----------------- | |
1631 | # | task: ls-2230 (uid:0 nice:0 policy:0 rt_prio:0) | |
1632 | # ----------------- | |
1633 | # => started at: ata_scsi_queuecmd | |
1634 | # => ended at: ata_scsi_queuecmd | |
1635 | # | |
1636 | # | |
1637 | # _------=> CPU# | |
1638 | # / _-----=> irqs-off | |
1639 | # | / _----=> need-resched | |
1640 | # || / _---=> hardirq/softirq | |
1641 | # ||| / _--=> preempt-depth | |
1642 | # |||| / delay | |
1643 | # cmd pid ||||| time | caller | |
1644 | # \ / ||||| \ | / | |
1645 | ls-2230 3d... 0us+: _raw_spin_lock_irqsave <-ata_scsi_queuecmd | |
1646 | ls-2230 3...1 100us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd | |
1647 | ls-2230 3...1 101us+: trace_preempt_on <-ata_scsi_queuecmd | |
1648 | ls-2230 3...1 111us : <stack trace> | |
1649 | => sub_preempt_count | |
1650 | => _raw_spin_unlock_irqrestore | |
1651 | => ata_scsi_queuecmd | |
1652 | => scsi_dispatch_cmd | |
1653 | => scsi_request_fn | |
1654 | => __blk_run_queue_uncond | |
1655 | => __blk_run_queue | |
1656 | => blk_queue_bio | |
1657 | => generic_make_request | |
1658 | => submit_bio | |
1659 | => submit_bh | |
1660 | => ext3_bread | |
1661 | => ext3_dir_bread | |
1662 | => htree_dirblock_to_tree | |
1663 | => ext3_htree_fill_tree | |
1664 | => ext3_readdir | |
1665 | => vfs_readdir | |
1666 | => sys_getdents | |
1667 | => system_call_fastpath | |
1668 | ||
1669 | ||
1670 | The trace_hardirqs_off_thunk is called from assembly on x86 when | |
1671 | interrupts are disabled in the assembly code. Without the | |
1672 | function tracing, we do not know if interrupts were enabled | |
1673 | within the preemption points. We do see that it started with | |
1674 | preemption enabled. | |
1675 | ||
1676 | Here is a trace with function-trace set:: | |
1677 | ||
1678 | # tracer: preemptirqsoff | |
1679 | # | |
1680 | # preemptirqsoff latency trace v1.1.5 on 3.8.0-test+ | |
1681 | # -------------------------------------------------------------------- | |
1682 | # latency: 161 us, #339/339, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1683 | # ----------------- | |
1684 | # | task: ls-2269 (uid:0 nice:0 policy:0 rt_prio:0) | |
1685 | # ----------------- | |
1686 | # => started at: schedule | |
1687 | # => ended at: mutex_unlock | |
1688 | # | |
1689 | # | |
1690 | # _------=> CPU# | |
1691 | # / _-----=> irqs-off | |
1692 | # | / _----=> need-resched | |
1693 | # || / _---=> hardirq/softirq | |
1694 | # ||| / _--=> preempt-depth | |
1695 | # |||| / delay | |
1696 | # cmd pid ||||| time | caller | |
1697 | # \ / ||||| \ | / | |
1698 | kworker/-59 3...1 0us : __schedule <-schedule | |
1699 | kworker/-59 3d..1 0us : rcu_preempt_qs <-rcu_note_context_switch | |
1700 | kworker/-59 3d..1 1us : add_preempt_count <-_raw_spin_lock_irq | |
1701 | kworker/-59 3d..2 1us : deactivate_task <-__schedule | |
1702 | kworker/-59 3d..2 1us : dequeue_task <-deactivate_task | |
1703 | kworker/-59 3d..2 2us : update_rq_clock <-dequeue_task | |
1704 | kworker/-59 3d..2 2us : dequeue_task_fair <-dequeue_task | |
1705 | kworker/-59 3d..2 2us : update_curr <-dequeue_task_fair | |
1706 | kworker/-59 3d..2 2us : update_min_vruntime <-update_curr | |
1707 | kworker/-59 3d..2 3us : cpuacct_charge <-update_curr | |
1708 | kworker/-59 3d..2 3us : __rcu_read_lock <-cpuacct_charge | |
1709 | kworker/-59 3d..2 3us : __rcu_read_unlock <-cpuacct_charge | |
1710 | kworker/-59 3d..2 3us : update_cfs_rq_blocked_load <-dequeue_task_fair | |
1711 | kworker/-59 3d..2 4us : clear_buddies <-dequeue_task_fair | |
1712 | kworker/-59 3d..2 4us : account_entity_dequeue <-dequeue_task_fair | |
1713 | kworker/-59 3d..2 4us : update_min_vruntime <-dequeue_task_fair | |
1714 | kworker/-59 3d..2 4us : update_cfs_shares <-dequeue_task_fair | |
1715 | kworker/-59 3d..2 5us : hrtick_update <-dequeue_task_fair | |
1716 | kworker/-59 3d..2 5us : wq_worker_sleeping <-__schedule | |
1717 | kworker/-59 3d..2 5us : kthread_data <-wq_worker_sleeping | |
1718 | kworker/-59 3d..2 5us : put_prev_task_fair <-__schedule | |
1719 | kworker/-59 3d..2 6us : pick_next_task_fair <-pick_next_task | |
1720 | kworker/-59 3d..2 6us : clear_buddies <-pick_next_task_fair | |
1721 | kworker/-59 3d..2 6us : set_next_entity <-pick_next_task_fair | |
1722 | kworker/-59 3d..2 6us : update_stats_wait_end <-set_next_entity | |
1723 | ls-2269 3d..2 7us : finish_task_switch <-__schedule | |
1724 | ls-2269 3d..2 7us : _raw_spin_unlock_irq <-finish_task_switch | |
1725 | ls-2269 3d..2 8us : do_IRQ <-ret_from_intr | |
1726 | ls-2269 3d..2 8us : irq_enter <-do_IRQ | |
1727 | ls-2269 3d..2 8us : rcu_irq_enter <-irq_enter | |
1728 | ls-2269 3d..2 9us : add_preempt_count <-irq_enter | |
1729 | ls-2269 3d.h2 9us : exit_idle <-do_IRQ | |
1730 | [...] | |
1731 | ls-2269 3d.h3 20us : sub_preempt_count <-_raw_spin_unlock | |
1732 | ls-2269 3d.h2 20us : irq_exit <-do_IRQ | |
1733 | ls-2269 3d.h2 21us : sub_preempt_count <-irq_exit | |
1734 | ls-2269 3d..3 21us : do_softirq <-irq_exit | |
1735 | ls-2269 3d..3 21us : __do_softirq <-call_softirq | |
1736 | ls-2269 3d..3 21us+: __local_bh_disable <-__do_softirq | |
1737 | ls-2269 3d.s4 29us : sub_preempt_count <-_local_bh_enable_ip | |
1738 | ls-2269 3d.s5 29us : sub_preempt_count <-_local_bh_enable_ip | |
1739 | ls-2269 3d.s5 31us : do_IRQ <-ret_from_intr | |
1740 | ls-2269 3d.s5 31us : irq_enter <-do_IRQ | |
1741 | ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter | |
1742 | [...] | |
1743 | ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter | |
1744 | ls-2269 3d.s5 32us : add_preempt_count <-irq_enter | |
1745 | ls-2269 3d.H5 32us : exit_idle <-do_IRQ | |
1746 | ls-2269 3d.H5 32us : handle_irq <-do_IRQ | |
1747 | ls-2269 3d.H5 32us : irq_to_desc <-handle_irq | |
1748 | ls-2269 3d.H5 33us : handle_fasteoi_irq <-handle_irq | |
1749 | [...] | |
1750 | ls-2269 3d.s5 158us : _raw_spin_unlock_irqrestore <-rtl8139_poll | |
1751 | ls-2269 3d.s3 158us : net_rps_action_and_irq_enable.isra.65 <-net_rx_action | |
1752 | ls-2269 3d.s3 159us : __local_bh_enable <-__do_softirq | |
1753 | ls-2269 3d.s3 159us : sub_preempt_count <-__local_bh_enable | |
1754 | ls-2269 3d..3 159us : idle_cpu <-irq_exit | |
1755 | ls-2269 3d..3 159us : rcu_irq_exit <-irq_exit | |
1756 | ls-2269 3d..3 160us : sub_preempt_count <-irq_exit | |
1757 | ls-2269 3d... 161us : __mutex_unlock_slowpath <-mutex_unlock | |
1758 | ls-2269 3d... 162us+: trace_hardirqs_on <-mutex_unlock | |
1759 | ls-2269 3d... 186us : <stack trace> | |
1760 | => __mutex_unlock_slowpath | |
1761 | => mutex_unlock | |
1762 | => process_output | |
1763 | => n_tty_write | |
1764 | => tty_write | |
1765 | => vfs_write | |
1766 | => sys_write | |
1767 | => system_call_fastpath | |
1768 | ||
1769 | This is an interesting trace. It started with kworker running and | |
1770 | scheduling out and ls taking over. But as soon as ls released the | |
1771 | rq lock and enabled interrupts (but not preemption) an interrupt | |
1772 | triggered. When the interrupt finished, it started running softirqs. | |
1773 | But while the softirq was running, another interrupt triggered. | |
1774 | When an interrupt is running inside a softirq, the annotation is 'H'. | |
1775 | ||
1776 | ||
1777 | wakeup | |
1778 | ------ | |
1779 | ||
1780 | One common case that people are interested in tracing is the | |
1781 | time it takes for a task that is woken to actually wake up. | |
1782 | Now for non Real-Time tasks, this can be arbitrary. But tracing | |
1783 | it none the less can be interesting. | |
1784 | ||
1785 | Without function tracing:: | |
1786 | ||
1787 | # echo 0 > options/function-trace | |
1788 | # echo wakeup > current_tracer | |
1789 | # echo 1 > tracing_on | |
1790 | # echo 0 > tracing_max_latency | |
1791 | # chrt -f 5 sleep 1 | |
1792 | # echo 0 > tracing_on | |
1793 | # cat trace | |
1794 | # tracer: wakeup | |
1795 | # | |
1796 | # wakeup latency trace v1.1.5 on 3.8.0-test+ | |
1797 | # -------------------------------------------------------------------- | |
1798 | # latency: 15 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1799 | # ----------------- | |
1800 | # | task: kworker/3:1H-312 (uid:0 nice:-20 policy:0 rt_prio:0) | |
1801 | # ----------------- | |
1802 | # | |
1803 | # _------=> CPU# | |
1804 | # / _-----=> irqs-off | |
1805 | # | / _----=> need-resched | |
1806 | # || / _---=> hardirq/softirq | |
1807 | # ||| / _--=> preempt-depth | |
1808 | # |||| / delay | |
1809 | # cmd pid ||||| time | caller | |
1810 | # \ / ||||| \ | / | |
1811 | <idle>-0 3dNs7 0us : 0:120:R + [003] 312:100:R kworker/3:1H | |
1812 | <idle>-0 3dNs7 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up | |
1813 | <idle>-0 3d..3 15us : __schedule <-schedule | |
1814 | <idle>-0 3d..3 15us : 0:120:R ==> [003] 312:100:R kworker/3:1H | |
1815 | ||
1816 | The tracer only traces the highest priority task in the system | |
1817 | to avoid tracing the normal circumstances. Here we see that | |
1818 | the kworker with a nice priority of -20 (not very nice), took | |
1819 | just 15 microseconds from the time it woke up, to the time it | |
1820 | ran. | |
1821 | ||
1822 | Non Real-Time tasks are not that interesting. A more interesting | |
1823 | trace is to concentrate only on Real-Time tasks. | |
1824 | ||
1825 | wakeup_rt | |
1826 | --------- | |
1827 | ||
1828 | In a Real-Time environment it is very important to know the | |
1829 | wakeup time it takes for the highest priority task that is woken | |
1830 | up to the time that it executes. This is also known as "schedule | |
1831 | latency". I stress the point that this is about RT tasks. It is | |
1832 | also important to know the scheduling latency of non-RT tasks, | |
1833 | but the average schedule latency is better for non-RT tasks. | |
1834 | Tools like LatencyTop are more appropriate for such | |
1835 | measurements. | |
1836 | ||
1837 | Real-Time environments are interested in the worst case latency. | |
1838 | That is the longest latency it takes for something to happen, | |
1839 | and not the average. We can have a very fast scheduler that may | |
1840 | only have a large latency once in a while, but that would not | |
1841 | work well with Real-Time tasks. The wakeup_rt tracer was designed | |
1842 | to record the worst case wakeups of RT tasks. Non-RT tasks are | |
1843 | not recorded because the tracer only records one worst case and | |
1844 | tracing non-RT tasks that are unpredictable will overwrite the | |
1845 | worst case latency of RT tasks (just run the normal wakeup | |
1846 | tracer for a while to see that effect). | |
1847 | ||
1848 | Since this tracer only deals with RT tasks, we will run this | |
1849 | slightly differently than we did with the previous tracers. | |
1850 | Instead of performing an 'ls', we will run 'sleep 1' under | |
1851 | 'chrt' which changes the priority of the task. | |
1852 | :: | |
1853 | ||
1854 | # echo 0 > options/function-trace | |
1855 | # echo wakeup_rt > current_tracer | |
1856 | # echo 1 > tracing_on | |
1857 | # echo 0 > tracing_max_latency | |
1858 | # chrt -f 5 sleep 1 | |
1859 | # echo 0 > tracing_on | |
1860 | # cat trace | |
1861 | # tracer: wakeup | |
1862 | # | |
1863 | # tracer: wakeup_rt | |
1864 | # | |
1865 | # wakeup_rt latency trace v1.1.5 on 3.8.0-test+ | |
1866 | # -------------------------------------------------------------------- | |
1867 | # latency: 5 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1868 | # ----------------- | |
1869 | # | task: sleep-2389 (uid:0 nice:0 policy:1 rt_prio:5) | |
1870 | # ----------------- | |
1871 | # | |
1872 | # _------=> CPU# | |
1873 | # / _-----=> irqs-off | |
1874 | # | / _----=> need-resched | |
1875 | # || / _---=> hardirq/softirq | |
1876 | # ||| / _--=> preempt-depth | |
1877 | # |||| / delay | |
1878 | # cmd pid ||||| time | caller | |
1879 | # \ / ||||| \ | / | |
1880 | <idle>-0 3d.h4 0us : 0:120:R + [003] 2389: 94:R sleep | |
1881 | <idle>-0 3d.h4 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up | |
1882 | <idle>-0 3d..3 5us : __schedule <-schedule | |
1883 | <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep | |
1884 | ||
1885 | ||
1886 | Running this on an idle system, we see that it only took 5 microseconds | |
1887 | to perform the task switch. Note, since the trace point in the schedule | |
1888 | is before the actual "switch", we stop the tracing when the recorded task | |
1889 | is about to schedule in. This may change if we add a new marker at the | |
1890 | end of the scheduler. | |
1891 | ||
1892 | Notice that the recorded task is 'sleep' with the PID of 2389 | |
1893 | and it has an rt_prio of 5. This priority is user-space priority | |
1894 | and not the internal kernel priority. The policy is 1 for | |
1895 | SCHED_FIFO and 2 for SCHED_RR. | |
1896 | ||
1897 | Note, that the trace data shows the internal priority (99 - rtprio). | |
1898 | :: | |
1899 | ||
1900 | <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep | |
1901 | ||
1902 | The 0:120:R means idle was running with a nice priority of 0 (120 - 120) | |
1903 | and in the running state 'R'. The sleep task was scheduled in with | |
1904 | 2389: 94:R. That is the priority is the kernel rtprio (99 - 5 = 94) | |
1905 | and it too is in the running state. | |
1906 | ||
1907 | Doing the same with chrt -r 5 and function-trace set. | |
1908 | :: | |
1909 | ||
1910 | echo 1 > options/function-trace | |
1911 | ||
1912 | # tracer: wakeup_rt | |
1913 | # | |
1914 | # wakeup_rt latency trace v1.1.5 on 3.8.0-test+ | |
1915 | # -------------------------------------------------------------------- | |
1916 | # latency: 29 us, #85/85, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1917 | # ----------------- | |
1918 | # | task: sleep-2448 (uid:0 nice:0 policy:1 rt_prio:5) | |
1919 | # ----------------- | |
1920 | # | |
1921 | # _------=> CPU# | |
1922 | # / _-----=> irqs-off | |
1923 | # | / _----=> need-resched | |
1924 | # || / _---=> hardirq/softirq | |
1925 | # ||| / _--=> preempt-depth | |
1926 | # |||| / delay | |
1927 | # cmd pid ||||| time | caller | |
1928 | # \ / ||||| \ | / | |
1929 | <idle>-0 3d.h4 1us+: 0:120:R + [003] 2448: 94:R sleep | |
1930 | <idle>-0 3d.h4 2us : ttwu_do_activate.constprop.87 <-try_to_wake_up | |
1931 | <idle>-0 3d.h3 3us : check_preempt_curr <-ttwu_do_wakeup | |
1932 | <idle>-0 3d.h3 3us : resched_curr <-check_preempt_curr | |
1933 | <idle>-0 3dNh3 4us : task_woken_rt <-ttwu_do_wakeup | |
1934 | <idle>-0 3dNh3 4us : _raw_spin_unlock <-try_to_wake_up | |
1935 | <idle>-0 3dNh3 4us : sub_preempt_count <-_raw_spin_unlock | |
1936 | <idle>-0 3dNh2 5us : ttwu_stat <-try_to_wake_up | |
1937 | <idle>-0 3dNh2 5us : _raw_spin_unlock_irqrestore <-try_to_wake_up | |
1938 | <idle>-0 3dNh2 6us : sub_preempt_count <-_raw_spin_unlock_irqrestore | |
1939 | <idle>-0 3dNh1 6us : _raw_spin_lock <-__run_hrtimer | |
1940 | <idle>-0 3dNh1 6us : add_preempt_count <-_raw_spin_lock | |
1941 | <idle>-0 3dNh2 7us : _raw_spin_unlock <-hrtimer_interrupt | |
1942 | <idle>-0 3dNh2 7us : sub_preempt_count <-_raw_spin_unlock | |
1943 | <idle>-0 3dNh1 7us : tick_program_event <-hrtimer_interrupt | |
1944 | <idle>-0 3dNh1 7us : clockevents_program_event <-tick_program_event | |
1945 | <idle>-0 3dNh1 8us : ktime_get <-clockevents_program_event | |
1946 | <idle>-0 3dNh1 8us : lapic_next_event <-clockevents_program_event | |
1947 | <idle>-0 3dNh1 8us : irq_exit <-smp_apic_timer_interrupt | |
1948 | <idle>-0 3dNh1 9us : sub_preempt_count <-irq_exit | |
1949 | <idle>-0 3dN.2 9us : idle_cpu <-irq_exit | |
1950 | <idle>-0 3dN.2 9us : rcu_irq_exit <-irq_exit | |
1951 | <idle>-0 3dN.2 10us : rcu_eqs_enter_common.isra.45 <-rcu_irq_exit | |
1952 | <idle>-0 3dN.2 10us : sub_preempt_count <-irq_exit | |
1953 | <idle>-0 3.N.1 11us : rcu_idle_exit <-cpu_idle | |
1954 | <idle>-0 3dN.1 11us : rcu_eqs_exit_common.isra.43 <-rcu_idle_exit | |
1955 | <idle>-0 3.N.1 11us : tick_nohz_idle_exit <-cpu_idle | |
1956 | <idle>-0 3dN.1 12us : menu_hrtimer_cancel <-tick_nohz_idle_exit | |
1957 | <idle>-0 3dN.1 12us : ktime_get <-tick_nohz_idle_exit | |
1958 | <idle>-0 3dN.1 12us : tick_do_update_jiffies64 <-tick_nohz_idle_exit | |
1959 | <idle>-0 3dN.1 13us : cpu_load_update_nohz <-tick_nohz_idle_exit | |
1960 | <idle>-0 3dN.1 13us : _raw_spin_lock <-cpu_load_update_nohz | |
1961 | <idle>-0 3dN.1 13us : add_preempt_count <-_raw_spin_lock | |
1962 | <idle>-0 3dN.2 13us : __cpu_load_update <-cpu_load_update_nohz | |
1963 | <idle>-0 3dN.2 14us : sched_avg_update <-__cpu_load_update | |
1964 | <idle>-0 3dN.2 14us : _raw_spin_unlock <-cpu_load_update_nohz | |
1965 | <idle>-0 3dN.2 14us : sub_preempt_count <-_raw_spin_unlock | |
1966 | <idle>-0 3dN.1 15us : calc_load_nohz_stop <-tick_nohz_idle_exit | |
1967 | <idle>-0 3dN.1 15us : touch_softlockup_watchdog <-tick_nohz_idle_exit | |
1968 | <idle>-0 3dN.1 15us : hrtimer_cancel <-tick_nohz_idle_exit | |
1969 | <idle>-0 3dN.1 15us : hrtimer_try_to_cancel <-hrtimer_cancel | |
1970 | <idle>-0 3dN.1 16us : lock_hrtimer_base.isra.18 <-hrtimer_try_to_cancel | |
1971 | <idle>-0 3dN.1 16us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18 | |
1972 | <idle>-0 3dN.1 16us : add_preempt_count <-_raw_spin_lock_irqsave | |
1973 | <idle>-0 3dN.2 17us : __remove_hrtimer <-remove_hrtimer.part.16 | |
1974 | <idle>-0 3dN.2 17us : hrtimer_force_reprogram <-__remove_hrtimer | |
1975 | <idle>-0 3dN.2 17us : tick_program_event <-hrtimer_force_reprogram | |
1976 | <idle>-0 3dN.2 18us : clockevents_program_event <-tick_program_event | |
1977 | <idle>-0 3dN.2 18us : ktime_get <-clockevents_program_event | |
1978 | <idle>-0 3dN.2 18us : lapic_next_event <-clockevents_program_event | |
1979 | <idle>-0 3dN.2 19us : _raw_spin_unlock_irqrestore <-hrtimer_try_to_cancel | |
1980 | <idle>-0 3dN.2 19us : sub_preempt_count <-_raw_spin_unlock_irqrestore | |
1981 | <idle>-0 3dN.1 19us : hrtimer_forward <-tick_nohz_idle_exit | |
1982 | <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward | |
1983 | <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward | |
1984 | <idle>-0 3dN.1 20us : hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11 | |
1985 | <idle>-0 3dN.1 20us : __hrtimer_start_range_ns <-hrtimer_start_range_ns | |
1986 | <idle>-0 3dN.1 21us : lock_hrtimer_base.isra.18 <-__hrtimer_start_range_ns | |
1987 | <idle>-0 3dN.1 21us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18 | |
1988 | <idle>-0 3dN.1 21us : add_preempt_count <-_raw_spin_lock_irqsave | |
1989 | <idle>-0 3dN.2 22us : ktime_add_safe <-__hrtimer_start_range_ns | |
1990 | <idle>-0 3dN.2 22us : enqueue_hrtimer <-__hrtimer_start_range_ns | |
1991 | <idle>-0 3dN.2 22us : tick_program_event <-__hrtimer_start_range_ns | |
1992 | <idle>-0 3dN.2 23us : clockevents_program_event <-tick_program_event | |
1993 | <idle>-0 3dN.2 23us : ktime_get <-clockevents_program_event | |
1994 | <idle>-0 3dN.2 23us : lapic_next_event <-clockevents_program_event | |
1995 | <idle>-0 3dN.2 24us : _raw_spin_unlock_irqrestore <-__hrtimer_start_range_ns | |
1996 | <idle>-0 3dN.2 24us : sub_preempt_count <-_raw_spin_unlock_irqrestore | |
1997 | <idle>-0 3dN.1 24us : account_idle_ticks <-tick_nohz_idle_exit | |
1998 | <idle>-0 3dN.1 24us : account_idle_time <-account_idle_ticks | |
1999 | <idle>-0 3.N.1 25us : sub_preempt_count <-cpu_idle | |
2000 | <idle>-0 3.N.. 25us : schedule <-cpu_idle | |
2001 | <idle>-0 3.N.. 25us : __schedule <-preempt_schedule | |
2002 | <idle>-0 3.N.. 26us : add_preempt_count <-__schedule | |
2003 | <idle>-0 3.N.1 26us : rcu_note_context_switch <-__schedule | |
2004 | <idle>-0 3.N.1 26us : rcu_sched_qs <-rcu_note_context_switch | |
2005 | <idle>-0 3dN.1 27us : rcu_preempt_qs <-rcu_note_context_switch | |
2006 | <idle>-0 3.N.1 27us : _raw_spin_lock_irq <-__schedule | |
2007 | <idle>-0 3dN.1 27us : add_preempt_count <-_raw_spin_lock_irq | |
2008 | <idle>-0 3dN.2 28us : put_prev_task_idle <-__schedule | |
2009 | <idle>-0 3dN.2 28us : pick_next_task_stop <-pick_next_task | |
2010 | <idle>-0 3dN.2 28us : pick_next_task_rt <-pick_next_task | |
2011 | <idle>-0 3dN.2 29us : dequeue_pushable_task <-pick_next_task_rt | |
2012 | <idle>-0 3d..3 29us : __schedule <-preempt_schedule | |
2013 | <idle>-0 3d..3 30us : 0:120:R ==> [003] 2448: 94:R sleep | |
2014 | ||
2015 | This isn't that big of a trace, even with function tracing enabled, | |
2016 | so I included the entire trace. | |
2017 | ||
2018 | The interrupt went off while when the system was idle. Somewhere | |
2019 | before task_woken_rt() was called, the NEED_RESCHED flag was set, | |
2020 | this is indicated by the first occurrence of the 'N' flag. | |
2021 | ||
2022 | Latency tracing and events | |
2023 | -------------------------- | |
2024 | As function tracing can induce a much larger latency, but without | |
2025 | seeing what happens within the latency it is hard to know what | |
2026 | caused it. There is a middle ground, and that is with enabling | |
2027 | events. | |
2028 | :: | |
2029 | ||
2030 | # echo 0 > options/function-trace | |
2031 | # echo wakeup_rt > current_tracer | |
2032 | # echo 1 > events/enable | |
2033 | # echo 1 > tracing_on | |
2034 | # echo 0 > tracing_max_latency | |
2035 | # chrt -f 5 sleep 1 | |
2036 | # echo 0 > tracing_on | |
2037 | # cat trace | |
2038 | # tracer: wakeup_rt | |
2039 | # | |
2040 | # wakeup_rt latency trace v1.1.5 on 3.8.0-test+ | |
2041 | # -------------------------------------------------------------------- | |
2042 | # latency: 6 us, #12/12, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
2043 | # ----------------- | |
2044 | # | task: sleep-5882 (uid:0 nice:0 policy:1 rt_prio:5) | |
2045 | # ----------------- | |
2046 | # | |
2047 | # _------=> CPU# | |
2048 | # / _-----=> irqs-off | |
2049 | # | / _----=> need-resched | |
2050 | # || / _---=> hardirq/softirq | |
2051 | # ||| / _--=> preempt-depth | |
2052 | # |||| / delay | |
2053 | # cmd pid ||||| time | caller | |
2054 | # \ / ||||| \ | / | |
2055 | <idle>-0 2d.h4 0us : 0:120:R + [002] 5882: 94:R sleep | |
2056 | <idle>-0 2d.h4 0us : ttwu_do_activate.constprop.87 <-try_to_wake_up | |
2057 | <idle>-0 2d.h4 1us : sched_wakeup: comm=sleep pid=5882 prio=94 success=1 target_cpu=002 | |
2058 | <idle>-0 2dNh2 1us : hrtimer_expire_exit: hrtimer=ffff88007796feb8 | |
2059 | <idle>-0 2.N.2 2us : power_end: cpu_id=2 | |
2060 | <idle>-0 2.N.2 3us : cpu_idle: state=4294967295 cpu_id=2 | |
2061 | <idle>-0 2dN.3 4us : hrtimer_cancel: hrtimer=ffff88007d50d5e0 | |
2062 | <idle>-0 2dN.3 4us : hrtimer_start: hrtimer=ffff88007d50d5e0 function=tick_sched_timer expires=34311211000000 softexpires=34311211000000 | |
2063 | <idle>-0 2.N.2 5us : rcu_utilization: Start context switch | |
2064 | <idle>-0 2.N.2 5us : rcu_utilization: End context switch | |
2065 | <idle>-0 2d..3 6us : __schedule <-schedule | |
2066 | <idle>-0 2d..3 6us : 0:120:R ==> [002] 5882: 94:R sleep | |
2067 | ||
2068 | ||
2069 | Hardware Latency Detector | |
2070 | ------------------------- | |
2071 | ||
2072 | The hardware latency detector is executed by enabling the "hwlat" tracer. | |
2073 | ||
2074 | NOTE, this tracer will affect the performance of the system as it will | |
2075 | periodically make a CPU constantly busy with interrupts disabled. | |
2076 | :: | |
2077 | ||
2078 | # echo hwlat > current_tracer | |
2079 | # sleep 100 | |
2080 | # cat trace | |
2081 | # tracer: hwlat | |
2082 | # | |
2083 | # _-----=> irqs-off | |
2084 | # / _----=> need-resched | |
2085 | # | / _---=> hardirq/softirq | |
2086 | # || / _--=> preempt-depth | |
2087 | # ||| / delay | |
2088 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
2089 | # | | | |||| | | | |
2090 | <...>-3638 [001] d... 19452.055471: #1 inner/outer(us): 12/14 ts:1499801089.066141940 | |
2091 | <...>-3638 [003] d... 19454.071354: #2 inner/outer(us): 11/9 ts:1499801091.082164365 | |
2092 | <...>-3638 [002] dn.. 19461.126852: #3 inner/outer(us): 12/9 ts:1499801098.138150062 | |
2093 | <...>-3638 [001] d... 19488.340960: #4 inner/outer(us): 8/12 ts:1499801125.354139633 | |
2094 | <...>-3638 [003] d... 19494.388553: #5 inner/outer(us): 8/12 ts:1499801131.402150961 | |
2095 | <...>-3638 [003] d... 19501.283419: #6 inner/outer(us): 0/12 ts:1499801138.297435289 nmi-total:4 nmi-count:1 | |
2096 | ||
2097 | ||
2098 | The above output is somewhat the same in the header. All events will have | |
2099 | interrupts disabled 'd'. Under the FUNCTION title there is: | |
2100 | ||
2101 | #1 | |
2102 | This is the count of events recorded that were greater than the | |
2103 | tracing_threshold (See below). | |
2104 | ||
2105 | inner/outer(us): 12/14 | |
2106 | ||
2107 | This shows two numbers as "inner latency" and "outer latency". The test | |
2108 | runs in a loop checking a timestamp twice. The latency detected within | |
2109 | the two timestamps is the "inner latency" and the latency detected | |
2110 | after the previous timestamp and the next timestamp in the loop is | |
2111 | the "outer latency". | |
2112 | ||
2113 | ts:1499801089.066141940 | |
2114 | ||
2115 | The absolute timestamp that the event happened. | |
2116 | ||
2117 | nmi-total:4 nmi-count:1 | |
2118 | ||
2119 | On architectures that support it, if an NMI comes in during the | |
2120 | test, the time spent in NMI is reported in "nmi-total" (in | |
2121 | microseconds). | |
2122 | ||
2123 | All architectures that have NMIs will show the "nmi-count" if an | |
2124 | NMI comes in during the test. | |
2125 | ||
2126 | hwlat files: | |
2127 | ||
2128 | tracing_threshold | |
2129 | This gets automatically set to "10" to represent 10 | |
2130 | microseconds. This is the threshold of latency that | |
2131 | needs to be detected before the trace will be recorded. | |
2132 | ||
2133 | Note, when hwlat tracer is finished (another tracer is | |
2134 | written into "current_tracer"), the original value for | |
2135 | tracing_threshold is placed back into this file. | |
2136 | ||
2137 | hwlat_detector/width | |
2138 | The length of time the test runs with interrupts disabled. | |
2139 | ||
2140 | hwlat_detector/window | |
2141 | The length of time of the window which the test | |
2142 | runs. That is, the test will run for "width" | |
2143 | microseconds per "window" microseconds | |
2144 | ||
2145 | tracing_cpumask | |
2146 | When the test is started. A kernel thread is created that | |
2147 | runs the test. This thread will alternate between CPUs | |
2148 | listed in the tracing_cpumask between each period | |
2149 | (one "window"). To limit the test to specific CPUs | |
2150 | set the mask in this file to only the CPUs that the test | |
2151 | should run on. | |
2152 | ||
2153 | function | |
2154 | -------- | |
2155 | ||
2156 | This tracer is the function tracer. Enabling the function tracer | |
2157 | can be done from the debug file system. Make sure the | |
2158 | ftrace_enabled is set; otherwise this tracer is a nop. | |
2159 | See the "ftrace_enabled" section below. | |
2160 | :: | |
2161 | ||
2162 | # sysctl kernel.ftrace_enabled=1 | |
2163 | # echo function > current_tracer | |
2164 | # echo 1 > tracing_on | |
2165 | # usleep 1 | |
2166 | # echo 0 > tracing_on | |
2167 | # cat trace | |
2168 | # tracer: function | |
2169 | # | |
2170 | # entries-in-buffer/entries-written: 24799/24799 #P:4 | |
2171 | # | |
2172 | # _-----=> irqs-off | |
2173 | # / _----=> need-resched | |
2174 | # | / _---=> hardirq/softirq | |
2175 | # || / _--=> preempt-depth | |
2176 | # ||| / delay | |
2177 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
2178 | # | | | |||| | | | |
2179 | bash-1994 [002] .... 3082.063030: mutex_unlock <-rb_simple_write | |
2180 | bash-1994 [002] .... 3082.063031: __mutex_unlock_slowpath <-mutex_unlock | |
2181 | bash-1994 [002] .... 3082.063031: __fsnotify_parent <-fsnotify_modify | |
2182 | bash-1994 [002] .... 3082.063032: fsnotify <-fsnotify_modify | |
2183 | bash-1994 [002] .... 3082.063032: __srcu_read_lock <-fsnotify | |
2184 | bash-1994 [002] .... 3082.063032: add_preempt_count <-__srcu_read_lock | |
2185 | bash-1994 [002] ...1 3082.063032: sub_preempt_count <-__srcu_read_lock | |
2186 | bash-1994 [002] .... 3082.063033: __srcu_read_unlock <-fsnotify | |
2187 | [...] | |
2188 | ||
2189 | ||
2190 | Note: function tracer uses ring buffers to store the above | |
2191 | entries. The newest data may overwrite the oldest data. | |
2192 | Sometimes using echo to stop the trace is not sufficient because | |
2193 | the tracing could have overwritten the data that you wanted to | |
2194 | record. For this reason, it is sometimes better to disable | |
2195 | tracing directly from a program. This allows you to stop the | |
2196 | tracing at the point that you hit the part that you are | |
2197 | interested in. To disable the tracing directly from a C program, | |
2198 | something like following code snippet can be used:: | |
2199 | ||
2200 | int trace_fd; | |
2201 | [...] | |
2202 | int main(int argc, char *argv[]) { | |
2203 | [...] | |
2204 | trace_fd = open(tracing_file("tracing_on"), O_WRONLY); | |
2205 | [...] | |
2206 | if (condition_hit()) { | |
2207 | write(trace_fd, "0", 1); | |
2208 | } | |
2209 | [...] | |
2210 | } | |
2211 | ||
2212 | ||
2213 | Single thread tracing | |
2214 | --------------------- | |
2215 | ||
2216 | By writing into set_ftrace_pid you can trace a | |
2217 | single thread. For example:: | |
2218 | ||
2219 | # cat set_ftrace_pid | |
2220 | no pid | |
2221 | # echo 3111 > set_ftrace_pid | |
2222 | # cat set_ftrace_pid | |
2223 | 3111 | |
2224 | # echo function > current_tracer | |
2225 | # cat trace | head | |
2226 | # tracer: function | |
2227 | # | |
2228 | # TASK-PID CPU# TIMESTAMP FUNCTION | |
2229 | # | | | | | | |
2230 | yum-updatesd-3111 [003] 1637.254676: finish_task_switch <-thread_return | |
2231 | yum-updatesd-3111 [003] 1637.254681: hrtimer_cancel <-schedule_hrtimeout_range | |
2232 | yum-updatesd-3111 [003] 1637.254682: hrtimer_try_to_cancel <-hrtimer_cancel | |
2233 | yum-updatesd-3111 [003] 1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel | |
2234 | yum-updatesd-3111 [003] 1637.254685: fget_light <-do_sys_poll | |
2235 | yum-updatesd-3111 [003] 1637.254686: pipe_poll <-do_sys_poll | |
2236 | # echo > set_ftrace_pid | |
2237 | # cat trace |head | |
2238 | # tracer: function | |
2239 | # | |
2240 | # TASK-PID CPU# TIMESTAMP FUNCTION | |
2241 | # | | | | | | |
2242 | ##### CPU 3 buffer started #### | |
2243 | yum-updatesd-3111 [003] 1701.957688: free_poll_entry <-poll_freewait | |
2244 | yum-updatesd-3111 [003] 1701.957689: remove_wait_queue <-free_poll_entry | |
2245 | yum-updatesd-3111 [003] 1701.957691: fput <-free_poll_entry | |
2246 | yum-updatesd-3111 [003] 1701.957692: audit_syscall_exit <-sysret_audit | |
2247 | yum-updatesd-3111 [003] 1701.957693: path_put <-audit_syscall_exit | |
2248 | ||
2249 | If you want to trace a function when executing, you could use | |
2250 | something like this simple program. | |
2251 | :: | |
2252 | ||
2253 | #include <stdio.h> | |
2254 | #include <stdlib.h> | |
2255 | #include <sys/types.h> | |
2256 | #include <sys/stat.h> | |
2257 | #include <fcntl.h> | |
2258 | #include <unistd.h> | |
2259 | #include <string.h> | |
2260 | ||
2261 | #define _STR(x) #x | |
2262 | #define STR(x) _STR(x) | |
2263 | #define MAX_PATH 256 | |
2264 | ||
2265 | const char *find_tracefs(void) | |
2266 | { | |
2267 | static char tracefs[MAX_PATH+1]; | |
2268 | static int tracefs_found; | |
2269 | char type[100]; | |
2270 | FILE *fp; | |
2271 | ||
2272 | if (tracefs_found) | |
2273 | return tracefs; | |
2274 | ||
2275 | if ((fp = fopen("/proc/mounts","r")) == NULL) { | |
2276 | perror("/proc/mounts"); | |
2277 | return NULL; | |
2278 | } | |
2279 | ||
2280 | while (fscanf(fp, "%*s %" | |
2281 | STR(MAX_PATH) | |
2282 | "s %99s %*s %*d %*d\n", | |
2283 | tracefs, type) == 2) { | |
2284 | if (strcmp(type, "tracefs") == 0) | |
2285 | break; | |
2286 | } | |
2287 | fclose(fp); | |
2288 | ||
2289 | if (strcmp(type, "tracefs") != 0) { | |
2290 | fprintf(stderr, "tracefs not mounted"); | |
2291 | return NULL; | |
2292 | } | |
2293 | ||
2294 | strcat(tracefs, "/tracing/"); | |
2295 | tracefs_found = 1; | |
2296 | ||
2297 | return tracefs; | |
2298 | } | |
2299 | ||
2300 | const char *tracing_file(const char *file_name) | |
2301 | { | |
2302 | static char trace_file[MAX_PATH+1]; | |
2303 | snprintf(trace_file, MAX_PATH, "%s/%s", find_tracefs(), file_name); | |
2304 | return trace_file; | |
2305 | } | |
2306 | ||
2307 | int main (int argc, char **argv) | |
2308 | { | |
2309 | if (argc < 1) | |
2310 | exit(-1); | |
2311 | ||
2312 | if (fork() > 0) { | |
2313 | int fd, ffd; | |
2314 | char line[64]; | |
2315 | int s; | |
2316 | ||
2317 | ffd = open(tracing_file("current_tracer"), O_WRONLY); | |
2318 | if (ffd < 0) | |
2319 | exit(-1); | |
2320 | write(ffd, "nop", 3); | |
2321 | ||
2322 | fd = open(tracing_file("set_ftrace_pid"), O_WRONLY); | |
2323 | s = sprintf(line, "%d\n", getpid()); | |
2324 | write(fd, line, s); | |
2325 | ||
2326 | write(ffd, "function", 8); | |
2327 | ||
2328 | close(fd); | |
2329 | close(ffd); | |
2330 | ||
2331 | execvp(argv[1], argv+1); | |
2332 | } | |
2333 | ||
2334 | return 0; | |
2335 | } | |
2336 | ||
2337 | Or this simple script! | |
2338 | :: | |
2339 | ||
2340 | #!/bin/bash | |
2341 | ||
2342 | tracefs=`sed -ne 's/^tracefs \(.*\) tracefs.*/\1/p' /proc/mounts` | |
2343 | echo nop > $tracefs/tracing/current_tracer | |
2344 | echo 0 > $tracefs/tracing/tracing_on | |
2345 | echo $$ > $tracefs/tracing/set_ftrace_pid | |
2346 | echo function > $tracefs/tracing/current_tracer | |
2347 | echo 1 > $tracefs/tracing/tracing_on | |
2348 | exec "$@" | |
2349 | ||
2350 | ||
2351 | function graph tracer | |
2352 | --------------------------- | |
2353 | ||
2354 | This tracer is similar to the function tracer except that it | |
2355 | probes a function on its entry and its exit. This is done by | |
2356 | using a dynamically allocated stack of return addresses in each | |
2357 | task_struct. On function entry the tracer overwrites the return | |
2358 | address of each function traced to set a custom probe. Thus the | |
2359 | original return address is stored on the stack of return address | |
2360 | in the task_struct. | |
2361 | ||
2362 | Probing on both ends of a function leads to special features | |
2363 | such as: | |
2364 | ||
2365 | - measure of a function's time execution | |
2366 | - having a reliable call stack to draw function calls graph | |
2367 | ||
2368 | This tracer is useful in several situations: | |
2369 | ||
2370 | - you want to find the reason of a strange kernel behavior and | |
2371 | need to see what happens in detail on any areas (or specific | |
2372 | ones). | |
2373 | ||
2374 | - you are experiencing weird latencies but it's difficult to | |
2375 | find its origin. | |
2376 | ||
2377 | - you want to find quickly which path is taken by a specific | |
2378 | function | |
2379 | ||
2380 | - you just want to peek inside a working kernel and want to see | |
2381 | what happens there. | |
2382 | ||
2383 | :: | |
2384 | ||
2385 | # tracer: function_graph | |
2386 | # | |
2387 | # CPU DURATION FUNCTION CALLS | |
2388 | # | | | | | | | | |
2389 | ||
2390 | 0) | sys_open() { | |
2391 | 0) | do_sys_open() { | |
2392 | 0) | getname() { | |
2393 | 0) | kmem_cache_alloc() { | |
2394 | 0) 1.382 us | __might_sleep(); | |
2395 | 0) 2.478 us | } | |
2396 | 0) | strncpy_from_user() { | |
2397 | 0) | might_fault() { | |
2398 | 0) 1.389 us | __might_sleep(); | |
2399 | 0) 2.553 us | } | |
2400 | 0) 3.807 us | } | |
2401 | 0) 7.876 us | } | |
2402 | 0) | alloc_fd() { | |
2403 | 0) 0.668 us | _spin_lock(); | |
2404 | 0) 0.570 us | expand_files(); | |
2405 | 0) 0.586 us | _spin_unlock(); | |
2406 | ||
2407 | ||
2408 | There are several columns that can be dynamically | |
2409 | enabled/disabled. You can use every combination of options you | |
2410 | want, depending on your needs. | |
2411 | ||
2412 | - The cpu number on which the function executed is default | |
2413 | enabled. It is sometimes better to only trace one cpu (see | |
2414 | tracing_cpu_mask file) or you might sometimes see unordered | |
2415 | function calls while cpu tracing switch. | |
2416 | ||
2417 | - hide: echo nofuncgraph-cpu > trace_options | |
2418 | - show: echo funcgraph-cpu > trace_options | |
2419 | ||
2420 | - The duration (function's time of execution) is displayed on | |
2421 | the closing bracket line of a function or on the same line | |
2422 | than the current function in case of a leaf one. It is default | |
2423 | enabled. | |
2424 | ||
2425 | - hide: echo nofuncgraph-duration > trace_options | |
2426 | - show: echo funcgraph-duration > trace_options | |
2427 | ||
2428 | - The overhead field precedes the duration field in case of | |
2429 | reached duration thresholds. | |
2430 | ||
2431 | - hide: echo nofuncgraph-overhead > trace_options | |
2432 | - show: echo funcgraph-overhead > trace_options | |
2433 | - depends on: funcgraph-duration | |
2434 | ||
2435 | ie:: | |
2436 | ||
2437 | 3) # 1837.709 us | } /* __switch_to */ | |
2438 | 3) | finish_task_switch() { | |
2439 | 3) 0.313 us | _raw_spin_unlock_irq(); | |
2440 | 3) 3.177 us | } | |
2441 | 3) # 1889.063 us | } /* __schedule */ | |
2442 | 3) ! 140.417 us | } /* __schedule */ | |
2443 | 3) # 2034.948 us | } /* schedule */ | |
2444 | 3) * 33998.59 us | } /* schedule_preempt_disabled */ | |
2445 | ||
2446 | [...] | |
2447 | ||
2448 | 1) 0.260 us | msecs_to_jiffies(); | |
2449 | 1) 0.313 us | __rcu_read_unlock(); | |
2450 | 1) + 61.770 us | } | |
2451 | 1) + 64.479 us | } | |
2452 | 1) 0.313 us | rcu_bh_qs(); | |
2453 | 1) 0.313 us | __local_bh_enable(); | |
2454 | 1) ! 217.240 us | } | |
2455 | 1) 0.365 us | idle_cpu(); | |
2456 | 1) | rcu_irq_exit() { | |
2457 | 1) 0.417 us | rcu_eqs_enter_common.isra.47(); | |
2458 | 1) 3.125 us | } | |
2459 | 1) ! 227.812 us | } | |
2460 | 1) ! 457.395 us | } | |
2461 | 1) @ 119760.2 us | } | |
2462 | ||
2463 | [...] | |
2464 | ||
2465 | 2) | handle_IPI() { | |
2466 | 1) 6.979 us | } | |
2467 | 2) 0.417 us | scheduler_ipi(); | |
2468 | 1) 9.791 us | } | |
2469 | 1) + 12.917 us | } | |
2470 | 2) 3.490 us | } | |
2471 | 1) + 15.729 us | } | |
2472 | 1) + 18.542 us | } | |
2473 | 2) $ 3594274 us | } | |
2474 | ||
2475 | Flags:: | |
2476 | ||
2477 | + means that the function exceeded 10 usecs. | |
2478 | ! means that the function exceeded 100 usecs. | |
2479 | # means that the function exceeded 1000 usecs. | |
2480 | * means that the function exceeded 10 msecs. | |
2481 | @ means that the function exceeded 100 msecs. | |
2482 | $ means that the function exceeded 1 sec. | |
2483 | ||
2484 | ||
2485 | - The task/pid field displays the thread cmdline and pid which | |
2486 | executed the function. It is default disabled. | |
2487 | ||
2488 | - hide: echo nofuncgraph-proc > trace_options | |
2489 | - show: echo funcgraph-proc > trace_options | |
2490 | ||
2491 | ie:: | |
2492 | ||
2493 | # tracer: function_graph | |
2494 | # | |
2495 | # CPU TASK/PID DURATION FUNCTION CALLS | |
2496 | # | | | | | | | | | | |
2497 | 0) sh-4802 | | d_free() { | |
2498 | 0) sh-4802 | | call_rcu() { | |
2499 | 0) sh-4802 | | __call_rcu() { | |
2500 | 0) sh-4802 | 0.616 us | rcu_process_gp_end(); | |
2501 | 0) sh-4802 | 0.586 us | check_for_new_grace_period(); | |
2502 | 0) sh-4802 | 2.899 us | } | |
2503 | 0) sh-4802 | 4.040 us | } | |
2504 | 0) sh-4802 | 5.151 us | } | |
2505 | 0) sh-4802 | + 49.370 us | } | |
2506 | ||
2507 | ||
2508 | - The absolute time field is an absolute timestamp given by the | |
2509 | system clock since it started. A snapshot of this time is | |
2510 | given on each entry/exit of functions | |
2511 | ||
2512 | - hide: echo nofuncgraph-abstime > trace_options | |
2513 | - show: echo funcgraph-abstime > trace_options | |
2514 | ||
2515 | ie:: | |
2516 | ||
2517 | # | |
2518 | # TIME CPU DURATION FUNCTION CALLS | |
2519 | # | | | | | | | | | |
2520 | 360.774522 | 1) 0.541 us | } | |
2521 | 360.774522 | 1) 4.663 us | } | |
2522 | 360.774523 | 1) 0.541 us | __wake_up_bit(); | |
2523 | 360.774524 | 1) 6.796 us | } | |
2524 | 360.774524 | 1) 7.952 us | } | |
2525 | 360.774525 | 1) 9.063 us | } | |
2526 | 360.774525 | 1) 0.615 us | journal_mark_dirty(); | |
2527 | 360.774527 | 1) 0.578 us | __brelse(); | |
2528 | 360.774528 | 1) | reiserfs_prepare_for_journal() { | |
2529 | 360.774528 | 1) | unlock_buffer() { | |
2530 | 360.774529 | 1) | wake_up_bit() { | |
2531 | 360.774529 | 1) | bit_waitqueue() { | |
2532 | 360.774530 | 1) 0.594 us | __phys_addr(); | |
2533 | ||
2534 | ||
2535 | The function name is always displayed after the closing bracket | |
2536 | for a function if the start of that function is not in the | |
2537 | trace buffer. | |
2538 | ||
2539 | Display of the function name after the closing bracket may be | |
2540 | enabled for functions whose start is in the trace buffer, | |
2541 | allowing easier searching with grep for function durations. | |
2542 | It is default disabled. | |
2543 | ||
2544 | - hide: echo nofuncgraph-tail > trace_options | |
2545 | - show: echo funcgraph-tail > trace_options | |
2546 | ||
2547 | Example with nofuncgraph-tail (default):: | |
2548 | ||
2549 | 0) | putname() { | |
2550 | 0) | kmem_cache_free() { | |
2551 | 0) 0.518 us | __phys_addr(); | |
2552 | 0) 1.757 us | } | |
2553 | 0) 2.861 us | } | |
2554 | ||
2555 | Example with funcgraph-tail:: | |
2556 | ||
2557 | 0) | putname() { | |
2558 | 0) | kmem_cache_free() { | |
2559 | 0) 0.518 us | __phys_addr(); | |
2560 | 0) 1.757 us | } /* kmem_cache_free() */ | |
2561 | 0) 2.861 us | } /* putname() */ | |
2562 | ||
2563 | You can put some comments on specific functions by using | |
2564 | trace_printk() For example, if you want to put a comment inside | |
2565 | the __might_sleep() function, you just have to include | |
2566 | <linux/ftrace.h> and call trace_printk() inside __might_sleep():: | |
2567 | ||
2568 | trace_printk("I'm a comment!\n") | |
2569 | ||
2570 | will produce:: | |
2571 | ||
2572 | 1) | __might_sleep() { | |
2573 | 1) | /* I'm a comment! */ | |
2574 | 1) 1.449 us | } | |
2575 | ||
2576 | ||
2577 | You might find other useful features for this tracer in the | |
2578 | following "dynamic ftrace" section such as tracing only specific | |
2579 | functions or tasks. | |
2580 | ||
2581 | dynamic ftrace | |
2582 | -------------- | |
2583 | ||
2584 | If CONFIG_DYNAMIC_FTRACE is set, the system will run with | |
2585 | virtually no overhead when function tracing is disabled. The way | |
2586 | this works is the mcount function call (placed at the start of | |
2587 | every kernel function, produced by the -pg switch in gcc), | |
2588 | starts of pointing to a simple return. (Enabling FTRACE will | |
2589 | include the -pg switch in the compiling of the kernel.) | |
2590 | ||
2591 | At compile time every C file object is run through the | |
2592 | recordmcount program (located in the scripts directory). This | |
2593 | program will parse the ELF headers in the C object to find all | |
2594 | the locations in the .text section that call mcount. Starting | |
2a1e03ca | 2595 | with gcc version 4.6, the -mfentry has been added for x86, which |
1f198e22 CD |
2596 | calls "__fentry__" instead of "mcount". Which is called before |
2597 | the creation of the stack frame. | |
2598 | ||
2599 | Note, not all sections are traced. They may be prevented by either | |
2600 | a notrace, or blocked another way and all inline functions are not | |
2601 | traced. Check the "available_filter_functions" file to see what functions | |
2602 | can be traced. | |
2603 | ||
2604 | A section called "__mcount_loc" is created that holds | |
2605 | references to all the mcount/fentry call sites in the .text section. | |
2606 | The recordmcount program re-links this section back into the | |
2607 | original object. The final linking stage of the kernel will add all these | |
2608 | references into a single table. | |
2609 | ||
2610 | On boot up, before SMP is initialized, the dynamic ftrace code | |
2611 | scans this table and updates all the locations into nops. It | |
2612 | also records the locations, which are added to the | |
2613 | available_filter_functions list. Modules are processed as they | |
2614 | are loaded and before they are executed. When a module is | |
2615 | unloaded, it also removes its functions from the ftrace function | |
2616 | list. This is automatic in the module unload code, and the | |
2617 | module author does not need to worry about it. | |
2618 | ||
2619 | When tracing is enabled, the process of modifying the function | |
2620 | tracepoints is dependent on architecture. The old method is to use | |
2621 | kstop_machine to prevent races with the CPUs executing code being | |
2622 | modified (which can cause the CPU to do undesirable things, especially | |
2623 | if the modified code crosses cache (or page) boundaries), and the nops are | |
2624 | patched back to calls. But this time, they do not call mcount | |
2625 | (which is just a function stub). They now call into the ftrace | |
2626 | infrastructure. | |
2627 | ||
2628 | The new method of modifying the function tracepoints is to place | |
2629 | a breakpoint at the location to be modified, sync all CPUs, modify | |
2630 | the rest of the instruction not covered by the breakpoint. Sync | |
2631 | all CPUs again, and then remove the breakpoint with the finished | |
2632 | version to the ftrace call site. | |
2633 | ||
2634 | Some archs do not even need to monkey around with the synchronization, | |
2635 | and can just slap the new code on top of the old without any | |
2636 | problems with other CPUs executing it at the same time. | |
2637 | ||
2638 | One special side-effect to the recording of the functions being | |
2639 | traced is that we can now selectively choose which functions we | |
2640 | wish to trace and which ones we want the mcount calls to remain | |
2641 | as nops. | |
2642 | ||
2643 | Two files are used, one for enabling and one for disabling the | |
2644 | tracing of specified functions. They are: | |
2645 | ||
2646 | set_ftrace_filter | |
2647 | ||
2648 | and | |
2649 | ||
2650 | set_ftrace_notrace | |
2651 | ||
2652 | A list of available functions that you can add to these files is | |
2653 | listed in: | |
2654 | ||
2655 | available_filter_functions | |
2656 | ||
2657 | :: | |
2658 | ||
2659 | # cat available_filter_functions | |
2660 | put_prev_task_idle | |
2661 | kmem_cache_create | |
2662 | pick_next_task_rt | |
2663 | get_online_cpus | |
2664 | pick_next_task_fair | |
2665 | mutex_lock | |
2666 | [...] | |
2667 | ||
2668 | If I am only interested in sys_nanosleep and hrtimer_interrupt:: | |
2669 | ||
2670 | # echo sys_nanosleep hrtimer_interrupt > set_ftrace_filter | |
2671 | # echo function > current_tracer | |
2672 | # echo 1 > tracing_on | |
2673 | # usleep 1 | |
2674 | # echo 0 > tracing_on | |
2675 | # cat trace | |
2676 | # tracer: function | |
2677 | # | |
2678 | # entries-in-buffer/entries-written: 5/5 #P:4 | |
2679 | # | |
2680 | # _-----=> irqs-off | |
2681 | # / _----=> need-resched | |
2682 | # | / _---=> hardirq/softirq | |
2683 | # || / _--=> preempt-depth | |
2684 | # ||| / delay | |
2685 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
2686 | # | | | |||| | | | |
2687 | usleep-2665 [001] .... 4186.475355: sys_nanosleep <-system_call_fastpath | |
2688 | <idle>-0 [001] d.h1 4186.475409: hrtimer_interrupt <-smp_apic_timer_interrupt | |
2689 | usleep-2665 [001] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt | |
2690 | <idle>-0 [003] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt | |
2691 | <idle>-0 [002] d.h1 4186.475427: hrtimer_interrupt <-smp_apic_timer_interrupt | |
2692 | ||
2693 | To see which functions are being traced, you can cat the file: | |
2694 | :: | |
2695 | ||
2696 | # cat set_ftrace_filter | |
2697 | hrtimer_interrupt | |
2698 | sys_nanosleep | |
2699 | ||
2700 | ||
2701 | Perhaps this is not enough. The filters also allow glob(7) matching. | |
2702 | ||
6234c7bd | 2703 | ``<match>*`` |
1f198e22 | 2704 | will match functions that begin with <match> |
6234c7bd | 2705 | ``*<match>`` |
1f198e22 | 2706 | will match functions that end with <match> |
6234c7bd | 2707 | ``*<match>*`` |
1f198e22 | 2708 | will match functions that have <match> in it |
6234c7bd | 2709 | ``<match1>*<match2>`` |
1f198e22 CD |
2710 | will match functions that begin with <match1> and end with <match2> |
2711 | ||
2712 | .. note:: | |
2713 | It is better to use quotes to enclose the wild cards, | |
2714 | otherwise the shell may expand the parameters into names | |
2715 | of files in the local directory. | |
2716 | ||
2717 | :: | |
2718 | ||
2719 | # echo 'hrtimer_*' > set_ftrace_filter | |
2720 | ||
2721 | Produces:: | |
2722 | ||
2723 | # tracer: function | |
2724 | # | |
2725 | # entries-in-buffer/entries-written: 897/897 #P:4 | |
2726 | # | |
2727 | # _-----=> irqs-off | |
2728 | # / _----=> need-resched | |
2729 | # | / _---=> hardirq/softirq | |
2730 | # || / _--=> preempt-depth | |
2731 | # ||| / delay | |
2732 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
2733 | # | | | |||| | | | |
2734 | <idle>-0 [003] dN.1 4228.547803: hrtimer_cancel <-tick_nohz_idle_exit | |
2735 | <idle>-0 [003] dN.1 4228.547804: hrtimer_try_to_cancel <-hrtimer_cancel | |
2736 | <idle>-0 [003] dN.2 4228.547805: hrtimer_force_reprogram <-__remove_hrtimer | |
2737 | <idle>-0 [003] dN.1 4228.547805: hrtimer_forward <-tick_nohz_idle_exit | |
2738 | <idle>-0 [003] dN.1 4228.547805: hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11 | |
2739 | <idle>-0 [003] d..1 4228.547858: hrtimer_get_next_event <-get_next_timer_interrupt | |
2740 | <idle>-0 [003] d..1 4228.547859: hrtimer_start <-__tick_nohz_idle_enter | |
2741 | <idle>-0 [003] d..2 4228.547860: hrtimer_force_reprogram <-__rem | |
2742 | ||
2743 | Notice that we lost the sys_nanosleep. | |
2744 | :: | |
2745 | ||
2746 | # cat set_ftrace_filter | |
2747 | hrtimer_run_queues | |
2748 | hrtimer_run_pending | |
2749 | hrtimer_init | |
2750 | hrtimer_cancel | |
2751 | hrtimer_try_to_cancel | |
2752 | hrtimer_forward | |
2753 | hrtimer_start | |
2754 | hrtimer_reprogram | |
2755 | hrtimer_force_reprogram | |
2756 | hrtimer_get_next_event | |
2757 | hrtimer_interrupt | |
2758 | hrtimer_nanosleep | |
2759 | hrtimer_wakeup | |
2760 | hrtimer_get_remaining | |
2761 | hrtimer_get_res | |
2762 | hrtimer_init_sleeper | |
2763 | ||
2764 | ||
2765 | This is because the '>' and '>>' act just like they do in bash. | |
2766 | To rewrite the filters, use '>' | |
2767 | To append to the filters, use '>>' | |
2768 | ||
2769 | To clear out a filter so that all functions will be recorded | |
2770 | again:: | |
2771 | ||
2772 | # echo > set_ftrace_filter | |
2773 | # cat set_ftrace_filter | |
2774 | # | |
2775 | ||
2776 | Again, now we want to append. | |
2777 | ||
2778 | :: | |
2779 | ||
2780 | # echo sys_nanosleep > set_ftrace_filter | |
2781 | # cat set_ftrace_filter | |
2782 | sys_nanosleep | |
2783 | # echo 'hrtimer_*' >> set_ftrace_filter | |
2784 | # cat set_ftrace_filter | |
2785 | hrtimer_run_queues | |
2786 | hrtimer_run_pending | |
2787 | hrtimer_init | |
2788 | hrtimer_cancel | |
2789 | hrtimer_try_to_cancel | |
2790 | hrtimer_forward | |
2791 | hrtimer_start | |
2792 | hrtimer_reprogram | |
2793 | hrtimer_force_reprogram | |
2794 | hrtimer_get_next_event | |
2795 | hrtimer_interrupt | |
2796 | sys_nanosleep | |
2797 | hrtimer_nanosleep | |
2798 | hrtimer_wakeup | |
2799 | hrtimer_get_remaining | |
2800 | hrtimer_get_res | |
2801 | hrtimer_init_sleeper | |
2802 | ||
2803 | ||
2804 | The set_ftrace_notrace prevents those functions from being | |
2805 | traced. | |
2806 | :: | |
2807 | ||
2808 | # echo '*preempt*' '*lock*' > set_ftrace_notrace | |
2809 | ||
2810 | Produces:: | |
2811 | ||
2812 | # tracer: function | |
2813 | # | |
2814 | # entries-in-buffer/entries-written: 39608/39608 #P:4 | |
2815 | # | |
2816 | # _-----=> irqs-off | |
2817 | # / _----=> need-resched | |
2818 | # | / _---=> hardirq/softirq | |
2819 | # || / _--=> preempt-depth | |
2820 | # ||| / delay | |
2821 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
2822 | # | | | |||| | | | |
2823 | bash-1994 [000] .... 4342.324896: file_ra_state_init <-do_dentry_open | |
2824 | bash-1994 [000] .... 4342.324897: open_check_o_direct <-do_last | |
2825 | bash-1994 [000] .... 4342.324897: ima_file_check <-do_last | |
2826 | bash-1994 [000] .... 4342.324898: process_measurement <-ima_file_check | |
2827 | bash-1994 [000] .... 4342.324898: ima_get_action <-process_measurement | |
2828 | bash-1994 [000] .... 4342.324898: ima_match_policy <-ima_get_action | |
2829 | bash-1994 [000] .... 4342.324899: do_truncate <-do_last | |
2830 | bash-1994 [000] .... 4342.324899: should_remove_suid <-do_truncate | |
2831 | bash-1994 [000] .... 4342.324899: notify_change <-do_truncate | |
2832 | bash-1994 [000] .... 4342.324900: current_fs_time <-notify_change | |
2833 | bash-1994 [000] .... 4342.324900: current_kernel_time <-current_fs_time | |
2834 | bash-1994 [000] .... 4342.324900: timespec_trunc <-current_fs_time | |
2835 | ||
2836 | We can see that there's no more lock or preempt tracing. | |
2837 | ||
2838 | ||
2839 | Dynamic ftrace with the function graph tracer | |
2840 | --------------------------------------------- | |
2841 | ||
2842 | Although what has been explained above concerns both the | |
2843 | function tracer and the function-graph-tracer, there are some | |
2844 | special features only available in the function-graph tracer. | |
2845 | ||
2846 | If you want to trace only one function and all of its children, | |
2847 | you just have to echo its name into set_graph_function:: | |
2848 | ||
2849 | echo __do_fault > set_graph_function | |
2850 | ||
2851 | will produce the following "expanded" trace of the __do_fault() | |
2852 | function:: | |
2853 | ||
2854 | 0) | __do_fault() { | |
2855 | 0) | filemap_fault() { | |
2856 | 0) | find_lock_page() { | |
2857 | 0) 0.804 us | find_get_page(); | |
2858 | 0) | __might_sleep() { | |
2859 | 0) 1.329 us | } | |
2860 | 0) 3.904 us | } | |
2861 | 0) 4.979 us | } | |
2862 | 0) 0.653 us | _spin_lock(); | |
2863 | 0) 0.578 us | page_add_file_rmap(); | |
2864 | 0) 0.525 us | native_set_pte_at(); | |
2865 | 0) 0.585 us | _spin_unlock(); | |
2866 | 0) | unlock_page() { | |
2867 | 0) 0.541 us | page_waitqueue(); | |
2868 | 0) 0.639 us | __wake_up_bit(); | |
2869 | 0) 2.786 us | } | |
2870 | 0) + 14.237 us | } | |
2871 | 0) | __do_fault() { | |
2872 | 0) | filemap_fault() { | |
2873 | 0) | find_lock_page() { | |
2874 | 0) 0.698 us | find_get_page(); | |
2875 | 0) | __might_sleep() { | |
2876 | 0) 1.412 us | } | |
2877 | 0) 3.950 us | } | |
2878 | 0) 5.098 us | } | |
2879 | 0) 0.631 us | _spin_lock(); | |
2880 | 0) 0.571 us | page_add_file_rmap(); | |
2881 | 0) 0.526 us | native_set_pte_at(); | |
2882 | 0) 0.586 us | _spin_unlock(); | |
2883 | 0) | unlock_page() { | |
2884 | 0) 0.533 us | page_waitqueue(); | |
2885 | 0) 0.638 us | __wake_up_bit(); | |
2886 | 0) 2.793 us | } | |
2887 | 0) + 14.012 us | } | |
2888 | ||
2889 | You can also expand several functions at once:: | |
2890 | ||
2891 | echo sys_open > set_graph_function | |
2892 | echo sys_close >> set_graph_function | |
2893 | ||
2894 | Now if you want to go back to trace all functions you can clear | |
2895 | this special filter via:: | |
2896 | ||
2897 | echo > set_graph_function | |
2898 | ||
2899 | ||
2900 | ftrace_enabled | |
2901 | -------------- | |
2902 | ||
2903 | Note, the proc sysctl ftrace_enable is a big on/off switch for the | |
2904 | function tracer. By default it is enabled (when function tracing is | |
2905 | enabled in the kernel). If it is disabled, all function tracing is | |
2906 | disabled. This includes not only the function tracers for ftrace, but | |
2907 | also for any other uses (perf, kprobes, stack tracing, profiling, etc). | |
2908 | ||
2909 | Please disable this with care. | |
2910 | ||
2911 | This can be disable (and enabled) with:: | |
2912 | ||
2913 | sysctl kernel.ftrace_enabled=0 | |
2914 | sysctl kernel.ftrace_enabled=1 | |
2915 | ||
2916 | or | |
2917 | ||
2918 | echo 0 > /proc/sys/kernel/ftrace_enabled | |
2919 | echo 1 > /proc/sys/kernel/ftrace_enabled | |
2920 | ||
2921 | ||
2922 | Filter commands | |
2923 | --------------- | |
2924 | ||
2925 | A few commands are supported by the set_ftrace_filter interface. | |
2926 | Trace commands have the following format:: | |
2927 | ||
2928 | <function>:<command>:<parameter> | |
2929 | ||
2930 | The following commands are supported: | |
2931 | ||
2932 | - mod: | |
2933 | This command enables function filtering per module. The | |
2934 | parameter defines the module. For example, if only the write* | |
2935 | functions in the ext3 module are desired, run: | |
2936 | ||
2937 | echo 'write*:mod:ext3' > set_ftrace_filter | |
2938 | ||
2939 | This command interacts with the filter in the same way as | |
2940 | filtering based on function names. Thus, adding more functions | |
2941 | in a different module is accomplished by appending (>>) to the | |
2942 | filter file. Remove specific module functions by prepending | |
2943 | '!':: | |
2944 | ||
2945 | echo '!writeback*:mod:ext3' >> set_ftrace_filter | |
2946 | ||
2947 | Mod command supports module globbing. Disable tracing for all | |
2948 | functions except a specific module:: | |
2949 | ||
2950 | echo '!*:mod:!ext3' >> set_ftrace_filter | |
2951 | ||
2952 | Disable tracing for all modules, but still trace kernel:: | |
2953 | ||
2954 | echo '!*:mod:*' >> set_ftrace_filter | |
2955 | ||
2956 | Enable filter only for kernel:: | |
2957 | ||
2958 | echo '*write*:mod:!*' >> set_ftrace_filter | |
2959 | ||
2960 | Enable filter for module globbing:: | |
2961 | ||
2962 | echo '*write*:mod:*snd*' >> set_ftrace_filter | |
2963 | ||
2964 | - traceon/traceoff: | |
2965 | These commands turn tracing on and off when the specified | |
2966 | functions are hit. The parameter determines how many times the | |
2967 | tracing system is turned on and off. If unspecified, there is | |
2968 | no limit. For example, to disable tracing when a schedule bug | |
2969 | is hit the first 5 times, run:: | |
2970 | ||
2971 | echo '__schedule_bug:traceoff:5' > set_ftrace_filter | |
2972 | ||
2973 | To always disable tracing when __schedule_bug is hit:: | |
2974 | ||
2975 | echo '__schedule_bug:traceoff' > set_ftrace_filter | |
2976 | ||
2977 | These commands are cumulative whether or not they are appended | |
2978 | to set_ftrace_filter. To remove a command, prepend it by '!' | |
2979 | and drop the parameter:: | |
2980 | ||
2981 | echo '!__schedule_bug:traceoff:0' > set_ftrace_filter | |
2982 | ||
2983 | The above removes the traceoff command for __schedule_bug | |
2984 | that have a counter. To remove commands without counters:: | |
2985 | ||
2986 | echo '!__schedule_bug:traceoff' > set_ftrace_filter | |
2987 | ||
2988 | - snapshot: | |
2989 | Will cause a snapshot to be triggered when the function is hit. | |
2990 | :: | |
2991 | ||
2992 | echo 'native_flush_tlb_others:snapshot' > set_ftrace_filter | |
2993 | ||
2994 | To only snapshot once: | |
2995 | :: | |
2996 | ||
2997 | echo 'native_flush_tlb_others:snapshot:1' > set_ftrace_filter | |
2998 | ||
2999 | To remove the above commands:: | |
3000 | ||
3001 | echo '!native_flush_tlb_others:snapshot' > set_ftrace_filter | |
3002 | echo '!native_flush_tlb_others:snapshot:0' > set_ftrace_filter | |
3003 | ||
3004 | - enable_event/disable_event: | |
3005 | These commands can enable or disable a trace event. Note, because | |
3006 | function tracing callbacks are very sensitive, when these commands | |
3007 | are registered, the trace point is activated, but disabled in | |
3008 | a "soft" mode. That is, the tracepoint will be called, but | |
3009 | just will not be traced. The event tracepoint stays in this mode | |
3010 | as long as there's a command that triggers it. | |
3011 | :: | |
3012 | ||
3013 | echo 'try_to_wake_up:enable_event:sched:sched_switch:2' > \ | |
3014 | set_ftrace_filter | |
3015 | ||
3016 | The format is:: | |
3017 | ||
3018 | <function>:enable_event:<system>:<event>[:count] | |
3019 | <function>:disable_event:<system>:<event>[:count] | |
3020 | ||
3021 | To remove the events commands:: | |
3022 | ||
3023 | echo '!try_to_wake_up:enable_event:sched:sched_switch:0' > \ | |
3024 | set_ftrace_filter | |
3025 | echo '!schedule:disable_event:sched:sched_switch' > \ | |
3026 | set_ftrace_filter | |
3027 | ||
3028 | - dump: | |
3029 | When the function is hit, it will dump the contents of the ftrace | |
3030 | ring buffer to the console. This is useful if you need to debug | |
3031 | something, and want to dump the trace when a certain function | |
2a1e03ca | 3032 | is hit. Perhaps it's a function that is called before a triple |
1f198e22 CD |
3033 | fault happens and does not allow you to get a regular dump. |
3034 | ||
3035 | - cpudump: | |
3036 | When the function is hit, it will dump the contents of the ftrace | |
3037 | ring buffer for the current CPU to the console. Unlike the "dump" | |
3038 | command, it only prints out the contents of the ring buffer for the | |
3039 | CPU that executed the function that triggered the dump. | |
3040 | ||
8a2933cf MH |
3041 | - stacktrace: |
3042 | When the function is hit, a stack trace is recorded. | |
3043 | ||
1f198e22 CD |
3044 | trace_pipe |
3045 | ---------- | |
3046 | ||
3047 | The trace_pipe outputs the same content as the trace file, but | |
3048 | the effect on the tracing is different. Every read from | |
3049 | trace_pipe is consumed. This means that subsequent reads will be | |
3050 | different. The trace is live. | |
3051 | :: | |
3052 | ||
3053 | # echo function > current_tracer | |
3054 | # cat trace_pipe > /tmp/trace.out & | |
3055 | [1] 4153 | |
3056 | # echo 1 > tracing_on | |
3057 | # usleep 1 | |
3058 | # echo 0 > tracing_on | |
3059 | # cat trace | |
3060 | # tracer: function | |
3061 | # | |
3062 | # entries-in-buffer/entries-written: 0/0 #P:4 | |
3063 | # | |
3064 | # _-----=> irqs-off | |
3065 | # / _----=> need-resched | |
3066 | # | / _---=> hardirq/softirq | |
3067 | # || / _--=> preempt-depth | |
3068 | # ||| / delay | |
3069 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
3070 | # | | | |||| | | | |
3071 | ||
3072 | # | |
3073 | # cat /tmp/trace.out | |
3074 | bash-1994 [000] .... 5281.568961: mutex_unlock <-rb_simple_write | |
3075 | bash-1994 [000] .... 5281.568963: __mutex_unlock_slowpath <-mutex_unlock | |
3076 | bash-1994 [000] .... 5281.568963: __fsnotify_parent <-fsnotify_modify | |
3077 | bash-1994 [000] .... 5281.568964: fsnotify <-fsnotify_modify | |
3078 | bash-1994 [000] .... 5281.568964: __srcu_read_lock <-fsnotify | |
3079 | bash-1994 [000] .... 5281.568964: add_preempt_count <-__srcu_read_lock | |
3080 | bash-1994 [000] ...1 5281.568965: sub_preempt_count <-__srcu_read_lock | |
3081 | bash-1994 [000] .... 5281.568965: __srcu_read_unlock <-fsnotify | |
3082 | bash-1994 [000] .... 5281.568967: sys_dup2 <-system_call_fastpath | |
3083 | ||
3084 | ||
3085 | Note, reading the trace_pipe file will block until more input is | |
3086 | added. | |
3087 | ||
3088 | trace entries | |
3089 | ------------- | |
3090 | ||
3091 | Having too much or not enough data can be troublesome in | |
3092 | diagnosing an issue in the kernel. The file buffer_size_kb is | |
3093 | used to modify the size of the internal trace buffers. The | |
3094 | number listed is the number of entries that can be recorded per | |
3095 | CPU. To know the full size, multiply the number of possible CPUs | |
3096 | with the number of entries. | |
3097 | :: | |
3098 | ||
3099 | # cat buffer_size_kb | |
3100 | 1408 (units kilobytes) | |
3101 | ||
3102 | Or simply read buffer_total_size_kb | |
3103 | :: | |
3104 | ||
3105 | # cat buffer_total_size_kb | |
3106 | 5632 | |
3107 | ||
3108 | To modify the buffer, simple echo in a number (in 1024 byte segments). | |
3109 | :: | |
3110 | ||
3111 | # echo 10000 > buffer_size_kb | |
3112 | # cat buffer_size_kb | |
3113 | 10000 (units kilobytes) | |
3114 | ||
3115 | It will try to allocate as much as possible. If you allocate too | |
3116 | much, it can cause Out-Of-Memory to trigger. | |
3117 | :: | |
3118 | ||
3119 | # echo 1000000000000 > buffer_size_kb | |
3120 | -bash: echo: write error: Cannot allocate memory | |
3121 | # cat buffer_size_kb | |
3122 | 85 | |
3123 | ||
3124 | The per_cpu buffers can be changed individually as well: | |
3125 | :: | |
3126 | ||
3127 | # echo 10000 > per_cpu/cpu0/buffer_size_kb | |
3128 | # echo 100 > per_cpu/cpu1/buffer_size_kb | |
3129 | ||
3130 | When the per_cpu buffers are not the same, the buffer_size_kb | |
3131 | at the top level will just show an X | |
3132 | :: | |
3133 | ||
3134 | # cat buffer_size_kb | |
3135 | X | |
3136 | ||
3137 | This is where the buffer_total_size_kb is useful: | |
3138 | :: | |
3139 | ||
3140 | # cat buffer_total_size_kb | |
3141 | 12916 | |
3142 | ||
3143 | Writing to the top level buffer_size_kb will reset all the buffers | |
3144 | to be the same again. | |
3145 | ||
3146 | Snapshot | |
3147 | -------- | |
3148 | CONFIG_TRACER_SNAPSHOT makes a generic snapshot feature | |
3149 | available to all non latency tracers. (Latency tracers which | |
3150 | record max latency, such as "irqsoff" or "wakeup", can't use | |
3151 | this feature, since those are already using the snapshot | |
3152 | mechanism internally.) | |
3153 | ||
3154 | Snapshot preserves a current trace buffer at a particular point | |
3155 | in time without stopping tracing. Ftrace swaps the current | |
3156 | buffer with a spare buffer, and tracing continues in the new | |
3157 | current (=previous spare) buffer. | |
3158 | ||
3159 | The following tracefs files in "tracing" are related to this | |
3160 | feature: | |
3161 | ||
3162 | snapshot: | |
3163 | ||
3164 | This is used to take a snapshot and to read the output | |
3165 | of the snapshot. Echo 1 into this file to allocate a | |
3166 | spare buffer and to take a snapshot (swap), then read | |
3167 | the snapshot from this file in the same format as | |
3168 | "trace" (described above in the section "The File | |
3169 | System"). Both reads snapshot and tracing are executable | |
3170 | in parallel. When the spare buffer is allocated, echoing | |
3171 | 0 frees it, and echoing else (positive) values clear the | |
3172 | snapshot contents. | |
3173 | More details are shown in the table below. | |
3174 | ||
3175 | +--------------+------------+------------+------------+ | |
3176 | |status\\input | 0 | 1 | else | | |
3177 | +==============+============+============+============+ | |
3178 | |not allocated |(do nothing)| alloc+swap |(do nothing)| | |
3179 | +--------------+------------+------------+------------+ | |
3180 | |allocated | free | swap | clear | | |
3181 | +--------------+------------+------------+------------+ | |
3182 | ||
3183 | Here is an example of using the snapshot feature. | |
3184 | :: | |
3185 | ||
3186 | # echo 1 > events/sched/enable | |
3187 | # echo 1 > snapshot | |
3188 | # cat snapshot | |
3189 | # tracer: nop | |
3190 | # | |
3191 | # entries-in-buffer/entries-written: 71/71 #P:8 | |
3192 | # | |
3193 | # _-----=> irqs-off | |
3194 | # / _----=> need-resched | |
3195 | # | / _---=> hardirq/softirq | |
3196 | # || / _--=> preempt-depth | |
3197 | # ||| / delay | |
3198 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
3199 | # | | | |||| | | | |
3200 | <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 | |
3201 | 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 | |
3202 | [...] | |
3203 | <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 | |
3204 | ||
3205 | # cat trace | |
3206 | # tracer: nop | |
3207 | # | |
3208 | # entries-in-buffer/entries-written: 77/77 #P:8 | |
3209 | # | |
3210 | # _-----=> irqs-off | |
3211 | # / _----=> need-resched | |
3212 | # | / _---=> hardirq/softirq | |
3213 | # || / _--=> preempt-depth | |
3214 | # ||| / delay | |
3215 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
3216 | # | | | |||| | | | |
3217 | <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 | |
3218 | 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 | |
3219 | [...] | |
3220 | ||
3221 | ||
3222 | If you try to use this snapshot feature when current tracer is | |
3223 | one of the latency tracers, you will get the following results. | |
3224 | :: | |
3225 | ||
3226 | # echo wakeup > current_tracer | |
3227 | # echo 1 > snapshot | |
3228 | bash: echo: write error: Device or resource busy | |
3229 | # cat snapshot | |
3230 | cat: snapshot: Device or resource busy | |
3231 | ||
3232 | ||
3233 | Instances | |
3234 | --------- | |
3235 | In the tracefs tracing directory is a directory called "instances". | |
3236 | This directory can have new directories created inside of it using | |
3237 | mkdir, and removing directories with rmdir. The directory created | |
3238 | with mkdir in this directory will already contain files and other | |
3239 | directories after it is created. | |
3240 | :: | |
3241 | ||
3242 | # mkdir instances/foo | |
3243 | # ls instances/foo | |
3244 | buffer_size_kb buffer_total_size_kb events free_buffer per_cpu | |
3245 | set_event snapshot trace trace_clock trace_marker trace_options | |
3246 | trace_pipe tracing_on | |
3247 | ||
3248 | As you can see, the new directory looks similar to the tracing directory | |
3249 | itself. In fact, it is very similar, except that the buffer and | |
3250 | events are agnostic from the main director, or from any other | |
3251 | instances that are created. | |
3252 | ||
3253 | The files in the new directory work just like the files with the | |
3254 | same name in the tracing directory except the buffer that is used | |
3255 | is a separate and new buffer. The files affect that buffer but do not | |
3256 | affect the main buffer with the exception of trace_options. Currently, | |
3257 | the trace_options affect all instances and the top level buffer | |
3258 | the same, but this may change in future releases. That is, options | |
3259 | may become specific to the instance they reside in. | |
3260 | ||
3261 | Notice that none of the function tracer files are there, nor is | |
3262 | current_tracer and available_tracers. This is because the buffers | |
3263 | can currently only have events enabled for them. | |
3264 | :: | |
3265 | ||
3266 | # mkdir instances/foo | |
3267 | # mkdir instances/bar | |
3268 | # mkdir instances/zoot | |
3269 | # echo 100000 > buffer_size_kb | |
3270 | # echo 1000 > instances/foo/buffer_size_kb | |
3271 | # echo 5000 > instances/bar/per_cpu/cpu1/buffer_size_kb | |
3272 | # echo function > current_trace | |
3273 | # echo 1 > instances/foo/events/sched/sched_wakeup/enable | |
3274 | # echo 1 > instances/foo/events/sched/sched_wakeup_new/enable | |
3275 | # echo 1 > instances/foo/events/sched/sched_switch/enable | |
3276 | # echo 1 > instances/bar/events/irq/enable | |
3277 | # echo 1 > instances/zoot/events/syscalls/enable | |
3278 | # cat trace_pipe | |
3279 | CPU:2 [LOST 11745 EVENTS] | |
3280 | bash-2044 [002] .... 10594.481032: _raw_spin_lock_irqsave <-get_page_from_freelist | |
3281 | bash-2044 [002] d... 10594.481032: add_preempt_count <-_raw_spin_lock_irqsave | |
3282 | bash-2044 [002] d..1 10594.481032: __rmqueue <-get_page_from_freelist | |
3283 | bash-2044 [002] d..1 10594.481033: _raw_spin_unlock <-get_page_from_freelist | |
3284 | bash-2044 [002] d..1 10594.481033: sub_preempt_count <-_raw_spin_unlock | |
3285 | bash-2044 [002] d... 10594.481033: get_pageblock_flags_group <-get_pageblock_migratetype | |
3286 | bash-2044 [002] d... 10594.481034: __mod_zone_page_state <-get_page_from_freelist | |
3287 | bash-2044 [002] d... 10594.481034: zone_statistics <-get_page_from_freelist | |
3288 | bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics | |
3289 | bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics | |
3290 | bash-2044 [002] .... 10594.481035: arch_dup_task_struct <-copy_process | |
3291 | [...] | |
3292 | ||
3293 | # cat instances/foo/trace_pipe | |
3294 | bash-1998 [000] d..4 136.676759: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000 | |
3295 | bash-1998 [000] dN.4 136.676760: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000 | |
3296 | <idle>-0 [003] d.h3 136.676906: sched_wakeup: comm=rcu_preempt pid=9 prio=120 success=1 target_cpu=003 | |
3297 | <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 | |
3298 | 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 | |
3299 | bash-1998 [000] d..4 136.677014: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000 | |
3300 | bash-1998 [000] dN.4 136.677016: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000 | |
3301 | 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 | |
3302 | kworker/0:1-59 [000] d..4 136.677022: sched_wakeup: comm=sshd pid=1995 prio=120 success=1 target_cpu=001 | |
3303 | 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 | |
3304 | [...] | |
3305 | ||
3306 | # cat instances/bar/trace_pipe | |
3307 | migration/1-14 [001] d.h3 138.732674: softirq_raise: vec=3 [action=NET_RX] | |
3308 | <idle>-0 [001] dNh3 138.732725: softirq_raise: vec=3 [action=NET_RX] | |
3309 | bash-1998 [000] d.h1 138.733101: softirq_raise: vec=1 [action=TIMER] | |
3310 | bash-1998 [000] d.h1 138.733102: softirq_raise: vec=9 [action=RCU] | |
3311 | bash-1998 [000] ..s2 138.733105: softirq_entry: vec=1 [action=TIMER] | |
3312 | bash-1998 [000] ..s2 138.733106: softirq_exit: vec=1 [action=TIMER] | |
3313 | bash-1998 [000] ..s2 138.733106: softirq_entry: vec=9 [action=RCU] | |
3314 | bash-1998 [000] ..s2 138.733109: softirq_exit: vec=9 [action=RCU] | |
3315 | sshd-1995 [001] d.h1 138.733278: irq_handler_entry: irq=21 name=uhci_hcd:usb4 | |
3316 | sshd-1995 [001] d.h1 138.733280: irq_handler_exit: irq=21 ret=unhandled | |
3317 | sshd-1995 [001] d.h1 138.733281: irq_handler_entry: irq=21 name=eth0 | |
3318 | sshd-1995 [001] d.h1 138.733283: irq_handler_exit: irq=21 ret=handled | |
3319 | [...] | |
3320 | ||
3321 | # cat instances/zoot/trace | |
3322 | # tracer: nop | |
3323 | # | |
3324 | # entries-in-buffer/entries-written: 18996/18996 #P:4 | |
3325 | # | |
3326 | # _-----=> irqs-off | |
3327 | # / _----=> need-resched | |
3328 | # | / _---=> hardirq/softirq | |
3329 | # || / _--=> preempt-depth | |
3330 | # ||| / delay | |
3331 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
3332 | # | | | |||| | | | |
3333 | bash-1998 [000] d... 140.733501: sys_write -> 0x2 | |
3334 | bash-1998 [000] d... 140.733504: sys_dup2(oldfd: a, newfd: 1) | |
3335 | bash-1998 [000] d... 140.733506: sys_dup2 -> 0x1 | |
3336 | bash-1998 [000] d... 140.733508: sys_fcntl(fd: a, cmd: 1, arg: 0) | |
3337 | bash-1998 [000] d... 140.733509: sys_fcntl -> 0x1 | |
3338 | bash-1998 [000] d... 140.733510: sys_close(fd: a) | |
3339 | bash-1998 [000] d... 140.733510: sys_close -> 0x0 | |
3340 | bash-1998 [000] d... 140.733514: sys_rt_sigprocmask(how: 0, nset: 0, oset: 6e2768, sigsetsize: 8) | |
3341 | bash-1998 [000] d... 140.733515: sys_rt_sigprocmask -> 0x0 | |
3342 | bash-1998 [000] d... 140.733516: sys_rt_sigaction(sig: 2, act: 7fff718846f0, oact: 7fff71884650, sigsetsize: 8) | |
3343 | bash-1998 [000] d... 140.733516: sys_rt_sigaction -> 0x0 | |
3344 | ||
3345 | You can see that the trace of the top most trace buffer shows only | |
3346 | the function tracing. The foo instance displays wakeups and task | |
3347 | switches. | |
3348 | ||
3349 | To remove the instances, simply delete their directories: | |
3350 | :: | |
3351 | ||
3352 | # rmdir instances/foo | |
3353 | # rmdir instances/bar | |
3354 | # rmdir instances/zoot | |
3355 | ||
3356 | Note, if a process has a trace file open in one of the instance | |
3357 | directories, the rmdir will fail with EBUSY. | |
3358 | ||
3359 | ||
3360 | Stack trace | |
3361 | ----------- | |
3362 | Since the kernel has a fixed sized stack, it is important not to | |
3363 | waste it in functions. A kernel developer must be conscience of | |
3364 | what they allocate on the stack. If they add too much, the system | |
3365 | can be in danger of a stack overflow, and corruption will occur, | |
3366 | usually leading to a system panic. | |
3367 | ||
3368 | There are some tools that check this, usually with interrupts | |
3369 | periodically checking usage. But if you can perform a check | |
3370 | at every function call that will become very useful. As ftrace provides | |
3371 | a function tracer, it makes it convenient to check the stack size | |
3372 | at every function call. This is enabled via the stack tracer. | |
3373 | ||
3374 | CONFIG_STACK_TRACER enables the ftrace stack tracing functionality. | |
3375 | To enable it, write a '1' into /proc/sys/kernel/stack_tracer_enabled. | |
3376 | :: | |
3377 | ||
3378 | # echo 1 > /proc/sys/kernel/stack_tracer_enabled | |
3379 | ||
3380 | You can also enable it from the kernel command line to trace | |
3381 | the stack size of the kernel during boot up, by adding "stacktrace" | |
3382 | to the kernel command line parameter. | |
3383 | ||
3384 | After running it for a few minutes, the output looks like: | |
3385 | :: | |
3386 | ||
3387 | # cat stack_max_size | |
3388 | 2928 | |
3389 | ||
3390 | # cat stack_trace | |
3391 | Depth Size Location (18 entries) | |
3392 | ----- ---- -------- | |
3393 | 0) 2928 224 update_sd_lb_stats+0xbc/0x4ac | |
3394 | 1) 2704 160 find_busiest_group+0x31/0x1f1 | |
3395 | 2) 2544 256 load_balance+0xd9/0x662 | |
3396 | 3) 2288 80 idle_balance+0xbb/0x130 | |
3397 | 4) 2208 128 __schedule+0x26e/0x5b9 | |
3398 | 5) 2080 16 schedule+0x64/0x66 | |
3399 | 6) 2064 128 schedule_timeout+0x34/0xe0 | |
3400 | 7) 1936 112 wait_for_common+0x97/0xf1 | |
3401 | 8) 1824 16 wait_for_completion+0x1d/0x1f | |
3402 | 9) 1808 128 flush_work+0xfe/0x119 | |
3403 | 10) 1680 16 tty_flush_to_ldisc+0x1e/0x20 | |
3404 | 11) 1664 48 input_available_p+0x1d/0x5c | |
3405 | 12) 1616 48 n_tty_poll+0x6d/0x134 | |
3406 | 13) 1568 64 tty_poll+0x64/0x7f | |
3407 | 14) 1504 880 do_select+0x31e/0x511 | |
3408 | 15) 624 400 core_sys_select+0x177/0x216 | |
3409 | 16) 224 96 sys_select+0x91/0xb9 | |
3410 | 17) 128 128 system_call_fastpath+0x16/0x1b | |
3411 | ||
3412 | Note, if -mfentry is being used by gcc, functions get traced before | |
3413 | they set up the stack frame. This means that leaf level functions | |
3414 | are not tested by the stack tracer when -mfentry is used. | |
3415 | ||
3416 | Currently, -mfentry is used by gcc 4.6.0 and above on x86 only. | |
3417 | ||
3418 | More | |
3419 | ---- | |
3420 | More details can be found in the source code, in the `kernel/trace/*.c` files. |