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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 | ||
3e28c5ca | 37 | See events.rst for more information. |
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38 | |
39 | ||
40 | Implementation Details | |
41 | ---------------------- | |
42 | ||
81a2d578 | 43 | See Documentation/trace/ftrace-design.rst for details for arch porters and such. |
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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 | |
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98 | that is configured. Changing the current tracer clears |
99 | the ring buffer content as well as the "snapshot" buffer. | |
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100 | |
101 | available_tracers: | |
102 | ||
103 | This holds the different types of tracers that | |
104 | have been compiled into the kernel. The | |
105 | tracers listed here can be configured by | |
106 | echoing their name into current_tracer. | |
107 | ||
108 | tracing_on: | |
109 | ||
110 | This sets or displays whether writing to the trace | |
111 | ring buffer is enabled. Echo 0 into this file to disable | |
112 | the tracer or 1 to enable it. Note, this only disables | |
113 | writing to the ring buffer, the tracing overhead may | |
114 | still be occurring. | |
115 | ||
116 | The kernel function tracing_off() can be used within the | |
117 | kernel to disable writing to the ring buffer, which will | |
118 | set this file to "0". User space can re-enable tracing by | |
119 | echoing "1" into the file. | |
120 | ||
121 | Note, the function and event trigger "traceoff" will also | |
122 | set this file to zero and stop tracing. Which can also | |
123 | be re-enabled by user space using this file. | |
124 | ||
125 | trace: | |
126 | ||
127 | This file holds the output of the trace in a human | |
8a815e6b | 128 | readable format (described below). Opening this file for |
d693b288 | 129 | writing with the O_TRUNC flag clears the ring buffer content. |
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130 | Note, this file is not a consumer. If tracing is off |
131 | (no tracer running, or tracing_on is zero), it will produce | |
132 | the same output each time it is read. When tracing is on, | |
133 | it may produce inconsistent results as it tries to read | |
134 | the entire buffer without consuming it. | |
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135 | |
136 | trace_pipe: | |
137 | ||
138 | The output is the same as the "trace" file but this | |
139 | file is meant to be streamed with live tracing. | |
140 | Reads from this file will block until new data is | |
141 | retrieved. Unlike the "trace" file, this file is a | |
142 | consumer. This means reading from this file causes | |
143 | sequential reads to display more current data. Once | |
144 | data is read from this file, it is consumed, and | |
145 | will not be read again with a sequential read. The | |
146 | "trace" file is static, and if the tracer is not | |
147 | adding more data, it will display the same | |
8a815e6b | 148 | information every time it is read. |
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149 | |
150 | trace_options: | |
151 | ||
152 | This file lets the user control the amount of data | |
153 | that is displayed in one of the above output | |
154 | files. Options also exist to modify how a tracer | |
155 | or events work (stack traces, timestamps, etc). | |
156 | ||
157 | options: | |
158 | ||
159 | This is a directory that has a file for every available | |
160 | trace option (also in trace_options). Options may also be set | |
161 | or cleared by writing a "1" or "0" respectively into the | |
162 | corresponding file with the option name. | |
163 | ||
164 | tracing_max_latency: | |
165 | ||
166 | Some of the tracers record the max latency. | |
167 | For example, the maximum time that interrupts are disabled. | |
168 | The maximum time is saved in this file. The max trace will also be | |
169 | stored, and displayed by "trace". A new max trace will only be | |
170 | recorded if the latency is greater than the value in this file | |
171 | (in microseconds). | |
172 | ||
173 | By echoing in a time into this file, no latency will be recorded | |
174 | unless it is greater than the time in this file. | |
175 | ||
176 | tracing_thresh: | |
177 | ||
178 | Some latency tracers will record a trace whenever the | |
179 | latency is greater than the number in this file. | |
180 | Only active when the file contains a number greater than 0. | |
181 | (in microseconds) | |
182 | ||
183 | buffer_size_kb: | |
184 | ||
185 | This sets or displays the number of kilobytes each CPU | |
186 | buffer holds. By default, the trace buffers are the same size | |
187 | for each CPU. The displayed number is the size of the | |
188 | CPU buffer and not total size of all buffers. The | |
189 | trace buffers are allocated in pages (blocks of memory | |
190 | that the kernel uses for allocation, usually 4 KB in size). | |
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191 | A few extra pages may be allocated to accommodate buffer management |
192 | meta-data. If the last page allocated has room for more bytes | |
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193 | than requested, the rest of the page will be used, |
194 | making the actual allocation bigger than requested or shown. | |
195 | ( Note, the size may not be a multiple of the page size | |
196 | due to buffer management meta-data. ) | |
197 | ||
198 | Buffer sizes for individual CPUs may vary | |
199 | (see "per_cpu/cpu0/buffer_size_kb" below), and if they do | |
200 | this file will show "X". | |
201 | ||
202 | buffer_total_size_kb: | |
203 | ||
204 | This displays the total combined size of all the trace buffers. | |
205 | ||
206 | free_buffer: | |
207 | ||
208 | If a process is performing tracing, and the ring buffer should be | |
209 | shrunk "freed" when the process is finished, even if it were to be | |
210 | killed by a signal, this file can be used for that purpose. On close | |
211 | of this file, the ring buffer will be resized to its minimum size. | |
212 | Having a process that is tracing also open this file, when the process | |
213 | exits its file descriptor for this file will be closed, and in doing so, | |
214 | the ring buffer will be "freed". | |
215 | ||
216 | It may also stop tracing if disable_on_free option is set. | |
217 | ||
218 | tracing_cpumask: | |
219 | ||
220 | This is a mask that lets the user only trace on specified CPUs. | |
221 | The format is a hex string representing the CPUs. | |
222 | ||
223 | set_ftrace_filter: | |
224 | ||
225 | When dynamic ftrace is configured in (see the | |
226 | section below "dynamic ftrace"), the code is dynamically | |
227 | modified (code text rewrite) to disable calling of the | |
228 | function profiler (mcount). This lets tracing be configured | |
229 | in with practically no overhead in performance. This also | |
230 | has a side effect of enabling or disabling specific functions | |
231 | to be traced. Echoing names of functions into this file | |
232 | will limit the trace to only those functions. | |
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233 | This influences the tracers "function" and "function_graph" |
234 | and thus also function profiling (see "function_profile_enabled"). | |
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235 | |
236 | The functions listed in "available_filter_functions" are what | |
237 | can be written into this file. | |
238 | ||
239 | This interface also allows for commands to be used. See the | |
240 | "Filter commands" section for more details. | |
241 | ||
5b8914a6 | 242 | As a speed up, since processing strings can be quite expensive |
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243 | and requires a check of all functions registered to tracing, instead |
244 | an index can be written into this file. A number (starting with "1") | |
245 | written will instead select the same corresponding at the line position | |
246 | of the "available_filter_functions" file. | |
247 | ||
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248 | set_ftrace_notrace: |
249 | ||
250 | This has an effect opposite to that of | |
251 | set_ftrace_filter. Any function that is added here will not | |
252 | be traced. If a function exists in both set_ftrace_filter | |
253 | and set_ftrace_notrace, the function will _not_ be traced. | |
254 | ||
255 | set_ftrace_pid: | |
256 | ||
257 | Have the function tracer only trace the threads whose PID are | |
258 | listed in this file. | |
259 | ||
260 | If the "function-fork" option is set, then when a task whose | |
261 | PID is listed in this file forks, the child's PID will | |
262 | automatically be added to this file, and the child will be | |
263 | traced by the function tracer as well. This option will also | |
264 | cause PIDs of tasks that exit to be removed from the file. | |
265 | ||
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266 | set_ftrace_notrace_pid: |
267 | ||
268 | Have the function tracer ignore threads whose PID are listed in | |
269 | this file. | |
270 | ||
271 | If the "function-fork" option is set, then when a task whose | |
272 | PID is listed in this file forks, the child's PID will | |
273 | automatically be added to this file, and the child will not be | |
274 | traced by the function tracer as well. This option will also | |
275 | cause PIDs of tasks that exit to be removed from the file. | |
276 | ||
277 | If a PID is in both this file and "set_ftrace_pid", then this | |
278 | file takes precedence, and the thread will not be traced. | |
279 | ||
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280 | set_event_pid: |
281 | ||
282 | Have the events only trace a task with a PID listed in this file. | |
283 | Note, sched_switch and sched_wake_up will also trace events | |
284 | listed in this file. | |
285 | ||
286 | To have the PIDs of children of tasks with their PID in this file | |
287 | added on fork, enable the "event-fork" option. That option will also | |
288 | cause the PIDs of tasks to be removed from this file when the task | |
289 | exits. | |
290 | ||
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291 | set_event_notrace_pid: |
292 | ||
293 | Have the events not trace a task with a PID listed in this file. | |
294 | Note, sched_switch and sched_wakeup will trace threads not listed | |
295 | in this file, even if a thread's PID is in the file if the | |
296 | sched_switch or sched_wakeup events also trace a thread that should | |
297 | be traced. | |
298 | ||
299 | To have the PIDs of children of tasks with their PID in this file | |
300 | added on fork, enable the "event-fork" option. That option will also | |
301 | cause the PIDs of tasks to be removed from this file when the task | |
302 | exits. | |
303 | ||
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304 | set_graph_function: |
305 | ||
306 | Functions listed in this file will cause the function graph | |
307 | tracer to only trace these functions and the functions that | |
308 | they call. (See the section "dynamic ftrace" for more details). | |
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309 | Note, set_ftrace_filter and set_ftrace_notrace still affects |
310 | what functions are being traced. | |
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311 | |
312 | set_graph_notrace: | |
313 | ||
314 | Similar to set_graph_function, but will disable function graph | |
315 | tracing when the function is hit until it exits the function. | |
316 | This makes it possible to ignore tracing functions that are called | |
317 | by a specific function. | |
318 | ||
319 | available_filter_functions: | |
320 | ||
321 | This lists the functions that ftrace has processed and can trace. | |
322 | These are the function names that you can pass to | |
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323 | "set_ftrace_filter", "set_ftrace_notrace", |
324 | "set_graph_function", or "set_graph_notrace". | |
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325 | (See the section "dynamic ftrace" below for more details.) |
326 | ||
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327 | available_filter_functions_addrs: |
328 | ||
329 | Similar to available_filter_functions, but with address displayed | |
330 | for each function. The displayed address is the patch-site address | |
331 | and can differ from /proc/kallsyms address. | |
332 | ||
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333 | dyn_ftrace_total_info: |
334 | ||
335 | This file is for debugging purposes. The number of functions that | |
336 | have been converted to nops and are available to be traced. | |
337 | ||
338 | enabled_functions: | |
339 | ||
340 | This file is more for debugging ftrace, but can also be useful | |
341 | in seeing if any function has a callback attached to it. | |
342 | Not only does the trace infrastructure use ftrace function | |
343 | trace utility, but other subsystems might too. This file | |
344 | displays all functions that have a callback attached to them | |
345 | as well as the number of callbacks that have been attached. | |
346 | Note, a callback may also call multiple functions which will | |
347 | not be listed in this count. | |
348 | ||
349 | If the callback registered to be traced by a function with | |
350 | the "save regs" attribute (thus even more overhead), a 'R' | |
351 | will be displayed on the same line as the function that | |
352 | is returning registers. | |
353 | ||
354 | If the callback registered to be traced by a function with | |
355 | the "ip modify" attribute (thus the regs->ip can be changed), | |
356 | an 'I' will be displayed on the same line as the function that | |
357 | can be overridden. | |
358 | ||
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359 | If a non ftrace trampoline is attached (BPF) a 'D' will be displayed. |
360 | Note, normal ftrace trampolines can also be attached, but only one | |
361 | "direct" trampoline can be attached to a given function at a time. | |
362 | ||
363 | Some architectures can not call direct trampolines, but instead have | |
364 | the ftrace ops function located above the function entry point. In | |
365 | such cases an 'O' will be displayed. | |
366 | ||
367 | If a function had either the "ip modify" or a "direct" call attached to | |
368 | it in the past, a 'M' will be shown. This flag is never cleared. It is | |
369 | used to know if a function was every modified by the ftrace infrastructure, | |
370 | and can be used for debugging. | |
371 | ||
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372 | If the architecture supports it, it will also show what callback |
373 | is being directly called by the function. If the count is greater | |
374 | than 1 it most likely will be ftrace_ops_list_func(). | |
375 | ||
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376 | If the callback of a function jumps to a trampoline that is |
377 | specific to the callback and which is not the standard trampoline, | |
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378 | its address will be printed as well as the function that the |
379 | trampoline calls. | |
380 | ||
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381 | touched_functions: |
382 | ||
383 | This file contains all the functions that ever had a function callback | |
384 | to it via the ftrace infrastructure. It has the same format as | |
385 | enabled_functions but shows all functions that have every been | |
386 | traced. | |
387 | ||
388 | To see any function that has every been modified by "ip modify" or a | |
389 | direct trampoline, one can perform the following command: | |
390 | ||
391 | grep ' M ' /sys/kernel/tracing/touched_functions | |
392 | ||
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393 | function_profile_enabled: |
394 | ||
395 | When set it will enable all functions with either the function | |
396 | tracer, or if configured, the function graph tracer. It will | |
397 | keep a histogram of the number of functions that were called | |
398 | and if the function graph tracer was configured, it will also keep | |
399 | track of the time spent in those functions. The histogram | |
400 | content can be displayed in the files: | |
401 | ||
1fee4f77 | 402 | trace_stat/function<cpu> ( function0, function1, etc). |
1f198e22 | 403 | |
1fee4f77 | 404 | trace_stat: |
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405 | |
406 | A directory that holds different tracing stats. | |
407 | ||
408 | kprobe_events: | |
409 | ||
3e28c5ca | 410 | Enable dynamic trace points. See kprobetrace.rst. |
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411 | |
412 | kprobe_profile: | |
413 | ||
3e28c5ca | 414 | Dynamic trace points stats. See kprobetrace.rst. |
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415 | |
416 | max_graph_depth: | |
417 | ||
418 | Used with the function graph tracer. This is the max depth | |
419 | it will trace into a function. Setting this to a value of | |
420 | one will show only the first kernel function that is called | |
421 | from user space. | |
422 | ||
423 | printk_formats: | |
424 | ||
425 | This is for tools that read the raw format files. If an event in | |
426 | the ring buffer references a string, only a pointer to the string | |
427 | is recorded into the buffer and not the string itself. This prevents | |
428 | tools from knowing what that string was. This file displays the string | |
429 | and address for the string allowing tools to map the pointers to what | |
430 | the strings were. | |
431 | ||
432 | saved_cmdlines: | |
433 | ||
434 | Only the pid of the task is recorded in a trace event unless | |
435 | the event specifically saves the task comm as well. Ftrace | |
436 | makes a cache of pid mappings to comms to try to display | |
437 | comms for events. If a pid for a comm is not listed, then | |
438 | "<...>" is displayed in the output. | |
439 | ||
440 | If the option "record-cmd" is set to "0", then comms of tasks | |
441 | will not be saved during recording. By default, it is enabled. | |
442 | ||
443 | saved_cmdlines_size: | |
444 | ||
445 | By default, 128 comms are saved (see "saved_cmdlines" above). To | |
446 | increase or decrease the amount of comms that are cached, echo | |
5b8914a6 | 447 | the number of comms to cache into this file. |
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448 | |
449 | saved_tgids: | |
450 | ||
451 | If the option "record-tgid" is set, on each scheduling context switch | |
452 | the Task Group ID of a task is saved in a table mapping the PID of | |
453 | the thread to its TGID. By default, the "record-tgid" option is | |
454 | disabled. | |
455 | ||
456 | snapshot: | |
457 | ||
458 | This displays the "snapshot" buffer and also lets the user | |
459 | take a snapshot of the current running trace. | |
460 | See the "Snapshot" section below for more details. | |
461 | ||
462 | stack_max_size: | |
463 | ||
464 | When the stack tracer is activated, this will display the | |
465 | maximum stack size it has encountered. | |
466 | See the "Stack Trace" section below. | |
467 | ||
468 | stack_trace: | |
469 | ||
470 | This displays the stack back trace of the largest stack | |
471 | that was encountered when the stack tracer is activated. | |
472 | See the "Stack Trace" section below. | |
473 | ||
474 | stack_trace_filter: | |
475 | ||
476 | This is similar to "set_ftrace_filter" but it limits what | |
477 | functions the stack tracer will check. | |
478 | ||
479 | trace_clock: | |
480 | ||
481 | Whenever an event is recorded into the ring buffer, a | |
482 | "timestamp" is added. This stamp comes from a specified | |
483 | clock. By default, ftrace uses the "local" clock. This | |
484 | clock is very fast and strictly per cpu, but on some | |
485 | systems it may not be monotonic with respect to other | |
486 | CPUs. In other words, the local clocks may not be in sync | |
487 | with local clocks on other CPUs. | |
488 | ||
489 | Usual clocks for tracing:: | |
490 | ||
491 | # cat trace_clock | |
492 | [local] global counter x86-tsc | |
493 | ||
494 | The clock with the square brackets around it is the one in effect. | |
495 | ||
496 | local: | |
497 | Default clock, but may not be in sync across CPUs | |
498 | ||
499 | global: | |
500 | This clock is in sync with all CPUs but may | |
501 | be a bit slower than the local clock. | |
502 | ||
503 | counter: | |
504 | This is not a clock at all, but literally an atomic | |
505 | counter. It counts up one by one, but is in sync | |
506 | with all CPUs. This is useful when you need to | |
507 | know exactly the order events occurred with respect to | |
508 | each other on different CPUs. | |
509 | ||
510 | uptime: | |
511 | This uses the jiffies counter and the time stamp | |
512 | is relative to the time since boot up. | |
513 | ||
514 | perf: | |
515 | This makes ftrace use the same clock that perf uses. | |
516 | Eventually perf will be able to read ftrace buffers | |
517 | and this will help out in interleaving the data. | |
518 | ||
519 | x86-tsc: | |
520 | Architectures may define their own clocks. For | |
521 | example, x86 uses its own TSC cycle clock here. | |
522 | ||
523 | ppc-tb: | |
524 | This uses the powerpc timebase register value. | |
525 | This is in sync across CPUs and can also be used | |
526 | to correlate events across hypervisor/guest if | |
527 | tb_offset is known. | |
528 | ||
529 | mono: | |
530 | This uses the fast monotonic clock (CLOCK_MONOTONIC) | |
531 | which is monotonic and is subject to NTP rate adjustments. | |
532 | ||
533 | mono_raw: | |
534 | This is the raw monotonic clock (CLOCK_MONOTONIC_RAW) | |
2a1e03ca | 535 | which is monotonic but is not subject to any rate adjustments |
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536 | and ticks at the same rate as the hardware clocksource. |
537 | ||
538 | boot: | |
a3ed0e43 TG |
539 | This is the boot clock (CLOCK_BOOTTIME) and is based on the |
540 | fast monotonic clock, but also accounts for time spent in | |
541 | suspend. Since the clock access is designed for use in | |
542 | tracing in the suspend path, some side effects are possible | |
543 | if clock is accessed after the suspend time is accounted before | |
544 | the fast mono clock is updated. In this case, the clock update | |
545 | appears to happen slightly sooner than it normally would have. | |
546 | Also on 32-bit systems, it's possible that the 64-bit boot offset | |
547 | sees a partial update. These effects are rare and post | |
548 | processing should be able to handle them. See comments in the | |
549 | ktime_get_boot_fast_ns() function for more information. | |
680014d6 | 550 | |
4d1257bb KK |
551 | tai: |
552 | This is the tai clock (CLOCK_TAI) and is derived from the wall- | |
553 | clock time. However, this clock does not experience | |
554 | discontinuities and backwards jumps caused by NTP inserting leap | |
555 | seconds. Since the clock access is designed for use in tracing, | |
556 | side effects are possible. The clock access may yield wrong | |
557 | readouts in case the internal TAI offset is updated e.g., caused | |
558 | by setting the system time or using adjtimex() with an offset. | |
559 | These effects are rare and post processing should be able to | |
560 | handle them. See comments in the ktime_get_tai_fast_ns() | |
561 | function for more information. | |
562 | ||
680014d6 LT |
563 | To set a clock, simply echo the clock name into this file:: |
564 | ||
565 | # echo global > trace_clock | |
1f198e22 | 566 | |
d693b288 FCB |
567 | Setting a clock clears the ring buffer content as well as the |
568 | "snapshot" buffer. | |
569 | ||
1f198e22 CD |
570 | trace_marker: |
571 | ||
572 | This is a very useful file for synchronizing user space | |
573 | with events happening in the kernel. Writing strings into | |
574 | this file will be written into the ftrace buffer. | |
575 | ||
576 | It is useful in applications to open this file at the start | |
577 | of the application and just reference the file descriptor | |
578 | for the file:: | |
579 | ||
580 | void trace_write(const char *fmt, ...) | |
581 | { | |
582 | va_list ap; | |
583 | char buf[256]; | |
584 | int n; | |
585 | ||
586 | if (trace_fd < 0) | |
587 | return; | |
588 | ||
589 | va_start(ap, fmt); | |
590 | n = vsnprintf(buf, 256, fmt, ap); | |
591 | va_end(ap); | |
592 | ||
593 | write(trace_fd, buf, n); | |
594 | } | |
595 | ||
596 | start:: | |
597 | ||
9c1ab6d5 | 598 | trace_fd = open("trace_marker", O_WRONLY); |
1f198e22 | 599 | |
d3439f9d SRV |
600 | Note: Writing into the trace_marker file can also initiate triggers |
601 | that are written into /sys/kernel/tracing/events/ftrace/print/trigger | |
602 | See "Event triggers" in Documentation/trace/events.rst and an | |
603 | example in Documentation/trace/histogram.rst (Section 3.) | |
604 | ||
1f198e22 CD |
605 | trace_marker_raw: |
606 | ||
1747db54 | 607 | This is similar to trace_marker above, but is meant for binary data |
1f198e22 CD |
608 | to be written to it, where a tool can be used to parse the data |
609 | from trace_pipe_raw. | |
610 | ||
611 | uprobe_events: | |
612 | ||
613 | Add dynamic tracepoints in programs. | |
3e28c5ca | 614 | See uprobetracer.rst |
1f198e22 CD |
615 | |
616 | uprobe_profile: | |
617 | ||
618 | Uprobe statistics. See uprobetrace.txt | |
619 | ||
620 | instances: | |
621 | ||
622 | This is a way to make multiple trace buffers where different | |
623 | events can be recorded in different buffers. | |
624 | See "Instances" section below. | |
625 | ||
626 | events: | |
627 | ||
628 | This is the trace event directory. It holds event tracepoints | |
629 | (also known as static tracepoints) that have been compiled | |
630 | into the kernel. It shows what event tracepoints exist | |
631 | and how they are grouped by system. There are "enable" | |
632 | files at various levels that can enable the tracepoints | |
633 | when a "1" is written to them. | |
634 | ||
3e28c5ca | 635 | See events.rst for more information. |
1f198e22 CD |
636 | |
637 | set_event: | |
638 | ||
639 | By echoing in the event into this file, will enable that event. | |
640 | ||
3e28c5ca | 641 | See events.rst for more information. |
1f198e22 CD |
642 | |
643 | available_events: | |
644 | ||
645 | A list of events that can be enabled in tracing. | |
646 | ||
3e28c5ca | 647 | See events.rst for more information. |
1f198e22 | 648 | |
2a56bb59 LT |
649 | timestamp_mode: |
650 | ||
651 | Certain tracers may change the timestamp mode used when | |
652 | logging trace events into the event buffer. Events with | |
653 | different modes can coexist within a buffer but the mode in | |
654 | effect when an event is logged determines which timestamp mode | |
655 | is used for that event. The default timestamp mode is | |
656 | 'delta'. | |
657 | ||
658 | Usual timestamp modes for tracing: | |
659 | ||
660 | # cat timestamp_mode | |
661 | [delta] absolute | |
662 | ||
663 | The timestamp mode with the square brackets around it is the | |
664 | one in effect. | |
665 | ||
666 | delta: Default timestamp mode - timestamp is a delta against | |
667 | a per-buffer timestamp. | |
668 | ||
669 | absolute: The timestamp is a full timestamp, not a delta | |
670 | against some other value. As such it takes up more | |
671 | space and is less efficient. | |
672 | ||
1f198e22 CD |
673 | hwlat_detector: |
674 | ||
675 | Directory for the Hardware Latency Detector. | |
676 | See "Hardware Latency Detector" section below. | |
677 | ||
678 | per_cpu: | |
679 | ||
680 | This is a directory that contains the trace per_cpu information. | |
681 | ||
682 | per_cpu/cpu0/buffer_size_kb: | |
683 | ||
684 | The ftrace buffer is defined per_cpu. That is, there's a separate | |
685 | buffer for each CPU to allow writes to be done atomically, | |
686 | and free from cache bouncing. These buffers may have different | |
687 | size buffers. This file is similar to the buffer_size_kb | |
688 | file, but it only displays or sets the buffer size for the | |
689 | specific CPU. (here cpu0). | |
690 | ||
691 | per_cpu/cpu0/trace: | |
692 | ||
693 | This is similar to the "trace" file, but it will only display | |
694 | the data specific for the CPU. If written to, it only clears | |
695 | the specific CPU buffer. | |
696 | ||
697 | per_cpu/cpu0/trace_pipe | |
698 | ||
699 | This is similar to the "trace_pipe" file, and is a consuming | |
700 | read, but it will only display (and consume) the data specific | |
701 | for the CPU. | |
702 | ||
703 | per_cpu/cpu0/trace_pipe_raw | |
704 | ||
705 | For tools that can parse the ftrace ring buffer binary format, | |
706 | the trace_pipe_raw file can be used to extract the data | |
707 | from the ring buffer directly. With the use of the splice() | |
708 | system call, the buffer data can be quickly transferred to | |
709 | a file or to the network where a server is collecting the | |
710 | data. | |
711 | ||
712 | Like trace_pipe, this is a consuming reader, where multiple | |
713 | reads will always produce different data. | |
714 | ||
715 | per_cpu/cpu0/snapshot: | |
716 | ||
717 | This is similar to the main "snapshot" file, but will only | |
718 | snapshot the current CPU (if supported). It only displays | |
719 | the content of the snapshot for a given CPU, and if | |
720 | written to, only clears this CPU buffer. | |
721 | ||
722 | per_cpu/cpu0/snapshot_raw: | |
723 | ||
724 | Similar to the trace_pipe_raw, but will read the binary format | |
725 | from the snapshot buffer for the given CPU. | |
726 | ||
727 | per_cpu/cpu0/stats: | |
728 | ||
729 | This displays certain stats about the ring buffer: | |
730 | ||
731 | entries: | |
732 | The number of events that are still in the buffer. | |
733 | ||
734 | overrun: | |
735 | The number of lost events due to overwriting when | |
736 | the buffer was full. | |
737 | ||
738 | commit overrun: | |
739 | Should always be zero. | |
740 | This gets set if so many events happened within a nested | |
741 | event (ring buffer is re-entrant), that it fills the | |
742 | buffer and starts dropping events. | |
743 | ||
744 | bytes: | |
745 | Bytes actually read (not overwritten). | |
746 | ||
747 | oldest event ts: | |
748 | The oldest timestamp in the buffer | |
749 | ||
750 | now ts: | |
751 | The current timestamp | |
752 | ||
753 | dropped events: | |
754 | Events lost due to overwrite option being off. | |
755 | ||
756 | read events: | |
757 | The number of events read. | |
758 | ||
759 | The Tracers | |
760 | ----------- | |
761 | ||
762 | Here is the list of current tracers that may be configured. | |
763 | ||
764 | "function" | |
765 | ||
766 | Function call tracer to trace all kernel functions. | |
767 | ||
768 | "function_graph" | |
769 | ||
770 | Similar to the function tracer except that the | |
771 | function tracer probes the functions on their entry | |
772 | whereas the function graph tracer traces on both entry | |
773 | and exit of the functions. It then provides the ability | |
774 | to draw a graph of function calls similar to C code | |
775 | source. | |
776 | ||
777 | "blk" | |
778 | ||
779 | The block tracer. The tracer used by the blktrace user | |
780 | application. | |
781 | ||
782 | "hwlat" | |
783 | ||
784 | The Hardware Latency tracer is used to detect if the hardware | |
785 | produces any latency. See "Hardware Latency Detector" section | |
786 | below. | |
787 | ||
788 | "irqsoff" | |
789 | ||
790 | Traces the areas that disable interrupts and saves | |
791 | the trace with the longest max latency. | |
792 | See tracing_max_latency. When a new max is recorded, | |
793 | it replaces the old trace. It is best to view this | |
794 | trace with the latency-format option enabled, which | |
795 | happens automatically when the tracer is selected. | |
796 | ||
797 | "preemptoff" | |
798 | ||
799 | Similar to irqsoff but traces and records the amount of | |
800 | time for which preemption is disabled. | |
801 | ||
802 | "preemptirqsoff" | |
803 | ||
804 | Similar to irqsoff and preemptoff, but traces and | |
805 | records the largest time for which irqs and/or preemption | |
806 | is disabled. | |
807 | ||
808 | "wakeup" | |
809 | ||
810 | Traces and records the max latency that it takes for | |
811 | the highest priority task to get scheduled after | |
812 | it has been woken up. | |
813 | Traces all tasks as an average developer would expect. | |
814 | ||
815 | "wakeup_rt" | |
816 | ||
817 | Traces and records the max latency that it takes for just | |
818 | RT tasks (as the current "wakeup" does). This is useful | |
819 | for those interested in wake up timings of RT tasks. | |
820 | ||
821 | "wakeup_dl" | |
822 | ||
823 | Traces and records the max latency that it takes for | |
824 | a SCHED_DEADLINE task to be woken (as the "wakeup" and | |
825 | "wakeup_rt" does). | |
826 | ||
827 | "mmiotrace" | |
828 | ||
829 | A special tracer that is used to trace binary module. | |
830 | It will trace all the calls that a module makes to the | |
831 | hardware. Everything it writes and reads from the I/O | |
832 | as well. | |
833 | ||
834 | "branch" | |
835 | ||
836 | This tracer can be configured when tracing likely/unlikely | |
837 | calls within the kernel. It will trace when a likely and | |
838 | unlikely branch is hit and if it was correct in its prediction | |
839 | of being correct. | |
840 | ||
841 | "nop" | |
842 | ||
843 | This is the "trace nothing" tracer. To remove all | |
844 | tracers from tracing simply echo "nop" into | |
845 | current_tracer. | |
846 | ||
26a94491 TZ |
847 | Error conditions |
848 | ---------------- | |
849 | ||
850 | For most ftrace commands, failure modes are obvious and communicated | |
851 | using standard return codes. | |
852 | ||
853 | For other more involved commands, extended error information may be | |
854 | available via the tracing/error_log file. For the commands that | |
855 | support it, reading the tracing/error_log file after an error will | |
856 | display more detailed information about what went wrong, if | |
857 | information is available. The tracing/error_log file is a circular | |
858 | error log displaying a small number (currently, 8) of ftrace errors | |
859 | for the last (8) failed commands. | |
860 | ||
861 | The extended error information and usage takes the form shown in | |
862 | this example:: | |
863 | ||
2abfcd29 | 864 | # echo xxx > /sys/kernel/tracing/events/sched/sched_wakeup/trigger |
26a94491 TZ |
865 | echo: write error: Invalid argument |
866 | ||
2abfcd29 | 867 | # cat /sys/kernel/tracing/error_log |
26a94491 TZ |
868 | [ 5348.887237] location: error: Couldn't yyy: zzz |
869 | Command: xxx | |
870 | ^ | |
871 | [ 7517.023364] location: error: Bad rrr: sss | |
872 | Command: ppp qqq | |
873 | ^ | |
874 | ||
875 | To clear the error log, echo the empty string into it:: | |
876 | ||
2abfcd29 | 877 | # echo > /sys/kernel/tracing/error_log |
1f198e22 CD |
878 | |
879 | Examples of using the tracer | |
880 | ---------------------------- | |
881 | ||
882 | Here are typical examples of using the tracers when controlling | |
883 | them only with the tracefs interface (without using any | |
884 | user-land utilities). | |
885 | ||
886 | Output format: | |
887 | -------------- | |
888 | ||
889 | Here is an example of the output format of the file "trace":: | |
890 | ||
891 | # tracer: function | |
892 | # | |
893 | # entries-in-buffer/entries-written: 140080/250280 #P:4 | |
894 | # | |
895 | # _-----=> irqs-off | |
896 | # / _----=> need-resched | |
897 | # | / _---=> hardirq/softirq | |
898 | # || / _--=> preempt-depth | |
899 | # ||| / delay | |
900 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
901 | # | | | |||| | | | |
902 | bash-1977 [000] .... 17284.993652: sys_close <-system_call_fastpath | |
903 | bash-1977 [000] .... 17284.993653: __close_fd <-sys_close | |
904 | bash-1977 [000] .... 17284.993653: _raw_spin_lock <-__close_fd | |
905 | sshd-1974 [003] .... 17284.993653: __srcu_read_unlock <-fsnotify | |
906 | bash-1977 [000] .... 17284.993654: add_preempt_count <-_raw_spin_lock | |
907 | bash-1977 [000] ...1 17284.993655: _raw_spin_unlock <-__close_fd | |
908 | bash-1977 [000] ...1 17284.993656: sub_preempt_count <-_raw_spin_unlock | |
909 | bash-1977 [000] .... 17284.993657: filp_close <-__close_fd | |
910 | bash-1977 [000] .... 17284.993657: dnotify_flush <-filp_close | |
911 | sshd-1974 [003] .... 17284.993658: sys_select <-system_call_fastpath | |
912 | .... | |
913 | ||
914 | A header is printed with the tracer name that is represented by | |
915 | the trace. In this case the tracer is "function". Then it shows the | |
916 | number of events in the buffer as well as the total number of entries | |
917 | that were written. The difference is the number of entries that were | |
918 | lost due to the buffer filling up (250280 - 140080 = 110200 events | |
919 | lost). | |
920 | ||
921 | The header explains the content of the events. Task name "bash", the task | |
922 | PID "1977", the CPU that it was running on "000", the latency format | |
923 | (explained below), the timestamp in <secs>.<usecs> format, the | |
924 | function name that was traced "sys_close" and the parent function that | |
925 | called this function "system_call_fastpath". The timestamp is the time | |
926 | at which the function was entered. | |
927 | ||
928 | Latency trace format | |
929 | -------------------- | |
930 | ||
931 | When the latency-format option is enabled or when one of the latency | |
932 | tracers is set, the trace file gives somewhat more information to see | |
933 | why a latency happened. Here is a typical trace:: | |
934 | ||
935 | # tracer: irqsoff | |
936 | # | |
937 | # irqsoff latency trace v1.1.5 on 3.8.0-test+ | |
938 | # -------------------------------------------------------------------- | |
939 | # latency: 259 us, #4/4, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
940 | # ----------------- | |
941 | # | task: ps-6143 (uid:0 nice:0 policy:0 rt_prio:0) | |
942 | # ----------------- | |
943 | # => started at: __lock_task_sighand | |
944 | # => ended at: _raw_spin_unlock_irqrestore | |
945 | # | |
946 | # | |
947 | # _------=> CPU# | |
948 | # / _-----=> irqs-off | |
949 | # | / _----=> need-resched | |
950 | # || / _---=> hardirq/softirq | |
951 | # ||| / _--=> preempt-depth | |
952 | # |||| / delay | |
953 | # cmd pid ||||| time | caller | |
954 | # \ / ||||| \ | / | |
955 | ps-6143 2d... 0us!: trace_hardirqs_off <-__lock_task_sighand | |
956 | ps-6143 2d..1 259us+: trace_hardirqs_on <-_raw_spin_unlock_irqrestore | |
957 | ps-6143 2d..1 263us+: time_hardirqs_on <-_raw_spin_unlock_irqrestore | |
958 | ps-6143 2d..1 306us : <stack trace> | |
959 | => trace_hardirqs_on_caller | |
960 | => trace_hardirqs_on | |
961 | => _raw_spin_unlock_irqrestore | |
962 | => do_task_stat | |
963 | => proc_tgid_stat | |
964 | => proc_single_show | |
965 | => seq_read | |
966 | => vfs_read | |
967 | => sys_read | |
968 | => system_call_fastpath | |
969 | ||
970 | ||
971 | This shows that the current tracer is "irqsoff" tracing the time | |
972 | for which interrupts were disabled. It gives the trace version (which | |
973 | never changes) and the version of the kernel upon which this was executed on | |
974 | (3.8). Then it displays the max latency in microseconds (259 us). The number | |
975 | of trace entries displayed and the total number (both are four: #4/4). | |
976 | VP, KP, SP, and HP are always zero and are reserved for later use. | |
977 | #P is the number of online CPUs (#P:4). | |
978 | ||
979 | The task is the process that was running when the latency | |
980 | occurred. (ps pid: 6143). | |
981 | ||
982 | The start and stop (the functions in which the interrupts were | |
983 | disabled and enabled respectively) that caused the latencies: | |
984 | ||
985 | - __lock_task_sighand is where the interrupts were disabled. | |
986 | - _raw_spin_unlock_irqrestore is where they were enabled again. | |
987 | ||
988 | The next lines after the header are the trace itself. The header | |
989 | explains which is which. | |
990 | ||
991 | cmd: The name of the process in the trace. | |
992 | ||
993 | pid: The PID of that process. | |
994 | ||
995 | CPU#: The CPU which the process was running on. | |
996 | ||
997 | irqs-off: 'd' interrupts are disabled. '.' otherwise. | |
998 | .. caution:: If the architecture does not support a way to | |
999 | read the irq flags variable, an 'X' will always | |
1000 | be printed here. | |
1001 | ||
1002 | need-resched: | |
1003 | - 'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set, | |
1004 | - 'n' only TIF_NEED_RESCHED is set, | |
1005 | - 'p' only PREEMPT_NEED_RESCHED is set, | |
1006 | - '.' otherwise. | |
1007 | ||
1008 | hardirq/softirq: | |
1009 | - 'Z' - NMI occurred inside a hardirq | |
1010 | - 'z' - NMI is running | |
1011 | - 'H' - hard irq occurred inside a softirq. | |
1012 | - 'h' - hard irq is running | |
1013 | - 's' - soft irq is running | |
1014 | - '.' - normal context. | |
1015 | ||
1016 | preempt-depth: The level of preempt_disabled | |
1017 | ||
1018 | The above is mostly meaningful for kernel developers. | |
1019 | ||
1020 | time: | |
1021 | When the latency-format option is enabled, the trace file | |
1022 | output includes a timestamp relative to the start of the | |
1023 | trace. This differs from the output when latency-format | |
1024 | is disabled, which includes an absolute timestamp. | |
1025 | ||
1026 | delay: | |
1027 | This is just to help catch your eye a bit better. And | |
1028 | needs to be fixed to be only relative to the same CPU. | |
1029 | The marks are determined by the difference between this | |
1030 | current trace and the next trace. | |
1031 | ||
1032 | - '$' - greater than 1 second | |
2a1e03ca AL |
1033 | - '@' - greater than 100 millisecond |
1034 | - '*' - greater than 10 millisecond | |
1f198e22 CD |
1035 | - '#' - greater than 1000 microsecond |
1036 | - '!' - greater than 100 microsecond | |
1037 | - '+' - greater than 10 microsecond | |
1038 | - ' ' - less than or equal to 10 microsecond. | |
1039 | ||
1040 | The rest is the same as the 'trace' file. | |
1041 | ||
1042 | Note, the latency tracers will usually end with a back trace | |
1043 | to easily find where the latency occurred. | |
1044 | ||
1045 | trace_options | |
1046 | ------------- | |
1047 | ||
1048 | The trace_options file (or the options directory) is used to control | |
1049 | what gets printed in the trace output, or manipulate the tracers. | |
1050 | To see what is available, simply cat the file:: | |
1051 | ||
1052 | cat trace_options | |
1053 | print-parent | |
1054 | nosym-offset | |
1055 | nosym-addr | |
1056 | noverbose | |
1057 | noraw | |
1058 | nohex | |
1059 | nobin | |
1060 | noblock | |
80a76994 | 1061 | nofields |
1f198e22 CD |
1062 | trace_printk |
1063 | annotate | |
1064 | nouserstacktrace | |
1065 | nosym-userobj | |
1066 | noprintk-msg-only | |
1067 | context-info | |
1068 | nolatency-format | |
1069 | record-cmd | |
1070 | norecord-tgid | |
1071 | overwrite | |
1072 | nodisable_on_free | |
1073 | irq-info | |
1074 | markers | |
1075 | noevent-fork | |
1076 | function-trace | |
1077 | nofunction-fork | |
1078 | nodisplay-graph | |
1079 | nostacktrace | |
1080 | nobranch | |
1081 | ||
1082 | To disable one of the options, echo in the option prepended with | |
1083 | "no":: | |
1084 | ||
1085 | echo noprint-parent > trace_options | |
1086 | ||
1087 | To enable an option, leave off the "no":: | |
1088 | ||
1089 | echo sym-offset > trace_options | |
1090 | ||
1091 | Here are the available options: | |
1092 | ||
1093 | print-parent | |
1094 | On function traces, display the calling (parent) | |
1095 | function as well as the function being traced. | |
1096 | :: | |
1097 | ||
1098 | print-parent: | |
1099 | bash-4000 [01] 1477.606694: simple_strtoul <-kstrtoul | |
1100 | ||
1101 | noprint-parent: | |
1102 | bash-4000 [01] 1477.606694: simple_strtoul | |
1103 | ||
1104 | ||
1105 | sym-offset | |
1106 | Display not only the function name, but also the | |
1107 | offset in the function. For example, instead of | |
1108 | seeing just "ktime_get", you will see | |
1109 | "ktime_get+0xb/0x20". | |
1110 | :: | |
1111 | ||
1112 | sym-offset: | |
1113 | bash-4000 [01] 1477.606694: simple_strtoul+0x6/0xa0 | |
1114 | ||
1115 | sym-addr | |
1116 | This will also display the function address as well | |
1117 | as the function name. | |
1118 | :: | |
1119 | ||
1120 | sym-addr: | |
1121 | bash-4000 [01] 1477.606694: simple_strtoul <c0339346> | |
1122 | ||
1123 | verbose | |
1124 | This deals with the trace file when the | |
1125 | latency-format option is enabled. | |
1126 | :: | |
1127 | ||
1128 | bash 4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \ | |
1129 | (+0.000ms): simple_strtoul (kstrtoul) | |
1130 | ||
1131 | raw | |
1132 | This will display raw numbers. This option is best for | |
1133 | use with user applications that can translate the raw | |
1134 | numbers better than having it done in the kernel. | |
1135 | ||
1136 | hex | |
1137 | Similar to raw, but the numbers will be in a hexadecimal format. | |
1138 | ||
1139 | bin | |
1140 | This will print out the formats in raw binary. | |
1141 | ||
1142 | block | |
1143 | When set, reading trace_pipe will not block when polled. | |
1144 | ||
80a76994 SRG |
1145 | fields |
1146 | Print the fields as described by their types. This is a better | |
1147 | option than using hex, bin or raw, as it gives a better parsing | |
1148 | of the content of the event. | |
1149 | ||
1f198e22 CD |
1150 | trace_printk |
1151 | Can disable trace_printk() from writing into the buffer. | |
1152 | ||
1153 | annotate | |
1154 | It is sometimes confusing when the CPU buffers are full | |
1155 | and one CPU buffer had a lot of events recently, thus | |
1156 | a shorter time frame, were another CPU may have only had | |
1157 | a few events, which lets it have older events. When | |
1158 | the trace is reported, it shows the oldest events first, | |
1159 | and it may look like only one CPU ran (the one with the | |
1160 | oldest events). When the annotate option is set, it will | |
1161 | display when a new CPU buffer started:: | |
1162 | ||
1163 | <idle>-0 [001] dNs4 21169.031481: wake_up_idle_cpu <-add_timer_on | |
1164 | <idle>-0 [001] dNs4 21169.031482: _raw_spin_unlock_irqrestore <-add_timer_on | |
1165 | <idle>-0 [001] .Ns4 21169.031484: sub_preempt_count <-_raw_spin_unlock_irqrestore | |
1166 | ##### CPU 2 buffer started #### | |
1167 | <idle>-0 [002] .N.1 21169.031484: rcu_idle_exit <-cpu_idle | |
1168 | <idle>-0 [001] .Ns3 21169.031484: _raw_spin_unlock <-clocksource_watchdog | |
1169 | <idle>-0 [001] .Ns3 21169.031485: sub_preempt_count <-_raw_spin_unlock | |
1170 | ||
1171 | userstacktrace | |
1172 | This option changes the trace. It records a | |
1173 | stacktrace of the current user space thread after | |
1174 | each trace event. | |
1175 | ||
1176 | sym-userobj | |
1177 | when user stacktrace are enabled, look up which | |
1178 | object the address belongs to, and print a | |
1179 | relative address. This is especially useful when | |
1180 | ASLR is on, otherwise you don't get a chance to | |
1181 | resolve the address to object/file/line after | |
1182 | the app is no longer running | |
1183 | ||
1184 | The lookup is performed when you read | |
1185 | trace,trace_pipe. Example:: | |
1186 | ||
1187 | a.out-1623 [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0 | |
1188 | x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6] | |
1189 | ||
1190 | ||
1191 | printk-msg-only | |
1192 | When set, trace_printk()s will only show the format | |
1193 | and not their parameters (if trace_bprintk() or | |
1194 | trace_bputs() was used to save the trace_printk()). | |
1195 | ||
1196 | context-info | |
1197 | Show only the event data. Hides the comm, PID, | |
1198 | timestamp, CPU, and other useful data. | |
1199 | ||
1200 | latency-format | |
1201 | This option changes the trace output. When it is enabled, | |
1202 | the trace displays additional information about the | |
1203 | latency, as described in "Latency trace format". | |
1204 | ||
06e0a548 SRV |
1205 | pause-on-trace |
1206 | When set, opening the trace file for read, will pause | |
1207 | writing to the ring buffer (as if tracing_on was set to zero). | |
1208 | This simulates the original behavior of the trace file. | |
1209 | When the file is closed, tracing will be enabled again. | |
1210 | ||
a345a671 MH |
1211 | hash-ptr |
1212 | When set, "%p" in the event printk format displays the | |
1213 | hashed pointer value instead of real address. | |
1214 | This will be useful if you want to find out which hashed | |
1215 | value is corresponding to the real value in trace log. | |
1216 | ||
1f198e22 CD |
1217 | record-cmd |
1218 | When any event or tracer is enabled, a hook is enabled | |
1219 | in the sched_switch trace point to fill comm cache | |
1220 | with mapped pids and comms. But this may cause some | |
1221 | overhead, and if you only care about pids, and not the | |
1222 | name of the task, disabling this option can lower the | |
1223 | impact of tracing. See "saved_cmdlines". | |
1224 | ||
1225 | record-tgid | |
1226 | When any event or tracer is enabled, a hook is enabled | |
1227 | in the sched_switch trace point to fill the cache of | |
1228 | mapped Thread Group IDs (TGID) mapping to pids. See | |
1229 | "saved_tgids". | |
1230 | ||
1231 | overwrite | |
1232 | This controls what happens when the trace buffer is | |
1233 | full. If "1" (default), the oldest events are | |
1234 | discarded and overwritten. If "0", then the newest | |
1235 | events are discarded. | |
1236 | (see per_cpu/cpu0/stats for overrun and dropped) | |
1237 | ||
1238 | disable_on_free | |
1239 | When the free_buffer is closed, tracing will | |
1240 | stop (tracing_on set to 0). | |
1241 | ||
1242 | irq-info | |
1243 | Shows the interrupt, preempt count, need resched data. | |
1244 | When disabled, the trace looks like:: | |
1245 | ||
1246 | # tracer: function | |
1247 | # | |
1248 | # entries-in-buffer/entries-written: 144405/9452052 #P:4 | |
1249 | # | |
1250 | # TASK-PID CPU# TIMESTAMP FUNCTION | |
1251 | # | | | | | | |
1252 | <idle>-0 [002] 23636.756054: ttwu_do_activate.constprop.89 <-try_to_wake_up | |
1253 | <idle>-0 [002] 23636.756054: activate_task <-ttwu_do_activate.constprop.89 | |
1254 | <idle>-0 [002] 23636.756055: enqueue_task <-activate_task | |
1255 | ||
1256 | ||
1257 | markers | |
1258 | When set, the trace_marker is writable (only by root). | |
1259 | When disabled, the trace_marker will error with EINVAL | |
1260 | on write. | |
1261 | ||
1262 | event-fork | |
1263 | When set, tasks with PIDs listed in set_event_pid will have | |
1264 | the PIDs of their children added to set_event_pid when those | |
1265 | tasks fork. Also, when tasks with PIDs in set_event_pid exit, | |
1266 | their PIDs will be removed from the file. | |
1267 | ||
2ab2a092 SRV |
1268 | This affects PIDs listed in set_event_notrace_pid as well. |
1269 | ||
1f198e22 CD |
1270 | function-trace |
1271 | The latency tracers will enable function tracing | |
1272 | if this option is enabled (default it is). When | |
1273 | it is disabled, the latency tracers do not trace | |
1274 | functions. This keeps the overhead of the tracer down | |
1275 | when performing latency tests. | |
1276 | ||
1277 | function-fork | |
1278 | When set, tasks with PIDs listed in set_ftrace_pid will | |
1279 | have the PIDs of their children added to set_ftrace_pid | |
1280 | when those tasks fork. Also, when tasks with PIDs in | |
1281 | set_ftrace_pid exit, their PIDs will be removed from the | |
1282 | file. | |
1283 | ||
2ab2a092 SRV |
1284 | This affects PIDs in set_ftrace_notrace_pid as well. |
1285 | ||
1f198e22 CD |
1286 | display-graph |
1287 | When set, the latency tracers (irqsoff, wakeup, etc) will | |
1288 | use function graph tracing instead of function tracing. | |
1289 | ||
1290 | stacktrace | |
1291 | When set, a stack trace is recorded after any trace event | |
1292 | is recorded. | |
1293 | ||
1294 | branch | |
1295 | Enable branch tracing with the tracer. This enables branch | |
1296 | tracer along with the currently set tracer. Enabling this | |
1297 | with the "nop" tracer is the same as just enabling the | |
1298 | "branch" tracer. | |
1299 | ||
1300 | .. tip:: Some tracers have their own options. They only appear in this | |
1301 | file when the tracer is active. They always appear in the | |
1302 | options directory. | |
1303 | ||
1304 | ||
1305 | Here are the per tracer options: | |
1306 | ||
1307 | Options for function tracer: | |
1308 | ||
1309 | func_stack_trace | |
1310 | When set, a stack trace is recorded after every | |
1311 | function that is recorded. NOTE! Limit the functions | |
1312 | that are recorded before enabling this, with | |
1313 | "set_ftrace_filter" otherwise the system performance | |
1314 | will be critically degraded. Remember to disable | |
1315 | this option before clearing the function filter. | |
1316 | ||
1317 | Options for function_graph tracer: | |
1318 | ||
1319 | Since the function_graph tracer has a slightly different output | |
1320 | it has its own options to control what is displayed. | |
1321 | ||
1322 | funcgraph-overrun | |
1323 | When set, the "overrun" of the graph stack is | |
1324 | displayed after each function traced. The | |
1325 | overrun, is when the stack depth of the calls | |
1326 | is greater than what is reserved for each task. | |
1327 | Each task has a fixed array of functions to | |
1328 | trace in the call graph. If the depth of the | |
1329 | calls exceeds that, the function is not traced. | |
1330 | The overrun is the number of functions missed | |
1331 | due to exceeding this array. | |
1332 | ||
1333 | funcgraph-cpu | |
1334 | When set, the CPU number of the CPU where the trace | |
1335 | occurred is displayed. | |
1336 | ||
1337 | funcgraph-overhead | |
1338 | When set, if the function takes longer than | |
1339 | A certain amount, then a delay marker is | |
1340 | displayed. See "delay" above, under the | |
1341 | header description. | |
1342 | ||
1343 | funcgraph-proc | |
1344 | Unlike other tracers, the process' command line | |
1345 | is not displayed by default, but instead only | |
1346 | when a task is traced in and out during a context | |
1347 | switch. Enabling this options has the command | |
1348 | of each process displayed at every line. | |
1349 | ||
1350 | funcgraph-duration | |
1351 | At the end of each function (the return) | |
1352 | the duration of the amount of time in the | |
1353 | function is displayed in microseconds. | |
1354 | ||
1355 | funcgraph-abstime | |
1356 | When set, the timestamp is displayed at each line. | |
1357 | ||
1358 | funcgraph-irqs | |
1359 | When disabled, functions that happen inside an | |
1360 | interrupt will not be traced. | |
1361 | ||
1362 | funcgraph-tail | |
1363 | When set, the return event will include the function | |
1364 | that it represents. By default this is off, and | |
1365 | only a closing curly bracket "}" is displayed for | |
1366 | the return of a function. | |
1367 | ||
21c094d3 DP |
1368 | funcgraph-retval |
1369 | When set, the return value of each traced function | |
1370 | will be printed after an equal sign "=". By default | |
1371 | this is off. | |
1372 | ||
1373 | funcgraph-retval-hex | |
1374 | When set, the return value will always be printed | |
1375 | in hexadecimal format. If the option is not set and | |
1376 | the return value is an error code, it will be printed | |
1377 | in signed decimal format; otherwise it will also be | |
1378 | printed in hexadecimal format. By default, this option | |
1379 | is off. | |
1380 | ||
1f198e22 CD |
1381 | sleep-time |
1382 | When running function graph tracer, to include | |
1383 | the time a task schedules out in its function. | |
1384 | When enabled, it will account time the task has been | |
1385 | scheduled out as part of the function call. | |
1386 | ||
1387 | graph-time | |
1388 | When running function profiler with function graph tracer, | |
1389 | to include the time to call nested functions. When this is | |
1390 | not set, the time reported for the function will only | |
1391 | include the time the function itself executed for, not the | |
1392 | time for functions that it called. | |
1393 | ||
1394 | Options for blk tracer: | |
1395 | ||
1396 | blk_classic | |
1397 | Shows a more minimalistic output. | |
1398 | ||
1399 | ||
1400 | irqsoff | |
1401 | ------- | |
1402 | ||
1403 | When interrupts are disabled, the CPU can not react to any other | |
1404 | external event (besides NMIs and SMIs). This prevents the timer | |
1405 | interrupt from triggering or the mouse interrupt from letting | |
1406 | the kernel know of a new mouse event. The result is a latency | |
1407 | with the reaction time. | |
1408 | ||
1409 | The irqsoff tracer tracks the time for which interrupts are | |
1410 | disabled. When a new maximum latency is hit, the tracer saves | |
1411 | the trace leading up to that latency point so that every time a | |
1412 | new maximum is reached, the old saved trace is discarded and the | |
1413 | new trace is saved. | |
1414 | ||
1415 | To reset the maximum, echo 0 into tracing_max_latency. Here is | |
1416 | an example:: | |
1417 | ||
1418 | # echo 0 > options/function-trace | |
1419 | # echo irqsoff > current_tracer | |
1420 | # echo 1 > tracing_on | |
1421 | # echo 0 > tracing_max_latency | |
1422 | # ls -ltr | |
1423 | [...] | |
1424 | # echo 0 > tracing_on | |
1425 | # cat trace | |
1426 | # tracer: irqsoff | |
1427 | # | |
1428 | # irqsoff latency trace v1.1.5 on 3.8.0-test+ | |
1429 | # -------------------------------------------------------------------- | |
1430 | # latency: 16 us, #4/4, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1431 | # ----------------- | |
1432 | # | task: swapper/0-0 (uid:0 nice:0 policy:0 rt_prio:0) | |
1433 | # ----------------- | |
1434 | # => started at: run_timer_softirq | |
1435 | # => ended at: run_timer_softirq | |
1436 | # | |
1437 | # | |
1438 | # _------=> CPU# | |
1439 | # / _-----=> irqs-off | |
1440 | # | / _----=> need-resched | |
1441 | # || / _---=> hardirq/softirq | |
1442 | # ||| / _--=> preempt-depth | |
1443 | # |||| / delay | |
1444 | # cmd pid ||||| time | caller | |
1445 | # \ / ||||| \ | / | |
1446 | <idle>-0 0d.s2 0us+: _raw_spin_lock_irq <-run_timer_softirq | |
1447 | <idle>-0 0dNs3 17us : _raw_spin_unlock_irq <-run_timer_softirq | |
1448 | <idle>-0 0dNs3 17us+: trace_hardirqs_on <-run_timer_softirq | |
1449 | <idle>-0 0dNs3 25us : <stack trace> | |
1450 | => _raw_spin_unlock_irq | |
1451 | => run_timer_softirq | |
1452 | => __do_softirq | |
1453 | => call_softirq | |
1454 | => do_softirq | |
1455 | => irq_exit | |
1456 | => smp_apic_timer_interrupt | |
1457 | => apic_timer_interrupt | |
1458 | => rcu_idle_exit | |
1459 | => cpu_idle | |
1460 | => rest_init | |
1461 | => start_kernel | |
1462 | => x86_64_start_reservations | |
1463 | => x86_64_start_kernel | |
1464 | ||
1747db54 | 1465 | Here we see that we had a latency of 16 microseconds (which is |
1f198e22 CD |
1466 | very good). The _raw_spin_lock_irq in run_timer_softirq disabled |
1467 | interrupts. The difference between the 16 and the displayed | |
1468 | timestamp 25us occurred because the clock was incremented | |
1469 | between the time of recording the max latency and the time of | |
1470 | recording the function that had that latency. | |
1471 | ||
1472 | Note the above example had function-trace not set. If we set | |
1473 | function-trace, we get a much larger output:: | |
1474 | ||
1475 | with echo 1 > options/function-trace | |
1476 | ||
1477 | # tracer: irqsoff | |
1478 | # | |
1479 | # irqsoff latency trace v1.1.5 on 3.8.0-test+ | |
1480 | # -------------------------------------------------------------------- | |
1481 | # latency: 71 us, #168/168, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1482 | # ----------------- | |
1483 | # | task: bash-2042 (uid:0 nice:0 policy:0 rt_prio:0) | |
1484 | # ----------------- | |
1485 | # => started at: ata_scsi_queuecmd | |
1486 | # => ended at: ata_scsi_queuecmd | |
1487 | # | |
1488 | # | |
1489 | # _------=> CPU# | |
1490 | # / _-----=> irqs-off | |
1491 | # | / _----=> need-resched | |
1492 | # || / _---=> hardirq/softirq | |
1493 | # ||| / _--=> preempt-depth | |
1494 | # |||| / delay | |
1495 | # cmd pid ||||| time | caller | |
1496 | # \ / ||||| \ | / | |
1497 | bash-2042 3d... 0us : _raw_spin_lock_irqsave <-ata_scsi_queuecmd | |
1498 | bash-2042 3d... 0us : add_preempt_count <-_raw_spin_lock_irqsave | |
1499 | bash-2042 3d..1 1us : ata_scsi_find_dev <-ata_scsi_queuecmd | |
1500 | bash-2042 3d..1 1us : __ata_scsi_find_dev <-ata_scsi_find_dev | |
1501 | bash-2042 3d..1 2us : ata_find_dev.part.14 <-__ata_scsi_find_dev | |
1502 | bash-2042 3d..1 2us : ata_qc_new_init <-__ata_scsi_queuecmd | |
1503 | bash-2042 3d..1 3us : ata_sg_init <-__ata_scsi_queuecmd | |
1504 | bash-2042 3d..1 4us : ata_scsi_rw_xlat <-__ata_scsi_queuecmd | |
1505 | bash-2042 3d..1 4us : ata_build_rw_tf <-ata_scsi_rw_xlat | |
1506 | [...] | |
1507 | bash-2042 3d..1 67us : delay_tsc <-__delay | |
1508 | bash-2042 3d..1 67us : add_preempt_count <-delay_tsc | |
1509 | bash-2042 3d..2 67us : sub_preempt_count <-delay_tsc | |
1510 | bash-2042 3d..1 67us : add_preempt_count <-delay_tsc | |
1511 | bash-2042 3d..2 68us : sub_preempt_count <-delay_tsc | |
1512 | bash-2042 3d..1 68us+: ata_bmdma_start <-ata_bmdma_qc_issue | |
1513 | bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd | |
1514 | bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd | |
1515 | bash-2042 3d..1 72us+: trace_hardirqs_on <-ata_scsi_queuecmd | |
1516 | bash-2042 3d..1 120us : <stack trace> | |
1517 | => _raw_spin_unlock_irqrestore | |
1518 | => ata_scsi_queuecmd | |
1519 | => scsi_dispatch_cmd | |
1520 | => scsi_request_fn | |
1521 | => __blk_run_queue_uncond | |
1522 | => __blk_run_queue | |
1523 | => blk_queue_bio | |
ed00aabd | 1524 | => submit_bio_noacct |
1f198e22 CD |
1525 | => submit_bio |
1526 | => submit_bh | |
1527 | => __ext3_get_inode_loc | |
1528 | => ext3_iget | |
1529 | => ext3_lookup | |
1530 | => lookup_real | |
1531 | => __lookup_hash | |
1532 | => walk_component | |
1533 | => lookup_last | |
1534 | => path_lookupat | |
1535 | => filename_lookup | |
1536 | => user_path_at_empty | |
1537 | => user_path_at | |
1538 | => vfs_fstatat | |
1539 | => vfs_stat | |
1540 | => sys_newstat | |
1541 | => system_call_fastpath | |
1542 | ||
1543 | ||
1544 | Here we traced a 71 microsecond latency. But we also see all the | |
1545 | functions that were called during that time. Note that by | |
1546 | enabling function tracing, we incur an added overhead. This | |
1547 | overhead may extend the latency times. But nevertheless, this | |
1548 | trace has provided some very helpful debugging information. | |
1549 | ||
88d380eb CD |
1550 | If we prefer function graph output instead of function, we can set |
1551 | display-graph option:: | |
3df5ffd2 | 1552 | |
88d380eb CD |
1553 | with echo 1 > options/display-graph |
1554 | ||
1555 | # tracer: irqsoff | |
1556 | # | |
1557 | # irqsoff latency trace v1.1.5 on 4.20.0-rc6+ | |
1558 | # -------------------------------------------------------------------- | |
1559 | # latency: 3751 us, #274/274, CPU#0 | (M:desktop VP:0, KP:0, SP:0 HP:0 #P:4) | |
1560 | # ----------------- | |
1561 | # | task: bash-1507 (uid:0 nice:0 policy:0 rt_prio:0) | |
1562 | # ----------------- | |
1563 | # => started at: free_debug_processing | |
1564 | # => ended at: return_to_handler | |
1565 | # | |
1566 | # | |
1567 | # _-----=> irqs-off | |
1568 | # / _----=> need-resched | |
1569 | # | / _---=> hardirq/softirq | |
1570 | # || / _--=> preempt-depth | |
1571 | # ||| / | |
1572 | # REL TIME CPU TASK/PID |||| DURATION FUNCTION CALLS | |
1573 | # | | | | |||| | | | | | | | |
1574 | 0 us | 0) bash-1507 | d... | 0.000 us | _raw_spin_lock_irqsave(); | |
1575 | 0 us | 0) bash-1507 | d..1 | 0.378 us | do_raw_spin_trylock(); | |
1576 | 1 us | 0) bash-1507 | d..2 | | set_track() { | |
1577 | 2 us | 0) bash-1507 | d..2 | | save_stack_trace() { | |
1578 | 2 us | 0) bash-1507 | d..2 | | __save_stack_trace() { | |
1579 | 3 us | 0) bash-1507 | d..2 | | __unwind_start() { | |
1580 | 3 us | 0) bash-1507 | d..2 | | get_stack_info() { | |
1581 | 3 us | 0) bash-1507 | d..2 | 0.351 us | in_task_stack(); | |
1582 | 4 us | 0) bash-1507 | d..2 | 1.107 us | } | |
1583 | [...] | |
1584 | 3750 us | 0) bash-1507 | d..1 | 0.516 us | do_raw_spin_unlock(); | |
1585 | 3750 us | 0) bash-1507 | d..1 | 0.000 us | _raw_spin_unlock_irqrestore(); | |
1586 | 3764 us | 0) bash-1507 | d..1 | 0.000 us | tracer_hardirqs_on(); | |
1587 | bash-1507 0d..1 3792us : <stack trace> | |
1588 | => free_debug_processing | |
1589 | => __slab_free | |
1590 | => kmem_cache_free | |
1591 | => vm_area_free | |
1592 | => remove_vma | |
1593 | => exit_mmap | |
1594 | => mmput | |
2388777a | 1595 | => begin_new_exec |
88d380eb CD |
1596 | => load_elf_binary |
1597 | => search_binary_handler | |
1598 | => __do_execve_file.isra.32 | |
1599 | => __x64_sys_execve | |
1600 | => do_syscall_64 | |
1601 | => entry_SYSCALL_64_after_hwframe | |
1f198e22 CD |
1602 | |
1603 | preemptoff | |
1604 | ---------- | |
1605 | ||
1606 | When preemption is disabled, we may be able to receive | |
1607 | interrupts but the task cannot be preempted and a higher | |
1608 | priority task must wait for preemption to be enabled again | |
1609 | before it can preempt a lower priority task. | |
1610 | ||
1611 | The preemptoff tracer traces the places that disable preemption. | |
1612 | Like the irqsoff tracer, it records the maximum latency for | |
1613 | which preemption was disabled. The control of preemptoff tracer | |
1614 | is much like the irqsoff tracer. | |
1615 | :: | |
1616 | ||
1617 | # echo 0 > options/function-trace | |
1618 | # echo preemptoff > 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: preemptoff | |
1626 | # | |
1627 | # preemptoff latency trace v1.1.5 on 3.8.0-test+ | |
1628 | # -------------------------------------------------------------------- | |
1629 | # latency: 46 us, #4/4, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1630 | # ----------------- | |
1631 | # | task: sshd-1991 (uid:0 nice:0 policy:0 rt_prio:0) | |
1632 | # ----------------- | |
1633 | # => started at: do_IRQ | |
1634 | # => ended at: do_IRQ | |
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 | sshd-1991 1d.h. 0us+: irq_enter <-do_IRQ | |
1646 | sshd-1991 1d..1 46us : irq_exit <-do_IRQ | |
1647 | sshd-1991 1d..1 47us+: trace_preempt_on <-do_IRQ | |
1648 | sshd-1991 1d..1 52us : <stack trace> | |
1649 | => sub_preempt_count | |
1650 | => irq_exit | |
1651 | => do_IRQ | |
1652 | => ret_from_intr | |
1653 | ||
1654 | ||
1655 | This has some more changes. Preemption was disabled when an | |
1656 | interrupt came in (notice the 'h'), and was enabled on exit. | |
1657 | But we also see that interrupts have been disabled when entering | |
1658 | the preempt off section and leaving it (the 'd'). We do not know if | |
1659 | interrupts were enabled in the mean time or shortly after this | |
1660 | was over. | |
1661 | :: | |
1662 | ||
1663 | # tracer: preemptoff | |
1664 | # | |
1665 | # preemptoff latency trace v1.1.5 on 3.8.0-test+ | |
1666 | # -------------------------------------------------------------------- | |
1667 | # latency: 83 us, #241/241, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1668 | # ----------------- | |
1669 | # | task: bash-1994 (uid:0 nice:0 policy:0 rt_prio:0) | |
1670 | # ----------------- | |
1671 | # => started at: wake_up_new_task | |
1672 | # => ended at: task_rq_unlock | |
1673 | # | |
1674 | # | |
1675 | # _------=> CPU# | |
1676 | # / _-----=> irqs-off | |
1677 | # | / _----=> need-resched | |
1678 | # || / _---=> hardirq/softirq | |
1679 | # ||| / _--=> preempt-depth | |
1680 | # |||| / delay | |
1681 | # cmd pid ||||| time | caller | |
1682 | # \ / ||||| \ | / | |
1683 | bash-1994 1d..1 0us : _raw_spin_lock_irqsave <-wake_up_new_task | |
1684 | bash-1994 1d..1 0us : select_task_rq_fair <-select_task_rq | |
1685 | bash-1994 1d..1 1us : __rcu_read_lock <-select_task_rq_fair | |
1686 | bash-1994 1d..1 1us : source_load <-select_task_rq_fair | |
1687 | bash-1994 1d..1 1us : source_load <-select_task_rq_fair | |
1688 | [...] | |
1689 | bash-1994 1d..1 12us : irq_enter <-smp_apic_timer_interrupt | |
1690 | bash-1994 1d..1 12us : rcu_irq_enter <-irq_enter | |
1691 | bash-1994 1d..1 13us : add_preempt_count <-irq_enter | |
1692 | bash-1994 1d.h1 13us : exit_idle <-smp_apic_timer_interrupt | |
1693 | bash-1994 1d.h1 13us : hrtimer_interrupt <-smp_apic_timer_interrupt | |
1694 | bash-1994 1d.h1 13us : _raw_spin_lock <-hrtimer_interrupt | |
1695 | bash-1994 1d.h1 14us : add_preempt_count <-_raw_spin_lock | |
1696 | bash-1994 1d.h2 14us : ktime_get_update_offsets <-hrtimer_interrupt | |
1697 | [...] | |
1698 | bash-1994 1d.h1 35us : lapic_next_event <-clockevents_program_event | |
1699 | bash-1994 1d.h1 35us : irq_exit <-smp_apic_timer_interrupt | |
1700 | bash-1994 1d.h1 36us : sub_preempt_count <-irq_exit | |
1701 | bash-1994 1d..2 36us : do_softirq <-irq_exit | |
1702 | bash-1994 1d..2 36us : __do_softirq <-call_softirq | |
1703 | bash-1994 1d..2 36us : __local_bh_disable <-__do_softirq | |
1704 | bash-1994 1d.s2 37us : add_preempt_count <-_raw_spin_lock_irq | |
1705 | bash-1994 1d.s3 38us : _raw_spin_unlock <-run_timer_softirq | |
1706 | bash-1994 1d.s3 39us : sub_preempt_count <-_raw_spin_unlock | |
1707 | bash-1994 1d.s2 39us : call_timer_fn <-run_timer_softirq | |
1708 | [...] | |
1709 | bash-1994 1dNs2 81us : cpu_needs_another_gp <-rcu_process_callbacks | |
1710 | bash-1994 1dNs2 82us : __local_bh_enable <-__do_softirq | |
1711 | bash-1994 1dNs2 82us : sub_preempt_count <-__local_bh_enable | |
1712 | bash-1994 1dN.2 82us : idle_cpu <-irq_exit | |
1713 | bash-1994 1dN.2 83us : rcu_irq_exit <-irq_exit | |
1714 | bash-1994 1dN.2 83us : sub_preempt_count <-irq_exit | |
1715 | bash-1994 1.N.1 84us : _raw_spin_unlock_irqrestore <-task_rq_unlock | |
1716 | bash-1994 1.N.1 84us+: trace_preempt_on <-task_rq_unlock | |
1717 | bash-1994 1.N.1 104us : <stack trace> | |
1718 | => sub_preempt_count | |
1719 | => _raw_spin_unlock_irqrestore | |
1720 | => task_rq_unlock | |
1721 | => wake_up_new_task | |
1722 | => do_fork | |
1723 | => sys_clone | |
1724 | => stub_clone | |
1725 | ||
1726 | ||
1727 | The above is an example of the preemptoff trace with | |
1728 | function-trace set. Here we see that interrupts were not disabled | |
1729 | the entire time. The irq_enter code lets us know that we entered | |
1730 | an interrupt 'h'. Before that, the functions being traced still | |
1731 | show that it is not in an interrupt, but we can see from the | |
1732 | functions themselves that this is not the case. | |
1733 | ||
1734 | preemptirqsoff | |
1735 | -------------- | |
1736 | ||
1737 | Knowing the locations that have interrupts disabled or | |
1738 | preemption disabled for the longest times is helpful. But | |
1739 | sometimes we would like to know when either preemption and/or | |
1740 | interrupts are disabled. | |
1741 | ||
1742 | Consider the following code:: | |
1743 | ||
1744 | local_irq_disable(); | |
1745 | call_function_with_irqs_off(); | |
1746 | preempt_disable(); | |
1747 | call_function_with_irqs_and_preemption_off(); | |
1748 | local_irq_enable(); | |
1749 | call_function_with_preemption_off(); | |
1750 | preempt_enable(); | |
1751 | ||
1752 | The irqsoff tracer will record the total length of | |
1753 | call_function_with_irqs_off() and | |
1754 | call_function_with_irqs_and_preemption_off(). | |
1755 | ||
1756 | The preemptoff tracer will record the total length of | |
1757 | call_function_with_irqs_and_preemption_off() and | |
1758 | call_function_with_preemption_off(). | |
1759 | ||
1760 | But neither will trace the time that interrupts and/or | |
1761 | preemption is disabled. This total time is the time that we can | |
1762 | not schedule. To record this time, use the preemptirqsoff | |
1763 | tracer. | |
1764 | ||
1765 | Again, using this trace is much like the irqsoff and preemptoff | |
1766 | tracers. | |
1767 | :: | |
1768 | ||
1769 | # echo 0 > options/function-trace | |
1770 | # echo preemptirqsoff > current_tracer | |
1771 | # echo 1 > tracing_on | |
1772 | # echo 0 > tracing_max_latency | |
1773 | # ls -ltr | |
1774 | [...] | |
1775 | # echo 0 > tracing_on | |
1776 | # cat trace | |
1777 | # tracer: preemptirqsoff | |
1778 | # | |
1779 | # preemptirqsoff latency trace v1.1.5 on 3.8.0-test+ | |
1780 | # -------------------------------------------------------------------- | |
1781 | # latency: 100 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1782 | # ----------------- | |
1783 | # | task: ls-2230 (uid:0 nice:0 policy:0 rt_prio:0) | |
1784 | # ----------------- | |
1785 | # => started at: ata_scsi_queuecmd | |
1786 | # => ended at: ata_scsi_queuecmd | |
1787 | # | |
1788 | # | |
1789 | # _------=> CPU# | |
1790 | # / _-----=> irqs-off | |
1791 | # | / _----=> need-resched | |
1792 | # || / _---=> hardirq/softirq | |
1793 | # ||| / _--=> preempt-depth | |
1794 | # |||| / delay | |
1795 | # cmd pid ||||| time | caller | |
1796 | # \ / ||||| \ | / | |
1797 | ls-2230 3d... 0us+: _raw_spin_lock_irqsave <-ata_scsi_queuecmd | |
1798 | ls-2230 3...1 100us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd | |
1799 | ls-2230 3...1 101us+: trace_preempt_on <-ata_scsi_queuecmd | |
1800 | ls-2230 3...1 111us : <stack trace> | |
1801 | => sub_preempt_count | |
1802 | => _raw_spin_unlock_irqrestore | |
1803 | => ata_scsi_queuecmd | |
1804 | => scsi_dispatch_cmd | |
1805 | => scsi_request_fn | |
1806 | => __blk_run_queue_uncond | |
1807 | => __blk_run_queue | |
1808 | => blk_queue_bio | |
ed00aabd | 1809 | => submit_bio_noacct |
1f198e22 CD |
1810 | => submit_bio |
1811 | => submit_bh | |
1812 | => ext3_bread | |
1813 | => ext3_dir_bread | |
1814 | => htree_dirblock_to_tree | |
1815 | => ext3_htree_fill_tree | |
1816 | => ext3_readdir | |
1817 | => vfs_readdir | |
1818 | => sys_getdents | |
1819 | => system_call_fastpath | |
1820 | ||
1821 | ||
1822 | The trace_hardirqs_off_thunk is called from assembly on x86 when | |
1823 | interrupts are disabled in the assembly code. Without the | |
1824 | function tracing, we do not know if interrupts were enabled | |
1825 | within the preemption points. We do see that it started with | |
1826 | preemption enabled. | |
1827 | ||
1828 | Here is a trace with function-trace set:: | |
1829 | ||
1830 | # tracer: preemptirqsoff | |
1831 | # | |
1832 | # preemptirqsoff latency trace v1.1.5 on 3.8.0-test+ | |
1833 | # -------------------------------------------------------------------- | |
1834 | # latency: 161 us, #339/339, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1835 | # ----------------- | |
1836 | # | task: ls-2269 (uid:0 nice:0 policy:0 rt_prio:0) | |
1837 | # ----------------- | |
1838 | # => started at: schedule | |
1839 | # => ended at: mutex_unlock | |
1840 | # | |
1841 | # | |
1842 | # _------=> CPU# | |
1843 | # / _-----=> irqs-off | |
1844 | # | / _----=> need-resched | |
1845 | # || / _---=> hardirq/softirq | |
1846 | # ||| / _--=> preempt-depth | |
1847 | # |||| / delay | |
1848 | # cmd pid ||||| time | caller | |
1849 | # \ / ||||| \ | / | |
1850 | kworker/-59 3...1 0us : __schedule <-schedule | |
1851 | kworker/-59 3d..1 0us : rcu_preempt_qs <-rcu_note_context_switch | |
1852 | kworker/-59 3d..1 1us : add_preempt_count <-_raw_spin_lock_irq | |
1853 | kworker/-59 3d..2 1us : deactivate_task <-__schedule | |
1854 | kworker/-59 3d..2 1us : dequeue_task <-deactivate_task | |
1855 | kworker/-59 3d..2 2us : update_rq_clock <-dequeue_task | |
1856 | kworker/-59 3d..2 2us : dequeue_task_fair <-dequeue_task | |
1857 | kworker/-59 3d..2 2us : update_curr <-dequeue_task_fair | |
1858 | kworker/-59 3d..2 2us : update_min_vruntime <-update_curr | |
1859 | kworker/-59 3d..2 3us : cpuacct_charge <-update_curr | |
1860 | kworker/-59 3d..2 3us : __rcu_read_lock <-cpuacct_charge | |
1861 | kworker/-59 3d..2 3us : __rcu_read_unlock <-cpuacct_charge | |
1862 | kworker/-59 3d..2 3us : update_cfs_rq_blocked_load <-dequeue_task_fair | |
1863 | kworker/-59 3d..2 4us : clear_buddies <-dequeue_task_fair | |
1864 | kworker/-59 3d..2 4us : account_entity_dequeue <-dequeue_task_fair | |
1865 | kworker/-59 3d..2 4us : update_min_vruntime <-dequeue_task_fair | |
1866 | kworker/-59 3d..2 4us : update_cfs_shares <-dequeue_task_fair | |
1867 | kworker/-59 3d..2 5us : hrtick_update <-dequeue_task_fair | |
1868 | kworker/-59 3d..2 5us : wq_worker_sleeping <-__schedule | |
1869 | kworker/-59 3d..2 5us : kthread_data <-wq_worker_sleeping | |
1870 | kworker/-59 3d..2 5us : put_prev_task_fair <-__schedule | |
1871 | kworker/-59 3d..2 6us : pick_next_task_fair <-pick_next_task | |
1872 | kworker/-59 3d..2 6us : clear_buddies <-pick_next_task_fair | |
1873 | kworker/-59 3d..2 6us : set_next_entity <-pick_next_task_fair | |
1874 | kworker/-59 3d..2 6us : update_stats_wait_end <-set_next_entity | |
1875 | ls-2269 3d..2 7us : finish_task_switch <-__schedule | |
1876 | ls-2269 3d..2 7us : _raw_spin_unlock_irq <-finish_task_switch | |
1877 | ls-2269 3d..2 8us : do_IRQ <-ret_from_intr | |
1878 | ls-2269 3d..2 8us : irq_enter <-do_IRQ | |
1879 | ls-2269 3d..2 8us : rcu_irq_enter <-irq_enter | |
1880 | ls-2269 3d..2 9us : add_preempt_count <-irq_enter | |
1881 | ls-2269 3d.h2 9us : exit_idle <-do_IRQ | |
1882 | [...] | |
1883 | ls-2269 3d.h3 20us : sub_preempt_count <-_raw_spin_unlock | |
1884 | ls-2269 3d.h2 20us : irq_exit <-do_IRQ | |
1885 | ls-2269 3d.h2 21us : sub_preempt_count <-irq_exit | |
1886 | ls-2269 3d..3 21us : do_softirq <-irq_exit | |
1887 | ls-2269 3d..3 21us : __do_softirq <-call_softirq | |
1888 | ls-2269 3d..3 21us+: __local_bh_disable <-__do_softirq | |
1889 | ls-2269 3d.s4 29us : sub_preempt_count <-_local_bh_enable_ip | |
1890 | ls-2269 3d.s5 29us : sub_preempt_count <-_local_bh_enable_ip | |
1891 | ls-2269 3d.s5 31us : do_IRQ <-ret_from_intr | |
1892 | ls-2269 3d.s5 31us : irq_enter <-do_IRQ | |
1893 | ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter | |
1894 | [...] | |
1895 | ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter | |
1896 | ls-2269 3d.s5 32us : add_preempt_count <-irq_enter | |
1897 | ls-2269 3d.H5 32us : exit_idle <-do_IRQ | |
1898 | ls-2269 3d.H5 32us : handle_irq <-do_IRQ | |
1899 | ls-2269 3d.H5 32us : irq_to_desc <-handle_irq | |
1900 | ls-2269 3d.H5 33us : handle_fasteoi_irq <-handle_irq | |
1901 | [...] | |
1902 | ls-2269 3d.s5 158us : _raw_spin_unlock_irqrestore <-rtl8139_poll | |
1903 | ls-2269 3d.s3 158us : net_rps_action_and_irq_enable.isra.65 <-net_rx_action | |
1904 | ls-2269 3d.s3 159us : __local_bh_enable <-__do_softirq | |
1905 | ls-2269 3d.s3 159us : sub_preempt_count <-__local_bh_enable | |
1906 | ls-2269 3d..3 159us : idle_cpu <-irq_exit | |
1907 | ls-2269 3d..3 159us : rcu_irq_exit <-irq_exit | |
1908 | ls-2269 3d..3 160us : sub_preempt_count <-irq_exit | |
1909 | ls-2269 3d... 161us : __mutex_unlock_slowpath <-mutex_unlock | |
1910 | ls-2269 3d... 162us+: trace_hardirqs_on <-mutex_unlock | |
1911 | ls-2269 3d... 186us : <stack trace> | |
1912 | => __mutex_unlock_slowpath | |
1913 | => mutex_unlock | |
1914 | => process_output | |
1915 | => n_tty_write | |
1916 | => tty_write | |
1917 | => vfs_write | |
1918 | => sys_write | |
1919 | => system_call_fastpath | |
1920 | ||
1921 | This is an interesting trace. It started with kworker running and | |
1922 | scheduling out and ls taking over. But as soon as ls released the | |
1923 | rq lock and enabled interrupts (but not preemption) an interrupt | |
1924 | triggered. When the interrupt finished, it started running softirqs. | |
1925 | But while the softirq was running, another interrupt triggered. | |
1926 | When an interrupt is running inside a softirq, the annotation is 'H'. | |
1927 | ||
1928 | ||
1929 | wakeup | |
1930 | ------ | |
1931 | ||
1932 | One common case that people are interested in tracing is the | |
1933 | time it takes for a task that is woken to actually wake up. | |
1934 | Now for non Real-Time tasks, this can be arbitrary. But tracing | |
1935 | it none the less can be interesting. | |
1936 | ||
1937 | Without function tracing:: | |
1938 | ||
1939 | # echo 0 > options/function-trace | |
1940 | # echo wakeup > current_tracer | |
1941 | # echo 1 > tracing_on | |
1942 | # echo 0 > tracing_max_latency | |
1943 | # chrt -f 5 sleep 1 | |
1944 | # echo 0 > tracing_on | |
1945 | # cat trace | |
1946 | # tracer: wakeup | |
1947 | # | |
1948 | # wakeup latency trace v1.1.5 on 3.8.0-test+ | |
1949 | # -------------------------------------------------------------------- | |
1950 | # latency: 15 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
1951 | # ----------------- | |
1952 | # | task: kworker/3:1H-312 (uid:0 nice:-20 policy:0 rt_prio:0) | |
1953 | # ----------------- | |
1954 | # | |
1955 | # _------=> CPU# | |
1956 | # / _-----=> irqs-off | |
1957 | # | / _----=> need-resched | |
1958 | # || / _---=> hardirq/softirq | |
1959 | # ||| / _--=> preempt-depth | |
1960 | # |||| / delay | |
1961 | # cmd pid ||||| time | caller | |
1962 | # \ / ||||| \ | / | |
1963 | <idle>-0 3dNs7 0us : 0:120:R + [003] 312:100:R kworker/3:1H | |
1964 | <idle>-0 3dNs7 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up | |
1965 | <idle>-0 3d..3 15us : __schedule <-schedule | |
1966 | <idle>-0 3d..3 15us : 0:120:R ==> [003] 312:100:R kworker/3:1H | |
1967 | ||
1968 | The tracer only traces the highest priority task in the system | |
1969 | to avoid tracing the normal circumstances. Here we see that | |
1970 | the kworker with a nice priority of -20 (not very nice), took | |
1971 | just 15 microseconds from the time it woke up, to the time it | |
1972 | ran. | |
1973 | ||
1974 | Non Real-Time tasks are not that interesting. A more interesting | |
1975 | trace is to concentrate only on Real-Time tasks. | |
1976 | ||
1977 | wakeup_rt | |
1978 | --------- | |
1979 | ||
1980 | In a Real-Time environment it is very important to know the | |
1981 | wakeup time it takes for the highest priority task that is woken | |
1982 | up to the time that it executes. This is also known as "schedule | |
1983 | latency". I stress the point that this is about RT tasks. It is | |
1984 | also important to know the scheduling latency of non-RT tasks, | |
1985 | but the average schedule latency is better for non-RT tasks. | |
1986 | Tools like LatencyTop are more appropriate for such | |
1987 | measurements. | |
1988 | ||
1989 | Real-Time environments are interested in the worst case latency. | |
1990 | That is the longest latency it takes for something to happen, | |
1991 | and not the average. We can have a very fast scheduler that may | |
1992 | only have a large latency once in a while, but that would not | |
1993 | work well with Real-Time tasks. The wakeup_rt tracer was designed | |
1994 | to record the worst case wakeups of RT tasks. Non-RT tasks are | |
1995 | not recorded because the tracer only records one worst case and | |
1996 | tracing non-RT tasks that are unpredictable will overwrite the | |
1997 | worst case latency of RT tasks (just run the normal wakeup | |
1998 | tracer for a while to see that effect). | |
1999 | ||
2000 | Since this tracer only deals with RT tasks, we will run this | |
2001 | slightly differently than we did with the previous tracers. | |
2002 | Instead of performing an 'ls', we will run 'sleep 1' under | |
2003 | 'chrt' which changes the priority of the task. | |
2004 | :: | |
2005 | ||
2006 | # echo 0 > options/function-trace | |
2007 | # echo wakeup_rt > current_tracer | |
2008 | # echo 1 > tracing_on | |
2009 | # echo 0 > tracing_max_latency | |
2010 | # chrt -f 5 sleep 1 | |
2011 | # echo 0 > tracing_on | |
2012 | # cat trace | |
2013 | # tracer: wakeup | |
2014 | # | |
2015 | # tracer: wakeup_rt | |
2016 | # | |
2017 | # wakeup_rt latency trace v1.1.5 on 3.8.0-test+ | |
2018 | # -------------------------------------------------------------------- | |
2019 | # latency: 5 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
2020 | # ----------------- | |
2021 | # | task: sleep-2389 (uid:0 nice:0 policy:1 rt_prio:5) | |
2022 | # ----------------- | |
2023 | # | |
2024 | # _------=> CPU# | |
2025 | # / _-----=> irqs-off | |
2026 | # | / _----=> need-resched | |
2027 | # || / _---=> hardirq/softirq | |
2028 | # ||| / _--=> preempt-depth | |
2029 | # |||| / delay | |
2030 | # cmd pid ||||| time | caller | |
2031 | # \ / ||||| \ | / | |
2032 | <idle>-0 3d.h4 0us : 0:120:R + [003] 2389: 94:R sleep | |
2033 | <idle>-0 3d.h4 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up | |
2034 | <idle>-0 3d..3 5us : __schedule <-schedule | |
2035 | <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep | |
2036 | ||
2037 | ||
2038 | Running this on an idle system, we see that it only took 5 microseconds | |
2039 | to perform the task switch. Note, since the trace point in the schedule | |
2040 | is before the actual "switch", we stop the tracing when the recorded task | |
2041 | is about to schedule in. This may change if we add a new marker at the | |
2042 | end of the scheduler. | |
2043 | ||
2044 | Notice that the recorded task is 'sleep' with the PID of 2389 | |
2045 | and it has an rt_prio of 5. This priority is user-space priority | |
2046 | and not the internal kernel priority. The policy is 1 for | |
2047 | SCHED_FIFO and 2 for SCHED_RR. | |
2048 | ||
2049 | Note, that the trace data shows the internal priority (99 - rtprio). | |
2050 | :: | |
2051 | ||
2052 | <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep | |
2053 | ||
2054 | The 0:120:R means idle was running with a nice priority of 0 (120 - 120) | |
2055 | and in the running state 'R'. The sleep task was scheduled in with | |
2056 | 2389: 94:R. That is the priority is the kernel rtprio (99 - 5 = 94) | |
2057 | and it too is in the running state. | |
2058 | ||
2059 | Doing the same with chrt -r 5 and function-trace set. | |
2060 | :: | |
2061 | ||
2062 | echo 1 > options/function-trace | |
2063 | ||
2064 | # tracer: wakeup_rt | |
2065 | # | |
2066 | # wakeup_rt latency trace v1.1.5 on 3.8.0-test+ | |
2067 | # -------------------------------------------------------------------- | |
2068 | # latency: 29 us, #85/85, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
2069 | # ----------------- | |
2070 | # | task: sleep-2448 (uid:0 nice:0 policy:1 rt_prio:5) | |
2071 | # ----------------- | |
2072 | # | |
2073 | # _------=> CPU# | |
2074 | # / _-----=> irqs-off | |
2075 | # | / _----=> need-resched | |
2076 | # || / _---=> hardirq/softirq | |
2077 | # ||| / _--=> preempt-depth | |
2078 | # |||| / delay | |
2079 | # cmd pid ||||| time | caller | |
2080 | # \ / ||||| \ | / | |
2081 | <idle>-0 3d.h4 1us+: 0:120:R + [003] 2448: 94:R sleep | |
2082 | <idle>-0 3d.h4 2us : ttwu_do_activate.constprop.87 <-try_to_wake_up | |
2083 | <idle>-0 3d.h3 3us : check_preempt_curr <-ttwu_do_wakeup | |
2084 | <idle>-0 3d.h3 3us : resched_curr <-check_preempt_curr | |
2085 | <idle>-0 3dNh3 4us : task_woken_rt <-ttwu_do_wakeup | |
2086 | <idle>-0 3dNh3 4us : _raw_spin_unlock <-try_to_wake_up | |
2087 | <idle>-0 3dNh3 4us : sub_preempt_count <-_raw_spin_unlock | |
2088 | <idle>-0 3dNh2 5us : ttwu_stat <-try_to_wake_up | |
2089 | <idle>-0 3dNh2 5us : _raw_spin_unlock_irqrestore <-try_to_wake_up | |
2090 | <idle>-0 3dNh2 6us : sub_preempt_count <-_raw_spin_unlock_irqrestore | |
2091 | <idle>-0 3dNh1 6us : _raw_spin_lock <-__run_hrtimer | |
2092 | <idle>-0 3dNh1 6us : add_preempt_count <-_raw_spin_lock | |
2093 | <idle>-0 3dNh2 7us : _raw_spin_unlock <-hrtimer_interrupt | |
2094 | <idle>-0 3dNh2 7us : sub_preempt_count <-_raw_spin_unlock | |
2095 | <idle>-0 3dNh1 7us : tick_program_event <-hrtimer_interrupt | |
2096 | <idle>-0 3dNh1 7us : clockevents_program_event <-tick_program_event | |
2097 | <idle>-0 3dNh1 8us : ktime_get <-clockevents_program_event | |
2098 | <idle>-0 3dNh1 8us : lapic_next_event <-clockevents_program_event | |
2099 | <idle>-0 3dNh1 8us : irq_exit <-smp_apic_timer_interrupt | |
2100 | <idle>-0 3dNh1 9us : sub_preempt_count <-irq_exit | |
2101 | <idle>-0 3dN.2 9us : idle_cpu <-irq_exit | |
2102 | <idle>-0 3dN.2 9us : rcu_irq_exit <-irq_exit | |
2103 | <idle>-0 3dN.2 10us : rcu_eqs_enter_common.isra.45 <-rcu_irq_exit | |
2104 | <idle>-0 3dN.2 10us : sub_preempt_count <-irq_exit | |
2105 | <idle>-0 3.N.1 11us : rcu_idle_exit <-cpu_idle | |
2106 | <idle>-0 3dN.1 11us : rcu_eqs_exit_common.isra.43 <-rcu_idle_exit | |
2107 | <idle>-0 3.N.1 11us : tick_nohz_idle_exit <-cpu_idle | |
2108 | <idle>-0 3dN.1 12us : menu_hrtimer_cancel <-tick_nohz_idle_exit | |
2109 | <idle>-0 3dN.1 12us : ktime_get <-tick_nohz_idle_exit | |
2110 | <idle>-0 3dN.1 12us : tick_do_update_jiffies64 <-tick_nohz_idle_exit | |
2111 | <idle>-0 3dN.1 13us : cpu_load_update_nohz <-tick_nohz_idle_exit | |
2112 | <idle>-0 3dN.1 13us : _raw_spin_lock <-cpu_load_update_nohz | |
2113 | <idle>-0 3dN.1 13us : add_preempt_count <-_raw_spin_lock | |
2114 | <idle>-0 3dN.2 13us : __cpu_load_update <-cpu_load_update_nohz | |
2115 | <idle>-0 3dN.2 14us : sched_avg_update <-__cpu_load_update | |
2116 | <idle>-0 3dN.2 14us : _raw_spin_unlock <-cpu_load_update_nohz | |
2117 | <idle>-0 3dN.2 14us : sub_preempt_count <-_raw_spin_unlock | |
2118 | <idle>-0 3dN.1 15us : calc_load_nohz_stop <-tick_nohz_idle_exit | |
2119 | <idle>-0 3dN.1 15us : touch_softlockup_watchdog <-tick_nohz_idle_exit | |
2120 | <idle>-0 3dN.1 15us : hrtimer_cancel <-tick_nohz_idle_exit | |
2121 | <idle>-0 3dN.1 15us : hrtimer_try_to_cancel <-hrtimer_cancel | |
2122 | <idle>-0 3dN.1 16us : lock_hrtimer_base.isra.18 <-hrtimer_try_to_cancel | |
2123 | <idle>-0 3dN.1 16us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18 | |
2124 | <idle>-0 3dN.1 16us : add_preempt_count <-_raw_spin_lock_irqsave | |
2125 | <idle>-0 3dN.2 17us : __remove_hrtimer <-remove_hrtimer.part.16 | |
2126 | <idle>-0 3dN.2 17us : hrtimer_force_reprogram <-__remove_hrtimer | |
2127 | <idle>-0 3dN.2 17us : tick_program_event <-hrtimer_force_reprogram | |
2128 | <idle>-0 3dN.2 18us : clockevents_program_event <-tick_program_event | |
2129 | <idle>-0 3dN.2 18us : ktime_get <-clockevents_program_event | |
2130 | <idle>-0 3dN.2 18us : lapic_next_event <-clockevents_program_event | |
2131 | <idle>-0 3dN.2 19us : _raw_spin_unlock_irqrestore <-hrtimer_try_to_cancel | |
2132 | <idle>-0 3dN.2 19us : sub_preempt_count <-_raw_spin_unlock_irqrestore | |
2133 | <idle>-0 3dN.1 19us : hrtimer_forward <-tick_nohz_idle_exit | |
2134 | <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward | |
2135 | <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward | |
2136 | <idle>-0 3dN.1 20us : hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11 | |
2137 | <idle>-0 3dN.1 20us : __hrtimer_start_range_ns <-hrtimer_start_range_ns | |
2138 | <idle>-0 3dN.1 21us : lock_hrtimer_base.isra.18 <-__hrtimer_start_range_ns | |
2139 | <idle>-0 3dN.1 21us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18 | |
2140 | <idle>-0 3dN.1 21us : add_preempt_count <-_raw_spin_lock_irqsave | |
2141 | <idle>-0 3dN.2 22us : ktime_add_safe <-__hrtimer_start_range_ns | |
2142 | <idle>-0 3dN.2 22us : enqueue_hrtimer <-__hrtimer_start_range_ns | |
2143 | <idle>-0 3dN.2 22us : tick_program_event <-__hrtimer_start_range_ns | |
2144 | <idle>-0 3dN.2 23us : clockevents_program_event <-tick_program_event | |
2145 | <idle>-0 3dN.2 23us : ktime_get <-clockevents_program_event | |
2146 | <idle>-0 3dN.2 23us : lapic_next_event <-clockevents_program_event | |
2147 | <idle>-0 3dN.2 24us : _raw_spin_unlock_irqrestore <-__hrtimer_start_range_ns | |
2148 | <idle>-0 3dN.2 24us : sub_preempt_count <-_raw_spin_unlock_irqrestore | |
2149 | <idle>-0 3dN.1 24us : account_idle_ticks <-tick_nohz_idle_exit | |
2150 | <idle>-0 3dN.1 24us : account_idle_time <-account_idle_ticks | |
2151 | <idle>-0 3.N.1 25us : sub_preempt_count <-cpu_idle | |
2152 | <idle>-0 3.N.. 25us : schedule <-cpu_idle | |
2153 | <idle>-0 3.N.. 25us : __schedule <-preempt_schedule | |
2154 | <idle>-0 3.N.. 26us : add_preempt_count <-__schedule | |
2155 | <idle>-0 3.N.1 26us : rcu_note_context_switch <-__schedule | |
2156 | <idle>-0 3.N.1 26us : rcu_sched_qs <-rcu_note_context_switch | |
2157 | <idle>-0 3dN.1 27us : rcu_preempt_qs <-rcu_note_context_switch | |
2158 | <idle>-0 3.N.1 27us : _raw_spin_lock_irq <-__schedule | |
2159 | <idle>-0 3dN.1 27us : add_preempt_count <-_raw_spin_lock_irq | |
2160 | <idle>-0 3dN.2 28us : put_prev_task_idle <-__schedule | |
2161 | <idle>-0 3dN.2 28us : pick_next_task_stop <-pick_next_task | |
2162 | <idle>-0 3dN.2 28us : pick_next_task_rt <-pick_next_task | |
2163 | <idle>-0 3dN.2 29us : dequeue_pushable_task <-pick_next_task_rt | |
2164 | <idle>-0 3d..3 29us : __schedule <-preempt_schedule | |
2165 | <idle>-0 3d..3 30us : 0:120:R ==> [003] 2448: 94:R sleep | |
2166 | ||
2167 | This isn't that big of a trace, even with function tracing enabled, | |
2168 | so I included the entire trace. | |
2169 | ||
2170 | The interrupt went off while when the system was idle. Somewhere | |
2171 | before task_woken_rt() was called, the NEED_RESCHED flag was set, | |
2172 | this is indicated by the first occurrence of the 'N' flag. | |
2173 | ||
2174 | Latency tracing and events | |
2175 | -------------------------- | |
2176 | As function tracing can induce a much larger latency, but without | |
2177 | seeing what happens within the latency it is hard to know what | |
2178 | caused it. There is a middle ground, and that is with enabling | |
2179 | events. | |
2180 | :: | |
2181 | ||
2182 | # echo 0 > options/function-trace | |
2183 | # echo wakeup_rt > current_tracer | |
2184 | # echo 1 > events/enable | |
2185 | # echo 1 > tracing_on | |
2186 | # echo 0 > tracing_max_latency | |
2187 | # chrt -f 5 sleep 1 | |
2188 | # echo 0 > tracing_on | |
2189 | # cat trace | |
2190 | # tracer: wakeup_rt | |
2191 | # | |
2192 | # wakeup_rt latency trace v1.1.5 on 3.8.0-test+ | |
2193 | # -------------------------------------------------------------------- | |
2194 | # latency: 6 us, #12/12, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4) | |
2195 | # ----------------- | |
2196 | # | task: sleep-5882 (uid:0 nice:0 policy:1 rt_prio:5) | |
2197 | # ----------------- | |
2198 | # | |
2199 | # _------=> CPU# | |
2200 | # / _-----=> irqs-off | |
2201 | # | / _----=> need-resched | |
2202 | # || / _---=> hardirq/softirq | |
2203 | # ||| / _--=> preempt-depth | |
2204 | # |||| / delay | |
2205 | # cmd pid ||||| time | caller | |
2206 | # \ / ||||| \ | / | |
2207 | <idle>-0 2d.h4 0us : 0:120:R + [002] 5882: 94:R sleep | |
2208 | <idle>-0 2d.h4 0us : ttwu_do_activate.constprop.87 <-try_to_wake_up | |
2209 | <idle>-0 2d.h4 1us : sched_wakeup: comm=sleep pid=5882 prio=94 success=1 target_cpu=002 | |
2210 | <idle>-0 2dNh2 1us : hrtimer_expire_exit: hrtimer=ffff88007796feb8 | |
2211 | <idle>-0 2.N.2 2us : power_end: cpu_id=2 | |
2212 | <idle>-0 2.N.2 3us : cpu_idle: state=4294967295 cpu_id=2 | |
2213 | <idle>-0 2dN.3 4us : hrtimer_cancel: hrtimer=ffff88007d50d5e0 | |
2214 | <idle>-0 2dN.3 4us : hrtimer_start: hrtimer=ffff88007d50d5e0 function=tick_sched_timer expires=34311211000000 softexpires=34311211000000 | |
2215 | <idle>-0 2.N.2 5us : rcu_utilization: Start context switch | |
2216 | <idle>-0 2.N.2 5us : rcu_utilization: End context switch | |
2217 | <idle>-0 2d..3 6us : __schedule <-schedule | |
2218 | <idle>-0 2d..3 6us : 0:120:R ==> [002] 5882: 94:R sleep | |
2219 | ||
2220 | ||
2221 | Hardware Latency Detector | |
2222 | ------------------------- | |
2223 | ||
2224 | The hardware latency detector is executed by enabling the "hwlat" tracer. | |
2225 | ||
2226 | NOTE, this tracer will affect the performance of the system as it will | |
2227 | periodically make a CPU constantly busy with interrupts disabled. | |
2228 | :: | |
2229 | ||
2230 | # echo hwlat > current_tracer | |
2231 | # sleep 100 | |
2232 | # cat trace | |
2233 | # tracer: hwlat | |
2234 | # | |
b396bfde SRV |
2235 | # entries-in-buffer/entries-written: 13/13 #P:8 |
2236 | # | |
1f198e22 CD |
2237 | # _-----=> irqs-off |
2238 | # / _----=> need-resched | |
2239 | # | / _---=> hardirq/softirq | |
2240 | # || / _--=> preempt-depth | |
2241 | # ||| / delay | |
2242 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
2243 | # | | | |||| | | | |
b396bfde SRV |
2244 | <...>-1729 [001] d... 678.473449: #1 inner/outer(us): 11/12 ts:1581527483.343962693 count:6 |
2245 | <...>-1729 [004] d... 689.556542: #2 inner/outer(us): 16/9 ts:1581527494.889008092 count:1 | |
2246 | <...>-1729 [005] d... 714.756290: #3 inner/outer(us): 16/16 ts:1581527519.678961629 count:5 | |
2247 | <...>-1729 [001] d... 718.788247: #4 inner/outer(us): 9/17 ts:1581527523.889012713 count:1 | |
2248 | <...>-1729 [002] d... 719.796341: #5 inner/outer(us): 13/9 ts:1581527524.912872606 count:1 | |
2249 | <...>-1729 [006] d... 844.787091: #6 inner/outer(us): 9/12 ts:1581527649.889048502 count:2 | |
2250 | <...>-1729 [003] d... 849.827033: #7 inner/outer(us): 18/9 ts:1581527654.889013793 count:1 | |
2251 | <...>-1729 [007] d... 853.859002: #8 inner/outer(us): 9/12 ts:1581527658.889065736 count:1 | |
2252 | <...>-1729 [001] d... 855.874978: #9 inner/outer(us): 9/11 ts:1581527660.861991877 count:1 | |
2253 | <...>-1729 [001] d... 863.938932: #10 inner/outer(us): 9/11 ts:1581527668.970010500 count:1 nmi-total:7 nmi-count:1 | |
2254 | <...>-1729 [007] d... 878.050780: #11 inner/outer(us): 9/12 ts:1581527683.385002600 count:1 nmi-total:5 nmi-count:1 | |
2255 | <...>-1729 [007] d... 886.114702: #12 inner/outer(us): 9/12 ts:1581527691.385001600 count:1 | |
1f198e22 CD |
2256 | |
2257 | ||
2258 | The above output is somewhat the same in the header. All events will have | |
2259 | interrupts disabled 'd'. Under the FUNCTION title there is: | |
2260 | ||
2261 | #1 | |
2262 | This is the count of events recorded that were greater than the | |
2263 | tracing_threshold (See below). | |
2264 | ||
b396bfde | 2265 | inner/outer(us): 11/11 |
1f198e22 CD |
2266 | |
2267 | This shows two numbers as "inner latency" and "outer latency". The test | |
2268 | runs in a loop checking a timestamp twice. The latency detected within | |
2269 | the two timestamps is the "inner latency" and the latency detected | |
2270 | after the previous timestamp and the next timestamp in the loop is | |
2271 | the "outer latency". | |
2272 | ||
b396bfde SRV |
2273 | ts:1581527483.343962693 |
2274 | ||
2275 | The absolute timestamp that the first latency was recorded in the window. | |
2276 | ||
2277 | count:6 | |
1f198e22 | 2278 | |
b396bfde | 2279 | The number of times a latency was detected during the window. |
1f198e22 | 2280 | |
b396bfde | 2281 | nmi-total:7 nmi-count:1 |
1f198e22 CD |
2282 | |
2283 | On architectures that support it, if an NMI comes in during the | |
2284 | test, the time spent in NMI is reported in "nmi-total" (in | |
2285 | microseconds). | |
2286 | ||
2287 | All architectures that have NMIs will show the "nmi-count" if an | |
2288 | NMI comes in during the test. | |
2289 | ||
2290 | hwlat files: | |
2291 | ||
2292 | tracing_threshold | |
2293 | This gets automatically set to "10" to represent 10 | |
2294 | microseconds. This is the threshold of latency that | |
2295 | needs to be detected before the trace will be recorded. | |
2296 | ||
2297 | Note, when hwlat tracer is finished (another tracer is | |
2298 | written into "current_tracer"), the original value for | |
2299 | tracing_threshold is placed back into this file. | |
2300 | ||
2301 | hwlat_detector/width | |
2302 | The length of time the test runs with interrupts disabled. | |
2303 | ||
2304 | hwlat_detector/window | |
2305 | The length of time of the window which the test | |
2306 | runs. That is, the test will run for "width" | |
2307 | microseconds per "window" microseconds | |
2308 | ||
2309 | tracing_cpumask | |
2310 | When the test is started. A kernel thread is created that | |
2311 | runs the test. This thread will alternate between CPUs | |
2312 | listed in the tracing_cpumask between each period | |
2313 | (one "window"). To limit the test to specific CPUs | |
2314 | set the mask in this file to only the CPUs that the test | |
2315 | should run on. | |
2316 | ||
2317 | function | |
2318 | -------- | |
2319 | ||
2320 | This tracer is the function tracer. Enabling the function tracer | |
2321 | can be done from the debug file system. Make sure the | |
2322 | ftrace_enabled is set; otherwise this tracer is a nop. | |
2323 | See the "ftrace_enabled" section below. | |
2324 | :: | |
2325 | ||
2326 | # sysctl kernel.ftrace_enabled=1 | |
2327 | # echo function > current_tracer | |
2328 | # echo 1 > tracing_on | |
2329 | # usleep 1 | |
2330 | # echo 0 > tracing_on | |
2331 | # cat trace | |
2332 | # tracer: function | |
2333 | # | |
2334 | # entries-in-buffer/entries-written: 24799/24799 #P:4 | |
2335 | # | |
2336 | # _-----=> irqs-off | |
2337 | # / _----=> need-resched | |
2338 | # | / _---=> hardirq/softirq | |
2339 | # || / _--=> preempt-depth | |
2340 | # ||| / delay | |
2341 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
2342 | # | | | |||| | | | |
2343 | bash-1994 [002] .... 3082.063030: mutex_unlock <-rb_simple_write | |
2344 | bash-1994 [002] .... 3082.063031: __mutex_unlock_slowpath <-mutex_unlock | |
2345 | bash-1994 [002] .... 3082.063031: __fsnotify_parent <-fsnotify_modify | |
2346 | bash-1994 [002] .... 3082.063032: fsnotify <-fsnotify_modify | |
2347 | bash-1994 [002] .... 3082.063032: __srcu_read_lock <-fsnotify | |
2348 | bash-1994 [002] .... 3082.063032: add_preempt_count <-__srcu_read_lock | |
2349 | bash-1994 [002] ...1 3082.063032: sub_preempt_count <-__srcu_read_lock | |
2350 | bash-1994 [002] .... 3082.063033: __srcu_read_unlock <-fsnotify | |
2351 | [...] | |
2352 | ||
2353 | ||
2354 | Note: function tracer uses ring buffers to store the above | |
2355 | entries. The newest data may overwrite the oldest data. | |
2356 | Sometimes using echo to stop the trace is not sufficient because | |
2357 | the tracing could have overwritten the data that you wanted to | |
2358 | record. For this reason, it is sometimes better to disable | |
2359 | tracing directly from a program. This allows you to stop the | |
2360 | tracing at the point that you hit the part that you are | |
2361 | interested in. To disable the tracing directly from a C program, | |
2362 | something like following code snippet can be used:: | |
2363 | ||
2364 | int trace_fd; | |
2365 | [...] | |
2366 | int main(int argc, char *argv[]) { | |
2367 | [...] | |
2368 | trace_fd = open(tracing_file("tracing_on"), O_WRONLY); | |
2369 | [...] | |
2370 | if (condition_hit()) { | |
2371 | write(trace_fd, "0", 1); | |
2372 | } | |
2373 | [...] | |
2374 | } | |
2375 | ||
2376 | ||
2377 | Single thread tracing | |
2378 | --------------------- | |
2379 | ||
2380 | By writing into set_ftrace_pid you can trace a | |
2381 | single thread. For example:: | |
2382 | ||
2383 | # cat set_ftrace_pid | |
2384 | no pid | |
2385 | # echo 3111 > set_ftrace_pid | |
2386 | # cat set_ftrace_pid | |
2387 | 3111 | |
2388 | # echo function > current_tracer | |
2389 | # cat trace | head | |
2390 | # tracer: function | |
2391 | # | |
2392 | # TASK-PID CPU# TIMESTAMP FUNCTION | |
2393 | # | | | | | | |
2394 | yum-updatesd-3111 [003] 1637.254676: finish_task_switch <-thread_return | |
2395 | yum-updatesd-3111 [003] 1637.254681: hrtimer_cancel <-schedule_hrtimeout_range | |
2396 | yum-updatesd-3111 [003] 1637.254682: hrtimer_try_to_cancel <-hrtimer_cancel | |
2397 | yum-updatesd-3111 [003] 1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel | |
2398 | yum-updatesd-3111 [003] 1637.254685: fget_light <-do_sys_poll | |
2399 | yum-updatesd-3111 [003] 1637.254686: pipe_poll <-do_sys_poll | |
2400 | # echo > set_ftrace_pid | |
2401 | # cat trace |head | |
2402 | # tracer: function | |
2403 | # | |
2404 | # TASK-PID CPU# TIMESTAMP FUNCTION | |
2405 | # | | | | | | |
2406 | ##### CPU 3 buffer started #### | |
2407 | yum-updatesd-3111 [003] 1701.957688: free_poll_entry <-poll_freewait | |
2408 | yum-updatesd-3111 [003] 1701.957689: remove_wait_queue <-free_poll_entry | |
2409 | yum-updatesd-3111 [003] 1701.957691: fput <-free_poll_entry | |
2410 | yum-updatesd-3111 [003] 1701.957692: audit_syscall_exit <-sysret_audit | |
2411 | yum-updatesd-3111 [003] 1701.957693: path_put <-audit_syscall_exit | |
2412 | ||
2413 | If you want to trace a function when executing, you could use | |
2414 | something like this simple program. | |
2415 | :: | |
2416 | ||
2417 | #include <stdio.h> | |
2418 | #include <stdlib.h> | |
2419 | #include <sys/types.h> | |
2420 | #include <sys/stat.h> | |
2421 | #include <fcntl.h> | |
2422 | #include <unistd.h> | |
2423 | #include <string.h> | |
2424 | ||
2425 | #define _STR(x) #x | |
2426 | #define STR(x) _STR(x) | |
2427 | #define MAX_PATH 256 | |
2428 | ||
2429 | const char *find_tracefs(void) | |
2430 | { | |
2431 | static char tracefs[MAX_PATH+1]; | |
2432 | static int tracefs_found; | |
2433 | char type[100]; | |
2434 | FILE *fp; | |
2435 | ||
2436 | if (tracefs_found) | |
2437 | return tracefs; | |
2438 | ||
2439 | if ((fp = fopen("/proc/mounts","r")) == NULL) { | |
2440 | perror("/proc/mounts"); | |
2441 | return NULL; | |
2442 | } | |
2443 | ||
2444 | while (fscanf(fp, "%*s %" | |
2445 | STR(MAX_PATH) | |
2446 | "s %99s %*s %*d %*d\n", | |
2447 | tracefs, type) == 2) { | |
2448 | if (strcmp(type, "tracefs") == 0) | |
2449 | break; | |
2450 | } | |
2451 | fclose(fp); | |
2452 | ||
2453 | if (strcmp(type, "tracefs") != 0) { | |
2454 | fprintf(stderr, "tracefs not mounted"); | |
2455 | return NULL; | |
2456 | } | |
2457 | ||
2458 | strcat(tracefs, "/tracing/"); | |
2459 | tracefs_found = 1; | |
2460 | ||
2461 | return tracefs; | |
2462 | } | |
2463 | ||
2464 | const char *tracing_file(const char *file_name) | |
2465 | { | |
2466 | static char trace_file[MAX_PATH+1]; | |
2467 | snprintf(trace_file, MAX_PATH, "%s/%s", find_tracefs(), file_name); | |
2468 | return trace_file; | |
2469 | } | |
2470 | ||
2471 | int main (int argc, char **argv) | |
2472 | { | |
2473 | if (argc < 1) | |
2474 | exit(-1); | |
2475 | ||
2476 | if (fork() > 0) { | |
2477 | int fd, ffd; | |
2478 | char line[64]; | |
2479 | int s; | |
2480 | ||
2481 | ffd = open(tracing_file("current_tracer"), O_WRONLY); | |
2482 | if (ffd < 0) | |
2483 | exit(-1); | |
2484 | write(ffd, "nop", 3); | |
2485 | ||
2486 | fd = open(tracing_file("set_ftrace_pid"), O_WRONLY); | |
2487 | s = sprintf(line, "%d\n", getpid()); | |
2488 | write(fd, line, s); | |
2489 | ||
2490 | write(ffd, "function", 8); | |
2491 | ||
2492 | close(fd); | |
2493 | close(ffd); | |
2494 | ||
2495 | execvp(argv[1], argv+1); | |
2496 | } | |
2497 | ||
2498 | return 0; | |
2499 | } | |
2500 | ||
2501 | Or this simple script! | |
2502 | :: | |
2503 | ||
2504 | #!/bin/bash | |
2505 | ||
2506 | tracefs=`sed -ne 's/^tracefs \(.*\) tracefs.*/\1/p' /proc/mounts` | |
951e0d00 ZL |
2507 | echo 0 > $tracefs/tracing_on |
2508 | echo $$ > $tracefs/set_ftrace_pid | |
2509 | echo function > $tracefs/current_tracer | |
2510 | echo 1 > $tracefs/tracing_on | |
1f198e22 CD |
2511 | exec "$@" |
2512 | ||
2513 | ||
2514 | function graph tracer | |
2515 | --------------------------- | |
2516 | ||
2517 | This tracer is similar to the function tracer except that it | |
2518 | probes a function on its entry and its exit. This is done by | |
2519 | using a dynamically allocated stack of return addresses in each | |
2520 | task_struct. On function entry the tracer overwrites the return | |
2521 | address of each function traced to set a custom probe. Thus the | |
2522 | original return address is stored on the stack of return address | |
2523 | in the task_struct. | |
2524 | ||
2525 | Probing on both ends of a function leads to special features | |
2526 | such as: | |
2527 | ||
2528 | - measure of a function's time execution | |
2529 | - having a reliable call stack to draw function calls graph | |
2530 | ||
2531 | This tracer is useful in several situations: | |
2532 | ||
2533 | - you want to find the reason of a strange kernel behavior and | |
2534 | need to see what happens in detail on any areas (or specific | |
2535 | ones). | |
2536 | ||
2537 | - you are experiencing weird latencies but it's difficult to | |
2538 | find its origin. | |
2539 | ||
2540 | - you want to find quickly which path is taken by a specific | |
2541 | function | |
2542 | ||
2543 | - you just want to peek inside a working kernel and want to see | |
2544 | what happens there. | |
2545 | ||
2546 | :: | |
2547 | ||
2548 | # tracer: function_graph | |
2549 | # | |
2550 | # CPU DURATION FUNCTION CALLS | |
2551 | # | | | | | | | | |
2552 | ||
2553 | 0) | sys_open() { | |
2554 | 0) | do_sys_open() { | |
2555 | 0) | getname() { | |
2556 | 0) | kmem_cache_alloc() { | |
2557 | 0) 1.382 us | __might_sleep(); | |
2558 | 0) 2.478 us | } | |
2559 | 0) | strncpy_from_user() { | |
2560 | 0) | might_fault() { | |
2561 | 0) 1.389 us | __might_sleep(); | |
2562 | 0) 2.553 us | } | |
2563 | 0) 3.807 us | } | |
2564 | 0) 7.876 us | } | |
2565 | 0) | alloc_fd() { | |
2566 | 0) 0.668 us | _spin_lock(); | |
2567 | 0) 0.570 us | expand_files(); | |
2568 | 0) 0.586 us | _spin_unlock(); | |
2569 | ||
2570 | ||
2571 | There are several columns that can be dynamically | |
2572 | enabled/disabled. You can use every combination of options you | |
2573 | want, depending on your needs. | |
2574 | ||
2575 | - The cpu number on which the function executed is default | |
2576 | enabled. It is sometimes better to only trace one cpu (see | |
2577 | tracing_cpu_mask file) or you might sometimes see unordered | |
2578 | function calls while cpu tracing switch. | |
2579 | ||
2580 | - hide: echo nofuncgraph-cpu > trace_options | |
2581 | - show: echo funcgraph-cpu > trace_options | |
2582 | ||
2583 | - The duration (function's time of execution) is displayed on | |
2584 | the closing bracket line of a function or on the same line | |
2585 | than the current function in case of a leaf one. It is default | |
2586 | enabled. | |
2587 | ||
2588 | - hide: echo nofuncgraph-duration > trace_options | |
2589 | - show: echo funcgraph-duration > trace_options | |
2590 | ||
2591 | - The overhead field precedes the duration field in case of | |
2592 | reached duration thresholds. | |
2593 | ||
2594 | - hide: echo nofuncgraph-overhead > trace_options | |
2595 | - show: echo funcgraph-overhead > trace_options | |
2596 | - depends on: funcgraph-duration | |
2597 | ||
2598 | ie:: | |
2599 | ||
2600 | 3) # 1837.709 us | } /* __switch_to */ | |
2601 | 3) | finish_task_switch() { | |
2602 | 3) 0.313 us | _raw_spin_unlock_irq(); | |
2603 | 3) 3.177 us | } | |
2604 | 3) # 1889.063 us | } /* __schedule */ | |
2605 | 3) ! 140.417 us | } /* __schedule */ | |
2606 | 3) # 2034.948 us | } /* schedule */ | |
2607 | 3) * 33998.59 us | } /* schedule_preempt_disabled */ | |
2608 | ||
2609 | [...] | |
2610 | ||
2611 | 1) 0.260 us | msecs_to_jiffies(); | |
2612 | 1) 0.313 us | __rcu_read_unlock(); | |
2613 | 1) + 61.770 us | } | |
2614 | 1) + 64.479 us | } | |
2615 | 1) 0.313 us | rcu_bh_qs(); | |
2616 | 1) 0.313 us | __local_bh_enable(); | |
2617 | 1) ! 217.240 us | } | |
2618 | 1) 0.365 us | idle_cpu(); | |
2619 | 1) | rcu_irq_exit() { | |
2620 | 1) 0.417 us | rcu_eqs_enter_common.isra.47(); | |
2621 | 1) 3.125 us | } | |
2622 | 1) ! 227.812 us | } | |
2623 | 1) ! 457.395 us | } | |
2624 | 1) @ 119760.2 us | } | |
2625 | ||
2626 | [...] | |
2627 | ||
2628 | 2) | handle_IPI() { | |
2629 | 1) 6.979 us | } | |
2630 | 2) 0.417 us | scheduler_ipi(); | |
2631 | 1) 9.791 us | } | |
2632 | 1) + 12.917 us | } | |
2633 | 2) 3.490 us | } | |
2634 | 1) + 15.729 us | } | |
2635 | 1) + 18.542 us | } | |
2636 | 2) $ 3594274 us | } | |
2637 | ||
2638 | Flags:: | |
2639 | ||
2640 | + means that the function exceeded 10 usecs. | |
2641 | ! means that the function exceeded 100 usecs. | |
2642 | # means that the function exceeded 1000 usecs. | |
2643 | * means that the function exceeded 10 msecs. | |
2644 | @ means that the function exceeded 100 msecs. | |
2645 | $ means that the function exceeded 1 sec. | |
2646 | ||
2647 | ||
2648 | - The task/pid field displays the thread cmdline and pid which | |
2649 | executed the function. It is default disabled. | |
2650 | ||
2651 | - hide: echo nofuncgraph-proc > trace_options | |
2652 | - show: echo funcgraph-proc > trace_options | |
2653 | ||
2654 | ie:: | |
2655 | ||
2656 | # tracer: function_graph | |
2657 | # | |
2658 | # CPU TASK/PID DURATION FUNCTION CALLS | |
2659 | # | | | | | | | | | | |
2660 | 0) sh-4802 | | d_free() { | |
2661 | 0) sh-4802 | | call_rcu() { | |
2662 | 0) sh-4802 | | __call_rcu() { | |
2663 | 0) sh-4802 | 0.616 us | rcu_process_gp_end(); | |
2664 | 0) sh-4802 | 0.586 us | check_for_new_grace_period(); | |
2665 | 0) sh-4802 | 2.899 us | } | |
2666 | 0) sh-4802 | 4.040 us | } | |
2667 | 0) sh-4802 | 5.151 us | } | |
2668 | 0) sh-4802 | + 49.370 us | } | |
2669 | ||
2670 | ||
2671 | - The absolute time field is an absolute timestamp given by the | |
2672 | system clock since it started. A snapshot of this time is | |
2673 | given on each entry/exit of functions | |
2674 | ||
2675 | - hide: echo nofuncgraph-abstime > trace_options | |
2676 | - show: echo funcgraph-abstime > trace_options | |
2677 | ||
2678 | ie:: | |
2679 | ||
2680 | # | |
2681 | # TIME CPU DURATION FUNCTION CALLS | |
2682 | # | | | | | | | | | |
2683 | 360.774522 | 1) 0.541 us | } | |
2684 | 360.774522 | 1) 4.663 us | } | |
2685 | 360.774523 | 1) 0.541 us | __wake_up_bit(); | |
2686 | 360.774524 | 1) 6.796 us | } | |
2687 | 360.774524 | 1) 7.952 us | } | |
2688 | 360.774525 | 1) 9.063 us | } | |
2689 | 360.774525 | 1) 0.615 us | journal_mark_dirty(); | |
2690 | 360.774527 | 1) 0.578 us | __brelse(); | |
2691 | 360.774528 | 1) | reiserfs_prepare_for_journal() { | |
2692 | 360.774528 | 1) | unlock_buffer() { | |
2693 | 360.774529 | 1) | wake_up_bit() { | |
2694 | 360.774529 | 1) | bit_waitqueue() { | |
2695 | 360.774530 | 1) 0.594 us | __phys_addr(); | |
2696 | ||
2697 | ||
2698 | The function name is always displayed after the closing bracket | |
2699 | for a function if the start of that function is not in the | |
2700 | trace buffer. | |
2701 | ||
2702 | Display of the function name after the closing bracket may be | |
2703 | enabled for functions whose start is in the trace buffer, | |
2704 | allowing easier searching with grep for function durations. | |
2705 | It is default disabled. | |
2706 | ||
2707 | - hide: echo nofuncgraph-tail > trace_options | |
2708 | - show: echo funcgraph-tail > trace_options | |
2709 | ||
2710 | Example with nofuncgraph-tail (default):: | |
2711 | ||
2712 | 0) | putname() { | |
2713 | 0) | kmem_cache_free() { | |
2714 | 0) 0.518 us | __phys_addr(); | |
2715 | 0) 1.757 us | } | |
2716 | 0) 2.861 us | } | |
2717 | ||
2718 | Example with funcgraph-tail:: | |
2719 | ||
2720 | 0) | putname() { | |
2721 | 0) | kmem_cache_free() { | |
2722 | 0) 0.518 us | __phys_addr(); | |
2723 | 0) 1.757 us | } /* kmem_cache_free() */ | |
2724 | 0) 2.861 us | } /* putname() */ | |
2725 | ||
21c094d3 DP |
2726 | The return value of each traced function can be displayed after |
2727 | an equal sign "=". When encountering system call failures, it | |
d56b699d | 2728 | can be very helpful to quickly locate the function that first |
21c094d3 DP |
2729 | returns an error code. |
2730 | ||
2731 | - hide: echo nofuncgraph-retval > trace_options | |
2732 | - show: echo funcgraph-retval > trace_options | |
2733 | ||
2734 | Example with funcgraph-retval:: | |
2735 | ||
2736 | 1) | cgroup_migrate() { | |
2737 | 1) 0.651 us | cgroup_migrate_add_task(); /* = 0xffff93fcfd346c00 */ | |
2738 | 1) | cgroup_migrate_execute() { | |
2739 | 1) | cpu_cgroup_can_attach() { | |
2740 | 1) | cgroup_taskset_first() { | |
2741 | 1) 0.732 us | cgroup_taskset_next(); /* = 0xffff93fc8fb20000 */ | |
2742 | 1) 1.232 us | } /* cgroup_taskset_first = 0xffff93fc8fb20000 */ | |
2743 | 1) 0.380 us | sched_rt_can_attach(); /* = 0x0 */ | |
2744 | 1) 2.335 us | } /* cpu_cgroup_can_attach = -22 */ | |
2745 | 1) 4.369 us | } /* cgroup_migrate_execute = -22 */ | |
2746 | 1) 7.143 us | } /* cgroup_migrate = -22 */ | |
2747 | ||
2748 | The above example shows that the function cpu_cgroup_can_attach | |
2749 | returned the error code -22 firstly, then we can read the code | |
2750 | of this function to get the root cause. | |
2751 | ||
2752 | When the option funcgraph-retval-hex is not set, the return value can | |
2753 | be displayed in a smart way. Specifically, if it is an error code, | |
2754 | it will be printed in signed decimal format, otherwise it will | |
2755 | printed in hexadecimal format. | |
2756 | ||
2757 | - smart: echo nofuncgraph-retval-hex > trace_options | |
2758 | - hexadecimal: echo funcgraph-retval-hex > trace_options | |
2759 | ||
2760 | Example with funcgraph-retval-hex:: | |
2761 | ||
2762 | 1) | cgroup_migrate() { | |
2763 | 1) 0.651 us | cgroup_migrate_add_task(); /* = 0xffff93fcfd346c00 */ | |
2764 | 1) | cgroup_migrate_execute() { | |
2765 | 1) | cpu_cgroup_can_attach() { | |
2766 | 1) | cgroup_taskset_first() { | |
2767 | 1) 0.732 us | cgroup_taskset_next(); /* = 0xffff93fc8fb20000 */ | |
2768 | 1) 1.232 us | } /* cgroup_taskset_first = 0xffff93fc8fb20000 */ | |
2769 | 1) 0.380 us | sched_rt_can_attach(); /* = 0x0 */ | |
2770 | 1) 2.335 us | } /* cpu_cgroup_can_attach = 0xffffffea */ | |
2771 | 1) 4.369 us | } /* cgroup_migrate_execute = 0xffffffea */ | |
2772 | 1) 7.143 us | } /* cgroup_migrate = 0xffffffea */ | |
2773 | ||
2774 | At present, there are some limitations when using the funcgraph-retval | |
2775 | option, and these limitations will be eliminated in the future: | |
2776 | ||
2777 | - Even if the function return type is void, a return value will still | |
2778 | be printed, and you can just ignore it. | |
2779 | ||
2780 | - Even if return values are stored in multiple registers, only the | |
2781 | value contained in the first register will be recorded and printed. | |
2782 | To illustrate, in the x86 architecture, eax and edx are used to store | |
2783 | a 64-bit return value, with the lower 32 bits saved in eax and the | |
2784 | upper 32 bits saved in edx. However, only the value stored in eax | |
2785 | will be recorded and printed. | |
2786 | ||
2787 | - In certain procedure call standards, such as arm64's AAPCS64, when a | |
2788 | type is smaller than a GPR, it is the responsibility of the consumer | |
2789 | to perform the narrowing, and the upper bits may contain UNKNOWN values. | |
2790 | Therefore, it is advisable to check the code for such cases. For instance, | |
2791 | when using a u8 in a 64-bit GPR, bits [63:8] may contain arbitrary values, | |
2792 | especially when larger types are truncated, whether explicitly or implicitly. | |
2793 | Here are some specific cases to illustrate this point: | |
2794 | ||
fc30ace0 | 2795 | **Case One**: |
21c094d3 DP |
2796 | |
2797 | The function narrow_to_u8 is defined as follows:: | |
2798 | ||
2799 | u8 narrow_to_u8(u64 val) | |
2800 | { | |
2801 | // implicitly truncated | |
2802 | return val; | |
2803 | } | |
2804 | ||
2805 | It may be compiled to:: | |
2806 | ||
2807 | narrow_to_u8: | |
2808 | < ... ftrace instrumentation ... > | |
2809 | RET | |
2810 | ||
2811 | If you pass 0x123456789abcdef to this function and want to narrow it, | |
2812 | it may be recorded as 0x123456789abcdef instead of 0xef. | |
2813 | ||
fc30ace0 | 2814 | **Case Two**: |
21c094d3 DP |
2815 | |
2816 | The function error_if_not_4g_aligned is defined as follows:: | |
2817 | ||
2818 | int error_if_not_4g_aligned(u64 val) | |
2819 | { | |
2820 | if (val & GENMASK(31, 0)) | |
2821 | return -EINVAL; | |
2822 | ||
2823 | return 0; | |
2824 | } | |
2825 | ||
2826 | It could be compiled to:: | |
2827 | ||
2828 | error_if_not_4g_aligned: | |
2829 | CBNZ w0, .Lnot_aligned | |
2830 | RET // bits [31:0] are zero, bits | |
2831 | // [63:32] are UNKNOWN | |
2832 | .Lnot_aligned: | |
2833 | MOV x0, #-EINVAL | |
2834 | RET | |
2835 | ||
2836 | When passing 0x2_0000_0000 to it, the return value may be recorded as | |
2837 | 0x2_0000_0000 instead of 0. | |
2838 | ||
1f198e22 CD |
2839 | You can put some comments on specific functions by using |
2840 | trace_printk() For example, if you want to put a comment inside | |
2841 | the __might_sleep() function, you just have to include | |
2842 | <linux/ftrace.h> and call trace_printk() inside __might_sleep():: | |
2843 | ||
2844 | trace_printk("I'm a comment!\n") | |
2845 | ||
2846 | will produce:: | |
2847 | ||
2848 | 1) | __might_sleep() { | |
2849 | 1) | /* I'm a comment! */ | |
2850 | 1) 1.449 us | } | |
2851 | ||
2852 | ||
2853 | You might find other useful features for this tracer in the | |
2854 | following "dynamic ftrace" section such as tracing only specific | |
2855 | functions or tasks. | |
2856 | ||
2857 | dynamic ftrace | |
2858 | -------------- | |
2859 | ||
2860 | If CONFIG_DYNAMIC_FTRACE is set, the system will run with | |
2861 | virtually no overhead when function tracing is disabled. The way | |
2862 | this works is the mcount function call (placed at the start of | |
2863 | every kernel function, produced by the -pg switch in gcc), | |
2864 | starts of pointing to a simple return. (Enabling FTRACE will | |
2865 | include the -pg switch in the compiling of the kernel.) | |
2866 | ||
2867 | At compile time every C file object is run through the | |
2868 | recordmcount program (located in the scripts directory). This | |
2869 | program will parse the ELF headers in the C object to find all | |
2870 | the locations in the .text section that call mcount. Starting | |
2a1e03ca | 2871 | with gcc version 4.6, the -mfentry has been added for x86, which |
1f198e22 CD |
2872 | calls "__fentry__" instead of "mcount". Which is called before |
2873 | the creation of the stack frame. | |
2874 | ||
2875 | Note, not all sections are traced. They may be prevented by either | |
2876 | a notrace, or blocked another way and all inline functions are not | |
2877 | traced. Check the "available_filter_functions" file to see what functions | |
2878 | can be traced. | |
2879 | ||
2880 | A section called "__mcount_loc" is created that holds | |
2881 | references to all the mcount/fentry call sites in the .text section. | |
2882 | The recordmcount program re-links this section back into the | |
2883 | original object. The final linking stage of the kernel will add all these | |
2884 | references into a single table. | |
2885 | ||
2886 | On boot up, before SMP is initialized, the dynamic ftrace code | |
2887 | scans this table and updates all the locations into nops. It | |
2888 | also records the locations, which are added to the | |
2889 | available_filter_functions list. Modules are processed as they | |
2890 | are loaded and before they are executed. When a module is | |
2891 | unloaded, it also removes its functions from the ftrace function | |
2892 | list. This is automatic in the module unload code, and the | |
2893 | module author does not need to worry about it. | |
2894 | ||
2895 | When tracing is enabled, the process of modifying the function | |
2896 | tracepoints is dependent on architecture. The old method is to use | |
2897 | kstop_machine to prevent races with the CPUs executing code being | |
2898 | modified (which can cause the CPU to do undesirable things, especially | |
2899 | if the modified code crosses cache (or page) boundaries), and the nops are | |
2900 | patched back to calls. But this time, they do not call mcount | |
2901 | (which is just a function stub). They now call into the ftrace | |
2902 | infrastructure. | |
2903 | ||
2904 | The new method of modifying the function tracepoints is to place | |
2905 | a breakpoint at the location to be modified, sync all CPUs, modify | |
2906 | the rest of the instruction not covered by the breakpoint. Sync | |
2907 | all CPUs again, and then remove the breakpoint with the finished | |
2908 | version to the ftrace call site. | |
2909 | ||
2910 | Some archs do not even need to monkey around with the synchronization, | |
2911 | and can just slap the new code on top of the old without any | |
2912 | problems with other CPUs executing it at the same time. | |
2913 | ||
2914 | One special side-effect to the recording of the functions being | |
2915 | traced is that we can now selectively choose which functions we | |
2916 | wish to trace and which ones we want the mcount calls to remain | |
2917 | as nops. | |
2918 | ||
2919 | Two files are used, one for enabling and one for disabling the | |
2920 | tracing of specified functions. They are: | |
2921 | ||
2922 | set_ftrace_filter | |
2923 | ||
2924 | and | |
2925 | ||
2926 | set_ftrace_notrace | |
2927 | ||
2928 | A list of available functions that you can add to these files is | |
2929 | listed in: | |
2930 | ||
2931 | available_filter_functions | |
2932 | ||
2933 | :: | |
2934 | ||
2935 | # cat available_filter_functions | |
2936 | put_prev_task_idle | |
2937 | kmem_cache_create | |
2938 | pick_next_task_rt | |
c7483d82 | 2939 | cpus_read_lock |
1f198e22 CD |
2940 | pick_next_task_fair |
2941 | mutex_lock | |
2942 | [...] | |
2943 | ||
2944 | If I am only interested in sys_nanosleep and hrtimer_interrupt:: | |
2945 | ||
2946 | # echo sys_nanosleep hrtimer_interrupt > set_ftrace_filter | |
2947 | # echo function > current_tracer | |
2948 | # echo 1 > tracing_on | |
2949 | # usleep 1 | |
2950 | # echo 0 > tracing_on | |
2951 | # cat trace | |
2952 | # tracer: function | |
2953 | # | |
2954 | # entries-in-buffer/entries-written: 5/5 #P:4 | |
2955 | # | |
2956 | # _-----=> irqs-off | |
2957 | # / _----=> need-resched | |
2958 | # | / _---=> hardirq/softirq | |
2959 | # || / _--=> preempt-depth | |
2960 | # ||| / delay | |
2961 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
2962 | # | | | |||| | | | |
2963 | usleep-2665 [001] .... 4186.475355: sys_nanosleep <-system_call_fastpath | |
2964 | <idle>-0 [001] d.h1 4186.475409: hrtimer_interrupt <-smp_apic_timer_interrupt | |
2965 | usleep-2665 [001] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt | |
2966 | <idle>-0 [003] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt | |
2967 | <idle>-0 [002] d.h1 4186.475427: hrtimer_interrupt <-smp_apic_timer_interrupt | |
2968 | ||
2969 | To see which functions are being traced, you can cat the file: | |
2970 | :: | |
2971 | ||
2972 | # cat set_ftrace_filter | |
2973 | hrtimer_interrupt | |
2974 | sys_nanosleep | |
2975 | ||
2976 | ||
2977 | Perhaps this is not enough. The filters also allow glob(7) matching. | |
2978 | ||
6234c7bd | 2979 | ``<match>*`` |
1f198e22 | 2980 | will match functions that begin with <match> |
6234c7bd | 2981 | ``*<match>`` |
1f198e22 | 2982 | will match functions that end with <match> |
6234c7bd | 2983 | ``*<match>*`` |
1f198e22 | 2984 | will match functions that have <match> in it |
6234c7bd | 2985 | ``<match1>*<match2>`` |
1f198e22 CD |
2986 | will match functions that begin with <match1> and end with <match2> |
2987 | ||
2988 | .. note:: | |
2989 | It is better to use quotes to enclose the wild cards, | |
2990 | otherwise the shell may expand the parameters into names | |
2991 | of files in the local directory. | |
2992 | ||
2993 | :: | |
2994 | ||
2995 | # echo 'hrtimer_*' > set_ftrace_filter | |
2996 | ||
2997 | Produces:: | |
2998 | ||
2999 | # tracer: function | |
3000 | # | |
3001 | # entries-in-buffer/entries-written: 897/897 #P:4 | |
3002 | # | |
3003 | # _-----=> irqs-off | |
3004 | # / _----=> need-resched | |
3005 | # | / _---=> hardirq/softirq | |
3006 | # || / _--=> preempt-depth | |
3007 | # ||| / delay | |
3008 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
3009 | # | | | |||| | | | |
3010 | <idle>-0 [003] dN.1 4228.547803: hrtimer_cancel <-tick_nohz_idle_exit | |
3011 | <idle>-0 [003] dN.1 4228.547804: hrtimer_try_to_cancel <-hrtimer_cancel | |
3012 | <idle>-0 [003] dN.2 4228.547805: hrtimer_force_reprogram <-__remove_hrtimer | |
3013 | <idle>-0 [003] dN.1 4228.547805: hrtimer_forward <-tick_nohz_idle_exit | |
3014 | <idle>-0 [003] dN.1 4228.547805: hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11 | |
3015 | <idle>-0 [003] d..1 4228.547858: hrtimer_get_next_event <-get_next_timer_interrupt | |
3016 | <idle>-0 [003] d..1 4228.547859: hrtimer_start <-__tick_nohz_idle_enter | |
3017 | <idle>-0 [003] d..2 4228.547860: hrtimer_force_reprogram <-__rem | |
3018 | ||
3019 | Notice that we lost the sys_nanosleep. | |
3020 | :: | |
3021 | ||
3022 | # cat set_ftrace_filter | |
3023 | hrtimer_run_queues | |
3024 | hrtimer_run_pending | |
3025 | hrtimer_init | |
3026 | hrtimer_cancel | |
3027 | hrtimer_try_to_cancel | |
3028 | hrtimer_forward | |
3029 | hrtimer_start | |
3030 | hrtimer_reprogram | |
3031 | hrtimer_force_reprogram | |
3032 | hrtimer_get_next_event | |
3033 | hrtimer_interrupt | |
3034 | hrtimer_nanosleep | |
3035 | hrtimer_wakeup | |
3036 | hrtimer_get_remaining | |
3037 | hrtimer_get_res | |
3038 | hrtimer_init_sleeper | |
3039 | ||
3040 | ||
3041 | This is because the '>' and '>>' act just like they do in bash. | |
3042 | To rewrite the filters, use '>' | |
3043 | To append to the filters, use '>>' | |
3044 | ||
3045 | To clear out a filter so that all functions will be recorded | |
3046 | again:: | |
3047 | ||
3048 | # echo > set_ftrace_filter | |
3049 | # cat set_ftrace_filter | |
3050 | # | |
3051 | ||
3052 | Again, now we want to append. | |
3053 | ||
3054 | :: | |
3055 | ||
3056 | # echo sys_nanosleep > set_ftrace_filter | |
3057 | # cat set_ftrace_filter | |
3058 | sys_nanosleep | |
3059 | # echo 'hrtimer_*' >> set_ftrace_filter | |
3060 | # cat set_ftrace_filter | |
3061 | hrtimer_run_queues | |
3062 | hrtimer_run_pending | |
3063 | hrtimer_init | |
3064 | hrtimer_cancel | |
3065 | hrtimer_try_to_cancel | |
3066 | hrtimer_forward | |
3067 | hrtimer_start | |
3068 | hrtimer_reprogram | |
3069 | hrtimer_force_reprogram | |
3070 | hrtimer_get_next_event | |
3071 | hrtimer_interrupt | |
3072 | sys_nanosleep | |
3073 | hrtimer_nanosleep | |
3074 | hrtimer_wakeup | |
3075 | hrtimer_get_remaining | |
3076 | hrtimer_get_res | |
3077 | hrtimer_init_sleeper | |
3078 | ||
3079 | ||
3080 | The set_ftrace_notrace prevents those functions from being | |
3081 | traced. | |
3082 | :: | |
3083 | ||
3084 | # echo '*preempt*' '*lock*' > set_ftrace_notrace | |
3085 | ||
3086 | Produces:: | |
3087 | ||
3088 | # tracer: function | |
3089 | # | |
3090 | # entries-in-buffer/entries-written: 39608/39608 #P:4 | |
3091 | # | |
3092 | # _-----=> irqs-off | |
3093 | # / _----=> need-resched | |
3094 | # | / _---=> hardirq/softirq | |
3095 | # || / _--=> preempt-depth | |
3096 | # ||| / delay | |
3097 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
3098 | # | | | |||| | | | |
3099 | bash-1994 [000] .... 4342.324896: file_ra_state_init <-do_dentry_open | |
3100 | bash-1994 [000] .... 4342.324897: open_check_o_direct <-do_last | |
3101 | bash-1994 [000] .... 4342.324897: ima_file_check <-do_last | |
3102 | bash-1994 [000] .... 4342.324898: process_measurement <-ima_file_check | |
3103 | bash-1994 [000] .... 4342.324898: ima_get_action <-process_measurement | |
3104 | bash-1994 [000] .... 4342.324898: ima_match_policy <-ima_get_action | |
3105 | bash-1994 [000] .... 4342.324899: do_truncate <-do_last | |
ed5a7047 | 3106 | bash-1994 [000] .... 4342.324899: setattr_should_drop_suidgid <-do_truncate |
1f198e22 CD |
3107 | bash-1994 [000] .... 4342.324899: notify_change <-do_truncate |
3108 | bash-1994 [000] .... 4342.324900: current_fs_time <-notify_change | |
3109 | bash-1994 [000] .... 4342.324900: current_kernel_time <-current_fs_time | |
3110 | bash-1994 [000] .... 4342.324900: timespec_trunc <-current_fs_time | |
3111 | ||
3112 | We can see that there's no more lock or preempt tracing. | |
3113 | ||
f79b3f33 SRV |
3114 | Selecting function filters via index |
3115 | ------------------------------------ | |
3116 | ||
3117 | Because processing of strings is expensive (the address of the function | |
3118 | needs to be looked up before comparing to the string being passed in), | |
3119 | an index can be used as well to enable functions. This is useful in the | |
3120 | case of setting thousands of specific functions at a time. By passing | |
3121 | in a list of numbers, no string processing will occur. Instead, the function | |
3122 | at the specific location in the internal array (which corresponds to the | |
3123 | functions in the "available_filter_functions" file), is selected. | |
3124 | ||
3125 | :: | |
3126 | ||
3127 | # echo 1 > set_ftrace_filter | |
3128 | ||
3129 | Will select the first function listed in "available_filter_functions" | |
3130 | ||
3131 | :: | |
3132 | ||
3133 | # head -1 available_filter_functions | |
3134 | trace_initcall_finish_cb | |
3135 | ||
3136 | # cat set_ftrace_filter | |
3137 | trace_initcall_finish_cb | |
3138 | ||
3139 | # head -50 available_filter_functions | tail -1 | |
3140 | x86_pmu_commit_txn | |
3141 | ||
3142 | # echo 1 50 > set_ftrace_filter | |
3143 | # cat set_ftrace_filter | |
3144 | trace_initcall_finish_cb | |
3145 | x86_pmu_commit_txn | |
1f198e22 CD |
3146 | |
3147 | Dynamic ftrace with the function graph tracer | |
3148 | --------------------------------------------- | |
3149 | ||
3150 | Although what has been explained above concerns both the | |
3151 | function tracer and the function-graph-tracer, there are some | |
3152 | special features only available in the function-graph tracer. | |
3153 | ||
3154 | If you want to trace only one function and all of its children, | |
3155 | you just have to echo its name into set_graph_function:: | |
3156 | ||
3157 | echo __do_fault > set_graph_function | |
3158 | ||
3159 | will produce the following "expanded" trace of the __do_fault() | |
3160 | function:: | |
3161 | ||
3162 | 0) | __do_fault() { | |
3163 | 0) | filemap_fault() { | |
3164 | 0) | find_lock_page() { | |
3165 | 0) 0.804 us | find_get_page(); | |
3166 | 0) | __might_sleep() { | |
3167 | 0) 1.329 us | } | |
3168 | 0) 3.904 us | } | |
3169 | 0) 4.979 us | } | |
3170 | 0) 0.653 us | _spin_lock(); | |
3171 | 0) 0.578 us | page_add_file_rmap(); | |
3172 | 0) 0.525 us | native_set_pte_at(); | |
3173 | 0) 0.585 us | _spin_unlock(); | |
3174 | 0) | unlock_page() { | |
3175 | 0) 0.541 us | page_waitqueue(); | |
3176 | 0) 0.639 us | __wake_up_bit(); | |
3177 | 0) 2.786 us | } | |
3178 | 0) + 14.237 us | } | |
3179 | 0) | __do_fault() { | |
3180 | 0) | filemap_fault() { | |
3181 | 0) | find_lock_page() { | |
3182 | 0) 0.698 us | find_get_page(); | |
3183 | 0) | __might_sleep() { | |
3184 | 0) 1.412 us | } | |
3185 | 0) 3.950 us | } | |
3186 | 0) 5.098 us | } | |
3187 | 0) 0.631 us | _spin_lock(); | |
3188 | 0) 0.571 us | page_add_file_rmap(); | |
3189 | 0) 0.526 us | native_set_pte_at(); | |
3190 | 0) 0.586 us | _spin_unlock(); | |
3191 | 0) | unlock_page() { | |
3192 | 0) 0.533 us | page_waitqueue(); | |
3193 | 0) 0.638 us | __wake_up_bit(); | |
3194 | 0) 2.793 us | } | |
3195 | 0) + 14.012 us | } | |
3196 | ||
3197 | You can also expand several functions at once:: | |
3198 | ||
3199 | echo sys_open > set_graph_function | |
3200 | echo sys_close >> set_graph_function | |
3201 | ||
3202 | Now if you want to go back to trace all functions you can clear | |
3203 | this special filter via:: | |
3204 | ||
3205 | echo > set_graph_function | |
3206 | ||
3207 | ||
3208 | ftrace_enabled | |
3209 | -------------- | |
3210 | ||
3211 | Note, the proc sysctl ftrace_enable is a big on/off switch for the | |
3212 | function tracer. By default it is enabled (when function tracing is | |
3213 | enabled in the kernel). If it is disabled, all function tracing is | |
3214 | disabled. This includes not only the function tracers for ftrace, but | |
7162431d MB |
3215 | also for any other uses (perf, kprobes, stack tracing, profiling, etc). It |
3216 | cannot be disabled if there is a callback with FTRACE_OPS_FL_PERMANENT set | |
3217 | registered. | |
1f198e22 CD |
3218 | |
3219 | Please disable this with care. | |
3220 | ||
3221 | This can be disable (and enabled) with:: | |
3222 | ||
3223 | sysctl kernel.ftrace_enabled=0 | |
3224 | sysctl kernel.ftrace_enabled=1 | |
3225 | ||
3226 | or | |
3227 | ||
3228 | echo 0 > /proc/sys/kernel/ftrace_enabled | |
3229 | echo 1 > /proc/sys/kernel/ftrace_enabled | |
3230 | ||
3231 | ||
3232 | Filter commands | |
3233 | --------------- | |
3234 | ||
3235 | A few commands are supported by the set_ftrace_filter interface. | |
3236 | Trace commands have the following format:: | |
3237 | ||
3238 | <function>:<command>:<parameter> | |
3239 | ||
3240 | The following commands are supported: | |
3241 | ||
3242 | - mod: | |
3243 | This command enables function filtering per module. The | |
3244 | parameter defines the module. For example, if only the write* | |
3245 | functions in the ext3 module are desired, run: | |
3246 | ||
3247 | echo 'write*:mod:ext3' > set_ftrace_filter | |
3248 | ||
3249 | This command interacts with the filter in the same way as | |
3250 | filtering based on function names. Thus, adding more functions | |
3251 | in a different module is accomplished by appending (>>) to the | |
3252 | filter file. Remove specific module functions by prepending | |
3253 | '!':: | |
3254 | ||
3255 | echo '!writeback*:mod:ext3' >> set_ftrace_filter | |
3256 | ||
3257 | Mod command supports module globbing. Disable tracing for all | |
3258 | functions except a specific module:: | |
3259 | ||
3260 | echo '!*:mod:!ext3' >> set_ftrace_filter | |
3261 | ||
3262 | Disable tracing for all modules, but still trace kernel:: | |
3263 | ||
3264 | echo '!*:mod:*' >> set_ftrace_filter | |
3265 | ||
3266 | Enable filter only for kernel:: | |
3267 | ||
3268 | echo '*write*:mod:!*' >> set_ftrace_filter | |
3269 | ||
3270 | Enable filter for module globbing:: | |
3271 | ||
3272 | echo '*write*:mod:*snd*' >> set_ftrace_filter | |
3273 | ||
3274 | - traceon/traceoff: | |
3275 | These commands turn tracing on and off when the specified | |
3276 | functions are hit. The parameter determines how many times the | |
3277 | tracing system is turned on and off. If unspecified, there is | |
3278 | no limit. For example, to disable tracing when a schedule bug | |
3279 | is hit the first 5 times, run:: | |
3280 | ||
3281 | echo '__schedule_bug:traceoff:5' > set_ftrace_filter | |
3282 | ||
3283 | To always disable tracing when __schedule_bug is hit:: | |
3284 | ||
3285 | echo '__schedule_bug:traceoff' > set_ftrace_filter | |
3286 | ||
3287 | These commands are cumulative whether or not they are appended | |
3288 | to set_ftrace_filter. To remove a command, prepend it by '!' | |
3289 | and drop the parameter:: | |
3290 | ||
3291 | echo '!__schedule_bug:traceoff:0' > set_ftrace_filter | |
3292 | ||
3293 | The above removes the traceoff command for __schedule_bug | |
3294 | that have a counter. To remove commands without counters:: | |
3295 | ||
3296 | echo '!__schedule_bug:traceoff' > set_ftrace_filter | |
3297 | ||
3298 | - snapshot: | |
3299 | Will cause a snapshot to be triggered when the function is hit. | |
3300 | :: | |
3301 | ||
3302 | echo 'native_flush_tlb_others:snapshot' > set_ftrace_filter | |
3303 | ||
3304 | To only snapshot once: | |
3305 | :: | |
3306 | ||
3307 | echo 'native_flush_tlb_others:snapshot:1' > set_ftrace_filter | |
3308 | ||
3309 | To remove the above commands:: | |
3310 | ||
3311 | echo '!native_flush_tlb_others:snapshot' > set_ftrace_filter | |
3312 | echo '!native_flush_tlb_others:snapshot:0' > set_ftrace_filter | |
3313 | ||
3314 | - enable_event/disable_event: | |
3315 | These commands can enable or disable a trace event. Note, because | |
3316 | function tracing callbacks are very sensitive, when these commands | |
3317 | are registered, the trace point is activated, but disabled in | |
3318 | a "soft" mode. That is, the tracepoint will be called, but | |
3319 | just will not be traced. The event tracepoint stays in this mode | |
3320 | as long as there's a command that triggers it. | |
3321 | :: | |
3322 | ||
3323 | echo 'try_to_wake_up:enable_event:sched:sched_switch:2' > \ | |
3324 | set_ftrace_filter | |
3325 | ||
3326 | The format is:: | |
3327 | ||
3328 | <function>:enable_event:<system>:<event>[:count] | |
3329 | <function>:disable_event:<system>:<event>[:count] | |
3330 | ||
3331 | To remove the events commands:: | |
3332 | ||
3333 | echo '!try_to_wake_up:enable_event:sched:sched_switch:0' > \ | |
3334 | set_ftrace_filter | |
3335 | echo '!schedule:disable_event:sched:sched_switch' > \ | |
3336 | set_ftrace_filter | |
3337 | ||
3338 | - dump: | |
3339 | When the function is hit, it will dump the contents of the ftrace | |
3340 | ring buffer to the console. This is useful if you need to debug | |
3341 | something, and want to dump the trace when a certain function | |
2a1e03ca | 3342 | is hit. Perhaps it's a function that is called before a triple |
1f198e22 CD |
3343 | fault happens and does not allow you to get a regular dump. |
3344 | ||
3345 | - cpudump: | |
3346 | When the function is hit, it will dump the contents of the ftrace | |
3347 | ring buffer for the current CPU to the console. Unlike the "dump" | |
3348 | command, it only prints out the contents of the ring buffer for the | |
3349 | CPU that executed the function that triggered the dump. | |
3350 | ||
8a2933cf MH |
3351 | - stacktrace: |
3352 | When the function is hit, a stack trace is recorded. | |
3353 | ||
1f198e22 CD |
3354 | trace_pipe |
3355 | ---------- | |
3356 | ||
3357 | The trace_pipe outputs the same content as the trace file, but | |
3358 | the effect on the tracing is different. Every read from | |
3359 | trace_pipe is consumed. This means that subsequent reads will be | |
3360 | different. The trace is live. | |
3361 | :: | |
3362 | ||
3363 | # echo function > current_tracer | |
3364 | # cat trace_pipe > /tmp/trace.out & | |
3365 | [1] 4153 | |
3366 | # echo 1 > tracing_on | |
3367 | # usleep 1 | |
3368 | # echo 0 > tracing_on | |
3369 | # cat trace | |
3370 | # tracer: function | |
3371 | # | |
3372 | # entries-in-buffer/entries-written: 0/0 #P:4 | |
3373 | # | |
3374 | # _-----=> irqs-off | |
3375 | # / _----=> need-resched | |
3376 | # | / _---=> hardirq/softirq | |
3377 | # || / _--=> preempt-depth | |
3378 | # ||| / delay | |
3379 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
3380 | # | | | |||| | | | |
3381 | ||
3382 | # | |
3383 | # cat /tmp/trace.out | |
3384 | bash-1994 [000] .... 5281.568961: mutex_unlock <-rb_simple_write | |
3385 | bash-1994 [000] .... 5281.568963: __mutex_unlock_slowpath <-mutex_unlock | |
3386 | bash-1994 [000] .... 5281.568963: __fsnotify_parent <-fsnotify_modify | |
3387 | bash-1994 [000] .... 5281.568964: fsnotify <-fsnotify_modify | |
3388 | bash-1994 [000] .... 5281.568964: __srcu_read_lock <-fsnotify | |
3389 | bash-1994 [000] .... 5281.568964: add_preempt_count <-__srcu_read_lock | |
3390 | bash-1994 [000] ...1 5281.568965: sub_preempt_count <-__srcu_read_lock | |
3391 | bash-1994 [000] .... 5281.568965: __srcu_read_unlock <-fsnotify | |
3392 | bash-1994 [000] .... 5281.568967: sys_dup2 <-system_call_fastpath | |
3393 | ||
3394 | ||
3395 | Note, reading the trace_pipe file will block until more input is | |
f12fcca6 PW |
3396 | added. This is contrary to the trace file. If any process opened |
3397 | the trace file for reading, it will actually disable tracing and | |
3398 | prevent new entries from being added. The trace_pipe file does | |
3399 | not have this limitation. | |
1f198e22 CD |
3400 | |
3401 | trace entries | |
3402 | ------------- | |
3403 | ||
3404 | Having too much or not enough data can be troublesome in | |
3405 | diagnosing an issue in the kernel. The file buffer_size_kb is | |
3406 | used to modify the size of the internal trace buffers. The | |
3407 | number listed is the number of entries that can be recorded per | |
3408 | CPU. To know the full size, multiply the number of possible CPUs | |
3409 | with the number of entries. | |
3410 | :: | |
3411 | ||
3412 | # cat buffer_size_kb | |
3413 | 1408 (units kilobytes) | |
3414 | ||
3415 | Or simply read buffer_total_size_kb | |
3416 | :: | |
3417 | ||
3418 | # cat buffer_total_size_kb | |
3419 | 5632 | |
3420 | ||
3421 | To modify the buffer, simple echo in a number (in 1024 byte segments). | |
3422 | :: | |
3423 | ||
3424 | # echo 10000 > buffer_size_kb | |
3425 | # cat buffer_size_kb | |
3426 | 10000 (units kilobytes) | |
3427 | ||
3428 | It will try to allocate as much as possible. If you allocate too | |
3429 | much, it can cause Out-Of-Memory to trigger. | |
3430 | :: | |
3431 | ||
3432 | # echo 1000000000000 > buffer_size_kb | |
3433 | -bash: echo: write error: Cannot allocate memory | |
3434 | # cat buffer_size_kb | |
3435 | 85 | |
3436 | ||
3437 | The per_cpu buffers can be changed individually as well: | |
3438 | :: | |
3439 | ||
3440 | # echo 10000 > per_cpu/cpu0/buffer_size_kb | |
3441 | # echo 100 > per_cpu/cpu1/buffer_size_kb | |
3442 | ||
3443 | When the per_cpu buffers are not the same, the buffer_size_kb | |
3444 | at the top level will just show an X | |
3445 | :: | |
3446 | ||
3447 | # cat buffer_size_kb | |
3448 | X | |
3449 | ||
3450 | This is where the buffer_total_size_kb is useful: | |
3451 | :: | |
3452 | ||
3453 | # cat buffer_total_size_kb | |
3454 | 12916 | |
3455 | ||
3456 | Writing to the top level buffer_size_kb will reset all the buffers | |
3457 | to be the same again. | |
3458 | ||
3459 | Snapshot | |
3460 | -------- | |
3461 | CONFIG_TRACER_SNAPSHOT makes a generic snapshot feature | |
3462 | available to all non latency tracers. (Latency tracers which | |
3463 | record max latency, such as "irqsoff" or "wakeup", can't use | |
3464 | this feature, since those are already using the snapshot | |
3465 | mechanism internally.) | |
3466 | ||
3467 | Snapshot preserves a current trace buffer at a particular point | |
3468 | in time without stopping tracing. Ftrace swaps the current | |
3469 | buffer with a spare buffer, and tracing continues in the new | |
3470 | current (=previous spare) buffer. | |
3471 | ||
3472 | The following tracefs files in "tracing" are related to this | |
3473 | feature: | |
3474 | ||
3475 | snapshot: | |
3476 | ||
3477 | This is used to take a snapshot and to read the output | |
3478 | of the snapshot. Echo 1 into this file to allocate a | |
3479 | spare buffer and to take a snapshot (swap), then read | |
3480 | the snapshot from this file in the same format as | |
3481 | "trace" (described above in the section "The File | |
3482 | System"). Both reads snapshot and tracing are executable | |
3483 | in parallel. When the spare buffer is allocated, echoing | |
3484 | 0 frees it, and echoing else (positive) values clear the | |
3485 | snapshot contents. | |
3486 | More details are shown in the table below. | |
3487 | ||
3488 | +--------------+------------+------------+------------+ | |
3489 | |status\\input | 0 | 1 | else | | |
3490 | +==============+============+============+============+ | |
3491 | |not allocated |(do nothing)| alloc+swap |(do nothing)| | |
3492 | +--------------+------------+------------+------------+ | |
3493 | |allocated | free | swap | clear | | |
3494 | +--------------+------------+------------+------------+ | |
3495 | ||
3496 | Here is an example of using the snapshot feature. | |
3497 | :: | |
3498 | ||
3499 | # echo 1 > events/sched/enable | |
3500 | # echo 1 > snapshot | |
3501 | # cat snapshot | |
3502 | # tracer: nop | |
3503 | # | |
3504 | # entries-in-buffer/entries-written: 71/71 #P:8 | |
3505 | # | |
3506 | # _-----=> irqs-off | |
3507 | # / _----=> need-resched | |
3508 | # | / _---=> hardirq/softirq | |
3509 | # || / _--=> preempt-depth | |
3510 | # ||| / delay | |
3511 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
3512 | # | | | |||| | | | |
3513 | <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 | |
3514 | 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 | |
3515 | [...] | |
3516 | <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 | |
3517 | ||
3518 | # cat trace | |
3519 | # tracer: nop | |
3520 | # | |
3521 | # entries-in-buffer/entries-written: 77/77 #P:8 | |
3522 | # | |
3523 | # _-----=> irqs-off | |
3524 | # / _----=> need-resched | |
3525 | # | / _---=> hardirq/softirq | |
3526 | # || / _--=> preempt-depth | |
3527 | # ||| / delay | |
3528 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
3529 | # | | | |||| | | | |
3530 | <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 | |
3531 | 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 | |
3532 | [...] | |
3533 | ||
3534 | ||
3535 | If you try to use this snapshot feature when current tracer is | |
3536 | one of the latency tracers, you will get the following results. | |
3537 | :: | |
3538 | ||
3539 | # echo wakeup > current_tracer | |
3540 | # echo 1 > snapshot | |
3541 | bash: echo: write error: Device or resource busy | |
3542 | # cat snapshot | |
3543 | cat: snapshot: Device or resource busy | |
3544 | ||
3545 | ||
3546 | Instances | |
3547 | --------- | |
cc2cf679 | 3548 | In the tracefs tracing directory, there is a directory called "instances". |
1f198e22 CD |
3549 | This directory can have new directories created inside of it using |
3550 | mkdir, and removing directories with rmdir. The directory created | |
3551 | with mkdir in this directory will already contain files and other | |
3552 | directories after it is created. | |
3553 | :: | |
3554 | ||
3555 | # mkdir instances/foo | |
3556 | # ls instances/foo | |
3557 | buffer_size_kb buffer_total_size_kb events free_buffer per_cpu | |
3558 | set_event snapshot trace trace_clock trace_marker trace_options | |
3559 | trace_pipe tracing_on | |
3560 | ||
3561 | As you can see, the new directory looks similar to the tracing directory | |
3562 | itself. In fact, it is very similar, except that the buffer and | |
5b8914a6 | 3563 | events are agnostic from the main directory, or from any other |
1f198e22 CD |
3564 | instances that are created. |
3565 | ||
3566 | The files in the new directory work just like the files with the | |
3567 | same name in the tracing directory except the buffer that is used | |
3568 | is a separate and new buffer. The files affect that buffer but do not | |
3569 | affect the main buffer with the exception of trace_options. Currently, | |
3570 | the trace_options affect all instances and the top level buffer | |
3571 | the same, but this may change in future releases. That is, options | |
3572 | may become specific to the instance they reside in. | |
3573 | ||
3574 | Notice that none of the function tracer files are there, nor is | |
3575 | current_tracer and available_tracers. This is because the buffers | |
3576 | can currently only have events enabled for them. | |
3577 | :: | |
3578 | ||
3579 | # mkdir instances/foo | |
3580 | # mkdir instances/bar | |
3581 | # mkdir instances/zoot | |
3582 | # echo 100000 > buffer_size_kb | |
3583 | # echo 1000 > instances/foo/buffer_size_kb | |
3584 | # echo 5000 > instances/bar/per_cpu/cpu1/buffer_size_kb | |
3585 | # echo function > current_trace | |
3586 | # echo 1 > instances/foo/events/sched/sched_wakeup/enable | |
3587 | # echo 1 > instances/foo/events/sched/sched_wakeup_new/enable | |
3588 | # echo 1 > instances/foo/events/sched/sched_switch/enable | |
3589 | # echo 1 > instances/bar/events/irq/enable | |
3590 | # echo 1 > instances/zoot/events/syscalls/enable | |
3591 | # cat trace_pipe | |
3592 | CPU:2 [LOST 11745 EVENTS] | |
3593 | bash-2044 [002] .... 10594.481032: _raw_spin_lock_irqsave <-get_page_from_freelist | |
3594 | bash-2044 [002] d... 10594.481032: add_preempt_count <-_raw_spin_lock_irqsave | |
3595 | bash-2044 [002] d..1 10594.481032: __rmqueue <-get_page_from_freelist | |
3596 | bash-2044 [002] d..1 10594.481033: _raw_spin_unlock <-get_page_from_freelist | |
3597 | bash-2044 [002] d..1 10594.481033: sub_preempt_count <-_raw_spin_unlock | |
3598 | bash-2044 [002] d... 10594.481033: get_pageblock_flags_group <-get_pageblock_migratetype | |
3599 | bash-2044 [002] d... 10594.481034: __mod_zone_page_state <-get_page_from_freelist | |
3600 | bash-2044 [002] d... 10594.481034: zone_statistics <-get_page_from_freelist | |
3601 | bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics | |
3602 | bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics | |
3603 | bash-2044 [002] .... 10594.481035: arch_dup_task_struct <-copy_process | |
3604 | [...] | |
3605 | ||
3606 | # cat instances/foo/trace_pipe | |
3607 | bash-1998 [000] d..4 136.676759: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000 | |
3608 | bash-1998 [000] dN.4 136.676760: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000 | |
3609 | <idle>-0 [003] d.h3 136.676906: sched_wakeup: comm=rcu_preempt pid=9 prio=120 success=1 target_cpu=003 | |
3610 | <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 | |
3611 | 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 | |
3612 | bash-1998 [000] d..4 136.677014: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000 | |
3613 | bash-1998 [000] dN.4 136.677016: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000 | |
3614 | 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 | |
3615 | kworker/0:1-59 [000] d..4 136.677022: sched_wakeup: comm=sshd pid=1995 prio=120 success=1 target_cpu=001 | |
3616 | 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 | |
3617 | [...] | |
3618 | ||
3619 | # cat instances/bar/trace_pipe | |
3620 | migration/1-14 [001] d.h3 138.732674: softirq_raise: vec=3 [action=NET_RX] | |
3621 | <idle>-0 [001] dNh3 138.732725: softirq_raise: vec=3 [action=NET_RX] | |
3622 | bash-1998 [000] d.h1 138.733101: softirq_raise: vec=1 [action=TIMER] | |
3623 | bash-1998 [000] d.h1 138.733102: softirq_raise: vec=9 [action=RCU] | |
3624 | bash-1998 [000] ..s2 138.733105: softirq_entry: vec=1 [action=TIMER] | |
3625 | bash-1998 [000] ..s2 138.733106: softirq_exit: vec=1 [action=TIMER] | |
3626 | bash-1998 [000] ..s2 138.733106: softirq_entry: vec=9 [action=RCU] | |
3627 | bash-1998 [000] ..s2 138.733109: softirq_exit: vec=9 [action=RCU] | |
3628 | sshd-1995 [001] d.h1 138.733278: irq_handler_entry: irq=21 name=uhci_hcd:usb4 | |
3629 | sshd-1995 [001] d.h1 138.733280: irq_handler_exit: irq=21 ret=unhandled | |
3630 | sshd-1995 [001] d.h1 138.733281: irq_handler_entry: irq=21 name=eth0 | |
3631 | sshd-1995 [001] d.h1 138.733283: irq_handler_exit: irq=21 ret=handled | |
3632 | [...] | |
3633 | ||
3634 | # cat instances/zoot/trace | |
3635 | # tracer: nop | |
3636 | # | |
3637 | # entries-in-buffer/entries-written: 18996/18996 #P:4 | |
3638 | # | |
3639 | # _-----=> irqs-off | |
3640 | # / _----=> need-resched | |
3641 | # | / _---=> hardirq/softirq | |
3642 | # || / _--=> preempt-depth | |
3643 | # ||| / delay | |
3644 | # TASK-PID CPU# |||| TIMESTAMP FUNCTION | |
3645 | # | | | |||| | | | |
3646 | bash-1998 [000] d... 140.733501: sys_write -> 0x2 | |
3647 | bash-1998 [000] d... 140.733504: sys_dup2(oldfd: a, newfd: 1) | |
3648 | bash-1998 [000] d... 140.733506: sys_dup2 -> 0x1 | |
3649 | bash-1998 [000] d... 140.733508: sys_fcntl(fd: a, cmd: 1, arg: 0) | |
3650 | bash-1998 [000] d... 140.733509: sys_fcntl -> 0x1 | |
3651 | bash-1998 [000] d... 140.733510: sys_close(fd: a) | |
3652 | bash-1998 [000] d... 140.733510: sys_close -> 0x0 | |
3653 | bash-1998 [000] d... 140.733514: sys_rt_sigprocmask(how: 0, nset: 0, oset: 6e2768, sigsetsize: 8) | |
3654 | bash-1998 [000] d... 140.733515: sys_rt_sigprocmask -> 0x0 | |
3655 | bash-1998 [000] d... 140.733516: sys_rt_sigaction(sig: 2, act: 7fff718846f0, oact: 7fff71884650, sigsetsize: 8) | |
3656 | bash-1998 [000] d... 140.733516: sys_rt_sigaction -> 0x0 | |
3657 | ||
3658 | You can see that the trace of the top most trace buffer shows only | |
3659 | the function tracing. The foo instance displays wakeups and task | |
3660 | switches. | |
3661 | ||
3662 | To remove the instances, simply delete their directories: | |
3663 | :: | |
3664 | ||
3665 | # rmdir instances/foo | |
3666 | # rmdir instances/bar | |
3667 | # rmdir instances/zoot | |
3668 | ||
3669 | Note, if a process has a trace file open in one of the instance | |
3670 | directories, the rmdir will fail with EBUSY. | |
3671 | ||
3672 | ||
3673 | Stack trace | |
3674 | ----------- | |
3675 | Since the kernel has a fixed sized stack, it is important not to | |
c9b951c3 | 3676 | waste it in functions. A kernel developer must be conscious of |
1f198e22 CD |
3677 | what they allocate on the stack. If they add too much, the system |
3678 | can be in danger of a stack overflow, and corruption will occur, | |
3679 | usually leading to a system panic. | |
3680 | ||
3681 | There are some tools that check this, usually with interrupts | |
3682 | periodically checking usage. But if you can perform a check | |
3683 | at every function call that will become very useful. As ftrace provides | |
3684 | a function tracer, it makes it convenient to check the stack size | |
3685 | at every function call. This is enabled via the stack tracer. | |
3686 | ||
3687 | CONFIG_STACK_TRACER enables the ftrace stack tracing functionality. | |
3688 | To enable it, write a '1' into /proc/sys/kernel/stack_tracer_enabled. | |
3689 | :: | |
3690 | ||
3691 | # echo 1 > /proc/sys/kernel/stack_tracer_enabled | |
3692 | ||
3693 | You can also enable it from the kernel command line to trace | |
3694 | the stack size of the kernel during boot up, by adding "stacktrace" | |
3695 | to the kernel command line parameter. | |
3696 | ||
3697 | After running it for a few minutes, the output looks like: | |
3698 | :: | |
3699 | ||
3700 | # cat stack_max_size | |
3701 | 2928 | |
3702 | ||
3703 | # cat stack_trace | |
3704 | Depth Size Location (18 entries) | |
3705 | ----- ---- -------- | |
3706 | 0) 2928 224 update_sd_lb_stats+0xbc/0x4ac | |
3707 | 1) 2704 160 find_busiest_group+0x31/0x1f1 | |
3708 | 2) 2544 256 load_balance+0xd9/0x662 | |
3709 | 3) 2288 80 idle_balance+0xbb/0x130 | |
3710 | 4) 2208 128 __schedule+0x26e/0x5b9 | |
3711 | 5) 2080 16 schedule+0x64/0x66 | |
3712 | 6) 2064 128 schedule_timeout+0x34/0xe0 | |
3713 | 7) 1936 112 wait_for_common+0x97/0xf1 | |
3714 | 8) 1824 16 wait_for_completion+0x1d/0x1f | |
3715 | 9) 1808 128 flush_work+0xfe/0x119 | |
3716 | 10) 1680 16 tty_flush_to_ldisc+0x1e/0x20 | |
3717 | 11) 1664 48 input_available_p+0x1d/0x5c | |
3718 | 12) 1616 48 n_tty_poll+0x6d/0x134 | |
3719 | 13) 1568 64 tty_poll+0x64/0x7f | |
3720 | 14) 1504 880 do_select+0x31e/0x511 | |
3721 | 15) 624 400 core_sys_select+0x177/0x216 | |
3722 | 16) 224 96 sys_select+0x91/0xb9 | |
3723 | 17) 128 128 system_call_fastpath+0x16/0x1b | |
3724 | ||
3725 | Note, if -mfentry is being used by gcc, functions get traced before | |
3726 | they set up the stack frame. This means that leaf level functions | |
3727 | are not tested by the stack tracer when -mfentry is used. | |
3728 | ||
3729 | Currently, -mfentry is used by gcc 4.6.0 and above on x86 only. | |
3730 | ||
3731 | More | |
3732 | ---- | |
3733 | More details can be found in the source code, in the `kernel/trace/*.c` files. |