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Steven Rostedteb6d42e2008-07-10 12:46:01 -04001 ftrace - Function Tracer
2 ========================
3
4Copyright 2008 Red Hat Inc.
Steven Rostedta41eeba2008-07-14 16:41:12 -04005 Author: Steven Rostedt <srostedt@redhat.com>
6 License: The GNU Free Documentation License, Version 1.2
Steven Rostedta97762a2008-07-31 12:40:52 -04007 (dual licensed under the GPL v2)
Steven Rostedtf2d9c742008-07-15 10:57:33 -04008Reviewers: Elias Oltmanns, Randy Dunlap, Andrew Morton,
9 John Kacur, and David Teigland.
Steven Rostedt42ec6322008-11-03 15:18:56 -050010Written for: 2.6.28-rc2
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -040011Updated for: 3.10
Steven Rostedteb6d42e2008-07-10 12:46:01 -040012
13Introduction
14------------
15
16Ftrace is an internal tracer designed to help out developers and
17designers of systems to find what is going on inside the kernel.
Ingo Molnar57526742009-02-19 12:54:10 +010018It can be used for debugging or analyzing latencies and
19performance issues that take place outside of user-space.
Steven Rostedteb6d42e2008-07-10 12:46:01 -040020
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -040021Although ftrace is typically considered the function tracer, it
22is really a frame work of several assorted tracing utilities.
23There's latency tracing to examine what occurs between interrupts
24disabled and enabled, as well as for preemption and from a time
25a task is woken to the task is actually scheduled in.
26
27One of the most common uses of ftrace is the event tracing.
28Through out the kernel is hundreds of static event points that
29can be enabled via the debugfs file system to see what is
30going on in certain parts of the kernel.
Steven Rostedteb6d42e2008-07-10 12:46:01 -040031
32
Mike Frysinger555f3862009-09-14 20:10:15 -040033Implementation Details
34----------------------
35
36See ftrace-design.txt for details for arch porters and such.
37
38
Steven Rostedteb6d42e2008-07-10 12:46:01 -040039The File System
40---------------
41
Ingo Molnar57526742009-02-19 12:54:10 +010042Ftrace uses the debugfs file system to hold the control files as
43well as the files to display output.
Steven Rostedteb6d42e2008-07-10 12:46:01 -040044
GeunSik Lim156f5a72009-06-02 15:01:37 +090045When debugfs is configured into the kernel (which selecting any ftrace
46option will do) the directory /sys/kernel/debug will be created. To mount
47this directory, you can add to your /etc/fstab file:
Steven Rostedteb6d42e2008-07-10 12:46:01 -040048
GeunSik Lim156f5a72009-06-02 15:01:37 +090049 debugfs /sys/kernel/debug debugfs defaults 0 0
Steven Rostedteb6d42e2008-07-10 12:46:01 -040050
GeunSik Lim156f5a72009-06-02 15:01:37 +090051Or you can mount it at run time with:
52
53 mount -t debugfs nodev /sys/kernel/debug
54
55For quicker access to that directory you may want to make a soft link to
56it:
57
58 ln -s /sys/kernel/debug /debug
59
60Any selected ftrace option will also create a directory called tracing
61within the debugfs. The rest of the document will assume that you are in
62the ftrace directory (cd /sys/kernel/debug/tracing) and will only concentrate
63on the files within that directory and not distract from the content with
64the extended "/sys/kernel/debug/tracing" path name.
Steven Rostedteb6d42e2008-07-10 12:46:01 -040065
66That's it! (assuming that you have ftrace configured into your kernel)
67
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -040068After mounting debugfs, you can see a directory called
Steven Rostedteb6d42e2008-07-10 12:46:01 -040069"tracing". This directory contains the control and output files
70of ftrace. Here is a list of some of the key files:
71
72
73 Note: all time values are in microseconds.
74
Ingo Molnar57526742009-02-19 12:54:10 +010075 current_tracer:
Steven Rostedteb6d42e2008-07-10 12:46:01 -040076
Ingo Molnar57526742009-02-19 12:54:10 +010077 This is used to set or display the current tracer
78 that is configured.
Steven Rostedteb6d42e2008-07-10 12:46:01 -040079
Ingo Molnar57526742009-02-19 12:54:10 +010080 available_tracers:
Steven Rostedteb6d42e2008-07-10 12:46:01 -040081
Ingo Molnar57526742009-02-19 12:54:10 +010082 This holds the different types of tracers that
83 have been compiled into the kernel. The
84 tracers listed here can be configured by
85 echoing their name into current_tracer.
Steven Rostedteb6d42e2008-07-10 12:46:01 -040086
Steven Rostedt6752ab42011-02-08 13:54:06 -050087 tracing_on:
Steven Rostedteb6d42e2008-07-10 12:46:01 -040088
Steven Rostedt6752ab42011-02-08 13:54:06 -050089 This sets or displays whether writing to the trace
90 ring buffer is enabled. Echo 0 into this file to disable
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -040091 the tracer or 1 to enable it. Note, this only disables
92 writing to the ring buffer, the tracing overhead may
93 still be occurring.
Steven Rostedteb6d42e2008-07-10 12:46:01 -040094
Ingo Molnar57526742009-02-19 12:54:10 +010095 trace:
Steven Rostedteb6d42e2008-07-10 12:46:01 -040096
Ingo Molnar57526742009-02-19 12:54:10 +010097 This file holds the output of the trace in a human
98 readable format (described below).
Steven Rostedteb6d42e2008-07-10 12:46:01 -040099
Ingo Molnar57526742009-02-19 12:54:10 +0100100 trace_pipe:
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400101
Ingo Molnar57526742009-02-19 12:54:10 +0100102 The output is the same as the "trace" file but this
103 file is meant to be streamed with live tracing.
Albin Tonnerre4a88d442009-08-31 22:40:08 +0200104 Reads from this file will block until new data is
105 retrieved. Unlike the "trace" file, this file is a
106 consumer. This means reading from this file causes
107 sequential reads to display more current data. Once
108 data is read from this file, it is consumed, and
109 will not be read again with a sequential read. The
110 "trace" file is static, and if the tracer is not
Rabin Vincent8547aa12015-05-04 19:48:54 +0200111 adding more data, it will display the same
112 information every time it is read.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400113
Ingo Molnar57526742009-02-19 12:54:10 +0100114 trace_options:
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400115
Ingo Molnar57526742009-02-19 12:54:10 +0100116 This file lets the user control the amount of data
117 that is displayed in one of the above output
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400118 files. Options also exist to modify how a tracer
119 or events work (stack traces, timestamps, etc).
120
121 options:
122
123 This is a directory that has a file for every available
124 trace option (also in trace_options). Options may also be set
125 or cleared by writing a "1" or "0" respectively into the
126 corresponding file with the option name.
Steven Rostedtdf4fc312008-11-26 00:16:23 -0500127
KOSAKI Motohiro42b40b32009-03-07 23:55:09 +0900128 tracing_max_latency:
Frederic Weisbecker985ec202009-02-18 06:35:34 +0100129
Ingo Molnar57526742009-02-19 12:54:10 +0100130 Some of the tracers record the max latency.
131 For example, the time interrupts are disabled.
132 This time is saved in this file. The max trace
Albin Tonnerre4a88d442009-08-31 22:40:08 +0200133 will also be stored, and displayed by "trace".
134 A new max trace will only be recorded if the
135 latency is greater than the value in this
136 file. (in microseconds)
Ingo Molnar57526742009-02-19 12:54:10 +0100137
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400138 tracing_thresh:
139
140 Some latency tracers will record a trace whenever the
141 latency is greater than the number in this file.
142 Only active when the file contains a number greater than 0.
143 (in microseconds)
144
Ingo Molnar57526742009-02-19 12:54:10 +0100145 buffer_size_kb:
146
147 This sets or displays the number of kilobytes each CPU
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400148 buffer holds. By default, the trace buffers are the same size
Ingo Molnar57526742009-02-19 12:54:10 +0100149 for each CPU. The displayed number is the size of the
150 CPU buffer and not total size of all buffers. The
151 trace buffers are allocated in pages (blocks of memory
152 that the kernel uses for allocation, usually 4 KB in size).
153 If the last page allocated has room for more bytes
154 than requested, the rest of the page will be used,
155 making the actual allocation bigger than requested.
156 ( Note, the size may not be a multiple of the page size
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400157 due to buffer management meta-data. )
Ingo Molnar57526742009-02-19 12:54:10 +0100158
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400159 buffer_total_size_kb:
160
161 This displays the total combined size of all the trace buffers.
162
163 free_buffer:
164
165 If a process is performing the tracing, and the ring buffer
166 should be shrunk "freed" when the process is finished, even
167 if it were to be killed by a signal, this file can be used
168 for that purpose. On close of this file, the ring buffer will
169 be resized to its minimum size. Having a process that is tracing
170 also open this file, when the process exits its file descriptor
171 for this file will be closed, and in doing so, the ring buffer
172 will be "freed".
173
174 It may also stop tracing if disable_on_free option is set.
Ingo Molnar57526742009-02-19 12:54:10 +0100175
176 tracing_cpumask:
177
178 This is a mask that lets the user only trace
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400179 on specified CPUs. The format is a hex string
180 representing the CPUs.
Ingo Molnar57526742009-02-19 12:54:10 +0100181
182 set_ftrace_filter:
183
184 When dynamic ftrace is configured in (see the
185 section below "dynamic ftrace"), the code is dynamically
186 modified (code text rewrite) to disable calling of the
187 function profiler (mcount). This lets tracing be configured
188 in with practically no overhead in performance. This also
189 has a side effect of enabling or disabling specific functions
190 to be traced. Echoing names of functions into this file
191 will limit the trace to only those functions.
192
Chase Douglas07271aa2010-04-23 14:02:39 -0400193 This interface also allows for commands to be used. See the
194 "Filter commands" section for more details.
195
Ingo Molnar57526742009-02-19 12:54:10 +0100196 set_ftrace_notrace:
197
198 This has an effect opposite to that of
199 set_ftrace_filter. Any function that is added here will not
200 be traced. If a function exists in both set_ftrace_filter
201 and set_ftrace_notrace, the function will _not_ be traced.
202
203 set_ftrace_pid:
204
205 Have the function tracer only trace a single thread.
206
Steven Rostedt (Red Hat)627645f2015-11-03 16:37:15 -0500207 set_event_pid:
208
209 Have the events only trace a task with a PID listed in this file.
210 Note, sched_switch and sched_wake_up will also trace events
211 listed in this file.
212
Steven Rostedt (Red Hat)540b5892016-04-19 10:24:38 -0400213 To have the PIDs of children of tasks with their PID in this file
214 added on fork, enable the "event-fork" option. That option will also
215 cause the PIDs of tasks to be removed from this file when the task
216 exits.
217
Ingo Molnar57526742009-02-19 12:54:10 +0100218 set_graph_function:
219
220 Set a "trigger" function where tracing should start
221 with the function graph tracer (See the section
222 "dynamic ftrace" for more details).
223
224 available_filter_functions:
225
226 This lists the functions that ftrace
227 has processed and can trace. These are the function
228 names that you can pass to "set_ftrace_filter" or
229 "set_ftrace_notrace". (See the section "dynamic ftrace"
230 below for more details.)
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400231
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400232 enabled_functions:
233
234 This file is more for debugging ftrace, but can also be useful
235 in seeing if any function has a callback attached to it.
236 Not only does the trace infrastructure use ftrace function
237 trace utility, but other subsystems might too. This file
238 displays all functions that have a callback attached to them
239 as well as the number of callbacks that have been attached.
240 Note, a callback may also call multiple functions which will
241 not be listed in this count.
242
243 If the callback registered to be traced by a function with
244 the "save regs" attribute (thus even more overhead), a 'R'
245 will be displayed on the same line as the function that
246 is returning registers.
247
Masami Hiramatsuf8b8be82014-11-21 05:25:16 -0500248 If the callback registered to be traced by a function with
249 the "ip modify" attribute (thus the regs->ip can be changed),
250 an 'I' will be displayed on the same line as the function that
251 can be overridden.
252
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400253 function_profile_enabled:
254
255 When set it will enable all functions with either the function
256 tracer, or if enabled, the function graph tracer. It will
257 keep a histogram of the number of functions that were called
258 and if run with the function graph tracer, it will also keep
259 track of the time spent in those functions. The histogram
260 content can be displayed in the files:
261
262 trace_stats/function<cpu> ( function0, function1, etc).
263
264 trace_stats:
265
266 A directory that holds different tracing stats.
267
268 kprobe_events:
269
270 Enable dynamic trace points. See kprobetrace.txt.
271
272 kprobe_profile:
273
274 Dynamic trace points stats. See kprobetrace.txt.
275
276 max_graph_depth:
277
278 Used with the function graph tracer. This is the max depth
279 it will trace into a function. Setting this to a value of
280 one will show only the first kernel function that is called
281 from user space.
282
283 printk_formats:
284
285 This is for tools that read the raw format files. If an event in
286 the ring buffer references a string (currently only trace_printk()
287 does this), only a pointer to the string is recorded into the buffer
288 and not the string itself. This prevents tools from knowing what
289 that string was. This file displays the string and address for
290 the string allowing tools to map the pointers to what the
291 strings were.
292
293 saved_cmdlines:
294
295 Only the pid of the task is recorded in a trace event unless
296 the event specifically saves the task comm as well. Ftrace
297 makes a cache of pid mappings to comms to try to display
298 comms for events. If a pid for a comm is not listed, then
299 "<...>" is displayed in the output.
300
301 snapshot:
302
303 This displays the "snapshot" buffer and also lets the user
304 take a snapshot of the current running trace.
305 See the "Snapshot" section below for more details.
306
307 stack_max_size:
308
309 When the stack tracer is activated, this will display the
310 maximum stack size it has encountered.
311 See the "Stack Trace" section below.
312
313 stack_trace:
314
315 This displays the stack back trace of the largest stack
316 that was encountered when the stack tracer is activated.
317 See the "Stack Trace" section below.
318
319 stack_trace_filter:
320
321 This is similar to "set_ftrace_filter" but it limits what
322 functions the stack tracer will check.
323
324 trace_clock:
325
326 Whenever an event is recorded into the ring buffer, a
327 "timestamp" is added. This stamp comes from a specified
328 clock. By default, ftrace uses the "local" clock. This
329 clock is very fast and strictly per cpu, but on some
330 systems it may not be monotonic with respect to other
331 CPUs. In other words, the local clocks may not be in sync
332 with local clocks on other CPUs.
333
334 Usual clocks for tracing:
335
336 # cat trace_clock
337 [local] global counter x86-tsc
338
339 local: Default clock, but may not be in sync across CPUs
340
341 global: This clock is in sync with all CPUs but may
342 be a bit slower than the local clock.
343
344 counter: This is not a clock at all, but literally an atomic
345 counter. It counts up one by one, but is in sync
346 with all CPUs. This is useful when you need to
347 know exactly the order events occurred with respect to
348 each other on different CPUs.
349
350 uptime: This uses the jiffies counter and the time stamp
351 is relative to the time since boot up.
352
353 perf: This makes ftrace use the same clock that perf uses.
354 Eventually perf will be able to read ftrace buffers
355 and this will help out in interleaving the data.
356
357 x86-tsc: Architectures may define their own clocks. For
358 example, x86 uses its own TSC cycle clock here.
359
Naveen N. Rao197165d2015-04-24 14:24:44 +0530360 ppc-tb: This uses the powerpc timebase register value.
361 This is in sync across CPUs and can also be used
362 to correlate events across hypervisor/guest if
363 tb_offset is known.
364
Joel Fernandes2924ecd2016-11-28 14:35:24 -0800365 mono: This uses the fast monotonic clock (CLOCK_MONOTONIC)
366 which is monotonic and is subject to NTP rate adjustments.
367
368 mono_raw:
369 This is the raw monotonic clock (CLOCK_MONOTONIC_RAW)
370 which is montonic but is not subject to any rate adjustments
371 and ticks at the same rate as the hardware clocksource.
372
373 boot: This is the boot clock (CLOCK_BOOTTIME) and is based on the
374 fast monotonic clock, but also accounts for time spent in
375 suspend. Since the clock access is designed for use in
376 tracing in the suspend path, some side effects are possible
377 if clock is accessed after the suspend time is accounted before
378 the fast mono clock is updated. In this case, the clock update
379 appears to happen slightly sooner than it normally would have.
380 Also on 32-bit systems, it's possible that the 64-bit boot offset
381 sees a partial update. These effects are rare and post
382 processing should be able to handle them. See comments in the
383 ktime_get_boot_fast_ns() function for more information.
384
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400385 To set a clock, simply echo the clock name into this file.
386
387 echo global > trace_clock
388
389 trace_marker:
390
391 This is a very useful file for synchronizing user space
392 with events happening in the kernel. Writing strings into
393 this file will be written into the ftrace buffer.
394
395 It is useful in applications to open this file at the start
396 of the application and just reference the file descriptor
397 for the file.
398
399 void trace_write(const char *fmt, ...)
400 {
401 va_list ap;
402 char buf[256];
403 int n;
404
405 if (trace_fd < 0)
406 return;
407
408 va_start(ap, fmt);
409 n = vsnprintf(buf, 256, fmt, ap);
410 va_end(ap);
411
412 write(trace_fd, buf, n);
413 }
414
415 start:
416
417 trace_fd = open("trace_marker", WR_ONLY);
418
Steven Rostedtfa32e852016-07-06 15:25:08 -0400419 trace_marker_raw:
420
421 This is similar to trace_marker above, but is meant for for binary data
422 to be written to it, where a tool can be used to parse the data
423 from trace_pipe_raw.
424
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400425 uprobe_events:
426
427 Add dynamic tracepoints in programs.
428 See uprobetracer.txt
429
430 uprobe_profile:
431
432 Uprobe statistics. See uprobetrace.txt
433
434 instances:
435
436 This is a way to make multiple trace buffers where different
437 events can be recorded in different buffers.
438 See "Instances" section below.
439
440 events:
441
442 This is the trace event directory. It holds event tracepoints
443 (also known as static tracepoints) that have been compiled
444 into the kernel. It shows what event tracepoints exist
445 and how they are grouped by system. There are "enable"
446 files at various levels that can enable the tracepoints
447 when a "1" is written to them.
448
449 See events.txt for more information.
450
451 per_cpu:
452
453 This is a directory that contains the trace per_cpu information.
454
455 per_cpu/cpu0/buffer_size_kb:
456
457 The ftrace buffer is defined per_cpu. That is, there's a separate
458 buffer for each CPU to allow writes to be done atomically,
459 and free from cache bouncing. These buffers may have different
460 size buffers. This file is similar to the buffer_size_kb
461 file, but it only displays or sets the buffer size for the
462 specific CPU. (here cpu0).
463
464 per_cpu/cpu0/trace:
465
466 This is similar to the "trace" file, but it will only display
467 the data specific for the CPU. If written to, it only clears
468 the specific CPU buffer.
469
470 per_cpu/cpu0/trace_pipe
471
472 This is similar to the "trace_pipe" file, and is a consuming
473 read, but it will only display (and consume) the data specific
474 for the CPU.
475
476 per_cpu/cpu0/trace_pipe_raw
477
478 For tools that can parse the ftrace ring buffer binary format,
479 the trace_pipe_raw file can be used to extract the data
480 from the ring buffer directly. With the use of the splice()
481 system call, the buffer data can be quickly transferred to
482 a file or to the network where a server is collecting the
483 data.
484
485 Like trace_pipe, this is a consuming reader, where multiple
486 reads will always produce different data.
487
488 per_cpu/cpu0/snapshot:
489
490 This is similar to the main "snapshot" file, but will only
491 snapshot the current CPU (if supported). It only displays
492 the content of the snapshot for a given CPU, and if
493 written to, only clears this CPU buffer.
494
495 per_cpu/cpu0/snapshot_raw:
496
497 Similar to the trace_pipe_raw, but will read the binary format
498 from the snapshot buffer for the given CPU.
499
500 per_cpu/cpu0/stats:
501
502 This displays certain stats about the ring buffer:
503
504 entries: The number of events that are still in the buffer.
505
506 overrun: The number of lost events due to overwriting when
507 the buffer was full.
508
509 commit overrun: Should always be zero.
510 This gets set if so many events happened within a nested
511 event (ring buffer is re-entrant), that it fills the
512 buffer and starts dropping events.
513
514 bytes: Bytes actually read (not overwritten).
515
516 oldest event ts: The oldest timestamp in the buffer
517
518 now ts: The current timestamp
519
520 dropped events: Events lost due to overwrite option being off.
521
522 read events: The number of events read.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400523
524The Tracers
525-----------
526
Steven Rostedtf2d9c742008-07-15 10:57:33 -0400527Here is the list of current tracers that may be configured.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400528
Ingo Molnar57526742009-02-19 12:54:10 +0100529 "function"
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400530
Ingo Molnar57526742009-02-19 12:54:10 +0100531 Function call tracer to trace all kernel functions.
Frederic Weisbecker985ec202009-02-18 06:35:34 +0100532
Mike Frysingerbc5c6c02009-06-10 04:48:41 -0400533 "function_graph"
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400534
Ingo Molnar57526742009-02-19 12:54:10 +0100535 Similar to the function tracer except that the
536 function tracer probes the functions on their entry
537 whereas the function graph tracer traces on both entry
538 and exit of the functions. It then provides the ability
539 to draw a graph of function calls similar to C code
540 source.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400541
Ingo Molnar57526742009-02-19 12:54:10 +0100542 "irqsoff"
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400543
Ingo Molnar57526742009-02-19 12:54:10 +0100544 Traces the areas that disable interrupts and saves
545 the trace with the longest max latency.
546 See tracing_max_latency. When a new max is recorded,
547 it replaces the old trace. It is best to view this
Albin Tonnerre4a88d442009-08-31 22:40:08 +0200548 trace with the latency-format option enabled.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400549
Ingo Molnar57526742009-02-19 12:54:10 +0100550 "preemptoff"
551
552 Similar to irqsoff but traces and records the amount of
553 time for which preemption is disabled.
554
555 "preemptirqsoff"
556
557 Similar to irqsoff and preemptoff, but traces and
558 records the largest time for which irqs and/or preemption
559 is disabled.
560
561 "wakeup"
562
563 Traces and records the max latency that it takes for
564 the highest priority task to get scheduled after
565 it has been woken up.
Geunsik Limcdfb0d32012-02-08 19:05:37 +0900566 Traces all tasks as an average developer would expect.
567
568 "wakeup_rt"
569
570 Traces and records the max latency that it takes for just
571 RT tasks (as the current "wakeup" does). This is useful
572 for those interested in wake up timings of RT tasks.
Ingo Molnar57526742009-02-19 12:54:10 +0100573
Ingo Molnar57526742009-02-19 12:54:10 +0100574 "nop"
575
576 This is the "trace nothing" tracer. To remove all
577 tracers from tracing simply echo "nop" into
578 current_tracer.
Markus Metzgere2ea5392009-01-19 10:35:58 +0100579
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400580
581Examples of using the tracer
582----------------------------
583
Ingo Molnar57526742009-02-19 12:54:10 +0100584Here are typical examples of using the tracers when controlling
585them only with the debugfs interface (without using any
586user-land utilities).
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400587
588Output format:
589--------------
590
Steven Rostedtf2d9c742008-07-15 10:57:33 -0400591Here is an example of the output format of the file "trace"
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400592
593 --------
Steven Rostedt9b803c02008-11-03 15:15:08 -0500594# tracer: function
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400595#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400596# entries-in-buffer/entries-written: 140080/250280 #P:4
597#
598# _-----=> irqs-off
599# / _----=> need-resched
600# | / _---=> hardirq/softirq
601# || / _--=> preempt-depth
602# ||| / delay
603# TASK-PID CPU# |||| TIMESTAMP FUNCTION
604# | | | |||| | |
605 bash-1977 [000] .... 17284.993652: sys_close <-system_call_fastpath
606 bash-1977 [000] .... 17284.993653: __close_fd <-sys_close
607 bash-1977 [000] .... 17284.993653: _raw_spin_lock <-__close_fd
608 sshd-1974 [003] .... 17284.993653: __srcu_read_unlock <-fsnotify
609 bash-1977 [000] .... 17284.993654: add_preempt_count <-_raw_spin_lock
610 bash-1977 [000] ...1 17284.993655: _raw_spin_unlock <-__close_fd
611 bash-1977 [000] ...1 17284.993656: sub_preempt_count <-_raw_spin_unlock
612 bash-1977 [000] .... 17284.993657: filp_close <-__close_fd
613 bash-1977 [000] .... 17284.993657: dnotify_flush <-filp_close
614 sshd-1974 [003] .... 17284.993658: sys_select <-system_call_fastpath
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400615 --------
616
Ingo Molnar57526742009-02-19 12:54:10 +0100617A header is printed with the tracer name that is represented by
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400618the trace. In this case the tracer is "function". Then it shows the
619number of events in the buffer as well as the total number of entries
620that were written. The difference is the number of entries that were
621lost due to the buffer filling up (250280 - 140080 = 110200 events
622lost).
623
624The header explains the content of the events. Task name "bash", the task
625PID "1977", the CPU that it was running on "000", the latency format
626(explained below), the timestamp in <secs>.<usecs> format, the
627function name that was traced "sys_close" and the parent function that
628called this function "system_call_fastpath". The timestamp is the time
629at which the function was entered.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400630
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400631Latency trace format
632--------------------
633
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400634When the latency-format option is enabled or when one of the latency
635tracers is set, the trace file gives somewhat more information to see
636why a latency happened. Here is a typical trace.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400637
638# tracer: irqsoff
639#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400640# irqsoff latency trace v1.1.5 on 3.8.0-test+
641# --------------------------------------------------------------------
642# latency: 259 us, #4/4, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
643# -----------------
644# | task: ps-6143 (uid:0 nice:0 policy:0 rt_prio:0)
645# -----------------
646# => started at: __lock_task_sighand
647# => ended at: _raw_spin_unlock_irqrestore
648#
649#
650# _------=> CPU#
651# / _-----=> irqs-off
652# | / _----=> need-resched
653# || / _---=> hardirq/softirq
654# ||| / _--=> preempt-depth
655# |||| / delay
656# cmd pid ||||| time | caller
657# \ / ||||| \ | /
658 ps-6143 2d... 0us!: trace_hardirqs_off <-__lock_task_sighand
659 ps-6143 2d..1 259us+: trace_hardirqs_on <-_raw_spin_unlock_irqrestore
660 ps-6143 2d..1 263us+: time_hardirqs_on <-_raw_spin_unlock_irqrestore
661 ps-6143 2d..1 306us : <stack trace>
662 => trace_hardirqs_on_caller
663 => trace_hardirqs_on
664 => _raw_spin_unlock_irqrestore
665 => do_task_stat
666 => proc_tgid_stat
667 => proc_single_show
668 => seq_read
669 => vfs_read
670 => sys_read
671 => system_call_fastpath
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400672
673
Ingo Molnar57526742009-02-19 12:54:10 +0100674This shows that the current tracer is "irqsoff" tracing the time
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400675for which interrupts were disabled. It gives the trace version (which
676never changes) and the version of the kernel upon which this was executed on
677(3.10). Then it displays the max latency in microseconds (259 us). The number
678of trace entries displayed and the total number (both are four: #4/4).
679VP, KP, SP, and HP are always zero and are reserved for later use.
680#P is the number of online CPUs (#P:4).
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400681
Ingo Molnar57526742009-02-19 12:54:10 +0100682The task is the process that was running when the latency
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400683occurred. (ps pid: 6143).
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400684
Ingo Molnar57526742009-02-19 12:54:10 +0100685The start and stop (the functions in which the interrupts were
686disabled and enabled respectively) that caused the latencies:
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400687
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400688 __lock_task_sighand is where the interrupts were disabled.
689 _raw_spin_unlock_irqrestore is where they were enabled again.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400690
691The next lines after the header are the trace itself. The header
692explains which is which.
693
694 cmd: The name of the process in the trace.
695
696 pid: The PID of that process.
697
Steven Rostedtf2d9c742008-07-15 10:57:33 -0400698 CPU#: The CPU which the process was running on.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400699
700 irqs-off: 'd' interrupts are disabled. '.' otherwise.
Steven Rostedt92444892008-10-24 09:42:59 -0400701 Note: If the architecture does not support a way to
702 read the irq flags variable, an 'X' will always
703 be printed here.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400704
Peter Zijlstrae5137b52013-10-04 17:28:26 +0200705 need-resched:
706 'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set,
707 'n' only TIF_NEED_RESCHED is set,
708 'p' only PREEMPT_NEED_RESCHED is set,
709 '.' otherwise.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400710
711 hardirq/softirq:
Steven Rostedtf2d9c742008-07-15 10:57:33 -0400712 'H' - hard irq occurred inside a softirq.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400713 'h' - hard irq is running
714 's' - soft irq is running
715 '.' - normal context.
716
717 preempt-depth: The level of preempt_disabled
718
719The above is mostly meaningful for kernel developers.
720
Albin Tonnerre4a88d442009-08-31 22:40:08 +0200721 time: When the latency-format option is enabled, the trace file
722 output includes a timestamp relative to the start of the
723 trace. This differs from the output when latency-format
724 is disabled, which includes an absolute timestamp.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400725
726 delay: This is just to help catch your eye a bit better. And
Ingo Molnar57526742009-02-19 12:54:10 +0100727 needs to be fixed to be only relative to the same CPU.
728 The marks are determined by the difference between this
729 current trace and the next trace.
Byungchul Park8e1e1df2014-11-24 09:34:19 +0900730 '$' - greater than 1 second
Jungseok Leeb838e1d2015-07-11 14:51:40 +0000731 '@' - greater than 100 milisecond
732 '*' - greater than 10 milisecond
Byungchul Park8e1e1df2014-11-24 09:34:19 +0900733 '#' - greater than 1000 microsecond
734 '!' - greater than 100 microsecond
735 '+' - greater than 10 microsecond
736 ' ' - less than or equal to 10 microsecond.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400737
738 The rest is the same as the 'trace' file.
739
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400740 Note, the latency tracers will usually end with a back trace
741 to easily find where the latency occurred.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400742
Steven Rostedtee6bce52008-11-12 17:52:37 -0500743trace_options
744-------------
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400745
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400746The trace_options file (or the options directory) is used to control
747what gets printed in the trace output, or manipulate the tracers.
748To see what is available, simply cat the file:
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400749
GeunSik Lim156f5a72009-06-02 15:01:37 +0900750 cat trace_options
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400751print-parent
752nosym-offset
753nosym-addr
754noverbose
755noraw
756nohex
757nobin
758noblock
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400759trace_printk
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400760nobranch
761annotate
762nouserstacktrace
763nosym-userobj
764noprintk-msg-only
765context-info
Steven Rostedt (Red Hat)540b5892016-04-19 10:24:38 -0400766nolatency-format
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400767sleep-time
768graph-time
769record-cmd
770overwrite
771nodisable_on_free
772irq-info
773markers
Steven Rostedt (Red Hat)540b5892016-04-19 10:24:38 -0400774noevent-fork
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400775function-trace
Steven Rostedt (Red Hat)540b5892016-04-19 10:24:38 -0400776nodisplay-graph
777nostacktrace
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400778
Ingo Molnar57526742009-02-19 12:54:10 +0100779To disable one of the options, echo in the option prepended with
780"no".
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400781
GeunSik Lim156f5a72009-06-02 15:01:37 +0900782 echo noprint-parent > trace_options
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400783
784To enable an option, leave off the "no".
785
GeunSik Lim156f5a72009-06-02 15:01:37 +0900786 echo sym-offset > trace_options
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400787
788Here are the available options:
789
Ingo Molnar57526742009-02-19 12:54:10 +0100790 print-parent - On function traces, display the calling (parent)
791 function as well as the function being traced.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400792
793 print-parent:
Jingoo Han0ab943b2013-07-31 14:59:16 -0700794 bash-4000 [01] 1477.606694: simple_strtoul <-kstrtoul
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400795
796 noprint-parent:
797 bash-4000 [01] 1477.606694: simple_strtoul
798
799
Ingo Molnar57526742009-02-19 12:54:10 +0100800 sym-offset - Display not only the function name, but also the
801 offset in the function. For example, instead of
802 seeing just "ktime_get", you will see
803 "ktime_get+0xb/0x20".
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400804
805 sym-offset:
806 bash-4000 [01] 1477.606694: simple_strtoul+0x6/0xa0
807
Ingo Molnar57526742009-02-19 12:54:10 +0100808 sym-addr - this will also display the function address as well
809 as the function name.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400810
811 sym-addr:
812 bash-4000 [01] 1477.606694: simple_strtoul <c0339346>
813
Albin Tonnerre4a88d442009-08-31 22:40:08 +0200814 verbose - This deals with the trace file when the
815 latency-format option is enabled.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400816
817 bash 4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \
Jingoo Han0ab943b2013-07-31 14:59:16 -0700818 (+0.000ms): simple_strtoul (kstrtoul)
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400819
Ingo Molnar57526742009-02-19 12:54:10 +0100820 raw - This will display raw numbers. This option is best for
821 use with user applications that can translate the raw
822 numbers better than having it done in the kernel.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400823
Ingo Molnar57526742009-02-19 12:54:10 +0100824 hex - Similar to raw, but the numbers will be in a hexadecimal
825 format.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400826
827 bin - This will print out the formats in raw binary.
828
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400829 block - When set, reading trace_pipe will not block when polled.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400830
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400831 trace_printk - Can disable trace_printk() from writing into the buffer.
832
833 branch - Enable branch tracing with the tracer.
834
835 annotate - It is sometimes confusing when the CPU buffers are full
836 and one CPU buffer had a lot of events recently, thus
837 a shorter time frame, were another CPU may have only had
838 a few events, which lets it have older events. When
839 the trace is reported, it shows the oldest events first,
840 and it may look like only one CPU ran (the one with the
841 oldest events). When the annotate option is set, it will
842 display when a new CPU buffer started:
843
844 <idle>-0 [001] dNs4 21169.031481: wake_up_idle_cpu <-add_timer_on
845 <idle>-0 [001] dNs4 21169.031482: _raw_spin_unlock_irqrestore <-add_timer_on
846 <idle>-0 [001] .Ns4 21169.031484: sub_preempt_count <-_raw_spin_unlock_irqrestore
847##### CPU 2 buffer started ####
848 <idle>-0 [002] .N.1 21169.031484: rcu_idle_exit <-cpu_idle
849 <idle>-0 [001] .Ns3 21169.031484: _raw_spin_unlock <-clocksource_watchdog
850 <idle>-0 [001] .Ns3 21169.031485: sub_preempt_count <-_raw_spin_unlock
851
Ingo Molnar57526742009-02-19 12:54:10 +0100852 userstacktrace - This option changes the trace. It records a
853 stacktrace of the current userspace thread.
Török Edwin02b67512008-11-22 13:28:47 +0200854
Ingo Molnar57526742009-02-19 12:54:10 +0100855 sym-userobj - when user stacktrace are enabled, look up which
856 object the address belongs to, and print a
857 relative address. This is especially useful when
858 ASLR is on, otherwise you don't get a chance to
859 resolve the address to object/file/line after
860 the app is no longer running
Török Edwinb54d3de2008-11-22 13:28:48 +0200861
Ingo Molnar57526742009-02-19 12:54:10 +0100862 The lookup is performed when you read
Albin Tonnerre4a88d442009-08-31 22:40:08 +0200863 trace,trace_pipe. Example:
Török Edwinb54d3de2008-11-22 13:28:48 +0200864
865 a.out-1623 [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0
866x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
867
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400868
869 printk-msg-only - When set, trace_printk()s will only show the format
870 and not their parameters (if trace_bprintk() or
871 trace_bputs() was used to save the trace_printk()).
872
873 context-info - Show only the event data. Hides the comm, PID,
874 timestamp, CPU, and other useful data.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400875
Albin Tonnerre4a88d442009-08-31 22:40:08 +0200876 latency-format - This option changes the trace. When
877 it is enabled, the trace displays
878 additional information about the
879 latencies, as described in "Latency
880 trace format".
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400881
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400882 sleep-time - When running function graph tracer, to include
883 the time a task schedules out in its function.
884 When enabled, it will account time the task has been
885 scheduled out as part of the function call.
886
Namhyung Kim8861dd32016-08-31 11:55:29 +0900887 graph-time - When running function profiler with function graph tracer,
888 to include the time to call nested functions. When this is
889 not set, the time reported for the function will only
890 include the time the function itself executed for, not the
891 time for functions that it called.
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400892
893 record-cmd - When any event or tracer is enabled, a hook is enabled
894 in the sched_switch trace point to fill comm cache
895 with mapped pids and comms. But this may cause some
896 overhead, and if you only care about pids, and not the
897 name of the task, disabling this option can lower the
898 impact of tracing.
899
David Sharp750912f2010-12-08 13:46:47 -0800900 overwrite - This controls what happens when the trace buffer is
901 full. If "1" (default), the oldest events are
902 discarded and overwritten. If "0", then the newest
903 events are discarded.
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400904 (see per_cpu/cpu0/stats for overrun and dropped)
David Sharp750912f2010-12-08 13:46:47 -0800905
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400906 disable_on_free - When the free_buffer is closed, tracing will
907 stop (tracing_on set to 0).
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400908
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400909 irq-info - Shows the interrupt, preempt count, need resched data.
910 When disabled, the trace looks like:
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400911
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400912# tracer: function
913#
914# entries-in-buffer/entries-written: 144405/9452052 #P:4
915#
916# TASK-PID CPU# TIMESTAMP FUNCTION
917# | | | | |
918 <idle>-0 [002] 23636.756054: ttwu_do_activate.constprop.89 <-try_to_wake_up
919 <idle>-0 [002] 23636.756054: activate_task <-ttwu_do_activate.constprop.89
920 <idle>-0 [002] 23636.756055: enqueue_task <-activate_task
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400921
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400922
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400923 markers - When set, the trace_marker is writable (only by root).
924 When disabled, the trace_marker will error with EINVAL
925 on write.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400926
Steven Rostedt (Red Hat)540b5892016-04-19 10:24:38 -0400927 event-fork - When set, tasks with PIDs listed in set_event_pid will have
928 the PIDs of their children added to set_event_pid when those
929 tasks fork. Also, when tasks with PIDs in set_event_pid exit,
930 their PIDs will be removed from the file.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400931
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400932 function-trace - The latency tracers will enable function tracing
933 if this option is enabled (default it is). When
934 it is disabled, the latency tracers do not trace
935 functions. This keeps the overhead of the tracer down
936 when performing latency tests.
937
Steven Rostedt (Red Hat)540b5892016-04-19 10:24:38 -0400938 display-graph - When set, the latency tracers (irqsoff, wakeup, etc) will
939 use function graph tracing instead of function tracing.
940
941 stacktrace - This is one of the options that changes the trace
942 itself. When a trace is recorded, so is the stack
943 of functions. This allows for back traces of
944 trace sites.
945
946 Note: Some tracers have their own options. They only appear in this
947 file when the tracer is active. They always appear in the
948 options directory.
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400949
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400950
951
952irqsoff
953-------
954
955When interrupts are disabled, the CPU can not react to any other
956external event (besides NMIs and SMIs). This prevents the timer
Ingo Molnar57526742009-02-19 12:54:10 +0100957interrupt from triggering or the mouse interrupt from letting
958the kernel know of a new mouse event. The result is a latency
959with the reaction time.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400960
Ingo Molnar57526742009-02-19 12:54:10 +0100961The irqsoff tracer tracks the time for which interrupts are
962disabled. When a new maximum latency is hit, the tracer saves
963the trace leading up to that latency point so that every time a
964new maximum is reached, the old saved trace is discarded and the
965new trace is saved.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400966
Ingo Molnar57526742009-02-19 12:54:10 +0100967To reset the maximum, echo 0 into tracing_max_latency. Here is
968an example:
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400969
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400970 # echo 0 > options/function-trace
GeunSik Lim156f5a72009-06-02 15:01:37 +0900971 # echo irqsoff > current_tracer
Steven Rostedt6752ab42011-02-08 13:54:06 -0500972 # echo 1 > tracing_on
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400973 # echo 0 > tracing_max_latency
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400974 # ls -ltr
975 [...]
Steven Rostedt6752ab42011-02-08 13:54:06 -0500976 # echo 0 > tracing_on
Albin Tonnerre4a88d442009-08-31 22:40:08 +0200977 # cat trace
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400978# tracer: irqsoff
979#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400980# irqsoff latency trace v1.1.5 on 3.8.0-test+
981# --------------------------------------------------------------------
982# latency: 16 us, #4/4, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
983# -----------------
984# | task: swapper/0-0 (uid:0 nice:0 policy:0 rt_prio:0)
985# -----------------
986# => started at: run_timer_softirq
987# => ended at: run_timer_softirq
988#
989#
990# _------=> CPU#
991# / _-----=> irqs-off
992# | / _----=> need-resched
993# || / _---=> hardirq/softirq
994# ||| / _--=> preempt-depth
995# |||| / delay
996# cmd pid ||||| time | caller
997# \ / ||||| \ | /
998 <idle>-0 0d.s2 0us+: _raw_spin_lock_irq <-run_timer_softirq
999 <idle>-0 0dNs3 17us : _raw_spin_unlock_irq <-run_timer_softirq
1000 <idle>-0 0dNs3 17us+: trace_hardirqs_on <-run_timer_softirq
1001 <idle>-0 0dNs3 25us : <stack trace>
1002 => _raw_spin_unlock_irq
1003 => run_timer_softirq
1004 => __do_softirq
1005 => call_softirq
1006 => do_softirq
1007 => irq_exit
1008 => smp_apic_timer_interrupt
1009 => apic_timer_interrupt
1010 => rcu_idle_exit
1011 => cpu_idle
1012 => rest_init
1013 => start_kernel
1014 => x86_64_start_reservations
1015 => x86_64_start_kernel
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001016
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001017Here we see that that we had a latency of 16 microseconds (which is
1018very good). The _raw_spin_lock_irq in run_timer_softirq disabled
1019interrupts. The difference between the 16 and the displayed
1020timestamp 25us occurred because the clock was incremented
Ingo Molnar57526742009-02-19 12:54:10 +01001021between the time of recording the max latency and the time of
1022recording the function that had that latency.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001023
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001024Note the above example had function-trace not set. If we set
1025function-trace, we get a much larger output:
1026
1027 with echo 1 > options/function-trace
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001028
1029# tracer: irqsoff
1030#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001031# irqsoff latency trace v1.1.5 on 3.8.0-test+
1032# --------------------------------------------------------------------
1033# latency: 71 us, #168/168, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1034# -----------------
1035# | task: bash-2042 (uid:0 nice:0 policy:0 rt_prio:0)
1036# -----------------
1037# => started at: ata_scsi_queuecmd
1038# => ended at: ata_scsi_queuecmd
1039#
1040#
1041# _------=> CPU#
1042# / _-----=> irqs-off
1043# | / _----=> need-resched
1044# || / _---=> hardirq/softirq
1045# ||| / _--=> preempt-depth
1046# |||| / delay
1047# cmd pid ||||| time | caller
1048# \ / ||||| \ | /
1049 bash-2042 3d... 0us : _raw_spin_lock_irqsave <-ata_scsi_queuecmd
1050 bash-2042 3d... 0us : add_preempt_count <-_raw_spin_lock_irqsave
1051 bash-2042 3d..1 1us : ata_scsi_find_dev <-ata_scsi_queuecmd
1052 bash-2042 3d..1 1us : __ata_scsi_find_dev <-ata_scsi_find_dev
1053 bash-2042 3d..1 2us : ata_find_dev.part.14 <-__ata_scsi_find_dev
1054 bash-2042 3d..1 2us : ata_qc_new_init <-__ata_scsi_queuecmd
1055 bash-2042 3d..1 3us : ata_sg_init <-__ata_scsi_queuecmd
1056 bash-2042 3d..1 4us : ata_scsi_rw_xlat <-__ata_scsi_queuecmd
1057 bash-2042 3d..1 4us : ata_build_rw_tf <-ata_scsi_rw_xlat
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001058[...]
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001059 bash-2042 3d..1 67us : delay_tsc <-__delay
1060 bash-2042 3d..1 67us : add_preempt_count <-delay_tsc
1061 bash-2042 3d..2 67us : sub_preempt_count <-delay_tsc
1062 bash-2042 3d..1 67us : add_preempt_count <-delay_tsc
1063 bash-2042 3d..2 68us : sub_preempt_count <-delay_tsc
1064 bash-2042 3d..1 68us+: ata_bmdma_start <-ata_bmdma_qc_issue
1065 bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
1066 bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
1067 bash-2042 3d..1 72us+: trace_hardirqs_on <-ata_scsi_queuecmd
1068 bash-2042 3d..1 120us : <stack trace>
1069 => _raw_spin_unlock_irqrestore
1070 => ata_scsi_queuecmd
1071 => scsi_dispatch_cmd
1072 => scsi_request_fn
1073 => __blk_run_queue_uncond
1074 => __blk_run_queue
1075 => blk_queue_bio
1076 => generic_make_request
1077 => submit_bio
1078 => submit_bh
1079 => __ext3_get_inode_loc
1080 => ext3_iget
1081 => ext3_lookup
1082 => lookup_real
1083 => __lookup_hash
1084 => walk_component
1085 => lookup_last
1086 => path_lookupat
1087 => filename_lookup
1088 => user_path_at_empty
1089 => user_path_at
1090 => vfs_fstatat
1091 => vfs_stat
1092 => sys_newstat
1093 => system_call_fastpath
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001094
1095
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001096Here we traced a 71 microsecond latency. But we also see all the
Ingo Molnar57526742009-02-19 12:54:10 +01001097functions that were called during that time. Note that by
1098enabling function tracing, we incur an added overhead. This
1099overhead may extend the latency times. But nevertheless, this
1100trace has provided some very helpful debugging information.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001101
1102
1103preemptoff
1104----------
1105
Ingo Molnar57526742009-02-19 12:54:10 +01001106When preemption is disabled, we may be able to receive
1107interrupts but the task cannot be preempted and a higher
1108priority task must wait for preemption to be enabled again
1109before it can preempt a lower priority task.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001110
Steven Rostedta41eeba2008-07-14 16:41:12 -04001111The preemptoff tracer traces the places that disable preemption.
Ingo Molnar57526742009-02-19 12:54:10 +01001112Like the irqsoff tracer, it records the maximum latency for
1113which preemption was disabled. The control of preemptoff tracer
1114is much like the irqsoff tracer.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001115
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001116 # echo 0 > options/function-trace
GeunSik Lim156f5a72009-06-02 15:01:37 +09001117 # echo preemptoff > current_tracer
Steven Rostedt6752ab42011-02-08 13:54:06 -05001118 # echo 1 > tracing_on
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001119 # echo 0 > tracing_max_latency
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001120 # ls -ltr
1121 [...]
Steven Rostedt6752ab42011-02-08 13:54:06 -05001122 # echo 0 > tracing_on
Albin Tonnerre4a88d442009-08-31 22:40:08 +02001123 # cat trace
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001124# tracer: preemptoff
1125#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001126# preemptoff latency trace v1.1.5 on 3.8.0-test+
1127# --------------------------------------------------------------------
1128# latency: 46 us, #4/4, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1129# -----------------
1130# | task: sshd-1991 (uid:0 nice:0 policy:0 rt_prio:0)
1131# -----------------
1132# => started at: do_IRQ
1133# => ended at: do_IRQ
1134#
1135#
1136# _------=> CPU#
1137# / _-----=> irqs-off
1138# | / _----=> need-resched
1139# || / _---=> hardirq/softirq
1140# ||| / _--=> preempt-depth
1141# |||| / delay
1142# cmd pid ||||| time | caller
1143# \ / ||||| \ | /
1144 sshd-1991 1d.h. 0us+: irq_enter <-do_IRQ
1145 sshd-1991 1d..1 46us : irq_exit <-do_IRQ
1146 sshd-1991 1d..1 47us+: trace_preempt_on <-do_IRQ
1147 sshd-1991 1d..1 52us : <stack trace>
1148 => sub_preempt_count
1149 => irq_exit
1150 => do_IRQ
1151 => ret_from_intr
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001152
1153
Ingo Molnar57526742009-02-19 12:54:10 +01001154This has some more changes. Preemption was disabled when an
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001155interrupt came in (notice the 'h'), and was enabled on exit.
1156But we also see that interrupts have been disabled when entering
1157the preempt off section and leaving it (the 'd'). We do not know if
1158interrupts were enabled in the mean time or shortly after this
1159was over.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001160
1161# tracer: preemptoff
1162#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001163# preemptoff latency trace v1.1.5 on 3.8.0-test+
1164# --------------------------------------------------------------------
1165# latency: 83 us, #241/241, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1166# -----------------
1167# | task: bash-1994 (uid:0 nice:0 policy:0 rt_prio:0)
1168# -----------------
1169# => started at: wake_up_new_task
1170# => ended at: task_rq_unlock
1171#
1172#
1173# _------=> CPU#
1174# / _-----=> irqs-off
1175# | / _----=> need-resched
1176# || / _---=> hardirq/softirq
1177# ||| / _--=> preempt-depth
1178# |||| / delay
1179# cmd pid ||||| time | caller
1180# \ / ||||| \ | /
1181 bash-1994 1d..1 0us : _raw_spin_lock_irqsave <-wake_up_new_task
1182 bash-1994 1d..1 0us : select_task_rq_fair <-select_task_rq
1183 bash-1994 1d..1 1us : __rcu_read_lock <-select_task_rq_fair
1184 bash-1994 1d..1 1us : source_load <-select_task_rq_fair
1185 bash-1994 1d..1 1us : source_load <-select_task_rq_fair
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001186[...]
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001187 bash-1994 1d..1 12us : irq_enter <-smp_apic_timer_interrupt
1188 bash-1994 1d..1 12us : rcu_irq_enter <-irq_enter
1189 bash-1994 1d..1 13us : add_preempt_count <-irq_enter
1190 bash-1994 1d.h1 13us : exit_idle <-smp_apic_timer_interrupt
1191 bash-1994 1d.h1 13us : hrtimer_interrupt <-smp_apic_timer_interrupt
1192 bash-1994 1d.h1 13us : _raw_spin_lock <-hrtimer_interrupt
1193 bash-1994 1d.h1 14us : add_preempt_count <-_raw_spin_lock
1194 bash-1994 1d.h2 14us : ktime_get_update_offsets <-hrtimer_interrupt
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001195[...]
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001196 bash-1994 1d.h1 35us : lapic_next_event <-clockevents_program_event
1197 bash-1994 1d.h1 35us : irq_exit <-smp_apic_timer_interrupt
1198 bash-1994 1d.h1 36us : sub_preempt_count <-irq_exit
1199 bash-1994 1d..2 36us : do_softirq <-irq_exit
1200 bash-1994 1d..2 36us : __do_softirq <-call_softirq
1201 bash-1994 1d..2 36us : __local_bh_disable <-__do_softirq
1202 bash-1994 1d.s2 37us : add_preempt_count <-_raw_spin_lock_irq
1203 bash-1994 1d.s3 38us : _raw_spin_unlock <-run_timer_softirq
1204 bash-1994 1d.s3 39us : sub_preempt_count <-_raw_spin_unlock
1205 bash-1994 1d.s2 39us : call_timer_fn <-run_timer_softirq
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001206[...]
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001207 bash-1994 1dNs2 81us : cpu_needs_another_gp <-rcu_process_callbacks
1208 bash-1994 1dNs2 82us : __local_bh_enable <-__do_softirq
1209 bash-1994 1dNs2 82us : sub_preempt_count <-__local_bh_enable
1210 bash-1994 1dN.2 82us : idle_cpu <-irq_exit
1211 bash-1994 1dN.2 83us : rcu_irq_exit <-irq_exit
1212 bash-1994 1dN.2 83us : sub_preempt_count <-irq_exit
1213 bash-1994 1.N.1 84us : _raw_spin_unlock_irqrestore <-task_rq_unlock
1214 bash-1994 1.N.1 84us+: trace_preempt_on <-task_rq_unlock
1215 bash-1994 1.N.1 104us : <stack trace>
1216 => sub_preempt_count
1217 => _raw_spin_unlock_irqrestore
1218 => task_rq_unlock
1219 => wake_up_new_task
1220 => do_fork
1221 => sys_clone
1222 => stub_clone
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001223
1224
Ingo Molnar57526742009-02-19 12:54:10 +01001225The above is an example of the preemptoff trace with
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001226function-trace set. Here we see that interrupts were not disabled
Ingo Molnar57526742009-02-19 12:54:10 +01001227the entire time. The irq_enter code lets us know that we entered
1228an interrupt 'h'. Before that, the functions being traced still
1229show that it is not in an interrupt, but we can see from the
1230functions themselves that this is not the case.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001231
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001232preemptirqsoff
1233--------------
1234
Ingo Molnar57526742009-02-19 12:54:10 +01001235Knowing the locations that have interrupts disabled or
1236preemption disabled for the longest times is helpful. But
1237sometimes we would like to know when either preemption and/or
1238interrupts are disabled.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001239
Steven Rostedtf2d9c742008-07-15 10:57:33 -04001240Consider the following code:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001241
1242 local_irq_disable();
1243 call_function_with_irqs_off();
1244 preempt_disable();
1245 call_function_with_irqs_and_preemption_off();
1246 local_irq_enable();
1247 call_function_with_preemption_off();
1248 preempt_enable();
1249
1250The irqsoff tracer will record the total length of
1251call_function_with_irqs_off() and
1252call_function_with_irqs_and_preemption_off().
1253
1254The preemptoff tracer will record the total length of
1255call_function_with_irqs_and_preemption_off() and
1256call_function_with_preemption_off().
1257
Ingo Molnar57526742009-02-19 12:54:10 +01001258But neither will trace the time that interrupts and/or
1259preemption is disabled. This total time is the time that we can
1260not schedule. To record this time, use the preemptirqsoff
1261tracer.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001262
Ingo Molnar57526742009-02-19 12:54:10 +01001263Again, using this trace is much like the irqsoff and preemptoff
1264tracers.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001265
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001266 # echo 0 > options/function-trace
GeunSik Lim156f5a72009-06-02 15:01:37 +09001267 # echo preemptirqsoff > current_tracer
Steven Rostedt6752ab42011-02-08 13:54:06 -05001268 # echo 1 > tracing_on
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001269 # echo 0 > tracing_max_latency
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001270 # ls -ltr
1271 [...]
Steven Rostedt6752ab42011-02-08 13:54:06 -05001272 # echo 0 > tracing_on
Albin Tonnerre4a88d442009-08-31 22:40:08 +02001273 # cat trace
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001274# tracer: preemptirqsoff
1275#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001276# preemptirqsoff latency trace v1.1.5 on 3.8.0-test+
1277# --------------------------------------------------------------------
1278# latency: 100 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1279# -----------------
1280# | task: ls-2230 (uid:0 nice:0 policy:0 rt_prio:0)
1281# -----------------
1282# => started at: ata_scsi_queuecmd
1283# => ended at: ata_scsi_queuecmd
1284#
1285#
1286# _------=> CPU#
1287# / _-----=> irqs-off
1288# | / _----=> need-resched
1289# || / _---=> hardirq/softirq
1290# ||| / _--=> preempt-depth
1291# |||| / delay
1292# cmd pid ||||| time | caller
1293# \ / ||||| \ | /
1294 ls-2230 3d... 0us+: _raw_spin_lock_irqsave <-ata_scsi_queuecmd
1295 ls-2230 3...1 100us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
1296 ls-2230 3...1 101us+: trace_preempt_on <-ata_scsi_queuecmd
1297 ls-2230 3...1 111us : <stack trace>
1298 => sub_preempt_count
1299 => _raw_spin_unlock_irqrestore
1300 => ata_scsi_queuecmd
1301 => scsi_dispatch_cmd
1302 => scsi_request_fn
1303 => __blk_run_queue_uncond
1304 => __blk_run_queue
1305 => blk_queue_bio
1306 => generic_make_request
1307 => submit_bio
1308 => submit_bh
1309 => ext3_bread
1310 => ext3_dir_bread
1311 => htree_dirblock_to_tree
1312 => ext3_htree_fill_tree
1313 => ext3_readdir
1314 => vfs_readdir
1315 => sys_getdents
1316 => system_call_fastpath
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001317
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001318
1319The trace_hardirqs_off_thunk is called from assembly on x86 when
Ingo Molnar57526742009-02-19 12:54:10 +01001320interrupts are disabled in the assembly code. Without the
1321function tracing, we do not know if interrupts were enabled
1322within the preemption points. We do see that it started with
1323preemption enabled.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001324
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001325Here is a trace with function-trace set:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001326
1327# tracer: preemptirqsoff
1328#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001329# preemptirqsoff latency trace v1.1.5 on 3.8.0-test+
1330# --------------------------------------------------------------------
1331# latency: 161 us, #339/339, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1332# -----------------
1333# | task: ls-2269 (uid:0 nice:0 policy:0 rt_prio:0)
1334# -----------------
1335# => started at: schedule
1336# => ended at: mutex_unlock
1337#
1338#
1339# _------=> CPU#
1340# / _-----=> irqs-off
1341# | / _----=> need-resched
1342# || / _---=> hardirq/softirq
1343# ||| / _--=> preempt-depth
1344# |||| / delay
1345# cmd pid ||||| time | caller
1346# \ / ||||| \ | /
1347kworker/-59 3...1 0us : __schedule <-schedule
1348kworker/-59 3d..1 0us : rcu_preempt_qs <-rcu_note_context_switch
1349kworker/-59 3d..1 1us : add_preempt_count <-_raw_spin_lock_irq
1350kworker/-59 3d..2 1us : deactivate_task <-__schedule
1351kworker/-59 3d..2 1us : dequeue_task <-deactivate_task
1352kworker/-59 3d..2 2us : update_rq_clock <-dequeue_task
1353kworker/-59 3d..2 2us : dequeue_task_fair <-dequeue_task
1354kworker/-59 3d..2 2us : update_curr <-dequeue_task_fair
1355kworker/-59 3d..2 2us : update_min_vruntime <-update_curr
1356kworker/-59 3d..2 3us : cpuacct_charge <-update_curr
1357kworker/-59 3d..2 3us : __rcu_read_lock <-cpuacct_charge
1358kworker/-59 3d..2 3us : __rcu_read_unlock <-cpuacct_charge
1359kworker/-59 3d..2 3us : update_cfs_rq_blocked_load <-dequeue_task_fair
1360kworker/-59 3d..2 4us : clear_buddies <-dequeue_task_fair
1361kworker/-59 3d..2 4us : account_entity_dequeue <-dequeue_task_fair
1362kworker/-59 3d..2 4us : update_min_vruntime <-dequeue_task_fair
1363kworker/-59 3d..2 4us : update_cfs_shares <-dequeue_task_fair
1364kworker/-59 3d..2 5us : hrtick_update <-dequeue_task_fair
1365kworker/-59 3d..2 5us : wq_worker_sleeping <-__schedule
1366kworker/-59 3d..2 5us : kthread_data <-wq_worker_sleeping
1367kworker/-59 3d..2 5us : put_prev_task_fair <-__schedule
1368kworker/-59 3d..2 6us : pick_next_task_fair <-pick_next_task
1369kworker/-59 3d..2 6us : clear_buddies <-pick_next_task_fair
1370kworker/-59 3d..2 6us : set_next_entity <-pick_next_task_fair
1371kworker/-59 3d..2 6us : update_stats_wait_end <-set_next_entity
1372 ls-2269 3d..2 7us : finish_task_switch <-__schedule
1373 ls-2269 3d..2 7us : _raw_spin_unlock_irq <-finish_task_switch
1374 ls-2269 3d..2 8us : do_IRQ <-ret_from_intr
1375 ls-2269 3d..2 8us : irq_enter <-do_IRQ
1376 ls-2269 3d..2 8us : rcu_irq_enter <-irq_enter
1377 ls-2269 3d..2 9us : add_preempt_count <-irq_enter
1378 ls-2269 3d.h2 9us : exit_idle <-do_IRQ
1379[...]
1380 ls-2269 3d.h3 20us : sub_preempt_count <-_raw_spin_unlock
1381 ls-2269 3d.h2 20us : irq_exit <-do_IRQ
1382 ls-2269 3d.h2 21us : sub_preempt_count <-irq_exit
1383 ls-2269 3d..3 21us : do_softirq <-irq_exit
1384 ls-2269 3d..3 21us : __do_softirq <-call_softirq
1385 ls-2269 3d..3 21us+: __local_bh_disable <-__do_softirq
1386 ls-2269 3d.s4 29us : sub_preempt_count <-_local_bh_enable_ip
1387 ls-2269 3d.s5 29us : sub_preempt_count <-_local_bh_enable_ip
1388 ls-2269 3d.s5 31us : do_IRQ <-ret_from_intr
1389 ls-2269 3d.s5 31us : irq_enter <-do_IRQ
1390 ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter
1391[...]
1392 ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter
1393 ls-2269 3d.s5 32us : add_preempt_count <-irq_enter
1394 ls-2269 3d.H5 32us : exit_idle <-do_IRQ
1395 ls-2269 3d.H5 32us : handle_irq <-do_IRQ
1396 ls-2269 3d.H5 32us : irq_to_desc <-handle_irq
1397 ls-2269 3d.H5 33us : handle_fasteoi_irq <-handle_irq
1398[...]
1399 ls-2269 3d.s5 158us : _raw_spin_unlock_irqrestore <-rtl8139_poll
1400 ls-2269 3d.s3 158us : net_rps_action_and_irq_enable.isra.65 <-net_rx_action
1401 ls-2269 3d.s3 159us : __local_bh_enable <-__do_softirq
1402 ls-2269 3d.s3 159us : sub_preempt_count <-__local_bh_enable
1403 ls-2269 3d..3 159us : idle_cpu <-irq_exit
1404 ls-2269 3d..3 159us : rcu_irq_exit <-irq_exit
1405 ls-2269 3d..3 160us : sub_preempt_count <-irq_exit
1406 ls-2269 3d... 161us : __mutex_unlock_slowpath <-mutex_unlock
1407 ls-2269 3d... 162us+: trace_hardirqs_on <-mutex_unlock
1408 ls-2269 3d... 186us : <stack trace>
1409 => __mutex_unlock_slowpath
1410 => mutex_unlock
1411 => process_output
1412 => n_tty_write
1413 => tty_write
1414 => vfs_write
1415 => sys_write
1416 => system_call_fastpath
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001417
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001418This is an interesting trace. It started with kworker running and
1419scheduling out and ls taking over. But as soon as ls released the
1420rq lock and enabled interrupts (but not preemption) an interrupt
1421triggered. When the interrupt finished, it started running softirqs.
1422But while the softirq was running, another interrupt triggered.
1423When an interrupt is running inside a softirq, the annotation is 'H'.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001424
1425
1426wakeup
1427------
1428
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001429One common case that people are interested in tracing is the
1430time it takes for a task that is woken to actually wake up.
1431Now for non Real-Time tasks, this can be arbitrary. But tracing
1432it none the less can be interesting.
1433
1434Without function tracing:
1435
1436 # echo 0 > options/function-trace
1437 # echo wakeup > current_tracer
1438 # echo 1 > tracing_on
1439 # echo 0 > tracing_max_latency
1440 # chrt -f 5 sleep 1
1441 # echo 0 > tracing_on
1442 # cat trace
1443# tracer: wakeup
1444#
1445# wakeup latency trace v1.1.5 on 3.8.0-test+
1446# --------------------------------------------------------------------
1447# latency: 15 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1448# -----------------
1449# | task: kworker/3:1H-312 (uid:0 nice:-20 policy:0 rt_prio:0)
1450# -----------------
1451#
1452# _------=> CPU#
1453# / _-----=> irqs-off
1454# | / _----=> need-resched
1455# || / _---=> hardirq/softirq
1456# ||| / _--=> preempt-depth
1457# |||| / delay
1458# cmd pid ||||| time | caller
1459# \ / ||||| \ | /
1460 <idle>-0 3dNs7 0us : 0:120:R + [003] 312:100:R kworker/3:1H
1461 <idle>-0 3dNs7 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up
1462 <idle>-0 3d..3 15us : __schedule <-schedule
1463 <idle>-0 3d..3 15us : 0:120:R ==> [003] 312:100:R kworker/3:1H
1464
1465The tracer only traces the highest priority task in the system
1466to avoid tracing the normal circumstances. Here we see that
1467the kworker with a nice priority of -20 (not very nice), took
1468just 15 microseconds from the time it woke up, to the time it
1469ran.
1470
1471Non Real-Time tasks are not that interesting. A more interesting
1472trace is to concentrate only on Real-Time tasks.
1473
1474wakeup_rt
1475---------
1476
Ingo Molnar57526742009-02-19 12:54:10 +01001477In a Real-Time environment it is very important to know the
1478wakeup time it takes for the highest priority task that is woken
1479up to the time that it executes. This is also known as "schedule
1480latency". I stress the point that this is about RT tasks. It is
1481also important to know the scheduling latency of non-RT tasks,
1482but the average schedule latency is better for non-RT tasks.
1483Tools like LatencyTop are more appropriate for such
1484measurements.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001485
Steven Rostedta41eeba2008-07-14 16:41:12 -04001486Real-Time environments are interested in the worst case latency.
Ingo Molnar57526742009-02-19 12:54:10 +01001487That is the longest latency it takes for something to happen,
1488and not the average. We can have a very fast scheduler that may
1489only have a large latency once in a while, but that would not
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001490work well with Real-Time tasks. The wakeup_rt tracer was designed
Ingo Molnar57526742009-02-19 12:54:10 +01001491to record the worst case wakeups of RT tasks. Non-RT tasks are
1492not recorded because the tracer only records one worst case and
1493tracing non-RT tasks that are unpredictable will overwrite the
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001494worst case latency of RT tasks (just run the normal wakeup
1495tracer for a while to see that effect).
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001496
Ingo Molnar57526742009-02-19 12:54:10 +01001497Since this tracer only deals with RT tasks, we will run this
1498slightly differently than we did with the previous tracers.
1499Instead of performing an 'ls', we will run 'sleep 1' under
1500'chrt' which changes the priority of the task.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001501
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001502 # echo 0 > options/function-trace
1503 # echo wakeup_rt > current_tracer
Steven Rostedt6752ab42011-02-08 13:54:06 -05001504 # echo 1 > tracing_on
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001505 # echo 0 > tracing_max_latency
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001506 # chrt -f 5 sleep 1
Steven Rostedt6752ab42011-02-08 13:54:06 -05001507 # echo 0 > tracing_on
Albin Tonnerre4a88d442009-08-31 22:40:08 +02001508 # cat trace
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001509# tracer: wakeup
1510#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001511# tracer: wakeup_rt
1512#
1513# wakeup_rt latency trace v1.1.5 on 3.8.0-test+
1514# --------------------------------------------------------------------
1515# latency: 5 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1516# -----------------
1517# | task: sleep-2389 (uid:0 nice:0 policy:1 rt_prio:5)
1518# -----------------
1519#
1520# _------=> CPU#
1521# / _-----=> irqs-off
1522# | / _----=> need-resched
1523# || / _---=> hardirq/softirq
1524# ||| / _--=> preempt-depth
1525# |||| / delay
1526# cmd pid ||||| time | caller
1527# \ / ||||| \ | /
1528 <idle>-0 3d.h4 0us : 0:120:R + [003] 2389: 94:R sleep
1529 <idle>-0 3d.h4 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up
1530 <idle>-0 3d..3 5us : __schedule <-schedule
1531 <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001532
1533
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001534Running this on an idle system, we see that it only took 5 microseconds
1535to perform the task switch. Note, since the trace point in the schedule
1536is before the actual "switch", we stop the tracing when the recorded task
1537is about to schedule in. This may change if we add a new marker at the
1538end of the scheduler.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001539
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001540Notice that the recorded task is 'sleep' with the PID of 2389
Ingo Molnar57526742009-02-19 12:54:10 +01001541and it has an rt_prio of 5. This priority is user-space priority
1542and not the internal kernel priority. The policy is 1 for
1543SCHED_FIFO and 2 for SCHED_RR.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001544
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001545Note, that the trace data shows the internal priority (99 - rtprio).
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001546
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001547 <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep
1548
1549The 0:120:R means idle was running with a nice priority of 0 (120 - 20)
1550and in the running state 'R'. The sleep task was scheduled in with
15512389: 94:R. That is the priority is the kernel rtprio (99 - 5 = 94)
1552and it too is in the running state.
1553
1554Doing the same with chrt -r 5 and function-trace set.
1555
1556 echo 1 > options/function-trace
1557
1558# tracer: wakeup_rt
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001559#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001560# wakeup_rt latency trace v1.1.5 on 3.8.0-test+
1561# --------------------------------------------------------------------
1562# latency: 29 us, #85/85, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1563# -----------------
1564# | task: sleep-2448 (uid:0 nice:0 policy:1 rt_prio:5)
1565# -----------------
1566#
1567# _------=> CPU#
1568# / _-----=> irqs-off
1569# | / _----=> need-resched
1570# || / _---=> hardirq/softirq
1571# ||| / _--=> preempt-depth
1572# |||| / delay
1573# cmd pid ||||| time | caller
1574# \ / ||||| \ | /
1575 <idle>-0 3d.h4 1us+: 0:120:R + [003] 2448: 94:R sleep
1576 <idle>-0 3d.h4 2us : ttwu_do_activate.constprop.87 <-try_to_wake_up
1577 <idle>-0 3d.h3 3us : check_preempt_curr <-ttwu_do_wakeup
Kirill Tkhai88751252014-06-29 00:03:57 +04001578 <idle>-0 3d.h3 3us : resched_curr <-check_preempt_curr
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001579 <idle>-0 3dNh3 4us : task_woken_rt <-ttwu_do_wakeup
1580 <idle>-0 3dNh3 4us : _raw_spin_unlock <-try_to_wake_up
1581 <idle>-0 3dNh3 4us : sub_preempt_count <-_raw_spin_unlock
1582 <idle>-0 3dNh2 5us : ttwu_stat <-try_to_wake_up
1583 <idle>-0 3dNh2 5us : _raw_spin_unlock_irqrestore <-try_to_wake_up
1584 <idle>-0 3dNh2 6us : sub_preempt_count <-_raw_spin_unlock_irqrestore
1585 <idle>-0 3dNh1 6us : _raw_spin_lock <-__run_hrtimer
1586 <idle>-0 3dNh1 6us : add_preempt_count <-_raw_spin_lock
1587 <idle>-0 3dNh2 7us : _raw_spin_unlock <-hrtimer_interrupt
1588 <idle>-0 3dNh2 7us : sub_preempt_count <-_raw_spin_unlock
1589 <idle>-0 3dNh1 7us : tick_program_event <-hrtimer_interrupt
1590 <idle>-0 3dNh1 7us : clockevents_program_event <-tick_program_event
1591 <idle>-0 3dNh1 8us : ktime_get <-clockevents_program_event
1592 <idle>-0 3dNh1 8us : lapic_next_event <-clockevents_program_event
1593 <idle>-0 3dNh1 8us : irq_exit <-smp_apic_timer_interrupt
1594 <idle>-0 3dNh1 9us : sub_preempt_count <-irq_exit
1595 <idle>-0 3dN.2 9us : idle_cpu <-irq_exit
1596 <idle>-0 3dN.2 9us : rcu_irq_exit <-irq_exit
1597 <idle>-0 3dN.2 10us : rcu_eqs_enter_common.isra.45 <-rcu_irq_exit
1598 <idle>-0 3dN.2 10us : sub_preempt_count <-irq_exit
1599 <idle>-0 3.N.1 11us : rcu_idle_exit <-cpu_idle
1600 <idle>-0 3dN.1 11us : rcu_eqs_exit_common.isra.43 <-rcu_idle_exit
1601 <idle>-0 3.N.1 11us : tick_nohz_idle_exit <-cpu_idle
1602 <idle>-0 3dN.1 12us : menu_hrtimer_cancel <-tick_nohz_idle_exit
1603 <idle>-0 3dN.1 12us : ktime_get <-tick_nohz_idle_exit
1604 <idle>-0 3dN.1 12us : tick_do_update_jiffies64 <-tick_nohz_idle_exit
Frederic Weisbeckercee1afc2016-04-13 15:56:50 +02001605 <idle>-0 3dN.1 13us : cpu_load_update_nohz <-tick_nohz_idle_exit
1606 <idle>-0 3dN.1 13us : _raw_spin_lock <-cpu_load_update_nohz
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001607 <idle>-0 3dN.1 13us : add_preempt_count <-_raw_spin_lock
Frederic Weisbeckercee1afc2016-04-13 15:56:50 +02001608 <idle>-0 3dN.2 13us : __cpu_load_update <-cpu_load_update_nohz
1609 <idle>-0 3dN.2 14us : sched_avg_update <-__cpu_load_update
1610 <idle>-0 3dN.2 14us : _raw_spin_unlock <-cpu_load_update_nohz
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001611 <idle>-0 3dN.2 14us : sub_preempt_count <-_raw_spin_unlock
1612 <idle>-0 3dN.1 15us : calc_load_exit_idle <-tick_nohz_idle_exit
1613 <idle>-0 3dN.1 15us : touch_softlockup_watchdog <-tick_nohz_idle_exit
1614 <idle>-0 3dN.1 15us : hrtimer_cancel <-tick_nohz_idle_exit
1615 <idle>-0 3dN.1 15us : hrtimer_try_to_cancel <-hrtimer_cancel
1616 <idle>-0 3dN.1 16us : lock_hrtimer_base.isra.18 <-hrtimer_try_to_cancel
1617 <idle>-0 3dN.1 16us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18
1618 <idle>-0 3dN.1 16us : add_preempt_count <-_raw_spin_lock_irqsave
1619 <idle>-0 3dN.2 17us : __remove_hrtimer <-remove_hrtimer.part.16
1620 <idle>-0 3dN.2 17us : hrtimer_force_reprogram <-__remove_hrtimer
1621 <idle>-0 3dN.2 17us : tick_program_event <-hrtimer_force_reprogram
1622 <idle>-0 3dN.2 18us : clockevents_program_event <-tick_program_event
1623 <idle>-0 3dN.2 18us : ktime_get <-clockevents_program_event
1624 <idle>-0 3dN.2 18us : lapic_next_event <-clockevents_program_event
1625 <idle>-0 3dN.2 19us : _raw_spin_unlock_irqrestore <-hrtimer_try_to_cancel
1626 <idle>-0 3dN.2 19us : sub_preempt_count <-_raw_spin_unlock_irqrestore
1627 <idle>-0 3dN.1 19us : hrtimer_forward <-tick_nohz_idle_exit
1628 <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward
1629 <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward
1630 <idle>-0 3dN.1 20us : hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11
1631 <idle>-0 3dN.1 20us : __hrtimer_start_range_ns <-hrtimer_start_range_ns
1632 <idle>-0 3dN.1 21us : lock_hrtimer_base.isra.18 <-__hrtimer_start_range_ns
1633 <idle>-0 3dN.1 21us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18
1634 <idle>-0 3dN.1 21us : add_preempt_count <-_raw_spin_lock_irqsave
1635 <idle>-0 3dN.2 22us : ktime_add_safe <-__hrtimer_start_range_ns
1636 <idle>-0 3dN.2 22us : enqueue_hrtimer <-__hrtimer_start_range_ns
1637 <idle>-0 3dN.2 22us : tick_program_event <-__hrtimer_start_range_ns
1638 <idle>-0 3dN.2 23us : clockevents_program_event <-tick_program_event
1639 <idle>-0 3dN.2 23us : ktime_get <-clockevents_program_event
1640 <idle>-0 3dN.2 23us : lapic_next_event <-clockevents_program_event
1641 <idle>-0 3dN.2 24us : _raw_spin_unlock_irqrestore <-__hrtimer_start_range_ns
1642 <idle>-0 3dN.2 24us : sub_preempt_count <-_raw_spin_unlock_irqrestore
1643 <idle>-0 3dN.1 24us : account_idle_ticks <-tick_nohz_idle_exit
1644 <idle>-0 3dN.1 24us : account_idle_time <-account_idle_ticks
1645 <idle>-0 3.N.1 25us : sub_preempt_count <-cpu_idle
1646 <idle>-0 3.N.. 25us : schedule <-cpu_idle
1647 <idle>-0 3.N.. 25us : __schedule <-preempt_schedule
1648 <idle>-0 3.N.. 26us : add_preempt_count <-__schedule
1649 <idle>-0 3.N.1 26us : rcu_note_context_switch <-__schedule
1650 <idle>-0 3.N.1 26us : rcu_sched_qs <-rcu_note_context_switch
1651 <idle>-0 3dN.1 27us : rcu_preempt_qs <-rcu_note_context_switch
1652 <idle>-0 3.N.1 27us : _raw_spin_lock_irq <-__schedule
1653 <idle>-0 3dN.1 27us : add_preempt_count <-_raw_spin_lock_irq
1654 <idle>-0 3dN.2 28us : put_prev_task_idle <-__schedule
1655 <idle>-0 3dN.2 28us : pick_next_task_stop <-pick_next_task
1656 <idle>-0 3dN.2 28us : pick_next_task_rt <-pick_next_task
1657 <idle>-0 3dN.2 29us : dequeue_pushable_task <-pick_next_task_rt
1658 <idle>-0 3d..3 29us : __schedule <-preempt_schedule
1659 <idle>-0 3d..3 30us : 0:120:R ==> [003] 2448: 94:R sleep
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001660
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001661This isn't that big of a trace, even with function tracing enabled,
1662so I included the entire trace.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001663
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001664The interrupt went off while when the system was idle. Somewhere
1665before task_woken_rt() was called, the NEED_RESCHED flag was set,
1666this is indicated by the first occurrence of the 'N' flag.
1667
1668Latency tracing and events
1669--------------------------
1670As function tracing can induce a much larger latency, but without
1671seeing what happens within the latency it is hard to know what
1672caused it. There is a middle ground, and that is with enabling
1673events.
1674
1675 # echo 0 > options/function-trace
1676 # echo wakeup_rt > current_tracer
1677 # echo 1 > events/enable
1678 # echo 1 > tracing_on
1679 # echo 0 > tracing_max_latency
1680 # chrt -f 5 sleep 1
1681 # echo 0 > tracing_on
1682 # cat trace
1683# tracer: wakeup_rt
1684#
1685# wakeup_rt latency trace v1.1.5 on 3.8.0-test+
1686# --------------------------------------------------------------------
1687# latency: 6 us, #12/12, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1688# -----------------
1689# | task: sleep-5882 (uid:0 nice:0 policy:1 rt_prio:5)
1690# -----------------
1691#
1692# _------=> CPU#
1693# / _-----=> irqs-off
1694# | / _----=> need-resched
1695# || / _---=> hardirq/softirq
1696# ||| / _--=> preempt-depth
1697# |||| / delay
1698# cmd pid ||||| time | caller
1699# \ / ||||| \ | /
1700 <idle>-0 2d.h4 0us : 0:120:R + [002] 5882: 94:R sleep
1701 <idle>-0 2d.h4 0us : ttwu_do_activate.constprop.87 <-try_to_wake_up
1702 <idle>-0 2d.h4 1us : sched_wakeup: comm=sleep pid=5882 prio=94 success=1 target_cpu=002
1703 <idle>-0 2dNh2 1us : hrtimer_expire_exit: hrtimer=ffff88007796feb8
1704 <idle>-0 2.N.2 2us : power_end: cpu_id=2
1705 <idle>-0 2.N.2 3us : cpu_idle: state=4294967295 cpu_id=2
1706 <idle>-0 2dN.3 4us : hrtimer_cancel: hrtimer=ffff88007d50d5e0
1707 <idle>-0 2dN.3 4us : hrtimer_start: hrtimer=ffff88007d50d5e0 function=tick_sched_timer expires=34311211000000 softexpires=34311211000000
1708 <idle>-0 2.N.2 5us : rcu_utilization: Start context switch
1709 <idle>-0 2.N.2 5us : rcu_utilization: End context switch
1710 <idle>-0 2d..3 6us : __schedule <-schedule
1711 <idle>-0 2d..3 6us : 0:120:R ==> [002] 5882: 94:R sleep
1712
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001713
Steven Rostedt9b803c02008-11-03 15:15:08 -05001714function
1715--------
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001716
Steven Rostedt9b803c02008-11-03 15:15:08 -05001717This tracer is the function tracer. Enabling the function tracer
Ingo Molnar57526742009-02-19 12:54:10 +01001718can be done from the debug file system. Make sure the
1719ftrace_enabled is set; otherwise this tracer is a nop.
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001720See the "ftrace_enabled" section below.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001721
1722 # sysctl kernel.ftrace_enabled=1
GeunSik Lim156f5a72009-06-02 15:01:37 +09001723 # echo function > current_tracer
Steven Rostedt6752ab42011-02-08 13:54:06 -05001724 # echo 1 > tracing_on
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001725 # usleep 1
Steven Rostedt6752ab42011-02-08 13:54:06 -05001726 # echo 0 > tracing_on
GeunSik Lim156f5a72009-06-02 15:01:37 +09001727 # cat trace
Steven Rostedt9b803c02008-11-03 15:15:08 -05001728# tracer: function
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001729#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001730# entries-in-buffer/entries-written: 24799/24799 #P:4
1731#
1732# _-----=> irqs-off
1733# / _----=> need-resched
1734# | / _---=> hardirq/softirq
1735# || / _--=> preempt-depth
1736# ||| / delay
1737# TASK-PID CPU# |||| TIMESTAMP FUNCTION
1738# | | | |||| | |
1739 bash-1994 [002] .... 3082.063030: mutex_unlock <-rb_simple_write
1740 bash-1994 [002] .... 3082.063031: __mutex_unlock_slowpath <-mutex_unlock
1741 bash-1994 [002] .... 3082.063031: __fsnotify_parent <-fsnotify_modify
1742 bash-1994 [002] .... 3082.063032: fsnotify <-fsnotify_modify
1743 bash-1994 [002] .... 3082.063032: __srcu_read_lock <-fsnotify
1744 bash-1994 [002] .... 3082.063032: add_preempt_count <-__srcu_read_lock
1745 bash-1994 [002] ...1 3082.063032: sub_preempt_count <-__srcu_read_lock
1746 bash-1994 [002] .... 3082.063033: __srcu_read_unlock <-fsnotify
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001747[...]
1748
1749
Ingo Molnar57526742009-02-19 12:54:10 +01001750Note: function tracer uses ring buffers to store the above
1751entries. The newest data may overwrite the oldest data.
1752Sometimes using echo to stop the trace is not sufficient because
1753the tracing could have overwritten the data that you wanted to
1754record. For this reason, it is sometimes better to disable
1755tracing directly from a program. This allows you to stop the
1756tracing at the point that you hit the part that you are
1757interested in. To disable the tracing directly from a C program,
1758something like following code snippet can be used:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001759
1760int trace_fd;
1761[...]
1762int main(int argc, char *argv[]) {
1763 [...]
Steven Rostedt6752ab42011-02-08 13:54:06 -05001764 trace_fd = open(tracing_file("tracing_on"), O_WRONLY);
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001765 [...]
1766 if (condition_hit()) {
Steven Rostedtf2d9c742008-07-15 10:57:33 -04001767 write(trace_fd, "0", 1);
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001768 }
1769 [...]
1770}
1771
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001772
1773Single thread tracing
1774---------------------
1775
GeunSik Lim156f5a72009-06-02 15:01:37 +09001776By writing into set_ftrace_pid you can trace a
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001777single thread. For example:
1778
GeunSik Lim156f5a72009-06-02 15:01:37 +09001779# cat set_ftrace_pid
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001780no pid
GeunSik Lim156f5a72009-06-02 15:01:37 +09001781# echo 3111 > set_ftrace_pid
1782# cat set_ftrace_pid
Steven Rostedtdf4fc312008-11-26 00:16:23 -050017833111
GeunSik Lim156f5a72009-06-02 15:01:37 +09001784# echo function > current_tracer
1785# cat trace | head
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001786 # tracer: function
1787 #
1788 # TASK-PID CPU# TIMESTAMP FUNCTION
1789 # | | | | |
1790 yum-updatesd-3111 [003] 1637.254676: finish_task_switch <-thread_return
1791 yum-updatesd-3111 [003] 1637.254681: hrtimer_cancel <-schedule_hrtimeout_range
1792 yum-updatesd-3111 [003] 1637.254682: hrtimer_try_to_cancel <-hrtimer_cancel
1793 yum-updatesd-3111 [003] 1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel
1794 yum-updatesd-3111 [003] 1637.254685: fget_light <-do_sys_poll
1795 yum-updatesd-3111 [003] 1637.254686: pipe_poll <-do_sys_poll
Wang Long52e68922015-02-05 05:16:14 +00001796# echo > set_ftrace_pid
GeunSik Lim156f5a72009-06-02 15:01:37 +09001797# cat trace |head
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001798 # tracer: function
1799 #
1800 # TASK-PID CPU# TIMESTAMP FUNCTION
1801 # | | | | |
1802 ##### CPU 3 buffer started ####
1803 yum-updatesd-3111 [003] 1701.957688: free_poll_entry <-poll_freewait
1804 yum-updatesd-3111 [003] 1701.957689: remove_wait_queue <-free_poll_entry
1805 yum-updatesd-3111 [003] 1701.957691: fput <-free_poll_entry
1806 yum-updatesd-3111 [003] 1701.957692: audit_syscall_exit <-sysret_audit
1807 yum-updatesd-3111 [003] 1701.957693: path_put <-audit_syscall_exit
1808
1809If you want to trace a function when executing, you could use
1810something like this simple program:
1811
1812#include <stdio.h>
1813#include <stdlib.h>
1814#include <sys/types.h>
1815#include <sys/stat.h>
1816#include <fcntl.h>
1817#include <unistd.h>
Jiri Olsa67b394f2009-10-23 19:36:18 -04001818#include <string.h>
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001819
GeunSik Lim156f5a72009-06-02 15:01:37 +09001820#define _STR(x) #x
1821#define STR(x) _STR(x)
1822#define MAX_PATH 256
1823
1824const char *find_debugfs(void)
1825{
1826 static char debugfs[MAX_PATH+1];
1827 static int debugfs_found;
1828 char type[100];
1829 FILE *fp;
1830
1831 if (debugfs_found)
1832 return debugfs;
1833
1834 if ((fp = fopen("/proc/mounts","r")) == NULL) {
1835 perror("/proc/mounts");
1836 return NULL;
1837 }
1838
1839 while (fscanf(fp, "%*s %"
1840 STR(MAX_PATH)
1841 "s %99s %*s %*d %*d\n",
1842 debugfs, type) == 2) {
1843 if (strcmp(type, "debugfs") == 0)
1844 break;
1845 }
1846 fclose(fp);
1847
1848 if (strcmp(type, "debugfs") != 0) {
1849 fprintf(stderr, "debugfs not mounted");
1850 return NULL;
1851 }
1852
Jiri Olsa67b394f2009-10-23 19:36:18 -04001853 strcat(debugfs, "/tracing/");
GeunSik Lim156f5a72009-06-02 15:01:37 +09001854 debugfs_found = 1;
1855
1856 return debugfs;
1857}
1858
1859const char *tracing_file(const char *file_name)
1860{
1861 static char trace_file[MAX_PATH+1];
1862 snprintf(trace_file, MAX_PATH, "%s/%s", find_debugfs(), file_name);
1863 return trace_file;
1864}
1865
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001866int main (int argc, char **argv)
1867{
1868 if (argc < 1)
1869 exit(-1);
1870
1871 if (fork() > 0) {
1872 int fd, ffd;
1873 char line[64];
1874 int s;
1875
GeunSik Lim156f5a72009-06-02 15:01:37 +09001876 ffd = open(tracing_file("current_tracer"), O_WRONLY);
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001877 if (ffd < 0)
1878 exit(-1);
1879 write(ffd, "nop", 3);
1880
GeunSik Lim156f5a72009-06-02 15:01:37 +09001881 fd = open(tracing_file("set_ftrace_pid"), O_WRONLY);
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001882 s = sprintf(line, "%d\n", getpid());
1883 write(fd, line, s);
1884
1885 write(ffd, "function", 8);
1886
1887 close(fd);
1888 close(ffd);
1889
1890 execvp(argv[1], argv+1);
1891 }
1892
1893 return 0;
1894}
1895
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001896Or this simple script!
Markus Metzgere2ea5392009-01-19 10:35:58 +01001897
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001898------
1899#!/bin/bash
Markus Metzgere2ea5392009-01-19 10:35:58 +01001900
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001901debugfs=`sed -ne 's/^debugfs \(.*\) debugfs.*/\1/p' /proc/mounts`
1902echo nop > $debugfs/tracing/current_tracer
1903echo 0 > $debugfs/tracing/tracing_on
1904echo $$ > $debugfs/tracing/set_ftrace_pid
1905echo function > $debugfs/tracing/current_tracer
1906echo 1 > $debugfs/tracing/tracing_on
1907exec "$@"
1908------
Markus Metzgere2ea5392009-01-19 10:35:58 +01001909
1910
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001911function graph tracer
1912---------------------------
1913
Ingo Molnar57526742009-02-19 12:54:10 +01001914This tracer is similar to the function tracer except that it
1915probes a function on its entry and its exit. This is done by
1916using a dynamically allocated stack of return addresses in each
1917task_struct. On function entry the tracer overwrites the return
1918address of each function traced to set a custom probe. Thus the
1919original return address is stored on the stack of return address
1920in the task_struct.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001921
Ingo Molnar57526742009-02-19 12:54:10 +01001922Probing on both ends of a function leads to special features
1923such as:
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001924
Ingo Molnar57526742009-02-19 12:54:10 +01001925- measure of a function's time execution
1926- having a reliable call stack to draw function calls graph
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001927
1928This tracer is useful in several situations:
1929
Ingo Molnar57526742009-02-19 12:54:10 +01001930- you want to find the reason of a strange kernel behavior and
1931 need to see what happens in detail on any areas (or specific
1932 ones).
1933
1934- you are experiencing weird latencies but it's difficult to
1935 find its origin.
1936
1937- you want to find quickly which path is taken by a specific
1938 function
1939
1940- you just want to peek inside a working kernel and want to see
1941 what happens there.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001942
1943# tracer: function_graph
1944#
1945# CPU DURATION FUNCTION CALLS
1946# | | | | | | |
1947
1948 0) | sys_open() {
1949 0) | do_sys_open() {
1950 0) | getname() {
1951 0) | kmem_cache_alloc() {
1952 0) 1.382 us | __might_sleep();
1953 0) 2.478 us | }
1954 0) | strncpy_from_user() {
1955 0) | might_fault() {
1956 0) 1.389 us | __might_sleep();
1957 0) 2.553 us | }
1958 0) 3.807 us | }
1959 0) 7.876 us | }
1960 0) | alloc_fd() {
1961 0) 0.668 us | _spin_lock();
1962 0) 0.570 us | expand_files();
1963 0) 0.586 us | _spin_unlock();
1964
1965
Ingo Molnar57526742009-02-19 12:54:10 +01001966There are several columns that can be dynamically
1967enabled/disabled. You can use every combination of options you
1968want, depending on your needs.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001969
Ingo Molnar57526742009-02-19 12:54:10 +01001970- The cpu number on which the function executed is default
1971 enabled. It is sometimes better to only trace one cpu (see
1972 tracing_cpu_mask file) or you might sometimes see unordered
1973 function calls while cpu tracing switch.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001974
GeunSik Lim156f5a72009-06-02 15:01:37 +09001975 hide: echo nofuncgraph-cpu > trace_options
1976 show: echo funcgraph-cpu > trace_options
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001977
Ingo Molnar57526742009-02-19 12:54:10 +01001978- The duration (function's time of execution) is displayed on
1979 the closing bracket line of a function or on the same line
1980 than the current function in case of a leaf one. It is default
1981 enabled.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001982
GeunSik Lim156f5a72009-06-02 15:01:37 +09001983 hide: echo nofuncgraph-duration > trace_options
1984 show: echo funcgraph-duration > trace_options
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001985
Ingo Molnar57526742009-02-19 12:54:10 +01001986- The overhead field precedes the duration field in case of
1987 reached duration thresholds.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001988
GeunSik Lim156f5a72009-06-02 15:01:37 +09001989 hide: echo nofuncgraph-overhead > trace_options
1990 show: echo funcgraph-overhead > trace_options
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001991 depends on: funcgraph-duration
1992
1993 ie:
1994
Jungseok Leeb838e1d2015-07-11 14:51:40 +00001995 3) # 1837.709 us | } /* __switch_to */
1996 3) | finish_task_switch() {
1997 3) 0.313 us | _raw_spin_unlock_irq();
1998 3) 3.177 us | }
1999 3) # 1889.063 us | } /* __schedule */
2000 3) ! 140.417 us | } /* __schedule */
2001 3) # 2034.948 us | } /* schedule */
2002 3) * 33998.59 us | } /* schedule_preempt_disabled */
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002003
2004 [...]
2005
Jungseok Leeb838e1d2015-07-11 14:51:40 +00002006 1) 0.260 us | msecs_to_jiffies();
2007 1) 0.313 us | __rcu_read_unlock();
2008 1) + 61.770 us | }
2009 1) + 64.479 us | }
2010 1) 0.313 us | rcu_bh_qs();
2011 1) 0.313 us | __local_bh_enable();
2012 1) ! 217.240 us | }
2013 1) 0.365 us | idle_cpu();
2014 1) | rcu_irq_exit() {
2015 1) 0.417 us | rcu_eqs_enter_common.isra.47();
2016 1) 3.125 us | }
2017 1) ! 227.812 us | }
2018 1) ! 457.395 us | }
2019 1) @ 119760.2 us | }
2020
2021 [...]
2022
2023 2) | handle_IPI() {
2024 1) 6.979 us | }
2025 2) 0.417 us | scheduler_ipi();
2026 1) 9.791 us | }
2027 1) + 12.917 us | }
2028 2) 3.490 us | }
2029 1) + 15.729 us | }
2030 1) + 18.542 us | }
2031 2) $ 3594274 us | }
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002032
2033 + means that the function exceeded 10 usecs.
2034 ! means that the function exceeded 100 usecs.
Byungchul Park8e1e1df2014-11-24 09:34:19 +09002035 # means that the function exceeded 1000 usecs.
Jungseok Leeb838e1d2015-07-11 14:51:40 +00002036 * means that the function exceeded 10 msecs.
2037 @ means that the function exceeded 100 msecs.
Byungchul Park8e1e1df2014-11-24 09:34:19 +09002038 $ means that the function exceeded 1 sec.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002039
2040
Ingo Molnar57526742009-02-19 12:54:10 +01002041- The task/pid field displays the thread cmdline and pid which
2042 executed the function. It is default disabled.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002043
GeunSik Lim156f5a72009-06-02 15:01:37 +09002044 hide: echo nofuncgraph-proc > trace_options
2045 show: echo funcgraph-proc > trace_options
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002046
2047 ie:
2048
2049 # tracer: function_graph
2050 #
2051 # CPU TASK/PID DURATION FUNCTION CALLS
2052 # | | | | | | | | |
2053 0) sh-4802 | | d_free() {
2054 0) sh-4802 | | call_rcu() {
2055 0) sh-4802 | | __call_rcu() {
2056 0) sh-4802 | 0.616 us | rcu_process_gp_end();
2057 0) sh-4802 | 0.586 us | check_for_new_grace_period();
2058 0) sh-4802 | 2.899 us | }
2059 0) sh-4802 | 4.040 us | }
2060 0) sh-4802 | 5.151 us | }
2061 0) sh-4802 | + 49.370 us | }
2062
2063
Ingo Molnar57526742009-02-19 12:54:10 +01002064- The absolute time field is an absolute timestamp given by the
2065 system clock since it started. A snapshot of this time is
2066 given on each entry/exit of functions
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002067
GeunSik Lim156f5a72009-06-02 15:01:37 +09002068 hide: echo nofuncgraph-abstime > trace_options
2069 show: echo funcgraph-abstime > trace_options
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002070
2071 ie:
2072
2073 #
2074 # TIME CPU DURATION FUNCTION CALLS
2075 # | | | | | | | |
2076 360.774522 | 1) 0.541 us | }
2077 360.774522 | 1) 4.663 us | }
2078 360.774523 | 1) 0.541 us | __wake_up_bit();
2079 360.774524 | 1) 6.796 us | }
2080 360.774524 | 1) 7.952 us | }
2081 360.774525 | 1) 9.063 us | }
2082 360.774525 | 1) 0.615 us | journal_mark_dirty();
2083 360.774527 | 1) 0.578 us | __brelse();
2084 360.774528 | 1) | reiserfs_prepare_for_journal() {
2085 360.774528 | 1) | unlock_buffer() {
2086 360.774529 | 1) | wake_up_bit() {
2087 360.774529 | 1) | bit_waitqueue() {
2088 360.774530 | 1) 0.594 us | __phys_addr();
2089
2090
Robert Elliott607e3a22014-05-20 17:10:51 -05002091The function name is always displayed after the closing bracket
2092for a function if the start of that function is not in the
2093trace buffer.
2094
2095Display of the function name after the closing bracket may be
2096enabled for functions whose start is in the trace buffer,
2097allowing easier searching with grep for function durations.
2098It is default disabled.
2099
2100 hide: echo nofuncgraph-tail > trace_options
2101 show: echo funcgraph-tail > trace_options
2102
2103 Example with nofuncgraph-tail (default):
2104 0) | putname() {
2105 0) | kmem_cache_free() {
2106 0) 0.518 us | __phys_addr();
2107 0) 1.757 us | }
2108 0) 2.861 us | }
2109
2110 Example with funcgraph-tail:
2111 0) | putname() {
2112 0) | kmem_cache_free() {
2113 0) 0.518 us | __phys_addr();
2114 0) 1.757 us | } /* kmem_cache_free() */
2115 0) 2.861 us | } /* putname() */
2116
Ingo Molnar57526742009-02-19 12:54:10 +01002117You can put some comments on specific functions by using
Ingo Molnar5e1607a2009-03-05 10:24:48 +01002118trace_printk() For example, if you want to put a comment inside
Ingo Molnar57526742009-02-19 12:54:10 +01002119the __might_sleep() function, you just have to include
Ingo Molnar5e1607a2009-03-05 10:24:48 +01002120<linux/ftrace.h> and call trace_printk() inside __might_sleep()
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002121
Ingo Molnar5e1607a2009-03-05 10:24:48 +01002122trace_printk("I'm a comment!\n")
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002123
2124will produce:
2125
2126 1) | __might_sleep() {
2127 1) | /* I'm a comment! */
2128 1) 1.449 us | }
2129
2130
Ingo Molnar57526742009-02-19 12:54:10 +01002131You might find other useful features for this tracer in the
2132following "dynamic ftrace" section such as tracing only specific
2133functions or tasks.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002134
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002135dynamic ftrace
2136--------------
2137
Steven Rostedtf2d9c742008-07-15 10:57:33 -04002138If CONFIG_DYNAMIC_FTRACE is set, the system will run with
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002139virtually no overhead when function tracing is disabled. The way
2140this works is the mcount function call (placed at the start of
Ingo Molnar57526742009-02-19 12:54:10 +01002141every kernel function, produced by the -pg switch in gcc),
2142starts of pointing to a simple return. (Enabling FTRACE will
2143include the -pg switch in the compiling of the kernel.)
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002144
Steven Rostedt9b803c02008-11-03 15:15:08 -05002145At compile time every C file object is run through the
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002146recordmcount program (located in the scripts directory). This
2147program will parse the ELF headers in the C object to find all
2148the locations in the .text section that call mcount. (Note, only
2149white listed .text sections are processed, since processing other
2150sections like .init.text may cause races due to those sections
2151being freed unexpectedly).
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002152
Ingo Molnar57526742009-02-19 12:54:10 +01002153A new section called "__mcount_loc" is created that holds
2154references to all the mcount call sites in the .text section.
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002155The recordmcount program re-links this section back into the
2156original object. The final linking stage of the kernel will add all these
2157references into a single table.
Steven Rostedt9b803c02008-11-03 15:15:08 -05002158
2159On boot up, before SMP is initialized, the dynamic ftrace code
Ingo Molnar57526742009-02-19 12:54:10 +01002160scans this table and updates all the locations into nops. It
2161also records the locations, which are added to the
2162available_filter_functions list. Modules are processed as they
2163are loaded and before they are executed. When a module is
2164unloaded, it also removes its functions from the ftrace function
2165list. This is automatic in the module unload code, and the
2166module author does not need to worry about it.
Steven Rostedt9b803c02008-11-03 15:15:08 -05002167
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002168When tracing is enabled, the process of modifying the function
2169tracepoints is dependent on architecture. The old method is to use
2170kstop_machine to prevent races with the CPUs executing code being
2171modified (which can cause the CPU to do undesirable things, especially
2172if the modified code crosses cache (or page) boundaries), and the nops are
Ingo Molnar57526742009-02-19 12:54:10 +01002173patched back to calls. But this time, they do not call mcount
2174(which is just a function stub). They now call into the ftrace
2175infrastructure.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002176
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002177The new method of modifying the function tracepoints is to place
2178a breakpoint at the location to be modified, sync all CPUs, modify
2179the rest of the instruction not covered by the breakpoint. Sync
2180all CPUs again, and then remove the breakpoint with the finished
2181version to the ftrace call site.
2182
2183Some archs do not even need to monkey around with the synchronization,
2184and can just slap the new code on top of the old without any
2185problems with other CPUs executing it at the same time.
2186
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002187One special side-effect to the recording of the functions being
Steven Rostedtf2d9c742008-07-15 10:57:33 -04002188traced is that we can now selectively choose which functions we
Ingo Molnar57526742009-02-19 12:54:10 +01002189wish to trace and which ones we want the mcount calls to remain
2190as nops.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002191
Ingo Molnar57526742009-02-19 12:54:10 +01002192Two files are used, one for enabling and one for disabling the
2193tracing of specified functions. They are:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002194
2195 set_ftrace_filter
2196
2197and
2198
2199 set_ftrace_notrace
2200
Ingo Molnar57526742009-02-19 12:54:10 +01002201A list of available functions that you can add to these files is
2202listed in:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002203
2204 available_filter_functions
2205
GeunSik Lim156f5a72009-06-02 15:01:37 +09002206 # cat available_filter_functions
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002207put_prev_task_idle
2208kmem_cache_create
2209pick_next_task_rt
2210get_online_cpus
2211pick_next_task_fair
2212mutex_lock
2213[...]
2214
Steven Rostedtf2d9c742008-07-15 10:57:33 -04002215If I am only interested in sys_nanosleep and hrtimer_interrupt:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002216
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002217 # echo sys_nanosleep hrtimer_interrupt > set_ftrace_filter
Yang Hongyang6993b1b2010-01-25 11:10:32 +08002218 # echo function > current_tracer
Steven Rostedt6752ab42011-02-08 13:54:06 -05002219 # echo 1 > tracing_on
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002220 # usleep 1
Steven Rostedt6752ab42011-02-08 13:54:06 -05002221 # echo 0 > tracing_on
GeunSik Lim156f5a72009-06-02 15:01:37 +09002222 # cat trace
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002223# tracer: function
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002224#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002225# entries-in-buffer/entries-written: 5/5 #P:4
2226#
2227# _-----=> irqs-off
2228# / _----=> need-resched
2229# | / _---=> hardirq/softirq
2230# || / _--=> preempt-depth
2231# ||| / delay
2232# TASK-PID CPU# |||| TIMESTAMP FUNCTION
2233# | | | |||| | |
2234 usleep-2665 [001] .... 4186.475355: sys_nanosleep <-system_call_fastpath
2235 <idle>-0 [001] d.h1 4186.475409: hrtimer_interrupt <-smp_apic_timer_interrupt
2236 usleep-2665 [001] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt
2237 <idle>-0 [003] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt
2238 <idle>-0 [002] d.h1 4186.475427: hrtimer_interrupt <-smp_apic_timer_interrupt
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002239
Steven Rostedtf2d9c742008-07-15 10:57:33 -04002240To see which functions are being traced, you can cat the file:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002241
GeunSik Lim156f5a72009-06-02 15:01:37 +09002242 # cat set_ftrace_filter
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002243hrtimer_interrupt
2244sys_nanosleep
2245
2246
Masami Hiramatsu60f1d5e2016-10-05 20:58:15 +09002247Perhaps this is not enough. The filters also allow glob(7) matching.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002248
Steven Rostedta41eeba2008-07-14 16:41:12 -04002249 <match>* - will match functions that begin with <match>
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002250 *<match> - will match functions that end with <match>
2251 *<match>* - will match functions that have <match> in it
Masami Hiramatsu60f1d5e2016-10-05 20:58:15 +09002252 <match1>*<match2> - will match functions that begin with
2253 <match1> and end with <match2>
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002254
Ingo Molnar57526742009-02-19 12:54:10 +01002255Note: It is better to use quotes to enclose the wild cards,
2256 otherwise the shell may expand the parameters into names
2257 of files in the local directory.
walimisc072c242008-11-28 12:21:19 +08002258
GeunSik Lim156f5a72009-06-02 15:01:37 +09002259 # echo 'hrtimer_*' > set_ftrace_filter
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002260
2261Produces:
2262
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002263# tracer: function
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002264#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002265# entries-in-buffer/entries-written: 897/897 #P:4
2266#
2267# _-----=> irqs-off
2268# / _----=> need-resched
2269# | / _---=> hardirq/softirq
2270# || / _--=> preempt-depth
2271# ||| / delay
2272# TASK-PID CPU# |||| TIMESTAMP FUNCTION
2273# | | | |||| | |
2274 <idle>-0 [003] dN.1 4228.547803: hrtimer_cancel <-tick_nohz_idle_exit
2275 <idle>-0 [003] dN.1 4228.547804: hrtimer_try_to_cancel <-hrtimer_cancel
2276 <idle>-0 [003] dN.2 4228.547805: hrtimer_force_reprogram <-__remove_hrtimer
2277 <idle>-0 [003] dN.1 4228.547805: hrtimer_forward <-tick_nohz_idle_exit
2278 <idle>-0 [003] dN.1 4228.547805: hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11
2279 <idle>-0 [003] d..1 4228.547858: hrtimer_get_next_event <-get_next_timer_interrupt
2280 <idle>-0 [003] d..1 4228.547859: hrtimer_start <-__tick_nohz_idle_enter
2281 <idle>-0 [003] d..2 4228.547860: hrtimer_force_reprogram <-__rem
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002282
2283Notice that we lost the sys_nanosleep.
2284
GeunSik Lim156f5a72009-06-02 15:01:37 +09002285 # cat set_ftrace_filter
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002286hrtimer_run_queues
2287hrtimer_run_pending
2288hrtimer_init
2289hrtimer_cancel
2290hrtimer_try_to_cancel
2291hrtimer_forward
2292hrtimer_start
2293hrtimer_reprogram
2294hrtimer_force_reprogram
2295hrtimer_get_next_event
2296hrtimer_interrupt
2297hrtimer_nanosleep
2298hrtimer_wakeup
2299hrtimer_get_remaining
2300hrtimer_get_res
2301hrtimer_init_sleeper
2302
2303
2304This is because the '>' and '>>' act just like they do in bash.
2305To rewrite the filters, use '>'
2306To append to the filters, use '>>'
2307
Ingo Molnar57526742009-02-19 12:54:10 +01002308To clear out a filter so that all functions will be recorded
2309again:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002310
GeunSik Lim156f5a72009-06-02 15:01:37 +09002311 # echo > set_ftrace_filter
2312 # cat set_ftrace_filter
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002313 #
2314
2315Again, now we want to append.
2316
GeunSik Lim156f5a72009-06-02 15:01:37 +09002317 # echo sys_nanosleep > set_ftrace_filter
2318 # cat set_ftrace_filter
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002319sys_nanosleep
GeunSik Lim156f5a72009-06-02 15:01:37 +09002320 # echo 'hrtimer_*' >> set_ftrace_filter
2321 # cat set_ftrace_filter
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002322hrtimer_run_queues
2323hrtimer_run_pending
2324hrtimer_init
2325hrtimer_cancel
2326hrtimer_try_to_cancel
2327hrtimer_forward
2328hrtimer_start
2329hrtimer_reprogram
2330hrtimer_force_reprogram
2331hrtimer_get_next_event
2332hrtimer_interrupt
2333sys_nanosleep
2334hrtimer_nanosleep
2335hrtimer_wakeup
2336hrtimer_get_remaining
2337hrtimer_get_res
2338hrtimer_init_sleeper
2339
2340
Ingo Molnar57526742009-02-19 12:54:10 +01002341The set_ftrace_notrace prevents those functions from being
2342traced.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002343
GeunSik Lim156f5a72009-06-02 15:01:37 +09002344 # echo '*preempt*' '*lock*' > set_ftrace_notrace
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002345
2346Produces:
2347
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002348# tracer: function
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002349#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002350# entries-in-buffer/entries-written: 39608/39608 #P:4
2351#
2352# _-----=> irqs-off
2353# / _----=> need-resched
2354# | / _---=> hardirq/softirq
2355# || / _--=> preempt-depth
2356# ||| / delay
2357# TASK-PID CPU# |||| TIMESTAMP FUNCTION
2358# | | | |||| | |
2359 bash-1994 [000] .... 4342.324896: file_ra_state_init <-do_dentry_open
2360 bash-1994 [000] .... 4342.324897: open_check_o_direct <-do_last
2361 bash-1994 [000] .... 4342.324897: ima_file_check <-do_last
2362 bash-1994 [000] .... 4342.324898: process_measurement <-ima_file_check
2363 bash-1994 [000] .... 4342.324898: ima_get_action <-process_measurement
2364 bash-1994 [000] .... 4342.324898: ima_match_policy <-ima_get_action
2365 bash-1994 [000] .... 4342.324899: do_truncate <-do_last
2366 bash-1994 [000] .... 4342.324899: should_remove_suid <-do_truncate
2367 bash-1994 [000] .... 4342.324899: notify_change <-do_truncate
2368 bash-1994 [000] .... 4342.324900: current_fs_time <-notify_change
2369 bash-1994 [000] .... 4342.324900: current_kernel_time <-current_fs_time
2370 bash-1994 [000] .... 4342.324900: timespec_trunc <-current_fs_time
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002371
2372We can see that there's no more lock or preempt tracing.
2373
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002374
Ingo Molnar57526742009-02-19 12:54:10 +01002375Dynamic ftrace with the function graph tracer
2376---------------------------------------------
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002377
Ingo Molnar57526742009-02-19 12:54:10 +01002378Although what has been explained above concerns both the
2379function tracer and the function-graph-tracer, there are some
2380special features only available in the function-graph tracer.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002381
Ingo Molnar57526742009-02-19 12:54:10 +01002382If you want to trace only one function and all of its children,
2383you just have to echo its name into set_graph_function:
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002384
Ingo Molnar57526742009-02-19 12:54:10 +01002385 echo __do_fault > set_graph_function
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002386
Ingo Molnar57526742009-02-19 12:54:10 +01002387will produce the following "expanded" trace of the __do_fault()
2388function:
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002389
2390 0) | __do_fault() {
2391 0) | filemap_fault() {
2392 0) | find_lock_page() {
2393 0) 0.804 us | find_get_page();
2394 0) | __might_sleep() {
2395 0) 1.329 us | }
2396 0) 3.904 us | }
2397 0) 4.979 us | }
2398 0) 0.653 us | _spin_lock();
2399 0) 0.578 us | page_add_file_rmap();
2400 0) 0.525 us | native_set_pte_at();
2401 0) 0.585 us | _spin_unlock();
2402 0) | unlock_page() {
2403 0) 0.541 us | page_waitqueue();
2404 0) 0.639 us | __wake_up_bit();
2405 0) 2.786 us | }
2406 0) + 14.237 us | }
2407 0) | __do_fault() {
2408 0) | filemap_fault() {
2409 0) | find_lock_page() {
2410 0) 0.698 us | find_get_page();
2411 0) | __might_sleep() {
2412 0) 1.412 us | }
2413 0) 3.950 us | }
2414 0) 5.098 us | }
2415 0) 0.631 us | _spin_lock();
2416 0) 0.571 us | page_add_file_rmap();
2417 0) 0.526 us | native_set_pte_at();
2418 0) 0.586 us | _spin_unlock();
2419 0) | unlock_page() {
2420 0) 0.533 us | page_waitqueue();
2421 0) 0.638 us | __wake_up_bit();
2422 0) 2.793 us | }
2423 0) + 14.012 us | }
2424
Ingo Molnar57526742009-02-19 12:54:10 +01002425You can also expand several functions at once:
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002426
Ingo Molnar57526742009-02-19 12:54:10 +01002427 echo sys_open > set_graph_function
2428 echo sys_close >> set_graph_function
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002429
Ingo Molnar57526742009-02-19 12:54:10 +01002430Now if you want to go back to trace all functions you can clear
2431this special filter via:
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002432
Ingo Molnar57526742009-02-19 12:54:10 +01002433 echo > set_graph_function
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002434
2435
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002436ftrace_enabled
2437--------------
2438
2439Note, the proc sysctl ftrace_enable is a big on/off switch for the
2440function tracer. By default it is enabled (when function tracing is
2441enabled in the kernel). If it is disabled, all function tracing is
2442disabled. This includes not only the function tracers for ftrace, but
2443also for any other uses (perf, kprobes, stack tracing, profiling, etc).
2444
2445Please disable this with care.
2446
2447This can be disable (and enabled) with:
2448
2449 sysctl kernel.ftrace_enabled=0
2450 sysctl kernel.ftrace_enabled=1
2451
2452 or
2453
2454 echo 0 > /proc/sys/kernel/ftrace_enabled
2455 echo 1 > /proc/sys/kernel/ftrace_enabled
2456
2457
Chase Douglas07271aa2010-04-23 14:02:39 -04002458Filter commands
2459---------------
2460
2461A few commands are supported by the set_ftrace_filter interface.
2462Trace commands have the following format:
2463
2464<function>:<command>:<parameter>
2465
2466The following commands are supported:
2467
2468- mod
2469 This command enables function filtering per module. The
2470 parameter defines the module. For example, if only the write*
2471 functions in the ext3 module are desired, run:
2472
2473 echo 'write*:mod:ext3' > set_ftrace_filter
2474
2475 This command interacts with the filter in the same way as
2476 filtering based on function names. Thus, adding more functions
2477 in a different module is accomplished by appending (>>) to the
2478 filter file. Remove specific module functions by prepending
2479 '!':
2480
2481 echo '!writeback*:mod:ext3' >> set_ftrace_filter
2482
Dmitry Safonovb86d9372015-09-29 19:46:16 +03002483 Mod command supports module globbing. Disable tracing for all
2484 functions except a specific module:
2485
2486 echo '!*:mod:!ext3' >> set_ftrace_filter
2487
2488 Disable tracing for all modules, but still trace kernel:
2489
2490 echo '!*:mod:*' >> set_ftrace_filter
2491
2492 Enable filter only for kernel:
2493
2494 echo '*write*:mod:!*' >> set_ftrace_filter
2495
2496 Enable filter for module globbing:
2497
2498 echo '*write*:mod:*snd*' >> set_ftrace_filter
2499
Chase Douglas07271aa2010-04-23 14:02:39 -04002500- traceon/traceoff
2501 These commands turn tracing on and off when the specified
2502 functions are hit. The parameter determines how many times the
2503 tracing system is turned on and off. If unspecified, there is
2504 no limit. For example, to disable tracing when a schedule bug
2505 is hit the first 5 times, run:
2506
2507 echo '__schedule_bug:traceoff:5' > set_ftrace_filter
2508
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002509 To always disable tracing when __schedule_bug is hit:
2510
2511 echo '__schedule_bug:traceoff' > set_ftrace_filter
2512
Chase Douglas07271aa2010-04-23 14:02:39 -04002513 These commands are cumulative whether or not they are appended
2514 to set_ftrace_filter. To remove a command, prepend it by '!'
2515 and drop the parameter:
2516
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002517 echo '!__schedule_bug:traceoff:0' > set_ftrace_filter
2518
2519 The above removes the traceoff command for __schedule_bug
2520 that have a counter. To remove commands without counters:
2521
Chase Douglas07271aa2010-04-23 14:02:39 -04002522 echo '!__schedule_bug:traceoff' > set_ftrace_filter
2523
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002524- snapshot
2525 Will cause a snapshot to be triggered when the function is hit.
2526
2527 echo 'native_flush_tlb_others:snapshot' > set_ftrace_filter
2528
2529 To only snapshot once:
2530
2531 echo 'native_flush_tlb_others:snapshot:1' > set_ftrace_filter
2532
2533 To remove the above commands:
2534
2535 echo '!native_flush_tlb_others:snapshot' > set_ftrace_filter
2536 echo '!native_flush_tlb_others:snapshot:0' > set_ftrace_filter
2537
2538- enable_event/disable_event
2539 These commands can enable or disable a trace event. Note, because
2540 function tracing callbacks are very sensitive, when these commands
2541 are registered, the trace point is activated, but disabled in
2542 a "soft" mode. That is, the tracepoint will be called, but
2543 just will not be traced. The event tracepoint stays in this mode
2544 as long as there's a command that triggers it.
2545
2546 echo 'try_to_wake_up:enable_event:sched:sched_switch:2' > \
2547 set_ftrace_filter
2548
2549 The format is:
2550
2551 <function>:enable_event:<system>:<event>[:count]
2552 <function>:disable_event:<system>:<event>[:count]
2553
2554 To remove the events commands:
2555
2556
2557 echo '!try_to_wake_up:enable_event:sched:sched_switch:0' > \
2558 set_ftrace_filter
2559 echo '!schedule:disable_event:sched:sched_switch' > \
2560 set_ftrace_filter
Chase Douglas07271aa2010-04-23 14:02:39 -04002561
Steven Rostedt (Red Hat)ad71d882013-04-30 15:46:14 -04002562- dump
2563 When the function is hit, it will dump the contents of the ftrace
2564 ring buffer to the console. This is useful if you need to debug
2565 something, and want to dump the trace when a certain function
2566 is hit. Perhaps its a function that is called before a tripple
2567 fault happens and does not allow you to get a regular dump.
2568
Steven Rostedt (Red Hat)90e3c032013-04-30 19:00:46 -04002569- cpudump
2570 When the function is hit, it will dump the contents of the ftrace
2571 ring buffer for the current CPU to the console. Unlike the "dump"
2572 command, it only prints out the contents of the ring buffer for the
2573 CPU that executed the function that triggered the dump.
2574
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002575trace_pipe
2576----------
2577
Ingo Molnar57526742009-02-19 12:54:10 +01002578The trace_pipe outputs the same content as the trace file, but
2579the effect on the tracing is different. Every read from
2580trace_pipe is consumed. This means that subsequent reads will be
2581different. The trace is live.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002582
GeunSik Lim156f5a72009-06-02 15:01:37 +09002583 # echo function > current_tracer
2584 # cat trace_pipe > /tmp/trace.out &
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002585[1] 4153
Steven Rostedt6752ab42011-02-08 13:54:06 -05002586 # echo 1 > tracing_on
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002587 # usleep 1
Steven Rostedt6752ab42011-02-08 13:54:06 -05002588 # echo 0 > tracing_on
GeunSik Lim156f5a72009-06-02 15:01:37 +09002589 # cat trace
Steven Rostedt9b803c02008-11-03 15:15:08 -05002590# tracer: function
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002591#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002592# entries-in-buffer/entries-written: 0/0 #P:4
2593#
2594# _-----=> irqs-off
2595# / _----=> need-resched
2596# | / _---=> hardirq/softirq
2597# || / _--=> preempt-depth
2598# ||| / delay
2599# TASK-PID CPU# |||| TIMESTAMP FUNCTION
2600# | | | |||| | |
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002601
2602 #
2603 # cat /tmp/trace.out
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002604 bash-1994 [000] .... 5281.568961: mutex_unlock <-rb_simple_write
2605 bash-1994 [000] .... 5281.568963: __mutex_unlock_slowpath <-mutex_unlock
2606 bash-1994 [000] .... 5281.568963: __fsnotify_parent <-fsnotify_modify
2607 bash-1994 [000] .... 5281.568964: fsnotify <-fsnotify_modify
2608 bash-1994 [000] .... 5281.568964: __srcu_read_lock <-fsnotify
2609 bash-1994 [000] .... 5281.568964: add_preempt_count <-__srcu_read_lock
2610 bash-1994 [000] ...1 5281.568965: sub_preempt_count <-__srcu_read_lock
2611 bash-1994 [000] .... 5281.568965: __srcu_read_unlock <-fsnotify
2612 bash-1994 [000] .... 5281.568967: sys_dup2 <-system_call_fastpath
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002613
2614
Ingo Molnar57526742009-02-19 12:54:10 +01002615Note, reading the trace_pipe file will block until more input is
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002616added.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002617
2618trace entries
2619-------------
2620
Ingo Molnar57526742009-02-19 12:54:10 +01002621Having too much or not enough data can be troublesome in
2622diagnosing an issue in the kernel. The file buffer_size_kb is
2623used to modify the size of the internal trace buffers. The
2624number listed is the number of entries that can be recorded per
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002625CPU. To know the full size, multiply the number of possible CPUs
Ingo Molnar57526742009-02-19 12:54:10 +01002626with the number of entries.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002627
GeunSik Lim156f5a72009-06-02 15:01:37 +09002628 # cat buffer_size_kb
Steven Rostedt1696b2b2008-11-13 00:09:35 -050026291408 (units kilobytes)
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002630
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002631Or simply read buffer_total_size_kb
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002632
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002633 # cat buffer_total_size_kb
26345632
2635
2636To modify the buffer, simple echo in a number (in 1024 byte segments).
2637
GeunSik Lim156f5a72009-06-02 15:01:37 +09002638 # echo 10000 > buffer_size_kb
2639 # cat buffer_size_kb
Steven Rostedt1696b2b2008-11-13 00:09:35 -0500264010000 (units kilobytes)
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002641
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002642It will try to allocate as much as possible. If you allocate too
2643much, it can cause Out-Of-Memory to trigger.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002644
GeunSik Lim156f5a72009-06-02 15:01:37 +09002645 # echo 1000000000000 > buffer_size_kb
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002646-bash: echo: write error: Cannot allocate memory
GeunSik Lim156f5a72009-06-02 15:01:37 +09002647 # cat buffer_size_kb
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400264885
2649
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002650The per_cpu buffers can be changed individually as well:
2651
2652 # echo 10000 > per_cpu/cpu0/buffer_size_kb
2653 # echo 100 > per_cpu/cpu1/buffer_size_kb
2654
2655When the per_cpu buffers are not the same, the buffer_size_kb
2656at the top level will just show an X
2657
2658 # cat buffer_size_kb
2659X
2660
2661This is where the buffer_total_size_kb is useful:
2662
2663 # cat buffer_total_size_kb
266412916
2665
2666Writing to the top level buffer_size_kb will reset all the buffers
2667to be the same again.
2668
Hiraku Toyookac1043fc2012-12-26 11:53:09 +09002669Snapshot
2670--------
2671CONFIG_TRACER_SNAPSHOT makes a generic snapshot feature
2672available to all non latency tracers. (Latency tracers which
2673record max latency, such as "irqsoff" or "wakeup", can't use
2674this feature, since those are already using the snapshot
2675mechanism internally.)
2676
2677Snapshot preserves a current trace buffer at a particular point
2678in time without stopping tracing. Ftrace swaps the current
2679buffer with a spare buffer, and tracing continues in the new
2680current (=previous spare) buffer.
2681
2682The following debugfs files in "tracing" are related to this
2683feature:
2684
2685 snapshot:
2686
2687 This is used to take a snapshot and to read the output
2688 of the snapshot. Echo 1 into this file to allocate a
2689 spare buffer and to take a snapshot (swap), then read
2690 the snapshot from this file in the same format as
2691 "trace" (described above in the section "The File
2692 System"). Both reads snapshot and tracing are executable
2693 in parallel. When the spare buffer is allocated, echoing
2694 0 frees it, and echoing else (positive) values clear the
2695 snapshot contents.
2696 More details are shown in the table below.
2697
2698 status\input | 0 | 1 | else |
2699 --------------+------------+------------+------------+
Hiraku Toyooka1abccd72013-03-08 16:32:25 +09002700 not allocated |(do nothing)| alloc+swap |(do nothing)|
Hiraku Toyookac1043fc2012-12-26 11:53:09 +09002701 --------------+------------+------------+------------+
2702 allocated | free | swap | clear |
2703 --------------+------------+------------+------------+
2704
2705Here is an example of using the snapshot feature.
2706
2707 # echo 1 > events/sched/enable
2708 # echo 1 > snapshot
2709 # cat snapshot
2710# tracer: nop
2711#
2712# entries-in-buffer/entries-written: 71/71 #P:8
2713#
2714# _-----=> irqs-off
2715# / _----=> need-resched
2716# | / _---=> hardirq/softirq
2717# || / _--=> preempt-depth
2718# ||| / delay
2719# TASK-PID CPU# |||| TIMESTAMP FUNCTION
2720# | | | |||| | |
2721 <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
2722 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
2723[...]
2724 <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
2725
2726 # cat trace
2727# tracer: nop
2728#
2729# entries-in-buffer/entries-written: 77/77 #P:8
2730#
2731# _-----=> irqs-off
2732# / _----=> need-resched
2733# | / _---=> hardirq/softirq
2734# || / _--=> preempt-depth
2735# ||| / delay
2736# TASK-PID CPU# |||| TIMESTAMP FUNCTION
2737# | | | |||| | |
2738 <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
2739 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
2740[...]
2741
2742
2743If you try to use this snapshot feature when current tracer is
2744one of the latency tracers, you will get the following results.
2745
2746 # echo wakeup > current_tracer
2747 # echo 1 > snapshot
2748bash: echo: write error: Device or resource busy
2749 # cat snapshot
2750cat: snapshot: Device or resource busy
2751
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002752
2753Instances
2754---------
2755In the debugfs tracing directory is a directory called "instances".
2756This directory can have new directories created inside of it using
2757mkdir, and removing directories with rmdir. The directory created
2758with mkdir in this directory will already contain files and other
2759directories after it is created.
2760
2761 # mkdir instances/foo
2762 # ls instances/foo
2763buffer_size_kb buffer_total_size_kb events free_buffer per_cpu
2764set_event snapshot trace trace_clock trace_marker trace_options
2765trace_pipe tracing_on
2766
2767As you can see, the new directory looks similar to the tracing directory
2768itself. In fact, it is very similar, except that the buffer and
2769events are agnostic from the main director, or from any other
2770instances that are created.
2771
2772The files in the new directory work just like the files with the
2773same name in the tracing directory except the buffer that is used
2774is a separate and new buffer. The files affect that buffer but do not
2775affect the main buffer with the exception of trace_options. Currently,
2776the trace_options affect all instances and the top level buffer
2777the same, but this may change in future releases. That is, options
2778may become specific to the instance they reside in.
2779
2780Notice that none of the function tracer files are there, nor is
2781current_tracer and available_tracers. This is because the buffers
2782can currently only have events enabled for them.
2783
2784 # mkdir instances/foo
2785 # mkdir instances/bar
2786 # mkdir instances/zoot
2787 # echo 100000 > buffer_size_kb
2788 # echo 1000 > instances/foo/buffer_size_kb
2789 # echo 5000 > instances/bar/per_cpu/cpu1/buffer_size_kb
2790 # echo function > current_trace
2791 # echo 1 > instances/foo/events/sched/sched_wakeup/enable
2792 # echo 1 > instances/foo/events/sched/sched_wakeup_new/enable
2793 # echo 1 > instances/foo/events/sched/sched_switch/enable
2794 # echo 1 > instances/bar/events/irq/enable
2795 # echo 1 > instances/zoot/events/syscalls/enable
2796 # cat trace_pipe
2797CPU:2 [LOST 11745 EVENTS]
2798 bash-2044 [002] .... 10594.481032: _raw_spin_lock_irqsave <-get_page_from_freelist
2799 bash-2044 [002] d... 10594.481032: add_preempt_count <-_raw_spin_lock_irqsave
2800 bash-2044 [002] d..1 10594.481032: __rmqueue <-get_page_from_freelist
2801 bash-2044 [002] d..1 10594.481033: _raw_spin_unlock <-get_page_from_freelist
2802 bash-2044 [002] d..1 10594.481033: sub_preempt_count <-_raw_spin_unlock
2803 bash-2044 [002] d... 10594.481033: get_pageblock_flags_group <-get_pageblock_migratetype
2804 bash-2044 [002] d... 10594.481034: __mod_zone_page_state <-get_page_from_freelist
2805 bash-2044 [002] d... 10594.481034: zone_statistics <-get_page_from_freelist
2806 bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics
2807 bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics
2808 bash-2044 [002] .... 10594.481035: arch_dup_task_struct <-copy_process
2809[...]
2810
2811 # cat instances/foo/trace_pipe
2812 bash-1998 [000] d..4 136.676759: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000
2813 bash-1998 [000] dN.4 136.676760: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000
2814 <idle>-0 [003] d.h3 136.676906: sched_wakeup: comm=rcu_preempt pid=9 prio=120 success=1 target_cpu=003
2815 <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
2816 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
2817 bash-1998 [000] d..4 136.677014: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000
2818 bash-1998 [000] dN.4 136.677016: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000
2819 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
2820 kworker/0:1-59 [000] d..4 136.677022: sched_wakeup: comm=sshd pid=1995 prio=120 success=1 target_cpu=001
2821 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
2822[...]
2823
2824 # cat instances/bar/trace_pipe
2825 migration/1-14 [001] d.h3 138.732674: softirq_raise: vec=3 [action=NET_RX]
2826 <idle>-0 [001] dNh3 138.732725: softirq_raise: vec=3 [action=NET_RX]
2827 bash-1998 [000] d.h1 138.733101: softirq_raise: vec=1 [action=TIMER]
2828 bash-1998 [000] d.h1 138.733102: softirq_raise: vec=9 [action=RCU]
2829 bash-1998 [000] ..s2 138.733105: softirq_entry: vec=1 [action=TIMER]
2830 bash-1998 [000] ..s2 138.733106: softirq_exit: vec=1 [action=TIMER]
2831 bash-1998 [000] ..s2 138.733106: softirq_entry: vec=9 [action=RCU]
2832 bash-1998 [000] ..s2 138.733109: softirq_exit: vec=9 [action=RCU]
2833 sshd-1995 [001] d.h1 138.733278: irq_handler_entry: irq=21 name=uhci_hcd:usb4
2834 sshd-1995 [001] d.h1 138.733280: irq_handler_exit: irq=21 ret=unhandled
2835 sshd-1995 [001] d.h1 138.733281: irq_handler_entry: irq=21 name=eth0
2836 sshd-1995 [001] d.h1 138.733283: irq_handler_exit: irq=21 ret=handled
2837[...]
2838
2839 # cat instances/zoot/trace
2840# tracer: nop
2841#
2842# entries-in-buffer/entries-written: 18996/18996 #P:4
2843#
2844# _-----=> irqs-off
2845# / _----=> need-resched
2846# | / _---=> hardirq/softirq
2847# || / _--=> preempt-depth
2848# ||| / delay
2849# TASK-PID CPU# |||| TIMESTAMP FUNCTION
2850# | | | |||| | |
2851 bash-1998 [000] d... 140.733501: sys_write -> 0x2
2852 bash-1998 [000] d... 140.733504: sys_dup2(oldfd: a, newfd: 1)
2853 bash-1998 [000] d... 140.733506: sys_dup2 -> 0x1
2854 bash-1998 [000] d... 140.733508: sys_fcntl(fd: a, cmd: 1, arg: 0)
2855 bash-1998 [000] d... 140.733509: sys_fcntl -> 0x1
2856 bash-1998 [000] d... 140.733510: sys_close(fd: a)
2857 bash-1998 [000] d... 140.733510: sys_close -> 0x0
2858 bash-1998 [000] d... 140.733514: sys_rt_sigprocmask(how: 0, nset: 0, oset: 6e2768, sigsetsize: 8)
2859 bash-1998 [000] d... 140.733515: sys_rt_sigprocmask -> 0x0
2860 bash-1998 [000] d... 140.733516: sys_rt_sigaction(sig: 2, act: 7fff718846f0, oact: 7fff71884650, sigsetsize: 8)
2861 bash-1998 [000] d... 140.733516: sys_rt_sigaction -> 0x0
2862
2863You can see that the trace of the top most trace buffer shows only
2864the function tracing. The foo instance displays wakeups and task
2865switches.
2866
2867To remove the instances, simply delete their directories:
2868
2869 # rmdir instances/foo
2870 # rmdir instances/bar
2871 # rmdir instances/zoot
2872
2873Note, if a process has a trace file open in one of the instance
2874directories, the rmdir will fail with EBUSY.
2875
2876
2877Stack trace
Ingo Molnar57526742009-02-19 12:54:10 +01002878-----------
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002879Since the kernel has a fixed sized stack, it is important not to
2880waste it in functions. A kernel developer must be conscience of
2881what they allocate on the stack. If they add too much, the system
2882can be in danger of a stack overflow, and corruption will occur,
2883usually leading to a system panic.
2884
2885There are some tools that check this, usually with interrupts
2886periodically checking usage. But if you can perform a check
2887at every function call that will become very useful. As ftrace provides
2888a function tracer, it makes it convenient to check the stack size
2889at every function call. This is enabled via the stack tracer.
2890
2891CONFIG_STACK_TRACER enables the ftrace stack tracing functionality.
2892To enable it, write a '1' into /proc/sys/kernel/stack_tracer_enabled.
2893
2894 # echo 1 > /proc/sys/kernel/stack_tracer_enabled
2895
2896You can also enable it from the kernel command line to trace
2897the stack size of the kernel during boot up, by adding "stacktrace"
2898to the kernel command line parameter.
2899
2900After running it for a few minutes, the output looks like:
2901
2902 # cat stack_max_size
29032928
2904
2905 # cat stack_trace
2906 Depth Size Location (18 entries)
2907 ----- ---- --------
2908 0) 2928 224 update_sd_lb_stats+0xbc/0x4ac
2909 1) 2704 160 find_busiest_group+0x31/0x1f1
2910 2) 2544 256 load_balance+0xd9/0x662
2911 3) 2288 80 idle_balance+0xbb/0x130
2912 4) 2208 128 __schedule+0x26e/0x5b9
2913 5) 2080 16 schedule+0x64/0x66
2914 6) 2064 128 schedule_timeout+0x34/0xe0
2915 7) 1936 112 wait_for_common+0x97/0xf1
2916 8) 1824 16 wait_for_completion+0x1d/0x1f
2917 9) 1808 128 flush_work+0xfe/0x119
2918 10) 1680 16 tty_flush_to_ldisc+0x1e/0x20
2919 11) 1664 48 input_available_p+0x1d/0x5c
2920 12) 1616 48 n_tty_poll+0x6d/0x134
2921 13) 1568 64 tty_poll+0x64/0x7f
2922 14) 1504 880 do_select+0x31e/0x511
2923 15) 624 400 core_sys_select+0x177/0x216
2924 16) 224 96 sys_select+0x91/0xb9
2925 17) 128 128 system_call_fastpath+0x16/0x1b
2926
2927Note, if -mfentry is being used by gcc, functions get traced before
2928they set up the stack frame. This means that leaf level functions
2929are not tested by the stack tracer when -mfentry is used.
2930
2931Currently, -mfentry is used by gcc 4.6.0 and above on x86 only.
2932
2933---------
Ingo Molnar57526742009-02-19 12:54:10 +01002934
2935More details can be found in the source code, in the
GeunSik Limbaf20b32009-06-01 10:49:41 +02002936kernel/trace/*.c files.