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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
111 adding more data,they will display the same
112 information every time they are 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
207 set_graph_function:
208
209 Set a "trigger" function where tracing should start
210 with the function graph tracer (See the section
211 "dynamic ftrace" for more details).
212
213 available_filter_functions:
214
215 This lists the functions that ftrace
216 has processed and can trace. These are the function
217 names that you can pass to "set_ftrace_filter" or
218 "set_ftrace_notrace". (See the section "dynamic ftrace"
219 below for more details.)
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400220
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400221 enabled_functions:
222
223 This file is more for debugging ftrace, but can also be useful
224 in seeing if any function has a callback attached to it.
225 Not only does the trace infrastructure use ftrace function
226 trace utility, but other subsystems might too. This file
227 displays all functions that have a callback attached to them
228 as well as the number of callbacks that have been attached.
229 Note, a callback may also call multiple functions which will
230 not be listed in this count.
231
232 If the callback registered to be traced by a function with
233 the "save regs" attribute (thus even more overhead), a 'R'
234 will be displayed on the same line as the function that
235 is returning registers.
236
237 function_profile_enabled:
238
239 When set it will enable all functions with either the function
240 tracer, or if enabled, the function graph tracer. It will
241 keep a histogram of the number of functions that were called
242 and if run with the function graph tracer, it will also keep
243 track of the time spent in those functions. The histogram
244 content can be displayed in the files:
245
246 trace_stats/function<cpu> ( function0, function1, etc).
247
248 trace_stats:
249
250 A directory that holds different tracing stats.
251
252 kprobe_events:
253
254 Enable dynamic trace points. See kprobetrace.txt.
255
256 kprobe_profile:
257
258 Dynamic trace points stats. See kprobetrace.txt.
259
260 max_graph_depth:
261
262 Used with the function graph tracer. This is the max depth
263 it will trace into a function. Setting this to a value of
264 one will show only the first kernel function that is called
265 from user space.
266
267 printk_formats:
268
269 This is for tools that read the raw format files. If an event in
270 the ring buffer references a string (currently only trace_printk()
271 does this), only a pointer to the string is recorded into the buffer
272 and not the string itself. This prevents tools from knowing what
273 that string was. This file displays the string and address for
274 the string allowing tools to map the pointers to what the
275 strings were.
276
277 saved_cmdlines:
278
279 Only the pid of the task is recorded in a trace event unless
280 the event specifically saves the task comm as well. Ftrace
281 makes a cache of pid mappings to comms to try to display
282 comms for events. If a pid for a comm is not listed, then
283 "<...>" is displayed in the output.
284
285 snapshot:
286
287 This displays the "snapshot" buffer and also lets the user
288 take a snapshot of the current running trace.
289 See the "Snapshot" section below for more details.
290
291 stack_max_size:
292
293 When the stack tracer is activated, this will display the
294 maximum stack size it has encountered.
295 See the "Stack Trace" section below.
296
297 stack_trace:
298
299 This displays the stack back trace of the largest stack
300 that was encountered when the stack tracer is activated.
301 See the "Stack Trace" section below.
302
303 stack_trace_filter:
304
305 This is similar to "set_ftrace_filter" but it limits what
306 functions the stack tracer will check.
307
308 trace_clock:
309
310 Whenever an event is recorded into the ring buffer, a
311 "timestamp" is added. This stamp comes from a specified
312 clock. By default, ftrace uses the "local" clock. This
313 clock is very fast and strictly per cpu, but on some
314 systems it may not be monotonic with respect to other
315 CPUs. In other words, the local clocks may not be in sync
316 with local clocks on other CPUs.
317
318 Usual clocks for tracing:
319
320 # cat trace_clock
321 [local] global counter x86-tsc
322
323 local: Default clock, but may not be in sync across CPUs
324
325 global: This clock is in sync with all CPUs but may
326 be a bit slower than the local clock.
327
328 counter: This is not a clock at all, but literally an atomic
329 counter. It counts up one by one, but is in sync
330 with all CPUs. This is useful when you need to
331 know exactly the order events occurred with respect to
332 each other on different CPUs.
333
334 uptime: This uses the jiffies counter and the time stamp
335 is relative to the time since boot up.
336
337 perf: This makes ftrace use the same clock that perf uses.
338 Eventually perf will be able to read ftrace buffers
339 and this will help out in interleaving the data.
340
341 x86-tsc: Architectures may define their own clocks. For
342 example, x86 uses its own TSC cycle clock here.
343
344 To set a clock, simply echo the clock name into this file.
345
346 echo global > trace_clock
347
348 trace_marker:
349
350 This is a very useful file for synchronizing user space
351 with events happening in the kernel. Writing strings into
352 this file will be written into the ftrace buffer.
353
354 It is useful in applications to open this file at the start
355 of the application and just reference the file descriptor
356 for the file.
357
358 void trace_write(const char *fmt, ...)
359 {
360 va_list ap;
361 char buf[256];
362 int n;
363
364 if (trace_fd < 0)
365 return;
366
367 va_start(ap, fmt);
368 n = vsnprintf(buf, 256, fmt, ap);
369 va_end(ap);
370
371 write(trace_fd, buf, n);
372 }
373
374 start:
375
376 trace_fd = open("trace_marker", WR_ONLY);
377
378 uprobe_events:
379
380 Add dynamic tracepoints in programs.
381 See uprobetracer.txt
382
383 uprobe_profile:
384
385 Uprobe statistics. See uprobetrace.txt
386
387 instances:
388
389 This is a way to make multiple trace buffers where different
390 events can be recorded in different buffers.
391 See "Instances" section below.
392
393 events:
394
395 This is the trace event directory. It holds event tracepoints
396 (also known as static tracepoints) that have been compiled
397 into the kernel. It shows what event tracepoints exist
398 and how they are grouped by system. There are "enable"
399 files at various levels that can enable the tracepoints
400 when a "1" is written to them.
401
402 See events.txt for more information.
403
404 per_cpu:
405
406 This is a directory that contains the trace per_cpu information.
407
408 per_cpu/cpu0/buffer_size_kb:
409
410 The ftrace buffer is defined per_cpu. That is, there's a separate
411 buffer for each CPU to allow writes to be done atomically,
412 and free from cache bouncing. These buffers may have different
413 size buffers. This file is similar to the buffer_size_kb
414 file, but it only displays or sets the buffer size for the
415 specific CPU. (here cpu0).
416
417 per_cpu/cpu0/trace:
418
419 This is similar to the "trace" file, but it will only display
420 the data specific for the CPU. If written to, it only clears
421 the specific CPU buffer.
422
423 per_cpu/cpu0/trace_pipe
424
425 This is similar to the "trace_pipe" file, and is a consuming
426 read, but it will only display (and consume) the data specific
427 for the CPU.
428
429 per_cpu/cpu0/trace_pipe_raw
430
431 For tools that can parse the ftrace ring buffer binary format,
432 the trace_pipe_raw file can be used to extract the data
433 from the ring buffer directly. With the use of the splice()
434 system call, the buffer data can be quickly transferred to
435 a file or to the network where a server is collecting the
436 data.
437
438 Like trace_pipe, this is a consuming reader, where multiple
439 reads will always produce different data.
440
441 per_cpu/cpu0/snapshot:
442
443 This is similar to the main "snapshot" file, but will only
444 snapshot the current CPU (if supported). It only displays
445 the content of the snapshot for a given CPU, and if
446 written to, only clears this CPU buffer.
447
448 per_cpu/cpu0/snapshot_raw:
449
450 Similar to the trace_pipe_raw, but will read the binary format
451 from the snapshot buffer for the given CPU.
452
453 per_cpu/cpu0/stats:
454
455 This displays certain stats about the ring buffer:
456
457 entries: The number of events that are still in the buffer.
458
459 overrun: The number of lost events due to overwriting when
460 the buffer was full.
461
462 commit overrun: Should always be zero.
463 This gets set if so many events happened within a nested
464 event (ring buffer is re-entrant), that it fills the
465 buffer and starts dropping events.
466
467 bytes: Bytes actually read (not overwritten).
468
469 oldest event ts: The oldest timestamp in the buffer
470
471 now ts: The current timestamp
472
473 dropped events: Events lost due to overwrite option being off.
474
475 read events: The number of events read.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400476
477The Tracers
478-----------
479
Steven Rostedtf2d9c742008-07-15 10:57:33 -0400480Here is the list of current tracers that may be configured.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400481
Ingo Molnar57526742009-02-19 12:54:10 +0100482 "function"
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400483
Ingo Molnar57526742009-02-19 12:54:10 +0100484 Function call tracer to trace all kernel functions.
Frederic Weisbecker985ec202009-02-18 06:35:34 +0100485
Mike Frysingerbc5c6c02009-06-10 04:48:41 -0400486 "function_graph"
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400487
Ingo Molnar57526742009-02-19 12:54:10 +0100488 Similar to the function tracer except that the
489 function tracer probes the functions on their entry
490 whereas the function graph tracer traces on both entry
491 and exit of the functions. It then provides the ability
492 to draw a graph of function calls similar to C code
493 source.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400494
Ingo Molnar57526742009-02-19 12:54:10 +0100495 "irqsoff"
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400496
Ingo Molnar57526742009-02-19 12:54:10 +0100497 Traces the areas that disable interrupts and saves
498 the trace with the longest max latency.
499 See tracing_max_latency. When a new max is recorded,
500 it replaces the old trace. It is best to view this
Albin Tonnerre4a88d442009-08-31 22:40:08 +0200501 trace with the latency-format option enabled.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400502
Ingo Molnar57526742009-02-19 12:54:10 +0100503 "preemptoff"
504
505 Similar to irqsoff but traces and records the amount of
506 time for which preemption is disabled.
507
508 "preemptirqsoff"
509
510 Similar to irqsoff and preemptoff, but traces and
511 records the largest time for which irqs and/or preemption
512 is disabled.
513
514 "wakeup"
515
516 Traces and records the max latency that it takes for
517 the highest priority task to get scheduled after
518 it has been woken up.
Geunsik Limcdfb0d32012-02-08 19:05:37 +0900519 Traces all tasks as an average developer would expect.
520
521 "wakeup_rt"
522
523 Traces and records the max latency that it takes for just
524 RT tasks (as the current "wakeup" does). This is useful
525 for those interested in wake up timings of RT tasks.
Ingo Molnar57526742009-02-19 12:54:10 +0100526
Ingo Molnar57526742009-02-19 12:54:10 +0100527 "nop"
528
529 This is the "trace nothing" tracer. To remove all
530 tracers from tracing simply echo "nop" into
531 current_tracer.
Markus Metzgere2ea5392009-01-19 10:35:58 +0100532
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400533
534Examples of using the tracer
535----------------------------
536
Ingo Molnar57526742009-02-19 12:54:10 +0100537Here are typical examples of using the tracers when controlling
538them only with the debugfs interface (without using any
539user-land utilities).
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400540
541Output format:
542--------------
543
Steven Rostedtf2d9c742008-07-15 10:57:33 -0400544Here is an example of the output format of the file "trace"
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400545
546 --------
Steven Rostedt9b803c02008-11-03 15:15:08 -0500547# tracer: function
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400548#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400549# entries-in-buffer/entries-written: 140080/250280 #P:4
550#
551# _-----=> irqs-off
552# / _----=> need-resched
553# | / _---=> hardirq/softirq
554# || / _--=> preempt-depth
555# ||| / delay
556# TASK-PID CPU# |||| TIMESTAMP FUNCTION
557# | | | |||| | |
558 bash-1977 [000] .... 17284.993652: sys_close <-system_call_fastpath
559 bash-1977 [000] .... 17284.993653: __close_fd <-sys_close
560 bash-1977 [000] .... 17284.993653: _raw_spin_lock <-__close_fd
561 sshd-1974 [003] .... 17284.993653: __srcu_read_unlock <-fsnotify
562 bash-1977 [000] .... 17284.993654: add_preempt_count <-_raw_spin_lock
563 bash-1977 [000] ...1 17284.993655: _raw_spin_unlock <-__close_fd
564 bash-1977 [000] ...1 17284.993656: sub_preempt_count <-_raw_spin_unlock
565 bash-1977 [000] .... 17284.993657: filp_close <-__close_fd
566 bash-1977 [000] .... 17284.993657: dnotify_flush <-filp_close
567 sshd-1974 [003] .... 17284.993658: sys_select <-system_call_fastpath
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400568 --------
569
Ingo Molnar57526742009-02-19 12:54:10 +0100570A header is printed with the tracer name that is represented by
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400571the trace. In this case the tracer is "function". Then it shows the
572number of events in the buffer as well as the total number of entries
573that were written. The difference is the number of entries that were
574lost due to the buffer filling up (250280 - 140080 = 110200 events
575lost).
576
577The header explains the content of the events. Task name "bash", the task
578PID "1977", the CPU that it was running on "000", the latency format
579(explained below), the timestamp in <secs>.<usecs> format, the
580function name that was traced "sys_close" and the parent function that
581called this function "system_call_fastpath". The timestamp is the time
582at which the function was entered.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400583
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400584Latency trace format
585--------------------
586
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400587When the latency-format option is enabled or when one of the latency
588tracers is set, the trace file gives somewhat more information to see
589why a latency happened. Here is a typical trace.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400590
591# tracer: irqsoff
592#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400593# irqsoff latency trace v1.1.5 on 3.8.0-test+
594# --------------------------------------------------------------------
595# latency: 259 us, #4/4, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
596# -----------------
597# | task: ps-6143 (uid:0 nice:0 policy:0 rt_prio:0)
598# -----------------
599# => started at: __lock_task_sighand
600# => ended at: _raw_spin_unlock_irqrestore
601#
602#
603# _------=> CPU#
604# / _-----=> irqs-off
605# | / _----=> need-resched
606# || / _---=> hardirq/softirq
607# ||| / _--=> preempt-depth
608# |||| / delay
609# cmd pid ||||| time | caller
610# \ / ||||| \ | /
611 ps-6143 2d... 0us!: trace_hardirqs_off <-__lock_task_sighand
612 ps-6143 2d..1 259us+: trace_hardirqs_on <-_raw_spin_unlock_irqrestore
613 ps-6143 2d..1 263us+: time_hardirqs_on <-_raw_spin_unlock_irqrestore
614 ps-6143 2d..1 306us : <stack trace>
615 => trace_hardirqs_on_caller
616 => trace_hardirqs_on
617 => _raw_spin_unlock_irqrestore
618 => do_task_stat
619 => proc_tgid_stat
620 => proc_single_show
621 => seq_read
622 => vfs_read
623 => sys_read
624 => system_call_fastpath
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400625
626
Ingo Molnar57526742009-02-19 12:54:10 +0100627This shows that the current tracer is "irqsoff" tracing the time
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400628for which interrupts were disabled. It gives the trace version (which
629never changes) and the version of the kernel upon which this was executed on
630(3.10). Then it displays the max latency in microseconds (259 us). The number
631of trace entries displayed and the total number (both are four: #4/4).
632VP, KP, SP, and HP are always zero and are reserved for later use.
633#P is the number of online CPUs (#P:4).
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400634
Ingo Molnar57526742009-02-19 12:54:10 +0100635The task is the process that was running when the latency
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400636occurred. (ps pid: 6143).
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400637
Ingo Molnar57526742009-02-19 12:54:10 +0100638The start and stop (the functions in which the interrupts were
639disabled and enabled respectively) that caused the latencies:
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400640
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400641 __lock_task_sighand is where the interrupts were disabled.
642 _raw_spin_unlock_irqrestore is where they were enabled again.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400643
644The next lines after the header are the trace itself. The header
645explains which is which.
646
647 cmd: The name of the process in the trace.
648
649 pid: The PID of that process.
650
Steven Rostedtf2d9c742008-07-15 10:57:33 -0400651 CPU#: The CPU which the process was running on.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400652
653 irqs-off: 'd' interrupts are disabled. '.' otherwise.
Steven Rostedt92444892008-10-24 09:42:59 -0400654 Note: If the architecture does not support a way to
655 read the irq flags variable, an 'X' will always
656 be printed here.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400657
Peter Zijlstrae5137b52013-10-04 17:28:26 +0200658 need-resched:
659 'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set,
660 'n' only TIF_NEED_RESCHED is set,
661 'p' only PREEMPT_NEED_RESCHED is set,
662 '.' otherwise.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400663
664 hardirq/softirq:
Steven Rostedtf2d9c742008-07-15 10:57:33 -0400665 'H' - hard irq occurred inside a softirq.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400666 'h' - hard irq is running
667 's' - soft irq is running
668 '.' - normal context.
669
670 preempt-depth: The level of preempt_disabled
671
672The above is mostly meaningful for kernel developers.
673
Albin Tonnerre4a88d442009-08-31 22:40:08 +0200674 time: When the latency-format option is enabled, the trace file
675 output includes a timestamp relative to the start of the
676 trace. This differs from the output when latency-format
677 is disabled, which includes an absolute timestamp.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400678
679 delay: This is just to help catch your eye a bit better. And
Ingo Molnar57526742009-02-19 12:54:10 +0100680 needs to be fixed to be only relative to the same CPU.
681 The marks are determined by the difference between this
682 current trace and the next trace.
683 '!' - greater than preempt_mark_thresh (default 100)
684 '+' - greater than 1 microsecond
685 ' ' - less than or equal to 1 microsecond.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400686
687 The rest is the same as the 'trace' file.
688
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400689 Note, the latency tracers will usually end with a back trace
690 to easily find where the latency occurred.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400691
Steven Rostedtee6bce52008-11-12 17:52:37 -0500692trace_options
693-------------
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400694
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400695The trace_options file (or the options directory) is used to control
696what gets printed in the trace output, or manipulate the tracers.
697To see what is available, simply cat the file:
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400698
GeunSik Lim156f5a72009-06-02 15:01:37 +0900699 cat trace_options
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400700print-parent
701nosym-offset
702nosym-addr
703noverbose
704noraw
705nohex
706nobin
707noblock
708nostacktrace
709trace_printk
710noftrace_preempt
711nobranch
712annotate
713nouserstacktrace
714nosym-userobj
715noprintk-msg-only
716context-info
717latency-format
718sleep-time
719graph-time
720record-cmd
721overwrite
722nodisable_on_free
723irq-info
724markers
725function-trace
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400726
Ingo Molnar57526742009-02-19 12:54:10 +0100727To disable one of the options, echo in the option prepended with
728"no".
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400729
GeunSik Lim156f5a72009-06-02 15:01:37 +0900730 echo noprint-parent > trace_options
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400731
732To enable an option, leave off the "no".
733
GeunSik Lim156f5a72009-06-02 15:01:37 +0900734 echo sym-offset > trace_options
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400735
736Here are the available options:
737
Ingo Molnar57526742009-02-19 12:54:10 +0100738 print-parent - On function traces, display the calling (parent)
739 function as well as the function being traced.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400740
741 print-parent:
Jingoo Han0ab943b2013-07-31 14:59:16 -0700742 bash-4000 [01] 1477.606694: simple_strtoul <-kstrtoul
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400743
744 noprint-parent:
745 bash-4000 [01] 1477.606694: simple_strtoul
746
747
Ingo Molnar57526742009-02-19 12:54:10 +0100748 sym-offset - Display not only the function name, but also the
749 offset in the function. For example, instead of
750 seeing just "ktime_get", you will see
751 "ktime_get+0xb/0x20".
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400752
753 sym-offset:
754 bash-4000 [01] 1477.606694: simple_strtoul+0x6/0xa0
755
Ingo Molnar57526742009-02-19 12:54:10 +0100756 sym-addr - this will also display the function address as well
757 as the function name.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400758
759 sym-addr:
760 bash-4000 [01] 1477.606694: simple_strtoul <c0339346>
761
Albin Tonnerre4a88d442009-08-31 22:40:08 +0200762 verbose - This deals with the trace file when the
763 latency-format option is enabled.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400764
765 bash 4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \
Jingoo Han0ab943b2013-07-31 14:59:16 -0700766 (+0.000ms): simple_strtoul (kstrtoul)
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400767
Ingo Molnar57526742009-02-19 12:54:10 +0100768 raw - This will display raw numbers. This option is best for
769 use with user applications that can translate the raw
770 numbers better than having it done in the kernel.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400771
Ingo Molnar57526742009-02-19 12:54:10 +0100772 hex - Similar to raw, but the numbers will be in a hexadecimal
773 format.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400774
775 bin - This will print out the formats in raw binary.
776
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400777 block - When set, reading trace_pipe will not block when polled.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400778
Ingo Molnar57526742009-02-19 12:54:10 +0100779 stacktrace - This is one of the options that changes the trace
780 itself. When a trace is recorded, so is the stack
781 of functions. This allows for back traces of
782 trace sites.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400783
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400784 trace_printk - Can disable trace_printk() from writing into the buffer.
785
786 branch - Enable branch tracing with the tracer.
787
788 annotate - It is sometimes confusing when the CPU buffers are full
789 and one CPU buffer had a lot of events recently, thus
790 a shorter time frame, were another CPU may have only had
791 a few events, which lets it have older events. When
792 the trace is reported, it shows the oldest events first,
793 and it may look like only one CPU ran (the one with the
794 oldest events). When the annotate option is set, it will
795 display when a new CPU buffer started:
796
797 <idle>-0 [001] dNs4 21169.031481: wake_up_idle_cpu <-add_timer_on
798 <idle>-0 [001] dNs4 21169.031482: _raw_spin_unlock_irqrestore <-add_timer_on
799 <idle>-0 [001] .Ns4 21169.031484: sub_preempt_count <-_raw_spin_unlock_irqrestore
800##### CPU 2 buffer started ####
801 <idle>-0 [002] .N.1 21169.031484: rcu_idle_exit <-cpu_idle
802 <idle>-0 [001] .Ns3 21169.031484: _raw_spin_unlock <-clocksource_watchdog
803 <idle>-0 [001] .Ns3 21169.031485: sub_preempt_count <-_raw_spin_unlock
804
Ingo Molnar57526742009-02-19 12:54:10 +0100805 userstacktrace - This option changes the trace. It records a
806 stacktrace of the current userspace thread.
Török Edwin02b67512008-11-22 13:28:47 +0200807
Ingo Molnar57526742009-02-19 12:54:10 +0100808 sym-userobj - when user stacktrace are enabled, look up which
809 object the address belongs to, and print a
810 relative address. This is especially useful when
811 ASLR is on, otherwise you don't get a chance to
812 resolve the address to object/file/line after
813 the app is no longer running
Török Edwinb54d3de2008-11-22 13:28:48 +0200814
Ingo Molnar57526742009-02-19 12:54:10 +0100815 The lookup is performed when you read
Albin Tonnerre4a88d442009-08-31 22:40:08 +0200816 trace,trace_pipe. Example:
Török Edwinb54d3de2008-11-22 13:28:48 +0200817
818 a.out-1623 [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0
819x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
820
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400821
822 printk-msg-only - When set, trace_printk()s will only show the format
823 and not their parameters (if trace_bprintk() or
824 trace_bputs() was used to save the trace_printk()).
825
826 context-info - Show only the event data. Hides the comm, PID,
827 timestamp, CPU, and other useful data.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400828
Albin Tonnerre4a88d442009-08-31 22:40:08 +0200829 latency-format - This option changes the trace. When
830 it is enabled, the trace displays
831 additional information about the
832 latencies, as described in "Latency
833 trace format".
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400834
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400835 sleep-time - When running function graph tracer, to include
836 the time a task schedules out in its function.
837 When enabled, it will account time the task has been
838 scheduled out as part of the function call.
839
840 graph-time - When running function graph tracer, to include the
841 time to call nested functions. When this is not set,
842 the time reported for the function will only include
843 the time the function itself executed for, not the time
844 for functions that it called.
845
846 record-cmd - When any event or tracer is enabled, a hook is enabled
847 in the sched_switch trace point to fill comm cache
848 with mapped pids and comms. But this may cause some
849 overhead, and if you only care about pids, and not the
850 name of the task, disabling this option can lower the
851 impact of tracing.
852
David Sharp750912f2010-12-08 13:46:47 -0800853 overwrite - This controls what happens when the trace buffer is
854 full. If "1" (default), the oldest events are
855 discarded and overwritten. If "0", then the newest
856 events are discarded.
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400857 (see per_cpu/cpu0/stats for overrun and dropped)
David Sharp750912f2010-12-08 13:46:47 -0800858
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400859 disable_on_free - When the free_buffer is closed, tracing will
860 stop (tracing_on set to 0).
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400861
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400862 irq-info - Shows the interrupt, preempt count, need resched data.
863 When disabled, the trace looks like:
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400864
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400865# tracer: function
866#
867# entries-in-buffer/entries-written: 144405/9452052 #P:4
868#
869# TASK-PID CPU# TIMESTAMP FUNCTION
870# | | | | |
871 <idle>-0 [002] 23636.756054: ttwu_do_activate.constprop.89 <-try_to_wake_up
872 <idle>-0 [002] 23636.756054: activate_task <-ttwu_do_activate.constprop.89
873 <idle>-0 [002] 23636.756055: enqueue_task <-activate_task
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400874
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400875
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400876 markers - When set, the trace_marker is writable (only by root).
877 When disabled, the trace_marker will error with EINVAL
878 on write.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400879
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400880
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400881 function-trace - The latency tracers will enable function tracing
882 if this option is enabled (default it is). When
883 it is disabled, the latency tracers do not trace
884 functions. This keeps the overhead of the tracer down
885 when performing latency tests.
886
887 Note: Some tracers have their own options. They only appear
888 when the tracer is active.
889
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400890
891
892irqsoff
893-------
894
895When interrupts are disabled, the CPU can not react to any other
896external event (besides NMIs and SMIs). This prevents the timer
Ingo Molnar57526742009-02-19 12:54:10 +0100897interrupt from triggering or the mouse interrupt from letting
898the kernel know of a new mouse event. The result is a latency
899with the reaction time.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400900
Ingo Molnar57526742009-02-19 12:54:10 +0100901The irqsoff tracer tracks the time for which interrupts are
902disabled. When a new maximum latency is hit, the tracer saves
903the trace leading up to that latency point so that every time a
904new maximum is reached, the old saved trace is discarded and the
905new trace is saved.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400906
Ingo Molnar57526742009-02-19 12:54:10 +0100907To reset the maximum, echo 0 into tracing_max_latency. Here is
908an example:
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400909
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400910 # echo 0 > options/function-trace
GeunSik Lim156f5a72009-06-02 15:01:37 +0900911 # echo irqsoff > current_tracer
Steven Rostedt6752ab42011-02-08 13:54:06 -0500912 # echo 1 > tracing_on
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400913 # echo 0 > tracing_max_latency
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400914 # ls -ltr
915 [...]
Steven Rostedt6752ab42011-02-08 13:54:06 -0500916 # echo 0 > tracing_on
Albin Tonnerre4a88d442009-08-31 22:40:08 +0200917 # cat trace
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400918# tracer: irqsoff
919#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400920# irqsoff latency trace v1.1.5 on 3.8.0-test+
921# --------------------------------------------------------------------
922# latency: 16 us, #4/4, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
923# -----------------
924# | task: swapper/0-0 (uid:0 nice:0 policy:0 rt_prio:0)
925# -----------------
926# => started at: run_timer_softirq
927# => ended at: run_timer_softirq
928#
929#
930# _------=> CPU#
931# / _-----=> irqs-off
932# | / _----=> need-resched
933# || / _---=> hardirq/softirq
934# ||| / _--=> preempt-depth
935# |||| / delay
936# cmd pid ||||| time | caller
937# \ / ||||| \ | /
938 <idle>-0 0d.s2 0us+: _raw_spin_lock_irq <-run_timer_softirq
939 <idle>-0 0dNs3 17us : _raw_spin_unlock_irq <-run_timer_softirq
940 <idle>-0 0dNs3 17us+: trace_hardirqs_on <-run_timer_softirq
941 <idle>-0 0dNs3 25us : <stack trace>
942 => _raw_spin_unlock_irq
943 => run_timer_softirq
944 => __do_softirq
945 => call_softirq
946 => do_softirq
947 => irq_exit
948 => smp_apic_timer_interrupt
949 => apic_timer_interrupt
950 => rcu_idle_exit
951 => cpu_idle
952 => rest_init
953 => start_kernel
954 => x86_64_start_reservations
955 => x86_64_start_kernel
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400956
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400957Here we see that that we had a latency of 16 microseconds (which is
958very good). The _raw_spin_lock_irq in run_timer_softirq disabled
959interrupts. The difference between the 16 and the displayed
960timestamp 25us occurred because the clock was incremented
Ingo Molnar57526742009-02-19 12:54:10 +0100961between the time of recording the max latency and the time of
962recording the function that had that latency.
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400963
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400964Note the above example had function-trace not set. If we set
965function-trace, we get a much larger output:
966
967 with echo 1 > options/function-trace
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400968
969# tracer: irqsoff
970#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400971# irqsoff latency trace v1.1.5 on 3.8.0-test+
972# --------------------------------------------------------------------
973# latency: 71 us, #168/168, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
974# -----------------
975# | task: bash-2042 (uid:0 nice:0 policy:0 rt_prio:0)
976# -----------------
977# => started at: ata_scsi_queuecmd
978# => ended at: ata_scsi_queuecmd
979#
980#
981# _------=> CPU#
982# / _-----=> irqs-off
983# | / _----=> need-resched
984# || / _---=> hardirq/softirq
985# ||| / _--=> preempt-depth
986# |||| / delay
987# cmd pid ||||| time | caller
988# \ / ||||| \ | /
989 bash-2042 3d... 0us : _raw_spin_lock_irqsave <-ata_scsi_queuecmd
990 bash-2042 3d... 0us : add_preempt_count <-_raw_spin_lock_irqsave
991 bash-2042 3d..1 1us : ata_scsi_find_dev <-ata_scsi_queuecmd
992 bash-2042 3d..1 1us : __ata_scsi_find_dev <-ata_scsi_find_dev
993 bash-2042 3d..1 2us : ata_find_dev.part.14 <-__ata_scsi_find_dev
994 bash-2042 3d..1 2us : ata_qc_new_init <-__ata_scsi_queuecmd
995 bash-2042 3d..1 3us : ata_sg_init <-__ata_scsi_queuecmd
996 bash-2042 3d..1 4us : ata_scsi_rw_xlat <-__ata_scsi_queuecmd
997 bash-2042 3d..1 4us : ata_build_rw_tf <-ata_scsi_rw_xlat
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400998[...]
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -0400999 bash-2042 3d..1 67us : delay_tsc <-__delay
1000 bash-2042 3d..1 67us : add_preempt_count <-delay_tsc
1001 bash-2042 3d..2 67us : sub_preempt_count <-delay_tsc
1002 bash-2042 3d..1 67us : add_preempt_count <-delay_tsc
1003 bash-2042 3d..2 68us : sub_preempt_count <-delay_tsc
1004 bash-2042 3d..1 68us+: ata_bmdma_start <-ata_bmdma_qc_issue
1005 bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
1006 bash-2042 3d..1 71us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
1007 bash-2042 3d..1 72us+: trace_hardirqs_on <-ata_scsi_queuecmd
1008 bash-2042 3d..1 120us : <stack trace>
1009 => _raw_spin_unlock_irqrestore
1010 => ata_scsi_queuecmd
1011 => scsi_dispatch_cmd
1012 => scsi_request_fn
1013 => __blk_run_queue_uncond
1014 => __blk_run_queue
1015 => blk_queue_bio
1016 => generic_make_request
1017 => submit_bio
1018 => submit_bh
1019 => __ext3_get_inode_loc
1020 => ext3_iget
1021 => ext3_lookup
1022 => lookup_real
1023 => __lookup_hash
1024 => walk_component
1025 => lookup_last
1026 => path_lookupat
1027 => filename_lookup
1028 => user_path_at_empty
1029 => user_path_at
1030 => vfs_fstatat
1031 => vfs_stat
1032 => sys_newstat
1033 => system_call_fastpath
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001034
1035
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001036Here we traced a 71 microsecond latency. But we also see all the
Ingo Molnar57526742009-02-19 12:54:10 +01001037functions that were called during that time. Note that by
1038enabling function tracing, we incur an added overhead. This
1039overhead may extend the latency times. But nevertheless, this
1040trace has provided some very helpful debugging information.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001041
1042
1043preemptoff
1044----------
1045
Ingo Molnar57526742009-02-19 12:54:10 +01001046When preemption is disabled, we may be able to receive
1047interrupts but the task cannot be preempted and a higher
1048priority task must wait for preemption to be enabled again
1049before it can preempt a lower priority task.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001050
Steven Rostedta41eeba2008-07-14 16:41:12 -04001051The preemptoff tracer traces the places that disable preemption.
Ingo Molnar57526742009-02-19 12:54:10 +01001052Like the irqsoff tracer, it records the maximum latency for
1053which preemption was disabled. The control of preemptoff tracer
1054is much like the irqsoff tracer.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001055
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001056 # echo 0 > options/function-trace
GeunSik Lim156f5a72009-06-02 15:01:37 +09001057 # echo preemptoff > current_tracer
Steven Rostedt6752ab42011-02-08 13:54:06 -05001058 # echo 1 > tracing_on
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001059 # echo 0 > tracing_max_latency
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001060 # ls -ltr
1061 [...]
Steven Rostedt6752ab42011-02-08 13:54:06 -05001062 # echo 0 > tracing_on
Albin Tonnerre4a88d442009-08-31 22:40:08 +02001063 # cat trace
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001064# tracer: preemptoff
1065#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001066# preemptoff latency trace v1.1.5 on 3.8.0-test+
1067# --------------------------------------------------------------------
1068# latency: 46 us, #4/4, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1069# -----------------
1070# | task: sshd-1991 (uid:0 nice:0 policy:0 rt_prio:0)
1071# -----------------
1072# => started at: do_IRQ
1073# => ended at: do_IRQ
1074#
1075#
1076# _------=> CPU#
1077# / _-----=> irqs-off
1078# | / _----=> need-resched
1079# || / _---=> hardirq/softirq
1080# ||| / _--=> preempt-depth
1081# |||| / delay
1082# cmd pid ||||| time | caller
1083# \ / ||||| \ | /
1084 sshd-1991 1d.h. 0us+: irq_enter <-do_IRQ
1085 sshd-1991 1d..1 46us : irq_exit <-do_IRQ
1086 sshd-1991 1d..1 47us+: trace_preempt_on <-do_IRQ
1087 sshd-1991 1d..1 52us : <stack trace>
1088 => sub_preempt_count
1089 => irq_exit
1090 => do_IRQ
1091 => ret_from_intr
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001092
1093
Ingo Molnar57526742009-02-19 12:54:10 +01001094This has some more changes. Preemption was disabled when an
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001095interrupt came in (notice the 'h'), and was enabled on exit.
1096But we also see that interrupts have been disabled when entering
1097the preempt off section and leaving it (the 'd'). We do not know if
1098interrupts were enabled in the mean time or shortly after this
1099was over.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001100
1101# tracer: preemptoff
1102#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001103# preemptoff latency trace v1.1.5 on 3.8.0-test+
1104# --------------------------------------------------------------------
1105# latency: 83 us, #241/241, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1106# -----------------
1107# | task: bash-1994 (uid:0 nice:0 policy:0 rt_prio:0)
1108# -----------------
1109# => started at: wake_up_new_task
1110# => ended at: task_rq_unlock
1111#
1112#
1113# _------=> CPU#
1114# / _-----=> irqs-off
1115# | / _----=> need-resched
1116# || / _---=> hardirq/softirq
1117# ||| / _--=> preempt-depth
1118# |||| / delay
1119# cmd pid ||||| time | caller
1120# \ / ||||| \ | /
1121 bash-1994 1d..1 0us : _raw_spin_lock_irqsave <-wake_up_new_task
1122 bash-1994 1d..1 0us : select_task_rq_fair <-select_task_rq
1123 bash-1994 1d..1 1us : __rcu_read_lock <-select_task_rq_fair
1124 bash-1994 1d..1 1us : source_load <-select_task_rq_fair
1125 bash-1994 1d..1 1us : source_load <-select_task_rq_fair
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001126[...]
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001127 bash-1994 1d..1 12us : irq_enter <-smp_apic_timer_interrupt
1128 bash-1994 1d..1 12us : rcu_irq_enter <-irq_enter
1129 bash-1994 1d..1 13us : add_preempt_count <-irq_enter
1130 bash-1994 1d.h1 13us : exit_idle <-smp_apic_timer_interrupt
1131 bash-1994 1d.h1 13us : hrtimer_interrupt <-smp_apic_timer_interrupt
1132 bash-1994 1d.h1 13us : _raw_spin_lock <-hrtimer_interrupt
1133 bash-1994 1d.h1 14us : add_preempt_count <-_raw_spin_lock
1134 bash-1994 1d.h2 14us : ktime_get_update_offsets <-hrtimer_interrupt
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001135[...]
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001136 bash-1994 1d.h1 35us : lapic_next_event <-clockevents_program_event
1137 bash-1994 1d.h1 35us : irq_exit <-smp_apic_timer_interrupt
1138 bash-1994 1d.h1 36us : sub_preempt_count <-irq_exit
1139 bash-1994 1d..2 36us : do_softirq <-irq_exit
1140 bash-1994 1d..2 36us : __do_softirq <-call_softirq
1141 bash-1994 1d..2 36us : __local_bh_disable <-__do_softirq
1142 bash-1994 1d.s2 37us : add_preempt_count <-_raw_spin_lock_irq
1143 bash-1994 1d.s3 38us : _raw_spin_unlock <-run_timer_softirq
1144 bash-1994 1d.s3 39us : sub_preempt_count <-_raw_spin_unlock
1145 bash-1994 1d.s2 39us : call_timer_fn <-run_timer_softirq
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001146[...]
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001147 bash-1994 1dNs2 81us : cpu_needs_another_gp <-rcu_process_callbacks
1148 bash-1994 1dNs2 82us : __local_bh_enable <-__do_softirq
1149 bash-1994 1dNs2 82us : sub_preempt_count <-__local_bh_enable
1150 bash-1994 1dN.2 82us : idle_cpu <-irq_exit
1151 bash-1994 1dN.2 83us : rcu_irq_exit <-irq_exit
1152 bash-1994 1dN.2 83us : sub_preempt_count <-irq_exit
1153 bash-1994 1.N.1 84us : _raw_spin_unlock_irqrestore <-task_rq_unlock
1154 bash-1994 1.N.1 84us+: trace_preempt_on <-task_rq_unlock
1155 bash-1994 1.N.1 104us : <stack trace>
1156 => sub_preempt_count
1157 => _raw_spin_unlock_irqrestore
1158 => task_rq_unlock
1159 => wake_up_new_task
1160 => do_fork
1161 => sys_clone
1162 => stub_clone
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001163
1164
Ingo Molnar57526742009-02-19 12:54:10 +01001165The above is an example of the preemptoff trace with
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001166function-trace set. Here we see that interrupts were not disabled
Ingo Molnar57526742009-02-19 12:54:10 +01001167the entire time. The irq_enter code lets us know that we entered
1168an interrupt 'h'. Before that, the functions being traced still
1169show that it is not in an interrupt, but we can see from the
1170functions themselves that this is not the case.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001171
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001172preemptirqsoff
1173--------------
1174
Ingo Molnar57526742009-02-19 12:54:10 +01001175Knowing the locations that have interrupts disabled or
1176preemption disabled for the longest times is helpful. But
1177sometimes we would like to know when either preemption and/or
1178interrupts are disabled.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001179
Steven Rostedtf2d9c742008-07-15 10:57:33 -04001180Consider the following code:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001181
1182 local_irq_disable();
1183 call_function_with_irqs_off();
1184 preempt_disable();
1185 call_function_with_irqs_and_preemption_off();
1186 local_irq_enable();
1187 call_function_with_preemption_off();
1188 preempt_enable();
1189
1190The irqsoff tracer will record the total length of
1191call_function_with_irqs_off() and
1192call_function_with_irqs_and_preemption_off().
1193
1194The preemptoff tracer will record the total length of
1195call_function_with_irqs_and_preemption_off() and
1196call_function_with_preemption_off().
1197
Ingo Molnar57526742009-02-19 12:54:10 +01001198But neither will trace the time that interrupts and/or
1199preemption is disabled. This total time is the time that we can
1200not schedule. To record this time, use the preemptirqsoff
1201tracer.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001202
Ingo Molnar57526742009-02-19 12:54:10 +01001203Again, using this trace is much like the irqsoff and preemptoff
1204tracers.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001205
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001206 # echo 0 > options/function-trace
GeunSik Lim156f5a72009-06-02 15:01:37 +09001207 # echo preemptirqsoff > current_tracer
Steven Rostedt6752ab42011-02-08 13:54:06 -05001208 # echo 1 > tracing_on
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001209 # echo 0 > tracing_max_latency
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001210 # ls -ltr
1211 [...]
Steven Rostedt6752ab42011-02-08 13:54:06 -05001212 # echo 0 > tracing_on
Albin Tonnerre4a88d442009-08-31 22:40:08 +02001213 # cat trace
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001214# tracer: preemptirqsoff
1215#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001216# preemptirqsoff latency trace v1.1.5 on 3.8.0-test+
1217# --------------------------------------------------------------------
1218# latency: 100 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1219# -----------------
1220# | task: ls-2230 (uid:0 nice:0 policy:0 rt_prio:0)
1221# -----------------
1222# => started at: ata_scsi_queuecmd
1223# => ended at: ata_scsi_queuecmd
1224#
1225#
1226# _------=> CPU#
1227# / _-----=> irqs-off
1228# | / _----=> need-resched
1229# || / _---=> hardirq/softirq
1230# ||| / _--=> preempt-depth
1231# |||| / delay
1232# cmd pid ||||| time | caller
1233# \ / ||||| \ | /
1234 ls-2230 3d... 0us+: _raw_spin_lock_irqsave <-ata_scsi_queuecmd
1235 ls-2230 3...1 100us : _raw_spin_unlock_irqrestore <-ata_scsi_queuecmd
1236 ls-2230 3...1 101us+: trace_preempt_on <-ata_scsi_queuecmd
1237 ls-2230 3...1 111us : <stack trace>
1238 => sub_preempt_count
1239 => _raw_spin_unlock_irqrestore
1240 => ata_scsi_queuecmd
1241 => scsi_dispatch_cmd
1242 => scsi_request_fn
1243 => __blk_run_queue_uncond
1244 => __blk_run_queue
1245 => blk_queue_bio
1246 => generic_make_request
1247 => submit_bio
1248 => submit_bh
1249 => ext3_bread
1250 => ext3_dir_bread
1251 => htree_dirblock_to_tree
1252 => ext3_htree_fill_tree
1253 => ext3_readdir
1254 => vfs_readdir
1255 => sys_getdents
1256 => system_call_fastpath
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001257
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001258
1259The trace_hardirqs_off_thunk is called from assembly on x86 when
Ingo Molnar57526742009-02-19 12:54:10 +01001260interrupts are disabled in the assembly code. Without the
1261function tracing, we do not know if interrupts were enabled
1262within the preemption points. We do see that it started with
1263preemption enabled.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001264
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001265Here is a trace with function-trace set:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001266
1267# tracer: preemptirqsoff
1268#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001269# preemptirqsoff latency trace v1.1.5 on 3.8.0-test+
1270# --------------------------------------------------------------------
1271# latency: 161 us, #339/339, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1272# -----------------
1273# | task: ls-2269 (uid:0 nice:0 policy:0 rt_prio:0)
1274# -----------------
1275# => started at: schedule
1276# => ended at: mutex_unlock
1277#
1278#
1279# _------=> CPU#
1280# / _-----=> irqs-off
1281# | / _----=> need-resched
1282# || / _---=> hardirq/softirq
1283# ||| / _--=> preempt-depth
1284# |||| / delay
1285# cmd pid ||||| time | caller
1286# \ / ||||| \ | /
1287kworker/-59 3...1 0us : __schedule <-schedule
1288kworker/-59 3d..1 0us : rcu_preempt_qs <-rcu_note_context_switch
1289kworker/-59 3d..1 1us : add_preempt_count <-_raw_spin_lock_irq
1290kworker/-59 3d..2 1us : deactivate_task <-__schedule
1291kworker/-59 3d..2 1us : dequeue_task <-deactivate_task
1292kworker/-59 3d..2 2us : update_rq_clock <-dequeue_task
1293kworker/-59 3d..2 2us : dequeue_task_fair <-dequeue_task
1294kworker/-59 3d..2 2us : update_curr <-dequeue_task_fair
1295kworker/-59 3d..2 2us : update_min_vruntime <-update_curr
1296kworker/-59 3d..2 3us : cpuacct_charge <-update_curr
1297kworker/-59 3d..2 3us : __rcu_read_lock <-cpuacct_charge
1298kworker/-59 3d..2 3us : __rcu_read_unlock <-cpuacct_charge
1299kworker/-59 3d..2 3us : update_cfs_rq_blocked_load <-dequeue_task_fair
1300kworker/-59 3d..2 4us : clear_buddies <-dequeue_task_fair
1301kworker/-59 3d..2 4us : account_entity_dequeue <-dequeue_task_fair
1302kworker/-59 3d..2 4us : update_min_vruntime <-dequeue_task_fair
1303kworker/-59 3d..2 4us : update_cfs_shares <-dequeue_task_fair
1304kworker/-59 3d..2 5us : hrtick_update <-dequeue_task_fair
1305kworker/-59 3d..2 5us : wq_worker_sleeping <-__schedule
1306kworker/-59 3d..2 5us : kthread_data <-wq_worker_sleeping
1307kworker/-59 3d..2 5us : put_prev_task_fair <-__schedule
1308kworker/-59 3d..2 6us : pick_next_task_fair <-pick_next_task
1309kworker/-59 3d..2 6us : clear_buddies <-pick_next_task_fair
1310kworker/-59 3d..2 6us : set_next_entity <-pick_next_task_fair
1311kworker/-59 3d..2 6us : update_stats_wait_end <-set_next_entity
1312 ls-2269 3d..2 7us : finish_task_switch <-__schedule
1313 ls-2269 3d..2 7us : _raw_spin_unlock_irq <-finish_task_switch
1314 ls-2269 3d..2 8us : do_IRQ <-ret_from_intr
1315 ls-2269 3d..2 8us : irq_enter <-do_IRQ
1316 ls-2269 3d..2 8us : rcu_irq_enter <-irq_enter
1317 ls-2269 3d..2 9us : add_preempt_count <-irq_enter
1318 ls-2269 3d.h2 9us : exit_idle <-do_IRQ
1319[...]
1320 ls-2269 3d.h3 20us : sub_preempt_count <-_raw_spin_unlock
1321 ls-2269 3d.h2 20us : irq_exit <-do_IRQ
1322 ls-2269 3d.h2 21us : sub_preempt_count <-irq_exit
1323 ls-2269 3d..3 21us : do_softirq <-irq_exit
1324 ls-2269 3d..3 21us : __do_softirq <-call_softirq
1325 ls-2269 3d..3 21us+: __local_bh_disable <-__do_softirq
1326 ls-2269 3d.s4 29us : sub_preempt_count <-_local_bh_enable_ip
1327 ls-2269 3d.s5 29us : sub_preempt_count <-_local_bh_enable_ip
1328 ls-2269 3d.s5 31us : do_IRQ <-ret_from_intr
1329 ls-2269 3d.s5 31us : irq_enter <-do_IRQ
1330 ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter
1331[...]
1332 ls-2269 3d.s5 31us : rcu_irq_enter <-irq_enter
1333 ls-2269 3d.s5 32us : add_preempt_count <-irq_enter
1334 ls-2269 3d.H5 32us : exit_idle <-do_IRQ
1335 ls-2269 3d.H5 32us : handle_irq <-do_IRQ
1336 ls-2269 3d.H5 32us : irq_to_desc <-handle_irq
1337 ls-2269 3d.H5 33us : handle_fasteoi_irq <-handle_irq
1338[...]
1339 ls-2269 3d.s5 158us : _raw_spin_unlock_irqrestore <-rtl8139_poll
1340 ls-2269 3d.s3 158us : net_rps_action_and_irq_enable.isra.65 <-net_rx_action
1341 ls-2269 3d.s3 159us : __local_bh_enable <-__do_softirq
1342 ls-2269 3d.s3 159us : sub_preempt_count <-__local_bh_enable
1343 ls-2269 3d..3 159us : idle_cpu <-irq_exit
1344 ls-2269 3d..3 159us : rcu_irq_exit <-irq_exit
1345 ls-2269 3d..3 160us : sub_preempt_count <-irq_exit
1346 ls-2269 3d... 161us : __mutex_unlock_slowpath <-mutex_unlock
1347 ls-2269 3d... 162us+: trace_hardirqs_on <-mutex_unlock
1348 ls-2269 3d... 186us : <stack trace>
1349 => __mutex_unlock_slowpath
1350 => mutex_unlock
1351 => process_output
1352 => n_tty_write
1353 => tty_write
1354 => vfs_write
1355 => sys_write
1356 => system_call_fastpath
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001357
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001358This is an interesting trace. It started with kworker running and
1359scheduling out and ls taking over. But as soon as ls released the
1360rq lock and enabled interrupts (but not preemption) an interrupt
1361triggered. When the interrupt finished, it started running softirqs.
1362But while the softirq was running, another interrupt triggered.
1363When an interrupt is running inside a softirq, the annotation is 'H'.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001364
1365
1366wakeup
1367------
1368
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001369One common case that people are interested in tracing is the
1370time it takes for a task that is woken to actually wake up.
1371Now for non Real-Time tasks, this can be arbitrary. But tracing
1372it none the less can be interesting.
1373
1374Without function tracing:
1375
1376 # echo 0 > options/function-trace
1377 # echo wakeup > current_tracer
1378 # echo 1 > tracing_on
1379 # echo 0 > tracing_max_latency
1380 # chrt -f 5 sleep 1
1381 # echo 0 > tracing_on
1382 # cat trace
1383# tracer: wakeup
1384#
1385# wakeup latency trace v1.1.5 on 3.8.0-test+
1386# --------------------------------------------------------------------
1387# latency: 15 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1388# -----------------
1389# | task: kworker/3:1H-312 (uid:0 nice:-20 policy:0 rt_prio:0)
1390# -----------------
1391#
1392# _------=> CPU#
1393# / _-----=> irqs-off
1394# | / _----=> need-resched
1395# || / _---=> hardirq/softirq
1396# ||| / _--=> preempt-depth
1397# |||| / delay
1398# cmd pid ||||| time | caller
1399# \ / ||||| \ | /
1400 <idle>-0 3dNs7 0us : 0:120:R + [003] 312:100:R kworker/3:1H
1401 <idle>-0 3dNs7 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up
1402 <idle>-0 3d..3 15us : __schedule <-schedule
1403 <idle>-0 3d..3 15us : 0:120:R ==> [003] 312:100:R kworker/3:1H
1404
1405The tracer only traces the highest priority task in the system
1406to avoid tracing the normal circumstances. Here we see that
1407the kworker with a nice priority of -20 (not very nice), took
1408just 15 microseconds from the time it woke up, to the time it
1409ran.
1410
1411Non Real-Time tasks are not that interesting. A more interesting
1412trace is to concentrate only on Real-Time tasks.
1413
1414wakeup_rt
1415---------
1416
Ingo Molnar57526742009-02-19 12:54:10 +01001417In a Real-Time environment it is very important to know the
1418wakeup time it takes for the highest priority task that is woken
1419up to the time that it executes. This is also known as "schedule
1420latency". I stress the point that this is about RT tasks. It is
1421also important to know the scheduling latency of non-RT tasks,
1422but the average schedule latency is better for non-RT tasks.
1423Tools like LatencyTop are more appropriate for such
1424measurements.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001425
Steven Rostedta41eeba2008-07-14 16:41:12 -04001426Real-Time environments are interested in the worst case latency.
Ingo Molnar57526742009-02-19 12:54:10 +01001427That is the longest latency it takes for something to happen,
1428and not the average. We can have a very fast scheduler that may
1429only have a large latency once in a while, but that would not
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001430work well with Real-Time tasks. The wakeup_rt tracer was designed
Ingo Molnar57526742009-02-19 12:54:10 +01001431to record the worst case wakeups of RT tasks. Non-RT tasks are
1432not recorded because the tracer only records one worst case and
1433tracing non-RT tasks that are unpredictable will overwrite the
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001434worst case latency of RT tasks (just run the normal wakeup
1435tracer for a while to see that effect).
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001436
Ingo Molnar57526742009-02-19 12:54:10 +01001437Since this tracer only deals with RT tasks, we will run this
1438slightly differently than we did with the previous tracers.
1439Instead of performing an 'ls', we will run 'sleep 1' under
1440'chrt' which changes the priority of the task.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001441
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001442 # echo 0 > options/function-trace
1443 # echo wakeup_rt > current_tracer
Steven Rostedt6752ab42011-02-08 13:54:06 -05001444 # echo 1 > tracing_on
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001445 # echo 0 > tracing_max_latency
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001446 # chrt -f 5 sleep 1
Steven Rostedt6752ab42011-02-08 13:54:06 -05001447 # echo 0 > tracing_on
Albin Tonnerre4a88d442009-08-31 22:40:08 +02001448 # cat trace
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001449# tracer: wakeup
1450#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001451# tracer: wakeup_rt
1452#
1453# wakeup_rt latency trace v1.1.5 on 3.8.0-test+
1454# --------------------------------------------------------------------
1455# latency: 5 us, #4/4, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1456# -----------------
1457# | task: sleep-2389 (uid:0 nice:0 policy:1 rt_prio:5)
1458# -----------------
1459#
1460# _------=> CPU#
1461# / _-----=> irqs-off
1462# | / _----=> need-resched
1463# || / _---=> hardirq/softirq
1464# ||| / _--=> preempt-depth
1465# |||| / delay
1466# cmd pid ||||| time | caller
1467# \ / ||||| \ | /
1468 <idle>-0 3d.h4 0us : 0:120:R + [003] 2389: 94:R sleep
1469 <idle>-0 3d.h4 1us+: ttwu_do_activate.constprop.87 <-try_to_wake_up
1470 <idle>-0 3d..3 5us : __schedule <-schedule
1471 <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001472
1473
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001474Running this on an idle system, we see that it only took 5 microseconds
1475to perform the task switch. Note, since the trace point in the schedule
1476is before the actual "switch", we stop the tracing when the recorded task
1477is about to schedule in. This may change if we add a new marker at the
1478end of the scheduler.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001479
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001480Notice that the recorded task is 'sleep' with the PID of 2389
Ingo Molnar57526742009-02-19 12:54:10 +01001481and it has an rt_prio of 5. This priority is user-space priority
1482and not the internal kernel priority. The policy is 1 for
1483SCHED_FIFO and 2 for SCHED_RR.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001484
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001485Note, that the trace data shows the internal priority (99 - rtprio).
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001486
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001487 <idle>-0 3d..3 5us : 0:120:R ==> [003] 2389: 94:R sleep
1488
1489The 0:120:R means idle was running with a nice priority of 0 (120 - 20)
1490and in the running state 'R'. The sleep task was scheduled in with
14912389: 94:R. That is the priority is the kernel rtprio (99 - 5 = 94)
1492and it too is in the running state.
1493
1494Doing the same with chrt -r 5 and function-trace set.
1495
1496 echo 1 > options/function-trace
1497
1498# tracer: wakeup_rt
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001499#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001500# wakeup_rt latency trace v1.1.5 on 3.8.0-test+
1501# --------------------------------------------------------------------
1502# latency: 29 us, #85/85, CPU#3 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1503# -----------------
1504# | task: sleep-2448 (uid:0 nice:0 policy:1 rt_prio:5)
1505# -----------------
1506#
1507# _------=> CPU#
1508# / _-----=> irqs-off
1509# | / _----=> need-resched
1510# || / _---=> hardirq/softirq
1511# ||| / _--=> preempt-depth
1512# |||| / delay
1513# cmd pid ||||| time | caller
1514# \ / ||||| \ | /
1515 <idle>-0 3d.h4 1us+: 0:120:R + [003] 2448: 94:R sleep
1516 <idle>-0 3d.h4 2us : ttwu_do_activate.constprop.87 <-try_to_wake_up
1517 <idle>-0 3d.h3 3us : check_preempt_curr <-ttwu_do_wakeup
1518 <idle>-0 3d.h3 3us : resched_task <-check_preempt_curr
1519 <idle>-0 3dNh3 4us : task_woken_rt <-ttwu_do_wakeup
1520 <idle>-0 3dNh3 4us : _raw_spin_unlock <-try_to_wake_up
1521 <idle>-0 3dNh3 4us : sub_preempt_count <-_raw_spin_unlock
1522 <idle>-0 3dNh2 5us : ttwu_stat <-try_to_wake_up
1523 <idle>-0 3dNh2 5us : _raw_spin_unlock_irqrestore <-try_to_wake_up
1524 <idle>-0 3dNh2 6us : sub_preempt_count <-_raw_spin_unlock_irqrestore
1525 <idle>-0 3dNh1 6us : _raw_spin_lock <-__run_hrtimer
1526 <idle>-0 3dNh1 6us : add_preempt_count <-_raw_spin_lock
1527 <idle>-0 3dNh2 7us : _raw_spin_unlock <-hrtimer_interrupt
1528 <idle>-0 3dNh2 7us : sub_preempt_count <-_raw_spin_unlock
1529 <idle>-0 3dNh1 7us : tick_program_event <-hrtimer_interrupt
1530 <idle>-0 3dNh1 7us : clockevents_program_event <-tick_program_event
1531 <idle>-0 3dNh1 8us : ktime_get <-clockevents_program_event
1532 <idle>-0 3dNh1 8us : lapic_next_event <-clockevents_program_event
1533 <idle>-0 3dNh1 8us : irq_exit <-smp_apic_timer_interrupt
1534 <idle>-0 3dNh1 9us : sub_preempt_count <-irq_exit
1535 <idle>-0 3dN.2 9us : idle_cpu <-irq_exit
1536 <idle>-0 3dN.2 9us : rcu_irq_exit <-irq_exit
1537 <idle>-0 3dN.2 10us : rcu_eqs_enter_common.isra.45 <-rcu_irq_exit
1538 <idle>-0 3dN.2 10us : sub_preempt_count <-irq_exit
1539 <idle>-0 3.N.1 11us : rcu_idle_exit <-cpu_idle
1540 <idle>-0 3dN.1 11us : rcu_eqs_exit_common.isra.43 <-rcu_idle_exit
1541 <idle>-0 3.N.1 11us : tick_nohz_idle_exit <-cpu_idle
1542 <idle>-0 3dN.1 12us : menu_hrtimer_cancel <-tick_nohz_idle_exit
1543 <idle>-0 3dN.1 12us : ktime_get <-tick_nohz_idle_exit
1544 <idle>-0 3dN.1 12us : tick_do_update_jiffies64 <-tick_nohz_idle_exit
1545 <idle>-0 3dN.1 13us : update_cpu_load_nohz <-tick_nohz_idle_exit
1546 <idle>-0 3dN.1 13us : _raw_spin_lock <-update_cpu_load_nohz
1547 <idle>-0 3dN.1 13us : add_preempt_count <-_raw_spin_lock
1548 <idle>-0 3dN.2 13us : __update_cpu_load <-update_cpu_load_nohz
1549 <idle>-0 3dN.2 14us : sched_avg_update <-__update_cpu_load
1550 <idle>-0 3dN.2 14us : _raw_spin_unlock <-update_cpu_load_nohz
1551 <idle>-0 3dN.2 14us : sub_preempt_count <-_raw_spin_unlock
1552 <idle>-0 3dN.1 15us : calc_load_exit_idle <-tick_nohz_idle_exit
1553 <idle>-0 3dN.1 15us : touch_softlockup_watchdog <-tick_nohz_idle_exit
1554 <idle>-0 3dN.1 15us : hrtimer_cancel <-tick_nohz_idle_exit
1555 <idle>-0 3dN.1 15us : hrtimer_try_to_cancel <-hrtimer_cancel
1556 <idle>-0 3dN.1 16us : lock_hrtimer_base.isra.18 <-hrtimer_try_to_cancel
1557 <idle>-0 3dN.1 16us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18
1558 <idle>-0 3dN.1 16us : add_preempt_count <-_raw_spin_lock_irqsave
1559 <idle>-0 3dN.2 17us : __remove_hrtimer <-remove_hrtimer.part.16
1560 <idle>-0 3dN.2 17us : hrtimer_force_reprogram <-__remove_hrtimer
1561 <idle>-0 3dN.2 17us : tick_program_event <-hrtimer_force_reprogram
1562 <idle>-0 3dN.2 18us : clockevents_program_event <-tick_program_event
1563 <idle>-0 3dN.2 18us : ktime_get <-clockevents_program_event
1564 <idle>-0 3dN.2 18us : lapic_next_event <-clockevents_program_event
1565 <idle>-0 3dN.2 19us : _raw_spin_unlock_irqrestore <-hrtimer_try_to_cancel
1566 <idle>-0 3dN.2 19us : sub_preempt_count <-_raw_spin_unlock_irqrestore
1567 <idle>-0 3dN.1 19us : hrtimer_forward <-tick_nohz_idle_exit
1568 <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward
1569 <idle>-0 3dN.1 20us : ktime_add_safe <-hrtimer_forward
1570 <idle>-0 3dN.1 20us : hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11
1571 <idle>-0 3dN.1 20us : __hrtimer_start_range_ns <-hrtimer_start_range_ns
1572 <idle>-0 3dN.1 21us : lock_hrtimer_base.isra.18 <-__hrtimer_start_range_ns
1573 <idle>-0 3dN.1 21us : _raw_spin_lock_irqsave <-lock_hrtimer_base.isra.18
1574 <idle>-0 3dN.1 21us : add_preempt_count <-_raw_spin_lock_irqsave
1575 <idle>-0 3dN.2 22us : ktime_add_safe <-__hrtimer_start_range_ns
1576 <idle>-0 3dN.2 22us : enqueue_hrtimer <-__hrtimer_start_range_ns
1577 <idle>-0 3dN.2 22us : tick_program_event <-__hrtimer_start_range_ns
1578 <idle>-0 3dN.2 23us : clockevents_program_event <-tick_program_event
1579 <idle>-0 3dN.2 23us : ktime_get <-clockevents_program_event
1580 <idle>-0 3dN.2 23us : lapic_next_event <-clockevents_program_event
1581 <idle>-0 3dN.2 24us : _raw_spin_unlock_irqrestore <-__hrtimer_start_range_ns
1582 <idle>-0 3dN.2 24us : sub_preempt_count <-_raw_spin_unlock_irqrestore
1583 <idle>-0 3dN.1 24us : account_idle_ticks <-tick_nohz_idle_exit
1584 <idle>-0 3dN.1 24us : account_idle_time <-account_idle_ticks
1585 <idle>-0 3.N.1 25us : sub_preempt_count <-cpu_idle
1586 <idle>-0 3.N.. 25us : schedule <-cpu_idle
1587 <idle>-0 3.N.. 25us : __schedule <-preempt_schedule
1588 <idle>-0 3.N.. 26us : add_preempt_count <-__schedule
1589 <idle>-0 3.N.1 26us : rcu_note_context_switch <-__schedule
1590 <idle>-0 3.N.1 26us : rcu_sched_qs <-rcu_note_context_switch
1591 <idle>-0 3dN.1 27us : rcu_preempt_qs <-rcu_note_context_switch
1592 <idle>-0 3.N.1 27us : _raw_spin_lock_irq <-__schedule
1593 <idle>-0 3dN.1 27us : add_preempt_count <-_raw_spin_lock_irq
1594 <idle>-0 3dN.2 28us : put_prev_task_idle <-__schedule
1595 <idle>-0 3dN.2 28us : pick_next_task_stop <-pick_next_task
1596 <idle>-0 3dN.2 28us : pick_next_task_rt <-pick_next_task
1597 <idle>-0 3dN.2 29us : dequeue_pushable_task <-pick_next_task_rt
1598 <idle>-0 3d..3 29us : __schedule <-preempt_schedule
1599 <idle>-0 3d..3 30us : 0:120:R ==> [003] 2448: 94:R sleep
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001600
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001601This isn't that big of a trace, even with function tracing enabled,
1602so I included the entire trace.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001603
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001604The interrupt went off while when the system was idle. Somewhere
1605before task_woken_rt() was called, the NEED_RESCHED flag was set,
1606this is indicated by the first occurrence of the 'N' flag.
1607
1608Latency tracing and events
1609--------------------------
1610As function tracing can induce a much larger latency, but without
1611seeing what happens within the latency it is hard to know what
1612caused it. There is a middle ground, and that is with enabling
1613events.
1614
1615 # echo 0 > options/function-trace
1616 # echo wakeup_rt > current_tracer
1617 # echo 1 > events/enable
1618 # echo 1 > tracing_on
1619 # echo 0 > tracing_max_latency
1620 # chrt -f 5 sleep 1
1621 # echo 0 > tracing_on
1622 # cat trace
1623# tracer: wakeup_rt
1624#
1625# wakeup_rt latency trace v1.1.5 on 3.8.0-test+
1626# --------------------------------------------------------------------
1627# latency: 6 us, #12/12, CPU#2 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
1628# -----------------
1629# | task: sleep-5882 (uid:0 nice:0 policy:1 rt_prio:5)
1630# -----------------
1631#
1632# _------=> CPU#
1633# / _-----=> irqs-off
1634# | / _----=> need-resched
1635# || / _---=> hardirq/softirq
1636# ||| / _--=> preempt-depth
1637# |||| / delay
1638# cmd pid ||||| time | caller
1639# \ / ||||| \ | /
1640 <idle>-0 2d.h4 0us : 0:120:R + [002] 5882: 94:R sleep
1641 <idle>-0 2d.h4 0us : ttwu_do_activate.constprop.87 <-try_to_wake_up
1642 <idle>-0 2d.h4 1us : sched_wakeup: comm=sleep pid=5882 prio=94 success=1 target_cpu=002
1643 <idle>-0 2dNh2 1us : hrtimer_expire_exit: hrtimer=ffff88007796feb8
1644 <idle>-0 2.N.2 2us : power_end: cpu_id=2
1645 <idle>-0 2.N.2 3us : cpu_idle: state=4294967295 cpu_id=2
1646 <idle>-0 2dN.3 4us : hrtimer_cancel: hrtimer=ffff88007d50d5e0
1647 <idle>-0 2dN.3 4us : hrtimer_start: hrtimer=ffff88007d50d5e0 function=tick_sched_timer expires=34311211000000 softexpires=34311211000000
1648 <idle>-0 2.N.2 5us : rcu_utilization: Start context switch
1649 <idle>-0 2.N.2 5us : rcu_utilization: End context switch
1650 <idle>-0 2d..3 6us : __schedule <-schedule
1651 <idle>-0 2d..3 6us : 0:120:R ==> [002] 5882: 94:R sleep
1652
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001653
Steven Rostedt9b803c02008-11-03 15:15:08 -05001654function
1655--------
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001656
Steven Rostedt9b803c02008-11-03 15:15:08 -05001657This tracer is the function tracer. Enabling the function tracer
Ingo Molnar57526742009-02-19 12:54:10 +01001658can be done from the debug file system. Make sure the
1659ftrace_enabled is set; otherwise this tracer is a nop.
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001660See the "ftrace_enabled" section below.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001661
1662 # sysctl kernel.ftrace_enabled=1
GeunSik Lim156f5a72009-06-02 15:01:37 +09001663 # echo function > current_tracer
Steven Rostedt6752ab42011-02-08 13:54:06 -05001664 # echo 1 > tracing_on
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001665 # usleep 1
Steven Rostedt6752ab42011-02-08 13:54:06 -05001666 # echo 0 > tracing_on
GeunSik Lim156f5a72009-06-02 15:01:37 +09001667 # cat trace
Steven Rostedt9b803c02008-11-03 15:15:08 -05001668# tracer: function
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001669#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001670# entries-in-buffer/entries-written: 24799/24799 #P:4
1671#
1672# _-----=> irqs-off
1673# / _----=> need-resched
1674# | / _---=> hardirq/softirq
1675# || / _--=> preempt-depth
1676# ||| / delay
1677# TASK-PID CPU# |||| TIMESTAMP FUNCTION
1678# | | | |||| | |
1679 bash-1994 [002] .... 3082.063030: mutex_unlock <-rb_simple_write
1680 bash-1994 [002] .... 3082.063031: __mutex_unlock_slowpath <-mutex_unlock
1681 bash-1994 [002] .... 3082.063031: __fsnotify_parent <-fsnotify_modify
1682 bash-1994 [002] .... 3082.063032: fsnotify <-fsnotify_modify
1683 bash-1994 [002] .... 3082.063032: __srcu_read_lock <-fsnotify
1684 bash-1994 [002] .... 3082.063032: add_preempt_count <-__srcu_read_lock
1685 bash-1994 [002] ...1 3082.063032: sub_preempt_count <-__srcu_read_lock
1686 bash-1994 [002] .... 3082.063033: __srcu_read_unlock <-fsnotify
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001687[...]
1688
1689
Ingo Molnar57526742009-02-19 12:54:10 +01001690Note: function tracer uses ring buffers to store the above
1691entries. The newest data may overwrite the oldest data.
1692Sometimes using echo to stop the trace is not sufficient because
1693the tracing could have overwritten the data that you wanted to
1694record. For this reason, it is sometimes better to disable
1695tracing directly from a program. This allows you to stop the
1696tracing at the point that you hit the part that you are
1697interested in. To disable the tracing directly from a C program,
1698something like following code snippet can be used:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001699
1700int trace_fd;
1701[...]
1702int main(int argc, char *argv[]) {
1703 [...]
Steven Rostedt6752ab42011-02-08 13:54:06 -05001704 trace_fd = open(tracing_file("tracing_on"), O_WRONLY);
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001705 [...]
1706 if (condition_hit()) {
Steven Rostedtf2d9c742008-07-15 10:57:33 -04001707 write(trace_fd, "0", 1);
Steven Rostedteb6d42e2008-07-10 12:46:01 -04001708 }
1709 [...]
1710}
1711
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001712
1713Single thread tracing
1714---------------------
1715
GeunSik Lim156f5a72009-06-02 15:01:37 +09001716By writing into set_ftrace_pid you can trace a
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001717single thread. For example:
1718
GeunSik Lim156f5a72009-06-02 15:01:37 +09001719# cat set_ftrace_pid
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001720no pid
GeunSik Lim156f5a72009-06-02 15:01:37 +09001721# echo 3111 > set_ftrace_pid
1722# cat set_ftrace_pid
Steven Rostedtdf4fc312008-11-26 00:16:23 -050017233111
GeunSik Lim156f5a72009-06-02 15:01:37 +09001724# echo function > current_tracer
1725# cat trace | head
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001726 # tracer: function
1727 #
1728 # TASK-PID CPU# TIMESTAMP FUNCTION
1729 # | | | | |
1730 yum-updatesd-3111 [003] 1637.254676: finish_task_switch <-thread_return
1731 yum-updatesd-3111 [003] 1637.254681: hrtimer_cancel <-schedule_hrtimeout_range
1732 yum-updatesd-3111 [003] 1637.254682: hrtimer_try_to_cancel <-hrtimer_cancel
1733 yum-updatesd-3111 [003] 1637.254683: lock_hrtimer_base <-hrtimer_try_to_cancel
1734 yum-updatesd-3111 [003] 1637.254685: fget_light <-do_sys_poll
1735 yum-updatesd-3111 [003] 1637.254686: pipe_poll <-do_sys_poll
GeunSik Lim156f5a72009-06-02 15:01:37 +09001736# echo -1 > set_ftrace_pid
1737# cat trace |head
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001738 # tracer: function
1739 #
1740 # TASK-PID CPU# TIMESTAMP FUNCTION
1741 # | | | | |
1742 ##### CPU 3 buffer started ####
1743 yum-updatesd-3111 [003] 1701.957688: free_poll_entry <-poll_freewait
1744 yum-updatesd-3111 [003] 1701.957689: remove_wait_queue <-free_poll_entry
1745 yum-updatesd-3111 [003] 1701.957691: fput <-free_poll_entry
1746 yum-updatesd-3111 [003] 1701.957692: audit_syscall_exit <-sysret_audit
1747 yum-updatesd-3111 [003] 1701.957693: path_put <-audit_syscall_exit
1748
1749If you want to trace a function when executing, you could use
1750something like this simple program:
1751
1752#include <stdio.h>
1753#include <stdlib.h>
1754#include <sys/types.h>
1755#include <sys/stat.h>
1756#include <fcntl.h>
1757#include <unistd.h>
Jiri Olsa67b394f2009-10-23 19:36:18 -04001758#include <string.h>
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001759
GeunSik Lim156f5a72009-06-02 15:01:37 +09001760#define _STR(x) #x
1761#define STR(x) _STR(x)
1762#define MAX_PATH 256
1763
1764const char *find_debugfs(void)
1765{
1766 static char debugfs[MAX_PATH+1];
1767 static int debugfs_found;
1768 char type[100];
1769 FILE *fp;
1770
1771 if (debugfs_found)
1772 return debugfs;
1773
1774 if ((fp = fopen("/proc/mounts","r")) == NULL) {
1775 perror("/proc/mounts");
1776 return NULL;
1777 }
1778
1779 while (fscanf(fp, "%*s %"
1780 STR(MAX_PATH)
1781 "s %99s %*s %*d %*d\n",
1782 debugfs, type) == 2) {
1783 if (strcmp(type, "debugfs") == 0)
1784 break;
1785 }
1786 fclose(fp);
1787
1788 if (strcmp(type, "debugfs") != 0) {
1789 fprintf(stderr, "debugfs not mounted");
1790 return NULL;
1791 }
1792
Jiri Olsa67b394f2009-10-23 19:36:18 -04001793 strcat(debugfs, "/tracing/");
GeunSik Lim156f5a72009-06-02 15:01:37 +09001794 debugfs_found = 1;
1795
1796 return debugfs;
1797}
1798
1799const char *tracing_file(const char *file_name)
1800{
1801 static char trace_file[MAX_PATH+1];
1802 snprintf(trace_file, MAX_PATH, "%s/%s", find_debugfs(), file_name);
1803 return trace_file;
1804}
1805
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001806int main (int argc, char **argv)
1807{
1808 if (argc < 1)
1809 exit(-1);
1810
1811 if (fork() > 0) {
1812 int fd, ffd;
1813 char line[64];
1814 int s;
1815
GeunSik Lim156f5a72009-06-02 15:01:37 +09001816 ffd = open(tracing_file("current_tracer"), O_WRONLY);
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001817 if (ffd < 0)
1818 exit(-1);
1819 write(ffd, "nop", 3);
1820
GeunSik Lim156f5a72009-06-02 15:01:37 +09001821 fd = open(tracing_file("set_ftrace_pid"), O_WRONLY);
Steven Rostedtdf4fc312008-11-26 00:16:23 -05001822 s = sprintf(line, "%d\n", getpid());
1823 write(fd, line, s);
1824
1825 write(ffd, "function", 8);
1826
1827 close(fd);
1828 close(ffd);
1829
1830 execvp(argv[1], argv+1);
1831 }
1832
1833 return 0;
1834}
1835
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001836Or this simple script!
Markus Metzgere2ea5392009-01-19 10:35:58 +01001837
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001838------
1839#!/bin/bash
Markus Metzgere2ea5392009-01-19 10:35:58 +01001840
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04001841debugfs=`sed -ne 's/^debugfs \(.*\) debugfs.*/\1/p' /proc/mounts`
1842echo nop > $debugfs/tracing/current_tracer
1843echo 0 > $debugfs/tracing/tracing_on
1844echo $$ > $debugfs/tracing/set_ftrace_pid
1845echo function > $debugfs/tracing/current_tracer
1846echo 1 > $debugfs/tracing/tracing_on
1847exec "$@"
1848------
Markus Metzgere2ea5392009-01-19 10:35:58 +01001849
1850
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001851function graph tracer
1852---------------------------
1853
Ingo Molnar57526742009-02-19 12:54:10 +01001854This tracer is similar to the function tracer except that it
1855probes a function on its entry and its exit. This is done by
1856using a dynamically allocated stack of return addresses in each
1857task_struct. On function entry the tracer overwrites the return
1858address of each function traced to set a custom probe. Thus the
1859original return address is stored on the stack of return address
1860in the task_struct.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001861
Ingo Molnar57526742009-02-19 12:54:10 +01001862Probing on both ends of a function leads to special features
1863such as:
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001864
Ingo Molnar57526742009-02-19 12:54:10 +01001865- measure of a function's time execution
1866- having a reliable call stack to draw function calls graph
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001867
1868This tracer is useful in several situations:
1869
Ingo Molnar57526742009-02-19 12:54:10 +01001870- you want to find the reason of a strange kernel behavior and
1871 need to see what happens in detail on any areas (or specific
1872 ones).
1873
1874- you are experiencing weird latencies but it's difficult to
1875 find its origin.
1876
1877- you want to find quickly which path is taken by a specific
1878 function
1879
1880- you just want to peek inside a working kernel and want to see
1881 what happens there.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001882
1883# tracer: function_graph
1884#
1885# CPU DURATION FUNCTION CALLS
1886# | | | | | | |
1887
1888 0) | sys_open() {
1889 0) | do_sys_open() {
1890 0) | getname() {
1891 0) | kmem_cache_alloc() {
1892 0) 1.382 us | __might_sleep();
1893 0) 2.478 us | }
1894 0) | strncpy_from_user() {
1895 0) | might_fault() {
1896 0) 1.389 us | __might_sleep();
1897 0) 2.553 us | }
1898 0) 3.807 us | }
1899 0) 7.876 us | }
1900 0) | alloc_fd() {
1901 0) 0.668 us | _spin_lock();
1902 0) 0.570 us | expand_files();
1903 0) 0.586 us | _spin_unlock();
1904
1905
Ingo Molnar57526742009-02-19 12:54:10 +01001906There are several columns that can be dynamically
1907enabled/disabled. You can use every combination of options you
1908want, depending on your needs.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001909
Ingo Molnar57526742009-02-19 12:54:10 +01001910- The cpu number on which the function executed is default
1911 enabled. It is sometimes better to only trace one cpu (see
1912 tracing_cpu_mask file) or you might sometimes see unordered
1913 function calls while cpu tracing switch.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001914
GeunSik Lim156f5a72009-06-02 15:01:37 +09001915 hide: echo nofuncgraph-cpu > trace_options
1916 show: echo funcgraph-cpu > trace_options
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001917
Ingo Molnar57526742009-02-19 12:54:10 +01001918- The duration (function's time of execution) is displayed on
1919 the closing bracket line of a function or on the same line
1920 than the current function in case of a leaf one. It is default
1921 enabled.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001922
GeunSik Lim156f5a72009-06-02 15:01:37 +09001923 hide: echo nofuncgraph-duration > trace_options
1924 show: echo funcgraph-duration > trace_options
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001925
Ingo Molnar57526742009-02-19 12:54:10 +01001926- The overhead field precedes the duration field in case of
1927 reached duration thresholds.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001928
GeunSik Lim156f5a72009-06-02 15:01:37 +09001929 hide: echo nofuncgraph-overhead > trace_options
1930 show: echo funcgraph-overhead > trace_options
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001931 depends on: funcgraph-duration
1932
1933 ie:
1934
1935 0) | up_write() {
1936 0) 0.646 us | _spin_lock_irqsave();
1937 0) 0.684 us | _spin_unlock_irqrestore();
1938 0) 3.123 us | }
1939 0) 0.548 us | fput();
1940 0) + 58.628 us | }
1941
1942 [...]
1943
1944 0) | putname() {
1945 0) | kmem_cache_free() {
1946 0) 0.518 us | __phys_addr();
1947 0) 1.757 us | }
1948 0) 2.861 us | }
1949 0) ! 115.305 us | }
1950 0) ! 116.402 us | }
1951
1952 + means that the function exceeded 10 usecs.
1953 ! means that the function exceeded 100 usecs.
1954
1955
Ingo Molnar57526742009-02-19 12:54:10 +01001956- The task/pid field displays the thread cmdline and pid which
1957 executed the function. It is default disabled.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001958
GeunSik Lim156f5a72009-06-02 15:01:37 +09001959 hide: echo nofuncgraph-proc > trace_options
1960 show: echo funcgraph-proc > trace_options
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001961
1962 ie:
1963
1964 # tracer: function_graph
1965 #
1966 # CPU TASK/PID DURATION FUNCTION CALLS
1967 # | | | | | | | | |
1968 0) sh-4802 | | d_free() {
1969 0) sh-4802 | | call_rcu() {
1970 0) sh-4802 | | __call_rcu() {
1971 0) sh-4802 | 0.616 us | rcu_process_gp_end();
1972 0) sh-4802 | 0.586 us | check_for_new_grace_period();
1973 0) sh-4802 | 2.899 us | }
1974 0) sh-4802 | 4.040 us | }
1975 0) sh-4802 | 5.151 us | }
1976 0) sh-4802 | + 49.370 us | }
1977
1978
Ingo Molnar57526742009-02-19 12:54:10 +01001979- The absolute time field is an absolute timestamp given by the
1980 system clock since it started. A snapshot of this time is
1981 given on each entry/exit of functions
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001982
GeunSik Lim156f5a72009-06-02 15:01:37 +09001983 hide: echo nofuncgraph-abstime > trace_options
1984 show: echo funcgraph-abstime > trace_options
Frederic Weisbecker985ec202009-02-18 06:35:34 +01001985
1986 ie:
1987
1988 #
1989 # TIME CPU DURATION FUNCTION CALLS
1990 # | | | | | | | |
1991 360.774522 | 1) 0.541 us | }
1992 360.774522 | 1) 4.663 us | }
1993 360.774523 | 1) 0.541 us | __wake_up_bit();
1994 360.774524 | 1) 6.796 us | }
1995 360.774524 | 1) 7.952 us | }
1996 360.774525 | 1) 9.063 us | }
1997 360.774525 | 1) 0.615 us | journal_mark_dirty();
1998 360.774527 | 1) 0.578 us | __brelse();
1999 360.774528 | 1) | reiserfs_prepare_for_journal() {
2000 360.774528 | 1) | unlock_buffer() {
2001 360.774529 | 1) | wake_up_bit() {
2002 360.774529 | 1) | bit_waitqueue() {
2003 360.774530 | 1) 0.594 us | __phys_addr();
2004
2005
Ingo Molnar57526742009-02-19 12:54:10 +01002006You can put some comments on specific functions by using
Ingo Molnar5e1607a2009-03-05 10:24:48 +01002007trace_printk() For example, if you want to put a comment inside
Ingo Molnar57526742009-02-19 12:54:10 +01002008the __might_sleep() function, you just have to include
Ingo Molnar5e1607a2009-03-05 10:24:48 +01002009<linux/ftrace.h> and call trace_printk() inside __might_sleep()
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002010
Ingo Molnar5e1607a2009-03-05 10:24:48 +01002011trace_printk("I'm a comment!\n")
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002012
2013will produce:
2014
2015 1) | __might_sleep() {
2016 1) | /* I'm a comment! */
2017 1) 1.449 us | }
2018
2019
Ingo Molnar57526742009-02-19 12:54:10 +01002020You might find other useful features for this tracer in the
2021following "dynamic ftrace" section such as tracing only specific
2022functions or tasks.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002023
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002024dynamic ftrace
2025--------------
2026
Steven Rostedtf2d9c742008-07-15 10:57:33 -04002027If CONFIG_DYNAMIC_FTRACE is set, the system will run with
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002028virtually no overhead when function tracing is disabled. The way
2029this works is the mcount function call (placed at the start of
Ingo Molnar57526742009-02-19 12:54:10 +01002030every kernel function, produced by the -pg switch in gcc),
2031starts of pointing to a simple return. (Enabling FTRACE will
2032include the -pg switch in the compiling of the kernel.)
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002033
Steven Rostedt9b803c02008-11-03 15:15:08 -05002034At compile time every C file object is run through the
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002035recordmcount program (located in the scripts directory). This
2036program will parse the ELF headers in the C object to find all
2037the locations in the .text section that call mcount. (Note, only
2038white listed .text sections are processed, since processing other
2039sections like .init.text may cause races due to those sections
2040being freed unexpectedly).
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002041
Ingo Molnar57526742009-02-19 12:54:10 +01002042A new section called "__mcount_loc" is created that holds
2043references to all the mcount call sites in the .text section.
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002044The recordmcount program re-links this section back into the
2045original object. The final linking stage of the kernel will add all these
2046references into a single table.
Steven Rostedt9b803c02008-11-03 15:15:08 -05002047
2048On boot up, before SMP is initialized, the dynamic ftrace code
Ingo Molnar57526742009-02-19 12:54:10 +01002049scans this table and updates all the locations into nops. It
2050also records the locations, which are added to the
2051available_filter_functions list. Modules are processed as they
2052are loaded and before they are executed. When a module is
2053unloaded, it also removes its functions from the ftrace function
2054list. This is automatic in the module unload code, and the
2055module author does not need to worry about it.
Steven Rostedt9b803c02008-11-03 15:15:08 -05002056
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002057When tracing is enabled, the process of modifying the function
2058tracepoints is dependent on architecture. The old method is to use
2059kstop_machine to prevent races with the CPUs executing code being
2060modified (which can cause the CPU to do undesirable things, especially
2061if the modified code crosses cache (or page) boundaries), and the nops are
Ingo Molnar57526742009-02-19 12:54:10 +01002062patched back to calls. But this time, they do not call mcount
2063(which is just a function stub). They now call into the ftrace
2064infrastructure.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002065
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002066The new method of modifying the function tracepoints is to place
2067a breakpoint at the location to be modified, sync all CPUs, modify
2068the rest of the instruction not covered by the breakpoint. Sync
2069all CPUs again, and then remove the breakpoint with the finished
2070version to the ftrace call site.
2071
2072Some archs do not even need to monkey around with the synchronization,
2073and can just slap the new code on top of the old without any
2074problems with other CPUs executing it at the same time.
2075
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002076One special side-effect to the recording of the functions being
Steven Rostedtf2d9c742008-07-15 10:57:33 -04002077traced is that we can now selectively choose which functions we
Ingo Molnar57526742009-02-19 12:54:10 +01002078wish to trace and which ones we want the mcount calls to remain
2079as nops.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002080
Ingo Molnar57526742009-02-19 12:54:10 +01002081Two files are used, one for enabling and one for disabling the
2082tracing of specified functions. They are:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002083
2084 set_ftrace_filter
2085
2086and
2087
2088 set_ftrace_notrace
2089
Ingo Molnar57526742009-02-19 12:54:10 +01002090A list of available functions that you can add to these files is
2091listed in:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002092
2093 available_filter_functions
2094
GeunSik Lim156f5a72009-06-02 15:01:37 +09002095 # cat available_filter_functions
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002096put_prev_task_idle
2097kmem_cache_create
2098pick_next_task_rt
2099get_online_cpus
2100pick_next_task_fair
2101mutex_lock
2102[...]
2103
Steven Rostedtf2d9c742008-07-15 10:57:33 -04002104If I am only interested in sys_nanosleep and hrtimer_interrupt:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002105
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002106 # echo sys_nanosleep hrtimer_interrupt > set_ftrace_filter
Yang Hongyang6993b1b2010-01-25 11:10:32 +08002107 # echo function > current_tracer
Steven Rostedt6752ab42011-02-08 13:54:06 -05002108 # echo 1 > tracing_on
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002109 # usleep 1
Steven Rostedt6752ab42011-02-08 13:54:06 -05002110 # echo 0 > tracing_on
GeunSik Lim156f5a72009-06-02 15:01:37 +09002111 # cat trace
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002112# tracer: function
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002113#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002114# entries-in-buffer/entries-written: 5/5 #P:4
2115#
2116# _-----=> irqs-off
2117# / _----=> need-resched
2118# | / _---=> hardirq/softirq
2119# || / _--=> preempt-depth
2120# ||| / delay
2121# TASK-PID CPU# |||| TIMESTAMP FUNCTION
2122# | | | |||| | |
2123 usleep-2665 [001] .... 4186.475355: sys_nanosleep <-system_call_fastpath
2124 <idle>-0 [001] d.h1 4186.475409: hrtimer_interrupt <-smp_apic_timer_interrupt
2125 usleep-2665 [001] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt
2126 <idle>-0 [003] d.h1 4186.475426: hrtimer_interrupt <-smp_apic_timer_interrupt
2127 <idle>-0 [002] d.h1 4186.475427: hrtimer_interrupt <-smp_apic_timer_interrupt
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002128
Steven Rostedtf2d9c742008-07-15 10:57:33 -04002129To see which functions are being traced, you can cat the file:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002130
GeunSik Lim156f5a72009-06-02 15:01:37 +09002131 # cat set_ftrace_filter
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002132hrtimer_interrupt
2133sys_nanosleep
2134
2135
Ingo Molnar57526742009-02-19 12:54:10 +01002136Perhaps this is not enough. The filters also allow simple wild
2137cards. Only the following are currently available
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002138
Steven Rostedta41eeba2008-07-14 16:41:12 -04002139 <match>* - will match functions that begin with <match>
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002140 *<match> - will match functions that end with <match>
2141 *<match>* - will match functions that have <match> in it
2142
Steven Rostedtf2d9c742008-07-15 10:57:33 -04002143These are the only wild cards which are supported.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002144
2145 <match>*<match> will not work.
2146
Ingo Molnar57526742009-02-19 12:54:10 +01002147Note: It is better to use quotes to enclose the wild cards,
2148 otherwise the shell may expand the parameters into names
2149 of files in the local directory.
walimisc072c242008-11-28 12:21:19 +08002150
GeunSik Lim156f5a72009-06-02 15:01:37 +09002151 # echo 'hrtimer_*' > set_ftrace_filter
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002152
2153Produces:
2154
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002155# tracer: function
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002156#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002157# entries-in-buffer/entries-written: 897/897 #P:4
2158#
2159# _-----=> irqs-off
2160# / _----=> need-resched
2161# | / _---=> hardirq/softirq
2162# || / _--=> preempt-depth
2163# ||| / delay
2164# TASK-PID CPU# |||| TIMESTAMP FUNCTION
2165# | | | |||| | |
2166 <idle>-0 [003] dN.1 4228.547803: hrtimer_cancel <-tick_nohz_idle_exit
2167 <idle>-0 [003] dN.1 4228.547804: hrtimer_try_to_cancel <-hrtimer_cancel
2168 <idle>-0 [003] dN.2 4228.547805: hrtimer_force_reprogram <-__remove_hrtimer
2169 <idle>-0 [003] dN.1 4228.547805: hrtimer_forward <-tick_nohz_idle_exit
2170 <idle>-0 [003] dN.1 4228.547805: hrtimer_start_range_ns <-hrtimer_start_expires.constprop.11
2171 <idle>-0 [003] d..1 4228.547858: hrtimer_get_next_event <-get_next_timer_interrupt
2172 <idle>-0 [003] d..1 4228.547859: hrtimer_start <-__tick_nohz_idle_enter
2173 <idle>-0 [003] d..2 4228.547860: hrtimer_force_reprogram <-__rem
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002174
2175Notice that we lost the sys_nanosleep.
2176
GeunSik Lim156f5a72009-06-02 15:01:37 +09002177 # cat set_ftrace_filter
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002178hrtimer_run_queues
2179hrtimer_run_pending
2180hrtimer_init
2181hrtimer_cancel
2182hrtimer_try_to_cancel
2183hrtimer_forward
2184hrtimer_start
2185hrtimer_reprogram
2186hrtimer_force_reprogram
2187hrtimer_get_next_event
2188hrtimer_interrupt
2189hrtimer_nanosleep
2190hrtimer_wakeup
2191hrtimer_get_remaining
2192hrtimer_get_res
2193hrtimer_init_sleeper
2194
2195
2196This is because the '>' and '>>' act just like they do in bash.
2197To rewrite the filters, use '>'
2198To append to the filters, use '>>'
2199
Ingo Molnar57526742009-02-19 12:54:10 +01002200To clear out a filter so that all functions will be recorded
2201again:
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002202
GeunSik Lim156f5a72009-06-02 15:01:37 +09002203 # echo > set_ftrace_filter
2204 # cat set_ftrace_filter
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002205 #
2206
2207Again, now we want to append.
2208
GeunSik Lim156f5a72009-06-02 15:01:37 +09002209 # echo sys_nanosleep > set_ftrace_filter
2210 # cat set_ftrace_filter
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002211sys_nanosleep
GeunSik Lim156f5a72009-06-02 15:01:37 +09002212 # echo 'hrtimer_*' >> set_ftrace_filter
2213 # cat set_ftrace_filter
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002214hrtimer_run_queues
2215hrtimer_run_pending
2216hrtimer_init
2217hrtimer_cancel
2218hrtimer_try_to_cancel
2219hrtimer_forward
2220hrtimer_start
2221hrtimer_reprogram
2222hrtimer_force_reprogram
2223hrtimer_get_next_event
2224hrtimer_interrupt
2225sys_nanosleep
2226hrtimer_nanosleep
2227hrtimer_wakeup
2228hrtimer_get_remaining
2229hrtimer_get_res
2230hrtimer_init_sleeper
2231
2232
Ingo Molnar57526742009-02-19 12:54:10 +01002233The set_ftrace_notrace prevents those functions from being
2234traced.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002235
GeunSik Lim156f5a72009-06-02 15:01:37 +09002236 # echo '*preempt*' '*lock*' > set_ftrace_notrace
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002237
2238Produces:
2239
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002240# tracer: function
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002241#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002242# entries-in-buffer/entries-written: 39608/39608 #P:4
2243#
2244# _-----=> irqs-off
2245# / _----=> need-resched
2246# | / _---=> hardirq/softirq
2247# || / _--=> preempt-depth
2248# ||| / delay
2249# TASK-PID CPU# |||| TIMESTAMP FUNCTION
2250# | | | |||| | |
2251 bash-1994 [000] .... 4342.324896: file_ra_state_init <-do_dentry_open
2252 bash-1994 [000] .... 4342.324897: open_check_o_direct <-do_last
2253 bash-1994 [000] .... 4342.324897: ima_file_check <-do_last
2254 bash-1994 [000] .... 4342.324898: process_measurement <-ima_file_check
2255 bash-1994 [000] .... 4342.324898: ima_get_action <-process_measurement
2256 bash-1994 [000] .... 4342.324898: ima_match_policy <-ima_get_action
2257 bash-1994 [000] .... 4342.324899: do_truncate <-do_last
2258 bash-1994 [000] .... 4342.324899: should_remove_suid <-do_truncate
2259 bash-1994 [000] .... 4342.324899: notify_change <-do_truncate
2260 bash-1994 [000] .... 4342.324900: current_fs_time <-notify_change
2261 bash-1994 [000] .... 4342.324900: current_kernel_time <-current_fs_time
2262 bash-1994 [000] .... 4342.324900: timespec_trunc <-current_fs_time
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002263
2264We can see that there's no more lock or preempt tracing.
2265
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002266
Ingo Molnar57526742009-02-19 12:54:10 +01002267Dynamic ftrace with the function graph tracer
2268---------------------------------------------
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002269
Ingo Molnar57526742009-02-19 12:54:10 +01002270Although what has been explained above concerns both the
2271function tracer and the function-graph-tracer, there are some
2272special features only available in the function-graph tracer.
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002273
Ingo Molnar57526742009-02-19 12:54:10 +01002274If you want to trace only one function and all of its children,
2275you just have to echo its name into set_graph_function:
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002276
Ingo Molnar57526742009-02-19 12:54:10 +01002277 echo __do_fault > set_graph_function
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002278
Ingo Molnar57526742009-02-19 12:54:10 +01002279will produce the following "expanded" trace of the __do_fault()
2280function:
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002281
2282 0) | __do_fault() {
2283 0) | filemap_fault() {
2284 0) | find_lock_page() {
2285 0) 0.804 us | find_get_page();
2286 0) | __might_sleep() {
2287 0) 1.329 us | }
2288 0) 3.904 us | }
2289 0) 4.979 us | }
2290 0) 0.653 us | _spin_lock();
2291 0) 0.578 us | page_add_file_rmap();
2292 0) 0.525 us | native_set_pte_at();
2293 0) 0.585 us | _spin_unlock();
2294 0) | unlock_page() {
2295 0) 0.541 us | page_waitqueue();
2296 0) 0.639 us | __wake_up_bit();
2297 0) 2.786 us | }
2298 0) + 14.237 us | }
2299 0) | __do_fault() {
2300 0) | filemap_fault() {
2301 0) | find_lock_page() {
2302 0) 0.698 us | find_get_page();
2303 0) | __might_sleep() {
2304 0) 1.412 us | }
2305 0) 3.950 us | }
2306 0) 5.098 us | }
2307 0) 0.631 us | _spin_lock();
2308 0) 0.571 us | page_add_file_rmap();
2309 0) 0.526 us | native_set_pte_at();
2310 0) 0.586 us | _spin_unlock();
2311 0) | unlock_page() {
2312 0) 0.533 us | page_waitqueue();
2313 0) 0.638 us | __wake_up_bit();
2314 0) 2.793 us | }
2315 0) + 14.012 us | }
2316
Ingo Molnar57526742009-02-19 12:54:10 +01002317You can also expand several functions at once:
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002318
Ingo Molnar57526742009-02-19 12:54:10 +01002319 echo sys_open > set_graph_function
2320 echo sys_close >> set_graph_function
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002321
Ingo Molnar57526742009-02-19 12:54:10 +01002322Now if you want to go back to trace all functions you can clear
2323this special filter via:
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002324
Ingo Molnar57526742009-02-19 12:54:10 +01002325 echo > set_graph_function
Frederic Weisbecker985ec202009-02-18 06:35:34 +01002326
2327
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002328ftrace_enabled
2329--------------
2330
2331Note, the proc sysctl ftrace_enable is a big on/off switch for the
2332function tracer. By default it is enabled (when function tracing is
2333enabled in the kernel). If it is disabled, all function tracing is
2334disabled. This includes not only the function tracers for ftrace, but
2335also for any other uses (perf, kprobes, stack tracing, profiling, etc).
2336
2337Please disable this with care.
2338
2339This can be disable (and enabled) with:
2340
2341 sysctl kernel.ftrace_enabled=0
2342 sysctl kernel.ftrace_enabled=1
2343
2344 or
2345
2346 echo 0 > /proc/sys/kernel/ftrace_enabled
2347 echo 1 > /proc/sys/kernel/ftrace_enabled
2348
2349
Chase Douglas07271aa2010-04-23 14:02:39 -04002350Filter commands
2351---------------
2352
2353A few commands are supported by the set_ftrace_filter interface.
2354Trace commands have the following format:
2355
2356<function>:<command>:<parameter>
2357
2358The following commands are supported:
2359
2360- mod
2361 This command enables function filtering per module. The
2362 parameter defines the module. For example, if only the write*
2363 functions in the ext3 module are desired, run:
2364
2365 echo 'write*:mod:ext3' > set_ftrace_filter
2366
2367 This command interacts with the filter in the same way as
2368 filtering based on function names. Thus, adding more functions
2369 in a different module is accomplished by appending (>>) to the
2370 filter file. Remove specific module functions by prepending
2371 '!':
2372
2373 echo '!writeback*:mod:ext3' >> set_ftrace_filter
2374
2375- traceon/traceoff
2376 These commands turn tracing on and off when the specified
2377 functions are hit. The parameter determines how many times the
2378 tracing system is turned on and off. If unspecified, there is
2379 no limit. For example, to disable tracing when a schedule bug
2380 is hit the first 5 times, run:
2381
2382 echo '__schedule_bug:traceoff:5' > set_ftrace_filter
2383
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002384 To always disable tracing when __schedule_bug is hit:
2385
2386 echo '__schedule_bug:traceoff' > set_ftrace_filter
2387
Chase Douglas07271aa2010-04-23 14:02:39 -04002388 These commands are cumulative whether or not they are appended
2389 to set_ftrace_filter. To remove a command, prepend it by '!'
2390 and drop the parameter:
2391
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002392 echo '!__schedule_bug:traceoff:0' > set_ftrace_filter
2393
2394 The above removes the traceoff command for __schedule_bug
2395 that have a counter. To remove commands without counters:
2396
Chase Douglas07271aa2010-04-23 14:02:39 -04002397 echo '!__schedule_bug:traceoff' > set_ftrace_filter
2398
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002399- snapshot
2400 Will cause a snapshot to be triggered when the function is hit.
2401
2402 echo 'native_flush_tlb_others:snapshot' > set_ftrace_filter
2403
2404 To only snapshot once:
2405
2406 echo 'native_flush_tlb_others:snapshot:1' > set_ftrace_filter
2407
2408 To remove the above commands:
2409
2410 echo '!native_flush_tlb_others:snapshot' > set_ftrace_filter
2411 echo '!native_flush_tlb_others:snapshot:0' > set_ftrace_filter
2412
2413- enable_event/disable_event
2414 These commands can enable or disable a trace event. Note, because
2415 function tracing callbacks are very sensitive, when these commands
2416 are registered, the trace point is activated, but disabled in
2417 a "soft" mode. That is, the tracepoint will be called, but
2418 just will not be traced. The event tracepoint stays in this mode
2419 as long as there's a command that triggers it.
2420
2421 echo 'try_to_wake_up:enable_event:sched:sched_switch:2' > \
2422 set_ftrace_filter
2423
2424 The format is:
2425
2426 <function>:enable_event:<system>:<event>[:count]
2427 <function>:disable_event:<system>:<event>[:count]
2428
2429 To remove the events commands:
2430
2431
2432 echo '!try_to_wake_up:enable_event:sched:sched_switch:0' > \
2433 set_ftrace_filter
2434 echo '!schedule:disable_event:sched:sched_switch' > \
2435 set_ftrace_filter
Chase Douglas07271aa2010-04-23 14:02:39 -04002436
Steven Rostedt (Red Hat)ad71d882013-04-30 15:46:14 -04002437- dump
2438 When the function is hit, it will dump the contents of the ftrace
2439 ring buffer to the console. This is useful if you need to debug
2440 something, and want to dump the trace when a certain function
2441 is hit. Perhaps its a function that is called before a tripple
2442 fault happens and does not allow you to get a regular dump.
2443
Steven Rostedt (Red Hat)90e3c032013-04-30 19:00:46 -04002444- cpudump
2445 When the function is hit, it will dump the contents of the ftrace
2446 ring buffer for the current CPU to the console. Unlike the "dump"
2447 command, it only prints out the contents of the ring buffer for the
2448 CPU that executed the function that triggered the dump.
2449
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002450trace_pipe
2451----------
2452
Ingo Molnar57526742009-02-19 12:54:10 +01002453The trace_pipe outputs the same content as the trace file, but
2454the effect on the tracing is different. Every read from
2455trace_pipe is consumed. This means that subsequent reads will be
2456different. The trace is live.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002457
GeunSik Lim156f5a72009-06-02 15:01:37 +09002458 # echo function > current_tracer
2459 # cat trace_pipe > /tmp/trace.out &
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002460[1] 4153
Steven Rostedt6752ab42011-02-08 13:54:06 -05002461 # echo 1 > tracing_on
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002462 # usleep 1
Steven Rostedt6752ab42011-02-08 13:54:06 -05002463 # echo 0 > tracing_on
GeunSik Lim156f5a72009-06-02 15:01:37 +09002464 # cat trace
Steven Rostedt9b803c02008-11-03 15:15:08 -05002465# tracer: function
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002466#
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002467# entries-in-buffer/entries-written: 0/0 #P:4
2468#
2469# _-----=> irqs-off
2470# / _----=> need-resched
2471# | / _---=> hardirq/softirq
2472# || / _--=> preempt-depth
2473# ||| / delay
2474# TASK-PID CPU# |||| TIMESTAMP FUNCTION
2475# | | | |||| | |
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002476
2477 #
2478 # cat /tmp/trace.out
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002479 bash-1994 [000] .... 5281.568961: mutex_unlock <-rb_simple_write
2480 bash-1994 [000] .... 5281.568963: __mutex_unlock_slowpath <-mutex_unlock
2481 bash-1994 [000] .... 5281.568963: __fsnotify_parent <-fsnotify_modify
2482 bash-1994 [000] .... 5281.568964: fsnotify <-fsnotify_modify
2483 bash-1994 [000] .... 5281.568964: __srcu_read_lock <-fsnotify
2484 bash-1994 [000] .... 5281.568964: add_preempt_count <-__srcu_read_lock
2485 bash-1994 [000] ...1 5281.568965: sub_preempt_count <-__srcu_read_lock
2486 bash-1994 [000] .... 5281.568965: __srcu_read_unlock <-fsnotify
2487 bash-1994 [000] .... 5281.568967: sys_dup2 <-system_call_fastpath
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002488
2489
Ingo Molnar57526742009-02-19 12:54:10 +01002490Note, reading the trace_pipe file will block until more input is
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002491added.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002492
2493trace entries
2494-------------
2495
Ingo Molnar57526742009-02-19 12:54:10 +01002496Having too much or not enough data can be troublesome in
2497diagnosing an issue in the kernel. The file buffer_size_kb is
2498used to modify the size of the internal trace buffers. The
2499number listed is the number of entries that can be recorded per
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002500CPU. To know the full size, multiply the number of possible CPUs
Ingo Molnar57526742009-02-19 12:54:10 +01002501with the number of entries.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002502
GeunSik Lim156f5a72009-06-02 15:01:37 +09002503 # cat buffer_size_kb
Steven Rostedt1696b2b2008-11-13 00:09:35 -050025041408 (units kilobytes)
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002505
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002506Or simply read buffer_total_size_kb
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002507
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002508 # cat buffer_total_size_kb
25095632
2510
2511To modify the buffer, simple echo in a number (in 1024 byte segments).
2512
GeunSik Lim156f5a72009-06-02 15:01:37 +09002513 # echo 10000 > buffer_size_kb
2514 # cat buffer_size_kb
Steven Rostedt1696b2b2008-11-13 00:09:35 -0500251510000 (units kilobytes)
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002516
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002517It will try to allocate as much as possible. If you allocate too
2518much, it can cause Out-Of-Memory to trigger.
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002519
GeunSik Lim156f5a72009-06-02 15:01:37 +09002520 # echo 1000000000000 > buffer_size_kb
Steven Rostedteb6d42e2008-07-10 12:46:01 -04002521-bash: echo: write error: Cannot allocate memory
GeunSik Lim156f5a72009-06-02 15:01:37 +09002522 # cat buffer_size_kb
Steven Rostedteb6d42e2008-07-10 12:46:01 -0400252385
2524
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002525The per_cpu buffers can be changed individually as well:
2526
2527 # echo 10000 > per_cpu/cpu0/buffer_size_kb
2528 # echo 100 > per_cpu/cpu1/buffer_size_kb
2529
2530When the per_cpu buffers are not the same, the buffer_size_kb
2531at the top level will just show an X
2532
2533 # cat buffer_size_kb
2534X
2535
2536This is where the buffer_total_size_kb is useful:
2537
2538 # cat buffer_total_size_kb
253912916
2540
2541Writing to the top level buffer_size_kb will reset all the buffers
2542to be the same again.
2543
Hiraku Toyookac1043fc2012-12-26 11:53:09 +09002544Snapshot
2545--------
2546CONFIG_TRACER_SNAPSHOT makes a generic snapshot feature
2547available to all non latency tracers. (Latency tracers which
2548record max latency, such as "irqsoff" or "wakeup", can't use
2549this feature, since those are already using the snapshot
2550mechanism internally.)
2551
2552Snapshot preserves a current trace buffer at a particular point
2553in time without stopping tracing. Ftrace swaps the current
2554buffer with a spare buffer, and tracing continues in the new
2555current (=previous spare) buffer.
2556
2557The following debugfs files in "tracing" are related to this
2558feature:
2559
2560 snapshot:
2561
2562 This is used to take a snapshot and to read the output
2563 of the snapshot. Echo 1 into this file to allocate a
2564 spare buffer and to take a snapshot (swap), then read
2565 the snapshot from this file in the same format as
2566 "trace" (described above in the section "The File
2567 System"). Both reads snapshot and tracing are executable
2568 in parallel. When the spare buffer is allocated, echoing
2569 0 frees it, and echoing else (positive) values clear the
2570 snapshot contents.
2571 More details are shown in the table below.
2572
2573 status\input | 0 | 1 | else |
2574 --------------+------------+------------+------------+
Hiraku Toyooka1abccd72013-03-08 16:32:25 +09002575 not allocated |(do nothing)| alloc+swap |(do nothing)|
Hiraku Toyookac1043fc2012-12-26 11:53:09 +09002576 --------------+------------+------------+------------+
2577 allocated | free | swap | clear |
2578 --------------+------------+------------+------------+
2579
2580Here is an example of using the snapshot feature.
2581
2582 # echo 1 > events/sched/enable
2583 # echo 1 > snapshot
2584 # cat snapshot
2585# tracer: nop
2586#
2587# entries-in-buffer/entries-written: 71/71 #P:8
2588#
2589# _-----=> irqs-off
2590# / _----=> need-resched
2591# | / _---=> hardirq/softirq
2592# || / _--=> preempt-depth
2593# ||| / delay
2594# TASK-PID CPU# |||| TIMESTAMP FUNCTION
2595# | | | |||| | |
2596 <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
2597 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
2598[...]
2599 <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
2600
2601 # cat trace
2602# tracer: nop
2603#
2604# entries-in-buffer/entries-written: 77/77 #P:8
2605#
2606# _-----=> irqs-off
2607# / _----=> need-resched
2608# | / _---=> hardirq/softirq
2609# || / _--=> preempt-depth
2610# ||| / delay
2611# TASK-PID CPU# |||| TIMESTAMP FUNCTION
2612# | | | |||| | |
2613 <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
2614 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
2615[...]
2616
2617
2618If you try to use this snapshot feature when current tracer is
2619one of the latency tracers, you will get the following results.
2620
2621 # echo wakeup > current_tracer
2622 # echo 1 > snapshot
2623bash: echo: write error: Device or resource busy
2624 # cat snapshot
2625cat: snapshot: Device or resource busy
2626
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002627
2628Instances
2629---------
2630In the debugfs tracing directory is a directory called "instances".
2631This directory can have new directories created inside of it using
2632mkdir, and removing directories with rmdir. The directory created
2633with mkdir in this directory will already contain files and other
2634directories after it is created.
2635
2636 # mkdir instances/foo
2637 # ls instances/foo
2638buffer_size_kb buffer_total_size_kb events free_buffer per_cpu
2639set_event snapshot trace trace_clock trace_marker trace_options
2640trace_pipe tracing_on
2641
2642As you can see, the new directory looks similar to the tracing directory
2643itself. In fact, it is very similar, except that the buffer and
2644events are agnostic from the main director, or from any other
2645instances that are created.
2646
2647The files in the new directory work just like the files with the
2648same name in the tracing directory except the buffer that is used
2649is a separate and new buffer. The files affect that buffer but do not
2650affect the main buffer with the exception of trace_options. Currently,
2651the trace_options affect all instances and the top level buffer
2652the same, but this may change in future releases. That is, options
2653may become specific to the instance they reside in.
2654
2655Notice that none of the function tracer files are there, nor is
2656current_tracer and available_tracers. This is because the buffers
2657can currently only have events enabled for them.
2658
2659 # mkdir instances/foo
2660 # mkdir instances/bar
2661 # mkdir instances/zoot
2662 # echo 100000 > buffer_size_kb
2663 # echo 1000 > instances/foo/buffer_size_kb
2664 # echo 5000 > instances/bar/per_cpu/cpu1/buffer_size_kb
2665 # echo function > current_trace
2666 # echo 1 > instances/foo/events/sched/sched_wakeup/enable
2667 # echo 1 > instances/foo/events/sched/sched_wakeup_new/enable
2668 # echo 1 > instances/foo/events/sched/sched_switch/enable
2669 # echo 1 > instances/bar/events/irq/enable
2670 # echo 1 > instances/zoot/events/syscalls/enable
2671 # cat trace_pipe
2672CPU:2 [LOST 11745 EVENTS]
2673 bash-2044 [002] .... 10594.481032: _raw_spin_lock_irqsave <-get_page_from_freelist
2674 bash-2044 [002] d... 10594.481032: add_preempt_count <-_raw_spin_lock_irqsave
2675 bash-2044 [002] d..1 10594.481032: __rmqueue <-get_page_from_freelist
2676 bash-2044 [002] d..1 10594.481033: _raw_spin_unlock <-get_page_from_freelist
2677 bash-2044 [002] d..1 10594.481033: sub_preempt_count <-_raw_spin_unlock
2678 bash-2044 [002] d... 10594.481033: get_pageblock_flags_group <-get_pageblock_migratetype
2679 bash-2044 [002] d... 10594.481034: __mod_zone_page_state <-get_page_from_freelist
2680 bash-2044 [002] d... 10594.481034: zone_statistics <-get_page_from_freelist
2681 bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics
2682 bash-2044 [002] d... 10594.481034: __inc_zone_state <-zone_statistics
2683 bash-2044 [002] .... 10594.481035: arch_dup_task_struct <-copy_process
2684[...]
2685
2686 # cat instances/foo/trace_pipe
2687 bash-1998 [000] d..4 136.676759: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000
2688 bash-1998 [000] dN.4 136.676760: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000
2689 <idle>-0 [003] d.h3 136.676906: sched_wakeup: comm=rcu_preempt pid=9 prio=120 success=1 target_cpu=003
2690 <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
2691 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
2692 bash-1998 [000] d..4 136.677014: sched_wakeup: comm=kworker/0:1 pid=59 prio=120 success=1 target_cpu=000
2693 bash-1998 [000] dN.4 136.677016: sched_wakeup: comm=bash pid=1998 prio=120 success=1 target_cpu=000
2694 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
2695 kworker/0:1-59 [000] d..4 136.677022: sched_wakeup: comm=sshd pid=1995 prio=120 success=1 target_cpu=001
2696 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
2697[...]
2698
2699 # cat instances/bar/trace_pipe
2700 migration/1-14 [001] d.h3 138.732674: softirq_raise: vec=3 [action=NET_RX]
2701 <idle>-0 [001] dNh3 138.732725: softirq_raise: vec=3 [action=NET_RX]
2702 bash-1998 [000] d.h1 138.733101: softirq_raise: vec=1 [action=TIMER]
2703 bash-1998 [000] d.h1 138.733102: softirq_raise: vec=9 [action=RCU]
2704 bash-1998 [000] ..s2 138.733105: softirq_entry: vec=1 [action=TIMER]
2705 bash-1998 [000] ..s2 138.733106: softirq_exit: vec=1 [action=TIMER]
2706 bash-1998 [000] ..s2 138.733106: softirq_entry: vec=9 [action=RCU]
2707 bash-1998 [000] ..s2 138.733109: softirq_exit: vec=9 [action=RCU]
2708 sshd-1995 [001] d.h1 138.733278: irq_handler_entry: irq=21 name=uhci_hcd:usb4
2709 sshd-1995 [001] d.h1 138.733280: irq_handler_exit: irq=21 ret=unhandled
2710 sshd-1995 [001] d.h1 138.733281: irq_handler_entry: irq=21 name=eth0
2711 sshd-1995 [001] d.h1 138.733283: irq_handler_exit: irq=21 ret=handled
2712[...]
2713
2714 # cat instances/zoot/trace
2715# tracer: nop
2716#
2717# entries-in-buffer/entries-written: 18996/18996 #P:4
2718#
2719# _-----=> irqs-off
2720# / _----=> need-resched
2721# | / _---=> hardirq/softirq
2722# || / _--=> preempt-depth
2723# ||| / delay
2724# TASK-PID CPU# |||| TIMESTAMP FUNCTION
2725# | | | |||| | |
2726 bash-1998 [000] d... 140.733501: sys_write -> 0x2
2727 bash-1998 [000] d... 140.733504: sys_dup2(oldfd: a, newfd: 1)
2728 bash-1998 [000] d... 140.733506: sys_dup2 -> 0x1
2729 bash-1998 [000] d... 140.733508: sys_fcntl(fd: a, cmd: 1, arg: 0)
2730 bash-1998 [000] d... 140.733509: sys_fcntl -> 0x1
2731 bash-1998 [000] d... 140.733510: sys_close(fd: a)
2732 bash-1998 [000] d... 140.733510: sys_close -> 0x0
2733 bash-1998 [000] d... 140.733514: sys_rt_sigprocmask(how: 0, nset: 0, oset: 6e2768, sigsetsize: 8)
2734 bash-1998 [000] d... 140.733515: sys_rt_sigprocmask -> 0x0
2735 bash-1998 [000] d... 140.733516: sys_rt_sigaction(sig: 2, act: 7fff718846f0, oact: 7fff71884650, sigsetsize: 8)
2736 bash-1998 [000] d... 140.733516: sys_rt_sigaction -> 0x0
2737
2738You can see that the trace of the top most trace buffer shows only
2739the function tracing. The foo instance displays wakeups and task
2740switches.
2741
2742To remove the instances, simply delete their directories:
2743
2744 # rmdir instances/foo
2745 # rmdir instances/bar
2746 # rmdir instances/zoot
2747
2748Note, if a process has a trace file open in one of the instance
2749directories, the rmdir will fail with EBUSY.
2750
2751
2752Stack trace
Ingo Molnar57526742009-02-19 12:54:10 +01002753-----------
Steven Rostedt (Red Hat)8d016092013-03-13 11:05:11 -04002754Since the kernel has a fixed sized stack, it is important not to
2755waste it in functions. A kernel developer must be conscience of
2756what they allocate on the stack. If they add too much, the system
2757can be in danger of a stack overflow, and corruption will occur,
2758usually leading to a system panic.
2759
2760There are some tools that check this, usually with interrupts
2761periodically checking usage. But if you can perform a check
2762at every function call that will become very useful. As ftrace provides
2763a function tracer, it makes it convenient to check the stack size
2764at every function call. This is enabled via the stack tracer.
2765
2766CONFIG_STACK_TRACER enables the ftrace stack tracing functionality.
2767To enable it, write a '1' into /proc/sys/kernel/stack_tracer_enabled.
2768
2769 # echo 1 > /proc/sys/kernel/stack_tracer_enabled
2770
2771You can also enable it from the kernel command line to trace
2772the stack size of the kernel during boot up, by adding "stacktrace"
2773to the kernel command line parameter.
2774
2775After running it for a few minutes, the output looks like:
2776
2777 # cat stack_max_size
27782928
2779
2780 # cat stack_trace
2781 Depth Size Location (18 entries)
2782 ----- ---- --------
2783 0) 2928 224 update_sd_lb_stats+0xbc/0x4ac
2784 1) 2704 160 find_busiest_group+0x31/0x1f1
2785 2) 2544 256 load_balance+0xd9/0x662
2786 3) 2288 80 idle_balance+0xbb/0x130
2787 4) 2208 128 __schedule+0x26e/0x5b9
2788 5) 2080 16 schedule+0x64/0x66
2789 6) 2064 128 schedule_timeout+0x34/0xe0
2790 7) 1936 112 wait_for_common+0x97/0xf1
2791 8) 1824 16 wait_for_completion+0x1d/0x1f
2792 9) 1808 128 flush_work+0xfe/0x119
2793 10) 1680 16 tty_flush_to_ldisc+0x1e/0x20
2794 11) 1664 48 input_available_p+0x1d/0x5c
2795 12) 1616 48 n_tty_poll+0x6d/0x134
2796 13) 1568 64 tty_poll+0x64/0x7f
2797 14) 1504 880 do_select+0x31e/0x511
2798 15) 624 400 core_sys_select+0x177/0x216
2799 16) 224 96 sys_select+0x91/0xb9
2800 17) 128 128 system_call_fastpath+0x16/0x1b
2801
2802Note, if -mfentry is being used by gcc, functions get traced before
2803they set up the stack frame. This means that leaf level functions
2804are not tested by the stack tracer when -mfentry is used.
2805
2806Currently, -mfentry is used by gcc 4.6.0 and above on x86 only.
2807
2808---------
Ingo Molnar57526742009-02-19 12:54:10 +01002809
2810More details can be found in the source code, in the
GeunSik Limbaf20b32009-06-01 10:49:41 +02002811kernel/trace/*.c files.