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1perf-intel-pt(1)
2================
3
4NAME
5----
6perf-intel-pt - Support for Intel Processor Trace within perf tools
7
8SYNOPSIS
9--------
10[verse]
11'perf record' -e intel_pt//
12
13DESCRIPTION
14-----------
15
16Intel Processor Trace (Intel PT) is an extension of Intel Architecture that
17collects information about software execution such as control flow, execution
18modes and timings and formats it into highly compressed binary packets.
19Technical details are documented in the Intel 64 and IA-32 Architectures
20Software Developer Manuals, Chapter 36 Intel Processor Trace.
21
22Intel PT is first supported in Intel Core M and 5th generation Intel Core
23processors that are based on the Intel micro-architecture code name Broadwell.
24
25Trace data is collected by 'perf record' and stored within the perf.data file.
26See below for options to 'perf record'.
27
28Trace data must be 'decoded' which involves walking the object code and matching
29the trace data packets. For example a TNT packet only tells whether a
30conditional branch was taken or not taken, so to make use of that packet the
31decoder must know precisely which instruction was being executed.
32
33Decoding is done on-the-fly. The decoder outputs samples in the same format as
34samples output by perf hardware events, for example as though the "instructions"
35or "branches" events had been recorded. Presently 3 tools support this:
36'perf script', 'perf report' and 'perf inject'. See below for more information
37on using those tools.
38
39The main distinguishing feature of Intel PT is that the decoder can determine
40the exact flow of software execution. Intel PT can be used to understand why
41and how did software get to a certain point, or behave a certain way. The
42software does not have to be recompiled, so Intel PT works with debug or release
43builds, however the executed images are needed - which makes use in JIT-compiled
44environments, or with self-modified code, a challenge. Also symbols need to be
45provided to make sense of addresses.
46
47A limitation of Intel PT is that it produces huge amounts of trace data
48(hundreds of megabytes per second per core) which takes a long time to decode,
49for example two or three orders of magnitude longer than it took to collect.
50Another limitation is the performance impact of tracing, something that will
51vary depending on the use-case and architecture.
52
53
54Quickstart
55----------
56
57It is important to start small. That is because it is easy to capture vastly
58more data than can possibly be processed.
59
60The simplest thing to do with Intel PT is userspace profiling of small programs.
61Data is captured with 'perf record' e.g. to trace 'ls' userspace-only:
62
63 perf record -e intel_pt//u ls
64
65And profiled with 'perf report' e.g.
66
67 perf report
68
69To also trace kernel space presents a problem, namely kernel self-modifying
70code. A fairly good kernel image is available in /proc/kcore but to get an
71accurate image a copy of /proc/kcore needs to be made under the same conditions
72as the data capture. 'perf record' can make a copy of /proc/kcore if the option
73--kcore is used, but access to /proc/kcore is restricted e.g.
74
75 sudo perf record -o pt_ls --kcore -e intel_pt// -- ls
76
77which will create a directory named 'pt_ls' and put the perf.data file (named
78simply 'data') and copies of /proc/kcore, /proc/kallsyms and /proc/modules into
79it. The other tools understand the directory format, so to use 'perf report'
80becomes:
81
82 sudo perf report -i pt_ls
83
84Because samples are synthesized after-the-fact, the sampling period can be
85selected for reporting. e.g. sample every microsecond
86
87 sudo perf report pt_ls --itrace=i1usge
88
89See the sections below for more information about the --itrace option.
90
91Beware the smaller the period, the more samples that are produced, and the
92longer it takes to process them.
93
94Also note that the coarseness of Intel PT timing information will start to
95distort the statistical value of the sampling as the sampling period becomes
96smaller.
97
98To represent software control flow, "branches" samples are produced. By default
99a branch sample is synthesized for every single branch. To get an idea what
100data is available you can use the 'perf script' tool with all itrace sampling
101options, which will list all the samples.
102
103 perf record -e intel_pt//u ls
104 perf script --itrace=ibxwpe
105
106An interesting field that is not printed by default is 'flags' which can be
107displayed as follows:
108
109 perf script --itrace=ibxwpe -F+flags
110
111The flags are "bcrosyiABExghDt" which stand for branch, call, return, conditional,
112system, asynchronous, interrupt, transaction abort, trace begin, trace end,
113in transaction, VM-entry, VM-exit, interrupt disabled, and interrupt disable
114toggle respectively.
115
116perf script also supports higher level ways to dump instruction traces:
117
118 perf script --insn-trace --xed
119
120Dump all instructions. This requires installing the xed tool (see XED below)
121Dumping all instructions in a long trace can be fairly slow. It is usually better
122to start with higher level decoding, like
123
124 perf script --call-trace
125
126or
127
128 perf script --call-ret-trace
129
130and then select a time range of interest. The time range can then be examined
131in detail with
132
133 perf script --time starttime,stoptime --insn-trace --xed
134
135While examining the trace it's also useful to filter on specific CPUs using
136the -C option
137
138 perf script --time starttime,stoptime --insn-trace --xed -C 1
139
140Dump all instructions in time range on CPU 1.
141
142Another interesting field that is not printed by default is 'ipc' which can be
143displayed as follows:
144
145 perf script --itrace=be -F+ipc
146
147There are two ways that instructions-per-cycle (IPC) can be calculated depending
148on the recording.
149
150If the 'cyc' config term (see config terms section below) was used, then IPC is
151calculated using the cycle count from CYC packets, otherwise MTC packets are
152used - refer to the 'mtc' config term. When MTC is used, however, the values
153are less accurate because the timing is less accurate.
154
155Because Intel PT does not update the cycle count on every branch or instruction,
156the values will often be zero. When there are values, they will be the number
157of instructions and number of cycles since the last update, and thus represent
158the average IPC since the last IPC for that event type. Note IPC for "branches"
159events is calculated separately from IPC for "instructions" events.
160
161Even with the 'cyc' config term, it is possible to produce IPC information for
162every change of timestamp, but at the expense of accuracy. That is selected by
163specifying the itrace 'A' option. Due to the granularity of timestamps, the
164actual number of cycles increases even though the cycles reported does not.
165The number of instructions is known, but if IPC is reported, cycles can be too
166low and so IPC is too high. Note that inaccuracy decreases as the period of
167sampling increases i.e. if the number of cycles is too low by a small amount,
168that becomes less significant if the number of cycles is large. It may also be
169useful to use the 'A' option in conjunction with dlfilter-show-cycles.so to
170provide higher granularity cycle information.
171
172Also note that the IPC instruction count may or may not include the current
173instruction. If the cycle count is associated with an asynchronous branch
174(e.g. page fault or interrupt), then the instruction count does not include the
175current instruction, otherwise it does. That is consistent with whether or not
176that instruction has retired when the cycle count is updated.
177
178Another note, in the case of "branches" events, non-taken branches are not
179presently sampled, so IPC values for them do not appear e.g. a CYC packet with a
180TNT packet that starts with a non-taken branch. To see every possible IPC
181value, "instructions" events can be used e.g. --itrace=i0ns
182
183While it is possible to create scripts to analyze the data, an alternative
184approach is available to export the data to a sqlite or postgresql database.
185Refer to script export-to-sqlite.py or export-to-postgresql.py for more details,
186and to script exported-sql-viewer.py for an example of using the database.
187
188There is also script intel-pt-events.py which provides an example of how to
189unpack the raw data for power events and PTWRITE. The script also displays
190branches, and supports 2 additional modes selected by option:
191
192 - --insn-trace - instruction trace
193 - --src-trace - source trace
194
195The intel-pt-events.py script also has options:
196
197 - --all-switch-events - display all switch events, not only the last consecutive.
198 - --interleave [<n>] - interleave sample output for the same timestamp so that
199 no more than n samples for a CPU are displayed in a row. 'n' defaults to 4.
200 Note this only affects the order of output, and only when the timestamp is the
201 same.
202
203As mentioned above, it is easy to capture too much data. One way to limit the
204data captured is to use 'snapshot' mode which is explained further below.
205Refer to 'new snapshot option' and 'Intel PT modes of operation' further below.
206
207Another problem that will be experienced is decoder errors. They can be caused
208by inability to access the executed image, self-modified or JIT-ed code, or the
209inability to match side-band information (such as context switches and mmaps)
210which results in the decoder not knowing what code was executed.
211
212There is also the problem of perf not being able to copy the data fast enough,
213resulting in data lost because the buffer was full. See 'Buffer handling' below
214for more details.
215
216
217perf record
218-----------
219
220new event
221~~~~~~~~~
222
223The Intel PT kernel driver creates a new PMU for Intel PT. PMU events are
224selected by providing the PMU name followed by the "config" separated by slashes.
225An enhancement has been made to allow default "config" e.g. the option
226
227 -e intel_pt//
228
229will use a default config value. Currently that is the same as
230
231 -e intel_pt/tsc,noretcomp=0/
232
233which is the same as
234
235 -e intel_pt/tsc=1,noretcomp=0/
236
237Note there are now new config terms - see section 'config terms' further below.
238
239The config terms are listed in /sys/devices/intel_pt/format. They are bit
240fields within the config member of the struct perf_event_attr which is
241passed to the kernel by the perf_event_open system call. They correspond to bit
242fields in the IA32_RTIT_CTL MSR. Here is a list of them and their definitions:
243
244 $ grep -H . /sys/bus/event_source/devices/intel_pt/format/*
245 /sys/bus/event_source/devices/intel_pt/format/cyc:config:1
246 /sys/bus/event_source/devices/intel_pt/format/cyc_thresh:config:19-22
247 /sys/bus/event_source/devices/intel_pt/format/mtc:config:9
248 /sys/bus/event_source/devices/intel_pt/format/mtc_period:config:14-17
249 /sys/bus/event_source/devices/intel_pt/format/noretcomp:config:11
250 /sys/bus/event_source/devices/intel_pt/format/psb_period:config:24-27
251 /sys/bus/event_source/devices/intel_pt/format/tsc:config:10
252
253Note that the default config must be overridden for each term i.e.
254
255 -e intel_pt/noretcomp=0/
256
257is the same as:
258
259 -e intel_pt/tsc=1,noretcomp=0/
260
261So, to disable TSC packets use:
262
263 -e intel_pt/tsc=0/
264
265It is also possible to specify the config value explicitly:
266
267 -e intel_pt/config=0x400/
268
269Note that, as with all events, the event is suffixed with event modifiers:
270
271 u userspace
272 k kernel
273 h hypervisor
274 G guest
275 H host
276 p precise ip
277
278'h', 'G' and 'H' are for virtualization which are not used by Intel PT.
279'p' is also not relevant to Intel PT. So only options 'u' and 'k' are
280meaningful for Intel PT.
281
282perf_event_attr is displayed if the -vv option is used e.g.
283
284 ------------------------------------------------------------
285 perf_event_attr:
286 type 6
287 size 112
288 config 0x400
289 { sample_period, sample_freq } 1
290 sample_type IP|TID|TIME|CPU|IDENTIFIER
291 read_format ID
292 disabled 1
293 inherit 1
294 exclude_kernel 1
295 exclude_hv 1
296 enable_on_exec 1
297 sample_id_all 1
298 ------------------------------------------------------------
299 sys_perf_event_open: pid 31104 cpu 0 group_fd -1 flags 0x8
300 sys_perf_event_open: pid 31104 cpu 1 group_fd -1 flags 0x8
301 sys_perf_event_open: pid 31104 cpu 2 group_fd -1 flags 0x8
302 sys_perf_event_open: pid 31104 cpu 3 group_fd -1 flags 0x8
303 ------------------------------------------------------------
304
305
306config terms
307~~~~~~~~~~~~
308
309The June 2015 version of Intel 64 and IA-32 Architectures Software Developer
310Manuals, Chapter 36 Intel Processor Trace, defined new Intel PT features.
311Some of the features are reflect in new config terms. All the config terms are
312described below.
313
314tsc Always supported. Produces TSC timestamp packets to provide
315 timing information. In some cases it is possible to decode
316 without timing information, for example a per-thread context
317 that does not overlap executable memory maps.
318
319 The default config selects tsc (i.e. tsc=1).
320
321noretcomp Always supported. Disables "return compression" so a TIP packet
322 is produced when a function returns. Causes more packets to be
323 produced but might make decoding more reliable.
324
325 The default config does not select noretcomp (i.e. noretcomp=0).
326
327psb_period Allows the frequency of PSB packets to be specified.
328
329 The PSB packet is a synchronization packet that provides a
330 starting point for decoding or recovery from errors.
331
332 Support for psb_period is indicated by:
333
334 /sys/bus/event_source/devices/intel_pt/caps/psb_cyc
335
336 which contains "1" if the feature is supported and "0"
337 otherwise.
338
339 Valid values are given by:
340
341 /sys/bus/event_source/devices/intel_pt/caps/psb_periods
342
343 which contains a hexadecimal value, the bits of which represent
344 valid values e.g. bit 2 set means value 2 is valid.
345
346 The psb_period value is converted to the approximate number of
347 trace bytes between PSB packets as:
348
349 2 ^ (value + 11)
350
351 e.g. value 3 means 16KiB bytes between PSBs
352
353 If an invalid value is entered, the error message
354 will give a list of valid values e.g.
355
356 $ perf record -e intel_pt/psb_period=15/u uname
357 Invalid psb_period for intel_pt. Valid values are: 0-5
358
359 If MTC packets are selected, the default config selects a value
360 of 3 (i.e. psb_period=3) or the nearest lower value that is
361 supported (0 is always supported). Otherwise the default is 0.
362
363 If decoding is expected to be reliable and the buffer is large
364 then a large PSB period can be used.
365
366 Because a TSC packet is produced with PSB, the PSB period can
367 also affect the granularity to timing information in the absence
368 of MTC or CYC.
369
370mtc Produces MTC timing packets.
371
372 MTC packets provide finer grain timestamp information than TSC
373 packets. MTC packets record time using the hardware crystal
374 clock (CTC) which is related to TSC packets using a TMA packet.
375
376 Support for this feature is indicated by:
377
378 /sys/bus/event_source/devices/intel_pt/caps/mtc
379
380 which contains "1" if the feature is supported and
381 "0" otherwise.
382
383 The frequency of MTC packets can also be specified - see
384 mtc_period below.
385
386mtc_period Specifies how frequently MTC packets are produced - see mtc
387 above for how to determine if MTC packets are supported.
388
389 Valid values are given by:
390
391 /sys/bus/event_source/devices/intel_pt/caps/mtc_periods
392
393 which contains a hexadecimal value, the bits of which represent
394 valid values e.g. bit 2 set means value 2 is valid.
395
396 The mtc_period value is converted to the MTC frequency as:
397
398 CTC-frequency / (2 ^ value)
399
400 e.g. value 3 means one eighth of CTC-frequency
401
402 Where CTC is the hardware crystal clock, the frequency of which
403 can be related to TSC via values provided in cpuid leaf 0x15.
404
405 If an invalid value is entered, the error message
406 will give a list of valid values e.g.
407
408 $ perf record -e intel_pt/mtc_period=15/u uname
409 Invalid mtc_period for intel_pt. Valid values are: 0,3,6,9
410
411 The default value is 3 or the nearest lower value
412 that is supported (0 is always supported).
413
414cyc Produces CYC timing packets.
415
416 CYC packets provide even finer grain timestamp information than
417 MTC and TSC packets. A CYC packet contains the number of CPU
418 cycles since the last CYC packet. Unlike MTC and TSC packets,
419 CYC packets are only sent when another packet is also sent.
420
421 Support for this feature is indicated by:
422
423 /sys/bus/event_source/devices/intel_pt/caps/psb_cyc
424
425 which contains "1" if the feature is supported and
426 "0" otherwise.
427
428 The number of CYC packets produced can be reduced by specifying
429 a threshold - see cyc_thresh below.
430
431cyc_thresh Specifies how frequently CYC packets are produced - see cyc
432 above for how to determine if CYC packets are supported.
433
434 Valid cyc_thresh values are given by:
435
436 /sys/bus/event_source/devices/intel_pt/caps/cycle_thresholds
437
438 which contains a hexadecimal value, the bits of which represent
439 valid values e.g. bit 2 set means value 2 is valid.
440
441 The cyc_thresh value represents the minimum number of CPU cycles
442 that must have passed before a CYC packet can be sent. The
443 number of CPU cycles is:
444
445 2 ^ (value - 1)
446
447 e.g. value 4 means 8 CPU cycles must pass before a CYC packet
448 can be sent. Note a CYC packet is still only sent when another
449 packet is sent, not at, e.g. every 8 CPU cycles.
450
451 If an invalid value is entered, the error message
452 will give a list of valid values e.g.
453
454 $ perf record -e intel_pt/cyc,cyc_thresh=15/u uname
455 Invalid cyc_thresh for intel_pt. Valid values are: 0-12
456
457 CYC packets are not requested by default.
458
459pt Specifies pass-through which enables the 'branch' config term.
460
461 The default config selects 'pt' if it is available, so a user will
462 never need to specify this term.
463
464branch Enable branch tracing. Branch tracing is enabled by default so to
465 disable branch tracing use 'branch=0'.
466
467 The default config selects 'branch' if it is available.
468
469ptw Enable PTWRITE packets which are produced when a ptwrite instruction
470 is executed.
471
472 Support for this feature is indicated by:
473
474 /sys/bus/event_source/devices/intel_pt/caps/ptwrite
475
476 which contains "1" if the feature is supported and
477 "0" otherwise.
478
479 As an alternative, refer to "Emulated PTWRITE" further below.
480
481fup_on_ptw Enable a FUP packet to follow the PTWRITE packet. The FUP packet
482 provides the address of the ptwrite instruction. In the absence of
483 fup_on_ptw, the decoder will use the address of the previous branch
484 if branch tracing is enabled, otherwise the address will be zero.
485 Note that fup_on_ptw will work even when branch tracing is disabled.
486
487pwr_evt Enable power events. The power events provide information about
488 changes to the CPU C-state.
489
490 Support for this feature is indicated by:
491
492 /sys/bus/event_source/devices/intel_pt/caps/power_event_trace
493
494 which contains "1" if the feature is supported and
495 "0" otherwise.
496
497event Enable Event Trace. The events provide information about asynchronous
498 events.
499
500 Support for this feature is indicated by:
501
502 /sys/bus/event_source/devices/intel_pt/caps/event_trace
503
504 which contains "1" if the feature is supported and
505 "0" otherwise.
506
507notnt Disable TNT packets. Without TNT packets, it is not possible to walk
508 executable code to reconstruct control flow, however FUP, TIP, TIP.PGE
509 and TIP.PGD packets still indicate asynchronous control flow, and (if
510 return compression is disabled - see noretcomp) return statements.
511 The advantage of eliminating TNT packets is reducing the size of the
512 trace and corresponding tracing overhead.
513
514 Support for this feature is indicated by:
515
516 /sys/bus/event_source/devices/intel_pt/caps/tnt_disable
517
518 which contains "1" if the feature is supported and
519 "0" otherwise.
520
521
522AUX area sampling option
523~~~~~~~~~~~~~~~~~~~~~~~~
524
525To select Intel PT "sampling" the AUX area sampling option can be used:
526
527 --aux-sample
528
529Optionally it can be followed by the sample size in bytes e.g.
530
531 --aux-sample=8192
532
533In addition, the Intel PT event to sample must be defined e.g.
534
535 -e intel_pt//u
536
537Samples on other events will be created containing Intel PT data e.g. the
538following will create Intel PT samples on the branch-misses event, note the
539events must be grouped using {}:
540
541 perf record --aux-sample -e '{intel_pt//u,branch-misses:u}'
542
543An alternative to '--aux-sample' is to add the config term 'aux-sample-size' to
544events. In this case, the grouping is implied e.g.
545
546 perf record -e intel_pt//u -e branch-misses/aux-sample-size=8192/u
547
548is the same as:
549
550 perf record -e '{intel_pt//u,branch-misses/aux-sample-size=8192/u}'
551
552but allows for also using an address filter e.g.:
553
554 perf record -e intel_pt//u --filter 'filter * @/bin/ls' -e branch-misses/aux-sample-size=8192/u -- ls
555
556It is important to select a sample size that is big enough to contain at least
557one PSB packet. If not a warning will be displayed:
558
559 Intel PT sample size (%zu) may be too small for PSB period (%zu)
560
561The calculation used for that is: if sample_size <= psb_period + 256 display the
562warning. When sampling is used, psb_period defaults to 0 (2KiB).
563
564The default sample size is 4KiB.
565
566The sample size is passed in aux_sample_size in struct perf_event_attr. The
567sample size is limited by the maximum event size which is 64KiB. It is
568difficult to know how big the event might be without the trace sample attached,
569but the tool validates that the sample size is not greater than 60KiB.
570
571
572new snapshot option
573~~~~~~~~~~~~~~~~~~~
574
575The difference between full trace and snapshot from the kernel's perspective is
576that in full trace we don't overwrite trace data that the user hasn't collected
577yet (and indicated that by advancing aux_tail), whereas in snapshot mode we let
578the trace run and overwrite older data in the buffer so that whenever something
579interesting happens, we can stop it and grab a snapshot of what was going on
580around that interesting moment.
581
582To select snapshot mode a new option has been added:
583
584 -S
585
586Optionally it can be followed by the snapshot size e.g.
587
588 -S0x100000
589
590The default snapshot size is the auxtrace mmap size. If neither auxtrace mmap size
591nor snapshot size is specified, then the default is 4MiB for privileged users
592(or if /proc/sys/kernel/perf_event_paranoid < 0), 128KiB for unprivileged users.
593If an unprivileged user does not specify mmap pages, the mmap pages will be
594reduced as described in the 'new auxtrace mmap size option' section below.
595
596The snapshot size is displayed if the option -vv is used e.g.
597
598 Intel PT snapshot size: %zu
599
600
601new auxtrace mmap size option
602~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
603
604Intel PT buffer size is specified by an addition to the -m option e.g.
605
606 -m,16
607
608selects a buffer size of 16 pages i.e. 64KiB.
609
610Note that the existing functionality of -m is unchanged. The auxtrace mmap size
611is specified by the optional addition of a comma and the value.
612
613The default auxtrace mmap size for Intel PT is 4MiB/page_size for privileged users
614(or if /proc/sys/kernel/perf_event_paranoid < 0), 128KiB for unprivileged users.
615If an unprivileged user does not specify mmap pages, the mmap pages will be
616reduced from the default 512KiB/page_size to 256KiB/page_size, otherwise the
617user is likely to get an error as they exceed their mlock limit (Max locked
618memory as shown in /proc/self/limits). Note that perf does not count the first
619512KiB (actually /proc/sys/kernel/perf_event_mlock_kb minus 1 page) per cpu
620against the mlock limit so an unprivileged user is allowed 512KiB per cpu plus
621their mlock limit (which defaults to 64KiB but is not multiplied by the number
622of cpus).
623
624In full-trace mode, powers of two are allowed for buffer size, with a minimum
625size of 2 pages. In snapshot mode or sampling mode, it is the same but the
626minimum size is 1 page.
627
628The mmap size and auxtrace mmap size are displayed if the -vv option is used e.g.
629
630 mmap length 528384
631 auxtrace mmap length 4198400
632
633
634Intel PT modes of operation
635~~~~~~~~~~~~~~~~~~~~~~~~~~~
636
637Intel PT can be used in 3 modes:
638 full-trace mode
639 sample mode
640 snapshot mode
641
642Full-trace mode traces continuously e.g.
643
644 perf record -e intel_pt//u uname
645
646Sample mode attaches a Intel PT sample to other events e.g.
647
648 perf record --aux-sample -e intel_pt//u -e branch-misses:u
649
650Snapshot mode captures the available data when a signal is sent or "snapshot"
651control command is issued. e.g. using a signal
652
653 perf record -v -e intel_pt//u -S ./loopy 1000000000 &
654 [1] 11435
655 kill -USR2 11435
656 Recording AUX area tracing snapshot
657
658Note that the signal sent is SIGUSR2.
659Note that "Recording AUX area tracing snapshot" is displayed because the -v
660option is used.
661
662The advantage of using "snapshot" control command is that the access is
663controlled by access to a FIFO e.g.
664
665 $ mkfifo perf.control
666 $ mkfifo perf.ack
667 $ cat perf.ack &
668 [1] 15235
669 $ sudo ~/bin/perf record --control fifo:perf.control,perf.ack -S -e intel_pt//u -- sleep 60 &
670 [2] 15243
671 $ ps -e | grep perf
672 15244 pts/1 00:00:00 perf
673 $ kill -USR2 15244
674 bash: kill: (15244) - Operation not permitted
675 $ echo snapshot > perf.control
676 ack
677
678The 3 Intel PT modes of operation cannot be used together.
679
680
681Buffer handling
682~~~~~~~~~~~~~~~
683
684There may be buffer limitations (i.e. single ToPa entry) which means that actual
685buffer sizes are limited to powers of 2 up to 4MiB (MAX_ORDER). In order to
686provide other sizes, and in particular an arbitrarily large size, multiple
687buffers are logically concatenated. However an interrupt must be used to switch
688between buffers. That has two potential problems:
689 a) the interrupt may not be handled in time so that the current buffer
690 becomes full and some trace data is lost.
691 b) the interrupts may slow the system and affect the performance
692 results.
693
694If trace data is lost, the driver sets 'truncated' in the PERF_RECORD_AUX event
695which the tools report as an error.
696
697In full-trace mode, the driver waits for data to be copied out before allowing
698the (logical) buffer to wrap-around. If data is not copied out quickly enough,
699again 'truncated' is set in the PERF_RECORD_AUX event. If the driver has to
700wait, the intel_pt event gets disabled. Because it is difficult to know when
701that happens, perf tools always re-enable the intel_pt event after copying out
702data.
703
704
705Intel PT and build ids
706~~~~~~~~~~~~~~~~~~~~~~
707
708By default "perf record" post-processes the event stream to find all build ids
709for executables for all addresses sampled. Deliberately, Intel PT is not
710decoded for that purpose (it would take too long). Instead the build ids for
711all executables encountered (due to mmap, comm or task events) are included
712in the perf.data file.
713
714To see buildids included in the perf.data file use the command:
715
716 perf buildid-list
717
718If the perf.data file contains Intel PT data, that is the same as:
719
720 perf buildid-list --with-hits
721
722
723Snapshot mode and event disabling
724~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
725
726In order to make a snapshot, the intel_pt event is disabled using an IOCTL,
727namely PERF_EVENT_IOC_DISABLE. However doing that can also disable the
728collection of side-band information. In order to prevent that, a dummy
729software event has been introduced that permits tracking events (like mmaps) to
730continue to be recorded while intel_pt is disabled. That is important to ensure
731there is complete side-band information to allow the decoding of subsequent
732snapshots.
733
734A test has been created for that. To find the test:
735
736 perf test list
737 ...
738 23: Test using a dummy software event to keep tracking
739
740To run the test:
741
742 perf test 23
743 23: Test using a dummy software event to keep tracking : Ok
744
745
746perf record modes (nothing new here)
747~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
748
749perf record essentially operates in one of three modes:
750 per thread
751 per cpu
752 workload only
753
754"per thread" mode is selected by -t or by --per-thread (with -p or -u or just a
755workload).
756"per cpu" is selected by -C or -a.
757"workload only" mode is selected by not using the other options but providing a
758command to run (i.e. the workload).
759
760In per-thread mode an exact list of threads is traced. There is no inheritance.
761Each thread has its own event buffer.
762
763In per-cpu mode all processes (or processes from the selected cgroup i.e. -G
764option, or processes selected with -p or -u) are traced. Each cpu has its own
765buffer. Inheritance is allowed.
766
767In workload-only mode, the workload is traced but with per-cpu buffers.
768Inheritance is allowed. Note that you can now trace a workload in per-thread
769mode by using the --per-thread option.
770
771
772Privileged vs non-privileged users
773~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
774
775Unless /proc/sys/kernel/perf_event_paranoid is set to -1, unprivileged users
776have memory limits imposed upon them. That affects what buffer sizes they can
777have as outlined above.
778
779The v4.2 kernel introduced support for a context switch metadata event,
780PERF_RECORD_SWITCH, which allows unprivileged users to see when their processes
781are scheduled out and in, just not by whom, which is left for the
782PERF_RECORD_SWITCH_CPU_WIDE, that is only accessible in system wide context,
783which in turn requires CAP_PERFMON or CAP_SYS_ADMIN.
784
785Please see the 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context
786switches") commit, that introduces these metadata events for further info.
787
788When working with kernels < v4.2, the following considerations must be taken,
789as the sched:sched_switch tracepoints will be used to receive such information:
790
791Unless /proc/sys/kernel/perf_event_paranoid is set to -1, unprivileged users are
792not permitted to use tracepoints which means there is insufficient side-band
793information to decode Intel PT in per-cpu mode, and potentially workload-only
794mode too if the workload creates new processes.
795
796Note also, that to use tracepoints, read-access to debugfs is required. So if
797debugfs is not mounted or the user does not have read-access, it will again not
798be possible to decode Intel PT in per-cpu mode.
799
800
801sched_switch tracepoint
802~~~~~~~~~~~~~~~~~~~~~~~
803
804The sched_switch tracepoint is used to provide side-band data for Intel PT
805decoding in kernels where the PERF_RECORD_SWITCH metadata event isn't
806available.
807
808The sched_switch events are automatically added. e.g. the second event shown
809below:
810
811 $ perf record -vv -e intel_pt//u uname
812 ------------------------------------------------------------
813 perf_event_attr:
814 type 6
815 size 112
816 config 0x400
817 { sample_period, sample_freq } 1
818 sample_type IP|TID|TIME|CPU|IDENTIFIER
819 read_format ID
820 disabled 1
821 inherit 1
822 exclude_kernel 1
823 exclude_hv 1
824 enable_on_exec 1
825 sample_id_all 1
826 ------------------------------------------------------------
827 sys_perf_event_open: pid 31104 cpu 0 group_fd -1 flags 0x8
828 sys_perf_event_open: pid 31104 cpu 1 group_fd -1 flags 0x8
829 sys_perf_event_open: pid 31104 cpu 2 group_fd -1 flags 0x8
830 sys_perf_event_open: pid 31104 cpu 3 group_fd -1 flags 0x8
831 ------------------------------------------------------------
832 perf_event_attr:
833 type 2
834 size 112
835 config 0x108
836 { sample_period, sample_freq } 1
837 sample_type IP|TID|TIME|CPU|PERIOD|RAW|IDENTIFIER
838 read_format ID
839 inherit 1
840 sample_id_all 1
841 exclude_guest 1
842 ------------------------------------------------------------
843 sys_perf_event_open: pid -1 cpu 0 group_fd -1 flags 0x8
844 sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8
845 sys_perf_event_open: pid -1 cpu 2 group_fd -1 flags 0x8
846 sys_perf_event_open: pid -1 cpu 3 group_fd -1 flags 0x8
847 ------------------------------------------------------------
848 perf_event_attr:
849 type 1
850 size 112
851 config 0x9
852 { sample_period, sample_freq } 1
853 sample_type IP|TID|TIME|IDENTIFIER
854 read_format ID
855 disabled 1
856 inherit 1
857 exclude_kernel 1
858 exclude_hv 1
859 mmap 1
860 comm 1
861 enable_on_exec 1
862 task 1
863 sample_id_all 1
864 mmap2 1
865 comm_exec 1
866 ------------------------------------------------------------
867 sys_perf_event_open: pid 31104 cpu 0 group_fd -1 flags 0x8
868 sys_perf_event_open: pid 31104 cpu 1 group_fd -1 flags 0x8
869 sys_perf_event_open: pid 31104 cpu 2 group_fd -1 flags 0x8
870 sys_perf_event_open: pid 31104 cpu 3 group_fd -1 flags 0x8
871 mmap size 528384B
872 AUX area mmap length 4194304
873 perf event ring buffer mmapped per cpu
874 Synthesizing auxtrace information
875 Linux
876 [ perf record: Woken up 1 times to write data ]
877 [ perf record: Captured and wrote 0.042 MB perf.data ]
878
879Note, the sched_switch event is only added if the user is permitted to use it
880and only in per-cpu mode.
881
882Note also, the sched_switch event is only added if TSC packets are requested.
883That is because, in the absence of timing information, the sched_switch events
884cannot be matched against the Intel PT trace.
885
886
887perf script
888-----------
889
890By default, perf script will decode trace data found in the perf.data file.
891This can be further controlled by new option --itrace.
892
893
894New --itrace option
895~~~~~~~~~~~~~~~~~~~
896
897Having no option is the same as
898
899 --itrace
900
901which, in turn, is the same as
902
903 --itrace=cepwx
904
905The letters are:
906
907 i synthesize "instructions" events
908 b synthesize "branches" events
909 x synthesize "transactions" events
910 w synthesize "ptwrite" events
911 p synthesize "power" events (incl. PSB events)
912 c synthesize branches events (calls only)
913 r synthesize branches events (returns only)
914 o synthesize PEBS-via-PT events
915 I synthesize Event Trace events
916 e synthesize tracing error events
917 d create a debug log
918 g synthesize a call chain (use with i or x)
919 G synthesize a call chain on existing event records
920 l synthesize last branch entries (use with i or x)
921 L synthesize last branch entries on existing event records
922 s skip initial number of events
923 q quicker (less detailed) decoding
924 A approximate IPC
925 Z prefer to ignore timestamps (so-called "timeless" decoding)
926
927"Instructions" events look like they were recorded by "perf record -e
928instructions".
929
930"Branches" events look like they were recorded by "perf record -e branches". "c"
931and "r" can be combined to get calls and returns.
932
933"Transactions" events correspond to the start or end of transactions. The
934'flags' field can be used in perf script to determine whether the event is a
935transaction start, commit or abort.
936
937Note that "instructions", "branches" and "transactions" events depend on code
938flow packets which can be disabled by using the config term "branch=0". Refer
939to the config terms section above.
940
941"ptwrite" events record the payload of the ptwrite instruction and whether
942"fup_on_ptw" was used. "ptwrite" events depend on PTWRITE packets which are
943recorded only if the "ptw" config term was used. Refer to the config terms
944section above. perf script "synth" field displays "ptwrite" information like
945this: "ip: 0 payload: 0x123456789abcdef0" where "ip" is 1 if "fup_on_ptw" was
946used.
947
948"Power" events correspond to power event packets and CBR (core-to-bus ratio)
949packets. While CBR packets are always recorded when tracing is enabled, power
950event packets are recorded only if the "pwr_evt" config term was used. Refer to
951the config terms section above. The power events record information about
952C-state changes, whereas CBR is indicative of CPU frequency. perf script
953"event,synth" fields display information like this:
954
955 cbr: cbr: 22 freq: 2189 MHz (200%)
956 mwait: hints: 0x60 extensions: 0x1
957 pwre: hw: 0 cstate: 2 sub-cstate: 0
958 exstop: ip: 1
959 pwrx: deepest cstate: 2 last cstate: 2 wake reason: 0x4
960
961Where:
962
963 "cbr" includes the frequency and the percentage of maximum non-turbo
964 "mwait" shows mwait hints and extensions
965 "pwre" shows C-state transitions (to a C-state deeper than C0) and
966 whether initiated by hardware
967 "exstop" indicates execution stopped and whether the IP was recorded
968 exactly,
969 "pwrx" indicates return to C0
970
971For more details refer to the Intel 64 and IA-32 Architectures Software
972Developer Manuals.
973
974PSB events show when a PSB+ occurred and also the byte-offset in the trace.
975Emitting a PSB+ can cause a CPU a slight delay. When doing timing analysis
976of code with Intel PT, it is useful to know if a timing bubble was caused
977by Intel PT or not.
978
979Error events show where the decoder lost the trace. Error events
980are quite important. Users must know if what they are seeing is a complete
981picture or not. The "e" option may be followed by flags which affect what errors
982will or will not be reported. Each flag must be preceded by either '+' or '-'.
983The flags supported by Intel PT are:
984
985 -o Suppress overflow errors
986 -l Suppress trace data lost errors
987
988For example, for errors but not overflow or data lost errors:
989
990 --itrace=e-o-l
991
992The "d" option will cause the creation of a file "intel_pt.log" containing all
993decoded packets and instructions. Note that this option slows down the decoder
994and that the resulting file may be very large. The "d" option may be followed
995by flags which affect what debug messages will or will not be logged. Each flag
996must be preceded by either '+' or '-'. The flags support by Intel PT are:
997
998 -a Suppress logging of perf events
999 +a Log all perf events
1000 +e Output only on decoding errors (size configurable)
1001 +o Output to stdout instead of "intel_pt.log"
1002
1003By default, logged perf events are filtered by any specified time ranges, but
1004flag +a overrides that. The +e flag can be useful for analyzing errors. By
1005default, the log size in that case is 16384 bytes, but can be altered by
1006linkperf:perf-config[1] e.g. perf config itrace.debug-log-buffer-size=30000
1007
1008In addition, the period of the "instructions" event can be specified. e.g.
1009
1010 --itrace=i10us
1011
1012sets the period to 10us i.e. one instruction sample is synthesized for each 10
1013microseconds of trace. Alternatives to "us" are "ms" (milliseconds),
1014"ns" (nanoseconds), "t" (TSC ticks) or "i" (instructions).
1015
1016"ms", "us" and "ns" are converted to TSC ticks.
1017
1018The timing information included with Intel PT does not give the time of every
1019instruction. Consequently, for the purpose of sampling, the decoder estimates
1020the time since the last timing packet based on 1 tick per instruction. The time
1021on the sample is *not* adjusted and reflects the last known value of TSC.
1022
1023For Intel PT, the default period is 100us.
1024
1025Setting it to a zero period means "as often as possible".
1026
1027In the case of Intel PT that is the same as a period of 1 and a unit of
1028'instructions' (i.e. --itrace=i1i).
1029
1030Also the call chain size (default 16, max. 1024) for instructions or
1031transactions events can be specified. e.g.
1032
1033 --itrace=ig32
1034 --itrace=xg32
1035
1036Also the number of last branch entries (default 64, max. 1024) for instructions or
1037transactions events can be specified. e.g.
1038
1039 --itrace=il10
1040 --itrace=xl10
1041
1042Note that last branch entries are cleared for each sample, so there is no overlap
1043from one sample to the next.
1044
1045The G and L options are designed in particular for sample mode, and work much
1046like g and l but add call chain and branch stack to the other selected events
1047instead of synthesized events. For example, to record branch-misses events for
1048'ls' and then add a call chain derived from the Intel PT trace:
1049
1050 perf record --aux-sample -e '{intel_pt//u,branch-misses:u}' -- ls
1051 perf report --itrace=Ge
1052
1053Although in fact G is a default for perf report, so that is the same as just:
1054
1055 perf report
1056
1057One caveat with the G and L options is that they work poorly with "Large PEBS".
1058Large PEBS means PEBS records will be accumulated by hardware and the written
1059into the event buffer in one go. That reduces interrupts, but can give very
1060late timestamps. Because the Intel PT trace is synchronized by timestamps,
1061the PEBS events do not match the trace. Currently, Large PEBS is used only in
1062certain circumstances:
1063 - hardware supports it
1064 - PEBS is used
1065 - event period is specified, instead of frequency
1066 - the sample type is limited to the following flags:
1067 PERF_SAMPLE_IP | PERF_SAMPLE_TID | PERF_SAMPLE_ADDR |
1068 PERF_SAMPLE_ID | PERF_SAMPLE_CPU | PERF_SAMPLE_STREAM_ID |
1069 PERF_SAMPLE_DATA_SRC | PERF_SAMPLE_IDENTIFIER |
1070 PERF_SAMPLE_TRANSACTION | PERF_SAMPLE_PHYS_ADDR |
1071 PERF_SAMPLE_REGS_INTR | PERF_SAMPLE_REGS_USER |
1072 PERF_SAMPLE_PERIOD (and sometimes) | PERF_SAMPLE_TIME
1073Because Intel PT sample mode uses a different sample type to the list above,
1074Large PEBS is not used with Intel PT sample mode. To avoid Large PEBS in other
1075cases, avoid specifying the event period i.e. avoid the 'perf record' -c option,
1076--count option, or 'period' config term.
1077
1078To disable trace decoding entirely, use the option --no-itrace.
1079
1080It is also possible to skip events generated (instructions, branches, transactions)
1081at the beginning. This is useful to ignore initialization code.
1082
1083 --itrace=i0nss1000000
1084
1085skips the first million instructions.
1086
1087The q option changes the way the trace is decoded. The decoding is much faster
1088but much less detailed. Specifically, with the q option, the decoder does not
1089decode TNT packets, and does not walk object code, but gets the ip from FUP and
1090TIP packets. The q option can be used with the b and i options but the period
1091is not used. The q option decodes more quickly, but is useful only if the
1092control flow of interest is represented or indicated by FUP, TIP, TIP.PGE, or
1093TIP.PGD packets (refer below). However the q option could be used to find time
1094ranges that could then be decoded fully using the --time option.
1095
1096What will *not* be decoded with the (single) q option:
1097
1098 - direct calls and jmps
1099 - conditional branches
1100 - non-branch instructions
1101
1102What *will* be decoded with the (single) q option:
1103
1104 - asynchronous branches such as interrupts
1105 - indirect branches
1106 - function return target address *if* the noretcomp config term (refer
1107 config terms section) was used
1108 - start of (control-flow) tracing
1109 - end of (control-flow) tracing, if it is not out of context
1110 - power events, ptwrite, transaction start and abort
1111 - instruction pointer associated with PSB packets
1112
1113Note the q option does not specify what events will be synthesized e.g. the p
1114option must be used also to show power events.
1115
1116Repeating the q option (double-q i.e. qq) results in even faster decoding and even
1117less detail. The decoder decodes only extended PSB (PSB+) packets, getting the
1118instruction pointer if there is a FUP packet within PSB+ (i.e. between PSB and
1119PSBEND). Note PSB packets occur regularly in the trace based on the psb_period
1120config term (refer config terms section). There will be a FUP packet if the
1121PSB+ occurs while control flow is being traced.
1122
1123What will *not* be decoded with the qq option:
1124
1125 - everything except instruction pointer associated with PSB packets
1126
1127What *will* be decoded with the qq option:
1128
1129 - instruction pointer associated with PSB packets
1130
1131The Z option is equivalent to having recorded a trace without TSC
1132(i.e. config term tsc=0). It can be useful to avoid timestamp issues when
1133decoding a trace of a virtual machine.
1134
1135
1136dlfilter-show-cycles.so
1137~~~~~~~~~~~~~~~~~~~~~~~
1138
1139Cycles can be displayed using dlfilter-show-cycles.so in which case the itrace A
1140option can be useful to provide higher granularity cycle information:
1141
1142 perf script --itrace=A --call-trace --dlfilter dlfilter-show-cycles.so
1143
1144To see a list of dlfilters:
1145
1146 perf script -v --list-dlfilters
1147
1148See also linkperf:perf-dlfilters[1]
1149
1150
1151dump option
1152~~~~~~~~~~~
1153
1154perf script has an option (-D) to "dump" the events i.e. display the binary
1155data.
1156
1157When -D is used, Intel PT packets are displayed. The packet decoder does not
1158pay attention to PSB packets, but just decodes the bytes - so the packets seen
1159by the actual decoder may not be identical in places where the data is corrupt.
1160One example of that would be when the buffer-switching interrupt has been too
1161slow, and the buffer has been filled completely. In that case, the last packet
1162in the buffer might be truncated and immediately followed by a PSB as the trace
1163continues in the next buffer.
1164
1165To disable the display of Intel PT packets, combine the -D option with
1166--no-itrace.
1167
1168
1169perf report
1170-----------
1171
1172By default, perf report will decode trace data found in the perf.data file.
1173This can be further controlled by new option --itrace exactly the same as
1174perf script, with the exception that the default is --itrace=igxe.
1175
1176
1177perf inject
1178-----------
1179
1180perf inject also accepts the --itrace option in which case tracing data is
1181removed and replaced with the synthesized events. e.g.
1182
1183 perf inject --itrace -i perf.data -o perf.data.new
1184
1185Below is an example of using Intel PT with autofdo. It requires autofdo
1186(https://github.com/google/autofdo) and gcc version 5. The bubble
1187sort example is from the AutoFDO tutorial (https://gcc.gnu.org/wiki/AutoFDO/Tutorial)
1188amended to take the number of elements as a parameter.
1189
1190 $ gcc-5 -O3 sort.c -o sort_optimized
1191 $ ./sort_optimized 30000
1192 Bubble sorting array of 30000 elements
1193 2254 ms
1194
1195 $ cat ~/.perfconfig
1196 [intel-pt]
1197 mispred-all = on
1198
1199 $ perf record -e intel_pt//u ./sort 3000
1200 Bubble sorting array of 3000 elements
1201 58 ms
1202 [ perf record: Woken up 2 times to write data ]
1203 [ perf record: Captured and wrote 3.939 MB perf.data ]
1204 $ perf inject -i perf.data -o inj --itrace=i100usle --strip
1205 $ ./create_gcov --binary=./sort --profile=inj --gcov=sort.gcov -gcov_version=1
1206 $ gcc-5 -O3 -fauto-profile=sort.gcov sort.c -o sort_autofdo
1207 $ ./sort_autofdo 30000
1208 Bubble sorting array of 30000 elements
1209 2155 ms
1210
1211Note there is currently no advantage to using Intel PT instead of LBR, but
1212that may change in the future if greater use is made of the data.
1213
1214
1215PEBS via Intel PT
1216-----------------
1217
1218Some hardware has the feature to redirect PEBS records to the Intel PT trace.
1219Recording is selected by using the aux-output config term e.g.
1220
1221 perf record -c 10000 -e '{intel_pt/branch=0/,cycles/aux-output/ppp}' uname
1222
1223Originally, software only supported redirecting at most one PEBS event because it
1224was not able to differentiate one event from another. To overcome that, more recent
1225kernels and perf tools add support for the PERF_RECORD_AUX_OUTPUT_HW_ID side-band event.
1226To check for the presence of that event in a PEBS-via-PT trace:
1227
1228 perf script -D --no-itrace | grep PERF_RECORD_AUX_OUTPUT_HW_ID
1229
1230To display PEBS events from the Intel PT trace, use the itrace 'o' option e.g.
1231
1232 perf script --itrace=oe
1233
1234XED
1235---
1236
1237include::build-xed.txt[]
1238
1239
1240Tracing Virtual Machines (kernel only)
1241--------------------------------------
1242
1243Currently, kernel tracing is supported with either "timeless" decoding
1244(i.e. no TSC timestamps) or VM Time Correlation. VM Time Correlation is an extra step
1245using 'perf inject' and requires unchanging VMX TSC Offset and no VMX TSC Scaling.
1246
1247Other limitations and caveats
1248
1249 VMX controls may suppress packets needed for decoding resulting in decoding errors
1250 VMX controls may block the perf NMI to the host potentially resulting in lost trace data
1251 Guest kernel self-modifying code (e.g. jump labels or JIT-compiled eBPF) will result in decoding errors
1252 Guest thread information is unknown
1253 Guest VCPU is unknown but may be able to be inferred from the host thread
1254 Callchains are not supported
1255
1256Example using "timeless" decoding
1257
1258Start VM
1259
1260 $ sudo virsh start kubuntu20.04
1261 Domain kubuntu20.04 started
1262
1263Mount the guest file system. Note sshfs needs -o direct_io to enable reading of proc files. root access is needed to read /proc/kcore.
1264
1265 $ mkdir vm0
1266 $ sshfs -o direct_io root@vm0:/ vm0
1267
1268Copy the guest /proc/kallsyms, /proc/modules and /proc/kcore
1269
1270 $ perf buildid-cache -v --kcore vm0/proc/kcore
1271 kcore added to build-id cache directory /home/user/.debug/[kernel.kcore]/9600f316a53a0f54278885e8d9710538ec5f6a08/2021021807494306
1272 $ KALLSYMS=/home/user/.debug/[kernel.kcore]/9600f316a53a0f54278885e8d9710538ec5f6a08/2021021807494306/kallsyms
1273
1274Find the VM process
1275
1276 $ ps -eLl | grep 'KVM\|PID'
1277 F S UID PID PPID LWP C PRI NI ADDR SZ WCHAN TTY TIME CMD
1278 3 S 64055 1430 1 1440 1 80 0 - 1921718 - ? 00:02:47 CPU 0/KVM
1279 3 S 64055 1430 1 1441 1 80 0 - 1921718 - ? 00:02:41 CPU 1/KVM
1280 3 S 64055 1430 1 1442 1 80 0 - 1921718 - ? 00:02:38 CPU 2/KVM
1281 3 S 64055 1430 1 1443 2 80 0 - 1921718 - ? 00:03:18 CPU 3/KVM
1282
1283Start an open-ended perf record, tracing the VM process, do something on the VM, and then ctrl-C to stop.
1284TSC is not supported and tsc=0 must be specified. That means mtc is useless, so add mtc=0.
1285However, IPC can still be determined, hence cyc=1 can be added.
1286Only kernel decoding is supported, so 'k' must be specified.
1287Intel PT traces both the host and the guest so --guest and --host need to be specified.
1288Without timestamps, --per-thread must be specified to distinguish threads.
1289
1290 $ sudo perf kvm --guest --host --guestkallsyms $KALLSYMS record --kcore -e intel_pt/tsc=0,mtc=0,cyc=1/k -p 1430 --per-thread
1291 ^C
1292 [ perf record: Woken up 1 times to write data ]
1293 [ perf record: Captured and wrote 5.829 MB ]
1294
1295perf script can be used to provide an instruction trace
1296
1297 $ perf script --guestkallsyms $KALLSYMS --insn-trace --xed -F+ipc | grep -C10 vmresume | head -21
1298 CPU 0/KVM 1440 ffffffff82133cdd __vmx_vcpu_run+0x3d ([kernel.kallsyms]) movq 0x48(%rax), %r9
1299 CPU 0/KVM 1440 ffffffff82133ce1 __vmx_vcpu_run+0x41 ([kernel.kallsyms]) movq 0x50(%rax), %r10
1300 CPU 0/KVM 1440 ffffffff82133ce5 __vmx_vcpu_run+0x45 ([kernel.kallsyms]) movq 0x58(%rax), %r11
1301 CPU 0/KVM 1440 ffffffff82133ce9 __vmx_vcpu_run+0x49 ([kernel.kallsyms]) movq 0x60(%rax), %r12
1302 CPU 0/KVM 1440 ffffffff82133ced __vmx_vcpu_run+0x4d ([kernel.kallsyms]) movq 0x68(%rax), %r13
1303 CPU 0/KVM 1440 ffffffff82133cf1 __vmx_vcpu_run+0x51 ([kernel.kallsyms]) movq 0x70(%rax), %r14
1304 CPU 0/KVM 1440 ffffffff82133cf5 __vmx_vcpu_run+0x55 ([kernel.kallsyms]) movq 0x78(%rax), %r15
1305 CPU 0/KVM 1440 ffffffff82133cf9 __vmx_vcpu_run+0x59 ([kernel.kallsyms]) movq (%rax), %rax
1306 CPU 0/KVM 1440 ffffffff82133cfc __vmx_vcpu_run+0x5c ([kernel.kallsyms]) callq 0xffffffff82133c40
1307 CPU 0/KVM 1440 ffffffff82133c40 vmx_vmenter+0x0 ([kernel.kallsyms]) jz 0xffffffff82133c46
1308 CPU 0/KVM 1440 ffffffff82133c42 vmx_vmenter+0x2 ([kernel.kallsyms]) vmresume IPC: 0.11 (50/445)
1309 :1440 1440 ffffffffbb678b06 native_write_msr+0x6 ([guest.kernel.kallsyms]) nopl %eax, (%rax,%rax,1)
1310 :1440 1440 ffffffffbb678b0b native_write_msr+0xb ([guest.kernel.kallsyms]) retq IPC: 0.04 (2/41)
1311 :1440 1440 ffffffffbb666646 lapic_next_deadline+0x26 ([guest.kernel.kallsyms]) data16 nop
1312 :1440 1440 ffffffffbb666648 lapic_next_deadline+0x28 ([guest.kernel.kallsyms]) xor %eax, %eax
1313 :1440 1440 ffffffffbb66664a lapic_next_deadline+0x2a ([guest.kernel.kallsyms]) popq %rbp
1314 :1440 1440 ffffffffbb66664b lapic_next_deadline+0x2b ([guest.kernel.kallsyms]) retq IPC: 0.16 (4/25)
1315 :1440 1440 ffffffffbb74607f clockevents_program_event+0x8f ([guest.kernel.kallsyms]) test %eax, %eax
1316 :1440 1440 ffffffffbb746081 clockevents_program_event+0x91 ([guest.kernel.kallsyms]) jz 0xffffffffbb74603c IPC: 0.06 (2/30)
1317 :1440 1440 ffffffffbb74603c clockevents_program_event+0x4c ([guest.kernel.kallsyms]) popq %rbx
1318 :1440 1440 ffffffffbb74603d clockevents_program_event+0x4d ([guest.kernel.kallsyms]) popq %r12
1319
1320Example using VM Time Correlation
1321
1322Start VM
1323
1324 $ sudo virsh start kubuntu20.04
1325 Domain kubuntu20.04 started
1326
1327Mount the guest file system. Note sshfs needs -o direct_io to enable reading of proc files. root access is needed to read /proc/kcore.
1328
1329 $ mkdir -p vm0
1330 $ sshfs -o direct_io root@vm0:/ vm0
1331
1332Copy the guest /proc/kallsyms, /proc/modules and /proc/kcore
1333
1334 $ perf buildid-cache -v --kcore vm0/proc/kcore
1335 same kcore found in /home/user/.debug/[kernel.kcore]/cc9c55a98c5e4ec0aeda69302554aabed5cd6491/2021021312450777
1336 $ KALLSYMS=/home/user/.debug/\[kernel.kcore\]/cc9c55a98c5e4ec0aeda69302554aabed5cd6491/2021021312450777/kallsyms
1337
1338Find the VM process
1339
1340 $ ps -eLl | grep 'KVM\|PID'
1341 F S UID PID PPID LWP C PRI NI ADDR SZ WCHAN TTY TIME CMD
1342 3 S 64055 16998 1 17005 13 80 0 - 1818189 - ? 00:00:16 CPU 0/KVM
1343 3 S 64055 16998 1 17006 4 80 0 - 1818189 - ? 00:00:05 CPU 1/KVM
1344 3 S 64055 16998 1 17007 3 80 0 - 1818189 - ? 00:00:04 CPU 2/KVM
1345 3 S 64055 16998 1 17008 4 80 0 - 1818189 - ? 00:00:05 CPU 3/KVM
1346
1347Start an open-ended perf record, tracing the VM process, do something on the VM, and then ctrl-C to stop.
1348IPC can be determined, hence cyc=1 can be added.
1349Only kernel decoding is supported, so 'k' must be specified.
1350Intel PT traces both the host and the guest so --guest and --host need to be specified.
1351
1352 $ sudo perf kvm --guest --host --guestkallsyms $KALLSYMS record --kcore -e intel_pt/cyc=1/k -p 16998
1353 ^C[ perf record: Woken up 1 times to write data ]
1354 [ perf record: Captured and wrote 9.041 MB perf.data.kvm ]
1355
1356Now 'perf inject' can be used to determine the VMX TCS Offset. Note, Intel PT TSC packets are
1357only 7-bytes, so the TSC Offset might differ from the actual value in the 8th byte. That will
1358have no effect i.e. the resulting timestamps will be correct anyway.
1359
1360 $ perf inject -i perf.data.kvm --vm-time-correlation=dry-run
1361 ERROR: Unknown TSC Offset for VMCS 0x1bff6a
1362 VMCS: 0x1bff6a TSC Offset 0xffffe42722c64c41
1363 ERROR: Unknown TSC Offset for VMCS 0x1cbc08
1364 VMCS: 0x1cbc08 TSC Offset 0xffffe42722c64c41
1365 ERROR: Unknown TSC Offset for VMCS 0x1c3ce8
1366 VMCS: 0x1c3ce8 TSC Offset 0xffffe42722c64c41
1367 ERROR: Unknown TSC Offset for VMCS 0x1cbce9
1368 VMCS: 0x1cbce9 TSC Offset 0xffffe42722c64c41
1369
1370Each virtual CPU has a different Virtual Machine Control Structure (VMCS)
1371shown above with the calculated TSC Offset. For an unchanging TSC Offset
1372they should all be the same for the same virtual machine.
1373
1374Now that the TSC Offset is known, it can be provided to 'perf inject'
1375
1376 $ perf inject -i perf.data.kvm --vm-time-correlation="dry-run 0xffffe42722c64c41"
1377
1378Note the options for 'perf inject' --vm-time-correlation are:
1379
1380 [ dry-run ] [ <TSC Offset> [ : <VMCS> [ , <VMCS> ]... ] ]...
1381
1382So it is possible to specify different TSC Offsets for different VMCS.
1383The option "dry-run" will cause the file to be processed but without updating it.
1384Note it is also possible to get a intel_pt.log file by adding option --itrace=d
1385
1386There were no errors so, do it for real
1387
1388 $ perf inject -i perf.data.kvm --vm-time-correlation=0xffffe42722c64c41 --force
1389
1390'perf script' can be used to see if there are any decoder errors
1391
1392 $ perf script -i perf.data.kvm --guestkallsyms $KALLSYMS --itrace=e-o
1393
1394There were none.
1395
1396'perf script' can be used to provide an instruction trace showing timestamps
1397
1398 $ perf script -i perf.data.kvm --guestkallsyms $KALLSYMS --insn-trace --xed -F+ipc | grep -C10 vmresume | head -21
1399 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133cdd __vmx_vcpu_run+0x3d ([kernel.kallsyms]) movq 0x48(%rax), %r9
1400 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133ce1 __vmx_vcpu_run+0x41 ([kernel.kallsyms]) movq 0x50(%rax), %r10
1401 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133ce5 __vmx_vcpu_run+0x45 ([kernel.kallsyms]) movq 0x58(%rax), %r11
1402 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133ce9 __vmx_vcpu_run+0x49 ([kernel.kallsyms]) movq 0x60(%rax), %r12
1403 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133ced __vmx_vcpu_run+0x4d ([kernel.kallsyms]) movq 0x68(%rax), %r13
1404 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133cf1 __vmx_vcpu_run+0x51 ([kernel.kallsyms]) movq 0x70(%rax), %r14
1405 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133cf5 __vmx_vcpu_run+0x55 ([kernel.kallsyms]) movq 0x78(%rax), %r15
1406 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133cf9 __vmx_vcpu_run+0x59 ([kernel.kallsyms]) movq (%rax), %rax
1407 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133cfc __vmx_vcpu_run+0x5c ([kernel.kallsyms]) callq 0xffffffff82133c40
1408 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133c40 vmx_vmenter+0x0 ([kernel.kallsyms]) jz 0xffffffff82133c46
1409 CPU 1/KVM 17006 [001] 11500.262866075: ffffffff82133c42 vmx_vmenter+0x2 ([kernel.kallsyms]) vmresume IPC: 0.05 (40/769)
1410 :17006 17006 [001] 11500.262869216: ffffffff82200cb0 asm_sysvec_apic_timer_interrupt+0x0 ([guest.kernel.kallsyms]) clac
1411 :17006 17006 [001] 11500.262869216: ffffffff82200cb3 asm_sysvec_apic_timer_interrupt+0x3 ([guest.kernel.kallsyms]) pushq $0xffffffffffffffff
1412 :17006 17006 [001] 11500.262869216: ffffffff82200cb5 asm_sysvec_apic_timer_interrupt+0x5 ([guest.kernel.kallsyms]) callq 0xffffffff82201160
1413 :17006 17006 [001] 11500.262869216: ffffffff82201160 error_entry+0x0 ([guest.kernel.kallsyms]) cld
1414 :17006 17006 [001] 11500.262869216: ffffffff82201161 error_entry+0x1 ([guest.kernel.kallsyms]) pushq %rsi
1415 :17006 17006 [001] 11500.262869216: ffffffff82201162 error_entry+0x2 ([guest.kernel.kallsyms]) movq 0x8(%rsp), %rsi
1416 :17006 17006 [001] 11500.262869216: ffffffff82201167 error_entry+0x7 ([guest.kernel.kallsyms]) movq %rdi, 0x8(%rsp)
1417 :17006 17006 [001] 11500.262869216: ffffffff8220116c error_entry+0xc ([guest.kernel.kallsyms]) pushq %rdx
1418 :17006 17006 [001] 11500.262869216: ffffffff8220116d error_entry+0xd ([guest.kernel.kallsyms]) pushq %rcx
1419 :17006 17006 [001] 11500.262869216: ffffffff8220116e error_entry+0xe ([guest.kernel.kallsyms]) pushq %rax
1420
1421
1422Tracing Virtual Machines (including user space)
1423-----------------------------------------------
1424
1425It is possible to use perf record to record sideband events within a virtual machine, so that an Intel PT trace on the host can be decoded.
1426Sideband events from the guest perf.data file can be injected into the host perf.data file using perf inject.
1427
1428Here is an example of the steps needed:
1429
1430On the guest machine:
1431
1432Check that no-kvmclock kernel command line option was used to boot:
1433
1434Note, this is essential to enable time correlation between host and guest machines.
1435
1436 $ cat /proc/cmdline
1437 BOOT_IMAGE=/boot/vmlinuz-5.10.0-16-amd64 root=UUID=cb49c910-e573-47e0-bce7-79e293df8e1d ro no-kvmclock
1438
1439There is no BPF support at present so, if possible, disable JIT compiling:
1440
1441 $ echo 0 | sudo tee /proc/sys/net/core/bpf_jit_enable
1442 0
1443
1444Start perf record to collect sideband events:
1445
1446 $ sudo perf record -o guest-sideband-testing-guest-perf.data --sample-identifier --buildid-all --switch-events --kcore -a -e dummy
1447
1448On the host machine:
1449
1450Start perf record to collect Intel PT trace:
1451
1452Note, the host trace will get very big, very fast, so the steps from starting to stopping the host trace really need to be done so that they happen in the shortest time possible.
1453
1454 $ sudo perf record -o guest-sideband-testing-host-perf.data -m,64M --kcore -a -e intel_pt/cyc/
1455
1456On the guest machine:
1457
1458Run a small test case, just 'uname' in this example:
1459
1460 $ uname
1461 Linux
1462
1463On the host machine:
1464
1465Stop the Intel PT trace:
1466
1467 ^C
1468 [ perf record: Woken up 1 times to write data ]
1469 [ perf record: Captured and wrote 76.122 MB guest-sideband-testing-host-perf.data ]
1470
1471On the guest machine:
1472
1473Stop the Intel PT trace:
1474
1475 ^C
1476 [ perf record: Woken up 1 times to write data ]
1477 [ perf record: Captured and wrote 1.247 MB guest-sideband-testing-guest-perf.data ]
1478
1479And then copy guest-sideband-testing-guest-perf.data to the host (not shown here).
1480
1481On the host machine:
1482
1483With the 2 perf.data recordings, and with their ownership changed to the user.
1484
1485Identify the TSC Offset:
1486
1487 $ perf inject -i guest-sideband-testing-host-perf.data --vm-time-correlation=dry-run
1488 VMCS: 0x103fc6 TSC Offset 0xfffffa6ae070cb20
1489 VMCS: 0x103ff2 TSC Offset 0xfffffa6ae070cb20
1490 VMCS: 0x10fdaa TSC Offset 0xfffffa6ae070cb20
1491 VMCS: 0x24d57c TSC Offset 0xfffffa6ae070cb20
1492
1493Correct Intel PT TSC timestamps for the guest machine:
1494
1495 $ perf inject -i guest-sideband-testing-host-perf.data --vm-time-correlation=0xfffffa6ae070cb20 --force
1496
1497Identify the guest machine PID:
1498
1499 $ perf script -i guest-sideband-testing-host-perf.data --no-itrace --show-task-events | grep KVM
1500 CPU 0/KVM 0 [000] 0.000000: PERF_RECORD_COMM: CPU 0/KVM:13376/13381
1501 CPU 1/KVM 0 [000] 0.000000: PERF_RECORD_COMM: CPU 1/KVM:13376/13382
1502 CPU 2/KVM 0 [000] 0.000000: PERF_RECORD_COMM: CPU 2/KVM:13376/13383
1503 CPU 3/KVM 0 [000] 0.000000: PERF_RECORD_COMM: CPU 3/KVM:13376/13384
1504
1505Note, the QEMU option -name debug-threads=on is needed so that thread names
1506can be used to determine which thread is running which VCPU as above. libvirt seems to use this by default.
1507
1508Create a guestmount, assuming the guest machine is 'vm_to_test':
1509
1510 $ mkdir -p ~/guestmount/13376
1511 $ sshfs -o direct_io vm_to_test:/ ~/guestmount/13376
1512
1513Inject the guest perf.data file into the host perf.data file:
1514
1515Note, due to the guestmount option, guest object files and debug files will be copied into the build ID cache from the guest machine, with the notable exception of VDSO.
1516If needed, VDSO can be copied manually in a fashion similar to that used by the perf-archive script.
1517
1518 $ perf inject -i guest-sideband-testing-host-perf.data -o inj --guestmount ~/guestmount --guest-data=guest-sideband-testing-guest-perf.data,13376,0xfffffa6ae070cb20
1519
1520Show an excerpt from the result. In this case the CPU and time range have been to chosen to show interaction between guest and host when 'uname' is starting to run on the guest machine:
1521
1522Notes:
1523
1524 - the CPU displayed, [002] in this case, is always the host CPU
1525 - events happening in the virtual machine start with VM:13376 VCPU:003, which shows the hypervisor PID 13376 and the VCPU number
1526 - only calls and errors are displayed i.e. --itrace=ce
1527 - branches entering and exiting the virtual machine are split, and show as 2 branches to/from "0 [unknown] ([unknown])"
1528
1529 $ perf script -i inj --itrace=ce -F+machine_pid,+vcpu,+addr,+pid,+tid,-period --ns --time 7919.408803365,7919.408804631 -C 2
1530 CPU 3/KVM 13376/13384 [002] 7919.408803365: branches: ffffffffc0f8ebe0 vmx_vcpu_enter_exit+0xc0 ([kernel.kallsyms]) => ffffffffc0f8edc0 __vmx_vcpu_run+0x0 ([kernel.kallsyms])
1531 CPU 3/KVM 13376/13384 [002] 7919.408803365: branches: ffffffffc0f8edd5 __vmx_vcpu_run+0x15 ([kernel.kallsyms]) => ffffffffc0f8eca0 vmx_update_host_rsp+0x0 ([kernel.kallsyms])
1532 CPU 3/KVM 13376/13384 [002] 7919.408803365: branches: ffffffffc0f8ee1b __vmx_vcpu_run+0x5b ([kernel.kallsyms]) => ffffffffc0f8ed60 vmx_vmenter+0x0 ([kernel.kallsyms])
1533 CPU 3/KVM 13376/13384 [002] 7919.408803461: branches: ffffffffc0f8ed62 vmx_vmenter+0x2 ([kernel.kallsyms]) => 0 [unknown] ([unknown])
1534 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408803461: branches: 0 [unknown] ([unknown]) => 7f851c9b5a5c init_cacheinfo+0x3ac (/usr/lib/x86_64-linux-gnu/libc-2.31.so)
1535 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408803567: branches: 7f851c9b5a5a init_cacheinfo+0x3aa (/usr/lib/x86_64-linux-gnu/libc-2.31.so) => 0 [unknown] ([unknown])
1536 CPU 3/KVM 13376/13384 [002] 7919.408803567: branches: 0 [unknown] ([unknown]) => ffffffffc0f8ed80 vmx_vmexit+0x0 ([kernel.kallsyms])
1537 CPU 3/KVM 13376/13384 [002] 7919.408803596: branches: ffffffffc0f6619a vmx_vcpu_run+0x26a ([kernel.kallsyms]) => ffffffffb2255c60 x86_virt_spec_ctrl+0x0 ([kernel.kallsyms])
1538 CPU 3/KVM 13376/13384 [002] 7919.408803801: branches: ffffffffc0f66445 vmx_vcpu_run+0x515 ([kernel.kallsyms]) => ffffffffb2290b30 native_write_msr+0x0 ([kernel.kallsyms])
1539 CPU 3/KVM 13376/13384 [002] 7919.408803850: branches: ffffffffc0f661f8 vmx_vcpu_run+0x2c8 ([kernel.kallsyms]) => ffffffffc1092300 kvm_load_host_xsave_state+0x0 ([kernel.kallsyms])
1540 CPU 3/KVM 13376/13384 [002] 7919.408803850: branches: ffffffffc1092327 kvm_load_host_xsave_state+0x27 ([kernel.kallsyms]) => ffffffffc1092220 kvm_load_host_xsave_state.part.0+0x0 ([kernel.kallsyms])
1541 CPU 3/KVM 13376/13384 [002] 7919.408803862: branches: ffffffffc0f662cf vmx_vcpu_run+0x39f ([kernel.kallsyms]) => ffffffffc0f63f90 vmx_recover_nmi_blocking+0x0 ([kernel.kallsyms])
1542 CPU 3/KVM 13376/13384 [002] 7919.408803862: branches: ffffffffc0f662e9 vmx_vcpu_run+0x3b9 ([kernel.kallsyms]) => ffffffffc0f619a0 __vmx_complete_interrupts+0x0 ([kernel.kallsyms])
1543 CPU 3/KVM 13376/13384 [002] 7919.408803872: branches: ffffffffc109cfb2 vcpu_enter_guest+0x752 ([kernel.kallsyms]) => ffffffffc0f5f570 vmx_handle_exit_irqoff+0x0 ([kernel.kallsyms])
1544 CPU 3/KVM 13376/13384 [002] 7919.408803881: branches: ffffffffc109d028 vcpu_enter_guest+0x7c8 ([kernel.kallsyms]) => ffffffffb234f900 __srcu_read_lock+0x0 ([kernel.kallsyms])
1545 CPU 3/KVM 13376/13384 [002] 7919.408803897: branches: ffffffffc109d06f vcpu_enter_guest+0x80f ([kernel.kallsyms]) => ffffffffc0f72e30 vmx_handle_exit+0x0 ([kernel.kallsyms])
1546 CPU 3/KVM 13376/13384 [002] 7919.408803897: branches: ffffffffc0f72e3d vmx_handle_exit+0xd ([kernel.kallsyms]) => ffffffffc0f727c0 __vmx_handle_exit+0x0 ([kernel.kallsyms])
1547 CPU 3/KVM 13376/13384 [002] 7919.408803897: branches: ffffffffc0f72b15 __vmx_handle_exit+0x355 ([kernel.kallsyms]) => ffffffffc0f60ae0 vmx_flush_pml_buffer+0x0 ([kernel.kallsyms])
1548 CPU 3/KVM 13376/13384 [002] 7919.408803903: branches: ffffffffc0f72994 __vmx_handle_exit+0x1d4 ([kernel.kallsyms]) => ffffffffc10b7090 kvm_emulate_cpuid+0x0 ([kernel.kallsyms])
1549 CPU 3/KVM 13376/13384 [002] 7919.408803903: branches: ffffffffc10b70f1 kvm_emulate_cpuid+0x61 ([kernel.kallsyms]) => ffffffffc10b6e10 kvm_cpuid+0x0 ([kernel.kallsyms])
1550 CPU 3/KVM 13376/13384 [002] 7919.408803941: branches: ffffffffc10b7125 kvm_emulate_cpuid+0x95 ([kernel.kallsyms]) => ffffffffc1093110 kvm_skip_emulated_instruction+0x0 ([kernel.kallsyms])
1551 CPU 3/KVM 13376/13384 [002] 7919.408803941: branches: ffffffffc109311f kvm_skip_emulated_instruction+0xf ([kernel.kallsyms]) => ffffffffc0f5e180 vmx_get_rflags+0x0 ([kernel.kallsyms])
1552 CPU 3/KVM 13376/13384 [002] 7919.408803951: branches: ffffffffc109312a kvm_skip_emulated_instruction+0x1a ([kernel.kallsyms]) => ffffffffc0f5fd30 vmx_skip_emulated_instruction+0x0 ([kernel.kallsyms])
1553 CPU 3/KVM 13376/13384 [002] 7919.408803951: branches: ffffffffc0f5fd79 vmx_skip_emulated_instruction+0x49 ([kernel.kallsyms]) => ffffffffc0f5fb50 skip_emulated_instruction+0x0 ([kernel.kallsyms])
1554 CPU 3/KVM 13376/13384 [002] 7919.408803956: branches: ffffffffc0f5fc68 skip_emulated_instruction+0x118 ([kernel.kallsyms]) => ffffffffc0f6a940 vmx_cache_reg+0x0 ([kernel.kallsyms])
1555 CPU 3/KVM 13376/13384 [002] 7919.408803964: branches: ffffffffc0f5fc11 skip_emulated_instruction+0xc1 ([kernel.kallsyms]) => ffffffffc0f5f9e0 vmx_set_interrupt_shadow+0x0 ([kernel.kallsyms])
1556 CPU 3/KVM 13376/13384 [002] 7919.408803980: branches: ffffffffc109f8b1 vcpu_run+0x71 ([kernel.kallsyms]) => ffffffffc10ad2f0 kvm_cpu_has_pending_timer+0x0 ([kernel.kallsyms])
1557 CPU 3/KVM 13376/13384 [002] 7919.408803980: branches: ffffffffc10ad2fb kvm_cpu_has_pending_timer+0xb ([kernel.kallsyms]) => ffffffffc10b0490 apic_has_pending_timer+0x0 ([kernel.kallsyms])
1558 CPU 3/KVM 13376/13384 [002] 7919.408803991: branches: ffffffffc109f899 vcpu_run+0x59 ([kernel.kallsyms]) => ffffffffc109c860 vcpu_enter_guest+0x0 ([kernel.kallsyms])
1559 CPU 3/KVM 13376/13384 [002] 7919.408803993: branches: ffffffffc109cd4c vcpu_enter_guest+0x4ec ([kernel.kallsyms]) => ffffffffc0f69140 vmx_prepare_switch_to_guest+0x0 ([kernel.kallsyms])
1560 CPU 3/KVM 13376/13384 [002] 7919.408803996: branches: ffffffffc109cd7d vcpu_enter_guest+0x51d ([kernel.kallsyms]) => ffffffffb234f930 __srcu_read_unlock+0x0 ([kernel.kallsyms])
1561 CPU 3/KVM 13376/13384 [002] 7919.408803996: branches: ffffffffc109cd9c vcpu_enter_guest+0x53c ([kernel.kallsyms]) => ffffffffc0f609b0 vmx_sync_pir_to_irr+0x0 ([kernel.kallsyms])
1562 CPU 3/KVM 13376/13384 [002] 7919.408803996: branches: ffffffffc0f60a6d vmx_sync_pir_to_irr+0xbd ([kernel.kallsyms]) => ffffffffc10adc20 kvm_lapic_find_highest_irr+0x0 ([kernel.kallsyms])
1563 CPU 3/KVM 13376/13384 [002] 7919.408804010: branches: ffffffffc0f60abd vmx_sync_pir_to_irr+0x10d ([kernel.kallsyms]) => ffffffffc0f60820 vmx_set_rvi+0x0 ([kernel.kallsyms])
1564 CPU 3/KVM 13376/13384 [002] 7919.408804019: branches: ffffffffc109ceca vcpu_enter_guest+0x66a ([kernel.kallsyms]) => ffffffffb2249840 fpregs_assert_state_consistent+0x0 ([kernel.kallsyms])
1565 CPU 3/KVM 13376/13384 [002] 7919.408804021: branches: ffffffffc109cf10 vcpu_enter_guest+0x6b0 ([kernel.kallsyms]) => ffffffffc0f65f30 vmx_vcpu_run+0x0 ([kernel.kallsyms])
1566 CPU 3/KVM 13376/13384 [002] 7919.408804024: branches: ffffffffc0f6603b vmx_vcpu_run+0x10b ([kernel.kallsyms]) => ffffffffb229bed0 __get_current_cr3_fast+0x0 ([kernel.kallsyms])
1567 CPU 3/KVM 13376/13384 [002] 7919.408804024: branches: ffffffffc0f66055 vmx_vcpu_run+0x125 ([kernel.kallsyms]) => ffffffffb2253050 cr4_read_shadow+0x0 ([kernel.kallsyms])
1568 CPU 3/KVM 13376/13384 [002] 7919.408804030: branches: ffffffffc0f6608d vmx_vcpu_run+0x15d ([kernel.kallsyms]) => ffffffffc10921e0 kvm_load_guest_xsave_state+0x0 ([kernel.kallsyms])
1569 CPU 3/KVM 13376/13384 [002] 7919.408804030: branches: ffffffffc1092207 kvm_load_guest_xsave_state+0x27 ([kernel.kallsyms]) => ffffffffc1092110 kvm_load_guest_xsave_state.part.0+0x0 ([kernel.kallsyms])
1570 CPU 3/KVM 13376/13384 [002] 7919.408804032: branches: ffffffffc0f660c6 vmx_vcpu_run+0x196 ([kernel.kallsyms]) => ffffffffb22061a0 perf_guest_get_msrs+0x0 ([kernel.kallsyms])
1571 CPU 3/KVM 13376/13384 [002] 7919.408804032: branches: ffffffffb22061a9 perf_guest_get_msrs+0x9 ([kernel.kallsyms]) => ffffffffb220cda0 intel_guest_get_msrs+0x0 ([kernel.kallsyms])
1572 CPU 3/KVM 13376/13384 [002] 7919.408804039: branches: ffffffffc0f66109 vmx_vcpu_run+0x1d9 ([kernel.kallsyms]) => ffffffffc0f652c0 clear_atomic_switch_msr+0x0 ([kernel.kallsyms])
1573 CPU 3/KVM 13376/13384 [002] 7919.408804040: branches: ffffffffc0f66119 vmx_vcpu_run+0x1e9 ([kernel.kallsyms]) => ffffffffc0f73f60 intel_pmu_lbr_is_enabled+0x0 ([kernel.kallsyms])
1574 CPU 3/KVM 13376/13384 [002] 7919.408804042: branches: ffffffffc0f73f81 intel_pmu_lbr_is_enabled+0x21 ([kernel.kallsyms]) => ffffffffc10b68e0 kvm_find_cpuid_entry+0x0 ([kernel.kallsyms])
1575 CPU 3/KVM 13376/13384 [002] 7919.408804045: branches: ffffffffc0f66454 vmx_vcpu_run+0x524 ([kernel.kallsyms]) => ffffffffc0f61ff0 vmx_update_hv_timer+0x0 ([kernel.kallsyms])
1576 CPU 3/KVM 13376/13384 [002] 7919.408804057: branches: ffffffffc0f66142 vmx_vcpu_run+0x212 ([kernel.kallsyms]) => ffffffffc10af100 kvm_wait_lapic_expire+0x0 ([kernel.kallsyms])
1577 CPU 3/KVM 13376/13384 [002] 7919.408804057: branches: ffffffffc0f66156 vmx_vcpu_run+0x226 ([kernel.kallsyms]) => ffffffffb2255c60 x86_virt_spec_ctrl+0x0 ([kernel.kallsyms])
1578 CPU 3/KVM 13376/13384 [002] 7919.408804057: branches: ffffffffc0f66161 vmx_vcpu_run+0x231 ([kernel.kallsyms]) => ffffffffc0f8eb20 vmx_vcpu_enter_exit+0x0 ([kernel.kallsyms])
1579 CPU 3/KVM 13376/13384 [002] 7919.408804057: branches: ffffffffc0f8eb44 vmx_vcpu_enter_exit+0x24 ([kernel.kallsyms]) => ffffffffb2353e10 rcu_note_context_switch+0x0 ([kernel.kallsyms])
1580 CPU 3/KVM 13376/13384 [002] 7919.408804057: branches: ffffffffb2353e1c rcu_note_context_switch+0xc ([kernel.kallsyms]) => ffffffffb2353db0 rcu_qs+0x0 ([kernel.kallsyms])
1581 CPU 3/KVM 13376/13384 [002] 7919.408804066: branches: ffffffffc0f8ebe0 vmx_vcpu_enter_exit+0xc0 ([kernel.kallsyms]) => ffffffffc0f8edc0 __vmx_vcpu_run+0x0 ([kernel.kallsyms])
1582 CPU 3/KVM 13376/13384 [002] 7919.408804066: branches: ffffffffc0f8edd5 __vmx_vcpu_run+0x15 ([kernel.kallsyms]) => ffffffffc0f8eca0 vmx_update_host_rsp+0x0 ([kernel.kallsyms])
1583 CPU 3/KVM 13376/13384 [002] 7919.408804066: branches: ffffffffc0f8ee1b __vmx_vcpu_run+0x5b ([kernel.kallsyms]) => ffffffffc0f8ed60 vmx_vmenter+0x0 ([kernel.kallsyms])
1584 CPU 3/KVM 13376/13384 [002] 7919.408804162: branches: ffffffffc0f8ed62 vmx_vmenter+0x2 ([kernel.kallsyms]) => 0 [unknown] ([unknown])
1585 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804162: branches: 0 [unknown] ([unknown]) => 7f851c9b5a5c init_cacheinfo+0x3ac (/usr/lib/x86_64-linux-gnu/libc-2.31.so)
1586 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804273: branches: 7f851cb7c0e4 _dl_init+0x74 (/usr/lib/x86_64-linux-gnu/ld-2.31.so) => 7f851cb7bf50 call_init.part.0+0x0 (/usr/lib/x86_64-linux-gnu/ld-2.31.so)
1587 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804526: branches: 55e0c00136f0 _start+0x0 (/usr/bin/uname) => ffffffff83200ac0 asm_exc_page_fault+0x0 ([kernel.kallsyms])
1588 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804526: branches: ffffffff83200ac3 asm_exc_page_fault+0x3 ([kernel.kallsyms]) => ffffffff83201290 error_entry+0x0 ([kernel.kallsyms])
1589 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804534: branches: ffffffff832012fa error_entry+0x6a ([kernel.kallsyms]) => ffffffff830b59a0 sync_regs+0x0 ([kernel.kallsyms])
1590 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804631: branches: ffffffff83200ad9 asm_exc_page_fault+0x19 ([kernel.kallsyms]) => ffffffff830b8210 exc_page_fault+0x0 ([kernel.kallsyms])
1591 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804631: branches: ffffffff830b82a4 exc_page_fault+0x94 ([kernel.kallsyms]) => ffffffff830b80e0 __kvm_handle_async_pf+0x0 ([kernel.kallsyms])
1592 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804631: branches: ffffffff830b80ed __kvm_handle_async_pf+0xd ([kernel.kallsyms]) => ffffffff830b80c0 kvm_read_and_reset_apf_flags+0x0 ([kernel.kallsyms])
1593
1594
1595Tracing Virtual Machines - Guest Code
1596-------------------------------------
1597
1598A common case for KVM test programs is that the test program acts as the
1599hypervisor, creating, running and destroying the virtual machine, and
1600providing the guest object code from its own object code. In this case,
1601the VM is not running an OS, but only the functions loaded into it by the
1602hypervisor test program, and conveniently, loaded at the same virtual
1603addresses. To support that, option "--guest-code" has been added to perf script
1604and perf kvm report.
1605
1606Here is an example tracing a test program from the kernel's KVM selftests:
1607
1608 # perf record --kcore -e intel_pt/cyc/ -- tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test
1609 [ perf record: Woken up 1 times to write data ]
1610 [ perf record: Captured and wrote 0.280 MB perf.data ]
1611 # perf script --guest-code --itrace=bep --ns -F-period,+addr,+flags
1612 [SNIP]
1613 tsc_msrs_test 18436 [007] 10897.962087733: branches: call ffffffffc13b2ff5 __vmx_vcpu_run+0x15 (vmlinux) => ffffffffc13b2f50 vmx_update_host_rsp+0x0 (vmlinux)
1614 tsc_msrs_test 18436 [007] 10897.962087733: branches: return ffffffffc13b2f5d vmx_update_host_rsp+0xd (vmlinux) => ffffffffc13b2ffa __vmx_vcpu_run+0x1a (vmlinux)
1615 tsc_msrs_test 18436 [007] 10897.962087733: branches: call ffffffffc13b303b __vmx_vcpu_run+0x5b (vmlinux) => ffffffffc13b2f80 vmx_vmenter+0x0 (vmlinux)
1616 tsc_msrs_test 18436 [007] 10897.962087836: branches: vmentry ffffffffc13b2f82 vmx_vmenter+0x2 (vmlinux) => 0 [unknown] ([unknown])
1617 [guest/18436] 18436 [007] 10897.962087836: branches: vmentry 0 [unknown] ([unknown]) => 402c81 guest_code+0x131 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test)
1618 [guest/18436] 18436 [007] 10897.962087836: branches: call 402c81 guest_code+0x131 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test) => 40dba0 ucall+0x0 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test)
1619 [guest/18436] 18436 [007] 10897.962088248: branches: vmexit 40dba0 ucall+0x0 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test) => 0 [unknown] ([unknown])
1620 tsc_msrs_test 18436 [007] 10897.962088248: branches: vmexit 0 [unknown] ([unknown]) => ffffffffc13b2fa0 vmx_vmexit+0x0 (vmlinux)
1621 tsc_msrs_test 18436 [007] 10897.962088248: branches: jmp ffffffffc13b2fa0 vmx_vmexit+0x0 (vmlinux) => ffffffffc13b2fd2 vmx_vmexit+0x32 (vmlinux)
1622 tsc_msrs_test 18436 [007] 10897.962088256: branches: return ffffffffc13b2fd2 vmx_vmexit+0x32 (vmlinux) => ffffffffc13b3040 __vmx_vcpu_run+0x60 (vmlinux)
1623 tsc_msrs_test 18436 [007] 10897.962088270: branches: return ffffffffc13b30b6 __vmx_vcpu_run+0xd6 (vmlinux) => ffffffffc13b2f2e vmx_vcpu_enter_exit+0x4e (vmlinux)
1624 [SNIP]
1625 tsc_msrs_test 18436 [007] 10897.962089321: branches: call ffffffffc13b2ff5 __vmx_vcpu_run+0x15 (vmlinux) => ffffffffc13b2f50 vmx_update_host_rsp+0x0 (vmlinux)
1626 tsc_msrs_test 18436 [007] 10897.962089321: branches: return ffffffffc13b2f5d vmx_update_host_rsp+0xd (vmlinux) => ffffffffc13b2ffa __vmx_vcpu_run+0x1a (vmlinux)
1627 tsc_msrs_test 18436 [007] 10897.962089321: branches: call ffffffffc13b303b __vmx_vcpu_run+0x5b (vmlinux) => ffffffffc13b2f80 vmx_vmenter+0x0 (vmlinux)
1628 tsc_msrs_test 18436 [007] 10897.962089424: branches: vmentry ffffffffc13b2f82 vmx_vmenter+0x2 (vmlinux) => 0 [unknown] ([unknown])
1629 [guest/18436] 18436 [007] 10897.962089424: branches: vmentry 0 [unknown] ([unknown]) => 40dba0 ucall+0x0 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test)
1630 [guest/18436] 18436 [007] 10897.962089701: branches: jmp 40dc1b ucall+0x7b (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test) => 40dc39 ucall+0x99 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test)
1631 [guest/18436] 18436 [007] 10897.962089701: branches: jcc 40dc3c ucall+0x9c (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test) => 40dc20 ucall+0x80 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test)
1632 [guest/18436] 18436 [007] 10897.962089701: branches: jcc 40dc3c ucall+0x9c (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test) => 40dc20 ucall+0x80 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test)
1633 [guest/18436] 18436 [007] 10897.962089701: branches: jcc 40dc37 ucall+0x97 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test) => 40dc50 ucall+0xb0 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test)
1634 [guest/18436] 18436 [007] 10897.962089878: branches: vmexit 40dc55 ucall+0xb5 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test) => 0 [unknown] ([unknown])
1635 tsc_msrs_test 18436 [007] 10897.962089878: branches: vmexit 0 [unknown] ([unknown]) => ffffffffc13b2fa0 vmx_vmexit+0x0 (vmlinux)
1636 tsc_msrs_test 18436 [007] 10897.962089878: branches: jmp ffffffffc13b2fa0 vmx_vmexit+0x0 (vmlinux) => ffffffffc13b2fd2 vmx_vmexit+0x32 (vmlinux)
1637 tsc_msrs_test 18436 [007] 10897.962089887: branches: return ffffffffc13b2fd2 vmx_vmexit+0x32 (vmlinux) => ffffffffc13b3040 __vmx_vcpu_run+0x60 (vmlinux)
1638 tsc_msrs_test 18436 [007] 10897.962089901: branches: return ffffffffc13b30b6 __vmx_vcpu_run+0xd6 (vmlinux) => ffffffffc13b2f2e vmx_vcpu_enter_exit+0x4e (vmlinux)
1639 [SNIP]
1640
1641 # perf kvm --guest-code --guest --host report -i perf.data --stdio | head -20
1642
1643 # To display the perf.data header info, please use --header/--header-only options.
1644 #
1645 #
1646 # Total Lost Samples: 0
1647 #
1648 # Samples: 12 of event 'instructions'
1649 # Event count (approx.): 2274583
1650 #
1651 # Children Self Command Shared Object Symbol
1652 # ........ ........ ............. .................... ...........................................
1653 #
1654 54.70% 0.00% tsc_msrs_test [kernel.vmlinux] [k] entry_SYSCALL_64_after_hwframe
1655 |
1656 ---entry_SYSCALL_64_after_hwframe
1657 do_syscall_64
1658 |
1659 |--29.44%--syscall_exit_to_user_mode
1660 | exit_to_user_mode_prepare
1661 | task_work_run
1662 | __fput
1663
1664
1665Event Trace
1666-----------
1667
1668Event Trace records information about asynchronous events, for example interrupts,
1669faults, VM exits and entries. The information is recorded in CFE and EVD packets,
1670and also the Interrupt Flag is recorded on the MODE.Exec packet. The CFE packet
1671contains a type field to identify one of the following:
1672
1673 1 INTR interrupt, fault, exception, NMI
1674 2 IRET interrupt return
1675 3 SMI system management interrupt
1676 4 RSM resume from system management mode
1677 5 SIPI startup interprocessor interrupt
1678 6 INIT INIT signal
1679 7 VMENTRY VM-Entry
1680 8 VMEXIT VM-Entry
1681 9 VMEXIT_INTR VM-Exit due to interrupt
1682 10 SHUTDOWN Shutdown
1683
1684For more details, refer to the Intel 64 and IA-32 Architectures Software
1685Developer Manuals (version 076 or later).
1686
1687The capability to do Event Trace is indicated by the
1688/sys/bus/event_source/devices/intel_pt/caps/event_trace file.
1689
1690Event trace is selected for recording using the "event" config term. e.g.
1691
1692 perf record -e intel_pt/event/u uname
1693
1694Event trace events are output using the --itrace I option. e.g.
1695
1696 perf script --itrace=Ie
1697
1698perf script displays events containing CFE type, vector and event data,
1699in the form:
1700
1701 evt: hw int (t) cfe: INTR IP: 1 vector: 3 PFA: 0x8877665544332211
1702
1703The IP flag indicates if the event binds to an IP, which includes any case where
1704flow control packet generation is enabled, as well as when CFE packet IP bit is
1705set.
1706
1707perf script displays events containing changes to the Interrupt Flag in the form:
1708
1709 iflag: t IFLAG: 1->0 via branch
1710
1711where "via branch" indicates a branch (interrupt or return from interrupt) and
1712"non branch" indicates an instruction such as CFI, STI or POPF).
1713
1714In addition, the current state of the interrupt flag is indicated by the presence
1715or absence of the "D" (interrupt disabled) perf script flag. If the interrupt
1716flag is changed, then the "t" flag is also included i.e.
1717
1718 no flag, interrupts enabled IF=1
1719 t interrupts become disabled IF=1 -> IF=0
1720 D interrupts are disabled IF=0
1721 Dt interrupts become enabled IF=0 -> IF=1
1722
1723The intel-pt-events.py script illustrates how to access Event Trace information
1724using a Python script.
1725
1726
1727TNT Disable
1728-----------
1729
1730TNT packets are disabled using the "notnt" config term. e.g.
1731
1732 perf record -e intel_pt/notnt/u uname
1733
1734In that case the --itrace q option is forced because walking executable code
1735to reconstruct the control flow is not possible.
1736
1737
1738Emulated PTWRITE
1739----------------
1740
1741Later perf tools support a method to emulate the ptwrite instruction, which
1742can be useful if hardware does not support the ptwrite instruction.
1743
1744Instead of using the ptwrite instruction, a function is used which produces
1745a trace that encodes the payload data into TNT packets. Here is an example
1746of the function:
1747
1748 #include <stdint.h>
1749
1750 void perf_emulate_ptwrite(uint64_t x)
1751 __attribute__((externally_visible, noipa, no_instrument_function, naked));
1752
1753 #define PERF_EMULATE_PTWRITE_8_BITS \
1754 "1: shl %rax\n" \
1755 " jc 1f\n" \
1756 "1: shl %rax\n" \
1757 " jc 1f\n" \
1758 "1: shl %rax\n" \
1759 " jc 1f\n" \
1760 "1: shl %rax\n" \
1761 " jc 1f\n" \
1762 "1: shl %rax\n" \
1763 " jc 1f\n" \
1764 "1: shl %rax\n" \
1765 " jc 1f\n" \
1766 "1: shl %rax\n" \
1767 " jc 1f\n" \
1768 "1: shl %rax\n" \
1769 " jc 1f\n"
1770
1771 /* Undefined instruction */
1772 #define PERF_EMULATE_PTWRITE_UD2 ".byte 0x0f, 0x0b\n"
1773
1774 #define PERF_EMULATE_PTWRITE_MAGIC PERF_EMULATE_PTWRITE_UD2 ".ascii \"perf,ptwrite \"\n"
1775
1776 void perf_emulate_ptwrite(uint64_t x __attribute__ ((__unused__)))
1777 {
1778 /* Assumes SysV ABI : x passed in rdi */
1779 __asm__ volatile (
1780 "jmp 1f\n"
1781 PERF_EMULATE_PTWRITE_MAGIC
1782 "1: mov %rdi, %rax\n"
1783 PERF_EMULATE_PTWRITE_8_BITS
1784 PERF_EMULATE_PTWRITE_8_BITS
1785 PERF_EMULATE_PTWRITE_8_BITS
1786 PERF_EMULATE_PTWRITE_8_BITS
1787 PERF_EMULATE_PTWRITE_8_BITS
1788 PERF_EMULATE_PTWRITE_8_BITS
1789 PERF_EMULATE_PTWRITE_8_BITS
1790 PERF_EMULATE_PTWRITE_8_BITS
1791 "1: ret\n"
1792 );
1793 }
1794
1795For example, a test program with the function above:
1796
1797 #include <stdio.h>
1798 #include <stdint.h>
1799 #include <stdlib.h>
1800
1801 #include "perf_emulate_ptwrite.h"
1802
1803 int main(int argc, char *argv[])
1804 {
1805 uint64_t x = 0;
1806
1807 if (argc > 1)
1808 x = strtoull(argv[1], NULL, 0);
1809 perf_emulate_ptwrite(x);
1810 return 0;
1811 }
1812
1813Can be compiled and traced:
1814
1815 $ gcc -Wall -Wextra -O3 -g -o eg_ptw eg_ptw.c
1816 $ perf record -e intel_pt//u ./eg_ptw 0x1234567890abcdef
1817 [ perf record: Woken up 1 times to write data ]
1818 [ perf record: Captured and wrote 0.017 MB perf.data ]
1819 $ perf script --itrace=ew
1820 eg_ptw 19875 [007] 8061.235912: ptwrite: IP: 0 payload: 0x1234567890abcdef 55701249a196 perf_emulate_ptwrite+0x16 (/home/user/eg_ptw)
1821 $
1822
1823
1824EXAMPLE
1825-------
1826
1827Examples can be found on perf wiki page "Perf tools support for Intel® Processor Trace":
1828
1829https://perf.wiki.kernel.org/index.php/Perf_tools_support_for_Intel%C2%AE_Processor_Trace
1830
1831
1832SEE ALSO
1833--------
1834
1835linkperf:perf-record[1], linkperf:perf-script[1], linkperf:perf-report[1],
1836linkperf:perf-inject[1]
1perf-intel-pt(1)
2================
3
4NAME
5----
6perf-intel-pt - Support for Intel Processor Trace within perf tools
7
8SYNOPSIS
9--------
10[verse]
11'perf record' -e intel_pt//
12
13DESCRIPTION
14-----------
15
16Intel Processor Trace (Intel PT) is an extension of Intel Architecture that
17collects information about software execution such as control flow, execution
18modes and timings and formats it into highly compressed binary packets.
19Technical details are documented in the Intel 64 and IA-32 Architectures
20Software Developer Manuals, Chapter 36 Intel Processor Trace.
21
22Intel PT is first supported in Intel Core M and 5th generation Intel Core
23processors that are based on the Intel micro-architecture code name Broadwell.
24
25Trace data is collected by 'perf record' and stored within the perf.data file.
26See below for options to 'perf record'.
27
28Trace data must be 'decoded' which involves walking the object code and matching
29the trace data packets. For example a TNT packet only tells whether a
30conditional branch was taken or not taken, so to make use of that packet the
31decoder must know precisely which instruction was being executed.
32
33Decoding is done on-the-fly. The decoder outputs samples in the same format as
34samples output by perf hardware events, for example as though the "instructions"
35or "branches" events had been recorded. Presently 3 tools support this:
36'perf script', 'perf report' and 'perf inject'. See below for more information
37on using those tools.
38
39The main distinguishing feature of Intel PT is that the decoder can determine
40the exact flow of software execution. Intel PT can be used to understand why
41and how did software get to a certain point, or behave a certain way. The
42software does not have to be recompiled, so Intel PT works with debug or release
43builds, however the executed images are needed - which makes use in JIT-compiled
44environments, or with self-modified code, a challenge. Also symbols need to be
45provided to make sense of addresses.
46
47A limitation of Intel PT is that it produces huge amounts of trace data
48(hundreds of megabytes per second per core) which takes a long time to decode,
49for example two or three orders of magnitude longer than it took to collect.
50Another limitation is the performance impact of tracing, something that will
51vary depending on the use-case and architecture.
52
53
54Quickstart
55----------
56
57It is important to start small. That is because it is easy to capture vastly
58more data than can possibly be processed.
59
60The simplest thing to do with Intel PT is userspace profiling of small programs.
61Data is captured with 'perf record' e.g. to trace 'ls' userspace-only:
62
63 perf record -e intel_pt//u ls
64
65And profiled with 'perf report' e.g.
66
67 perf report
68
69To also trace kernel space presents a problem, namely kernel self-modifying
70code. A fairly good kernel image is available in /proc/kcore but to get an
71accurate image a copy of /proc/kcore needs to be made under the same conditions
72as the data capture. 'perf record' can make a copy of /proc/kcore if the option
73--kcore is used, but access to /proc/kcore is restricted e.g.
74
75 sudo perf record -o pt_ls --kcore -e intel_pt// -- ls
76
77which will create a directory named 'pt_ls' and put the perf.data file (named
78simply 'data') and copies of /proc/kcore, /proc/kallsyms and /proc/modules into
79it. The other tools understand the directory format, so to use 'perf report'
80becomes:
81
82 sudo perf report -i pt_ls
83
84Because samples are synthesized after-the-fact, the sampling period can be
85selected for reporting. e.g. sample every microsecond
86
87 sudo perf report pt_ls --itrace=i1usge
88
89See the sections below for more information about the --itrace option.
90
91Beware the smaller the period, the more samples that are produced, and the
92longer it takes to process them.
93
94Also note that the coarseness of Intel PT timing information will start to
95distort the statistical value of the sampling as the sampling period becomes
96smaller.
97
98To represent software control flow, "branches" samples are produced. By default
99a branch sample is synthesized for every single branch. To get an idea what
100data is available you can use the 'perf script' tool with all itrace sampling
101options, which will list all the samples.
102
103 perf record -e intel_pt//u ls
104 perf script --itrace=iybxwpe
105
106An interesting field that is not printed by default is 'flags' which can be
107displayed as follows:
108
109 perf script --itrace=iybxwpe -F+flags
110
111The flags are "bcrosyiABExghDt" which stand for branch, call, return, conditional,
112system, asynchronous, interrupt, transaction abort, trace begin, trace end,
113in transaction, VM-entry, VM-exit, interrupt disabled, and interrupt disable
114toggle respectively.
115
116perf script also supports higher level ways to dump instruction traces:
117
118 perf script --insn-trace --xed
119
120Dump all instructions. This requires installing the xed tool (see XED below)
121Dumping all instructions in a long trace can be fairly slow. It is usually better
122to start with higher level decoding, like
123
124 perf script --call-trace
125
126or
127
128 perf script --call-ret-trace
129
130and then select a time range of interest. The time range can then be examined
131in detail with
132
133 perf script --time starttime,stoptime --insn-trace --xed
134
135While examining the trace it's also useful to filter on specific CPUs using
136the -C option
137
138 perf script --time starttime,stoptime --insn-trace --xed -C 1
139
140Dump all instructions in time range on CPU 1.
141
142Another interesting field that is not printed by default is 'ipc' which can be
143displayed as follows:
144
145 perf script --itrace=be -F+ipc
146
147There are two ways that instructions-per-cycle (IPC) can be calculated depending
148on the recording.
149
150If the 'cyc' config term (see config terms section below) was used, then IPC
151and cycle events are calculated using the cycle count from CYC packets, otherwise
152MTC packets are used - refer to the 'mtc' config term. When MTC is used, however,
153the values are less accurate because the timing is less accurate.
154
155Because Intel PT does not update the cycle count on every branch or instruction,
156the values will often be zero. When there are values, they will be the number
157of instructions and number of cycles since the last update, and thus represent
158the average IPC cycle count since the last IPC for that event type.
159Note IPC for "branches" events is calculated separately from IPC for "instructions"
160events.
161
162Even with the 'cyc' config term, it is possible to produce IPC information for
163every change of timestamp, but at the expense of accuracy. That is selected by
164specifying the itrace 'A' option. Due to the granularity of timestamps, the
165actual number of cycles increases even though the cycles reported does not.
166The number of instructions is known, but if IPC is reported, cycles can be too
167low and so IPC is too high. Note that inaccuracy decreases as the period of
168sampling increases i.e. if the number of cycles is too low by a small amount,
169that becomes less significant if the number of cycles is large. It may also be
170useful to use the 'A' option in conjunction with dlfilter-show-cycles.so to
171provide higher granularity cycle information.
172
173Also note that the IPC instruction count may or may not include the current
174instruction. If the cycle count is associated with an asynchronous branch
175(e.g. page fault or interrupt), then the instruction count does not include the
176current instruction, otherwise it does. That is consistent with whether or not
177that instruction has retired when the cycle count is updated.
178
179Another note, in the case of "branches" events, non-taken branches are not
180presently sampled, so IPC values for them do not appear e.g. a CYC packet with a
181TNT packet that starts with a non-taken branch. To see every possible IPC
182value, "instructions" events can be used e.g. --itrace=i0ns
183
184While it is possible to create scripts to analyze the data, an alternative
185approach is available to export the data to a sqlite or postgresql database.
186Refer to script export-to-sqlite.py or export-to-postgresql.py for more details,
187and to script exported-sql-viewer.py for an example of using the database.
188
189There is also script intel-pt-events.py which provides an example of how to
190unpack the raw data for power events and PTWRITE. The script also displays
191branches, and supports 2 additional modes selected by option:
192
193 - --insn-trace - instruction trace
194 - --src-trace - source trace
195
196The intel-pt-events.py script also has options:
197
198 - --all-switch-events - display all switch events, not only the last consecutive.
199 - --interleave [<n>] - interleave sample output for the same timestamp so that
200 no more than n samples for a CPU are displayed in a row. 'n' defaults to 4.
201 Note this only affects the order of output, and only when the timestamp is the
202 same.
203
204As mentioned above, it is easy to capture too much data. One way to limit the
205data captured is to use 'snapshot' mode which is explained further below.
206Refer to 'new snapshot option' and 'Intel PT modes of operation' further below.
207
208Another problem that will be experienced is decoder errors. They can be caused
209by inability to access the executed image, self-modified or JIT-ed code, or the
210inability to match side-band information (such as context switches and mmaps)
211which results in the decoder not knowing what code was executed.
212
213There is also the problem of perf not being able to copy the data fast enough,
214resulting in data lost because the buffer was full. See 'Buffer handling' below
215for more details.
216
217
218perf record
219-----------
220
221new event
222~~~~~~~~~
223
224The Intel PT kernel driver creates a new PMU for Intel PT. PMU events are
225selected by providing the PMU name followed by the "config" separated by slashes.
226An enhancement has been made to allow default "config" e.g. the option
227
228 -e intel_pt//
229
230will use a default config value. Currently that is the same as
231
232 -e intel_pt/tsc,noretcomp=0/
233
234which is the same as
235
236 -e intel_pt/tsc=1,noretcomp=0/
237
238Note there are now new config terms - see section 'config terms' further below.
239
240The config terms are listed in /sys/devices/intel_pt/format. They are bit
241fields within the config member of the struct perf_event_attr which is
242passed to the kernel by the perf_event_open system call. They correspond to bit
243fields in the IA32_RTIT_CTL MSR. Here is a list of them and their definitions:
244
245 $ grep -H . /sys/bus/event_source/devices/intel_pt/format/*
246 /sys/bus/event_source/devices/intel_pt/format/cyc:config:1
247 /sys/bus/event_source/devices/intel_pt/format/cyc_thresh:config:19-22
248 /sys/bus/event_source/devices/intel_pt/format/mtc:config:9
249 /sys/bus/event_source/devices/intel_pt/format/mtc_period:config:14-17
250 /sys/bus/event_source/devices/intel_pt/format/noretcomp:config:11
251 /sys/bus/event_source/devices/intel_pt/format/psb_period:config:24-27
252 /sys/bus/event_source/devices/intel_pt/format/tsc:config:10
253
254Note that the default config must be overridden for each term i.e.
255
256 -e intel_pt/noretcomp=0/
257
258is the same as:
259
260 -e intel_pt/tsc=1,noretcomp=0/
261
262So, to disable TSC packets use:
263
264 -e intel_pt/tsc=0/
265
266It is also possible to specify the config value explicitly:
267
268 -e intel_pt/config=0x400/
269
270Note that, as with all events, the event is suffixed with event modifiers:
271
272 u userspace
273 k kernel
274 h hypervisor
275 G guest
276 H host
277 p precise ip
278
279'h', 'G' and 'H' are for virtualization which are not used by Intel PT.
280'p' is also not relevant to Intel PT. So only options 'u' and 'k' are
281meaningful for Intel PT.
282
283perf_event_attr is displayed if the -vv option is used e.g.
284
285 ------------------------------------------------------------
286 perf_event_attr:
287 type 6
288 size 112
289 config 0x400
290 { sample_period, sample_freq } 1
291 sample_type IP|TID|TIME|CPU|IDENTIFIER
292 read_format ID
293 disabled 1
294 inherit 1
295 exclude_kernel 1
296 exclude_hv 1
297 enable_on_exec 1
298 sample_id_all 1
299 ------------------------------------------------------------
300 sys_perf_event_open: pid 31104 cpu 0 group_fd -1 flags 0x8
301 sys_perf_event_open: pid 31104 cpu 1 group_fd -1 flags 0x8
302 sys_perf_event_open: pid 31104 cpu 2 group_fd -1 flags 0x8
303 sys_perf_event_open: pid 31104 cpu 3 group_fd -1 flags 0x8
304 ------------------------------------------------------------
305
306
307config terms
308~~~~~~~~~~~~
309
310The June 2015 version of Intel 64 and IA-32 Architectures Software Developer
311Manuals, Chapter 36 Intel Processor Trace, defined new Intel PT features.
312Some of the features are reflect in new config terms. All the config terms are
313described below.
314
315tsc Always supported. Produces TSC timestamp packets to provide
316 timing information. In some cases it is possible to decode
317 without timing information, for example a per-thread context
318 that does not overlap executable memory maps.
319
320 The default config selects tsc (i.e. tsc=1).
321
322noretcomp Always supported. Disables "return compression" so a TIP packet
323 is produced when a function returns. Causes more packets to be
324 produced but might make decoding more reliable.
325
326 The default config does not select noretcomp (i.e. noretcomp=0).
327
328psb_period Allows the frequency of PSB packets to be specified.
329
330 The PSB packet is a synchronization packet that provides a
331 starting point for decoding or recovery from errors.
332
333 Support for psb_period is indicated by:
334
335 /sys/bus/event_source/devices/intel_pt/caps/psb_cyc
336
337 which contains "1" if the feature is supported and "0"
338 otherwise.
339
340 Valid values are given by:
341
342 /sys/bus/event_source/devices/intel_pt/caps/psb_periods
343
344 which contains a hexadecimal value, the bits of which represent
345 valid values e.g. bit 2 set means value 2 is valid.
346
347 The psb_period value is converted to the approximate number of
348 trace bytes between PSB packets as:
349
350 2 ^ (value + 11)
351
352 e.g. value 3 means 16KiB bytes between PSBs
353
354 If an invalid value is entered, the error message
355 will give a list of valid values e.g.
356
357 $ perf record -e intel_pt/psb_period=15/u uname
358 Invalid psb_period for intel_pt. Valid values are: 0-5
359
360 If MTC packets are selected, the default config selects a value
361 of 3 (i.e. psb_period=3) or the nearest lower value that is
362 supported (0 is always supported). Otherwise the default is 0.
363
364 If decoding is expected to be reliable and the buffer is large
365 then a large PSB period can be used.
366
367 Because a TSC packet is produced with PSB, the PSB period can
368 also affect the granularity to timing information in the absence
369 of MTC or CYC.
370
371mtc Produces MTC timing packets.
372
373 MTC packets provide finer grain timestamp information than TSC
374 packets. MTC packets record time using the hardware crystal
375 clock (CTC) which is related to TSC packets using a TMA packet.
376
377 Support for this feature is indicated by:
378
379 /sys/bus/event_source/devices/intel_pt/caps/mtc
380
381 which contains "1" if the feature is supported and
382 "0" otherwise.
383
384 The frequency of MTC packets can also be specified - see
385 mtc_period below.
386
387mtc_period Specifies how frequently MTC packets are produced - see mtc
388 above for how to determine if MTC packets are supported.
389
390 Valid values are given by:
391
392 /sys/bus/event_source/devices/intel_pt/caps/mtc_periods
393
394 which contains a hexadecimal value, the bits of which represent
395 valid values e.g. bit 2 set means value 2 is valid.
396
397 The mtc_period value is converted to the MTC frequency as:
398
399 CTC-frequency / (2 ^ value)
400
401 e.g. value 3 means one eighth of CTC-frequency
402
403 Where CTC is the hardware crystal clock, the frequency of which
404 can be related to TSC via values provided in cpuid leaf 0x15.
405
406 If an invalid value is entered, the error message
407 will give a list of valid values e.g.
408
409 $ perf record -e intel_pt/mtc_period=15/u uname
410 Invalid mtc_period for intel_pt. Valid values are: 0,3,6,9
411
412 The default value is 3 or the nearest lower value
413 that is supported (0 is always supported).
414
415cyc Produces CYC timing packets.
416
417 CYC packets provide even finer grain timestamp information than
418 MTC and TSC packets. A CYC packet contains the number of CPU
419 cycles since the last CYC packet. Unlike MTC and TSC packets,
420 CYC packets are only sent when another packet is also sent.
421
422 Support for this feature is indicated by:
423
424 /sys/bus/event_source/devices/intel_pt/caps/psb_cyc
425
426 which contains "1" if the feature is supported and
427 "0" otherwise.
428
429 The number of CYC packets produced can be reduced by specifying
430 a threshold - see cyc_thresh below.
431
432cyc_thresh Specifies how frequently CYC packets are produced - see cyc
433 above for how to determine if CYC packets are supported.
434
435 Valid cyc_thresh values are given by:
436
437 /sys/bus/event_source/devices/intel_pt/caps/cycle_thresholds
438
439 which contains a hexadecimal value, the bits of which represent
440 valid values e.g. bit 2 set means value 2 is valid.
441
442 The cyc_thresh value represents the minimum number of CPU cycles
443 that must have passed before a CYC packet can be sent. The
444 number of CPU cycles is:
445
446 2 ^ (value - 1)
447
448 e.g. value 4 means 8 CPU cycles must pass before a CYC packet
449 can be sent. Note a CYC packet is still only sent when another
450 packet is sent, not at, e.g. every 8 CPU cycles.
451
452 If an invalid value is entered, the error message
453 will give a list of valid values e.g.
454
455 $ perf record -e intel_pt/cyc,cyc_thresh=15/u uname
456 Invalid cyc_thresh for intel_pt. Valid values are: 0-12
457
458 CYC packets are not requested by default.
459
460pt Specifies pass-through which enables the 'branch' config term.
461
462 The default config selects 'pt' if it is available, so a user will
463 never need to specify this term.
464
465branch Enable branch tracing. Branch tracing is enabled by default so to
466 disable branch tracing use 'branch=0'.
467
468 The default config selects 'branch' if it is available.
469
470ptw Enable PTWRITE packets which are produced when a ptwrite instruction
471 is executed.
472
473 Support for this feature is indicated by:
474
475 /sys/bus/event_source/devices/intel_pt/caps/ptwrite
476
477 which contains "1" if the feature is supported and
478 "0" otherwise.
479
480 As an alternative, refer to "Emulated PTWRITE" further below.
481
482fup_on_ptw Enable a FUP packet to follow the PTWRITE packet. The FUP packet
483 provides the address of the ptwrite instruction. In the absence of
484 fup_on_ptw, the decoder will use the address of the previous branch
485 if branch tracing is enabled, otherwise the address will be zero.
486 Note that fup_on_ptw will work even when branch tracing is disabled.
487
488pwr_evt Enable power events. The power events provide information about
489 changes to the CPU C-state.
490
491 Support for this feature is indicated by:
492
493 /sys/bus/event_source/devices/intel_pt/caps/power_event_trace
494
495 which contains "1" if the feature is supported and
496 "0" otherwise.
497
498event Enable Event Trace. The events provide information about asynchronous
499 events.
500
501 Support for this feature is indicated by:
502
503 /sys/bus/event_source/devices/intel_pt/caps/event_trace
504
505 which contains "1" if the feature is supported and
506 "0" otherwise.
507
508notnt Disable TNT packets. Without TNT packets, it is not possible to walk
509 executable code to reconstruct control flow, however FUP, TIP, TIP.PGE
510 and TIP.PGD packets still indicate asynchronous control flow, and (if
511 return compression is disabled - see noretcomp) return statements.
512 The advantage of eliminating TNT packets is reducing the size of the
513 trace and corresponding tracing overhead.
514
515 Support for this feature is indicated by:
516
517 /sys/bus/event_source/devices/intel_pt/caps/tnt_disable
518
519 which contains "1" if the feature is supported and
520 "0" otherwise.
521
522
523AUX area sampling option
524~~~~~~~~~~~~~~~~~~~~~~~~
525
526To select Intel PT "sampling" the AUX area sampling option can be used:
527
528 --aux-sample
529
530Optionally it can be followed by the sample size in bytes e.g.
531
532 --aux-sample=8192
533
534In addition, the Intel PT event to sample must be defined e.g.
535
536 -e intel_pt//u
537
538Samples on other events will be created containing Intel PT data e.g. the
539following will create Intel PT samples on the branch-misses event, note the
540events must be grouped using {}:
541
542 perf record --aux-sample -e '{intel_pt//u,branch-misses:u}'
543
544An alternative to '--aux-sample' is to add the config term 'aux-sample-size' to
545events. In this case, the grouping is implied e.g.
546
547 perf record -e intel_pt//u -e branch-misses/aux-sample-size=8192/u
548
549is the same as:
550
551 perf record -e '{intel_pt//u,branch-misses/aux-sample-size=8192/u}'
552
553but allows for also using an address filter e.g.:
554
555 perf record -e intel_pt//u --filter 'filter * @/bin/ls' -e branch-misses/aux-sample-size=8192/u -- ls
556
557It is important to select a sample size that is big enough to contain at least
558one PSB packet. If not a warning will be displayed:
559
560 Intel PT sample size (%zu) may be too small for PSB period (%zu)
561
562The calculation used for that is: if sample_size <= psb_period + 256 display the
563warning. When sampling is used, psb_period defaults to 0 (2KiB).
564
565The default sample size is 4KiB.
566
567The sample size is passed in aux_sample_size in struct perf_event_attr. The
568sample size is limited by the maximum event size which is 64KiB. It is
569difficult to know how big the event might be without the trace sample attached,
570but the tool validates that the sample size is not greater than 60KiB.
571
572
573new snapshot option
574~~~~~~~~~~~~~~~~~~~
575
576The difference between full trace and snapshot from the kernel's perspective is
577that in full trace we don't overwrite trace data that the user hasn't collected
578yet (and indicated that by advancing aux_tail), whereas in snapshot mode we let
579the trace run and overwrite older data in the buffer so that whenever something
580interesting happens, we can stop it and grab a snapshot of what was going on
581around that interesting moment.
582
583To select snapshot mode a new option has been added:
584
585 -S
586
587Optionally it can be followed by the snapshot size e.g.
588
589 -S0x100000
590
591The default snapshot size is the auxtrace mmap size. If neither auxtrace mmap size
592nor snapshot size is specified, then the default is 4MiB for privileged users
593(or if /proc/sys/kernel/perf_event_paranoid < 0), 128KiB for unprivileged users.
594If an unprivileged user does not specify mmap pages, the mmap pages will be
595reduced as described in the 'new auxtrace mmap size option' section below.
596
597The snapshot size is displayed if the option -vv is used e.g.
598
599 Intel PT snapshot size: %zu
600
601
602new auxtrace mmap size option
603~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
604
605Intel PT buffer size is specified by an addition to the -m option e.g.
606
607 -m,16
608
609selects a buffer size of 16 pages i.e. 64KiB.
610
611Note that the existing functionality of -m is unchanged. The auxtrace mmap size
612is specified by the optional addition of a comma and the value.
613
614The default auxtrace mmap size for Intel PT is 4MiB/page_size for privileged users
615(or if /proc/sys/kernel/perf_event_paranoid < 0), 128KiB for unprivileged users.
616If an unprivileged user does not specify mmap pages, the mmap pages will be
617reduced from the default 512KiB/page_size to 256KiB/page_size, otherwise the
618user is likely to get an error as they exceed their mlock limit (Max locked
619memory as shown in /proc/self/limits). Note that perf does not count the first
620512KiB (actually /proc/sys/kernel/perf_event_mlock_kb minus 1 page) per cpu
621against the mlock limit so an unprivileged user is allowed 512KiB per cpu plus
622their mlock limit (which defaults to 64KiB but is not multiplied by the number
623of cpus).
624
625In full-trace mode, powers of two are allowed for buffer size, with a minimum
626size of 2 pages. In snapshot mode or sampling mode, it is the same but the
627minimum size is 1 page.
628
629The mmap size and auxtrace mmap size are displayed if the -vv option is used e.g.
630
631 mmap length 528384
632 auxtrace mmap length 4198400
633
634
635Intel PT modes of operation
636~~~~~~~~~~~~~~~~~~~~~~~~~~~
637
638Intel PT can be used in 3 modes:
639 full-trace mode
640 sample mode
641 snapshot mode
642
643Full-trace mode traces continuously e.g.
644
645 perf record -e intel_pt//u uname
646
647Sample mode attaches a Intel PT sample to other events e.g.
648
649 perf record --aux-sample -e intel_pt//u -e branch-misses:u
650
651Snapshot mode captures the available data when a signal is sent or "snapshot"
652control command is issued. e.g. using a signal
653
654 perf record -v -e intel_pt//u -S ./loopy 1000000000 &
655 [1] 11435
656 kill -USR2 11435
657 Recording AUX area tracing snapshot
658
659Note that the signal sent is SIGUSR2.
660Note that "Recording AUX area tracing snapshot" is displayed because the -v
661option is used.
662
663The advantage of using "snapshot" control command is that the access is
664controlled by access to a FIFO e.g.
665
666 $ mkfifo perf.control
667 $ mkfifo perf.ack
668 $ cat perf.ack &
669 [1] 15235
670 $ sudo ~/bin/perf record --control fifo:perf.control,perf.ack -S -e intel_pt//u -- sleep 60 &
671 [2] 15243
672 $ ps -e | grep perf
673 15244 pts/1 00:00:00 perf
674 $ kill -USR2 15244
675 bash: kill: (15244) - Operation not permitted
676 $ echo snapshot > perf.control
677 ack
678
679The 3 Intel PT modes of operation cannot be used together.
680
681
682Buffer handling
683~~~~~~~~~~~~~~~
684
685There may be buffer limitations (i.e. single ToPa entry) which means that actual
686buffer sizes are limited to powers of 2 up to 4MiB (MAX_PAGE_ORDER). In order to
687provide other sizes, and in particular an arbitrarily large size, multiple
688buffers are logically concatenated. However an interrupt must be used to switch
689between buffers. That has two potential problems:
690 a) the interrupt may not be handled in time so that the current buffer
691 becomes full and some trace data is lost.
692 b) the interrupts may slow the system and affect the performance
693 results.
694
695If trace data is lost, the driver sets 'truncated' in the PERF_RECORD_AUX event
696which the tools report as an error.
697
698In full-trace mode, the driver waits for data to be copied out before allowing
699the (logical) buffer to wrap-around. If data is not copied out quickly enough,
700again 'truncated' is set in the PERF_RECORD_AUX event. If the driver has to
701wait, the intel_pt event gets disabled. Because it is difficult to know when
702that happens, perf tools always re-enable the intel_pt event after copying out
703data.
704
705
706Intel PT and build ids
707~~~~~~~~~~~~~~~~~~~~~~
708
709By default "perf record" post-processes the event stream to find all build ids
710for executables for all addresses sampled. Deliberately, Intel PT is not
711decoded for that purpose (it would take too long). Instead the build ids for
712all executables encountered (due to mmap, comm or task events) are included
713in the perf.data file.
714
715To see buildids included in the perf.data file use the command:
716
717 perf buildid-list
718
719If the perf.data file contains Intel PT data, that is the same as:
720
721 perf buildid-list --with-hits
722
723
724Snapshot mode and event disabling
725~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
726
727In order to make a snapshot, the intel_pt event is disabled using an IOCTL,
728namely PERF_EVENT_IOC_DISABLE. However doing that can also disable the
729collection of side-band information. In order to prevent that, a dummy
730software event has been introduced that permits tracking events (like mmaps) to
731continue to be recorded while intel_pt is disabled. That is important to ensure
732there is complete side-band information to allow the decoding of subsequent
733snapshots.
734
735A test has been created for that. To find the test:
736
737 perf test list
738 ...
739 23: Test using a dummy software event to keep tracking
740
741To run the test:
742
743 perf test 23
744 23: Test using a dummy software event to keep tracking : Ok
745
746
747perf record modes (nothing new here)
748~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
749
750perf record essentially operates in one of three modes:
751 per thread
752 per cpu
753 workload only
754
755"per thread" mode is selected by -t or by --per-thread (with -p or -u or just a
756workload).
757"per cpu" is selected by -C or -a.
758"workload only" mode is selected by not using the other options but providing a
759command to run (i.e. the workload).
760
761In per-thread mode an exact list of threads is traced. There is no inheritance.
762Each thread has its own event buffer.
763
764In per-cpu mode all processes (or processes from the selected cgroup i.e. -G
765option, or processes selected with -p or -u) are traced. Each cpu has its own
766buffer. Inheritance is allowed.
767
768In workload-only mode, the workload is traced but with per-cpu buffers.
769Inheritance is allowed. Note that you can now trace a workload in per-thread
770mode by using the --per-thread option.
771
772
773Privileged vs non-privileged users
774~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
775
776Unless /proc/sys/kernel/perf_event_paranoid is set to -1, unprivileged users
777have memory limits imposed upon them. That affects what buffer sizes they can
778have as outlined above.
779
780The v4.2 kernel introduced support for a context switch metadata event,
781PERF_RECORD_SWITCH, which allows unprivileged users to see when their processes
782are scheduled out and in, just not by whom, which is left for the
783PERF_RECORD_SWITCH_CPU_WIDE, that is only accessible in system wide context,
784which in turn requires CAP_PERFMON or CAP_SYS_ADMIN.
785
786Please see the 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context
787switches") commit, that introduces these metadata events for further info.
788
789When working with kernels < v4.2, the following considerations must be taken,
790as the sched:sched_switch tracepoints will be used to receive such information:
791
792Unless /proc/sys/kernel/perf_event_paranoid is set to -1, unprivileged users are
793not permitted to use tracepoints which means there is insufficient side-band
794information to decode Intel PT in per-cpu mode, and potentially workload-only
795mode too if the workload creates new processes.
796
797Note also, that to use tracepoints, read-access to debugfs is required. So if
798debugfs is not mounted or the user does not have read-access, it will again not
799be possible to decode Intel PT in per-cpu mode.
800
801
802sched_switch tracepoint
803~~~~~~~~~~~~~~~~~~~~~~~
804
805The sched_switch tracepoint is used to provide side-band data for Intel PT
806decoding in kernels where the PERF_RECORD_SWITCH metadata event isn't
807available.
808
809The sched_switch events are automatically added. e.g. the second event shown
810below:
811
812 $ perf record -vv -e intel_pt//u uname
813 ------------------------------------------------------------
814 perf_event_attr:
815 type 6
816 size 112
817 config 0x400
818 { sample_period, sample_freq } 1
819 sample_type IP|TID|TIME|CPU|IDENTIFIER
820 read_format ID
821 disabled 1
822 inherit 1
823 exclude_kernel 1
824 exclude_hv 1
825 enable_on_exec 1
826 sample_id_all 1
827 ------------------------------------------------------------
828 sys_perf_event_open: pid 31104 cpu 0 group_fd -1 flags 0x8
829 sys_perf_event_open: pid 31104 cpu 1 group_fd -1 flags 0x8
830 sys_perf_event_open: pid 31104 cpu 2 group_fd -1 flags 0x8
831 sys_perf_event_open: pid 31104 cpu 3 group_fd -1 flags 0x8
832 ------------------------------------------------------------
833 perf_event_attr:
834 type 2
835 size 112
836 config 0x108
837 { sample_period, sample_freq } 1
838 sample_type IP|TID|TIME|CPU|PERIOD|RAW|IDENTIFIER
839 read_format ID
840 inherit 1
841 sample_id_all 1
842 exclude_guest 1
843 ------------------------------------------------------------
844 sys_perf_event_open: pid -1 cpu 0 group_fd -1 flags 0x8
845 sys_perf_event_open: pid -1 cpu 1 group_fd -1 flags 0x8
846 sys_perf_event_open: pid -1 cpu 2 group_fd -1 flags 0x8
847 sys_perf_event_open: pid -1 cpu 3 group_fd -1 flags 0x8
848 ------------------------------------------------------------
849 perf_event_attr:
850 type 1
851 size 112
852 config 0x9
853 { sample_period, sample_freq } 1
854 sample_type IP|TID|TIME|IDENTIFIER
855 read_format ID
856 disabled 1
857 inherit 1
858 exclude_kernel 1
859 exclude_hv 1
860 mmap 1
861 comm 1
862 enable_on_exec 1
863 task 1
864 sample_id_all 1
865 mmap2 1
866 comm_exec 1
867 ------------------------------------------------------------
868 sys_perf_event_open: pid 31104 cpu 0 group_fd -1 flags 0x8
869 sys_perf_event_open: pid 31104 cpu 1 group_fd -1 flags 0x8
870 sys_perf_event_open: pid 31104 cpu 2 group_fd -1 flags 0x8
871 sys_perf_event_open: pid 31104 cpu 3 group_fd -1 flags 0x8
872 mmap size 528384B
873 AUX area mmap length 4194304
874 perf event ring buffer mmapped per cpu
875 Synthesizing auxtrace information
876 Linux
877 [ perf record: Woken up 1 times to write data ]
878 [ perf record: Captured and wrote 0.042 MB perf.data ]
879
880Note, the sched_switch event is only added if the user is permitted to use it
881and only in per-cpu mode.
882
883Note also, the sched_switch event is only added if TSC packets are requested.
884That is because, in the absence of timing information, the sched_switch events
885cannot be matched against the Intel PT trace.
886
887
888perf script
889-----------
890
891By default, perf script will decode trace data found in the perf.data file.
892This can be further controlled by new option --itrace.
893
894
895New --itrace option
896~~~~~~~~~~~~~~~~~~~
897
898Having no option is the same as
899
900 --itrace
901
902which, in turn, is the same as
903
904 --itrace=cepwxy
905
906The letters are:
907
908 i synthesize "instructions" events
909 y synthesize "cycles" events
910 b synthesize "branches" events
911 x synthesize "transactions" events
912 w synthesize "ptwrite" events
913 p synthesize "power" events (incl. PSB events)
914 c synthesize branches events (calls only)
915 r synthesize branches events (returns only)
916 o synthesize PEBS-via-PT events
917 I synthesize Event Trace events
918 e synthesize tracing error events
919 d create a debug log
920 g synthesize a call chain (use with i or x)
921 G synthesize a call chain on existing event records
922 l synthesize last branch entries (use with i or x)
923 L synthesize last branch entries on existing event records
924 s skip initial number of events
925 q quicker (less detailed) decoding
926 A approximate IPC
927 Z prefer to ignore timestamps (so-called "timeless" decoding)
928
929"Instructions" events look like they were recorded by "perf record -e
930instructions".
931
932"Cycles" events look like they were recorded by "perf record -e cycles"
933(ie., the default). Note that even with CYC packets enabled and no sampling,
934these are not fully accurate, since CYC packets are not emitted for each
935instruction, only when some other event (like an indirect branch, or a
936TNT packet representing multiple branches) happens causes a packet to
937be emitted. Thus, it is more effective for attributing cycles to functions
938(and possibly basic blocks) than to individual instructions, although it
939is not even perfect for functions (although it becomes better if the noretcomp
940option is active).
941
942"Branches" events look like they were recorded by "perf record -e branches". "c"
943and "r" can be combined to get calls and returns.
944
945"Transactions" events correspond to the start or end of transactions. The
946'flags' field can be used in perf script to determine whether the event is a
947transaction start, commit or abort.
948
949Note that "instructions", "cycles", "branches" and "transactions" events
950depend on code flow packets which can be disabled by using the config term
951"branch=0". Refer to the config terms section above.
952
953"ptwrite" events record the payload of the ptwrite instruction and whether
954"fup_on_ptw" was used. "ptwrite" events depend on PTWRITE packets which are
955recorded only if the "ptw" config term was used. Refer to the config terms
956section above. perf script "synth" field displays "ptwrite" information like
957this: "ip: 0 payload: 0x123456789abcdef0" where "ip" is 1 if "fup_on_ptw" was
958used.
959
960"Power" events correspond to power event packets and CBR (core-to-bus ratio)
961packets. While CBR packets are always recorded when tracing is enabled, power
962event packets are recorded only if the "pwr_evt" config term was used. Refer to
963the config terms section above. The power events record information about
964C-state changes, whereas CBR is indicative of CPU frequency. perf script
965"event,synth" fields display information like this:
966
967 cbr: cbr: 22 freq: 2189 MHz (200%)
968 mwait: hints: 0x60 extensions: 0x1
969 pwre: hw: 0 cstate: 2 sub-cstate: 0
970 exstop: ip: 1
971 pwrx: deepest cstate: 2 last cstate: 2 wake reason: 0x4
972
973Where:
974
975 "cbr" includes the frequency and the percentage of maximum non-turbo
976 "mwait" shows mwait hints and extensions
977 "pwre" shows C-state transitions (to a C-state deeper than C0) and
978 whether initiated by hardware
979 "exstop" indicates execution stopped and whether the IP was recorded
980 exactly,
981 "pwrx" indicates return to C0
982
983For more details refer to the Intel 64 and IA-32 Architectures Software
984Developer Manuals.
985
986PSB events show when a PSB+ occurred and also the byte-offset in the trace.
987Emitting a PSB+ can cause a CPU a slight delay. When doing timing analysis
988of code with Intel PT, it is useful to know if a timing bubble was caused
989by Intel PT or not.
990
991Error events show where the decoder lost the trace. Error events
992are quite important. Users must know if what they are seeing is a complete
993picture or not. The "e" option may be followed by flags which affect what errors
994will or will not be reported. Each flag must be preceded by either '+' or '-'.
995The flags supported by Intel PT are:
996
997 -o Suppress overflow errors
998 -l Suppress trace data lost errors
999
1000For example, for errors but not overflow or data lost errors:
1001
1002 --itrace=e-o-l
1003
1004The "d" option will cause the creation of a file "intel_pt.log" containing all
1005decoded packets and instructions. Note that this option slows down the decoder
1006and that the resulting file may be very large. The "d" option may be followed
1007by flags which affect what debug messages will or will not be logged. Each flag
1008must be preceded by either '+' or '-'. The flags support by Intel PT are:
1009
1010 -a Suppress logging of perf events
1011 +a Log all perf events
1012 +e Output only on decoding errors (size configurable)
1013 +o Output to stdout instead of "intel_pt.log"
1014
1015By default, logged perf events are filtered by any specified time ranges, but
1016flag +a overrides that. The +e flag can be useful for analyzing errors. By
1017default, the log size in that case is 16384 bytes, but can be altered by
1018linkperf:perf-config[1] e.g. perf config itrace.debug-log-buffer-size=30000
1019
1020In addition, the period of the "instructions" event can be specified. e.g.
1021
1022 --itrace=i10us
1023
1024sets the period to 10us i.e. one instruction sample is synthesized for each 10
1025microseconds of trace. Alternatives to "us" are "ms" (milliseconds),
1026"ns" (nanoseconds), "t" (TSC ticks) or "i" (instructions).
1027
1028"ms", "us" and "ns" are converted to TSC ticks.
1029
1030The timing information included with Intel PT does not give the time of every
1031instruction. Consequently, for the purpose of sampling, the decoder estimates
1032the time since the last timing packet based on 1 tick per instruction. The time
1033on the sample is *not* adjusted and reflects the last known value of TSC.
1034
1035For Intel PT, the default period is 100us.
1036
1037Setting it to a zero period means "as often as possible".
1038
1039In the case of Intel PT that is the same as a period of 1 and a unit of
1040'instructions' (i.e. --itrace=i1i).
1041
1042Also the call chain size (default 16, max. 1024) for instructions or
1043transactions events can be specified. e.g.
1044
1045 --itrace=ig32
1046 --itrace=xg32
1047
1048Also the number of last branch entries (default 64, max. 1024) for instructions or
1049transactions events can be specified. e.g.
1050
1051 --itrace=il10
1052 --itrace=xl10
1053
1054Note that last branch entries are cleared for each sample, so there is no overlap
1055from one sample to the next.
1056
1057The G and L options are designed in particular for sample mode, and work much
1058like g and l but add call chain and branch stack to the other selected events
1059instead of synthesized events. For example, to record branch-misses events for
1060'ls' and then add a call chain derived from the Intel PT trace:
1061
1062 perf record --aux-sample -e '{intel_pt//u,branch-misses:u}' -- ls
1063 perf report --itrace=Ge
1064
1065Although in fact G is a default for perf report, so that is the same as just:
1066
1067 perf report
1068
1069One caveat with the G and L options is that they work poorly with "Large PEBS".
1070Large PEBS means PEBS records will be accumulated by hardware and the written
1071into the event buffer in one go. That reduces interrupts, but can give very
1072late timestamps. Because the Intel PT trace is synchronized by timestamps,
1073the PEBS events do not match the trace. Currently, Large PEBS is used only in
1074certain circumstances:
1075 - hardware supports it
1076 - PEBS is used
1077 - event period is specified, instead of frequency
1078 - the sample type is limited to the following flags:
1079 PERF_SAMPLE_IP | PERF_SAMPLE_TID | PERF_SAMPLE_ADDR |
1080 PERF_SAMPLE_ID | PERF_SAMPLE_CPU | PERF_SAMPLE_STREAM_ID |
1081 PERF_SAMPLE_DATA_SRC | PERF_SAMPLE_IDENTIFIER |
1082 PERF_SAMPLE_TRANSACTION | PERF_SAMPLE_PHYS_ADDR |
1083 PERF_SAMPLE_REGS_INTR | PERF_SAMPLE_REGS_USER |
1084 PERF_SAMPLE_PERIOD (and sometimes) | PERF_SAMPLE_TIME
1085Because Intel PT sample mode uses a different sample type to the list above,
1086Large PEBS is not used with Intel PT sample mode. To avoid Large PEBS in other
1087cases, avoid specifying the event period i.e. avoid the 'perf record' -c option,
1088--count option, or 'period' config term.
1089
1090To disable trace decoding entirely, use the option --no-itrace.
1091
1092It is also possible to skip events generated (instructions, branches, transactions)
1093at the beginning. This is useful to ignore initialization code.
1094
1095 --itrace=i0nss1000000
1096
1097skips the first million instructions.
1098
1099The q option changes the way the trace is decoded. The decoding is much faster
1100but much less detailed. Specifically, with the q option, the decoder does not
1101decode TNT packets, and does not walk object code, but gets the ip from FUP and
1102TIP packets. The q option can be used with the b and i options but the period
1103is not used. The q option decodes more quickly, but is useful only if the
1104control flow of interest is represented or indicated by FUP, TIP, TIP.PGE, or
1105TIP.PGD packets (refer below). However the q option could be used to find time
1106ranges that could then be decoded fully using the --time option.
1107
1108What will *not* be decoded with the (single) q option:
1109
1110 - direct calls and jmps
1111 - conditional branches
1112 - non-branch instructions
1113
1114What *will* be decoded with the (single) q option:
1115
1116 - asynchronous branches such as interrupts
1117 - indirect branches
1118 - function return target address *if* the noretcomp config term (refer
1119 config terms section) was used
1120 - start of (control-flow) tracing
1121 - end of (control-flow) tracing, if it is not out of context
1122 - power events, ptwrite, transaction start and abort
1123 - instruction pointer associated with PSB packets
1124
1125Note the q option does not specify what events will be synthesized e.g. the p
1126option must be used also to show power events.
1127
1128Repeating the q option (double-q i.e. qq) results in even faster decoding and even
1129less detail. The decoder decodes only extended PSB (PSB+) packets, getting the
1130instruction pointer if there is a FUP packet within PSB+ (i.e. between PSB and
1131PSBEND). Note PSB packets occur regularly in the trace based on the psb_period
1132config term (refer config terms section). There will be a FUP packet if the
1133PSB+ occurs while control flow is being traced.
1134
1135What will *not* be decoded with the qq option:
1136
1137 - everything except instruction pointer associated with PSB packets
1138
1139What *will* be decoded with the qq option:
1140
1141 - instruction pointer associated with PSB packets
1142
1143The Z option is equivalent to having recorded a trace without TSC
1144(i.e. config term tsc=0). It can be useful to avoid timestamp issues when
1145decoding a trace of a virtual machine.
1146
1147
1148dlfilter-show-cycles.so
1149~~~~~~~~~~~~~~~~~~~~~~~
1150
1151Cycles can be displayed using dlfilter-show-cycles.so in which case the itrace A
1152option can be useful to provide higher granularity cycle information:
1153
1154 perf script --itrace=A --call-trace --dlfilter dlfilter-show-cycles.so
1155
1156To see a list of dlfilters:
1157
1158 perf script -v --list-dlfilters
1159
1160See also linkperf:perf-dlfilters[1]
1161
1162
1163dump option
1164~~~~~~~~~~~
1165
1166perf script has an option (-D) to "dump" the events i.e. display the binary
1167data.
1168
1169When -D is used, Intel PT packets are displayed. The packet decoder does not
1170pay attention to PSB packets, but just decodes the bytes - so the packets seen
1171by the actual decoder may not be identical in places where the data is corrupt.
1172One example of that would be when the buffer-switching interrupt has been too
1173slow, and the buffer has been filled completely. In that case, the last packet
1174in the buffer might be truncated and immediately followed by a PSB as the trace
1175continues in the next buffer.
1176
1177To disable the display of Intel PT packets, combine the -D option with
1178--no-itrace.
1179
1180
1181perf report
1182-----------
1183
1184By default, perf report will decode trace data found in the perf.data file.
1185This can be further controlled by new option --itrace exactly the same as
1186perf script, with the exception that the default is --itrace=igxe.
1187
1188
1189perf inject
1190-----------
1191
1192perf inject also accepts the --itrace option in which case tracing data is
1193removed and replaced with the synthesized events. e.g.
1194
1195 perf inject --itrace -i perf.data -o perf.data.new
1196
1197Below is an example of using Intel PT with autofdo. It requires autofdo
1198(https://github.com/google/autofdo) and gcc version 5. The bubble
1199sort example is from the AutoFDO tutorial (https://gcc.gnu.org/wiki/AutoFDO/Tutorial)
1200amended to take the number of elements as a parameter.
1201
1202 $ gcc-5 -O3 sort.c -o sort_optimized
1203 $ ./sort_optimized 30000
1204 Bubble sorting array of 30000 elements
1205 2254 ms
1206
1207 $ cat ~/.perfconfig
1208 [intel-pt]
1209 mispred-all = on
1210
1211 $ perf record -e intel_pt//u ./sort 3000
1212 Bubble sorting array of 3000 elements
1213 58 ms
1214 [ perf record: Woken up 2 times to write data ]
1215 [ perf record: Captured and wrote 3.939 MB perf.data ]
1216 $ perf inject -i perf.data -o inj --itrace=i100usle --strip
1217 $ ./create_gcov --binary=./sort --profile=inj --gcov=sort.gcov -gcov_version=1
1218 $ gcc-5 -O3 -fauto-profile=sort.gcov sort.c -o sort_autofdo
1219 $ ./sort_autofdo 30000
1220 Bubble sorting array of 30000 elements
1221 2155 ms
1222
1223Note there is currently no advantage to using Intel PT instead of LBR, but
1224that may change in the future if greater use is made of the data.
1225
1226
1227PEBS via Intel PT
1228-----------------
1229
1230Some hardware has the feature to redirect PEBS records to the Intel PT trace.
1231Recording is selected by using the aux-output config term e.g.
1232
1233 perf record -c 10000 -e '{intel_pt/branch=0/,cycles/aux-output/ppp}' uname
1234
1235Originally, software only supported redirecting at most one PEBS event because it
1236was not able to differentiate one event from another. To overcome that, more recent
1237kernels and perf tools add support for the PERF_RECORD_AUX_OUTPUT_HW_ID side-band event.
1238To check for the presence of that event in a PEBS-via-PT trace:
1239
1240 perf script -D --no-itrace | grep PERF_RECORD_AUX_OUTPUT_HW_ID
1241
1242To display PEBS events from the Intel PT trace, use the itrace 'o' option e.g.
1243
1244 perf script --itrace=oe
1245
1246XED
1247---
1248
1249include::build-xed.txt[]
1250
1251
1252Tracing Virtual Machines (kernel only)
1253--------------------------------------
1254
1255Currently, kernel tracing is supported with either "timeless" decoding
1256(i.e. no TSC timestamps) or VM Time Correlation. VM Time Correlation is an extra step
1257using 'perf inject' and requires unchanging VMX TSC Offset and no VMX TSC Scaling.
1258
1259Other limitations and caveats
1260
1261 VMX controls may suppress packets needed for decoding resulting in decoding errors
1262 VMX controls may block the perf NMI to the host potentially resulting in lost trace data
1263 Guest kernel self-modifying code (e.g. jump labels or JIT-compiled eBPF) will result in decoding errors
1264 Guest thread information is unknown
1265 Guest VCPU is unknown but may be able to be inferred from the host thread
1266 Callchains are not supported
1267
1268Example using "timeless" decoding
1269
1270Start VM
1271
1272 $ sudo virsh start kubuntu20.04
1273 Domain kubuntu20.04 started
1274
1275Mount the guest file system. Note sshfs needs -o direct_io to enable reading of proc files. root access is needed to read /proc/kcore.
1276
1277 $ mkdir vm0
1278 $ sshfs -o direct_io root@vm0:/ vm0
1279
1280Copy the guest /proc/kallsyms, /proc/modules and /proc/kcore
1281
1282 $ perf buildid-cache -v --kcore vm0/proc/kcore
1283 kcore added to build-id cache directory /home/user/.debug/[kernel.kcore]/9600f316a53a0f54278885e8d9710538ec5f6a08/2021021807494306
1284 $ KALLSYMS=/home/user/.debug/[kernel.kcore]/9600f316a53a0f54278885e8d9710538ec5f6a08/2021021807494306/kallsyms
1285
1286Find the VM process
1287
1288 $ ps -eLl | grep 'KVM\|PID'
1289 F S UID PID PPID LWP C PRI NI ADDR SZ WCHAN TTY TIME CMD
1290 3 S 64055 1430 1 1440 1 80 0 - 1921718 - ? 00:02:47 CPU 0/KVM
1291 3 S 64055 1430 1 1441 1 80 0 - 1921718 - ? 00:02:41 CPU 1/KVM
1292 3 S 64055 1430 1 1442 1 80 0 - 1921718 - ? 00:02:38 CPU 2/KVM
1293 3 S 64055 1430 1 1443 2 80 0 - 1921718 - ? 00:03:18 CPU 3/KVM
1294
1295Start an open-ended perf record, tracing the VM process, do something on the VM, and then ctrl-C to stop.
1296TSC is not supported and tsc=0 must be specified. That means mtc is useless, so add mtc=0.
1297However, IPC can still be determined, hence cyc=1 can be added.
1298Only kernel decoding is supported, so 'k' must be specified.
1299Intel PT traces both the host and the guest so --guest and --host need to be specified.
1300Without timestamps, --per-thread must be specified to distinguish threads.
1301
1302 $ sudo perf kvm --guest --host --guestkallsyms $KALLSYMS record --kcore -e intel_pt/tsc=0,mtc=0,cyc=1/k -p 1430 --per-thread
1303 ^C
1304 [ perf record: Woken up 1 times to write data ]
1305 [ perf record: Captured and wrote 5.829 MB ]
1306
1307perf script can be used to provide an instruction trace
1308
1309 $ perf script --guestkallsyms $KALLSYMS --insn-trace --xed -F+ipc | grep -C10 vmresume | head -21
1310 CPU 0/KVM 1440 ffffffff82133cdd __vmx_vcpu_run+0x3d ([kernel.kallsyms]) movq 0x48(%rax), %r9
1311 CPU 0/KVM 1440 ffffffff82133ce1 __vmx_vcpu_run+0x41 ([kernel.kallsyms]) movq 0x50(%rax), %r10
1312 CPU 0/KVM 1440 ffffffff82133ce5 __vmx_vcpu_run+0x45 ([kernel.kallsyms]) movq 0x58(%rax), %r11
1313 CPU 0/KVM 1440 ffffffff82133ce9 __vmx_vcpu_run+0x49 ([kernel.kallsyms]) movq 0x60(%rax), %r12
1314 CPU 0/KVM 1440 ffffffff82133ced __vmx_vcpu_run+0x4d ([kernel.kallsyms]) movq 0x68(%rax), %r13
1315 CPU 0/KVM 1440 ffffffff82133cf1 __vmx_vcpu_run+0x51 ([kernel.kallsyms]) movq 0x70(%rax), %r14
1316 CPU 0/KVM 1440 ffffffff82133cf5 __vmx_vcpu_run+0x55 ([kernel.kallsyms]) movq 0x78(%rax), %r15
1317 CPU 0/KVM 1440 ffffffff82133cf9 __vmx_vcpu_run+0x59 ([kernel.kallsyms]) movq (%rax), %rax
1318 CPU 0/KVM 1440 ffffffff82133cfc __vmx_vcpu_run+0x5c ([kernel.kallsyms]) callq 0xffffffff82133c40
1319 CPU 0/KVM 1440 ffffffff82133c40 vmx_vmenter+0x0 ([kernel.kallsyms]) jz 0xffffffff82133c46
1320 CPU 0/KVM 1440 ffffffff82133c42 vmx_vmenter+0x2 ([kernel.kallsyms]) vmresume IPC: 0.11 (50/445)
1321 :1440 1440 ffffffffbb678b06 native_write_msr+0x6 ([guest.kernel.kallsyms]) nopl %eax, (%rax,%rax,1)
1322 :1440 1440 ffffffffbb678b0b native_write_msr+0xb ([guest.kernel.kallsyms]) retq IPC: 0.04 (2/41)
1323 :1440 1440 ffffffffbb666646 lapic_next_deadline+0x26 ([guest.kernel.kallsyms]) data16 nop
1324 :1440 1440 ffffffffbb666648 lapic_next_deadline+0x28 ([guest.kernel.kallsyms]) xor %eax, %eax
1325 :1440 1440 ffffffffbb66664a lapic_next_deadline+0x2a ([guest.kernel.kallsyms]) popq %rbp
1326 :1440 1440 ffffffffbb66664b lapic_next_deadline+0x2b ([guest.kernel.kallsyms]) retq IPC: 0.16 (4/25)
1327 :1440 1440 ffffffffbb74607f clockevents_program_event+0x8f ([guest.kernel.kallsyms]) test %eax, %eax
1328 :1440 1440 ffffffffbb746081 clockevents_program_event+0x91 ([guest.kernel.kallsyms]) jz 0xffffffffbb74603c IPC: 0.06 (2/30)
1329 :1440 1440 ffffffffbb74603c clockevents_program_event+0x4c ([guest.kernel.kallsyms]) popq %rbx
1330 :1440 1440 ffffffffbb74603d clockevents_program_event+0x4d ([guest.kernel.kallsyms]) popq %r12
1331
1332Example using VM Time Correlation
1333
1334Start VM
1335
1336 $ sudo virsh start kubuntu20.04
1337 Domain kubuntu20.04 started
1338
1339Mount the guest file system. Note sshfs needs -o direct_io to enable reading of proc files. root access is needed to read /proc/kcore.
1340
1341 $ mkdir -p vm0
1342 $ sshfs -o direct_io root@vm0:/ vm0
1343
1344Copy the guest /proc/kallsyms, /proc/modules and /proc/kcore
1345
1346 $ perf buildid-cache -v --kcore vm0/proc/kcore
1347 same kcore found in /home/user/.debug/[kernel.kcore]/cc9c55a98c5e4ec0aeda69302554aabed5cd6491/2021021312450777
1348 $ KALLSYMS=/home/user/.debug/\[kernel.kcore\]/cc9c55a98c5e4ec0aeda69302554aabed5cd6491/2021021312450777/kallsyms
1349
1350Find the VM process
1351
1352 $ ps -eLl | grep 'KVM\|PID'
1353 F S UID PID PPID LWP C PRI NI ADDR SZ WCHAN TTY TIME CMD
1354 3 S 64055 16998 1 17005 13 80 0 - 1818189 - ? 00:00:16 CPU 0/KVM
1355 3 S 64055 16998 1 17006 4 80 0 - 1818189 - ? 00:00:05 CPU 1/KVM
1356 3 S 64055 16998 1 17007 3 80 0 - 1818189 - ? 00:00:04 CPU 2/KVM
1357 3 S 64055 16998 1 17008 4 80 0 - 1818189 - ? 00:00:05 CPU 3/KVM
1358
1359Start an open-ended perf record, tracing the VM process, do something on the VM, and then ctrl-C to stop.
1360IPC can be determined, hence cyc=1 can be added.
1361Only kernel decoding is supported, so 'k' must be specified.
1362Intel PT traces both the host and the guest so --guest and --host need to be specified.
1363
1364 $ sudo perf kvm --guest --host --guestkallsyms $KALLSYMS record --kcore -e intel_pt/cyc=1/k -p 16998
1365 ^C[ perf record: Woken up 1 times to write data ]
1366 [ perf record: Captured and wrote 9.041 MB perf.data.kvm ]
1367
1368Now 'perf inject' can be used to determine the VMX TCS Offset. Note, Intel PT TSC packets are
1369only 7-bytes, so the TSC Offset might differ from the actual value in the 8th byte. That will
1370have no effect i.e. the resulting timestamps will be correct anyway.
1371
1372 $ perf inject -i perf.data.kvm --vm-time-correlation=dry-run
1373 ERROR: Unknown TSC Offset for VMCS 0x1bff6a
1374 VMCS: 0x1bff6a TSC Offset 0xffffe42722c64c41
1375 ERROR: Unknown TSC Offset for VMCS 0x1cbc08
1376 VMCS: 0x1cbc08 TSC Offset 0xffffe42722c64c41
1377 ERROR: Unknown TSC Offset for VMCS 0x1c3ce8
1378 VMCS: 0x1c3ce8 TSC Offset 0xffffe42722c64c41
1379 ERROR: Unknown TSC Offset for VMCS 0x1cbce9
1380 VMCS: 0x1cbce9 TSC Offset 0xffffe42722c64c41
1381
1382Each virtual CPU has a different Virtual Machine Control Structure (VMCS)
1383shown above with the calculated TSC Offset. For an unchanging TSC Offset
1384they should all be the same for the same virtual machine.
1385
1386Now that the TSC Offset is known, it can be provided to 'perf inject'
1387
1388 $ perf inject -i perf.data.kvm --vm-time-correlation="dry-run 0xffffe42722c64c41"
1389
1390Note the options for 'perf inject' --vm-time-correlation are:
1391
1392 [ dry-run ] [ <TSC Offset> [ : <VMCS> [ , <VMCS> ]... ] ]...
1393
1394So it is possible to specify different TSC Offsets for different VMCS.
1395The option "dry-run" will cause the file to be processed but without updating it.
1396Note it is also possible to get a intel_pt.log file by adding option --itrace=d
1397
1398There were no errors so, do it for real
1399
1400 $ perf inject -i perf.data.kvm --vm-time-correlation=0xffffe42722c64c41 --force
1401
1402'perf script' can be used to see if there are any decoder errors
1403
1404 $ perf script -i perf.data.kvm --guestkallsyms $KALLSYMS --itrace=e-o
1405
1406There were none.
1407
1408'perf script' can be used to provide an instruction trace showing timestamps
1409
1410 $ perf script -i perf.data.kvm --guestkallsyms $KALLSYMS --insn-trace --xed -F+ipc | grep -C10 vmresume | head -21
1411 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133cdd __vmx_vcpu_run+0x3d ([kernel.kallsyms]) movq 0x48(%rax), %r9
1412 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133ce1 __vmx_vcpu_run+0x41 ([kernel.kallsyms]) movq 0x50(%rax), %r10
1413 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133ce5 __vmx_vcpu_run+0x45 ([kernel.kallsyms]) movq 0x58(%rax), %r11
1414 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133ce9 __vmx_vcpu_run+0x49 ([kernel.kallsyms]) movq 0x60(%rax), %r12
1415 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133ced __vmx_vcpu_run+0x4d ([kernel.kallsyms]) movq 0x68(%rax), %r13
1416 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133cf1 __vmx_vcpu_run+0x51 ([kernel.kallsyms]) movq 0x70(%rax), %r14
1417 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133cf5 __vmx_vcpu_run+0x55 ([kernel.kallsyms]) movq 0x78(%rax), %r15
1418 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133cf9 __vmx_vcpu_run+0x59 ([kernel.kallsyms]) movq (%rax), %rax
1419 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133cfc __vmx_vcpu_run+0x5c ([kernel.kallsyms]) callq 0xffffffff82133c40
1420 CPU 1/KVM 17006 [001] 11500.262865593: ffffffff82133c40 vmx_vmenter+0x0 ([kernel.kallsyms]) jz 0xffffffff82133c46
1421 CPU 1/KVM 17006 [001] 11500.262866075: ffffffff82133c42 vmx_vmenter+0x2 ([kernel.kallsyms]) vmresume IPC: 0.05 (40/769)
1422 :17006 17006 [001] 11500.262869216: ffffffff82200cb0 asm_sysvec_apic_timer_interrupt+0x0 ([guest.kernel.kallsyms]) clac
1423 :17006 17006 [001] 11500.262869216: ffffffff82200cb3 asm_sysvec_apic_timer_interrupt+0x3 ([guest.kernel.kallsyms]) pushq $0xffffffffffffffff
1424 :17006 17006 [001] 11500.262869216: ffffffff82200cb5 asm_sysvec_apic_timer_interrupt+0x5 ([guest.kernel.kallsyms]) callq 0xffffffff82201160
1425 :17006 17006 [001] 11500.262869216: ffffffff82201160 error_entry+0x0 ([guest.kernel.kallsyms]) cld
1426 :17006 17006 [001] 11500.262869216: ffffffff82201161 error_entry+0x1 ([guest.kernel.kallsyms]) pushq %rsi
1427 :17006 17006 [001] 11500.262869216: ffffffff82201162 error_entry+0x2 ([guest.kernel.kallsyms]) movq 0x8(%rsp), %rsi
1428 :17006 17006 [001] 11500.262869216: ffffffff82201167 error_entry+0x7 ([guest.kernel.kallsyms]) movq %rdi, 0x8(%rsp)
1429 :17006 17006 [001] 11500.262869216: ffffffff8220116c error_entry+0xc ([guest.kernel.kallsyms]) pushq %rdx
1430 :17006 17006 [001] 11500.262869216: ffffffff8220116d error_entry+0xd ([guest.kernel.kallsyms]) pushq %rcx
1431 :17006 17006 [001] 11500.262869216: ffffffff8220116e error_entry+0xe ([guest.kernel.kallsyms]) pushq %rax
1432
1433
1434Tracing Virtual Machines (including user space)
1435-----------------------------------------------
1436
1437It is possible to use perf record to record sideband events within a virtual machine, so that an Intel PT trace on the host can be decoded.
1438Sideband events from the guest perf.data file can be injected into the host perf.data file using perf inject.
1439
1440Here is an example of the steps needed:
1441
1442On the guest machine:
1443
1444Check that no-kvmclock kernel command line option was used to boot:
1445
1446Note, this is essential to enable time correlation between host and guest machines.
1447
1448 $ cat /proc/cmdline
1449 BOOT_IMAGE=/boot/vmlinuz-5.10.0-16-amd64 root=UUID=cb49c910-e573-47e0-bce7-79e293df8e1d ro no-kvmclock
1450
1451There is no BPF support at present so, if possible, disable JIT compiling:
1452
1453 $ echo 0 | sudo tee /proc/sys/net/core/bpf_jit_enable
1454 0
1455
1456Start perf record to collect sideband events:
1457
1458 $ sudo perf record -o guest-sideband-testing-guest-perf.data --sample-identifier --buildid-all --switch-events --kcore -a -e dummy
1459
1460On the host machine:
1461
1462Start perf record to collect Intel PT trace:
1463
1464Note, the host trace will get very big, very fast, so the steps from starting to stopping the host trace really need to be done so that they happen in the shortest time possible.
1465
1466 $ sudo perf record -o guest-sideband-testing-host-perf.data -m,64M --kcore -a -e intel_pt/cyc/
1467
1468On the guest machine:
1469
1470Run a small test case, just 'uname' in this example:
1471
1472 $ uname
1473 Linux
1474
1475On the host machine:
1476
1477Stop the Intel PT trace:
1478
1479 ^C
1480 [ perf record: Woken up 1 times to write data ]
1481 [ perf record: Captured and wrote 76.122 MB guest-sideband-testing-host-perf.data ]
1482
1483On the guest machine:
1484
1485Stop the Intel PT trace:
1486
1487 ^C
1488 [ perf record: Woken up 1 times to write data ]
1489 [ perf record: Captured and wrote 1.247 MB guest-sideband-testing-guest-perf.data ]
1490
1491And then copy guest-sideband-testing-guest-perf.data to the host (not shown here).
1492
1493On the host machine:
1494
1495With the 2 perf.data recordings, and with their ownership changed to the user.
1496
1497Identify the TSC Offset:
1498
1499 $ perf inject -i guest-sideband-testing-host-perf.data --vm-time-correlation=dry-run
1500 VMCS: 0x103fc6 TSC Offset 0xfffffa6ae070cb20
1501 VMCS: 0x103ff2 TSC Offset 0xfffffa6ae070cb20
1502 VMCS: 0x10fdaa TSC Offset 0xfffffa6ae070cb20
1503 VMCS: 0x24d57c TSC Offset 0xfffffa6ae070cb20
1504
1505Correct Intel PT TSC timestamps for the guest machine:
1506
1507 $ perf inject -i guest-sideband-testing-host-perf.data --vm-time-correlation=0xfffffa6ae070cb20 --force
1508
1509Identify the guest machine PID:
1510
1511 $ perf script -i guest-sideband-testing-host-perf.data --no-itrace --show-task-events | grep KVM
1512 CPU 0/KVM 0 [000] 0.000000: PERF_RECORD_COMM: CPU 0/KVM:13376/13381
1513 CPU 1/KVM 0 [000] 0.000000: PERF_RECORD_COMM: CPU 1/KVM:13376/13382
1514 CPU 2/KVM 0 [000] 0.000000: PERF_RECORD_COMM: CPU 2/KVM:13376/13383
1515 CPU 3/KVM 0 [000] 0.000000: PERF_RECORD_COMM: CPU 3/KVM:13376/13384
1516
1517Note, the QEMU option -name debug-threads=on is needed so that thread names
1518can be used to determine which thread is running which VCPU as above. libvirt seems to use this by default.
1519
1520Create a guestmount, assuming the guest machine is 'vm_to_test':
1521
1522 $ mkdir -p ~/guestmount/13376
1523 $ sshfs -o direct_io vm_to_test:/ ~/guestmount/13376
1524
1525Inject the guest perf.data file into the host perf.data file:
1526
1527Note, due to the guestmount option, guest object files and debug files will be copied into the build ID cache from the guest machine, with the notable exception of VDSO.
1528If needed, VDSO can be copied manually in a fashion similar to that used by the perf-archive script.
1529
1530 $ perf inject -i guest-sideband-testing-host-perf.data -o inj --guestmount ~/guestmount --guest-data=guest-sideband-testing-guest-perf.data,13376,0xfffffa6ae070cb20
1531
1532Show an excerpt from the result. In this case the CPU and time range have been to chosen to show interaction between guest and host when 'uname' is starting to run on the guest machine:
1533
1534Notes:
1535
1536 - the CPU displayed, [002] in this case, is always the host CPU
1537 - events happening in the virtual machine start with VM:13376 VCPU:003, which shows the hypervisor PID 13376 and the VCPU number
1538 - only calls and errors are displayed i.e. --itrace=ce
1539 - branches entering and exiting the virtual machine are split, and show as 2 branches to/from "0 [unknown] ([unknown])"
1540
1541 $ perf script -i inj --itrace=ce -F+machine_pid,+vcpu,+addr,+pid,+tid,-period --ns --time 7919.408803365,7919.408804631 -C 2
1542 CPU 3/KVM 13376/13384 [002] 7919.408803365: branches: ffffffffc0f8ebe0 vmx_vcpu_enter_exit+0xc0 ([kernel.kallsyms]) => ffffffffc0f8edc0 __vmx_vcpu_run+0x0 ([kernel.kallsyms])
1543 CPU 3/KVM 13376/13384 [002] 7919.408803365: branches: ffffffffc0f8edd5 __vmx_vcpu_run+0x15 ([kernel.kallsyms]) => ffffffffc0f8eca0 vmx_update_host_rsp+0x0 ([kernel.kallsyms])
1544 CPU 3/KVM 13376/13384 [002] 7919.408803365: branches: ffffffffc0f8ee1b __vmx_vcpu_run+0x5b ([kernel.kallsyms]) => ffffffffc0f8ed60 vmx_vmenter+0x0 ([kernel.kallsyms])
1545 CPU 3/KVM 13376/13384 [002] 7919.408803461: branches: ffffffffc0f8ed62 vmx_vmenter+0x2 ([kernel.kallsyms]) => 0 [unknown] ([unknown])
1546 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408803461: branches: 0 [unknown] ([unknown]) => 7f851c9b5a5c init_cacheinfo+0x3ac (/usr/lib/x86_64-linux-gnu/libc-2.31.so)
1547 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408803567: branches: 7f851c9b5a5a init_cacheinfo+0x3aa (/usr/lib/x86_64-linux-gnu/libc-2.31.so) => 0 [unknown] ([unknown])
1548 CPU 3/KVM 13376/13384 [002] 7919.408803567: branches: 0 [unknown] ([unknown]) => ffffffffc0f8ed80 vmx_vmexit+0x0 ([kernel.kallsyms])
1549 CPU 3/KVM 13376/13384 [002] 7919.408803596: branches: ffffffffc0f6619a vmx_vcpu_run+0x26a ([kernel.kallsyms]) => ffffffffb2255c60 x86_virt_spec_ctrl+0x0 ([kernel.kallsyms])
1550 CPU 3/KVM 13376/13384 [002] 7919.408803801: branches: ffffffffc0f66445 vmx_vcpu_run+0x515 ([kernel.kallsyms]) => ffffffffb2290b30 native_write_msr+0x0 ([kernel.kallsyms])
1551 CPU 3/KVM 13376/13384 [002] 7919.408803850: branches: ffffffffc0f661f8 vmx_vcpu_run+0x2c8 ([kernel.kallsyms]) => ffffffffc1092300 kvm_load_host_xsave_state+0x0 ([kernel.kallsyms])
1552 CPU 3/KVM 13376/13384 [002] 7919.408803850: branches: ffffffffc1092327 kvm_load_host_xsave_state+0x27 ([kernel.kallsyms]) => ffffffffc1092220 kvm_load_host_xsave_state.part.0+0x0 ([kernel.kallsyms])
1553 CPU 3/KVM 13376/13384 [002] 7919.408803862: branches: ffffffffc0f662cf vmx_vcpu_run+0x39f ([kernel.kallsyms]) => ffffffffc0f63f90 vmx_recover_nmi_blocking+0x0 ([kernel.kallsyms])
1554 CPU 3/KVM 13376/13384 [002] 7919.408803862: branches: ffffffffc0f662e9 vmx_vcpu_run+0x3b9 ([kernel.kallsyms]) => ffffffffc0f619a0 __vmx_complete_interrupts+0x0 ([kernel.kallsyms])
1555 CPU 3/KVM 13376/13384 [002] 7919.408803872: branches: ffffffffc109cfb2 vcpu_enter_guest+0x752 ([kernel.kallsyms]) => ffffffffc0f5f570 vmx_handle_exit_irqoff+0x0 ([kernel.kallsyms])
1556 CPU 3/KVM 13376/13384 [002] 7919.408803881: branches: ffffffffc109d028 vcpu_enter_guest+0x7c8 ([kernel.kallsyms]) => ffffffffb234f900 __srcu_read_lock+0x0 ([kernel.kallsyms])
1557 CPU 3/KVM 13376/13384 [002] 7919.408803897: branches: ffffffffc109d06f vcpu_enter_guest+0x80f ([kernel.kallsyms]) => ffffffffc0f72e30 vmx_handle_exit+0x0 ([kernel.kallsyms])
1558 CPU 3/KVM 13376/13384 [002] 7919.408803897: branches: ffffffffc0f72e3d vmx_handle_exit+0xd ([kernel.kallsyms]) => ffffffffc0f727c0 __vmx_handle_exit+0x0 ([kernel.kallsyms])
1559 CPU 3/KVM 13376/13384 [002] 7919.408803897: branches: ffffffffc0f72b15 __vmx_handle_exit+0x355 ([kernel.kallsyms]) => ffffffffc0f60ae0 vmx_flush_pml_buffer+0x0 ([kernel.kallsyms])
1560 CPU 3/KVM 13376/13384 [002] 7919.408803903: branches: ffffffffc0f72994 __vmx_handle_exit+0x1d4 ([kernel.kallsyms]) => ffffffffc10b7090 kvm_emulate_cpuid+0x0 ([kernel.kallsyms])
1561 CPU 3/KVM 13376/13384 [002] 7919.408803903: branches: ffffffffc10b70f1 kvm_emulate_cpuid+0x61 ([kernel.kallsyms]) => ffffffffc10b6e10 kvm_cpuid+0x0 ([kernel.kallsyms])
1562 CPU 3/KVM 13376/13384 [002] 7919.408803941: branches: ffffffffc10b7125 kvm_emulate_cpuid+0x95 ([kernel.kallsyms]) => ffffffffc1093110 kvm_skip_emulated_instruction+0x0 ([kernel.kallsyms])
1563 CPU 3/KVM 13376/13384 [002] 7919.408803941: branches: ffffffffc109311f kvm_skip_emulated_instruction+0xf ([kernel.kallsyms]) => ffffffffc0f5e180 vmx_get_rflags+0x0 ([kernel.kallsyms])
1564 CPU 3/KVM 13376/13384 [002] 7919.408803951: branches: ffffffffc109312a kvm_skip_emulated_instruction+0x1a ([kernel.kallsyms]) => ffffffffc0f5fd30 vmx_skip_emulated_instruction+0x0 ([kernel.kallsyms])
1565 CPU 3/KVM 13376/13384 [002] 7919.408803951: branches: ffffffffc0f5fd79 vmx_skip_emulated_instruction+0x49 ([kernel.kallsyms]) => ffffffffc0f5fb50 skip_emulated_instruction+0x0 ([kernel.kallsyms])
1566 CPU 3/KVM 13376/13384 [002] 7919.408803956: branches: ffffffffc0f5fc68 skip_emulated_instruction+0x118 ([kernel.kallsyms]) => ffffffffc0f6a940 vmx_cache_reg+0x0 ([kernel.kallsyms])
1567 CPU 3/KVM 13376/13384 [002] 7919.408803964: branches: ffffffffc0f5fc11 skip_emulated_instruction+0xc1 ([kernel.kallsyms]) => ffffffffc0f5f9e0 vmx_set_interrupt_shadow+0x0 ([kernel.kallsyms])
1568 CPU 3/KVM 13376/13384 [002] 7919.408803980: branches: ffffffffc109f8b1 vcpu_run+0x71 ([kernel.kallsyms]) => ffffffffc10ad2f0 kvm_cpu_has_pending_timer+0x0 ([kernel.kallsyms])
1569 CPU 3/KVM 13376/13384 [002] 7919.408803980: branches: ffffffffc10ad2fb kvm_cpu_has_pending_timer+0xb ([kernel.kallsyms]) => ffffffffc10b0490 apic_has_pending_timer+0x0 ([kernel.kallsyms])
1570 CPU 3/KVM 13376/13384 [002] 7919.408803991: branches: ffffffffc109f899 vcpu_run+0x59 ([kernel.kallsyms]) => ffffffffc109c860 vcpu_enter_guest+0x0 ([kernel.kallsyms])
1571 CPU 3/KVM 13376/13384 [002] 7919.408803993: branches: ffffffffc109cd4c vcpu_enter_guest+0x4ec ([kernel.kallsyms]) => ffffffffc0f69140 vmx_prepare_switch_to_guest+0x0 ([kernel.kallsyms])
1572 CPU 3/KVM 13376/13384 [002] 7919.408803996: branches: ffffffffc109cd7d vcpu_enter_guest+0x51d ([kernel.kallsyms]) => ffffffffb234f930 __srcu_read_unlock+0x0 ([kernel.kallsyms])
1573 CPU 3/KVM 13376/13384 [002] 7919.408803996: branches: ffffffffc109cd9c vcpu_enter_guest+0x53c ([kernel.kallsyms]) => ffffffffc0f609b0 vmx_sync_pir_to_irr+0x0 ([kernel.kallsyms])
1574 CPU 3/KVM 13376/13384 [002] 7919.408803996: branches: ffffffffc0f60a6d vmx_sync_pir_to_irr+0xbd ([kernel.kallsyms]) => ffffffffc10adc20 kvm_lapic_find_highest_irr+0x0 ([kernel.kallsyms])
1575 CPU 3/KVM 13376/13384 [002] 7919.408804010: branches: ffffffffc0f60abd vmx_sync_pir_to_irr+0x10d ([kernel.kallsyms]) => ffffffffc0f60820 vmx_set_rvi+0x0 ([kernel.kallsyms])
1576 CPU 3/KVM 13376/13384 [002] 7919.408804019: branches: ffffffffc109ceca vcpu_enter_guest+0x66a ([kernel.kallsyms]) => ffffffffb2249840 fpregs_assert_state_consistent+0x0 ([kernel.kallsyms])
1577 CPU 3/KVM 13376/13384 [002] 7919.408804021: branches: ffffffffc109cf10 vcpu_enter_guest+0x6b0 ([kernel.kallsyms]) => ffffffffc0f65f30 vmx_vcpu_run+0x0 ([kernel.kallsyms])
1578 CPU 3/KVM 13376/13384 [002] 7919.408804024: branches: ffffffffc0f6603b vmx_vcpu_run+0x10b ([kernel.kallsyms]) => ffffffffb229bed0 __get_current_cr3_fast+0x0 ([kernel.kallsyms])
1579 CPU 3/KVM 13376/13384 [002] 7919.408804024: branches: ffffffffc0f66055 vmx_vcpu_run+0x125 ([kernel.kallsyms]) => ffffffffb2253050 cr4_read_shadow+0x0 ([kernel.kallsyms])
1580 CPU 3/KVM 13376/13384 [002] 7919.408804030: branches: ffffffffc0f6608d vmx_vcpu_run+0x15d ([kernel.kallsyms]) => ffffffffc10921e0 kvm_load_guest_xsave_state+0x0 ([kernel.kallsyms])
1581 CPU 3/KVM 13376/13384 [002] 7919.408804030: branches: ffffffffc1092207 kvm_load_guest_xsave_state+0x27 ([kernel.kallsyms]) => ffffffffc1092110 kvm_load_guest_xsave_state.part.0+0x0 ([kernel.kallsyms])
1582 CPU 3/KVM 13376/13384 [002] 7919.408804032: branches: ffffffffc0f660c6 vmx_vcpu_run+0x196 ([kernel.kallsyms]) => ffffffffb22061a0 perf_guest_get_msrs+0x0 ([kernel.kallsyms])
1583 CPU 3/KVM 13376/13384 [002] 7919.408804032: branches: ffffffffb22061a9 perf_guest_get_msrs+0x9 ([kernel.kallsyms]) => ffffffffb220cda0 intel_guest_get_msrs+0x0 ([kernel.kallsyms])
1584 CPU 3/KVM 13376/13384 [002] 7919.408804039: branches: ffffffffc0f66109 vmx_vcpu_run+0x1d9 ([kernel.kallsyms]) => ffffffffc0f652c0 clear_atomic_switch_msr+0x0 ([kernel.kallsyms])
1585 CPU 3/KVM 13376/13384 [002] 7919.408804040: branches: ffffffffc0f66119 vmx_vcpu_run+0x1e9 ([kernel.kallsyms]) => ffffffffc0f73f60 intel_pmu_lbr_is_enabled+0x0 ([kernel.kallsyms])
1586 CPU 3/KVM 13376/13384 [002] 7919.408804042: branches: ffffffffc0f73f81 intel_pmu_lbr_is_enabled+0x21 ([kernel.kallsyms]) => ffffffffc10b68e0 kvm_find_cpuid_entry+0x0 ([kernel.kallsyms])
1587 CPU 3/KVM 13376/13384 [002] 7919.408804045: branches: ffffffffc0f66454 vmx_vcpu_run+0x524 ([kernel.kallsyms]) => ffffffffc0f61ff0 vmx_update_hv_timer+0x0 ([kernel.kallsyms])
1588 CPU 3/KVM 13376/13384 [002] 7919.408804057: branches: ffffffffc0f66142 vmx_vcpu_run+0x212 ([kernel.kallsyms]) => ffffffffc10af100 kvm_wait_lapic_expire+0x0 ([kernel.kallsyms])
1589 CPU 3/KVM 13376/13384 [002] 7919.408804057: branches: ffffffffc0f66156 vmx_vcpu_run+0x226 ([kernel.kallsyms]) => ffffffffb2255c60 x86_virt_spec_ctrl+0x0 ([kernel.kallsyms])
1590 CPU 3/KVM 13376/13384 [002] 7919.408804057: branches: ffffffffc0f66161 vmx_vcpu_run+0x231 ([kernel.kallsyms]) => ffffffffc0f8eb20 vmx_vcpu_enter_exit+0x0 ([kernel.kallsyms])
1591 CPU 3/KVM 13376/13384 [002] 7919.408804057: branches: ffffffffc0f8eb44 vmx_vcpu_enter_exit+0x24 ([kernel.kallsyms]) => ffffffffb2353e10 rcu_note_context_switch+0x0 ([kernel.kallsyms])
1592 CPU 3/KVM 13376/13384 [002] 7919.408804057: branches: ffffffffb2353e1c rcu_note_context_switch+0xc ([kernel.kallsyms]) => ffffffffb2353db0 rcu_qs+0x0 ([kernel.kallsyms])
1593 CPU 3/KVM 13376/13384 [002] 7919.408804066: branches: ffffffffc0f8ebe0 vmx_vcpu_enter_exit+0xc0 ([kernel.kallsyms]) => ffffffffc0f8edc0 __vmx_vcpu_run+0x0 ([kernel.kallsyms])
1594 CPU 3/KVM 13376/13384 [002] 7919.408804066: branches: ffffffffc0f8edd5 __vmx_vcpu_run+0x15 ([kernel.kallsyms]) => ffffffffc0f8eca0 vmx_update_host_rsp+0x0 ([kernel.kallsyms])
1595 CPU 3/KVM 13376/13384 [002] 7919.408804066: branches: ffffffffc0f8ee1b __vmx_vcpu_run+0x5b ([kernel.kallsyms]) => ffffffffc0f8ed60 vmx_vmenter+0x0 ([kernel.kallsyms])
1596 CPU 3/KVM 13376/13384 [002] 7919.408804162: branches: ffffffffc0f8ed62 vmx_vmenter+0x2 ([kernel.kallsyms]) => 0 [unknown] ([unknown])
1597 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804162: branches: 0 [unknown] ([unknown]) => 7f851c9b5a5c init_cacheinfo+0x3ac (/usr/lib/x86_64-linux-gnu/libc-2.31.so)
1598 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804273: branches: 7f851cb7c0e4 _dl_init+0x74 (/usr/lib/x86_64-linux-gnu/ld-2.31.so) => 7f851cb7bf50 call_init.part.0+0x0 (/usr/lib/x86_64-linux-gnu/ld-2.31.so)
1599 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804526: branches: 55e0c00136f0 _start+0x0 (/usr/bin/uname) => ffffffff83200ac0 asm_exc_page_fault+0x0 ([kernel.kallsyms])
1600 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804526: branches: ffffffff83200ac3 asm_exc_page_fault+0x3 ([kernel.kallsyms]) => ffffffff83201290 error_entry+0x0 ([kernel.kallsyms])
1601 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804534: branches: ffffffff832012fa error_entry+0x6a ([kernel.kallsyms]) => ffffffff830b59a0 sync_regs+0x0 ([kernel.kallsyms])
1602 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804631: branches: ffffffff83200ad9 asm_exc_page_fault+0x19 ([kernel.kallsyms]) => ffffffff830b8210 exc_page_fault+0x0 ([kernel.kallsyms])
1603 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804631: branches: ffffffff830b82a4 exc_page_fault+0x94 ([kernel.kallsyms]) => ffffffff830b80e0 __kvm_handle_async_pf+0x0 ([kernel.kallsyms])
1604 VM:13376 VCPU:003 uname 3404/3404 [002] 7919.408804631: branches: ffffffff830b80ed __kvm_handle_async_pf+0xd ([kernel.kallsyms]) => ffffffff830b80c0 kvm_read_and_reset_apf_flags+0x0 ([kernel.kallsyms])
1605
1606
1607Tracing Virtual Machines - Guest Code
1608-------------------------------------
1609
1610A common case for KVM test programs is that the test program acts as the
1611hypervisor, creating, running and destroying the virtual machine, and
1612providing the guest object code from its own object code. In this case,
1613the VM is not running an OS, but only the functions loaded into it by the
1614hypervisor test program, and conveniently, loaded at the same virtual
1615addresses. To support that, option "--guest-code" has been added to perf script
1616and perf kvm report.
1617
1618Here is an example tracing a test program from the kernel's KVM selftests:
1619
1620 # perf record --kcore -e intel_pt/cyc/ -- tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test
1621 [ perf record: Woken up 1 times to write data ]
1622 [ perf record: Captured and wrote 0.280 MB perf.data ]
1623 # perf script --guest-code --itrace=bep --ns -F-period,+addr,+flags
1624 [SNIP]
1625 tsc_msrs_test 18436 [007] 10897.962087733: branches: call ffffffffc13b2ff5 __vmx_vcpu_run+0x15 (vmlinux) => ffffffffc13b2f50 vmx_update_host_rsp+0x0 (vmlinux)
1626 tsc_msrs_test 18436 [007] 10897.962087733: branches: return ffffffffc13b2f5d vmx_update_host_rsp+0xd (vmlinux) => ffffffffc13b2ffa __vmx_vcpu_run+0x1a (vmlinux)
1627 tsc_msrs_test 18436 [007] 10897.962087733: branches: call ffffffffc13b303b __vmx_vcpu_run+0x5b (vmlinux) => ffffffffc13b2f80 vmx_vmenter+0x0 (vmlinux)
1628 tsc_msrs_test 18436 [007] 10897.962087836: branches: vmentry ffffffffc13b2f82 vmx_vmenter+0x2 (vmlinux) => 0 [unknown] ([unknown])
1629 [guest/18436] 18436 [007] 10897.962087836: branches: vmentry 0 [unknown] ([unknown]) => 402c81 guest_code+0x131 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test)
1630 [guest/18436] 18436 [007] 10897.962087836: branches: call 402c81 guest_code+0x131 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test) => 40dba0 ucall+0x0 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test)
1631 [guest/18436] 18436 [007] 10897.962088248: branches: vmexit 40dba0 ucall+0x0 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test) => 0 [unknown] ([unknown])
1632 tsc_msrs_test 18436 [007] 10897.962088248: branches: vmexit 0 [unknown] ([unknown]) => ffffffffc13b2fa0 vmx_vmexit+0x0 (vmlinux)
1633 tsc_msrs_test 18436 [007] 10897.962088248: branches: jmp ffffffffc13b2fa0 vmx_vmexit+0x0 (vmlinux) => ffffffffc13b2fd2 vmx_vmexit+0x32 (vmlinux)
1634 tsc_msrs_test 18436 [007] 10897.962088256: branches: return ffffffffc13b2fd2 vmx_vmexit+0x32 (vmlinux) => ffffffffc13b3040 __vmx_vcpu_run+0x60 (vmlinux)
1635 tsc_msrs_test 18436 [007] 10897.962088270: branches: return ffffffffc13b30b6 __vmx_vcpu_run+0xd6 (vmlinux) => ffffffffc13b2f2e vmx_vcpu_enter_exit+0x4e (vmlinux)
1636 [SNIP]
1637 tsc_msrs_test 18436 [007] 10897.962089321: branches: call ffffffffc13b2ff5 __vmx_vcpu_run+0x15 (vmlinux) => ffffffffc13b2f50 vmx_update_host_rsp+0x0 (vmlinux)
1638 tsc_msrs_test 18436 [007] 10897.962089321: branches: return ffffffffc13b2f5d vmx_update_host_rsp+0xd (vmlinux) => ffffffffc13b2ffa __vmx_vcpu_run+0x1a (vmlinux)
1639 tsc_msrs_test 18436 [007] 10897.962089321: branches: call ffffffffc13b303b __vmx_vcpu_run+0x5b (vmlinux) => ffffffffc13b2f80 vmx_vmenter+0x0 (vmlinux)
1640 tsc_msrs_test 18436 [007] 10897.962089424: branches: vmentry ffffffffc13b2f82 vmx_vmenter+0x2 (vmlinux) => 0 [unknown] ([unknown])
1641 [guest/18436] 18436 [007] 10897.962089424: branches: vmentry 0 [unknown] ([unknown]) => 40dba0 ucall+0x0 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test)
1642 [guest/18436] 18436 [007] 10897.962089701: branches: jmp 40dc1b ucall+0x7b (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test) => 40dc39 ucall+0x99 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test)
1643 [guest/18436] 18436 [007] 10897.962089701: branches: jcc 40dc3c ucall+0x9c (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test) => 40dc20 ucall+0x80 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test)
1644 [guest/18436] 18436 [007] 10897.962089701: branches: jcc 40dc3c ucall+0x9c (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test) => 40dc20 ucall+0x80 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test)
1645 [guest/18436] 18436 [007] 10897.962089701: branches: jcc 40dc37 ucall+0x97 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test) => 40dc50 ucall+0xb0 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test)
1646 [guest/18436] 18436 [007] 10897.962089878: branches: vmexit 40dc55 ucall+0xb5 (/home/user/git/work/tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test) => 0 [unknown] ([unknown])
1647 tsc_msrs_test 18436 [007] 10897.962089878: branches: vmexit 0 [unknown] ([unknown]) => ffffffffc13b2fa0 vmx_vmexit+0x0 (vmlinux)
1648 tsc_msrs_test 18436 [007] 10897.962089878: branches: jmp ffffffffc13b2fa0 vmx_vmexit+0x0 (vmlinux) => ffffffffc13b2fd2 vmx_vmexit+0x32 (vmlinux)
1649 tsc_msrs_test 18436 [007] 10897.962089887: branches: return ffffffffc13b2fd2 vmx_vmexit+0x32 (vmlinux) => ffffffffc13b3040 __vmx_vcpu_run+0x60 (vmlinux)
1650 tsc_msrs_test 18436 [007] 10897.962089901: branches: return ffffffffc13b30b6 __vmx_vcpu_run+0xd6 (vmlinux) => ffffffffc13b2f2e vmx_vcpu_enter_exit+0x4e (vmlinux)
1651 [SNIP]
1652
1653 # perf kvm --guest-code --guest --host report -i perf.data --stdio | head -20
1654
1655 # To display the perf.data header info, please use --header/--header-only options.
1656 #
1657 #
1658 # Total Lost Samples: 0
1659 #
1660 # Samples: 12 of event 'instructions'
1661 # Event count (approx.): 2274583
1662 #
1663 # Children Self Command Shared Object Symbol
1664 # ........ ........ ............. .................... ...........................................
1665 #
1666 54.70% 0.00% tsc_msrs_test [kernel.vmlinux] [k] entry_SYSCALL_64_after_hwframe
1667 |
1668 ---entry_SYSCALL_64_after_hwframe
1669 do_syscall_64
1670 |
1671 |--29.44%--syscall_exit_to_user_mode
1672 | exit_to_user_mode_prepare
1673 | task_work_run
1674 | __fput
1675
1676
1677Event Trace
1678-----------
1679
1680Event Trace records information about asynchronous events, for example interrupts,
1681faults, VM exits and entries. The information is recorded in CFE and EVD packets,
1682and also the Interrupt Flag is recorded on the MODE.Exec packet. The CFE packet
1683contains a type field to identify one of the following:
1684
1685 1 INTR interrupt, fault, exception, NMI
1686 2 IRET interrupt return
1687 3 SMI system management interrupt
1688 4 RSM resume from system management mode
1689 5 SIPI startup interprocessor interrupt
1690 6 INIT INIT signal
1691 7 VMENTRY VM-Entry
1692 8 VMEXIT VM-Entry
1693 9 VMEXIT_INTR VM-Exit due to interrupt
1694 10 SHUTDOWN Shutdown
1695
1696For more details, refer to the Intel 64 and IA-32 Architectures Software
1697Developer Manuals (version 076 or later).
1698
1699The capability to do Event Trace is indicated by the
1700/sys/bus/event_source/devices/intel_pt/caps/event_trace file.
1701
1702Event trace is selected for recording using the "event" config term. e.g.
1703
1704 perf record -e intel_pt/event/u uname
1705
1706Event trace events are output using the --itrace I option. e.g.
1707
1708 perf script --itrace=Ie
1709
1710perf script displays events containing CFE type, vector and event data,
1711in the form:
1712
1713 evt: hw int (t) cfe: INTR IP: 1 vector: 3 PFA: 0x8877665544332211
1714
1715The IP flag indicates if the event binds to an IP, which includes any case where
1716flow control packet generation is enabled, as well as when CFE packet IP bit is
1717set.
1718
1719perf script displays events containing changes to the Interrupt Flag in the form:
1720
1721 iflag: t IFLAG: 1->0 via branch
1722
1723where "via branch" indicates a branch (interrupt or return from interrupt) and
1724"non branch" indicates an instruction such as CFI, STI or POPF).
1725
1726In addition, the current state of the interrupt flag is indicated by the presence
1727or absence of the "D" (interrupt disabled) perf script flag. If the interrupt
1728flag is changed, then the "t" flag is also included i.e.
1729
1730 no flag, interrupts enabled IF=1
1731 t interrupts become disabled IF=1 -> IF=0
1732 D interrupts are disabled IF=0
1733 Dt interrupts become enabled IF=0 -> IF=1
1734
1735The intel-pt-events.py script illustrates how to access Event Trace information
1736using a Python script.
1737
1738
1739TNT Disable
1740-----------
1741
1742TNT packets are disabled using the "notnt" config term. e.g.
1743
1744 perf record -e intel_pt/notnt/u uname
1745
1746In that case the --itrace q option is forced because walking executable code
1747to reconstruct the control flow is not possible.
1748
1749
1750Emulated PTWRITE
1751----------------
1752
1753Later perf tools support a method to emulate the ptwrite instruction, which
1754can be useful if hardware does not support the ptwrite instruction.
1755
1756Instead of using the ptwrite instruction, a function is used which produces
1757a trace that encodes the payload data into TNT packets. Here is an example
1758of the function:
1759
1760 #include <stdint.h>
1761
1762 void perf_emulate_ptwrite(uint64_t x)
1763 __attribute__((externally_visible, noipa, no_instrument_function, naked));
1764
1765 #define PERF_EMULATE_PTWRITE_8_BITS \
1766 "1: shl %rax\n" \
1767 " jc 1f\n" \
1768 "1: shl %rax\n" \
1769 " jc 1f\n" \
1770 "1: shl %rax\n" \
1771 " jc 1f\n" \
1772 "1: shl %rax\n" \
1773 " jc 1f\n" \
1774 "1: shl %rax\n" \
1775 " jc 1f\n" \
1776 "1: shl %rax\n" \
1777 " jc 1f\n" \
1778 "1: shl %rax\n" \
1779 " jc 1f\n" \
1780 "1: shl %rax\n" \
1781 " jc 1f\n"
1782
1783 /* Undefined instruction */
1784 #define PERF_EMULATE_PTWRITE_UD2 ".byte 0x0f, 0x0b\n"
1785
1786 #define PERF_EMULATE_PTWRITE_MAGIC PERF_EMULATE_PTWRITE_UD2 ".ascii \"perf,ptwrite \"\n"
1787
1788 void perf_emulate_ptwrite(uint64_t x __attribute__ ((__unused__)))
1789 {
1790 /* Assumes SysV ABI : x passed in rdi */
1791 __asm__ volatile (
1792 "jmp 1f\n"
1793 PERF_EMULATE_PTWRITE_MAGIC
1794 "1: mov %rdi, %rax\n"
1795 PERF_EMULATE_PTWRITE_8_BITS
1796 PERF_EMULATE_PTWRITE_8_BITS
1797 PERF_EMULATE_PTWRITE_8_BITS
1798 PERF_EMULATE_PTWRITE_8_BITS
1799 PERF_EMULATE_PTWRITE_8_BITS
1800 PERF_EMULATE_PTWRITE_8_BITS
1801 PERF_EMULATE_PTWRITE_8_BITS
1802 PERF_EMULATE_PTWRITE_8_BITS
1803 "1: ret\n"
1804 );
1805 }
1806
1807For example, a test program with the function above:
1808
1809 #include <stdio.h>
1810 #include <stdint.h>
1811 #include <stdlib.h>
1812
1813 #include "perf_emulate_ptwrite.h"
1814
1815 int main(int argc, char *argv[])
1816 {
1817 uint64_t x = 0;
1818
1819 if (argc > 1)
1820 x = strtoull(argv[1], NULL, 0);
1821 perf_emulate_ptwrite(x);
1822 return 0;
1823 }
1824
1825Can be compiled and traced:
1826
1827 $ gcc -Wall -Wextra -O3 -g -o eg_ptw eg_ptw.c
1828 $ perf record -e intel_pt//u ./eg_ptw 0x1234567890abcdef
1829 [ perf record: Woken up 1 times to write data ]
1830 [ perf record: Captured and wrote 0.017 MB perf.data ]
1831 $ perf script --itrace=ew
1832 eg_ptw 19875 [007] 8061.235912: ptwrite: IP: 0 payload: 0x1234567890abcdef 55701249a196 perf_emulate_ptwrite+0x16 (/home/user/eg_ptw)
1833 $
1834
1835
1836Pipe mode
1837---------
1838Pipe mode is a problem for Intel PT and possibly other auxtrace users.
1839It's not recommended to use a pipe as data output with Intel PT because
1840of the following reason.
1841
1842Essentially the auxtrace buffers do not behave like the regular perf
1843event buffers. That is because the head and tail are updated by
1844software, but in the auxtrace case the data is written by hardware.
1845So the head and tail do not get updated as data is written.
1846
1847In the Intel PT case, the head and tail are updated only when the trace
1848is disabled by software, for example:
1849 - full-trace, system wide : when buffer passes watermark
1850 - full-trace, not system-wide : when buffer passes watermark or
1851 context switches
1852 - snapshot mode : as above but also when a snapshot is made
1853 - sample mode : as above but also when a sample is made
1854
1855That means finished-round ordering doesn't work. An auxtrace buffer
1856can turn up that has data that extends back in time, possibly to the
1857very beginning of tracing.
1858
1859For a perf.data file, that problem is solved by going through the trace
1860and queuing up the auxtrace buffers in advance.
1861
1862For pipe mode, the order of events and timestamps can presumably
1863be messed up.
1864
1865
1866EXAMPLE
1867-------
1868
1869Examples can be found on perf wiki page "Perf tools support for Intel® Processor Trace":
1870
1871https://perf.wiki.kernel.org/index.php/Perf_tools_support_for_Intel%C2%AE_Processor_Trace
1872
1873
1874SEE ALSO
1875--------
1876
1877linkperf:perf-record[1], linkperf:perf-script[1], linkperf:perf-report[1],
1878linkperf:perf-inject[1]