summaryrefslogtreecommitdiffstats
path: root/tools/perf/Documentation/perf-intel-pt.txt
blob: 4c90cc176f813db90485dc1e0da6f79afab69709 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
perf-intel-pt(1)
================

NAME
----
perf-intel-pt - Support for Intel Processor Trace within perf tools

SYNOPSIS
--------
[verse]
'perf record' -e intel_pt//

DESCRIPTION
-----------

Intel Processor Trace (Intel PT) is an extension of Intel Architecture that
collects information about software execution such as control flow, execution
modes and timings and formats it into highly compressed binary packets.
Technical details are documented in the Intel 64 and IA-32 Architectures
Software Developer Manuals, Chapter 36 Intel Processor Trace.

Intel PT is first supported in Intel Core M and 5th generation Intel Core
processors that are based on the Intel micro-architecture code name Broadwell.

Trace data is collected by 'perf record' and stored within the perf.data file.
See below for options to 'perf record'.

Trace data must be 'decoded' which involves walking the object code and matching
the trace data packets. For example a TNT packet only tells whether a
conditional branch was taken or not taken, so to make use of that packet the
decoder must know precisely which instruction was being executed.

Decoding is done on-the-fly.  The decoder outputs samples in the same format as
samples output by perf hardware events, for example as though the "instructions"
or "branches" events had been recorded.  Presently 3 tools support this:
'perf script', 'perf report' and 'perf inject'.  See below for more information
on using those tools.

The main distinguishing feature of Intel PT is that the decoder can determine
the exact flow of software execution.  Intel PT can be used to understand why
and how did software get to a certain point, or behave a certain way.  The
software does not have to be recompiled, so Intel PT works with debug or release
builds, however the executed images are needed - which makes use in JIT-compiled
environments, or with self-modified code, a challenge.  Also symbols need to be
provided to make sense of addresses.

A limitation of Intel PT is that it produces huge amounts of trace data
(hundreds of megabytes per second per core) which takes a long time to decode,
for example two or three orders of magnitude longer than it took to collect.
Another limitation is the performance impact of tracing, something that will
vary depending on the use-case and architecture.


Quickstart
----------

It is important to start small.  That is because it is easy to capture vastly
more data than can possibly be processed.

The simplest thing to do with Intel PT is userspace profiling of small programs.
Data is captured with 'perf record' e.g. to trace 'ls' userspace-only:

	perf record -e intel_pt//u ls

And profiled with 'perf report' e.g.

	perf report

To also trace kernel space presents a problem, namely kernel self-modifying
code.  A fairly good kernel image is available in /proc/kcore but to get an
accurate image a copy of /proc/kcore needs to be made under the same conditions
as the data capture. 'perf record' can make a copy of /proc/kcore if the option
--kcore is used, but access to /proc/kcore is restricted e.g.

	sudo perf record -o pt_ls --kcore -e intel_pt// -- ls

which will create a directory named 'pt_ls' and put the perf.data file (named
simply 'data') and copies of /proc/kcore, /proc/kallsyms and /proc/modules into
it.  The other tools understand the directory format, so to use 'perf report'
becomes:

	sudo perf report -i pt_ls

Because samples are synthesized after-the-fact, the sampling period can be
selected for reporting. e.g. sample every microsecond

	sudo perf report pt_ls --itrace=i1usge

See the sections below for more information about the --itrace option.

Beware the smaller the period, the more samples that are produced, and the
longer it takes to process them.

Also note that the coarseness of Intel PT timing information will start to
distort the statistical value of the sampling as the sampling period becomes
smaller.

To represent software control flow, "branches" samples are produced.  By default
a branch sample is synthesized for every single branch.  To get an idea what
data is available you can use the 'perf script' tool with all itrace sampling
options, which will list all the samples.

	perf record -e intel_pt//u ls
	perf script --itrace=iybxwpe

An interesting field that is not printed by default is 'flags' which can be
displayed as follows:

	perf script --itrace=iybxwpe -F+flags

The flags are "bcrosyiABExghDt" which stand for branch, call, return, conditional,
system, asynchronous, interrupt, transaction abort, trace begin, trace end,
in transaction, VM-entry, VM-exit, interrupt disabled, and interrupt disable
toggle respectively.

perf script also supports higher level ways to dump instruction traces:

	perf script --insn-trace --xed

Dump all instructions. This requires installing the xed tool (see XED below)
Dumping all instructions in a long trace can be fairly slow. It is usually better
to start with higher level decoding, like

	perf script --call-trace

or

	perf script --call-ret-trace

and then select a time range of interest. The time range can then be examined
in detail with

	perf script --time starttime,stoptime --insn-trace --xed

While examining the trace it's also useful to filter on specific CPUs using
the -C option

	perf script --time starttime,stoptime --insn-trace --xed -C 1

Dump all instructions in time range on CPU 1.

Another interesting field that is not printed by default is 'ipc' which can be
displayed as follows:

	perf script --itrace=be -F+ipc

There are two ways that instructions-per-cycle (IPC) can be calculated depending
on the recording.

If the 'cyc' config term (see config terms section below) was used, then IPC
and cycle events are calculated using the cycle count from CYC packets, otherwise
MTC packets are used - refer to the 'mtc' config term.  When MTC is used, however,
the values are less accurate because the timing is less accurate.

Because Intel PT does not update the cycle count on every branch or instruction,
the values will often be zero.  When there are values, they will be the number
of instructions and number of cycles since the last update, and thus represent
the average IPC cycle count since the last IPC for that event type.
Note IPC for "branches" events is calculated separately from IPC for "instructions"
events.

Even with the 'cyc' config term, it is possible to produce IPC information for
every change of timestamp, but at the expense of accuracy.  That is selected by
specifying the itrace 'A' option.  Due to the granularity of timestamps, the
actual number of cycles increases even though the cycles reported does not.
The number of instructions is known, but if IPC is reported, cycles can be too
low and so IPC is too high.  Note that inaccuracy decreases as the period of
sampling increases i.e. if the number of cycles is too low by a small amount,
that becomes less significant if the number of cycles is large.  It may also be
useful to use the 'A' option in conjunction with dlfilter-show-cycles.so to
provide higher granularity cycle information.

Also note that the IPC instruction count may or may not include the current
instruction.  If the cycle count is associated with an asynchronous branch
(e.g. page fault or interrupt), then the instruction count does not include the
current instruction, otherwise it does.  That is consistent with whether or not
that instruction has retired when the cycle count is updated.

Another note, in the case of "branches" events, non-taken branches are not
presently sampled, so IPC values for them do not appear e.g. a CYC packet with a
TNT packet that starts with a non-taken branch.  To see every possible IPC
value, "instructions" events can be used e.g. --itrace=i0ns

While it is possible to create scripts to analyze the data, an alternative
approach is available to export the data to a sqlite or postgresql database.
Refer to script export-to-sqlite.py or export-to-postgresql.py for more details,
and to script exported-sql-viewer.py for an example of using the database.

There is also script intel-pt-events.py which provides an example of how to
unpack the raw data for power events and PTWRITE. The script also displays
branches, and supports 2 additional modes selected by option:

 - --insn-trace - instruction trace
 - --src-trace - source trace

The intel-pt-events.py script also has options:

 - --all-switch-events - display all switch events, not only the last consecutive.
 - --interleave [<n>] - interleave sample output for the same timestamp so that
 no more than n samples for a CPU are displayed in a row. 'n' defaults to 4.
 Note this only affects the order of output, and only when the timestamp is the
 same.

As mentioned above, it is easy to capture too much data.  One way to limit the
data captured is to use 'snapshot' mode which is explained further below.
Refer to 'new snapshot option' and 'Intel PT modes of operation' further below.

Another problem that will be experienced is decoder errors.  They can be caused
by inability to access the executed image, self-modified or JIT-ed code, or the
inability to match side-band information (such as context switches and mmaps)
which results in the decoder not knowing what code was executed.

There is also the problem of perf not being able to copy the data fast enough,
resulting in data lost because the buffer was full.  See 'Buffer handling' below
for more details.


perf record
-----------

new event
~~~~~~~~~

The Intel PT kernel driver creates a new PMU for Intel PT.  PMU events are
selected by providing the PMU name followed by the "config" separated by slashes.
An enhancement has been made to allow default "config" e.g. the option

	-e intel_pt//

will use a default config value.  Currently that is the same as

	-e intel_pt/tsc,noretcomp=0/

which is the same as

	-e intel_pt/tsc=1,noretcomp=0/

Note there are now new config terms - see section 'config terms' further below.

The config terms are listed in /sys/devices/intel_pt/format.  They are bit
fields within the config member of the struct perf_event_attr which is
passed to the kernel by the perf_event_open system call.  They correspond to bit
fields in the IA32_RTIT_CTL MSR.  Here is a list of them and their definitions:

	$ grep -H . /sys/bus/event_source/devices/intel_pt/format/*
	/sys/bus/event_source/devices/intel_pt/format/cyc:config:1
	/sys/bus/event_source/devices/intel_pt/format/cyc_thresh:config:19-22
	/sys/bus/event_source/devices/intel_pt/format/mtc:config:9
	/sys/bus/event_source/devices/intel_pt/format/mtc_period:config:14-17
	/sys/bus/event_source/devices/intel_pt/format/noretcomp:config:11
	/sys/bus/event_source/devices/intel_pt/format/psb_period:config:24-27
	/sys/bus/event_source/devices/intel_pt/format/tsc:config:10

Note that the default config must be overridden for each term i.e.

	-e intel_pt/noretcomp=0/

is the same as:

	-e intel_pt/tsc=1,noretcomp=0/

So, to disable TSC packets use:

	-e intel_pt/tsc=0/

It is also possible to specify the config value explicitly:

	-e intel_pt/config=0x400/

Note that, as with all events, the event is suffixed with event modifiers:

	u	userspace
	k	kernel
	h	hypervisor
	G	guest
	H	host
	p	precise ip

'h', 'G' and 'H' are for virtualization which are not used by Intel PT.
'p' is also not relevant to Intel PT.  So only options 'u' and 'k' are
meaningful for Intel PT.

perf_event_attr is displayed if the -vv option is used e.g.

	------------------------------------------------------------
	perf_event_attr:
	type                             6
	size                             112
	config                           0x400
	{ sample_period, sample_freq }   1
	sample_type                      IP|TID|TIME|CPU|IDENTIFIER
	read_format                      ID
	disabled                         1
	inherit                          1
	exclude_kernel                   1
	exclude_hv                       1
	enable_on_exec                   1
	sample_id_all                    1
	------------------------------------------------------------
	sys_perf_event_open: pid 31104  cpu 0  group_fd -1  flags 0x8
	sys_perf_event_open: pid 31104  cpu 1  group_fd -1  flags 0x8
	sys_perf_event_open: pid 31104  cpu 2  group_fd -1  flags 0x8
	sys_perf_event_open: pid 31104  cpu 3  group_fd -1  flags 0x8
	------------------------------------------------------------


config terms
~~~~~~~~~~~~

The June 2015 version of Intel 64 and IA-32 Architectures Software Developer
Manuals, Chapter 36 Intel Processor Trace, defined new Intel PT features.
Some of the features are reflect in new config terms.  All the config terms are
described below.

tsc		Always supported.  Produces TSC timestamp packets to provide
		timing information.  In some cases it is possible to decode
		without timing information, for example a per-thread context
		that does not overlap executable memory maps.

		The default config selects tsc (i.e. tsc=1).

noretcomp	Always supported.  Disables "return compression" so a TIP packet
		is produced when a function returns.  Causes more packets to be
		produced but might make decoding more reliable.

		The default config does not select noretcomp (i.e. noretcomp=0).

psb_period	Allows the frequency of PSB packets to be specified.

		The PSB packet is a synchronization packet that provides a
		starting point for decoding or recovery from errors.

		Support for psb_period is indicated by:

			/sys/bus/event_source/devices/intel_pt/caps/psb_cyc

		which contains "1" if the feature is supported and "0"
		otherwise.

		Valid values are given by:

			/sys/bus/event_source/devices/intel_pt/caps/psb_periods

		which contains a hexadecimal value, the bits of which represent
		valid values e.g. bit 2 set means value 2 is valid.

		The psb_period value is converted to the approximate number of
		trace bytes between PSB packets as:

			2 ^ (value + 11)

		e.g. value 3 means 16KiB bytes between PSBs

		If an invalid value is entered, the error message
		will give a list of valid values e.g.

			$ perf record -e intel_pt/psb_period=15/u uname
			Invalid psb_period for intel_pt. Valid values are: 0-5

		If MTC packets are selected, the default config selects a value
		of 3 (i.e. psb_period=3) or the nearest lower value that is
		supported (0 is always supported).  Otherwise the default is 0.

		If decoding is expected to be reliable and the buffer is large
		then a large PSB period can be used.

		Because a TSC packet is produced with PSB, the PSB period can
		also affect the granularity to timing information in the absence
		of MTC or CYC.

mtc		Produces MTC timing packets.

		MTC packets provide finer grain timestamp information than TSC
		packets.  MTC packets record time using the hardware crystal
		clock (CTC) which is related to TSC packets using a TMA packet.

		Support for this feature is indicated by:

			/sys/bus/event_source/devices/intel_pt/caps/mtc

		which contains "1" if the feature is supported and
		"0" otherwise.

		The frequency of MTC packets can also be specified - see
		mtc_period below.

mtc_period	Specifies how frequently MTC packets are produced - see mtc
		above for how to determine if MTC packets are supported.

		Valid values are given by:

			/sys/bus/event_source/devices/intel_pt/caps/mtc_periods

		which contains a hexadecimal value, the bits of which represent
		valid values e.g. bit 2 set means value 2 is valid.

		The mtc_period value is converted to the MTC frequency as:

			CTC-frequency / (2 ^ value)

		e.g. value 3 means one eighth of CTC-frequency

		Where CTC is the hardware crystal clock, the frequency of which
		can be related to TSC via values provided in cpuid leaf 0x15.

		If an invalid value is entered, the error message
		will give a list of valid values e.g.

			$ perf record -e intel_pt/mtc_period=15/u uname
			Invalid mtc_period for intel_pt. Valid values are: 0,3,6,9

		The default value is 3 or the nearest lower value
		that is supported (0 is always supported).

cyc		Produces CYC timing packets.

		CYC packets provide even finer grain timestamp information than
		MTC and TSC packets.  A CYC packet contains the number of CPU
		cycles since the last CYC packet. Unlike MTC and TSC packets,
		CYC packets are only sent when another packet is also sent.

		Support for this feature is indicated by:

			/sys/bus/event_source/devices/intel_pt/caps/psb_cyc

		which contains "1" if the feature is supported and
		"0" otherwise.

		The number of CYC packets produced can be reduced by specifying
		a threshold - see cyc_thresh below.

cyc_thresh	Specifies how frequently CYC packets are produced - see cyc
		above for how to determine if CYC packets are supported.

		Valid cyc_thresh values are given by:

			/sys/bus/event_source/devices/intel_pt/caps/cycle_thresholds

		which contains a hexadecimal value, the bits of which represent
		valid values e.g. bit 2 set means value 2 is valid.

		The cyc_thresh value represents the minimum number of CPU cycles
		that must have passed before a CYC packet can be sent.  The
		number of CPU cycles is:

			2 ^ (value - 1)

		e.g. value 4 means 8 CPU cycles must pass before a CYC packet
		can be sent.  Note a CYC packet is still only sent when another
		packet is sent, not at, e.g. every 8 CPU cycles.

		If an invalid value is entered, the error message
		will give a list of valid values e.g.

			$ perf record -e intel_pt/cyc,cyc_thresh=15/u uname
			Invalid cyc_thresh for intel_pt. Valid values are: 0-12

		CYC packets are not requested by default.

pt		Specifies pass-through which enables the 'branch' config term.

		The default config selects 'pt' if it is available, so a user will
		never need to specify this term.

branch		Enable branch tracing.  Branch tracing is enabled by default so to
		disable branch tracing use 'branch=0'.

		The default config selects 'branch' if it is available.

ptw		Enable PTWRITE packets which are produced when a ptwrite instruction
		is executed.

		Support for this feature is indicated by:

			/sys/bus/event_source/devices/intel_pt/caps/ptwrite

		which contains "1" if the feature is supported and
		"0" otherwise.

		As an alternative, refer to "Emulated PTWRITE" further below.

fup_on_ptw	Enable a FUP packet to follow the PTWRITE packet.  The FUP packet
		provides the address of the ptwrite instruction.  In the absence of
		fup_on_ptw, the decoder will use the address of the previous branch
		if branch tracing is enabled, otherwise the address will be zero.
		Note that fup_on_ptw will work even when branch tracing is disabled.

pwr_evt		Enable power events.  The power events provide information about
		changes to the CPU C-state.

		Support for this feature is indicated by:

			/sys/bus/event_source/devices/intel_pt/caps/power_event_trace

		which contains "1" if the feature is supported and
		"0" otherwise.

event		Enable Event Trace.  The events provide information about asynchronous
		events.

		Support for this feature is indicated by:

			/sys/bus/event_source/devices/intel_pt/caps/event_trace

		which contains "1" if the feature is supported and
		"0" otherwise.

notnt		Disable TNT packets.  Without TNT packets, it is not possible to walk
		executable code to reconstruct control flow, however FUP, TIP, TIP.PGE
		and TIP.PGD packets still indicate asynchronous control flow, and (if
		return compression is disabled - see noretcomp) return statements.
		The advantage of eliminating TNT packets is reducing the size of the
		trace and corresponding tracing overhead.

		Support for this feature is indicated by:

			/sys/bus/event_source/devices/intel_pt/caps/tnt_disable

		which contains "1" if the feature is supported and
		"0" otherwise.


AUX area sampling option
~~~~~~~~~~~~~~~~~~~~~~~~

To select Intel PT "sampling" the AUX area sampling option can be used:

	--aux-sample

Optionally it can be followed by the sample size in bytes e.g.

	--aux-sample=8192

In addition, the Intel PT event to sample must be defined e.g.

	-e intel_pt//u

Samples on other events will be created containing Intel PT data e.g. the
following will create Intel PT samples on the branch-misses event, note the
events must be grouped using {}:

	perf record --aux-sample -e '{intel_pt//u,branch-misses:u}'

An alternative to '--aux-sample' is to add the config term 'aux-sample-size' to
events.  In this case, the grouping is implied e.g.

	perf record -e intel_pt//u -e branch-misses/aux-sample-size=8192/u

is the same as:

	perf record -e '{intel_pt//u,branch-misses/aux-sample-size=8192/u}'

but allows for also using an address filter e.g.:

	perf record -e intel_pt//u --filter 'filter * @/bin/ls' -e branch-misses/aux-sample-size=8192/u -- ls

It is important to select a sample size that is big enough to contain at least
one PSB packet.  If not a warning will be displayed:

	Intel PT sample size (%zu) may be too small for PSB period (%zu)

The calculation used for that is: if sample_size <= psb_period + 256 display the
warning.  When sampling is used, psb_period defaults to 0 (2KiB).

The default sample size is 4KiB.

The sample size is passed in aux_sample_size in struct perf_event_attr.  The
sample size is limited by the maximum event size which is 64KiB.  It is
difficult to know how big the event might be without the trace sample attached,
but the tool validates that the sample size is not greater than 60KiB.


new snapshot option
~~~~~~~~~~~~~~~~~~~

The difference between full trace and snapshot from the kernel's perspective is
that in full trace we don't overwrite trace data that the user hasn't collected
yet (and indicated that by advancing aux_tail), whereas in snapshot mode we let
the trace run and overwrite older data in the buffer so that whenever something
interesting happens, we can stop it and grab a snapshot of what was going on
around that interesting moment.

To select snapshot mode a new option has been added:

	-S

Optionally it can be followed by the snapshot size e.g.

	-S0x100000

The default snapshot size is the auxtrace mmap size.  If neither auxtrace mmap size
nor snapshot size is specified, then the default is 4MiB for privileged users
(or if /proc/sys/kernel/perf_event_paranoid < 0), 128KiB for unprivileged users.
If an unprivileged user does not specify mmap pages, the mmap pages will be
reduced as described in the 'new auxtrace mmap size option' section below.

The snapshot size is displayed if the option -vv is used e.g.

	Intel PT snapshot size: %zu


new auxtrace mmap size option
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Intel PT buffer size is specified by an addition to the -m option e.g.

	-m,16

selects a buffer size of 16 pages i.e. 64KiB.

Note that the existing functionality of -m is unchanged.  The auxtrace mmap size
is specified by the optional addition of a comma and the value.

The default auxtrace mmap size for Intel PT is 4MiB/page_size for privileged users
(or if /proc/sys/kernel/perf_event_paranoid < 0), 128KiB for unprivileged users.
If an unprivileged user does not specify mmap pages, the mmap pages will be
reduced from the default 512KiB/page_size to 256KiB/page_size, otherwise the
user is likely to get an error as they exceed their mlock limit (Max locked
memory as shown in /proc/self/limits).  Note that perf does not count the first
512KiB (actually /proc/sys/kernel/perf_event_mlock_kb minus 1 page) per cpu
against the mlock limit so an unprivileged user is allowed 512KiB per cpu plus
their mlock limit (which defaults to 64KiB but is not multiplied by the number
of cpus).

In full-trace mode, powers of two are allowed for buffer size, with a minimum
size of 2 pages.  In snapshot mode or sampling mode, it is the same but the
minimum size is 1 page.

The mmap size and auxtrace mmap size are displayed if the -vv option is used e.g.

	mmap length 528384
	auxtrace mmap length 4198400


Intel PT modes of operation
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Intel PT can be used in 3 modes:
	full-trace mode
	sample mode
	snapshot mode

Full-trace mode traces continuously e.g.

	perf record -e intel_pt//u uname

Sample mode attaches a Intel PT sample to other events e.g.

	perf record --aux-sample -e intel_pt//u -e branch-misses:u

Snapshot mode captures the available data when a signal is sent or "snapshot"
control command is issued. e.g. using a signal

	perf record -v -e intel_pt//u -S ./loopy 1000000000 &
	[1] 11435
	kill -USR2 11435
	Recording AUX area tracing snapshot

Note that the signal sent is SIGUSR2.
Note that "Recording AUX area tracing snapshot" is displayed because the -v
option is used.

The advantage of using "snapshot" control command is that the access is
controlled by access to a FIFO e.g.

	$ mkfifo perf.control
	$ mkfifo perf.ack
	$ cat perf.ack &
	[1] 15235
	$ sudo ~/bin/perf record --control fifo:perf.control,perf.ack -S -e intel_pt//u -- sleep 60 &
	[2] 15243
	$ ps -e | grep perf
	15244 pts/1    00:00:00 perf
	$ kill -USR2 15244
	bash: kill: (15244) - Operation not permitted
	$ echo snapshot > perf.control
	ack

The 3 Intel PT modes of operation cannot be used together.


Buffer handling
~~~~~~~~~~~~~~~

There may be buffer limitations (i.e. single ToPa entry) which means that actual
buffer sizes are limited to powers of 2 up to 4MiB (MAX_ORDER).  In order to
provide other sizes, and in particular an arbitrarily large size, multiple
buffers are logically concatenated.  However an interrupt must be used to switch
between buffers.  That has two potential problems:
	a) the interrupt may not be handled in time so that the current buffer
	becomes full and some trace data is lost.
	b) the interrupts may slow the system and affect the performance
	results.

If trace data is lost, the driver sets 'truncated' in the PERF_RECORD_AUX event
which the tools report as an error.

In full-trace mode, the driver waits for data to be copied out before allowing
the (logical) buffer to wrap-around.  If data is not copied out quickly enough,
again 'truncated' is set in the PERF_RECORD_AUX event.  If the driver has to
wait, the intel_pt event gets disabled.  Because it is difficult to know when
that happens, perf tools always re-enable the intel_pt event after copying out
data.


Intel PT and build ids
~~~~~~~~~~~~~~~~~~~~~~

By default "perf record" post-processes the event stream to find all build ids
for executables for all addresses sampled.  Deliberately, Intel PT is not
decoded for that purpose (it would take too long).  Instead the build ids for
all executables encountered (due to mmap, comm or task events) are included
in the perf.data file.

To see buildids included in the perf.data file use the command:

	perf buildid-list

If the perf.data file contains Intel PT data, that is the same as:

	perf buildid-list --with-hits


Snapshot mode and event disabling
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In order to make a snapshot, the intel_pt event is disabled using an IOCTL,
namely PERF_EVENT_IOC_DISABLE.  However doing that can also disable the
collection of side-band information.  In order to prevent that,  a dummy
software event has been introduced that permits tracking events (like mmaps) to
continue to be recorded while intel_pt is disabled.  That is important to ensure
there is complete side-band information to allow the decoding of subsequent
snapshots.

A test has been created for that.  To find the test:

	perf test list
	...
	23: Test using a dummy software event to keep tracking

To run the test:

	perf test 23
	23: Test using a dummy software event to keep tracking     : Ok


perf record modes (nothing new here)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

perf record essentially operates in one of three modes:
	per thread
	per cpu
	workload only

"per thread" mode is selected by -t or by --per-thread (with -p or -u or just a
workload).
"per cpu" is selected by -C or -a.
"workload only" mode is selected by not using the other options but providing a
command to run (i.e. the workload).

In per-thread mode an exact list of threads is traced.  There is no inheritance.
Each thread has its own event buffer.

In per-cpu mode all processes (or processes from the selected cgroup i.e. -G
option, or processes selected with -p or -u) are traced.  Each cpu has its own
buffer. Inheritance is allowed.

In workload-only mode, the workload is traced but with per-cpu buffers.
Inheritance is allowed.  Note that you can now trace a workload in per-thread
mode by using the --per-thread option.


Privileged vs non-privileged users
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Unless /proc/sys/kernel/perf_event_paranoid is set to -1, unprivileged users
have memory limits imposed upon them.  That affects what buffer sizes they can
have as outlined above.

The v4.2 kernel introduced support for a context switch metadata event,
PERF_RECORD_SWITCH, which allows unprivileged users to see when their processes
are scheduled out and in, just not by whom, which is left for the
PERF_RECORD_SWITCH_CPU_WIDE, that is only accessible in system wide context,
which in turn requires CAP_PERFMON or CAP_SYS_ADMIN.

Please see the 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context
switches") commit, that introduces these metadata events for further info.

When working with kernels < v4.2, the following considerations must be taken,
as the sched:sched_switch tracepoints will be used to receive such information:

Unless /proc/sys/kernel/perf_event_paranoid is set to -1, unprivileged users are
not permitted to use tracepoints which means there is insufficient side-band
information to decode Intel PT in per-cpu mode, and potentially workload-only
mode too if the workload creates new processes.

Note also, that to use tracepoints, read-access to debugfs is required.  So if
debugfs is not mounted or the user does not have read-access, it will again not
be possible to decode Intel PT in per-cpu mode.


sched_switch tracepoint
~~~~~~~~~~~~~~~~~~~~~~~

The sched_switch tracepoint is used to provide side-band data for Intel PT
decoding in kernels where the PERF_RECORD_SWITCH metadata event isn't
available.

The sched_switch events are automatically added. e.g. the second event shown
below:

	$ perf record -vv -e intel_pt//u uname
	------------------------------------------------------------
	perf_event_attr:
	type                             6
	size                             112
	config                           0x400
	{ sample_period, sample_freq }   1
	sample_type                      IP|TID|TIME|CPU|IDENTIFIER
	read_format                      ID
	disabled                         1
	inherit                          1
	exclude_kernel                   1
	exclude_hv                       1
	enable_on_exec                   1
	sample_id_all                    1
	------------------------------------------------------------
	sys_perf_event_open: pid 31104  cpu 0  group_fd -1  flags 0x8
	sys_perf_event_open: pid 31104  cpu 1  group_fd -1  flags 0x8
	sys_perf_event_open: pid 31104  cpu 2  group_fd -1  flags 0x8
	sys_perf_event_open: pid 31104  cpu 3  group_fd -1  flags 0x8
	------------------------------------------------------------
	perf_event_attr:
	type                             2
	size                             112
	config                           0x108
	{ sample_period, sample_freq }   1
	sample_type                      IP|TID|TIME|CPU|PERIOD|RAW|IDENTIFIER
	read_format                      ID
	inherit                          1
	sample_id_all                    1
	exclude_guest                    1
	------------------------------------------------------------
	sys_perf_event_open: pid -1  cpu 0  group_fd -1  flags 0x8
	sys_perf_event_open: pid -1  cpu 1  group_fd -1  flags 0x8
	sys_perf_event_open: pid -1  cpu 2  group_fd -1  flags 0x8
	sys_perf_event_open: pid -1  cpu 3  group_fd -1  flags 0x8
	------------------------------------------------------------
	perf_event_attr:
	type                             1
	size                             112
	config                           0x9
	{ sample_period, sample_freq }   1
	sample_type                      IP|TID|TIME|IDENTIFIER
	read_format                      ID
	disabled                         1
	inherit                          1
	exclude_kernel                   1
	exclude_hv                       1
	mmap                             1
	comm                             1
	enable_on_exec                   1
	task                             1
	sample_id_all                    1
	mmap2                            1
	comm_exec                        1
	------------------------------------------------------------
	sys_perf_event_open: pid 31104  cpu 0  group_fd -1  flags 0x8
	sys_perf_event_open: pid 31104  cpu 1  group_fd -1  flags 0x8
	sys_perf_event_open: pid 31104  cpu 2  group_fd -1  flags 0x8
	sys_perf_event_open: pid 31104  cpu 3  group_fd -1  flags 0x8
	mmap size 528384B
	AUX area mmap length 4194304
	perf event ring buffer mmapped per cpu
	Synthesizing auxtrace information
	Linux
	[ perf record: Woken up 1 times to write data ]
	[ perf record: Captured and wrote 0.042 MB perf.data ]

Note, the sched_switch event is only added if the user is permitted to use it
and only in per-cpu mode.

Note also, the sched_switch event is only added if TSC packets are requested.
That is because, in the absence of timing information, the sched_switch events
cannot be matched against the Intel PT trace.


perf script
-----------

By default, perf script will decode trace data found in the perf.data file.
This can be further controlled by new option --itrace.


New --itrace option
~~~~~~~~~~~~~~~~~~~

Having no option is the same as

	--itrace

which, in turn, is the same as

	--itrace=cepwxy

The letters are:

	i	synthesize "instructions" events
	y	synthesize "cycles" events
	b	synthesize "branches" events
	x	synthesize "transactions" events
	w	synthesize "ptwrite" events
	p	synthesize "power" events (incl. PSB events)
	c	synthesize branches events (calls only)
	r	synthesize branches events (returns only)
	o	synthesize PEBS-via-PT events
	I	synthesize Event Trace events
	e	synthesize tracing error events
	d	create a debug log
	g	synthesize a call chain (use with i or x)
	G	synthesize a call chain on existing event records
	l	synthesize last branch entries (use with i or x)
	L	synthesize last branch entries on existing event records
	s	skip initial number of events
	q	quicker (less detailed) decoding
	A	approximate IPC
	Z	prefer to ignore timestamps (so-called "timeless" decoding)

"Instructions" events look like they were recorded by "perf record -e
instructions".

"Cycles" events look like they were recorded by "perf record -e cycles"
(ie., the default). Note that even with CYC packets enabled and no sampling,
these are not fully accurate, since CYC packets are not emitted for each
instruction, only when some other event (like an indirect branch, or a
TNT packet representing multiple branches) happens causes a packet to
be emitted. Thus, it is more effective for attributing cycles to functions
(and possibly basic blocks) than to individual instructions, although it
is not even perfect for functions (although it becomes better if the noretcomp
option is active).

"Branches" events look like they were recorded by "perf record -e branches". "c"
and "r" can be combined to get calls and returns.

"Transactions" events correspond to the start or end of transactions. The
'flags' field can be used in perf script to determine whether the event is a
transaction start, commit or abort.

Note that "instructions", "cycles", "branches" and "transactions" events
depend on code flow packets which can be disabled by using the config term
"branch=0".  Refer to the config terms section above.

"ptwrite" events record the payload of the ptwrite instruction and whether
"fup_on_ptw" was used.  "ptwrite" events depend on PTWRITE packets which are
recorded only if the "ptw" config term was used.  Refer to the config terms
section above.  perf script "synth" field displays "ptwrite" information like
this: "ip: 0 payload: 0x123456789abcdef0"  where "ip" is 1 if "fup_on_ptw" was
used.

"Power" events correspond to power event packets and CBR (core-to-bus ratio)
packets.  While CBR packets are always recorded when tracing is enabled, power
event packets are recorded only if the "pwr_evt" config term was used.  Refer to
the config terms section above.  The power events record information about
C-state changes, whereas CBR is indicative of CPU frequency.  perf script
"event,synth" fields display information like this:

	cbr:  cbr: 22 freq: 2189 MHz (200%)
	mwait:  hints: 0x60 extensions: 0x1
	pwre:  hw: 0 cstate: 2 sub-cstate: 0
	exstop:  ip: 1
	pwrx:  deepest cstate: 2 last cstate: 2 wake reason: 0x4

Where:

	"cbr" includes the frequency and the percentage of maximum non-turbo
	"mwait" shows mwait hints and extensions
	"pwre" shows C-state transitions (to a C-state deeper than C0) and
	whether	initiated by hardware
	"exstop" indicates execution stopped and whether the IP was recorded
	exactly,
	"pwrx" indicates return to C0

For more details refer to the Intel 64 and IA-32 Architectures Software
Developer Manuals.

PSB events show when a PSB+ occurred and also the byte-offset in the trace.
Emitting a PSB+ can cause a CPU a slight delay. When doing timing analysis
of code with Intel PT, it is useful to know if a timing bubble was caused
by Intel PT or not.

Error events show where the decoder lost the trace.  Error events
are quite important.  Users must know if what they are seeing is a complete
picture or not. The "e" option may be followed by flags which affect what errors
will or will not be reported.  Each flag must be preceded by either '+' or '-'.
The flags supported by Intel PT are:

		-o	Suppress overflow errors
		-l	Suppress trace data lost errors

For example, for errors but not overflow or data lost errors:

	--itrace=e-o-l

The "d" option will cause the creation of a file "intel_pt.log" containing all
decoded packets and instructions.  Note that this option slows down the decoder
and that the resulting file may be very large.  The "d" option may be followed
by flags which affect what debug messages will or will not be logged. Each flag
must be preceded by either '+' or '-'. The flags support by Intel PT are:

		-a	Suppress logging of perf events
		+a	Log all perf events
		+e	Output only on decoding errors (size configurable)
		+o	Output to stdout instead of "intel_pt.log"

By default, logged perf events are filtered by any specified time ranges, but
flag +a overrides that.  The +e flag can be useful for analyzing errors.  By
default, the log size in that case is 16384 bytes, but can be altered by
linkperf:perf-config[1] e.g. perf config itrace.debug-log-buffer-size=30000

In addition, the period of the "instructions" event can be specified. e.g.

	--itrace=i10us

sets the period to 10us i.e. one  instruction sample is synthesized for each 10
microseconds of trace.  Alternatives to "us" are "ms" (milliseconds),
"ns" (nanoseconds), "t" (TSC ticks) or "i" (instructions).

"ms", "us" and "ns" are converted to TSC ticks.

The timing information included with Intel PT does not give the time of every
instruction.  Consequently, for the purpose of sampling, the decoder estimates
the time since the last timing packet based on 1 tick per instruction.  The time
on the sample is *not* adjusted and reflects the last known value of TSC.

For Intel PT, the default period is 100us.

Setting it to a zero period means "as often as possible".

In the case of Intel PT that is the same as a period of 1 and a unit of
'instructions' (i.e. --itrace=i1i).

Also the call chain size (default 16, max. 1024) for instructions or
transactions events can be specified. e.g.

	--itrace=ig32
	--itrace=xg32

Also the number of last branch entries (default 64, max. 1024) for instructions or
transactions events can be specified. e.g.

       --itrace=il10
       --itrace=xl10

Note that last branch entries are cleared for each sample, so there is no overlap
from one sample to the next.

The G and L options are designed in particular for sample mode, and work much
like g and l but add call chain and branch stack to the other selected events
instead of synthesized events. For example, to record branch-misses events for
'ls' and then add a call chain derived from the Intel PT trace:

	perf record --aux-sample -e '{intel_pt//u,branch-misses:u}' -- ls
	perf report --itrace=Ge

Although in fact G is a default for perf report, so that is the same as just:

	perf report

One caveat with the G and L options is that they work poorly with "Large PEBS".
Large PEBS means PEBS records will be accumulated by hardware and the written
into the event buffer in one go.  That reduces interrupts, but can give very
late timestamps.  Because the Intel PT trace is synchronized by timestamps,
the PEBS events do not match the trace.  Currently, Large PEBS is used only in
certain circumstances:
	- hardware supports it
	- PEBS is used
	- event period is specified, instead of frequency
	- the sample type is limited to the following flags:
		PERF_SAMPLE_IP | PERF_SAMPLE_TID | PERF_SAMPLE_ADDR |
		PERF_SAMPLE_ID | PERF_SAMPLE_CPU | PERF_SAMPLE_STREAM_ID |
		PERF_SAMPLE_DATA_SRC | PERF_SAMPLE_IDENTIFIER |
		PERF_SAMPLE_TRANSACTION | PERF_SAMPLE_PHYS_ADDR |
		PERF_SAMPLE_REGS_INTR | PERF_SAMPLE_REGS_USER |
		PERF_SAMPLE_PERIOD (and sometimes) | PERF_SAMPLE_TIME
Because Intel PT sample mode uses a different sample type to the list above,
Large PEBS is not used with Intel PT sample mode. To avoid Large PEBS in other
cases, avoid specifying the event period i.e. avoid the 'perf record' -c option,
--count option, or 'period' config term.

To disable trace decoding entirely, use the option --no-itrace.

It is also possible to skip events generated (instructions, branches, transactions)
at the beginning. This is useful to ignore initialization code.

	--itrace=i0nss1000000

skips the first million instructions.

The q option changes the way the trace is decoded.  The decoding is much faster
but much less detailed.  Specifically, with the q option, the decoder does not
decode TNT packets, and does not walk object code, but gets the ip from FUP and
TIP packets.  The q option can be used with the b and i options but the period
is not used.  The q option decodes more quickly, but is useful only if the
control flow of interest is represented or indicated by FUP, TIP, TIP.PGE, or
TIP.PGD packets (refer below).  However the q option could be used to find time
ranges that could then be decoded fully using the --time option.

What will *not* be decoded with the (single) q option:

	- direct calls and jmps
	- conditional branches
	- non-branch instructions

What *will* be decoded with the (single) q option:

	- asynchronous branches such as interrupts
	- indirect branches
	- function return target address *if* the noretcomp config term (refer
	config terms section) was used
	- start of (control-flow) tracing
	- end of (control-flow) tracing, if it is not out of context
	- power events, ptwrite, transaction start and abort
	- instruction pointer associated with PSB packets

Note the q option does not specify what events will be synthesized e.g. the p
option must be used also to show power events.

Repeating the q option (double-q i.e. qq) results in even faster decoding and even
less detail.  The decoder decodes only extended PSB (PSB+) packets, getting the
instruction pointer if there is a FUP packet within PSB+ (i.e. between PSB and
PSBEND).  Note PSB packets occur regularly in the trace based on the psb_period
config term (refer config terms section).  There will be a FUP packet if the
PSB+ occurs while control flow is being traced.

What will *not* be decoded with the qq option:

	- everything except instruction pointer associated with PSB packets

What *will* be decoded with the qq option:

	- instruction pointer associated with PSB packets

The Z option is equivalent to having recorded a trace without TSC
(i.e. config term tsc=0). It can be useful to avoid timestamp issues when
decoding a trace of a virtual machine.


dlfilter-show-cycles.so
~~~~~~~~~~~~~~~~~~~~~~~

Cycles can be displayed using dlfilter-show-cycles.so in which case the itrace A
option can be useful to provide higher granularity cycle information:

	perf script --itrace=A --call-trace --dlfilter dlfilter-show-cycles.so

To see a list of dlfilters:

	perf script -v --list-dlfilters

See also linkperf:perf-dlfilters[1]


dump option
~~~~~~~~~~~

perf script has an option (-D) to "dump" the events i.e. display the binary
data.

When -D is used, Intel PT packets are displayed.  The packet decoder does not
pay attention to PSB packets, but just decodes the bytes - so the packets seen
by the actual decoder may not be identical in places where the data is corrupt.
One example of that would be when the buffer-switching interrupt has been too
slow, and the buffer has been filled completely.  In that case, the last packet
in the buffer might be truncated and immediately followed by a PSB as the trace
continues in the next buffer.

To disable the display of Intel PT packets, combine the -D option with
--no-itrace.


perf report
-----------

By default, perf report will decode trace data found in the perf.data file.
This can be further controlled by new option --itrace exactly the same as
perf script, with the exception that the default is --itrace=igxe.


perf inject
-----------

perf inject also accepts the --itrace option in which case tracing data is
removed and replaced with the synthesized events. e.g.

	perf inject --itrace -i perf.data -o perf.data.new

Below is an example of using Intel PT with autofdo.  It requires autofdo
(https://github.com/google/autofdo) and gcc version 5.  The bubble
sort example is from the AutoFDO tutorial (https://gcc.gnu.org/wiki/AutoFDO/Tutorial)
amended to take the number of elements as a parameter.

	$ gcc-5 -O3 sort.c -o sort_optimized
	$ ./sort_optimized 30000
	Bubble sorting array of 30000 elements
	2254 ms

	$ cat ~/.perfconfig
	[intel-pt]
		mispred-all = on

	$ perf record -e intel_pt//u ./sort 3000
	Bubble sorting array of 3000 elements
	58 ms
	[ perf record: Woken up 2 times to write data ]
	[ perf record: Captured and wrote 3.939 MB perf.data ]
	$ perf inject -i perf.data -o inj --itrace=i100usle --strip
	$ ./create_gcov --binary=./sort --profile=inj --gcov=sort.gcov -gcov_version=1
	$ gcc-5 -O3 -fauto-profile=sort.gcov sort.c -o sort_autofdo
	$ ./sort_autofdo 30000
	Bubble sorting array of 30000 elements
	2155 ms

Note there is currently no advantage to using Intel PT instead of LBR, but
that may change in the future if greater use is made of the data.


PEBS via Intel PT
-----------------

Some hardware has the feature to redirect PEBS records to the Intel PT trace.
Recording is selected by using the aux-output config term e.g.

	perf record -c 10000 -e '{intel_pt/branch=0/,cycles/aux-output/ppp}' uname

Originally, software only supported redirecting at most one PEBS event because it
was not able to differentiate one event from another. To overcome that, more recent
kernels and perf tools add support for the PERF_RECORD_AUX_OUTPUT_HW_ID side-band event.
To check for the presence of that event in a PEBS-via-PT trace:

	perf script -D --no-itrace | grep PERF_RECORD_AUX_OUTPUT_HW_ID

To display PEBS events from the Intel PT trace, use the itrace 'o' option e.g.

	perf script --itrace=oe

XED
---

include::build-xed.txt[]


Tracing Virtual Machines (kernel only)
--------------------------------------

Currently, kernel tracing is supported with either "timeless" decoding
(i.e. no TSC timestamps) or VM Time Correlation. VM Time Correlation is an extra step
using 'perf inject' and requires unchanging VMX TSC Offset and no VMX TSC Scaling.

Other limitations and caveats

 VMX controls may suppress packets needed for decoding resulting in decoding errors
 VMX controls may block the perf NMI to the host potentially resulting in lost trace data
 Guest kernel self-modifying code (e.g. jump labels or JIT-compiled eBPF) will result in decoding errors
 Guest thread information is unknown
 Guest VCPU is unknown but may be able to be inferred from the host thread
 Callchains are not supported

Example using "timeless" decoding

Start VM

 $ sudo virsh start kubuntu20.04
 Domain kubuntu20.04 started

Mount the guest file system.  Note sshfs needs -o direct_io to enable reading of proc files.  root access is needed to read /proc/kcore.

 $ mkdir vm0
 $ sshfs -o direct_io root@vm0:/ vm0

Copy the guest /proc/kallsyms, /proc/modules and /proc/kcore

 $ perf buildid-cache -v --kcore vm0/proc/kcore
 kcore added to build-id cache directory /home/user/.debug/[kernel.kcore]/9600f316a53a0f54278885e8d9710538ec5f6a08/2021021807494306
 $ KALLSYMS=/home/user/.debug/[kernel.kcore]/9600f316a53a0f54278885e8d9710538ec5f6a08/2021021807494306/kallsyms

Find the VM process

 $ ps -eLl | grep 'KVM\|PID'
 F S   UID     PID    PPID     LWP  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
 3 S 64055    1430       1    1440  1  80   0 - 1921718 -    ?        00:02:47 CPU 0/KVM
 3 S 64055    1430       1    1441  1  80   0 - 1921718 -    ?        00:02:41 CPU 1/KVM
 3 S 64055    1430       1    1442  1  80   0 - 1921718 -    ?        00:02:38 CPU 2/KVM
 3 S 64055    1430       1    1443  2  80   0 - 1921718 -    ?        00:03:18 CPU 3/KVM

Start an open-ended perf record, tracing the VM process, do something on the VM, and then ctrl-C to stop.
TSC is not supported and tsc=0 must be specified.  That means mtc is useless, so add mtc=0.
However, IPC can still be determined, hence cyc=1 can be added.
Only kernel decoding is supported, so 'k' must be specified.
Intel PT traces both the host and the guest so --guest and --host need to be specified.
Without timestamps, --per-thread must be specified to distinguish threads.

 $ sudo perf kvm --guest --host --guestkallsyms $KALLSYMS record --kcore -e intel_pt/tsc=0,mtc=0,cyc=1/k -p 1430 --per-thread
 ^C
 [ perf record: Woken up 1 times to write data ]
 [ perf record: Captured and wrote 5.829 MB ]

perf script can be used to provide an instruction trace

 $ perf script --guestkallsyms $KALLSYMS --insn-trace --xed -F+ipc | grep -C10 vmresume | head -21
       CPU 0/KVM  1440  ffffffff82133cdd __vmx_vcpu_run+0x3d ([kernel.kallsyms])                movq  0x48(%rax), %r9
       CPU 0/KVM  1440  ffffffff82133ce1 __vmx_vcpu_run+0x41 ([kernel.kallsyms])                movq  0x50(%rax), %r10
       CPU 0/KVM  1440  ffffffff82133ce5 __vmx_vcpu_run+0x45 ([kernel.kallsyms])                movq  0x58(%rax), %r11
       CPU 0/KVM  1440  ffffffff82133ce9 __vmx_vcpu_run+0x49 ([kernel.kallsyms])                movq  0x60(%rax), %r12
       CPU 0/KVM  1440  ffffffff82133ced __vmx_vcpu_run+0x4d ([kernel.kallsyms])                movq  0x68(%rax), %r13
       CPU 0/KVM  1440  ffffffff82133cf1 __vmx_vcpu_run+0x51 ([kernel.kallsyms])                movq  0x70(%rax), %r14
       CPU 0/KVM  1440  ffffffff82133cf5 __vmx_vcpu_run+0x55 ([kernel.kallsyms])                movq  0x78(%rax), %r15
       CPU 0/KVM  1440  ffffffff82133cf9 __vmx_vcpu_run+0x59 ([kernel.kallsyms])                movq  (%rax), %rax
       CPU 0/KVM  1440  ffffffff82133cfc __vmx_vcpu_run+0x5c ([kernel.kallsyms])                callq  0xffffffff82133c40
       CPU 0/KVM  1440  ffffffff82133c40 vmx_vmenter+0x0 ([kernel.kallsyms])            jz 0xffffffff82133c46
       CPU 0/KVM  1440  ffffffff82133c42 vmx_vmenter+0x2 ([kernel.kallsyms])            vmresume         IPC: 0.11 (50/445)
           :1440  1440  ffffffffbb678b06 native_write_msr+0x6 ([guest.kernel.kallsyms])                 nopl  %eax, (%rax,%rax,1)
           :1440  1440  ffffffffbb678b0b native_write_msr+0xb ([guest.kernel.kallsyms])                 retq     IPC: 0.04 (2/41)
           :1440  1440  ffffffffbb666646 lapic_next_deadline+0x26 ([guest.kernel.kallsyms])             data16 nop
           :1440  1440  ffffffffbb666648 lapic_next_deadline+0x28 ([guest.kernel.kallsyms])             xor %eax, %eax
           :1440  1440  ffffffffbb66664a lapic_next_deadline+0x2a ([guest.kernel.kallsyms])             popq  %rbp
           :1440  1440  ffffffffbb66664b lapic_next_deadline+0x2b ([guest.kernel.kallsyms])             retq     IPC: 0.16 (4/25)
           :1440  1440  ffffffffbb74607f clockevents_program_event+0x8f ([guest.kernel.kallsyms])               test %eax, %eax
           :1440  1440  ffffffffbb746081 clockevents_program_event+0x91 ([guest.kernel.kallsyms])               jz 0xffffffffbb74603c    IPC: 0.06 (2/30)
           :1440  1440  ffffffffbb74603c clockevents_program_event+0x4c ([guest.kernel.kallsyms])               popq  %rbx
           :1440  1440  ffffffffbb74603d clockevents_program_event+0x4d ([guest.kernel.kallsyms])               popq  %r12

Example using VM Time Correlation

Start VM

 $ sudo virsh start kubuntu20.04
 Domain kubuntu20.04 started

Mount the guest file system.  Note sshfs needs -o direct_io to enable reading of proc files.  root access is needed to read /proc/kcore.

 $ mkdir -p vm0
 $ sshfs -o direct_io root@vm0:/ vm0

Copy the guest /proc/kallsyms, /proc/modules and /proc/kcore

 $ perf buildid-cache -v --kcore vm0/proc/kcore
 same kcore found in /home/user/.debug/[kernel.kcore]/cc9c55a98c5e4ec0aeda69302554aabed5cd6491/2021021312450777
 $ KALLSYMS=/home/user/.debug/\[kernel.kcore\]/cc9c55a98c5e4ec0aeda69302554aabed5cd6491/2021021312450777/kallsyms

Find the VM process

 $ ps -eLl | grep 'KVM\|PID'
 F S   UID     PID    PPID     LWP  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
 3 S 64055   16998       1   17005 13  80   0 - 1818189 -    ?        00:00:16 CPU 0/KVM
 3 S 64055   16998       1   17006  4  80   0 - 1818189 -    ?        00:00:05 CPU 1/KVM
 3 S 64055   16998       1   17007  3  80   0 - 1818189 -    ?        00:00:04 CPU 2/KVM
 3 S 64055   16998       1   17008  4  80   0 - 1818189 -    ?        00:00:05 CPU 3/KVM

Start an open-ended perf record, tracing the VM process, do something on the VM, and then ctrl-C to stop.
IPC can be determined, hence cyc=1 can be added.
Only kernel decoding is supported, so 'k' must be specified.
Intel PT traces both the host and the guest so --guest and --host need to be specified.

 $ sudo perf kvm --guest --host --guestkallsyms $KALLSYMS record --kcore -e intel_pt/cyc=1/k -p 16998
 ^C[ perf record: Woken up 1 times to write data ]
 [ perf record: Captured and wrote 9.041 MB perf.data.kvm ]

Now 'perf inject' can be used to determine the VMX TCS Offset. Note, Intel PT TSC packets are
only 7-bytes, so the TSC Offset might differ from the actual value in the 8th byte. That will
have no effect i.e. the resulting timestamps will be correct anyway.

 $ perf inject -i perf.data.kvm --vm-time-correlation=dry-run
 ERROR: Unknown TSC Offset for VMCS 0x1bff6a
 VMCS: 0x1bff6a  TSC Offset 0xffffe42722c64c41
 ERROR: Unknown TSC Offset for VMCS 0x1cbc08
 VMCS: 0x1cbc08  TSC Offset 0xffffe42722c64c41
 ERROR: Unknown TSC Offset for VMCS 0x1c3ce8
 VMCS: 0x1c3ce8  TSC Offset 0xffffe42722c64c41
 ERROR: Unknown TSC Offset for VMCS 0x1cbce9
 VMCS: 0x1cbce9  TSC Offset 0xffffe42722c64c41

Each virtual CPU has a different Virtual Machine Control Structure (VMCS)
shown above with the calculated TSC Offset. For an unchanging TSC Offset
they should all be the same for the same virtual machine.

Now that the TSC Offset is known, it can be provided to 'perf inject'

 $ perf inject -i perf.data.kvm --vm-time-correlation="dry-run 0xffffe42722c64c41"

Note the options for 'perf inject' --vm-time-correlation are:

 [ dry-run ] [ <TSC Offset> [ : <VMCS> [ , <VMCS> ]... ]  ]...

So it is possible to specify different TSC Offsets for different VMCS.
The option "dry-run" will cause the file to be processed but without updating it.
Note it is also possible to get a intel_pt.log file by adding option --itrace=d

There were no errors so, do it for real

 $ perf inject -i perf.data.kvm --vm-time-correlation=0xffffe42722c64c41 --force

'perf script' can be used to see if there are any decoder errors

 $ perf script -i perf.data.kvm --guestkallsyms $KALLSYMS --itrace=e-o

There were none.

'perf script' can be used to provide an instruction trace showing timestamps

 $ perf script -i perf.data.kvm --guestkallsyms $KALLSYMS --insn-trace --xed -F+ipc | grep -C10 vmresume | head -21
       CPU 1/KVM 17006 [001] 11500.262865593:  ffffffff82133cdd __vmx_vcpu_run+0x3d ([kernel.kallsyms])                 movq  0x48(%rax), %r9
       CPU 1/KVM 17006 [001] 11500.262865593:  ffffffff82133ce1 __vmx_vcpu_run+0x41 ([kernel.kallsyms])                 movq  0x50(%rax), %r10
       CPU 1/KVM 17006 [001] 11500.262865593:  ffffffff82133ce5 __vmx_vcpu_run+0x45 ([kernel.kallsyms])                 movq  0x58(%rax), %r11
       CPU 1/KVM 17006 [001] 11500.262865593:  ffffffff82133ce9 __vmx_vcpu_run+0x49 ([kernel.kallsyms])                 movq  0x60(%rax), %r12
       CPU 1/KVM 17006 [001] 11500.262865593:  ffffffff82133ced __vmx_vcpu_run+0x4d ([kernel.kallsyms])                 movq  0x68(%rax), %r13
       CPU 1/KVM 17006 [001] 11500.262865593:  ffffffff82133cf1 __vmx_vcpu_run+0x51 ([kernel.kallsyms])                 movq  0x70(%rax), %r14
       CPU 1/KVM 17006 [001] 11500.262865593:  ffffffff82133cf5 __vmx_vcpu_run+0x55 ([kernel.kallsyms])                 movq  0x78(%rax), %r15
       CPU 1/KVM 17006 [001] 11500.262865593:  ffffffff82133cf9 __vmx_vcpu_run+0x59 ([kernel.kallsyms])                 movq  (%rax), %rax
       CPU 1/KVM 17006 [001] 11500.262865593:  ffffffff82133cfc __vmx_vcpu_run+0x5c ([kernel.kallsyms])                 callq  0xffffffff82133c40
       CPU 1/KVM 17006 [001] 11500.262865593:  ffffffff82133c40 vmx_vmenter+0x0 ([kernel.kallsyms])             jz 0xffffffff82133c46
       CPU 1/KVM 17006 [001] 11500.262866075:  ffffffff82133c42 vmx_vmenter+0x2 ([kernel.kallsyms])             vmresume         IPC: 0.05 (40/769)
          :17006 17006 [001] 11500.262869216:  ffffffff82200cb0 asm_sysvec_apic_timer_interrupt+0x0 ([guest.kernel.kallsyms])           clac
          :17006 17006 [001] 11500.262869216:  ffffffff82200cb3 asm_sysvec_apic_timer_interrupt+0x3 ([guest.kernel.kallsyms])           pushq  $0xffffffffffffffff
          :17006 17006 [001] 11500.262869216:  ffffffff82200cb5 asm_sysvec_apic_timer_interrupt+0x5 ([guest.kernel.kallsyms])           callq  0xffffffff82201160
          :17006 17006 [001] 11500.262869216:  ffffffff82201160 error_entry+0x0 ([guest.kernel.kallsyms])               cld
          :17006 17006 [001] 11500.262869216:  ffffffff82201161 error_entry+0x1 ([guest.kernel.kallsyms])               pushq  %rsi
          :17006 17006 [001] 11500.262869216:  ffffffff82201162 error_entry+0x2 ([guest.kernel.kallsyms])               movq  0x8(%rsp), %rsi
          :17006 17006 [001] 11500.262869216:  ffffffff82201167 error_entry+0x7 ([guest.kernel.kallsyms])               movq  %rdi, 0x8(%rsp)
          :17006 17006 [001] 11500.262869216:  ffffffff8220116c error_entry+0xc ([guest.kernel.kallsyms])               pushq  %rdx
          :17006 17006 [001] 11500.262869216:  ffffffff8220116d error_entry+0xd ([guest.kernel.kallsyms])               pushq  %rcx
          :17006 17006 [001] 11500.262869216:  ffffffff8220116e error_entry+0xe ([guest.kernel.kallsyms])               pushq  %rax


Tracing Virtual Machines (including user space)
-----------------------------------------------

It 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.
Sideband events from the guest perf.data file can be injected into the host perf.data file using perf inject.

Here is an example of the steps needed:

On the guest machine:

Check that no-kvmclock kernel command line option was used to boot:

Note, this is essential to enable time correlation between host and guest machines.

 $ cat /proc/cmdline
 BOOT_IMAGE=/boot/vmlinuz-5.10.0-16-amd64 root=UUID=cb49c910-e573-47e0-bce7-79e293df8e1d ro no-kvmclock

There is no BPF support at present so, if possible, disable JIT compiling:

 $ echo 0 | sudo tee /proc/sys/net/core/bpf_jit_enable
 0

Start perf record to collect sideband events:

 $ sudo perf record -o guest-sideband-testing-guest-perf.data --sample-identifier --buildid-all --switch-events --kcore -a -e dummy

On the host machine:

Start perf record to collect Intel PT trace:

Note, 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.

 $ sudo perf record -o guest-sideband-testing-host-perf.data -m,64M --kcore -a -e intel_pt/cyc/

On the guest machine:

Run a small test case, just 'uname' in this example:

 $ uname
 Linux

On the host machine:

Stop the Intel PT trace:

 ^C
 [ perf record: Woken up 1 times to write data ]
 [ perf record: Captured and wrote 76.122 MB guest-sideband-testing-host-perf.data ]

On the guest machine:

Stop the Intel PT trace:

 ^C
 [ perf record: Woken up 1 times to write data ]
 [ perf record: Captured and wrote 1.247 MB guest-sideband-testing-guest-perf.data ]

And then copy guest-sideband-testing-guest-perf.data to the host (not shown here).

On the host machine:

With the 2 perf.data recordings, and with their ownership changed to the user.

Identify the TSC Offset:

 $ perf inject -i guest-sideband-testing-host-perf.data --vm-time-correlation=dry-run
 VMCS: 0x103fc6  TSC Offset 0xfffffa6ae070cb20
 VMCS: 0x103ff2  TSC Offset 0xfffffa6ae070cb20
 VMCS: 0x10fdaa  TSC Offset 0xfffffa6ae070cb20
 VMCS: 0x24d57c  TSC Offset 0xfffffa6ae070cb20

Correct Intel PT TSC timestamps for the guest machine:

 $ perf inject -i guest-sideband-testing-host-perf.data --vm-time-correlation=0xfffffa6ae070cb20 --force

Identify the guest machine PID:

 $ perf script -i guest-sideband-testing-host-perf.data --no-itrace --show-task-events | grep KVM
       CPU 0/KVM     0 [000]     0.000000: PERF_RECORD_COMM: CPU 0/KVM:13376/13381
       CPU 1/KVM     0 [000]     0.000000: PERF_RECORD_COMM: CPU 1/KVM:13376/13382
       CPU 2/KVM     0 [000]     0.000000: PERF_RECORD_COMM: CPU 2/KVM:13376/13383
       CPU 3/KVM     0 [000]     0.000000: PERF_RECORD_COMM: CPU 3/KVM:13376/13384

Note, the QEMU option -name debug-threads=on is needed so that thread names
can be used to determine which thread is running which VCPU as above. libvirt seems to use this by default.

Create a guestmount, assuming the guest machine is 'vm_to_test':

 $ mkdir -p ~/guestmount/13376
 $ sshfs -o direct_io vm_to_test:/ ~/guestmount/13376

Inject the guest perf.data file into the host perf.data file:

Note, 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.
If needed, VDSO can be copied manually in a fashion similar to that used by the perf-archive script.

 $ perf inject -i guest-sideband-testing-host-perf.data -o inj --guestmount ~/guestmount --guest-data=guest-sideband-testing-guest-perf.data,13376,0xfffffa6ae070cb20

Show 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:

Notes:

	- the CPU displayed, [002] in this case, is always the host CPU
	- events happening in the virtual machine start with VM:13376 VCPU:003, which shows the hypervisor PID 13376 and the VCPU number
	- only calls and errors are displayed i.e. --itrace=ce
	- branches entering and exiting the virtual machine are split, and show as 2 branches to/from "0 [unknown] ([unknown])"

 $ perf script -i inj --itrace=ce -F+machine_pid,+vcpu,+addr,+pid,+tid,-period --ns --time 7919.408803365,7919.408804631 -C 2
       CPU 3/KVM 13376/13384 [002]  7919.408803365:      branches:  ffffffffc0f8ebe0 vmx_vcpu_enter_exit+0xc0 ([kernel.kallsyms]) => ffffffffc0f8edc0 __vmx_vcpu_run+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803365:      branches:  ffffffffc0f8edd5 __vmx_vcpu_run+0x15 ([kernel.kallsyms]) => ffffffffc0f8eca0 vmx_update_host_rsp+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803365:      branches:  ffffffffc0f8ee1b __vmx_vcpu_run+0x5b ([kernel.kallsyms]) => ffffffffc0f8ed60 vmx_vmenter+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803461:      branches:  ffffffffc0f8ed62 vmx_vmenter+0x2 ([kernel.kallsyms]) =>                0 [unknown] ([unknown])
 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)
 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])
       CPU 3/KVM 13376/13384 [002]  7919.408803567:      branches:                 0 [unknown] ([unknown]) => ffffffffc0f8ed80 vmx_vmexit+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803596:      branches:  ffffffffc0f6619a vmx_vcpu_run+0x26a ([kernel.kallsyms]) => ffffffffb2255c60 x86_virt_spec_ctrl+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803801:      branches:  ffffffffc0f66445 vmx_vcpu_run+0x515 ([kernel.kallsyms]) => ffffffffb2290b30 native_write_msr+0x0 ([kernel.kallsyms])
       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])
       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])
       CPU 3/KVM 13376/13384 [002]  7919.408803862:      branches:  ffffffffc0f662cf vmx_vcpu_run+0x39f ([kernel.kallsyms]) => ffffffffc0f63f90 vmx_recover_nmi_blocking+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803862:      branches:  ffffffffc0f662e9 vmx_vcpu_run+0x3b9 ([kernel.kallsyms]) => ffffffffc0f619a0 __vmx_complete_interrupts+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803872:      branches:  ffffffffc109cfb2 vcpu_enter_guest+0x752 ([kernel.kallsyms]) => ffffffffc0f5f570 vmx_handle_exit_irqoff+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803881:      branches:  ffffffffc109d028 vcpu_enter_guest+0x7c8 ([kernel.kallsyms]) => ffffffffb234f900 __srcu_read_lock+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803897:      branches:  ffffffffc109d06f vcpu_enter_guest+0x80f ([kernel.kallsyms]) => ffffffffc0f72e30 vmx_handle_exit+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803897:      branches:  ffffffffc0f72e3d vmx_handle_exit+0xd ([kernel.kallsyms]) => ffffffffc0f727c0 __vmx_handle_exit+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803897:      branches:  ffffffffc0f72b15 __vmx_handle_exit+0x355 ([kernel.kallsyms]) => ffffffffc0f60ae0 vmx_flush_pml_buffer+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803903:      branches:  ffffffffc0f72994 __vmx_handle_exit+0x1d4 ([kernel.kallsyms]) => ffffffffc10b7090 kvm_emulate_cpuid+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803903:      branches:  ffffffffc10b70f1 kvm_emulate_cpuid+0x61 ([kernel.kallsyms]) => ffffffffc10b6e10 kvm_cpuid+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803941:      branches:  ffffffffc10b7125 kvm_emulate_cpuid+0x95 ([kernel.kallsyms]) => ffffffffc1093110 kvm_skip_emulated_instruction+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803941:      branches:  ffffffffc109311f kvm_skip_emulated_instruction+0xf ([kernel.kallsyms]) => ffffffffc0f5e180 vmx_get_rflags+0x0 ([kernel.kallsyms])
       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])
       CPU 3/KVM 13376/13384 [002]  7919.408803951:      branches:  ffffffffc0f5fd79 vmx_skip_emulated_instruction+0x49 ([kernel.kallsyms]) => ffffffffc0f5fb50 skip_emulated_instruction+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803956:      branches:  ffffffffc0f5fc68 skip_emulated_instruction+0x118 ([kernel.kallsyms]) => ffffffffc0f6a940 vmx_cache_reg+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803964:      branches:  ffffffffc0f5fc11 skip_emulated_instruction+0xc1 ([kernel.kallsyms]) => ffffffffc0f5f9e0 vmx_set_interrupt_shadow+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408803980:      branches:  ffffffffc109f8b1 vcpu_run+0x71 ([kernel.kallsyms]) => ffffffffc10ad2f0 kvm_cpu_has_pending_timer+0x0 ([kernel.kallsyms])
       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])
       CPU 3/KVM 13376/13384 [002]  7919.408803991:      branches:  ffffffffc109f899 vcpu_run+0x59 ([kernel.kallsyms]) => ffffffffc109c860 vcpu_enter_guest+0x0 ([kernel.kallsyms])
       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])
       CPU 3/KVM 13376/13384 [002]  7919.408803996:      branches:  ffffffffc109cd7d vcpu_enter_guest+0x51d ([kernel.kallsyms]) => ffffffffb234f930 __srcu_read_unlock+0x0 ([kernel.kallsyms])
       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])
       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])
       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])
       CPU 3/KVM 13376/13384 [002]  7919.408804019:      branches:  ffffffffc109ceca vcpu_enter_guest+0x66a ([kernel.kallsyms]) => ffffffffb2249840 fpregs_assert_state_consistent+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408804021:      branches:  ffffffffc109cf10 vcpu_enter_guest+0x6b0 ([kernel.kallsyms]) => ffffffffc0f65f30 vmx_vcpu_run+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408804024:      branches:  ffffffffc0f6603b vmx_vcpu_run+0x10b ([kernel.kallsyms]) => ffffffffb229bed0 __get_current_cr3_fast+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408804024:      branches:  ffffffffc0f66055 vmx_vcpu_run+0x125 ([kernel.kallsyms]) => ffffffffb2253050 cr4_read_shadow+0x0 ([kernel.kallsyms])
       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])
       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])
       CPU 3/KVM 13376/13384 [002]  7919.408804032:      branches:  ffffffffc0f660c6 vmx_vcpu_run+0x196 ([kernel.kallsyms]) => ffffffffb22061a0 perf_guest_get_msrs+0x0 ([kernel.kallsyms])
       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])
       CPU 3/KVM 13376/13384 [002]  7919.408804039:      branches:  ffffffffc0f66109 vmx_vcpu_run+0x1d9 ([kernel.kallsyms]) => ffffffffc0f652c0 clear_atomic_switch_msr+0x0 ([kernel.kallsyms])
       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])
       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])
       CPU 3/KVM 13376/13384 [002]  7919.408804045:      branches:  ffffffffc0f66454 vmx_vcpu_run+0x524 ([kernel.kallsyms]) => ffffffffc0f61ff0 vmx_update_hv_timer+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408804057:      branches:  ffffffffc0f66142 vmx_vcpu_run+0x212 ([kernel.kallsyms]) => ffffffffc10af100 kvm_wait_lapic_expire+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408804057:      branches:  ffffffffc0f66156 vmx_vcpu_run+0x226 ([kernel.kallsyms]) => ffffffffb2255c60 x86_virt_spec_ctrl+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408804057:      branches:  ffffffffc0f66161 vmx_vcpu_run+0x231 ([kernel.kallsyms]) => ffffffffc0f8eb20 vmx_vcpu_enter_exit+0x0 ([kernel.kallsyms])
       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])
       CPU 3/KVM 13376/13384 [002]  7919.408804057:      branches:  ffffffffb2353e1c rcu_note_context_switch+0xc ([kernel.kallsyms]) => ffffffffb2353db0 rcu_qs+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408804066:      branches:  ffffffffc0f8ebe0 vmx_vcpu_enter_exit+0xc0 ([kernel.kallsyms]) => ffffffffc0f8edc0 __vmx_vcpu_run+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408804066:      branches:  ffffffffc0f8edd5 __vmx_vcpu_run+0x15 ([kernel.kallsyms]) => ffffffffc0f8eca0 vmx_update_host_rsp+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408804066:      branches:  ffffffffc0f8ee1b __vmx_vcpu_run+0x5b ([kernel.kallsyms]) => ffffffffc0f8ed60 vmx_vmenter+0x0 ([kernel.kallsyms])
       CPU 3/KVM 13376/13384 [002]  7919.408804162:      branches:  ffffffffc0f8ed62 vmx_vmenter+0x2 ([kernel.kallsyms]) =>                0 [unknown] ([unknown])
 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)
 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)
 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])
 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])
 VM:13376 VCPU:003            uname  3404/3404  [002]  7919.408804534:      branches:  ffffffff832012fa error_entry+0x6a ([kernel.kallsyms]) => ffffffff830b59a0 sync_regs+0x0 ([kernel.kallsyms])
 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])
 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])
 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])


Tracing Virtual Machines - Guest Code
-------------------------------------

A common case for KVM test programs is that the test program acts as the
hypervisor, creating, running and destroying the virtual machine, and
providing the guest object code from its own object code. In this case,
the VM is not running an OS, but only the functions loaded into it by the
hypervisor test program, and conveniently, loaded at the same virtual
addresses. To support that, option "--guest-code" has been added to perf script
and perf kvm report.

Here is an example tracing a test program from the kernel's KVM selftests:

 # perf record --kcore -e intel_pt/cyc/ -- tools/testing/selftests/kselftest_install/kvm/tsc_msrs_test
 [ perf record: Woken up 1 times to write data ]
 [ perf record: Captured and wrote 0.280 MB perf.data ]
 # perf script --guest-code --itrace=bep --ns -F-period,+addr,+flags
 [SNIP]
   tsc_msrs_test 18436 [007] 10897.962087733:      branches:   call                   ffffffffc13b2ff5 __vmx_vcpu_run+0x15 (vmlinux) => ffffffffc13b2f50 vmx_update_host_rsp+0x0 (vmlinux)
   tsc_msrs_test 18436 [007] 10897.962087733:      branches:   return                 ffffffffc13b2f5d vmx_update_host_rsp+0xd (vmlinux) => ffffffffc13b2ffa __vmx_vcpu_run+0x1a (vmlinux)
   tsc_msrs_test 18436 [007] 10897.962087733:      branches:   call                   ffffffffc13b303b __vmx_vcpu_run+0x5b (vmlinux) => ffffffffc13b2f80 vmx_vmenter+0x0 (vmlinux)
   tsc_msrs_test 18436 [007] 10897.962087836:      branches:   vmentry                ffffffffc13b2f82 vmx_vmenter+0x2 (vmlinux) =>                0 [unknown] ([unknown])
   [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)
   [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)
   [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])
   tsc_msrs_test 18436 [007] 10897.962088248:      branches:   vmexit                                0 [unknown] ([unknown]) => ffffffffc13b2fa0 vmx_vmexit+0x0 (vmlinux)
   tsc_msrs_test 18436 [007] 10897.962088248:      branches:   jmp                    ffffffffc13b2fa0 vmx_vmexit+0x0 (vmlinux) => ffffffffc13b2fd2 vmx_vmexit+0x32 (vmlinux)
   tsc_msrs_test 18436 [007] 10897.962088256:      branches:   return                 ffffffffc13b2fd2 vmx_vmexit+0x32 (vmlinux) => ffffffffc13b3040 __vmx_vcpu_run+0x60 (vmlinux)
   tsc_msrs_test 18436 [007] 10897.962088270:      branches:   return                 ffffffffc13b30b6 __vmx_vcpu_run+0xd6 (vmlinux) => ffffffffc13b2f2e vmx_vcpu_enter_exit+0x4e (vmlinux)
 [SNIP]
   tsc_msrs_test 18436 [007] 10897.962089321:      branches:   call                   ffffffffc13b2ff5 __vmx_vcpu_run+0x15 (vmlinux) => ffffffffc13b2f50 vmx_update_host_rsp+0x0 (vmlinux)
   tsc_msrs_test 18436 [007] 10897.962089321:      branches:   return                 ffffffffc13b2f5d vmx_update_host_rsp+0xd (vmlinux) => ffffffffc13b2ffa __vmx_vcpu_run+0x1a (vmlinux)
   tsc_msrs_test 18436 [007] 10897.962089321:      branches:   call                   ffffffffc13b303b __vmx_vcpu_run+0x5b (vmlinux) => ffffffffc13b2f80 vmx_vmenter+0x0 (vmlinux)
   tsc_msrs_test 18436 [007] 10897.962089424:      branches:   vmentry                ffffffffc13b2f82 vmx_vmenter+0x2 (vmlinux) =>                0 [unknown] ([unknown])
   [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)
   [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)
   [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)
   [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)
   [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)
   [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])
   tsc_msrs_test 18436 [007] 10897.962089878:      branches:   vmexit                                0 [unknown] ([unknown]) => ffffffffc13b2fa0 vmx_vmexit+0x0 (vmlinux)
   tsc_msrs_test 18436 [007] 10897.962089878:      branches:   jmp                    ffffffffc13b2fa0 vmx_vmexit+0x0 (vmlinux) => ffffffffc13b2fd2 vmx_vmexit+0x32 (vmlinux)
   tsc_msrs_test 18436 [007] 10897.962089887:      branches:   return                 ffffffffc13b2fd2 vmx_vmexit+0x32 (vmlinux) => ffffffffc13b3040 __vmx_vcpu_run+0x60 (vmlinux)
   tsc_msrs_test 18436 [007] 10897.962089901:      branches:   return                 ffffffffc13b30b6 __vmx_vcpu_run+0xd6 (vmlinux) => ffffffffc13b2f2e vmx_vcpu_enter_exit+0x4e (vmlinux)
 [SNIP]

 # perf kvm --guest-code --guest --host report -i perf.data --stdio | head -20

 # To display the perf.data header info, please use --header/--header-only options.
 #
 #
 # Total Lost Samples: 0
 #
 # Samples: 12  of event 'instructions'
 # Event count (approx.): 2274583
 #
 # Children      Self  Command        Shared Object         Symbol
 # ........  ........  .............  ....................  ...........................................
 #
    54.70%     0.00%  tsc_msrs_test  [kernel.vmlinux]      [k] entry_SYSCALL_64_after_hwframe
            |
            ---entry_SYSCALL_64_after_hwframe
               do_syscall_64
               |
               |--29.44%--syscall_exit_to_user_mode
               |          exit_to_user_mode_prepare
               |          task_work_run
               |          __fput


Event Trace
-----------

Event Trace records information about asynchronous events, for example interrupts,
faults, VM exits and entries.  The information is recorded in CFE and EVD packets,
and also the Interrupt Flag is recorded on the MODE.Exec packet.  The CFE packet
contains a type field to identify one of the following:

	 1	INTR		interrupt, fault, exception, NMI
	 2	IRET		interrupt return
	 3	SMI		system management interrupt
	 4	RSM		resume from system management mode
	 5	SIPI		startup interprocessor interrupt
	 6	INIT		INIT signal
	 7	VMENTRY		VM-Entry
	 8	VMEXIT		VM-Entry
	 9	VMEXIT_INTR	VM-Exit due to interrupt
	10	SHUTDOWN	Shutdown

For more details, refer to the Intel 64 and IA-32 Architectures Software
Developer Manuals (version 076 or later).

The capability to do Event Trace is indicated by the
/sys/bus/event_source/devices/intel_pt/caps/event_trace file.

Event trace is selected for recording using the "event" config term. e.g.

	perf record -e intel_pt/event/u uname

Event trace events are output using the --itrace I option. e.g.

	perf script --itrace=Ie

perf script displays events containing CFE type, vector and event data,
in the form:

	  evt:   hw int            (t)  cfe: INTR IP: 1 vector: 3 PFA: 0x8877665544332211

The IP flag indicates if the event binds to an IP, which includes any case where
flow control packet generation is enabled, as well as when CFE packet IP bit is
set.

perf script displays events containing changes to the Interrupt Flag in the form:

	iflag:   t                      IFLAG: 1->0 via branch

where "via branch" indicates a branch (interrupt or return from interrupt) and
"non branch" indicates an instruction such as CFI, STI or POPF).

In addition, the current state of the interrupt flag is indicated by the presence
or absence of the "D" (interrupt disabled) perf script flag.  If the interrupt
flag is changed, then the "t" flag is also included i.e.

		no flag, interrupts enabled IF=1
	t	interrupts become disabled IF=1 -> IF=0
	D	interrupts are disabled IF=0
	Dt	interrupts become enabled  IF=0 -> IF=1

The intel-pt-events.py script illustrates how to access Event Trace information
using a Python script.


TNT Disable
-----------

TNT packets are disabled using the "notnt" config term. e.g.

	perf record -e intel_pt/notnt/u uname

In that case the --itrace q option is forced because walking executable code
to reconstruct the control flow is not possible.


Emulated PTWRITE
----------------

Later perf tools support a method to emulate the ptwrite instruction, which
can be useful if hardware does not support the ptwrite instruction.

Instead of using the ptwrite instruction, a function is used which produces
a trace that encodes the payload data into TNT packets.  Here is an example
of the function:

 #include <stdint.h>

 void perf_emulate_ptwrite(uint64_t x)
 __attribute__((externally_visible, noipa, no_instrument_function, naked));

 #define PERF_EMULATE_PTWRITE_8_BITS \
                 "1: shl %rax\n"     \
                 "   jc 1f\n"        \
                 "1: shl %rax\n"     \
                 "   jc 1f\n"        \
                 "1: shl %rax\n"     \
                 "   jc 1f\n"        \
                 "1: shl %rax\n"     \
                 "   jc 1f\n"        \
                 "1: shl %rax\n"     \
                 "   jc 1f\n"        \
                 "1: shl %rax\n"     \
                 "   jc 1f\n"        \
                 "1: shl %rax\n"     \
                 "   jc 1f\n"        \
                 "1: shl %rax\n"     \
                 "   jc 1f\n"

 /* Undefined instruction */
 #define PERF_EMULATE_PTWRITE_UD2        ".byte 0x0f, 0x0b\n"

 #define PERF_EMULATE_PTWRITE_MAGIC        PERF_EMULATE_PTWRITE_UD2 ".ascii \"perf,ptwrite  \"\n"

 void perf_emulate_ptwrite(uint64_t x __attribute__ ((__unused__)))
 {
          /* Assumes SysV ABI : x passed in rdi */
         __asm__ volatile (
                 "jmp 1f\n"
                 PERF_EMULATE_PTWRITE_MAGIC
                 "1: mov %rdi, %rax\n"
                 PERF_EMULATE_PTWRITE_8_BITS
                 PERF_EMULATE_PTWRITE_8_BITS
                 PERF_EMULATE_PTWRITE_8_BITS
                 PERF_EMULATE_PTWRITE_8_BITS
                 PERF_EMULATE_PTWRITE_8_BITS
                 PERF_EMULATE_PTWRITE_8_BITS
                 PERF_EMULATE_PTWRITE_8_BITS
                 PERF_EMULATE_PTWRITE_8_BITS
                 "1: ret\n"
         );
 }

For example, a test program with the function above:

 #include <stdio.h>
 #include <stdint.h>
 #include <stdlib.h>

 #include "perf_emulate_ptwrite.h"

 int main(int argc, char *argv[])
 {
         uint64_t x = 0;

         if (argc > 1)
                 x = strtoull(argv[1], NULL, 0);
         perf_emulate_ptwrite(x);
         return 0;
 }

Can be compiled and traced:

 $ gcc -Wall -Wextra -O3 -g -o eg_ptw eg_ptw.c
 $ perf record -e intel_pt//u ./eg_ptw 0x1234567890abcdef
 [ perf record: Woken up 1 times to write data ]
 [ perf record: Captured and wrote 0.017 MB perf.data ]
 $ perf script --itrace=ew
           eg_ptw 19875 [007]  8061.235912:     ptwrite:  IP: 0 payload: 0x1234567890abcdef      55701249a196 perf_emulate_ptwrite+0x16 (/home/user/eg_ptw)
 $


Pipe mode
---------
Pipe mode is a problem for Intel PT and possibly other auxtrace users.
It's not recommended to use a pipe as data output with Intel PT because
of the following reason.

Essentially the auxtrace buffers do not behave like the regular perf
event buffers.  That is because the head and tail are updated by
software, but in the auxtrace case the data is written by hardware.
So the head and tail do not get updated as data is written.

In the Intel PT case, the head and tail are updated only when the trace
is disabled by software, for example:
    - full-trace, system wide : when buffer passes watermark
    - full-trace, not system-wide : when buffer passes watermark or
                                    context switches
    - snapshot mode : as above but also when a snapshot is made
    - sample mode : as above but also when a sample is made

That means finished-round ordering doesn't work.  An auxtrace buffer
can turn up that has data that extends back in time, possibly to the
very beginning of tracing.

For a perf.data file, that problem is solved by going through the trace
and queuing up the auxtrace buffers in advance.

For pipe mode, the order of events and timestamps can presumably
be messed up.


EXAMPLE
-------

Examples can be found on perf wiki page "Perf tools support for Intel® Processor Trace":

https://perf.wiki.kernel.org/index.php/Perf_tools_support_for_Intel%C2%AE_Processor_Trace


SEE ALSO
--------

linkperf:perf-record[1], linkperf:perf-script[1], linkperf:perf-report[1],
linkperf:perf-inject[1]