1PERF_EVENT_OPEN(2)         Linux Programmer's Manual        PERF_EVENT_OPEN(2)
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NAME

6       perf_event_open - set up performance monitoring
7

SYNOPSIS

9       #include <linux/perf_event.h>
10       #include <linux/hw_breakpoint.h>
11
12       int perf_event_open(struct perf_event_attr *attr,
13                           pid_t pid, int cpu, int group_fd,
14                           unsigned long flags);
15
16       Note: There is no glibc wrapper for this system call; see NOTES.
17

DESCRIPTION

19       Given  a  list of parameters, perf_event_open() returns a file descrip‐
20       tor, for use in subsequent system calls  (read(2),  mmap(2),  prctl(2),
21       fcntl(2), etc.).
22
23       A  call to perf_event_open() creates a file descriptor that allows mea‐
24       suring performance information.  Each file  descriptor  corresponds  to
25       one  event  that  is measured; these can be grouped together to measure
26       multiple events simultaneously.
27
28       Events can be enabled and disabled in two ways: via  ioctl(2)  and  via
29       prctl(2).   When  an  event  is  disabled it does not count or generate
30       overflows but does continue to exist and maintain its count value.
31
32       Events come in two flavors: counting and sampled.  A counting event  is
33       one  that  is  used  for  counting  the aggregate number of events that
34       occur.  In general, counting event results are gathered with a  read(2)
35       call.   A  sampling  event periodically writes measurements to a buffer
36       that can then be accessed via mmap(2).
37
38   Arguments
39       The pid and cpu arguments allow specifying which  process  and  CPU  to
40       monitor:
41
42       pid == 0 and cpu == -1
43              This measures the calling process/thread on any CPU.
44
45       pid == 0 and cpu >= 0
46              This  measures  the  calling process/thread only when running on
47              the specified CPU.
48
49       pid > 0 and cpu == -1
50              This measures the specified process/thread on any CPU.
51
52       pid > 0 and cpu >= 0
53              This measures the specified process/thread only when running  on
54              the specified CPU.
55
56       pid == -1 and cpu >= 0
57              This  measures all processes/threads on the specified CPU.  This
58              requires   CAP_SYS_ADMIN   capability   or   a    /proc/sys/ker‐
59              nel/perf_event_paranoid value of less than 1.
60
61       pid == -1 and cpu == -1
62              This setting is invalid and will return an error.
63
64       When  pid  is greater than zero, permission to perform this system call
65       is governed by a ptrace access mode  PTRACE_MODE_READ_REALCREDS  check;
66       see ptrace(2).
67
68       The  group_fd  argument  allows  event  groups to be created.  An event
69       group has one event which is the group leader.  The leader  is  created
70       first,  with  group_fd = -1.  The rest of the group members are created
71       with subsequent perf_event_open() calls with group_fd being set to  the
72       file  descriptor  of  the  group leader.  (A single event on its own is
73       created with group_fd = -1 and is considered to be a group with only  1
74       member.)   An  event group is scheduled onto the CPU as a unit: it will
75       be put onto the CPU only if all of the events in the group can  be  put
76       onto  the  CPU.  This means that the values of the member events can be
77       meaningfully compared—added, divided (to get ratios),  and  so  on—with
78       each other, since they have counted events for the same set of executed
79       instructions.
80
81       The flags argument is formed by ORing together zero or more of the fol‐
82       lowing values:
83
84       PERF_FLAG_FD_CLOEXEC (since Linux 3.14)
85              This  flag  enables the close-on-exec flag for the created event
86              file descriptor, so that the file  descriptor  is  automatically
87              closed  on  execve(2).   Setting the close-on-exec flags at cre‐
88              ation time, rather than later with  fcntl(2),  avoids  potential
89              race    conditions    where    the    calling   thread   invokes
90              perf_event_open() and fcntl(2)  at  the  same  time  as  another
91              thread calls fork(2) then execve(2).
92
93       PERF_FLAG_FD_NO_GROUP
94              This  flag  tells  the  event  to  ignore the group_fd parameter
95              except for the purpose of setting up  output  redirection  using
96              the PERF_FLAG_FD_OUTPUT flag.
97
98       PERF_FLAG_FD_OUTPUT (broken since Linux 2.6.35)
99              This  flag  re-routes  the  event's sampled output to instead be
100              included in the mmap buffer of the event specified by group_fd.
101
102       PERF_FLAG_PID_CGROUP (since Linux 2.6.39)
103              This flag activates  per-container  system-wide  monitoring.   A
104              container is an abstraction that isolates a set of resources for
105              finer-grained control (CPUs, memory, etc.).  In this  mode,  the
106              event  is  measured  only if the thread running on the monitored
107              CPU belongs to the designated container (cgroup).  The cgroup is
108              identified  by passing a file descriptor opened on its directory
109              in the cgroupfs filesystem.  For instance, if the cgroup to mon‐
110              itor   is   called  test,  then  a  file  descriptor  opened  on
111              /dev/cgroup/test (assuming cgroupfs is mounted  on  /dev/cgroup)
112              must  be  passed  as  the  pid  parameter.  cgroup monitoring is
113              available only for system-wide events and may therefore  require
114              extra permissions.
115
116       The  perf_event_attr structure provides detailed configuration informa‐
117       tion for the event being created.
118
119           struct perf_event_attr {
120               __u32 type;                 /* Type of event */
121               __u32 size;                 /* Size of attribute structure */
122               __u64 config;               /* Type-specific configuration */
123
124               union {
125                   __u64 sample_period;    /* Period of sampling */
126                   __u64 sample_freq;      /* Frequency of sampling */
127               };
128
129               __u64 sample_type;  /* Specifies values included in sample */
130               __u64 read_format;  /* Specifies values returned in read */
131
132               __u64 disabled       : 1,   /* off by default */
133                     inherit        : 1,   /* children inherit it */
134                     pinned         : 1,   /* must always be on PMU */
135                     exclusive      : 1,   /* only group on PMU */
136                     exclude_user   : 1,   /* don't count user */
137                     exclude_kernel : 1,   /* don't count kernel */
138                     exclude_hv     : 1,   /* don't count hypervisor */
139                     exclude_idle   : 1,   /* don't count when idle */
140                     mmap           : 1,   /* include mmap data */
141                     comm           : 1,   /* include comm data */
142                     freq           : 1,   /* use freq, not period */
143                     inherit_stat   : 1,   /* per task counts */
144                     enable_on_exec : 1,   /* next exec enables */
145                     task           : 1,   /* trace fork/exit */
146                     watermark      : 1,   /* wakeup_watermark */
147                     precise_ip     : 2,   /* skid constraint */
148                     mmap_data      : 1,   /* non-exec mmap data */
149                     sample_id_all  : 1,   /* sample_type all events */
150                     exclude_host   : 1,   /* don't count in host */
151                     exclude_guest  : 1,   /* don't count in guest */
152                     exclude_callchain_kernel : 1,
153                                           /* exclude kernel callchains */
154                     exclude_callchain_user   : 1,
155                                           /* exclude user callchains */
156                     mmap2          :  1,  /* include mmap with inode data */
157                     comm_exec      :  1,  /* flag comm events that are
158                                              due to exec */
159                     use_clockid    :  1,  /* use clockid for time fields */
160                     context_switch :  1,  /* context switch data */
161
162                     __reserved_1   : 37;
163
164               union {
165                   __u32 wakeup_events;    /* wakeup every n events */
166                   __u32 wakeup_watermark; /* bytes before wakeup */
167               };
168
169               __u32     bp_type;          /* breakpoint type */
170
171               union {
172                   __u64 bp_addr;          /* breakpoint address */
173                   __u64 kprobe_func;      /* for perf_kprobe */
174                   __u64 uprobe_path;      /* for perf_uprobe */
175                   __u64 config1;          /* extension of config */
176               };
177
178               union {
179                   __u64 bp_len;           /* breakpoint length */
180                   __u64 kprobe_addr;      /* with kprobe_func == NULL */
181                   __u64 probe_offset;     /* for perf_[k,u]probe */
182                   __u64 config2;          /* extension of config1 */
183               };
184               __u64 branch_sample_type;   /* enum perf_branch_sample_type */
185               __u64 sample_regs_user;     /* user regs to dump on samples */
186               __u32 sample_stack_user;    /* size of stack to dump on
187                                              samples */
188               __s32 clockid;              /* clock to use for time fields */
189               __u64 sample_regs_intr;     /* regs to dump on samples */
190               __u32 aux_watermark;        /* aux bytes before wakeup */
191               __u16 sample_max_stack;     /* max frames in callchain */
192               __u16 __reserved_2;         /* align to u64 */
193
194           };
195
196       The fields of the  perf_event_attr  structure  are  described  in  more
197       detail below:
198
199       type   This  field specifies the overall event type.  It has one of the
200              following values:
201
202              PERF_TYPE_HARDWARE
203                     This indicates one of the "generalized"  hardware  events
204                     provided  by the kernel.  See the config field definition
205                     for more details.
206
207              PERF_TYPE_SOFTWARE
208                     This indicates one of the  software-defined  events  pro‐
209                     vided  by  the  kernel  (even  if  no hardware support is
210                     available).
211
212              PERF_TYPE_TRACEPOINT
213                     This indicates a tracepoint provided by the kernel trace‐
214                     point infrastructure.
215
216              PERF_TYPE_HW_CACHE
217                     This  indicates  a hardware cache event.  This has a spe‐
218                     cial encoding, described in the config field definition.
219
220              PERF_TYPE_RAW
221                     This indicates a "raw" implementation-specific  event  in
222                     the config field.
223
224              PERF_TYPE_BREAKPOINT (since Linux 2.6.33)
225                     This  indicates  a hardware breakpoint as provided by the
226                     CPU.   Breakpoints  can  be  read/write  accesses  to  an
227                     address as well as execution of an instruction address.
228
229              dynamic PMU
230                     Since  Linux 2.6.38, perf_event_open() can support multi‐
231                     ple PMUs.  To enable this, a value exported by the kernel
232                     can  be  used  in the type field to indicate which PMU to
233                     use.  The value to use can be found in the sysfs filesys‐
234                     tem:  there  is  a  subdirectory  per  PMU instance under
235                     /sys/bus/event_source/devices.   In   each   subdirectory
236                     there is a type file whose content is an integer that can
237                     be   used   in   the   type   field.     For    instance,
238                     /sys/bus/event_source/devices/cpu/type contains the value
239                     for the core CPU PMU, which is usually 4.
240
241              kprobe and uprobe (since Linux 4.17)
242                     These two dynamic PMUs create a kprobe/uprobe and  attach
243                     it  to  the file descriptor generated by perf_event_open.
244                     The kprobe/uprobe will be destroyed on the destruction of
245                     the    file    descriptor.    See   fields   kprobe_func,
246                     uprobe_path,  kprobe_addr,  and  probe_offset  for   more
247                     details.
248
249       size   The  size  of the perf_event_attr structure for forward/backward
250              compatibility.  Set this using sizeof(struct perf_event_attr) to
251              allow  the kernel to see the struct size at the time of compila‐
252              tion.
253
254              The related define PERF_ATTR_SIZE_VER0 is set to  64;  this  was
255              the  size of the first published struct.  PERF_ATTR_SIZE_VER1 is
256              72, corresponding  to  the  addition  of  breakpoints  in  Linux
257              2.6.33.  PERF_ATTR_SIZE_VER2 is 80 corresponding to the addition
258              of branch sampling in Linux 3.4.  PERF_ATTR_SIZE_VER3 is 96 cor‐
259              responding   to   the  addition  of  sample_regs_user  and  sam‐
260              ple_stack_user in Linux 3.7.  PERF_ATTR_SIZE_VER4 is 104  corre‐
261              sponding  to  the  addition  of  sample_regs_intr in Linux 3.19.
262              PERF_ATTR_SIZE_VER5 is 112  corresponding  to  the  addition  of
263              aux_watermark in Linux 4.1.
264
265       config This  specifies  which  event  you want, in conjunction with the
266              type field.  The config1 and config2 fields are also taken  into
267              account  in  cases  where 64 bits is not enough to fully specify
268              the event.  The encoding of these fields are event dependent.
269
270              There are various ways to set the config field that  are  depen‐
271              dent  on the value of the previously described type field.  What
272              follows are various possible settings for config  separated  out
273              by type.
274
275              If  type is PERF_TYPE_HARDWARE, we are measuring one of the gen‐
276              eralized hardware CPU events.  Not all of these are available on
277              all platforms.  Set config to one of the following:
278
279                   PERF_COUNT_HW_CPU_CYCLES
280                          Total  cycles.   Be  wary of what happens during CPU
281                          frequency scaling.
282
283                   PERF_COUNT_HW_INSTRUCTIONS
284                          Retired instructions.   Be  careful,  these  can  be
285                          affected  by  various  issues, most notably hardware
286                          interrupt counts.
287
288                   PERF_COUNT_HW_CACHE_REFERENCES
289                          Cache accesses.  Usually this indicates  Last  Level
290                          Cache  accesses  but this may vary depending on your
291                          CPU.  This may include prefetches and coherency mes‐
292                          sages; again this depends on the design of your CPU.
293
294                   PERF_COUNT_HW_CACHE_MISSES
295                          Cache  misses.   Usually  this  indicates Last Level
296                          Cache misses; this is intended to be  used  in  con‐
297                          junction   with  the  PERF_COUNT_HW_CACHE_REFERENCES
298                          event to calculate cache miss rates.
299
300                   PERF_COUNT_HW_BRANCH_INSTRUCTIONS
301                          Retired branch instructions.  Prior to Linux 2.6.35,
302                          this used the wrong event on AMD processors.
303
304                   PERF_COUNT_HW_BRANCH_MISSES
305                          Mispredicted branch instructions.
306
307                   PERF_COUNT_HW_BUS_CYCLES
308                          Bus  cycles,  which  can  be  different  from  total
309                          cycles.
310
311                   PERF_COUNT_HW_STALLED_CYCLES_FRONTEND (since Linux 3.0)
312                          Stalled cycles during issue.
313
314                   PERF_COUNT_HW_STALLED_CYCLES_BACKEND (since Linux 3.0)
315                          Stalled cycles during retirement.
316
317                   PERF_COUNT_HW_REF_CPU_CYCLES (since Linux 3.3)
318                          Total cycles; not affected by CPU frequency scaling.
319
320              If type is PERF_TYPE_SOFTWARE, we are measuring software  events
321              provided by the kernel.  Set config to one of the following:
322
323                   PERF_COUNT_SW_CPU_CLOCK
324                          This  reports  the CPU clock, a high-resolution per-
325                          CPU timer.
326
327                   PERF_COUNT_SW_TASK_CLOCK
328                          This reports a clock count specific to the task that
329                          is running.
330
331                   PERF_COUNT_SW_PAGE_FAULTS
332                          This reports the number of page faults.
333
334                   PERF_COUNT_SW_CONTEXT_SWITCHES
335                          This  counts  context switches.  Until Linux 2.6.34,
336                          these were all reported as user-space events,  after
337                          that they are reported as happening in the kernel.
338
339                   PERF_COUNT_SW_CPU_MIGRATIONS
340                          This  reports  the  number  of times the process has
341                          migrated to a new CPU.
342
343                   PERF_COUNT_SW_PAGE_FAULTS_MIN
344                          This counts the number of minor page faults.   These
345                          did not require disk I/O to handle.
346
347                   PERF_COUNT_SW_PAGE_FAULTS_MAJ
348                          This  counts the number of major page faults.  These
349                          required disk I/O to handle.
350
351                   PERF_COUNT_SW_ALIGNMENT_FAULTS (since Linux 2.6.33)
352                          This counts the number of alignment  faults.   These
353                          happen  when  unaligned  memory accesses happen; the
354                          kernel can handle these but it reduces  performance.
355                          This  happens  only  on some architectures (never on
356                          x86).
357
358                   PERF_COUNT_SW_EMULATION_FAULTS (since Linux 2.6.33)
359                          This counts the number  of  emulation  faults.   The
360                          kernel sometimes traps on unimplemented instructions
361                          and emulates them for user space.   This  can  nega‐
362                          tively impact performance.
363
364                   PERF_COUNT_SW_DUMMY (since Linux 3.12)
365                          This  is  a  placeholder  event that counts nothing.
366                          Informational sample record types such  as  mmap  or
367                          comm  must be associated with an active event.  This
368                          dummy event allows gathering  such  records  without
369                          requiring a counting event.
370
371              If  type  is  PERF_TYPE_TRACEPOINT, then we are measuring kernel
372              tracepoints.  The value to use in config can  be  obtained  from
373              under  debugfs tracing/events/*/*/id if ftrace is enabled in the
374              kernel.
375
376              If type is PERF_TYPE_HW_CACHE, then we are measuring a  hardware
377              CPU  cache event.  To calculate the appropriate config value use
378              the following equation:
379
380                      (perf_hw_cache_id) | (perf_hw_cache_op_id << 8) |
381                      (perf_hw_cache_op_result_id << 16)
382
383                  where perf_hw_cache_id is one of:
384
385                      PERF_COUNT_HW_CACHE_L1D
386                             for measuring Level 1 Data Cache
387
388                      PERF_COUNT_HW_CACHE_L1I
389                             for measuring Level 1 Instruction Cache
390
391                      PERF_COUNT_HW_CACHE_LL
392                             for measuring Last-Level Cache
393
394                      PERF_COUNT_HW_CACHE_DTLB
395                             for measuring the Data TLB
396
397                      PERF_COUNT_HW_CACHE_ITLB
398                             for measuring the Instruction TLB
399
400                      PERF_COUNT_HW_CACHE_BPU
401                             for measuring the branch prediction unit
402
403                      PERF_COUNT_HW_CACHE_NODE (since Linux 3.1)
404                             for measuring local memory accesses
405
406                  and perf_hw_cache_op_id is one of:
407
408                      PERF_COUNT_HW_CACHE_OP_READ
409                             for read accesses
410
411                      PERF_COUNT_HW_CACHE_OP_WRITE
412                             for write accesses
413
414                      PERF_COUNT_HW_CACHE_OP_PREFETCH
415                             for prefetch accesses
416
417                  and perf_hw_cache_op_result_id is one of:
418
419                      PERF_COUNT_HW_CACHE_RESULT_ACCESS
420                             to measure accesses
421
422                      PERF_COUNT_HW_CACHE_RESULT_MISS
423                             to measure misses
424
425              If type is PERF_TYPE_RAW, then a custom "raw"  config  value  is
426              needed.   Most  CPUs  support events that are not covered by the
427              "generalized" events.  These  are  implementation  defined;  see
428              your  CPU  manual (for example the Intel Volume 3B documentation
429              or the AMD  BIOS  and  Kernel  Developer  Guide).   The  libpfm4
430              library  can be used to translate from the name in the architec‐
431              tural manuals to the raw hex value perf_event_open() expects  in
432              this field.
433
434              If  type is PERF_TYPE_BREAKPOINT, then leave config set to zero.
435              Its parameters are set in other places.
436
437              If type is kprobe or uprobe, set retprobe (bit 0 of config,  see
438              /sys/bus/event_source/devices/[k,u]probe/format/retprobe)    for
439              kretprobe/uretprobe.   See  fields   kprobe_func,   uprobe_path,
440              kprobe_addr, and probe_offset for more details.
441
442       kprobe_func, uprobe_path, kprobe_addr, and probe_offset
443              These  fields describe the kprobe/uprobe for dynamic PMUs kprobe
444              and uprobe.  For kprobe: use kprobe_func  and  probe_offset,  or
445              use  kprobe_addr and leave kprobe_func as NULL.  For uprobe: use
446              uprobe_path and probe_offset.
447
448       sample_period, sample_freq
449              A "sampling" event is one that generates an  overflow  notifica‐
450              tion  every N events, where N is given by sample_period.  A sam‐
451              pling event has sample_period > 0.   When  an  overflow  occurs,
452              requested  data is recorded in the mmap buffer.  The sample_type
453              field controls what data is recorded on each overflow.
454
455              sample_freq can be used if you wish to use frequency rather than
456              period.   In  this case, you set the freq flag.  The kernel will
457              adjust the sampling period to try and achieve the desired  rate.
458              The rate of adjustment is a timer tick.
459
460       sample_type
461              The  various  bits in this field specify which values to include
462              in the sample.  They will be recorded in a ring-buffer, which is
463              available  to  user space using mmap(2).  The order in which the
464              values are saved in the sample are documented in the MMAP Layout
465              subsection  below;  it  is not the enum perf_event_sample_format
466              order.
467
468              PERF_SAMPLE_IP
469                     Records instruction pointer.
470
471              PERF_SAMPLE_TID
472                     Records the process and thread IDs.
473
474              PERF_SAMPLE_TIME
475                     Records a timestamp.
476
477              PERF_SAMPLE_ADDR
478                     Records an address, if applicable.
479
480              PERF_SAMPLE_READ
481                     Record counter values for all events in a group, not just
482                     the group leader.
483
484              PERF_SAMPLE_CALLCHAIN
485                     Records the callchain (stack backtrace).
486
487              PERF_SAMPLE_ID
488                     Records a unique ID for the opened event's group leader.
489
490              PERF_SAMPLE_CPU
491                     Records CPU number.
492
493              PERF_SAMPLE_PERIOD
494                     Records the current sampling period.
495
496              PERF_SAMPLE_STREAM_ID
497                     Records  a  unique  ID  for  the  opened  event.   Unlike
498                     PERF_SAMPLE_ID the actual ID is returned, not  the  group
499                     leader.   This  ID  is  the  same  as the one returned by
500                     PERF_FORMAT_ID.
501
502              PERF_SAMPLE_RAW
503                     Records additional data, if applicable.  Usually returned
504                     by tracepoint events.
505
506              PERF_SAMPLE_BRANCH_STACK (since Linux 3.4)
507                     This provides a record of recent branches, as provided by
508                     CPU branch sampling hardware (such as Intel  Last  Branch
509                     Record).  Not all hardware supports this feature.
510
511                     See  the branch_sample_type field for how to filter which
512                     branches are reported.
513
514              PERF_SAMPLE_REGS_USER (since Linux 3.7)
515                     Records the current user-level CPU  register  state  (the
516                     values in the process before the kernel was called).
517
518              PERF_SAMPLE_STACK_USER (since Linux 3.7)
519                     Records the user level stack, allowing stack unwinding.
520
521              PERF_SAMPLE_WEIGHT (since Linux 3.10)
522                     Records  a  hardware provided weight value that expresses
523                     how costly the sampled event was.  This allows the  hard‐
524                     ware to highlight expensive events in a profile.
525
526              PERF_SAMPLE_DATA_SRC (since Linux 3.10)
527                     Records  the  data  source: where in the memory hierarchy
528                     the data associated with  the  sampled  instruction  came
529                     from.   This is available only if the underlying hardware
530                     supports this feature.
531
532              PERF_SAMPLE_IDENTIFIER (since Linux 3.12)
533                     Places the SAMPLE_ID value in a  fixed  position  in  the
534                     record, either at the beginning (for sample events) or at
535                     the end (if a non-sample event).
536
537                     This was necessary  because  a  sample  stream  may  have
538                     records from various different event sources with differ‐
539                     ent sample_type settings.  Parsing the event stream prop‐
540                     erly  was  not  possible because the format of the record
541                     was needed to find SAMPLE_ID, but the format could not be
542                     found  without  knowing what event the sample belonged to
543                     (causing a circular dependency).
544
545                     The PERF_SAMPLE_IDENTIFIER setting makes the event stream
546                     always parsable by putting SAMPLE_ID in a fixed location,
547                     even though it means having duplicate SAMPLE_ID values in
548                     records.
549
550              PERF_SAMPLE_TRANSACTION (since Linux 3.13)
551                     Records  reasons  for  transactional  memory abort events
552                     (for example, from Intel TSX  transactional  memory  sup‐
553                     port).
554
555                     The  precise_ip  setting  must  be  greater  than 0 and a
556                     transactional memory abort event must be measured  or  no
557                     values  will be recorded.  Also note that some perf_event
558                     measurements, such as sampled cycle counting,  may  cause
559                     extraneous  aborts  (by  causing  an  interrupt  during a
560                     transaction).
561
562              PERF_SAMPLE_REGS_INTR (since Linux 3.19)
563                     Records a subset of the current  CPU  register  state  as
564                     specified    by   sample_regs_intr.    Unlike   PERF_SAM‐
565                     PLE_REGS_USER the register values will return kernel reg‐
566                     ister state if the overflow happened while kernel code is
567                     running.  If the CPU supports hardware sampling of regis‐
568                     ter state (i.e., PEBS on Intel x86) and precise_ip is set
569                     higher than zero then the register  values  returned  are
570                     those  captured  by  hardware  at the time of the sampled
571                     instruction's retirement.
572
573       read_format
574              This field specifies the format of the data returned by  read(2)
575              on a perf_event_open() file descriptor.
576
577              PERF_FORMAT_TOTAL_TIME_ENABLED
578                     Adds  the 64-bit time_enabled field.  This can be used to
579                     calculate estimated totals if the  PMU  is  overcommitted
580                     and multiplexing is happening.
581
582              PERF_FORMAT_TOTAL_TIME_RUNNING
583                     Adds  the 64-bit time_running field.  This can be used to
584                     calculate estimated totals if the  PMU  is  overcommitted
585                     and multiplexing is happening.
586
587              PERF_FORMAT_ID
588                     Adds  a 64-bit unique value that corresponds to the event
589                     group.
590
591              PERF_FORMAT_GROUP
592                     Allows all counter values in an event group  to  be  read
593                     with one read.
594
595       disabled
596              The  disabled  bit specifies whether the counter starts out dis‐
597              abled or enabled.  If disabled, the event can later  be  enabled
598              by ioctl(2), prctl(2), or enable_on_exec.
599
600              When creating an event group, typically the group leader is ini‐
601              tialized with disabled set to 1 and any child  events  are  ini‐
602              tialized  with disabled set to 0.  Despite disabled being 0, the
603              child events will not start until the group leader is enabled.
604
605       inherit
606              The inherit bit specifies that this counter should count  events
607              of child tasks as well as the task specified.  This applies only
608              to new children, not to any existing children at  the  time  the
609              counter  is  created  (nor to any new children of existing chil‐
610              dren).
611
612              Inherit does not work for some combinations of read_format  val‐
613              ues, such as PERF_FORMAT_GROUP.
614
615       pinned The  pinned  bit  specifies that the counter should always be on
616              the CPU if at all possible.  It applies only to  hardware  coun‐
617              ters  and  only to group leaders.  If a pinned counter cannot be
618              put onto the CPU (e.g., because there are  not  enough  hardware
619              counters  or  because of a conflict with some other event), then
620              the counter goes into an 'error' state, where reads return  end-
621              of-file  (i.e.,  read(2)  returns 0) until the counter is subse‐
622              quently enabled or disabled.
623
624       exclusive
625              The exclusive bit specifies that when this counter's group is on
626              the  CPU,  it should be the only group using the CPU's counters.
627              In the future this may allow monitoring programs to support  PMU
628              features  that  need  to  run  alone so that they do not disrupt
629              other hardware counters.
630
631              Note that many unexpected situations may prevent events with the
632              exclusive  bit  set  from ever running.  This includes any users
633              running a system-wide measurement as well as any kernel  use  of
634              the  performance  counters  (including  the commonly enabled NMI
635              Watchdog Timer interface).
636
637       exclude_user
638              If this bit is set, the count excludes  events  that  happen  in
639              user space.
640
641       exclude_kernel
642              If  this  bit  is  set, the count excludes events that happen in
643              kernel space.
644
645       exclude_hv
646              If this bit is set, the count excludes events that happen in the
647              hypervisor.   This is mainly for PMUs that have built-in support
648              for handling this (such as POWER).  Extra support is needed  for
649              handling hypervisor measurements on most machines.
650
651       exclude_idle
652              If  set,  don't  count  when  the  CPU is running the idle task.
653              While you can currently enable this for any event  type,  it  is
654              ignored for all but software events.
655
656       mmap   The  mmap bit enables generation of PERF_RECORD_MMAP samples for
657              every mmap(2) call that has PROT_EXEC set.  This allows tools to
658              notice  new executable code being mapped into a program (dynamic
659              shared libraries for example) so that addresses  can  be  mapped
660              back to the original code.
661
662       comm   The  comm  bit enables tracking of process command name as modi‐
663              fied by the exec(2) and prctl(PR_SET_NAME) system calls as  well
664              as  writing  to  /proc/self/comm.  If the comm_exec flag is also
665              successfully set (possible since Linux 3.16), then the misc flag
666              PERF_RECORD_MISC_COMM_EXEC  can  be  used  to  differentiate the
667              exec(2) case from the others.
668
669       freq   If this bit is set, then sample_frequency not  sample_period  is
670              used when setting up the sampling interval.
671
672       inherit_stat
673              This  bit  enables  saving of event counts on context switch for
674              inherited tasks.  This is meaningful only if the  inherit  field
675              is set.
676
677       enable_on_exec
678              If  this  bit is set, a counter is automatically enabled after a
679              call to exec(2).
680
681       task   If this bit is set, then fork/exit notifications are included in
682              the ring buffer.
683
684       watermark
685              If  set,  have an overflow notification happen when we cross the
686              wakeup_watermark boundary.   Otherwise,  overflow  notifications
687              happen after wakeup_events samples.
688
689       precise_ip (since Linux 2.6.35)
690              This controls the amount of skid.  Skid is how many instructions
691              execute between an event of interest happening  and  the  kernel
692              being able to stop and record the event.  Smaller skid is better
693              and allows more accurate reporting of which events correspond to
694              which instructions, but hardware is often limited with how small
695              this can be.
696
697              The possible values of this field are the following:
698
699              0  SAMPLE_IP can have arbitrary skid.
700
701              1  SAMPLE_IP must have constant skid.
702
703              2  SAMPLE_IP requested to have 0 skid.
704
705              3  SAMPLE_IP must have 0 skid.   See  also  the  description  of
706                 PERF_RECORD_MISC_EXACT_IP.
707
708       mmap_data (since Linux 2.6.36)
709              This is the counterpart of the mmap field.  This enables genera‐
710              tion of PERF_RECORD_MMAP samples for mmap(2) calls that  do  not
711              have PROT_EXEC set (for example data and SysV shared memory).
712
713       sample_id_all (since Linux 2.6.38)
714              If  set, then TID, TIME, ID, STREAM_ID, and CPU can additionally
715              be included in non-PERF_RECORD_SAMPLEs if the corresponding sam‐
716              ple_type is selected.
717
718              If  PERF_SAMPLE_IDENTIFIER  is  specified, then an additional ID
719              value is included as the last value to ease parsing  the  record
720              stream.  This may lead to the id value appearing twice.
721
722              The layout is described by this pseudo-structure:
723
724                  struct sample_id {
725                      { u32 pid, tid; }   /* if PERF_SAMPLE_TID set */
726                      { u64 time;     }   /* if PERF_SAMPLE_TIME set */
727                      { u64 id;       }   /* if PERF_SAMPLE_ID set */
728                      { u64 stream_id;}   /* if PERF_SAMPLE_STREAM_ID set  */
729                      { u32 cpu, res; }   /* if PERF_SAMPLE_CPU set */
730                      { u64 id;       }   /* if PERF_SAMPLE_IDENTIFIER set */
731                  };
732
733       exclude_host (since Linux 3.2)
734              When  conducting  measurements that include processes running VM
735              instances (i.e., have executed a KVM_RUN ioctl(2)), only measure
736              events happening inside a guest instance.  This is only meaning‐
737              ful outside the guests; this  setting  does  not  change  counts
738              gathered  inside  of  a guest.  Currently, this functionality is
739              x86 only.
740
741       exclude_guest (since Linux 3.2)
742              When conducting measurements that include processes  running  VM
743              instances  (i.e., have executed a KVM_RUN ioctl(2)), do not mea‐
744              sure events happening inside  guest  instances.   This  is  only
745              meaningful  outside  the  guests;  this  setting does not change
746              counts gathered inside of a guest.  Currently, this  functional‐
747              ity is x86 only.
748
749       exclude_callchain_kernel (since Linux 3.7)
750              Do not include kernel callchains.
751
752       exclude_callchain_user (since Linux 3.7)
753              Do not include user callchains.
754
755       mmap2 (since Linux 3.16)
756              Generate an extended executable mmap record that contains enough
757              additional information to  uniquely  identify  shared  mappings.
758              The mmap flag must also be set for this to work.
759
760       comm_exec (since Linux 3.16)
761              This is purely a feature-detection flag, it does not change ker‐
762              nel behavior.  If this flag can successfully be set, then,  when
763              comm is enabled, the PERF_RECORD_MISC_COMM_EXEC flag will be set
764              in the misc field of a comm record header if  the  rename  event
765              being  reported  was  caused  by a call to exec(2).  This allows
766              tools to distinguish between the various types of process renam‐
767              ing.
768
769       use_clockid (since Linux 4.1)
770              This  allows  selecting  which  internal Linux clock to use when
771              generating timestamps via the clockid field.  This can  make  it
772              easier  to correlate perf sample times with timestamps generated
773              by other tools.
774
775       context_switch (since Linux 4.3)
776              This enables the generation of PERF_RECORD_SWITCH records when a
777              context  switch  occurs.   It  also  enables  the  generation of
778              PERF_RECORD_SWITCH_CPU_WIDE records when  sampling  in  CPU-wide
779              mode.   This functionality is in addition to existing tracepoint
780              and software events for measuring context switches.  The  advan‐
781              tage  of  this method is that it will give full information even
782              with strict perf_event_paranoid settings.
783
784       wakeup_events, wakeup_watermark
785              This union  sets  how  many  samples  (wakeup_events)  or  bytes
786              (wakeup_watermark)  happen  before an overflow notification hap‐
787              pens.  Which one is used is selected by the watermark bit flag.
788
789              wakeup_events counts only PERF_RECORD_SAMPLE record  types.   To
790              receive  overflow  notification for all PERF_RECORD types choose
791              watermark and set wakeup_watermark to 1.
792
793              Prior to Linux 3.0, setting wakeup_events to 0  resulted  in  no
794              overflow  notifications; more recent kernels treat 0 the same as
795              1.
796
797       bp_type (since Linux 2.6.33)
798              This chooses the breakpoint type.  It is one of:
799
800              HW_BREAKPOINT_EMPTY
801                     No breakpoint.
802
803              HW_BREAKPOINT_R
804                     Count when we read the memory location.
805
806              HW_BREAKPOINT_W
807                     Count when we write the memory location.
808
809              HW_BREAKPOINT_RW
810                     Count when we read or write the memory location.
811
812              HW_BREAKPOINT_X
813                     Count when we execute code at the memory location.
814
815              The values can be combined via a bitwise or, but the combination
816              of  HW_BREAKPOINT_R  or  HW_BREAKPOINT_W with HW_BREAKPOINT_X is
817              not allowed.
818
819       bp_addr (since Linux 2.6.33)
820              This is the address of the  breakpoint.   For  execution  break‐
821              points,  this is the memory address of the instruction of inter‐
822              est; for read and write breakpoints, it is the memory address of
823              the memory location of interest.
824
825       config1 (since Linux 2.6.39)
826              config1  is  used for setting events that need an extra register
827              or otherwise do not fit in the regular config field.   Raw  OFF‐
828              CORE_EVENTS  on  Nehalem/Westmere/SandyBridge  use this field on
829              Linux 3.3 and later kernels.
830
831       bp_len (since Linux 2.6.33)
832              bp_len is the length of the breakpoint being measured if type is
833              PERF_TYPE_BREAKPOINT.     Options    are    HW_BREAKPOINT_LEN_1,
834              HW_BREAKPOINT_LEN_2,    HW_BREAKPOINT_LEN_4,    and    HW_BREAK‐
835              POINT_LEN_8.    For   an   execution  breakpoint,  set  this  to
836              sizeof(long).
837
838       config2 (since Linux 2.6.39)
839              config2 is a further extension of the config1 field.
840
841       branch_sample_type (since Linux 3.4)
842              If PERF_SAMPLE_BRANCH_STACK is enabled, then this specifies what
843              branches to include in the branch record.
844
845              The  first  part of the value is the privilege level, which is a
846              combination of one of the values listed below.  If the user does
847              not  set  privilege  level  explicitly,  the kernel will use the
848              event's privilege level.  Event and branch privilege  levels  do
849              not have to match.
850
851              PERF_SAMPLE_BRANCH_USER
852                     Branch target is in user space.
853
854              PERF_SAMPLE_BRANCH_KERNEL
855                     Branch target is in kernel space.
856
857              PERF_SAMPLE_BRANCH_HV
858                     Branch target is in hypervisor.
859
860              PERF_SAMPLE_BRANCH_PLM_ALL
861                     A  convenience  value  that is the three preceding values
862                     ORed together.
863
864              In addition to the privilege value, at least one or more of  the
865              following bits must be set.
866
867              PERF_SAMPLE_BRANCH_ANY
868                     Any branch type.
869
870              PERF_SAMPLE_BRANCH_ANY_CALL
871                     Any  call  branch (includes direct calls, indirect calls,
872                     and far jumps).
873
874              PERF_SAMPLE_BRANCH_IND_CALL
875                     Indirect calls.
876
877              PERF_SAMPLE_BRANCH_CALL (since Linux 4.4)
878                     Direct calls.
879
880              PERF_SAMPLE_BRANCH_ANY_RETURN
881                     Any return branch.
882
883              PERF_SAMPLE_BRANCH_IND_JUMP (since Linux 4.2)
884                     Indirect jumps.
885
886              PERF_SAMPLE_BRANCH_COND (since Linux 3.16)
887                     Conditional branches.
888
889              PERF_SAMPLE_BRANCH_ABORT_TX (since Linux 3.11)
890                     Transactional memory aborts.
891
892              PERF_SAMPLE_BRANCH_IN_TX (since Linux 3.11)
893                     Branch in transactional memory transaction.
894
895              PERF_SAMPLE_BRANCH_NO_TX (since Linux 3.11)
896                     Branch   not   in   transactional   memory   transaction.
897                     PERF_SAMPLE_BRANCH_CALL_STACK (since Linux 4.1) Branch is
898                     part of a hardware-generated call stack.   This  requires
899                     hardware  support,  currently  only  found  on  Intel x86
900                     Haswell or newer.
901
902       sample_regs_user (since Linux 3.7)
903              This bit mask defines the set of user CPU registers to  dump  on
904              samples.   The  layout of the register mask is architecture-spe‐
905              cific   and   is   described   in   the   kernel   header   file
906              arch/ARCH/include/uapi/asm/perf_regs.h.
907
908       sample_stack_user (since Linux 3.7)
909              This  defines  the  size  of the user stack to dump if PERF_SAM‐
910              PLE_STACK_USER is specified.
911
912       clockid (since Linux 4.1)
913              If use_clockid is set, then this field  selects  which  internal
914              Linux  timer  to  use  for timestamps.  The available timers are
915              defined  in  linux/time.h,  with  CLOCK_MONOTONIC,   CLOCK_MONO‐
916              TONIC_RAW,  CLOCK_REALTIME,  CLOCK_BOOTTIME,  and CLOCK_TAI cur‐
917              rently supported.
918
919       aux_watermark (since Linux 4.1)
920              This  specifies  how  much  data  is  required  to   trigger   a
921              PERF_RECORD_AUX sample.
922
923       sample_max_stack (since Linux 4.8)
924              When  sample_type  includes  PERF_SAMPLE_CALLCHAIN,  this  field
925              specifies how many stack frames to report  when  generating  the
926              callchain.
927
928   Reading results
929       Once a perf_event_open() file descriptor has been opened, the values of
930       the events can be read from the file descriptor.  The values  that  are
931       there  are  specified by the read_format field in the attr structure at
932       open time.
933
934       If you attempt to read into a buffer that is not big enough to hold the
935       data, the error ENOSPC results.
936
937       Here is the layout of the data returned by a read:
938
939       * If  PERF_FORMAT_GROUP  was specified to allow reading all events in a
940         group at once:
941
942             struct read_format {
943                 u64 nr;            /* The number of events */
944                 u64 time_enabled;  /* if PERF_FORMAT_TOTAL_TIME_ENABLED */
945                 u64 time_running;  /* if PERF_FORMAT_TOTAL_TIME_RUNNING */
946                 struct {
947                     u64 value;     /* The value of the event */
948                     u64 id;        /* if PERF_FORMAT_ID */
949                 } values[nr];
950             };
951
952       * If PERF_FORMAT_GROUP was not specified:
953
954             struct read_format {
955                 u64 value;         /* The value of the event */
956                 u64 time_enabled;  /* if PERF_FORMAT_TOTAL_TIME_ENABLED */
957                 u64 time_running;  /* if PERF_FORMAT_TOTAL_TIME_RUNNING */
958                 u64 id;            /* if PERF_FORMAT_ID */
959             };
960
961       The values read are as follows:
962
963       nr     The number of events in this file descriptor.  Available only if
964              PERF_FORMAT_GROUP was specified.
965
966       time_enabled, time_running
967              Total  time  the  event was enabled and running.  Normally these
968              values are the same.  Multiplexing  happens  if  the  number  of
969              events  is  more than the number of available PMU counter slots.
970              In that case the events run  only  part  of  the  time  and  the
971              time_enabled  and  time  running  values can be used to scale an
972              estimated value for the count.
973
974       value  An unsigned 64-bit value containing the counter result.
975
976       id     A globally unique value for this particular event; only  present
977              if PERF_FORMAT_ID was specified in read_format.
978
979   MMAP layout
980       When using perf_event_open() in sampled mode, asynchronous events (like
981       counter overflow or PROT_EXEC mmap tracking) are logged  into  a  ring-
982       buffer.  This ring-buffer is created and accessed through mmap(2).
983
984       The mmap size should be 1+2^n pages, where the first page is a metadata
985       page (struct perf_event_mmap_page) that contains various bits of infor‐
986       mation such as where the ring-buffer head is.
987
988       Before  kernel  2.6.39,  there is a bug that means you must allocate an
989       mmap ring buffer when sampling even if you do not plan to access it.
990
991       The structure of the first metadata mmap page is as follows:
992
993           struct perf_event_mmap_page {
994               __u32 version;        /* version number of this structure */
995               __u32 compat_version; /* lowest version this is compat with */
996               __u32 lock;           /* seqlock for synchronization */
997               __u32 index;          /* hardware counter identifier */
998               __s64 offset;         /* add to hardware counter value */
999               __u64 time_enabled;   /* time event active */
1000               __u64 time_running;   /* time event on CPU */
1001               union {
1002                   __u64   capabilities;
1003                   struct {
1004                       __u64 cap_usr_time / cap_usr_rdpmc / cap_bit0 : 1,
1005                             cap_bit0_is_deprecated : 1,
1006                             cap_user_rdpmc         : 1,
1007                             cap_user_time          : 1,
1008                             cap_user_time_zero     : 1,
1009                   };
1010               };
1011               __u16 pmc_width;
1012               __u16 time_shift;
1013               __u32 time_mult;
1014               __u64 time_offset;
1015               __u64 __reserved[120];   /* Pad to 1 k */
1016               __u64 data_head;         /* head in the data section */
1017               __u64 data_tail;         /* user-space written tail */
1018               __u64 data_offset;       /* where the buffer starts */
1019               __u64 data_size;         /* data buffer size */
1020               __u64 aux_head;
1021               __u64 aux_tail;
1022               __u64 aux_offset;
1023               __u64 aux_size;
1024
1025           }
1026
1027       The following list describes the  fields  in  the  perf_event_mmap_page
1028       structure in more detail:
1029
1030       version
1031              Version number of this structure.
1032
1033       compat_version
1034              The lowest version this is compatible with.
1035
1036       lock   A seqlock for synchronization.
1037
1038       index  A unique hardware counter identifier.
1039
1040       offset When  using  rdpmc  for reads this offset value must be added to
1041              the one returned by rdpmc to get the current total event count.
1042
1043       time_enabled
1044              Time the event was active.
1045
1046       time_running
1047              Time the event was running.
1048
1049       cap_usr_time / cap_usr_rdpmc / cap_bit0 (since Linux 3.4)
1050              There  was  a  bug  in  the  definition  of   cap_usr_time   and
1051              cap_usr_rdpmc  from  Linux 3.4 until Linux 3.11.  Both bits were
1052              defined to point to the same location, so it was  impossible  to
1053              know if cap_usr_time or cap_usr_rdpmc were actually set.
1054
1055              Starting  with Linux 3.12, these are renamed to cap_bit0 and you
1056              should use the cap_user_time and cap_user_rdpmc fields instead.
1057
1058       cap_bit0_is_deprecated (since Linux 3.12)
1059              If set, this bit indicates that the kernel supports the properly
1060              separated cap_user_time and cap_user_rdpmc bits.
1061
1062              If  not-set, it indicates an older kernel where cap_usr_time and
1063              cap_usr_rdpmc map to the same bit and thus both features  should
1064              be used with caution.
1065
1066       cap_user_rdpmc (since Linux 3.12)
1067              If the hardware supports user-space read of performance counters
1068              without syscall (this is the "rdpmc" instruction on  x86),  then
1069              the following code can be used to do a read:
1070
1071                  u32 seq, time_mult, time_shift, idx, width;
1072                  u64 count, enabled, running;
1073                  u64 cyc, time_offset;
1074
1075                  do {
1076                      seq = pc->lock;
1077                      barrier();
1078                      enabled = pc->time_enabled;
1079                      running = pc->time_running;
1080
1081                      if (pc->cap_usr_time && enabled != running) {
1082                          cyc = rdtsc();
1083                          time_offset = pc->time_offset;
1084                          time_mult   = pc->time_mult;
1085                          time_shift  = pc->time_shift;
1086                      }
1087
1088                      idx = pc->index;
1089                      count = pc->offset;
1090
1091                      if (pc->cap_usr_rdpmc && idx) {
1092                          width = pc->pmc_width;
1093                          count += rdpmc(idx - 1);
1094                      }
1095
1096                      barrier();
1097                  } while (pc->lock != seq);
1098
1099       cap_user_time (since Linux 3.12)
1100              This  bit  indicates  the hardware has a constant, nonstop time‐
1101              stamp counter (TSC on x86).
1102
1103       cap_user_time_zero (since Linux 3.12)
1104              Indicates the presence of time_zero which allows  mapping  time‐
1105              stamp values to the hardware clock.
1106
1107       pmc_width
1108              If cap_usr_rdpmc, this field provides the bit-width of the value
1109              read using the rdpmc or equivalent  instruction.   This  can  be
1110              used to sign extend the result like:
1111
1112                  pmc <<= 64 - pmc_width;
1113                  pmc >>= 64 - pmc_width; // signed shift right
1114                  count += pmc;
1115
1116       time_shift, time_mult, time_offset
1117
1118              If  cap_usr_time,  these  fields can be used to compute the time
1119              delta since time_enabled (in nanoseconds) using rdtsc  or  simi‐
1120              lar.
1121
1122                  u64 quot, rem;
1123                  u64 delta;
1124                  quot = (cyc >> time_shift);
1125                  rem = cyc & (((u64)1 << time_shift) - 1);
1126                  delta = time_offset + quot * time_mult +
1127                          ((rem * time_mult) >> time_shift);
1128
1129              Where  time_offset,  time_mult,  time_shift, and cyc are read in
1130              the seqcount loop described above.  This delta can then be added
1131              to enabled and possible running (if idx), improving the scaling:
1132
1133                  enabled += delta;
1134                  if (idx)
1135                      running += delta;
1136                  quot = count / running;
1137                  rem  = count % running;
1138                  count = quot * enabled + (rem * enabled) / running;
1139
1140       time_zero (since Linux 3.12)
1141
1142              If  cap_usr_time_zero  is  set, then the hardware clock (the TSC
1143              timestamp counter on x86) can be calculated from the  time_zero,
1144              time_mult, and time_shift values:
1145
1146                  time = timestamp - time_zero;
1147                  quot = time / time_mult;
1148                  rem  = time % time_mult;
1149                  cyc = (quot << time_shift) + (rem << time_shift) / time_mult;
1150
1151              And vice versa:
1152
1153                  quot = cyc >> time_shift;
1154                  rem  = cyc & (((u64)1 << time_shift) - 1);
1155                  timestamp = time_zero + quot * time_mult +
1156                      ((rem * time_mult) >> time_shift);
1157
1158       data_head
1159              This points to the head of the data section.  The value continu‐
1160              ously increases, it does not wrap.  The value needs to be  manu‐
1161              ally wrapped by the size of the mmap buffer before accessing the
1162              samples.
1163
1164              On SMP-capable platforms, after  reading  the  data_head  value,
1165              user space should issue an rmb().
1166
1167       data_tail
1168              When  the  mapping  is PROT_WRITE, the data_tail value should be
1169              written by user space to reflect the last read  data.   In  this
1170              case, the kernel will not overwrite unread data.
1171
1172       data_offset (since Linux 4.1)
1173              Contains  the  offset  of  the location in the mmap buffer where
1174              perf sample data begins.
1175
1176       data_size (since Linux 4.1)
1177              Contains the size of the perf sample region within the mmap buf‐
1178              fer.
1179
1180       aux_head, aux_tail, aux_offset, aux_size (since Linux 4.1)
1181              The AUX region allows mmaping a separate sample buffer for high-
1182              bandwidth data streams (separate from the main perf sample  buf‐
1183              fer).   An  example  of  a  high-bandwidth stream is instruction
1184              tracing support, as is found in newer Intel processors.
1185
1186              To set up an AUX area, first aux_offset needs to be set with  an
1187              offset  greater than data_offset+data_size and aux_size needs to
1188              be set to the desired buffer size.  The desired offset and  size
1189              must  be  page  aligned,  and  the  size must be a power of two.
1190              These values are then passed to mmap in order  to  map  the  AUX
1191              buffer.   Pages  in  the  AUX buffer are included as part of the
1192              RLIMIT_MEMLOCK resource limit (see setrlimit(2)),  and  also  as
1193              part of the perf_event_mlock_kb allowance.
1194
1195              By  default, the AUX buffer will be truncated if it will not fit
1196              in the available space in the ring buffer.  If the AUX buffer is
1197              mapped  as a read only buffer, then it will operate in ring buf‐
1198              fer mode where old data will be overwritten by  new.   In  over‐
1199              write mode, it might not be possible to infer where the new data
1200              began, and it is the consumer's job to disable measurement while
1201              reading to avoid possible data races.
1202
1203              The  aux_head  and  aux_tail  ring buffer pointers have the same
1204              behavior and ordering rules as the previous described  data_head
1205              and data_tail.
1206
1207       The following 2^n ring-buffer pages have the layout described below.
1208
1209       If perf_event_attr.sample_id_all is set, then all event types will have
1210       the sample_type selected fields related  to  where/when  (identity)  an
1211       event   took  place  (TID,  TIME,  ID,  CPU,  STREAM_ID)  described  in
1212       PERF_RECORD_SAMPLE  below,  it  will  be   stashed   just   after   the
1213       perf_event_header  and  the  fields  already  present  for the existing
1214       fields, that is, at the end  of  the  payload.   This  allows  a  newer
1215       perf.data  file  to  be  supported  by  older  perf tools, with the new
1216       optional fields being ignored.
1217
1218       The mmap values start with a header:
1219
1220           struct perf_event_header {
1221               __u32   type;
1222               __u16   misc;
1223               __u16   size;
1224           };
1225
1226       Below, we describe the perf_event_header fields in  more  detail.   For
1227       ease  of  reading,  the  fields with shorter descriptions are presented
1228       first.
1229
1230       size   This indicates the size of the record.
1231
1232       misc   The misc field contains additional information about the sample.
1233
1234              The CPU mode can be determined from this value by  masking  with
1235              PERF_RECORD_MISC_CPUMODE_MASK and looking for one of the follow‐
1236              ing (note these are not bit masks, only one  can  be  set  at  a
1237              time):
1238
1239              PERF_RECORD_MISC_CPUMODE_UNKNOWN
1240                     Unknown CPU mode.
1241
1242              PERF_RECORD_MISC_KERNEL
1243                     Sample happened in the kernel.
1244
1245              PERF_RECORD_MISC_USER
1246                     Sample happened in user code.
1247
1248              PERF_RECORD_MISC_HYPERVISOR
1249                     Sample happened in the hypervisor.
1250
1251              PERF_RECORD_MISC_GUEST_KERNEL (since Linux 2.6.35)
1252                     Sample happened in the guest kernel.
1253
1254              PERF_RECORD_MISC_GUEST_USER  (since Linux 2.6.35)
1255                     Sample happened in guest user code.
1256
1257              Since  the  following  three statuses are generated by different
1258              record types, they alias to the same bit:
1259
1260              PERF_RECORD_MISC_MMAP_DATA (since Linux 3.10)
1261                     This is set when the mapping is not executable; otherwise
1262                     the mapping is executable.
1263
1264              PERF_RECORD_MISC_COMM_EXEC (since Linux 3.16)
1265                     This is set for a PERF_RECORD_COMM record on kernels more
1266                     recent than Linux 3.16  if  a  process  name  change  was
1267                     caused by an exec(2) system call.
1268
1269              PERF_RECORD_MISC_SWITCH_OUT (since Linux 4.3)
1270                     When  a PERF_RECORD_SWITCH or PERF_RECORD_SWITCH_CPU_WIDE
1271                     record is generated, this bit indicates that the  context
1272                     switch  is away from the current process (instead of into
1273                     the current process).
1274
1275              In addition, the following bits can be set:
1276
1277              PERF_RECORD_MISC_EXACT_IP
1278                     This indicates that the content of PERF_SAMPLE_IP  points
1279                     to  the actual instruction that triggered the event.  See
1280                     also perf_event_attr.precise_ip.
1281
1282              PERF_RECORD_MISC_EXT_RESERVED (since Linux 2.6.35)
1283                     This indicates there is  extended  data  available  (cur‐
1284                     rently not used).
1285
1286              PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT
1287                     This  bit  is  not set by the kernel.  It is reserved for
1288                     the   user-space   perf   utility   to   indicate    that
1289                     /proc/i[pid]/maps  parsing  was  taking  too long and was
1290                     stopped, and thus the mmap records may be truncated.
1291
1292       type   The type value is one of the below.  The values  in  the  corre‐
1293              sponding  record  (that  follows  the header) depend on the type
1294              selected as shown.
1295
1296              PERF_RECORD_MMAP
1297                  The MMAP events record the PROT_EXEC mappings so that we can
1298                  correlate  user-space  IPs to code.  They have the following
1299                  structure:
1300
1301                      struct {
1302                          struct perf_event_header header;
1303                          u32    pid, tid;
1304                          u64    addr;
1305                          u64    len;
1306                          u64    pgoff;
1307                          char   filename[];
1308                      };
1309
1310                  pid    is the process ID.
1311
1312                  tid    is the thread ID.
1313
1314                  addr   is the address of the allocated memory.  len  is  the
1315                         length  of  the  allocated memory.  pgoff is the page
1316                         offset of the allocated memory.  filename is a string
1317                         describing the backing of the allocated memory.
1318
1319              PERF_RECORD_LOST
1320                  This record indicates when events are lost.
1321
1322                      struct {
1323                          struct perf_event_header header;
1324                          u64    id;
1325                          u64    lost;
1326                          struct sample_id sample_id;
1327                      };
1328
1329                  id     is  the  unique  event  ID  for the samples that were
1330                         lost.
1331
1332                  lost   is the number of events that were lost.
1333
1334              PERF_RECORD_COMM
1335                  This record indicates a change in the process name.
1336
1337                      struct {
1338                          struct perf_event_header header;
1339                          u32    pid;
1340                          u32    tid;
1341                          char   comm[];
1342                          struct sample_id sample_id;
1343                      };
1344
1345                  pid    is the process ID.
1346
1347                  tid    is the thread ID.
1348
1349                  comm   is a string containing the new name of the process.
1350
1351              PERF_RECORD_EXIT
1352                  This record indicates a process exit event.
1353
1354                      struct {
1355                          struct perf_event_header header;
1356                          u32    pid, ppid;
1357                          u32    tid, ptid;
1358                          u64    time;
1359                          struct sample_id sample_id;
1360                      };
1361
1362              PERF_RECORD_THROTTLE, PERF_RECORD_UNTHROTTLE
1363                  This record indicates a throttle/unthrottle event.
1364
1365                      struct {
1366                          struct perf_event_header header;
1367                          u64    time;
1368                          u64    id;
1369                          u64    stream_id;
1370                          struct sample_id sample_id;
1371                      };
1372
1373              PERF_RECORD_FORK
1374                  This record indicates a fork event.
1375
1376                      struct {
1377                          struct perf_event_header header;
1378                          u32    pid, ppid;
1379                          u32    tid, ptid;
1380                          u64    time;
1381                          struct sample_id sample_id;
1382                      };
1383
1384              PERF_RECORD_READ
1385                  This record indicates a read event.
1386
1387                      struct {
1388                          struct perf_event_header header;
1389                          u32    pid, tid;
1390                          struct read_format values;
1391                          struct sample_id sample_id;
1392                      };
1393
1394              PERF_RECORD_SAMPLE
1395                  This record indicates a sample.
1396
1397                      struct {
1398                          struct perf_event_header header;
1399                          u64    sample_id;   /* if PERF_SAMPLE_IDENTIFIER */
1400                          u64    ip;          /* if PERF_SAMPLE_IP */
1401                          u32    pid, tid;    /* if PERF_SAMPLE_TID */
1402                          u64    time;        /* if PERF_SAMPLE_TIME */
1403                          u64    addr;        /* if PERF_SAMPLE_ADDR */
1404                          u64    id;          /* if PERF_SAMPLE_ID */
1405                          u64    stream_id;   /* if PERF_SAMPLE_STREAM_ID */
1406                          u32    cpu, res;    /* if PERF_SAMPLE_CPU */
1407                          u64    period;      /* if PERF_SAMPLE_PERIOD */
1408                          struct read_format v;
1409                                              /* if PERF_SAMPLE_READ */
1410                          u64    nr;          /* if PERF_SAMPLE_CALLCHAIN */
1411                          u64    ips[nr];     /* if PERF_SAMPLE_CALLCHAIN */
1412                          u32    size;        /* if PERF_SAMPLE_RAW */
1413                          char  data[size];   /* if PERF_SAMPLE_RAW */
1414                          u64    bnr;         /* if PERF_SAMPLE_BRANCH_STACK */
1415                          struct perf_branch_entry lbr[bnr];
1416                                              /* if PERF_SAMPLE_BRANCH_STACK */
1417                          u64    abi;         /* if PERF_SAMPLE_REGS_USER */
1418                          u64    regs[weight(mask)];
1419                                              /* if PERF_SAMPLE_REGS_USER */
1420                          u64    size;        /* if PERF_SAMPLE_STACK_USER */
1421                          char   data[size];  /* if PERF_SAMPLE_STACK_USER */
1422                          u64    dyn_size;    /* if PERF_SAMPLE_STACK_USER &&
1423                                                 size != 0 */
1424                          u64    weight;      /* if PERF_SAMPLE_WEIGHT */
1425                          u64    data_src;    /* if PERF_SAMPLE_DATA_SRC */
1426                          u64    transaction; /* if PERF_SAMPLE_TRANSACTION */
1427                          u64    abi;         /* if PERF_SAMPLE_REGS_INTR */
1428                          u64    regs[weight(mask)];
1429                                              /* if PERF_SAMPLE_REGS_INTR */
1430                      };
1431
1432                  sample_id
1433                      If PERF_SAMPLE_IDENTIFIER is enabled, a 64-bit unique ID
1434                      is  included.   This  is  a duplication of the PERF_SAM‐
1435                      PLE_ID id value, but included at the  beginning  of  the
1436                      sample so parsers can easily obtain the value.
1437
1438                  ip  If  PERF_SAMPLE_IP is enabled, then a 64-bit instruction
1439                      pointer value is included.
1440
1441                  pid, tid
1442                      If PERF_SAMPLE_TID is enabled, then a 32-bit process  ID
1443                      and 32-bit thread ID are included.
1444
1445                  time
1446                      If  PERF_SAMPLE_TIME is enabled, then a 64-bit timestamp
1447                      is included.  This is obtained via  local_clock()  which
1448                      is  a  hardware  timestamp  if available and the jiffies
1449                      value if not.
1450
1451                  addr
1452                      If PERF_SAMPLE_ADDR is enabled, then a 64-bit address is
1453                      included.   This is usually the address of a tracepoint,
1454                      breakpoint, or software event; otherwise the value is 0.
1455
1456                  id  If PERF_SAMPLE_ID is enabled,  a  64-bit  unique  ID  is
1457                      included.   If  the event is a member of an event group,
1458                      the group leader ID is returned.  This ID is the same as
1459                      the one returned by PERF_FORMAT_ID.
1460
1461                  stream_id
1462                      If  PERF_SAMPLE_STREAM_ID is enabled, a 64-bit unique ID
1463                      is included.  Unlike PERF_SAMPLE_ID  the  actual  ID  is
1464                      returned,  not the group leader.  This ID is the same as
1465                      the one returned by PERF_FORMAT_ID.
1466
1467                  cpu, res
1468                      If PERF_SAMPLE_CPU is enabled, this is  a  32-bit  value
1469                      indicating  which  CPU  was being used, in addition to a
1470                      reserved (unused) 32-bit value.
1471
1472                  period
1473                      If PERF_SAMPLE_PERIOD is enabled, a 64-bit  value  indi‐
1474                      cating the current sampling period is written.
1475
1476                  v   If  PERF_SAMPLE_READ  is  enabled,  a  structure of type
1477                      read_format is included which has values for all  events
1478                      in  the  event group.  The values included depend on the
1479                      read_format value used at perf_event_open() time.
1480
1481                  nr, ips[nr]
1482                      If PERF_SAMPLE_CALLCHAIN is enabled, then a 64-bit  num‐
1483                      ber  is  included  which  indicates  how  many following
1484                      64-bit instruction pointers will follow.   This  is  the
1485                      current callchain.
1486
1487                  size, data[size]
1488                      If PERF_SAMPLE_RAW is enabled, then a 32-bit value indi‐
1489                      cating size is included followed by an  array  of  8-bit
1490                      values  of length size.  The values are padded with 0 to
1491                      have 64-bit alignment.
1492
1493                      This RAW record data is opaque with respect to the  ABI.
1494                      The  ABI  doesn't  make any promises with respect to the
1495                      stability of its  content,  it  may  vary  depending  on
1496                      event, hardware, and kernel version.
1497
1498                  bnr, lbr[bnr]
1499                      If  PERF_SAMPLE_BRANCH_STACK  is  enabled, then a 64-bit
1500                      value indicating the number of records is included, fol‐
1501                      lowed  by  bnr  perf_branch_entry  structures which each
1502                      include the fields:
1503
1504                      from   This indicates the source instruction (may not be
1505                             a branch).
1506
1507                      to     The branch target.
1508
1509                      mispred
1510                             The branch target was mispredicted.
1511
1512                      predicted
1513                             The branch target was predicted.
1514
1515                      in_tx (since Linux 3.11)
1516                             The branch was in a transactional memory transac‐
1517                             tion.
1518
1519                      abort (since Linux 3.11)
1520                             The branch was in an aborted transactional memory
1521                             transaction.
1522
1523                      cycles (since Linux 4.3)
1524                             This  reports  the number of cycles elapsed since
1525                             the previous branch stack update.
1526
1527                      The entries are from most to least recent, so the  first
1528                      entry has the most recent branch.
1529
1530                      Support  for mispred, predicted, and cycles is optional;
1531                      if not supported, those values will be 0.
1532
1533                      The type  of  branches  recorded  is  specified  by  the
1534                      branch_sample_type field.
1535
1536                  abi, regs[weight(mask)]
1537                      If  PERF_SAMPLE_REGS_USER  is enabled, then the user CPU
1538                      registers are recorded.
1539
1540                      The  abi  field  is  one  of  PERF_SAMPLE_REGS_ABI_NONE,
1541                      PERF_SAMPLE_REGS_ABI_32 or PERF_SAMPLE_REGS_ABI_64.
1542
1543                      The  regs  field  is  an array of the CPU registers that
1544                      were specified by the sample_regs_user attr field.   The
1545                      number  of  values is the number of bits set in the sam‐
1546                      ple_regs_user bit mask.
1547
1548                  size, data[size], dyn_size
1549                      If PERF_SAMPLE_STACK_USER  is  enabled,  then  the  user
1550                      stack  is  recorded.  This can be used to generate stack
1551                      backtraces.  size is the size requested by the  user  in
1552                      sample_stack_user or else the maximum record size.  data
1553                      is the stack data (a raw dump of the memory  pointed  to
1554                      by the stack pointer at the time of sampling).  dyn_size
1555                      is the amount of data actually dumped (can be less  than
1556                      size).  Note that dyn_size is omitted if size is 0.
1557
1558                  weight
1559                      If  PERF_SAMPLE_WEIGHT  is  enabled, then a 64-bit value
1560                      provided by the hardware is recorded that indicates  how
1561                      costly  the  event was.  This allows expensive events to
1562                      stand out more clearly in profiles.
1563
1564                  data_src
1565                      If PERF_SAMPLE_DATA_SRC is enabled, then a 64-bit  value
1566                      is recorded that is made up of the following fields:
1567
1568                      mem_op
1569                          Type of opcode, a bitwise combination of:
1570
1571                          PERF_MEM_OP_NA          Not available
1572                          PERF_MEM_OP_LOAD        Load instruction
1573                          PERF_MEM_OP_STORE       Store instruction
1574                          PERF_MEM_OP_PFETCH      Prefetch
1575                          PERF_MEM_OP_EXEC        Executable code
1576
1577                      mem_lvl
1578                          Memory hierarchy level hit or miss, a bitwise combi‐
1579                          nation   of   the   following,   shifted   left   by
1580                          PERF_MEM_LVL_SHIFT:
1581
1582                          PERF_MEM_LVL_NA         Not available
1583                          PERF_MEM_LVL_HIT        Hit
1584                          PERF_MEM_LVL_MISS       Miss
1585                          PERF_MEM_LVL_L1         Level 1 cache
1586                          PERF_MEM_LVL_LFB        Line fill buffer
1587                          PERF_MEM_LVL_L2         Level 2 cache
1588                          PERF_MEM_LVL_L3         Level 3 cache
1589                          PERF_MEM_LVL_LOC_RAM    Local DRAM
1590                          PERF_MEM_LVL_REM_RAM1   Remote DRAM 1 hop
1591                          PERF_MEM_LVL_REM_RAM2   Remote DRAM 2 hops
1592                          PERF_MEM_LVL_REM_CCE1   Remote cache 1 hop
1593                          PERF_MEM_LVL_REM_CCE2   Remote cache 2 hops
1594                          PERF_MEM_LVL_IO         I/O memory
1595                          PERF_MEM_LVL_UNC        Uncached memory
1596
1597                      mem_snoop
1598                          Snoop  mode, a bitwise combination of the following,
1599                          shifted left by PERF_MEM_SNOOP_SHIFT:
1600
1601                          PERF_MEM_SNOOP_NA       Not available
1602                          PERF_MEM_SNOOP_NONE     No snoop
1603                          PERF_MEM_SNOOP_HIT      Snoop hit
1604                          PERF_MEM_SNOOP_MISS     Snoop miss
1605                          PERF_MEM_SNOOP_HITM     Snoop hit modified
1606
1607                      mem_lock
1608                          Lock instruction, a bitwise combination of the  fol‐
1609                          lowing, shifted left by PERF_MEM_LOCK_SHIFT:
1610
1611                          PERF_MEM_LOCK_NA        Not available
1612                          PERF_MEM_LOCK_LOCKED    Locked transaction
1613
1614                      mem_dtlb
1615                          TLB access hit or miss, a bitwise combination of the
1616                          following, shifted left by PERF_MEM_TLB_SHIFT:
1617
1618                          PERF_MEM_TLB_NA         Not available
1619                          PERF_MEM_TLB_HIT        Hit
1620                          PERF_MEM_TLB_MISS       Miss
1621                          PERF_MEM_TLB_L1         Level 1 TLB
1622                          PERF_MEM_TLB_L2         Level 2 TLB
1623                          PERF_MEM_TLB_WK         Hardware walker
1624                          PERF_MEM_TLB_OS         OS fault handler
1625
1626                  transaction
1627                      If the  PERF_SAMPLE_TRANSACTION  flag  is  set,  then  a
1628                      64-bit  field  is recorded describing the sources of any
1629                      transactional memory aborts.
1630
1631                      The field is a bitwise combination of the following val‐
1632                      ues:
1633
1634                      PERF_TXN_ELISION
1635                             Abort  from  an  elision type transaction (Intel-
1636                             CPU-specific).
1637
1638                      PERF_TXN_TRANSACTION
1639                             Abort from a generic transaction.
1640
1641                      PERF_TXN_SYNC
1642                             Synchronous  abort  (related  to   the   reported
1643                             instruction).
1644
1645                      PERF_TXN_ASYNC
1646                             Asynchronous  abort  (not related to the reported
1647                             instruction).
1648
1649                      PERF_TXN_RETRY
1650                             Retryable abort  (retrying  the  transaction  may
1651                             have succeeded).
1652
1653                      PERF_TXN_CONFLICT
1654                             Abort due to memory conflicts with other threads.
1655
1656                      PERF_TXN_CAPACITY_WRITE
1657                             Abort due to write capacity overflow.
1658
1659                      PERF_TXN_CAPACITY_READ
1660                             Abort due to read capacity overflow.
1661
1662                      In addition, a user-specified abort code can be obtained
1663                      from the high 32 bits of the field by shifting right  by
1664                      PERF_TXN_ABORT_SHIFT   and   masking   with   the  value
1665                      PERF_TXN_ABORT_MASK.
1666
1667                  abi, regs[weight(mask)]
1668                      If PERF_SAMPLE_REGS_INTR is enabled, then the  user  CPU
1669                      registers are recorded.
1670
1671                      The  abi  field  is  one  of  PERF_SAMPLE_REGS_ABI_NONE,
1672                      PERF_SAMPLE_REGS_ABI_32, or PERF_SAMPLE_REGS_ABI_64.
1673
1674                      The regs field is an array of  the  CPU  registers  that
1675                      were  specified by the sample_regs_intr attr field.  The
1676                      number of values is the number of bits set in  the  sam‐
1677                      ple_regs_intr bit mask.
1678
1679              PERF_RECORD_MMAP2
1680                  This  record  includes extended information on mmap(2) calls
1681                  returning executable mappings.  The  format  is  similar  to
1682                  that of the PERF_RECORD_MMAP record, but includes extra val‐
1683                  ues that allow uniquely identifying shared mappings.
1684
1685                      struct {
1686                          struct perf_event_header header;
1687                          u32    pid;
1688                          u32    tid;
1689                          u64    addr;
1690                          u64    len;
1691                          u64    pgoff;
1692                          u32    maj;
1693                          u32    min;
1694                          u64    ino;
1695                          u64    ino_generation;
1696                          u32    prot;
1697                          u32    flags;
1698                          char   filename[];
1699                          struct sample_id sample_id;
1700                      };
1701
1702                  pid    is the process ID.
1703
1704                  tid    is the thread ID.
1705
1706                  addr   is the address of the allocated memory.
1707
1708                  len    is the length of the allocated memory.
1709
1710                  pgoff  is the page offset of the allocated memory.
1711
1712                  maj    is the major ID of the underlying device.
1713
1714                  min    is the minor ID of the underlying device.
1715
1716                  ino    is the inode number.
1717
1718                  ino_generation
1719                         is the inode generation.
1720
1721                  prot   is the protection information.
1722
1723                  flags  is the flags information.
1724
1725                  filename
1726                         is a string describing the backing of  the  allocated
1727                         memory.
1728
1729              PERF_RECORD_AUX (since Linux 4.1)
1730
1731                  This  record reports that new data is available in the sepa‐
1732                  rate AUX buffer region.
1733
1734                      struct {
1735                          struct perf_event_header header;
1736                          u64    aux_offset;
1737                          u64    aux_size;
1738                          u64    flags;
1739                          struct sample_id sample_id;
1740                      };
1741
1742                  aux_offset
1743                         offset in the AUX mmap  region  where  the  new  data
1744                         begins.
1745
1746                  aux_size
1747                         size of the data made available.
1748
1749                  flags  describes the AUX update.
1750
1751                         PERF_AUX_FLAG_TRUNCATED
1752                                if  set,  then the data returned was truncated
1753                                to fit the available buffer size.
1754
1755                         PERF_AUX_FLAG_OVERWRITE
1756                                if set, then the data returned has overwritten
1757                                previous data.
1758
1759              PERF_RECORD_ITRACE_START (since Linux 4.1)
1760
1761                  This   record  indicates  which  process  has  initiated  an
1762                  instruction trace event, allowing tools to  properly  corre‐
1763                  late  the  instruction  addresses in the AUX buffer with the
1764                  proper executable.
1765
1766                      struct {
1767                          struct perf_event_header header;
1768                          u32    pid;
1769                          u32    tid;
1770                      };
1771
1772                  pid    process ID of  the  thread  starting  an  instruction
1773                         trace.
1774
1775                  tid    thread  ID  of  the  thread  starting  an instruction
1776                         trace.
1777
1778              PERF_RECORD_LOST_SAMPLES (since Linux 4.2)
1779
1780                  When using hardware  sampling  (such  as  Intel  PEBS)  this
1781                  record  indicates  some number of samples that may have been
1782                  lost.
1783
1784                      struct {
1785                          struct perf_event_header header;
1786                          u64    lost;
1787                          struct sample_id sample_id;
1788                      };
1789
1790                  lost   the number of potentially lost samples.
1791
1792              PERF_RECORD_SWITCH (since Linux 4.3)
1793
1794                  This record indicates a context switch  has  happened.   The
1795                  PERF_RECORD_MISC_SWITCH_OUT  bit in the misc field indicates
1796                  whether it was a context switch into or away from  the  cur‐
1797                  rent process.
1798
1799                      struct {
1800                          struct perf_event_header header;
1801                          struct sample_id sample_id;
1802                      };
1803
1804              PERF_RECORD_SWITCH_CPU_WIDE (since Linux 4.3)
1805
1806                  As  with  PERF_RECORD_SWITCH this record indicates a context
1807                  switch has happened, but it only  occurs  when  sampling  in
1808                  CPU-wide  mode  and  provides  additional information on the
1809                  process       being       switched       to/from.        The
1810                  PERF_RECORD_MISC_SWITCH_OUT  bit in the misc field indicates
1811                  whether it was a context switch into or away from  the  cur‐
1812                  rent process.
1813
1814                      struct {
1815                          struct perf_event_header header;
1816                          u32 next_prev_pid;
1817                          u32 next_prev_tid;
1818                          struct sample_id sample_id;
1819                      };
1820
1821                  next_prev_pid
1822                         The  process  ID of the previous (if switching in) or
1823                         next (if switching out) process on the CPU.
1824
1825                  next_prev_tid
1826                         The thread ID of the previous (if  switching  in)  or
1827                         next (if switching out) thread on the CPU.
1828
1829   Overflow handling
1830       Events  can be set to notify when a threshold is crossed, indicating an
1831       overflow.  Overflow conditions can be captured by monitoring the  event
1832       file  descriptor  with poll(2), select(2), or epoll(7).  Alternatively,
1833       the overflow events can be captured via sa signal handler, by  enabling
1834       I/O  signaling  on  the  file  descriptor;  see  the  discussion of the
1835       F_SETOWN and F_SETSIG operations in fcntl(2).
1836
1837       Overflows are generated only by  sampling  events  (sample_period  must
1838       have a nonzero value).
1839
1840       There are two ways to generate overflow notifications.
1841
1842       The first is to set a wakeup_events or wakeup_watermark value that will
1843       trigger if a certain number of samples or bytes have  been  written  to
1844       the mmap ring buffer.  In this case, POLL_IN is indicated.
1845
1846       The  other  way  is  by  use of the PERF_EVENT_IOC_REFRESH ioctl.  This
1847       ioctl adds to a counter that decrements each time the event  overflows.
1848       When  nonzero,  POLL_IN  is  indicated,  but once the counter reaches 0
1849       POLL_HUP is indicated and the underlying event is disabled.
1850
1851       Refreshing an event group leader refreshes all siblings and  refreshing
1852       with  a  parameter  of  0  currently  enables infinite refreshes; these
1853       behaviors are unsupported and should not be relied on.
1854
1855       Starting with Linux 3.18, POLL_HUP is indicated if the event being mon‐
1856       itored is attached to a different process and that process exits.
1857
1858   rdpmc instruction
1859       Starting  with  Linux  3.4 on x86, you can use the rdpmc instruction to
1860       get low-latency reads without having to enter the  kernel.   Note  that
1861       using  rdpmc  is  not necessarily faster than other methods for reading
1862       event values.
1863
1864       Support for this can be detected with the cap_usr_rdpmc  field  in  the
1865       mmap  page; documentation on how to calculate event values can be found
1866       in that section.
1867
1868       Originally, when rdpmc support was enabled, any process (not just  ones
1869       with  an  active  perf event) could use the rdpmc instruction to access
1870       the counters.  Starting with Linux 4.0, rdpmc support is  only  allowed
1871       if  an  event  is currently enabled in a process's context.  To restore
1872       the old behavior, write the value 2 to /sys/devices/cpu/rdpmc.
1873
1874   perf_event ioctl calls
1875       Various ioctls act on perf_event_open() file descriptors:
1876
1877       PERF_EVENT_IOC_ENABLE
1878              This enables the individual event or event  group  specified  by
1879              the file descriptor argument.
1880
1881              If  the  PERF_IOC_FLAG_GROUP  bit  is set in the ioctl argument,
1882              then all events in a group are enabled, even if the event speci‐
1883              fied is not the group leader (but see BUGS).
1884
1885       PERF_EVENT_IOC_DISABLE
1886              This disables the individual counter or event group specified by
1887              the file descriptor argument.
1888
1889              Enabling or disabling the leader of a group enables or  disables
1890              the  entire  group; that is, while the group leader is disabled,
1891              none of the counters in the group will count.  Enabling or  dis‐
1892              abling  a  member  of a group other than the leader affects only
1893              that counter; disabling a non-leader  stops  that  counter  from
1894              counting but doesn't affect any other counter.
1895
1896              If  the  PERF_IOC_FLAG_GROUP  bit  is set in the ioctl argument,
1897              then all events in a group are disabled, even if the event spec‐
1898              ified is not the group leader (but see BUGS).
1899
1900       PERF_EVENT_IOC_REFRESH
1901              Non-inherited overflow counters can use this to enable a counter
1902              for a number of overflows specified by the argument, after which
1903              it is disabled.  Subsequent calls of this ioctl add the argument
1904              value to the  current  count.   An  overflow  notification  with
1905              POLL_IN set will happen on each overflow until the count reaches
1906              0; when that happens a notification with POLL_HUP  set  is  sent
1907              and the event is disabled.  Using an argument of 0 is considered
1908              undefined behavior.
1909
1910       PERF_EVENT_IOC_RESET
1911              Reset the event count specified by the file descriptor  argument
1912              to  zero.  This resets only the counts; there is no way to reset
1913              the multiplexing time_enabled or time_running values.
1914
1915              If the PERF_IOC_FLAG_GROUP bit is set  in  the  ioctl  argument,
1916              then  all  events in a group are reset, even if the event speci‐
1917              fied is not the group leader (but see BUGS).
1918
1919       PERF_EVENT_IOC_PERIOD
1920              This updates the overflow period for the event.
1921
1922              Since Linux 3.7 (on ARM) and Linux  3.14  (all  other  architec‐
1923              tures),  the new period takes effect immediately.  On older ker‐
1924              nels, the new period did not take effect until  after  the  next
1925              overflow.
1926
1927              The  argument  is  a  pointer  to  a 64-bit value containing the
1928              desired new period.
1929
1930              Prior to Linux 2.6.36, this ioctl always failed due to a bug  in
1931              the kernel.
1932
1933       PERF_EVENT_IOC_SET_OUTPUT
1934              This tells the kernel to report event notifications to the spec‐
1935              ified file descriptor rather than the  default  one.   The  file
1936              descriptors must all be on the same CPU.
1937
1938              The  argument  specifies  the  desired file descriptor, or -1 if
1939              output should be ignored.
1940
1941       PERF_EVENT_IOC_SET_FILTER (since Linux 2.6.33)
1942              This adds an ftrace filter to this event.
1943
1944              The argument is a pointer to the desired ftrace filter.
1945
1946       PERF_EVENT_IOC_ID (since Linux 3.12)
1947              This returns the  event  ID  value  for  the  given  event  file
1948              descriptor.
1949
1950              The  argument  is a pointer to a 64-bit unsigned integer to hold
1951              the result.
1952
1953       PERF_EVENT_IOC_SET_BPF (since Linux 4.1)
1954              This allows attaching a Berkeley Packet Filter (BPF) program  to
1955              an  existing  kprobe  tracepoint  event.  You need CAP_SYS_ADMIN
1956              privileges to use this ioctl.
1957
1958              The argument is a BPF program file descriptor that  was  created
1959              by a previous bpf(2) system call.
1960
1961       PERF_EVENT_IOC_PAUSE_OUTPUT (since Linux 4.7)
1962              This  allows  pausing  and  resuming the event's ring-buffer.  A
1963              paused ring-buffer does not prevent generation of  samples,  but
1964              simply  discards  them.   The  discarded  samples are considered
1965              lost, and cause a PERF_RECORD_LOST sample to be  generated  when
1966              possible.  An overflow signal may still be triggered by the dis‐
1967              carded sample even though the ring-buffer remains empty.
1968
1969              The argument is an unsigned 32-bit  integer.   A  nonzero  value
1970              pauses the ring-buffer, while a zero value resumes the ring-buf‐
1971              fer.
1972
1973       PERF_EVENT_MODIFY_ATTRIBUTES (since Linux 4.17)
1974              This allows modifying an existing event without the overhead  of
1975              closing  and reopening a new event.  Currently this is supported
1976              only for breakpoint events.
1977
1978              The argument is a pointer to a  perf_event_attr  structure  con‐
1979              taining the updated event settings.
1980
1981       PERF_EVENT_IOC_QUERY_BPF (since Linux 4.16)
1982              This allows querying which Berkeley Packet Filter (BPF) programs
1983              are attached to an existing kprobe  tracepoint.   You  can  only
1984              attach  one  BPF  program  per  event, but you can have multiple
1985              events attached to a tracepoint.  Querying  this  value  on  one
1986              tracepoint  event  returns  the  id  of  all BPF programs in all
1987              events attached to the tracepoint.  You need CAP_SYS_ADMIN priv‐
1988              ileges to use this ioctl.
1989
1990              The argument is a pointer to a structure
1991                  struct perf_event_query_bpf {
1992                      __u32    ids_len;
1993                      __u32    prog_cnt;
1994                      __u32    ids[0];
1995                  };
1996
1997              The  ids_len  field  indicates the number of ids that can fit in
1998              the provided ids array.  The prog_cnt value is filled in by  the
1999              kernel  with the number of attached BPF programs.  The ids array
2000              is filled with the id of each attached BPF  program.   If  there
2001              are  more  programs  than will fit in the array, then the kernel
2002              will return ENOSPC and ids_len will indicate the number of  pro‐
2003              gram IDs that were successfully copied.
2004
2005   Using prctl(2)
2006       A  process  can enable or disable all currently open event groups using
2007       the prctl(2) PR_TASK_PERF_EVENTS_ENABLE and PR_TASK_PERF_EVENTS_DISABLE
2008       operations.  This applies only to events created locally by the calling
2009       process.  This does not apply to  events  created  by  other  processes
2010       attached  to  the  calling  process  or  inherited events from a parent
2011       process.  Only group leaders are enabled and disabled,  not  any  other
2012       members of the groups.
2013
2014   perf_event related configuration files
2015       Files in /proc/sys/kernel/
2016
2017           /proc/sys/kernel/perf_event_paranoid
2018                  The  perf_event_paranoid  file can be set to restrict access
2019                  to the performance counters.
2020
2021                  2   allow only user-space measurements (default since  Linux
2022                      4.6).
2023                  1   allow  both kernel and user measurements (default before
2024                      Linux 4.6).
2025                  0   allow access to CPU-specific data but not raw tracepoint
2026                      samples.
2027                  -1  no restrictions.
2028
2029                  The  existence  of the perf_event_paranoid file is the offi‐
2030                  cial  method  for   determining   if   a   kernel   supports
2031                  perf_event_open().
2032
2033           /proc/sys/kernel/perf_event_max_sample_rate
2034                  This  sets  the  maximum sample rate.  Setting this too high
2035                  can allow users to sample at a  rate  that  impacts  overall
2036                  machine  performance  and  potentially  lock up the machine.
2037                  The default value is 100000 (samples per second).
2038
2039           /proc/sys/kernel/perf_event_max_stack
2040                  This file sets the maximum  depth  of  stack  frame  entries
2041                  reported when generating a call trace.
2042
2043           /proc/sys/kernel/perf_event_mlock_kb
2044                  Maximum  number  of pages an unprivileged user can mlock(2).
2045                  The default is 516 (kB).
2046
2047       Files in /sys/bus/event_source/devices/
2048
2049           Since Linux 2.6.34, the kernel supports having multiple PMUs avail‐
2050           able  for monitoring.  Information on how to program these PMUs can
2051           be found under /sys/bus/event_source/devices/.   Each  subdirectory
2052           corresponds to a different PMU.
2053
2054           /sys/bus/event_source/devices/*/type (since Linux 2.6.38)
2055                  This  contains an integer that can be used in the type field
2056                  of perf_event_attr to indicate that you  wish  to  use  this
2057                  PMU.
2058
2059           /sys/bus/event_source/devices/cpu/rdpmc (since Linux 3.4)
2060                  If this file is 1, then direct user-space access to the per‐
2061                  formance counter registers is allowed via the rdpmc instruc‐
2062                  tion.  This can be disabled by echoing 0 to the file.
2063
2064                  As  of  Linux  4.0  the  behavior has changed, so that 1 now
2065                  means only  allow  access  to  processes  with  active  perf
2066                  events, with 2 indicating the old allow-anyone-access behav‐
2067                  ior.
2068
2069           /sys/bus/event_source/devices/*/format/ (since Linux 3.4)
2070                  This subdirectory contains information on the  architecture-
2071                  specific  subfields  available  for  programming the various
2072                  config fields in the perf_event_attr struct.
2073
2074                  The content of each file is the name of  the  config  field,
2075                  followed  by  a  colon,  followed by a series of integer bit
2076                  ranges separated by commas.  For example, the file event may
2077                  contain  the  value  config1:1,6-10,44  which indicates that
2078                  event is an attribute that occupies bits 1,6–10, and  44  of
2079                  perf_event_attr::config1.
2080
2081           /sys/bus/event_source/devices/*/events/ (since Linux 3.4)
2082                  This  subdirectory  contains  files  with predefined events.
2083                  The contents  are  strings  describing  the  event  settings
2084                  expressed  in  terms  of  the fields found in the previously
2085                  mentioned ./format/ directory.  These  are  not  necessarily
2086                  complete lists of all events supported by a PMU, but usually
2087                  a subset of events deemed useful or interesting.
2088
2089                  The content of each file is a list of attribute names  sepa‐
2090                  rated  by  commas.  Each entry has an optional value (either
2091                  hex or decimal).  If no  value  is  specified,  then  it  is
2092                  assumed  to  be  a  single-bit  field with a value of 1.  An
2093                  example entry may look like this: event=0x2,inv,ldlat=3.
2094
2095           /sys/bus/event_source/devices/*/uevent
2096                  This file  is  the  standard  kernel  device  interface  for
2097                  injecting hotplug events.
2098
2099           /sys/bus/event_source/devices/*/cpumask (since Linux 3.7)
2100                  The cpumask file contains a comma-separated list of integers
2101                  that indicate a representative CPU number  for  each  socket
2102                  (package)  on  the motherboard.  This is needed when setting
2103                  up uncore or  northbridge  events,  as  those  PMUs  present
2104                  socket-wide events.
2105

RETURN VALUE

2107       perf_event_open()  returns  the  new file descriptor, or -1 if an error
2108       occurred (in which case, errno is set appropriately).
2109

ERRORS

2111       The errors returned by perf_event_open() can be inconsistent,  and  may
2112       vary across processor architectures and performance monitoring units.
2113
2114       E2BIG  Returned if the perf_event_attr size value is too small (smaller
2115              than PERF_ATTR_SIZE_VER0), too big (larger than the page  size),
2116              or  larger  than the kernel supports and the extra bytes are not
2117              zero.  When E2BIG is returned, the perf_event_attr size field is
2118              overwritten by the kernel to be the size of the structure it was
2119              expecting.
2120
2121       EACCES Returned when the requested event requires CAP_SYS_ADMIN permis‐
2122              sions  (or a more permissive perf_event paranoid setting).  Some
2123              common cases where an unprivileged process  may  encounter  this
2124              error:  attaching  to a process owned by a different user; moni‐
2125              toring all processes on a given CPU (i.e.,  specifying  the  pid
2126              argument  as  -1); and not setting exclude_kernel when the para‐
2127              noid setting requires it.
2128
2129       EBADF  Returned if the group_fd file descriptor is not  valid,  or,  if
2130              PERF_FLAG_PID_CGROUP  is  set, the cgroup file descriptor in pid
2131              is not valid.
2132
2133       EBUSY (since Linux 4.1)
2134              Returned if another event already has exclusive  access  to  the
2135              PMU.
2136
2137       EFAULT Returned  if  the  attr  pointer  points  at  an  invalid memory
2138              address.
2139
2140       EINVAL Returned if the specified event is invalid.  There are many pos‐
2141              sible  reasons  for this.  A not-exhaustive list: sample_freq is
2142              higher than the maximum setting; the cpu  to  monitor  does  not
2143              exist; read_format is out of range; sample_type is out of range;
2144              the flags value is out of range; exclusive or pinned set and the
2145              event  is not a group leader; the event config values are out of
2146              range or set reserved bits; the generic event  selected  is  not
2147              supported;  or  there  is  not  enough  room to add the selected
2148              event.
2149
2150       EMFILE Each opened event uses one file descriptor.  If a  large  number
2151              of  events  are  opened,  the per-process limit on the number of
2152              open file descriptors will be reached, and no more events can be
2153              created.
2154
2155       ENODEV Returned  when the event involves a feature not supported by the
2156              current CPU.
2157
2158       ENOENT Returned if the type setting is not valid.  This error  is  also
2159              returned for some unsupported generic events.
2160
2161       ENOSPC Prior  to Linux 3.3, if there was not enough room for the event,
2162              ENOSPC was returned.  In Linux 3.3, this was changed to  EINVAL.
2163              ENOSPC  is  still  returned  if  you  try to add more breakpoint
2164              events than supported by the hardware.
2165
2166       ENOSYS Returned if PERF_SAMPLE_STACK_USER is set in sample_type and  it
2167              is not supported by hardware.
2168
2169       EOPNOTSUPP
2170              Returned  if  an  event requiring a specific hardware feature is
2171              requested but there  is  no  hardware  support.   This  includes
2172              requesting  low-skid  events if not supported, branch tracing if
2173              it is not available, sampling if no PMU interrupt is  available,
2174              and branch stacks for software events.
2175
2176       EOVERFLOW (since Linux 4.8)
2177              Returned   if   PERF_SAMPLE_CALLCHAIN   is  requested  and  sam‐
2178              ple_max_stack  is  larger  than   the   maximum   specified   in
2179              /proc/sys/kernel/perf_event_max_stack.
2180
2181       EPERM  Returned on many (but not all) architectures when an unsupported
2182              exclude_hv, exclude_idle, exclude_user, or  exclude_kernel  set‐
2183              ting is specified.
2184
2185              It  can  also  happen,  as with EACCES, when the requested event
2186              requires  CAP_SYS_ADMIN  permissions  (or  a   more   permissive
2187              perf_event  paranoid  setting).   This includes setting a break‐
2188              point on a kernel address, and (since Linux 3.13) setting a ker‐
2189              nel function-trace tracepoint.
2190
2191       ESRCH  Returned  if  attempting  to  attach  to a process that does not
2192              exist.
2193

VERSION

2195       perf_event_open()  was  introduced  in  Linux  2.6.31  but  was  called
2196       perf_counter_open().  It was renamed in Linux 2.6.32.
2197

CONFORMING TO

2199       This  perf_event_open()  system  call  Linux-specific and should not be
2200       used in programs intended to be portable.
2201

NOTES

2203       Glibc does not provide a wrapper for this system call;  call  it  using
2204       syscall(2).  See the example below.
2205
2206       The  official way of knowing if perf_event_open() support is enabled is
2207       checking   for   the   existence    of    the    file    /proc/sys/ker‐
2208       nel/perf_event_paranoid.
2209

BUGS

2211       The  F_SETOWN_EX  option to fcntl(2) is needed to properly get overflow
2212       signals in threads.  This was introduced in Linux 2.6.32.
2213
2214       Prior to Linux 2.6.33 (at least for x86), the kernel did not  check  if
2215       events  could  be scheduled together until read time.  The same happens
2216       on all known kernels if the NMI watchdog is enabled.  This means to see
2217       if  a  given  set of events works you have to perf_event_open(), start,
2218       then read before you know for sure you can get valid measurements.
2219
2220       Prior to Linux 2.6.34, event constraints were not enforced by the  ker‐
2221       nel.  In that case, some events would silently return "0" if the kernel
2222       scheduled them in an improper counter slot.
2223
2224       Prior to Linux 2.6.34, there was a  bug  when  multiplexing  where  the
2225       wrong results could be returned.
2226
2227       Kernels  from Linux 2.6.35 to Linux 2.6.39 can quickly crash the kernel
2228       if "inherit" is enabled and many threads are started.
2229
2230       Prior to Linux 2.6.35, PERF_FORMAT_GROUP did  not  work  with  attached
2231       processes.
2232
2233       There  is  a  bug in the kernel code between Linux 2.6.36 and Linux 3.0
2234       that ignores the "watermark" field and acts as if  a  wakeup_event  was
2235       chosen if the union has a nonzero value in it.
2236
2237       From  Linux 2.6.31 to Linux 3.4, the PERF_IOC_FLAG_GROUP ioctl argument
2238       was broken and would repeatedly operate on the event  specified  rather
2239       than iterating across all sibling events in a group.
2240
2241       From  Linux  3.4 to Linux 3.11, the mmap cap_usr_rdpmc and cap_usr_time
2242       bits mapped to the same location.   Code  should  migrate  to  the  new
2243       cap_user_rdpmc and cap_user_time fields instead.
2244
2245       Always  double-check your results!  Various generalized events have had
2246       wrong values.  For example, retired branches measured the  wrong  thing
2247       on AMD machines until Linux 2.6.35.
2248

EXAMPLE

2250       The  following  is  a short example that measures the total instruction
2251       count of a call to printf(3).
2252
2253       #include <stdlib.h>
2254       #include <stdio.h>
2255       #include <unistd.h>
2256       #include <string.h>
2257       #include <sys/ioctl.h>
2258       #include <linux/perf_event.h>
2259       #include <asm/unistd.h>
2260
2261       static long
2262       perf_event_open(struct perf_event_attr *hw_event, pid_t pid,
2263                       int cpu, int group_fd, unsigned long flags)
2264       {
2265           int ret;
2266
2267           ret = syscall(__NR_perf_event_open, hw_event, pid, cpu,
2268                          group_fd, flags);
2269           return ret;
2270       }
2271
2272       int
2273       main(int argc, char **argv)
2274       {
2275           struct perf_event_attr pe;
2276           long long count;
2277           int fd;
2278
2279           memset(&pe, 0, sizeof(struct perf_event_attr));
2280           pe.type = PERF_TYPE_HARDWARE;
2281           pe.size = sizeof(struct perf_event_attr);
2282           pe.config = PERF_COUNT_HW_INSTRUCTIONS;
2283           pe.disabled = 1;
2284           pe.exclude_kernel = 1;
2285           pe.exclude_hv = 1;
2286
2287           fd = perf_event_open(&pe, 0, -1, -1, 0);
2288           if (fd == -1) {
2289              fprintf(stderr, "Error opening leader %llx\n", pe.config);
2290              exit(EXIT_FAILURE);
2291           }
2292
2293           ioctl(fd, PERF_EVENT_IOC_RESET, 0);
2294           ioctl(fd, PERF_EVENT_IOC_ENABLE, 0);
2295
2296           printf("Measuring instruction count for this printf\n");
2297
2298           ioctl(fd, PERF_EVENT_IOC_DISABLE, 0);
2299           read(fd, &count, sizeof(long long));
2300
2301           printf("Used %lld instructions\n", count);
2302
2303           close(fd);
2304       }
2305

SEE ALSO

2307       perf(1), fcntl(2), mmap(2), open(2), prctl(2), read(2)
2308
2309       Documentation/admin-guide/perf-security.rst in the kernel source tree
2310

COLOPHON

2312       This page is part of release 5.04 of the Linux  man-pages  project.   A
2313       description  of  the project, information about reporting bugs, and the
2314       latest    version    of    this    page,    can     be     found     at
2315       https://www.kernel.org/doc/man-pages/.
2316
2317
2318
2319Linux                             2019-10-10                PERF_EVENT_OPEN(2)
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