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man:perf_event_open

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

NAME

     perf_event_open - set up performance monitoring

SYNOPSIS

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

DESCRIPTION

     Given  a  list of parameters, perf_event_open() returns a file descrip-
     tor, for use in subsequent system calls  (read(2),  mmap(2),  prctl(2),
     fcntl(2), etc.).
     A  call to perf_event_open() creates a file descriptor that allows mea-
     suring performance information.  Each file  descriptor  corresponds  to
     one  event  that  is measured; these can be grouped together to measure
     multiple events simultaneously.
     Events can be enabled and disabled in two ways: via  ioctl(2)  and  via
     prctl(2).   When  an  event  is  disabled it does not count or generate
     overflows but does continue to exist and maintain its count value.
     Events come in two flavors: counting and sampled.  A counting event  is
     one  that  is  used  for  counting  the aggregate number of events that
     occur.  In general, counting event results are gathered with a  read(2)
     call.   A  sampling  event periodically writes measurements to a buffer
     that can then be accessed via mmap(2).
 Arguments
     The pid and cpu arguments allow specifying which  process  and  CPU  to
     monitor:
     pid == 0 and cpu == -1
            This measures the calling process/thread on any CPU.
     pid == 0 and cpu >= 0
            This  measures  the  calling process/thread only when running on
            the specified CPU.
     pid > 0 and cpu == -1
            This measures the specified process/thread on any CPU.
     pid > 0 and cpu >= 0
            This measures the specified process/thread only when running  on
            the specified CPU.
     pid == -1 and cpu >= 0
            This  measures all processes/threads on the specified CPU.  This
            requires   CAP_SYS_ADMIN   capability   or   a    /proc/sys/ker-
            nel/perf_event_paranoid value of less than 1.
     pid == -1 and cpu == -1
            This setting is invalid and will return an error.
     When  pid  is greater than zero, permission to perform this system call
     is governed by a ptrace access mode  PTRACE_MODE_READ_REALCREDS  check;
     see ptrace(2).
     The  group_fd  argument  allows  event  groups to be created.  An event
     group has one event which is the group leader.  The leader  is  created
     first,  with  group_fd = -1.  The rest of the group members are created
     with subsequent perf_event_open() calls with group_fd being set to  the
     file  descriptor  of  the  group leader.  (A single event on its own is
     created with group_fd = -1 and is considered to be a group with only  1
     member.)   An  event group is scheduled onto the CPU as a unit: it will
     be put onto the CPU only if all of the events in the group can  be  put
     onto  the  CPU.  This means that the values of the member events can be
     meaningfully compared--added, divided (to get ratios), and so  on--with
     each other, since they have counted events for the same set of executed
     instructions.
     The flags argument is formed by ORing together zero or more of the fol-
     lowing values:
     PERF_FLAG_FD_CLOEXEC (since Linux 3.14)
            This  flag  enables the close-on-exec flag for the created event
            file descriptor, so that the file  descriptor  is  automatically
            closed  on  execve(2).   Setting the close-on-exec flags at cre-
            ation time, rather than later with  fcntl(2),  avoids  potential
            race    conditions    where    the    calling   thread   invokes
            perf_event_open() and fcntl(2)  at  the  same  time  as  another
            thread calls fork(2) then execve(2).
     PERF_FLAG_FD_NO_GROUP
            This  flag  tells  the  event  to  ignore the group_fd parameter
            except for the purpose of setting up  output  redirection  using
            the PERF_FLAG_FD_OUTPUT flag.
     PERF_FLAG_FD_OUTPUT (broken since Linux 2.6.35)
            This  flag  re-routes  the  event's sampled output to instead be
            included in the mmap buffer of the event specified by  group_fd.
     PERF_FLAG_PID_CGROUP (since Linux 2.6.39)
            This  flag  activates  per-container  system-wide monitoring.  A
            container is an abstraction that isolates a set of resources for
            finer-grained  control  (CPUs, memory, etc.).  In this mode, the
            event is measured only if the thread running  on  the  monitored
            CPU belongs to the designated container (cgroup).  The cgroup is
            identified by passing a file descriptor opened on its  directory
            in the cgroupfs filesystem.  For instance, if the cgroup to mon-
            itor  is  called  test,  then  a  file  descriptor   opened   on
            /dev/cgroup/test  (assuming  cgroupfs is mounted on /dev/cgroup)
            must be passed as  the  pid  parameter.   cgroup  monitoring  is
            available  only for system-wide events and may therefore require
            extra permissions.
     The perf_event_attr structure provides detailed configuration  informa-
     tion for the event being created.
         struct perf_event_attr {
             __u32 type;                 /* Type of event */
             __u32 size;                 /* Size of attribute structure */
             __u64 config;               /* Type-specific configuration */
             union {
                 __u64 sample_period;    /* Period of sampling */
                 __u64 sample_freq;      /* Frequency of sampling */
             };
             __u64 sample_type;  /* Specifies values included in sample */
             __u64 read_format;  /* Specifies values returned in read */
             __u64 disabled       : 1,   /* off by default */
                   inherit        : 1,   /* children inherit it */
                   pinned         : 1,   /* must always be on PMU */
                   exclusive      : 1,   /* only group on PMU */
                   exclude_user   : 1,   /* don't count user */
                   exclude_kernel : 1,   /* don't count kernel */
                   exclude_hv     : 1,   /* don't count hypervisor */
                   exclude_idle   : 1,   /* don't count when idle */
                   mmap           : 1,   /* include mmap data */
                   comm           : 1,   /* include comm data */
                   freq           : 1,   /* use freq, not period */
                   inherit_stat   : 1,   /* per task counts */
                   enable_on_exec : 1,   /* next exec enables */
                   task           : 1,   /* trace fork/exit */
                   watermark      : 1,   /* wakeup_watermark */
                   precise_ip     : 2,   /* skid constraint */
                   mmap_data      : 1,   /* non-exec mmap data */
                   sample_id_all  : 1,   /* sample_type all events */
                   exclude_host   : 1,   /* don't count in host */
                   exclude_guest  : 1,   /* don't count in guest */
                   exclude_callchain_kernel : 1,
                                         /* exclude kernel callchains */
                   exclude_callchain_user   : 1,
                                         /* exclude user callchains */
                   mmap2          :  1,  /* include mmap with inode data */
                   comm_exec      :  1,  /* flag comm events that are
                                            due to exec */
                   use_clockid    :  1,  /* use clockid for time fields */
                   context_switch :  1,  /* context switch data */
                   __reserved_1   : 37;
             union {
                 __u32 wakeup_events;    /* wakeup every n events */
                 __u32 wakeup_watermark; /* bytes before wakeup */
             };
             __u32     bp_type;          /* breakpoint type */
             union {
                 __u64 bp_addr;          /* breakpoint address */
                 __u64 kprobe_func;      /* for perf_kprobe */
                 __u64 uprobe_path;      /* for perf_uprobe */
                 __u64 config1;          /* extension of config */
             };
             union {
                 __u64 bp_len;           /* breakpoint length */
                 __u64 kprobe_addr;      /* with kprobe_func == NULL */
                 __u64 probe_offset;     /* for perf_[k,u]probe */
                 __u64 config2;          /* extension of config1 */
             };
             __u64 branch_sample_type;   /* enum perf_branch_sample_type */
             __u64 sample_regs_user;     /* user regs to dump on samples */
             __u32 sample_stack_user;    /* size of stack to dump on
                                            samples */
             __s32 clockid;              /* clock to use for time fields */
             __u64 sample_regs_intr;     /* regs to dump on samples */
             __u32 aux_watermark;        /* aux bytes before wakeup */
             __u16 sample_max_stack;     /* max frames in callchain */
             __u16 __reserved_2;         /* align to u64 */
         };
     The  fields  of  the  perf_event_attr  structure  are described in more
     detail below:
     type   This field specifies the overall event type.  It has one of  the
            following values:
            PERF_TYPE_HARDWARE
                   This  indicates  one of the "generalized" hardware events
                   provided by the kernel.  See the config field  definition
                   for more details.
            PERF_TYPE_SOFTWARE
                   This  indicates  one  of the software-defined events pro-
                   vided by the kernel  (even  if  no  hardware  support  is
                   available).
            PERF_TYPE_TRACEPOINT
                   This indicates a tracepoint provided by the kernel trace-
                   point infrastructure.
            PERF_TYPE_HW_CACHE
                   This indicates a hardware cache event.  This has  a  spe-
                   cial  encoding, described in the config field definition.
            PERF_TYPE_RAW
                   This indicates a "raw" implementation-specific  event  in
                   the config field.
            PERF_TYPE_BREAKPOINT (since Linux 2.6.33)
                   This  indicates  a hardware breakpoint as provided by the
                   CPU.   Breakpoints  can  be  read/write  accesses  to  an
                   address as well as execution of an instruction address.
            dynamic PMU
                   Since  Linux 2.6.38, perf_event_open() can support multi-
                   ple PMUs.  To enable this, a value exported by the kernel
                   can  be  used  in the type field to indicate which PMU to
                   use.  The value to use can be found in the sysfs filesys-
                   tem:  there  is  a  subdirectory  per  PMU instance under
                   /sys/bus/event_source/devices.   In   each   subdirectory
                   there is a type file whose content is an integer that can
                   be   used   in   the   type   field.     For    instance,
                   /sys/bus/event_source/devices/cpu/type contains the value
                   for the core CPU PMU, which is usually 4.
            kprobe and uprobe (since Linux 4.17)
                   These two dynamic PMUs create a kprobe/uprobe and  attach
                   it  to  the file descriptor generated by perf_event_open.
                   The kprobe/uprobe will be destroyed on the destruction of
                   the    file    descriptor.    See   fields   kprobe_func,
                   uprobe_path,  kprobe_addr,  and  probe_offset  for   more
                   details.
     size   The  size  of the perf_event_attr structure for forward/backward
            compatibility.  Set this using sizeof(struct perf_event_attr) to
            allow  the kernel to see the struct size at the time of compila-
            tion.
            The related define PERF_ATTR_SIZE_VER0 is set to  64;  this  was
            the  size of the first published struct.  PERF_ATTR_SIZE_VER1 is
            72, corresponding  to  the  addition  of  breakpoints  in  Linux
            2.6.33.  PERF_ATTR_SIZE_VER2 is 80 corresponding to the addition
            of branch sampling in Linux 3.4.  PERF_ATTR_SIZE_VER3 is 96 cor-
            responding   to   the  addition  of  sample_regs_user  and  sam-
            ple_stack_user in Linux 3.7.  PERF_ATTR_SIZE_VER4 is 104  corre-
            sponding  to  the  addition  of  sample_regs_intr in Linux 3.19.
            PERF_ATTR_SIZE_VER5 is 112  corresponding  to  the  addition  of
            aux_watermark in Linux 4.1.
     config This  specifies  which  event  you want, in conjunction with the
            type field.  The config1 and config2 fields are also taken  into
            account  in  cases  where 64 bits is not enough to fully specify
            the event.  The encoding of these fields are event dependent.
            There are various ways to set the config field that  are  depen-
            dent  on the value of the previously described type field.  What
            follows are various possible settings for config  separated  out
            by type.
            If  type is PERF_TYPE_HARDWARE, we are measuring one of the gen-
            eralized hardware CPU events.  Not all of these are available on
            all platforms.  Set config to one of the following:
                 PERF_COUNT_HW_CPU_CYCLES
                        Total  cycles.   Be  wary of what happens during CPU
                        frequency scaling.
                 PERF_COUNT_HW_INSTRUCTIONS
                        Retired instructions.   Be  careful,  these  can  be
                        affected  by  various  issues, most notably hardware
                        interrupt counts.
                 PERF_COUNT_HW_CACHE_REFERENCES
                        Cache accesses.  Usually this indicates  Last  Level
                        Cache  accesses  but this may vary depending on your
                        CPU.  This may include prefetches and coherency mes-
                        sages; again this depends on the design of your CPU.
                 PERF_COUNT_HW_CACHE_MISSES
                        Cache misses.  Usually  this  indicates  Last  Level
                        Cache  misses;  this  is intended to be used in con-
                        junction  with  the   PERF_COUNT_HW_CACHE_REFERENCES
                        event to calculate cache miss rates.
                 PERF_COUNT_HW_BRANCH_INSTRUCTIONS
                        Retired branch instructions.  Prior to Linux 2.6.35,
                        this used the wrong event on AMD processors.
                 PERF_COUNT_HW_BRANCH_MISSES
                        Mispredicted branch instructions.
                 PERF_COUNT_HW_BUS_CYCLES
                        Bus  cycles,  which  can  be  different  from  total
                        cycles.
                 PERF_COUNT_HW_STALLED_CYCLES_FRONTEND (since Linux 3.0)
                        Stalled cycles during issue.
                 PERF_COUNT_HW_STALLED_CYCLES_BACKEND (since Linux 3.0)
                        Stalled cycles during retirement.
                 PERF_COUNT_HW_REF_CPU_CYCLES (since Linux 3.3)
                        Total cycles; not affected by CPU frequency scaling.
            If type is PERF_TYPE_SOFTWARE, we are measuring software  events
            provided by the kernel.  Set config to one of the following:
                 PERF_COUNT_SW_CPU_CLOCK
                        This  reports  the CPU clock, a high-resolution per-
                        CPU timer.
                 PERF_COUNT_SW_TASK_CLOCK
                        This reports a clock count specific to the task that
                        is running.
                 PERF_COUNT_SW_PAGE_FAULTS
                        This reports the number of page faults.
                 PERF_COUNT_SW_CONTEXT_SWITCHES
                        This  counts  context switches.  Until Linux 2.6.34,
                        these were all reported as user-space events,  after
                        that they are reported as happening in the kernel.
                 PERF_COUNT_SW_CPU_MIGRATIONS
                        This  reports  the  number  of times the process has
                        migrated to a new CPU.
                 PERF_COUNT_SW_PAGE_FAULTS_MIN
                        This counts the number of minor page faults.   These
                        did not require disk I/O to handle.
                 PERF_COUNT_SW_PAGE_FAULTS_MAJ
                        This  counts the number of major page faults.  These
                        required disk I/O to handle.
                 PERF_COUNT_SW_ALIGNMENT_FAULTS (since Linux 2.6.33)
                        This counts the number of alignment  faults.   These
                        happen  when  unaligned  memory accesses happen; the
                        kernel can handle these but it reduces  performance.
                        This  happens  only  on some architectures (never on
                        x86).
                 PERF_COUNT_SW_EMULATION_FAULTS (since Linux 2.6.33)
                        This counts the number  of  emulation  faults.   The
                        kernel sometimes traps on unimplemented instructions
                        and emulates them for user space.   This  can  nega-
                        tively impact performance.
                 PERF_COUNT_SW_DUMMY (since Linux 3.12)
                        This  is  a  placeholder  event that counts nothing.
                        Informational sample record types such  as  mmap  or
                        comm  must be associated with an active event.  This
                        dummy event allows gathering  such  records  without
                        requiring a counting event.
            If  type  is  PERF_TYPE_TRACEPOINT, then we are measuring kernel
            tracepoints.  The value to use in config can  be  obtained  from
            under  debugfs tracing/events/*/*/id if ftrace is enabled in the
            kernel.
            If type is PERF_TYPE_HW_CACHE, then we are measuring a  hardware
            CPU  cache event.  To calculate the appropriate config value use
            the following equation:
                    (perf_hw_cache_id) | (perf_hw_cache_op_id << 8) |
                    (perf_hw_cache_op_result_id << 16)
                where perf_hw_cache_id is one of:
                    PERF_COUNT_HW_CACHE_L1D
                           for measuring Level 1 Data Cache
                    PERF_COUNT_HW_CACHE_L1I
                           for measuring Level 1 Instruction Cache
                    PERF_COUNT_HW_CACHE_LL
                           for measuring Last-Level Cache
                    PERF_COUNT_HW_CACHE_DTLB
                           for measuring the Data TLB
                    PERF_COUNT_HW_CACHE_ITLB
                           for measuring the Instruction TLB
                    PERF_COUNT_HW_CACHE_BPU
                           for measuring the branch prediction unit
                    PERF_COUNT_HW_CACHE_NODE (since Linux 3.1)
                           for measuring local memory accesses
                and perf_hw_cache_op_id is one of:
                    PERF_COUNT_HW_CACHE_OP_READ
                           for read accesses
                    PERF_COUNT_HW_CACHE_OP_WRITE
                           for write accesses
                    PERF_COUNT_HW_CACHE_OP_PREFETCH
                           for prefetch accesses
                and perf_hw_cache_op_result_id is one of:
                    PERF_COUNT_HW_CACHE_RESULT_ACCESS
                           to measure accesses
                    PERF_COUNT_HW_CACHE_RESULT_MISS
                           to measure misses
            If type is PERF_TYPE_RAW, then a custom "raw"  config  value  is
            needed.   Most  CPUs  support events that are not covered by the
            "generalized" events.  These  are  implementation  defined;  see
            your  CPU  manual (for example the Intel Volume 3B documentation
            or the AMD  BIOS  and  Kernel  Developer  Guide).   The  libpfm4
            library  can be used to translate from the name in the architec-
            tural manuals to the raw hex value perf_event_open() expects  in
            this field.
            If  type is PERF_TYPE_BREAKPOINT, then leave config set to zero.
            Its parameters are set in other places.
            If type is kprobe or uprobe, set retprobe (bit 0 of config,  see
            /sys/bus/event_source/devices/[k,u]probe/format/retprobe)    for
            kretprobe/uretprobe.   See  fields   kprobe_func,   uprobe_path,
            kprobe_addr, and probe_offset for more details.
     kprobe_func, uprobe_path, kprobe_addr, and probe_offset
            These  fields describe the kprobe/uprobe for dynamic PMUs kprobe
            and uprobe.  For kprobe: use kprobe_func  and  probe_offset,  or
            use  kprobe_addr and leave kprobe_func as NULL.  For uprobe: use
            uprobe_path and probe_offset.
     sample_period, sample_freq
            A "sampling" event is one that generates an  overflow  notifica-
            tion  every N events, where N is given by sample_period.  A sam-
            pling event has sample_period > 0.   When  an  overflow  occurs,
            requested  data is recorded in the mmap buffer.  The sample_type
            field controls what data is recorded on each overflow.
            sample_freq can be used if you wish to use frequency rather than
            period.   In  this case, you set the freq flag.  The kernel will
            adjust the sampling period to try and achieve the desired  rate.
            The rate of adjustment is a timer tick.
     sample_type
            The  various  bits in this field specify which values to include
            in the sample.  They will be recorded in a ring-buffer, which is
            available  to  user space using mmap(2).  The order in which the
            values are saved in the sample are documented in the MMAP Layout
            subsection  below;  it  is not the enum perf_event_sample_format
            order.
            PERF_SAMPLE_IP
                   Records instruction pointer.
            PERF_SAMPLE_TID
                   Records the process and thread IDs.
            PERF_SAMPLE_TIME
                   Records a timestamp.
            PERF_SAMPLE_ADDR
                   Records an address, if applicable.
            PERF_SAMPLE_READ
                   Record counter values for all events in a group, not just
                   the group leader.
            PERF_SAMPLE_CALLCHAIN
                   Records the callchain (stack backtrace).
            PERF_SAMPLE_ID
                   Records  a unique ID for the opened event's group leader.
            PERF_SAMPLE_CPU
                   Records CPU number.
            PERF_SAMPLE_PERIOD
                   Records the current sampling period.
            PERF_SAMPLE_STREAM_ID
                   Records  a  unique  ID  for  the  opened  event.   Unlike
                   PERF_SAMPLE_ID  the  actual ID is returned, not the group
                   leader.  This ID is the  same  as  the  one  returned  by
                   PERF_FORMAT_ID.
            PERF_SAMPLE_RAW
                   Records additional data, if applicable.  Usually returned
                   by tracepoint events.
            PERF_SAMPLE_BRANCH_STACK (since Linux 3.4)
                   This provides a record of recent branches, as provided by
                   CPU  branch  sampling hardware (such as Intel Last Branch
                   Record).  Not all hardware supports this feature.
                   See the branch_sample_type field for how to filter  which
                   branches are reported.
            PERF_SAMPLE_REGS_USER (since Linux 3.7)
                   Records  the  current  user-level CPU register state (the
                   values in the process before the kernel was called).
            PERF_SAMPLE_STACK_USER (since Linux 3.7)
                   Records the user level stack, allowing stack unwinding.
            PERF_SAMPLE_WEIGHT (since Linux 3.10)
                   Records a hardware provided weight value  that  expresses
                   how  costly the sampled event was.  This allows the hard-
                   ware to highlight expensive events in a profile.
            PERF_SAMPLE_DATA_SRC (since Linux 3.10)
                   Records the data source: where in  the  memory  hierarchy
                   the  data  associated  with  the sampled instruction came
                   from.  This is available only if the underlying  hardware
                   supports this feature.
            PERF_SAMPLE_IDENTIFIER (since Linux 3.12)
                   Places  the  SAMPLE_ID  value  in a fixed position in the
                   record, either at the beginning (for sample events) or at
                   the end (if a non-sample event).
                   This  was  necessary  because  a  sample  stream may have
                   records from various different event sources with differ-
                   ent sample_type settings.  Parsing the event stream prop-
                   erly was not possible because the format  of  the  record
                   was needed to find SAMPLE_ID, but the format could not be
                   found without knowing what event the sample  belonged  to
                   (causing a circular dependency).
                   The PERF_SAMPLE_IDENTIFIER setting makes the event stream
                   always parsable by putting SAMPLE_ID in a fixed location,
                   even though it means having duplicate SAMPLE_ID values in
                   records.
            PERF_SAMPLE_TRANSACTION (since Linux 3.13)
                   Records reasons for  transactional  memory  abort  events
                   (for  example,  from  Intel TSX transactional memory sup-
                   port).
                   The precise_ip setting must  be  greater  than  0  and  a
                   transactional  memory  abort event must be measured or no
                   values will be recorded.  Also note that some  perf_event
                   measurements,  such  as sampled cycle counting, may cause
                   extraneous aborts  (by  causing  an  interrupt  during  a
                   transaction).
            PERF_SAMPLE_REGS_INTR (since Linux 3.19)
                   Records  a  subset  of  the current CPU register state as
                   specified   by   sample_regs_intr.    Unlike    PERF_SAM-
                   PLE_REGS_USER the register values will return kernel reg-
                   ister state if the overflow happened while kernel code is
                   running.  If the CPU supports hardware sampling of regis-
                   ter state (i.e., PEBS on Intel x86) and precise_ip is set
                   higher  than  zero  then the register values returned are
                   those captured by hardware at the  time  of  the  sampled
                   instruction's retirement.
     read_format
            This  field specifies the format of the data returned by read(2)
            on a perf_event_open() file descriptor.
            PERF_FORMAT_TOTAL_TIME_ENABLED
                   Adds the 64-bit time_enabled field.  This can be used  to
                   calculate  estimated  totals  if the PMU is overcommitted
                   and multiplexing is happening.
            PERF_FORMAT_TOTAL_TIME_RUNNING
                   Adds the 64-bit time_running field.  This can be used  to
                   calculate  estimated  totals  if the PMU is overcommitted
                   and multiplexing is happening.
            PERF_FORMAT_ID
                   Adds a 64-bit unique value that corresponds to the  event
                   group.
            PERF_FORMAT_GROUP
                   Allows  all  counter  values in an event group to be read
                   with one read.
     disabled
            The disabled bit specifies whether the counter starts  out  dis-
            abled  or  enabled.  If disabled, the event can later be enabled
            by ioctl(2), prctl(2), or enable_on_exec.
            When creating an event group, typically the group leader is ini-
            tialized  with  disabled  set to 1 and any child events are ini-
            tialized with disabled set to 0.  Despite disabled being 0,  the
            child events will not start until the group leader is enabled.
     inherit
            The  inherit bit specifies that this counter should count events
            of child tasks as well as the task specified.  This applies only
            to  new  children,  not to any existing children at the time the
            counter is created (nor to any new children  of  existing  chil-
            dren).
            Inherit  does not work for some combinations of read_format val-
            ues, such as PERF_FORMAT_GROUP.
     pinned The pinned bit specifies that the counter should  always  be  on
            the  CPU  if at all possible.  It applies only to hardware coun-
            ters and only to group leaders.  If a pinned counter  cannot  be
            put  onto  the  CPU (e.g., because there are not enough hardware
            counters or because of a conflict with some other  event),  then
            the  counter goes into an 'error' state, where reads return end-
            of-file (i.e., read(2) returns 0) until the  counter  is  subse-
            quently enabled or disabled.
     exclusive
            The exclusive bit specifies that when this counter's group is on
            the CPU, it should be the only group using the  CPU's  counters.
            In  the future this may allow monitoring programs to support PMU
            features that need to run alone so  that  they  do  not  disrupt
            other hardware counters.
            Note that many unexpected situations may prevent events with the
            exclusive bit set from ever running.  This  includes  any  users
            running  a  system-wide measurement as well as any kernel use of
            the performance counters (including  the  commonly  enabled  NMI
            Watchdog Timer interface).
     exclude_user
            If  this  bit  is  set, the count excludes events that happen in
            user space.
     exclude_kernel
            If this bit is set, the count excludes  events  that  happen  in
            kernel space.
     exclude_hv
            If this bit is set, the count excludes events that happen in the
            hypervisor.  This is mainly for PMUs that have built-in  support
            for  handling this (such as POWER).  Extra support is needed for
            handling hypervisor measurements on most machines.
     exclude_idle
            If set, don't count when the CPU is idle.
     mmap   The mmap bit enables generation of PERF_RECORD_MMAP samples  for
            every mmap(2) call that has PROT_EXEC set.  This allows tools to
            notice new executable code being mapped into a program  (dynamic
            shared  libraries  for  example) so that addresses can be mapped
            back to the original code.
     comm   The comm bit enables tracking of process command name  as  modi-
            fied  by the exec(2) and prctl(PR_SET_NAME) system calls as well
            as writing to /proc/self/comm.  If the comm_exec  flag  is  also
            successfully set (possible since Linux 3.16), then the misc flag
            PERF_RECORD_MISC_COMM_EXEC can  be  used  to  differentiate  the
            exec(2) case from the others.
     freq   If  this  bit is set, then sample_frequency not sample_period is
            used when setting up the sampling interval.
     inherit_stat
            This bit enables saving of event counts on  context  switch  for
            inherited  tasks.   This is meaningful only if the inherit field
            is set.
     enable_on_exec
            If this bit is set, a counter is automatically enabled  after  a
            call to exec(2).
     task   If this bit is set, then fork/exit notifications are included in
            the ring buffer.
     watermark
            If set, have an overflow notification happen when we  cross  the
            wakeup_watermark  boundary.   Otherwise,  overflow notifications
            happen after wakeup_events samples.
     precise_ip (since Linux 2.6.35)
            This controls the amount of skid.  Skid is how many instructions
            execute  between  an  event of interest happening and the kernel
            being able to stop and record the event.  Smaller skid is better
            and allows more accurate reporting of which events correspond to
            which instructions, but hardware is often limited with how small
            this can be.
            The possible values of this field are the following:
            0  SAMPLE_IP can have arbitrary skid.
            1  SAMPLE_IP must have constant skid.
            2  SAMPLE_IP requested to have 0 skid.
            3  SAMPLE_IP  must  have  0  skid.   See also the description of
               PERF_RECORD_MISC_EXACT_IP.
     mmap_data (since Linux 2.6.36)
            This is the counterpart of the mmap field.  This enables genera-
            tion  of  PERF_RECORD_MMAP samples for mmap(2) calls that do not
            have PROT_EXEC set (for example data and SysV shared memory).
     sample_id_all (since Linux 2.6.38)
            If set, then TID, TIME, ID, STREAM_ID, and CPU can  additionally
            be included in non-PERF_RECORD_SAMPLEs if the corresponding sam-
            ple_type is selected.
            If PERF_SAMPLE_IDENTIFIER is specified, then  an  additional  ID
            value  is  included as the last value to ease parsing the record
            stream.  This may lead to the id value appearing twice.
            The layout is described by this pseudo-structure:
                struct sample_id {
                    { u32 pid, tid; }   /* if PERF_SAMPLE_TID set */
                    { u64 time;     }   /* if PERF_SAMPLE_TIME set */
                    { u64 id;       }   /* if PERF_SAMPLE_ID set */
                    { u64 stream_id;}   /* if PERF_SAMPLE_STREAM_ID set  */
                    { u32 cpu, res; }   /* if PERF_SAMPLE_CPU set */
                    { u64 id;       }   /* if PERF_SAMPLE_IDENTIFIER set  */
                }; ,in
     exclude_host (since Linux 3.2)
            When  conducting  measurements that include processes running VM
            instances (i.e., have executed a KVM_RUN ioctl(2)), only measure
            events happening inside a guest instance.  This is only meaning-
            ful outside the guests; this  setting  does  not  change  counts
            gathered  inside  of  a guest.  Currently, this functionality is
            x86 only.
     exclude_guest (since Linux 3.2)
            When conducting measurements that include processes  running  VM
            instances  (i.e., have executed a KVM_RUN ioctl(2)), do not mea-
            sure events happening inside  guest  instances.   This  is  only
            meaningful  outside  the  guests;  this  setting does not change
            counts gathered inside of a guest.  Currently, this  functional-
            ity is x86 only.
     exclude_callchain_kernel (since Linux 3.7)
            Do not include kernel callchains.
     exclude_callchain_user (since Linux 3.7)
            Do not include user callchains.
     mmap2 (since Linux 3.16)
            Generate an extended executable mmap record that contains enough
            additional information to  uniquely  identify  shared  mappings.
            The mmap flag must also be set for this to work.
     comm_exec (since Linux 3.16)
            This is purely a feature-detection flag, it does not change ker-
            nel behavior.  If this flag can successfully be set, then,  when
            comm is enabled, the PERF_RECORD_MISC_COMM_EXEC flag will be set
            in the misc field of a comm record header if  the  rename  event
            being  reported  was  caused  by a call to exec(2).  This allows
            tools to distinguish between the various types of process renam-
            ing.
     use_clockid (since Linux 4.1)
            This  allows  selecting  which  internal Linux clock to use when
            generating timestamps via the clockid field.  This can  make  it
            easier  to correlate perf sample times with timestamps generated
            by other tools.
     context_switch (since Linux 4.3)
            This enables the generation of PERF_RECORD_SWITCH records when a
            context  switch  occurs.   It  also  enables  the  generation of
            PERF_RECORD_SWITCH_CPU_WIDE records when  sampling  in  CPU-wide
            mode.   This functionality is in addition to existing tracepoint
            and software events for measuring context switches.  The  advan-
            tage  of  this method is that it will give full information even
            with strict perf_event_paranoid settings.
     wakeup_events, wakeup_watermark
            This union  sets  how  many  samples  (wakeup_events)  or  bytes
            (wakeup_watermark)  happen  before an overflow notification hap-
            pens.  Which one is used is selected by the watermark bit  flag.
            wakeup_events  counts  only PERF_RECORD_SAMPLE record types.  To
            receive overflow notification for all PERF_RECORD  types  choose
            watermark and set wakeup_watermark to 1.
            Prior  to  Linux  3.0, setting wakeup_events to 0 resulted in no
            overflow notifications; more recent kernels treat 0 the same  as
            1.
     bp_type (since Linux 2.6.33)
            This chooses the breakpoint type.  It is one of:
            HW_BREAKPOINT_EMPTY
                   No breakpoint.
            HW_BREAKPOINT_R
                   Count when we read the memory location.
            HW_BREAKPOINT_W
                   Count when we write the memory location.
            HW_BREAKPOINT_RW
                   Count when we read or write the memory location.
            HW_BREAKPOINT_X
                   Count when we execute code at the memory location.
            The values can be combined via a bitwise or, but the combination
            of HW_BREAKPOINT_R or HW_BREAKPOINT_W  with  HW_BREAKPOINT_X  is
            not allowed.
     bp_addr (since Linux 2.6.33)
            This  is  the  address  of the breakpoint.  For execution break-
            points, this is the memory address of the instruction of  inter-
            est; for read and write breakpoints, it is the memory address of
            the memory location of interest.
     config1 (since Linux 2.6.39)
            config1 is used for setting events that need an  extra  register
            or  otherwise  do not fit in the regular config field.  Raw OFF-
            CORE_EVENTS on Nehalem/Westmere/SandyBridge use  this  field  on
            Linux 3.3 and later kernels.
     bp_len (since Linux 2.6.33)
            bp_len is the length of the breakpoint being measured if type is
            PERF_TYPE_BREAKPOINT.     Options    are    HW_BREAKPOINT_LEN_1,
            HW_BREAKPOINT_LEN_2,    HW_BREAKPOINT_LEN_4,    and    HW_BREAK-
            POINT_LEN_8.   For  an  execution  breakpoint,   set   this   to
            sizeof(long).
     config2 (since Linux 2.6.39)
            config2 is a further extension of the config1 field.
     branch_sample_type (since Linux 3.4)
            If PERF_SAMPLE_BRANCH_STACK is enabled, then this specifies what
            branches to include in the branch record.
            The first part of the value is the privilege level, which  is  a
            combination of one of the values listed below.  If the user does
            not set privilege level explicitly,  the  kernel  will  use  the
            event's  privilege  level.  Event and branch privilege levels do
            not have to match.
            PERF_SAMPLE_BRANCH_USER
                   Branch target is in user space.
            PERF_SAMPLE_BRANCH_KERNEL
                   Branch target is in kernel space.
            PERF_SAMPLE_BRANCH_HV
                   Branch target is in hypervisor.
            PERF_SAMPLE_BRANCH_PLM_ALL
                   A convenience value that is the  three  preceding  values
                   ORed together.
            In  addition to the privilege value, at least one or more of the
            following bits must be set.
            PERF_SAMPLE_BRANCH_ANY
                   Any branch type.
            PERF_SAMPLE_BRANCH_ANY_CALL
                   Any call branch (includes direct calls,  indirect  calls,
                   and far jumps).
            PERF_SAMPLE_BRANCH_IND_CALL
                   Indirect calls.
            PERF_SAMPLE_BRANCH_CALL (since Linux 4.4)
                   Direct calls.
            PERF_SAMPLE_BRANCH_ANY_RETURN
                   Any return branch.
            PERF_SAMPLE_BRANCH_IND_JUMP (since Linux 4.2)
                   Indirect jumps.
            PERF_SAMPLE_BRANCH_COND (since Linux 3.16)
                   Conditional branches.
            PERF_SAMPLE_BRANCH_ABORT_TX (since Linux 3.11)
                   Transactional memory aborts.
            PERF_SAMPLE_BRANCH_IN_TX (since Linux 3.11)
                   Branch in transactional memory transaction.
            PERF_SAMPLE_BRANCH_NO_TX (since Linux 3.11)
                   Branch   not   in   transactional   memory   transaction.
                   PERF_SAMPLE_BRANCH_CALL_STACK (since Linux 4.1) Branch is
                   part  of  a hardware-generated call stack.  This requires
                   hardware support,  currently  only  found  on  Intel  x86
                   Haswell or newer.
     sample_regs_user (since Linux 3.7)
            This  bit  mask defines the set of user CPU registers to dump on
            samples.  The layout of the register mask  is  architecture-spe-
            cific   and   is   described   in   the   kernel   header   file
            arch/ARCH/include/uapi/asm/perf_regs.h.
     sample_stack_user (since Linux 3.7)
            This defines the size of the user stack  to  dump  if  PERF_SAM-
            PLE_STACK_USER is specified.
     clockid (since Linux 4.1)
            If  use_clockid  is  set, then this field selects which internal
            Linux timer to use for timestamps.   The  available  timers  are
            defined   in  linux/time.h,  with  CLOCK_MONOTONIC,  CLOCK_MONO-
            TONIC_RAW, CLOCK_REALTIME, CLOCK_BOOTTIME,  and  CLOCK_TAI  cur-
            rently supported.
     aux_watermark (since Linux 4.1)
            This   specifies   how  much  data  is  required  to  trigger  a
            PERF_RECORD_AUX sample.
     sample_max_stack (since Linux 4.8)
            When  sample_type  includes  PERF_SAMPLE_CALLCHAIN,  this  field
            specifies  how  many  stack frames to report when generating the
            callchain.
 Reading results
     Once a perf_event_open() file descriptor has been opened, the values of
     the  events  can be read from the file descriptor.  The values that are
     there are specified by the read_format field in the attr  structure  at
     open time.
     If you attempt to read into a buffer that is not big enough to hold the
     data, the error ENOSPC results.
     Here is the layout of the data returned by a read:
  • If PERF_FORMAT_GROUP was specified to allow reading all events in a

group at once:

           struct read_format {
               u64 nr;            /* The number of events */
               u64 time_enabled;  /* if PERF_FORMAT_TOTAL_TIME_ENABLED */
               u64 time_running;  /* if PERF_FORMAT_TOTAL_TIME_RUNNING */
               struct {
                   u64 value;     /* The value of the event */
                   u64 id;        /* if PERF_FORMAT_ID */
               } values[nr]; };
  • If PERF_FORMAT_GROUP was not specified:
           struct read_format {
               u64 value;         /* The value of the event */
               u64 time_enabled;  /* if PERF_FORMAT_TOTAL_TIME_ENABLED */
               u64 time_running;  /* if PERF_FORMAT_TOTAL_TIME_RUNNING */
               u64 id;            /* if PERF_FORMAT_ID */ };
     The values read are as follows:
     nr     The number of events in this file descriptor.  Available only if
            PERF_FORMAT_GROUP was specified.
     time_enabled, time_running
            Total time the event was enabled and  running.   Normally  these
            values are the same.  If more events are started, then available
            counter slots on the PMU, then multiplexing happens  and  events
            run  only  part of the time.  In that case, the time_enabled and
            time running values can be used to scale an estimated value  for
            the count.
     value  An unsigned 64-bit value containing the counter result.
     id     A  globally unique value for this particular event; only present
            if PERF_FORMAT_ID was specified in read_format.
 MMAP layout
     When using perf_event_open() in sampled mode, asynchronous events (like
     counter  overflow  or  PROT_EXEC mmap tracking) are logged into a ring-
     buffer.  This ring-buffer is created and accessed through mmap(2).
     The mmap size should be 1+2^n pages, where the first page is a metadata
     page (struct perf_event_mmap_page) that contains various bits of infor-
     mation such as where the ring-buffer head is.
     Before kernel 2.6.39, there is a bug that means you  must  allocate  an
     mmap ring buffer when sampling even if you do not plan to access it.
     The structure of the first metadata mmap page is as follows:
         struct perf_event_mmap_page {
             __u32 version;        /* version number of this structure */
             __u32 compat_version; /* lowest version this is compat with */
             __u32 lock;           /* seqlock for synchronization */
             __u32 index;          /* hardware counter identifier */
             __s64 offset;         /* add to hardware counter value */
             __u64 time_enabled;   /* time event active */
             __u64 time_running;   /* time event on CPU */
             union {
                 __u64   capabilities;
                 struct {
                     __u64 cap_usr_time / cap_usr_rdpmc / cap_bit0 : 1,
                           cap_bit0_is_deprecated : 1,
                           cap_user_rdpmc         : 1,
                           cap_user_time          : 1,
                           cap_user_time_zero     : 1,
                 };
             };
             __u16 pmc_width;
             __u16 time_shift;
             __u32 time_mult;
             __u64 time_offset;
             __u64 __reserved[120];   /* Pad to 1 k */
             __u64 data_head;         /* head in the data section */
             __u64 data_tail;         /* user-space written tail */
             __u64 data_offset;       /* where the buffer starts */
             __u64 data_size;         /* data buffer size */
             __u64 aux_head;
             __u64 aux_tail;
             __u64 aux_offset;
             __u64 aux_size;
         }
     The  following  list  describes  the fields in the perf_event_mmap_page
     structure in more detail:
     version
            Version number of this structure.
     compat_version
            The lowest version this is compatible with.
     lock   A seqlock for synchronization.
     index  A unique hardware counter identifier.
     offset When using rdpmc for reads this offset value must  be  added  to
            the  one returned by rdpmc to get the current total event count.
     time_enabled
            Time the event was active.
     time_running
            Time the event was running.
     cap_usr_time / cap_usr_rdpmc / cap_bit0 (since Linux 3.4)
            There  was  a  bug  in  the  definition  of   cap_usr_time   and
            cap_usr_rdpmc  from  Linux 3.4 until Linux 3.11.  Both bits were
            defined to point to the same location, so it was  impossible  to
            know if cap_usr_time or cap_usr_rdpmc were actually set.
            Starting  with Linux 3.12, these are renamed to cap_bit0 and you
            should use the cap_user_time and cap_user_rdpmc fields  instead.
     cap_bit0_is_deprecated (since Linux 3.12)
            If set, this bit indicates that the kernel supports the properly
            separated cap_user_time and cap_user_rdpmc bits.
            If not-set, it indicates an older kernel where cap_usr_time  and
            cap_usr_rdpmc  map to the same bit and thus both features should
            be used with caution.
     cap_user_rdpmc (since Linux 3.12)
            If the hardware supports user-space read of performance counters
            without  syscall  (this is the "rdpmc" instruction on x86), then
            the following code can be used to do a read:
                u32 seq,  time_mult,  time_shift,  idx,  width;  u64  count,
                enabled, running; u64 cyc, time_offset;
                do {
                    seq = pc->lock;
                    barrier();
                    enabled = pc->time_enabled;
                    running = pc->time_running;
                    if (pc->cap_usr_time && enabled != running) {
                        cyc = rdtsc();
                        time_offset = pc->time_offset;
                        time_mult   = pc->time_mult;
                        time_shift  = pc->time_shift;
                    }
                    idx = pc->index;
                    count = pc->offset;
                    if (pc->cap_usr_rdpmc && idx) {
                        width = pc->pmc_width;
                        count += rdpmc(idx - 1);
                    }
                    barrier(); } while (pc->lock != seq);
     cap_user_time (since Linux 3.12)
            This  bit  indicates  the hardware has a constant, nonstop time-
            stamp counter (TSC on x86).
     cap_user_time_zero (since Linux 3.12)
            Indicates the presence of time_zero which allows  mapping  time-
            stamp values to the hardware clock.
     pmc_width
            If cap_usr_rdpmc, this field provides the bit-width of the value
            read using the rdpmc or equivalent  instruction.   This  can  be
            used to sign extend the result like:
                pmc  <<=  64  - pmc_width; pmc >>= 64 - pmc_width; // signed
                shift right count += pmc;
     time_shift, time_mult, time_offset
            If cap_usr_time, these fields can be used to  compute  the  time
            delta  since  time_enabled (in nanoseconds) using rdtsc or simi-
            lar.
                u64 quot, rem;
                u64 delta;
                quot = (cyc >> time_shift);
                rem = cyc & (((u64)1 << time_shift) - 1);
                delta = time_offset + quot * time_mult +
                        ((rem * time_mult) >> time_shift);
            Where time_offset, time_mult, time_shift, and cyc  are  read  in
            the seqcount loop described above.  This delta can then be added
            to enabled and possible running (if idx), improving the scaling:
                enabled += delta;
                if (idx)
                    running += delta;
                quot = count / running;
                rem  = count % running;
                count = quot * enabled + (rem * enabled) / running;
     time_zero (since Linux 3.12)
            If  cap_usr_time_zero  is  set, then the hardware clock (the TSC
            timestamp counter on x86) can be calculated from the  time_zero,
            time_mult, and time_shift values:
                time = timestamp - time_zero;
                quot = time / time_mult;
                rem  = time % time_mult;
                cyc = (quot << time_shift) + (rem << time_shift) / time_mult;
            And vice versa:
                quot = cyc >> time_shift;
                rem  = cyc & (((u64)1 << time_shift) - 1);
                timestamp = time_zero + quot * time_mult +
                    ((rem * time_mult) >> time_shift);
     data_head
            This points to the head of the data section.  The value continu-
            ously increases, it does not wrap.  The value needs to be  manu-
            ally wrapped by the size of the mmap buffer before accessing the
            samples.
            On SMP-capable platforms, after  reading  the  data_head  value,
            user space should issue an rmb().
     data_tail
            When  the  mapping  is PROT_WRITE, the data_tail value should be
            written by user space to reflect the last read  data.   In  this
            case, the kernel will not overwrite unread data.
     data_offset (since Linux 4.1)
            Contains  the  offset  of  the location in the mmap buffer where
            perf sample data begins.
     data_size (since Linux 4.1)
            Contains the size of the perf  sample  region  within  the  mmap
            buffer.
     aux_head, aux_tail, aux_offset, aux_size (since Linux 4.1)
            The AUX region allows mmaping a separate sample buffer for high-
            bandwidth data streams  (separate  from  the  main  perf  sample
            buffer).   An  example of a high-bandwidth stream is instruction
            tracing support, as is found in newer Intel processors.
            To set up an AUX area, first aux_offset needs to be set with  an
            offset  greater than data_offset+data_size and aux_size needs to
            be set to the desired buffer size.  The desired offset and  size
            must  be  page  aligned,  and  the  size must be a power of two.
            These values are then passed to mmap in order  to  map  the  AUX
            buffer.   Pages  in  the  AUX buffer are included as part of the
            RLIMIT_MEMLOCK resource limit (see setrlimit(2)),  and  also  as
            part of the perf_event_mlock_kb allowance.
            By  default, the AUX buffer will be truncated if it will not fit
            in the available space in the ring buffer.  If the AUX buffer is
            mapped  as  a  read  only  buffer,  then it will operate in ring
            buffer mode where old data will be overwritten by new.  In over-
            write mode, it might not be possible to infer where the new data
            began, and it is the consumer's job to disable measurement while
            reading to avoid possible data races.
            The  aux_head  and  aux_tail  ring buffer pointers have the same
            behavior and ordering rules as the previous described  data_head
            and data_tail.
     The following 2^n ring-buffer pages have the layout described below.
     If perf_event_attr.sample_id_all is set, then all event types will have
     the sample_type selected fields related  to  where/when  (identity)  an
     event   took  place  (TID,  TIME,  ID,  CPU,  STREAM_ID)  described  in
     PERF_RECORD_SAMPLE  below,  it  will  be   stashed   just   after   the
     perf_event_header  and  the  fields  already  present  for the existing
     fields, that is, at the end  of  the  payload.   This  allows  a  newer
     perf.data  file  to  be  supported  by  older  perf tools, with the new
     optional fields being ignored.
     The mmap values start with a header:
         struct perf_event_header {
             __u32   type;
             __u16   misc;
             __u16   size; };
     Below, we describe the perf_event_header fields in  more  detail.   For
     ease  of  reading,  the  fields with shorter descriptions are presented
     first.
     size   This indicates the size of the record.
     misc   The misc field contains additional information about the sample.
            The  CPU  mode can be determined from this value by masking with
            PERF_RECORD_MISC_CPUMODE_MASK and looking for one of the follow-
            ing  (note  these  are  not  bit masks, only one can be set at a
            time):
            PERF_RECORD_MISC_CPUMODE_UNKNOWN
                   Unknown CPU mode.
            PERF_RECORD_MISC_KERNEL
                   Sample happened in the kernel.
            PERF_RECORD_MISC_USER
                   Sample happened in user code.
            PERF_RECORD_MISC_HYPERVISOR
                   Sample happened in the hypervisor.
            PERF_RECORD_MISC_GUEST_KERNEL (since Linux 2.6.35)
                   Sample happened in the guest kernel.
            PERF_RECORD_MISC_GUEST_USER  (since Linux 2.6.35)
                   Sample happened in guest user code.
            Since the following three statuses are  generated  by  different
            record types, they alias to the same bit:
            PERF_RECORD_MISC_MMAP_DATA (since Linux 3.10)
                   This is set when the mapping is not executable; otherwise
                   the mapping is executable.
            PERF_RECORD_MISC_COMM_EXEC (since Linux 3.16)
                   This is set for a PERF_RECORD_COMM record on kernels more
                   recent  than  Linux  3.16  if  a  process name change was
                   caused by an exec(2) system call.
            PERF_RECORD_MISC_SWITCH_OUT (since Linux 4.3)
                   When a PERF_RECORD_SWITCH or  PERF_RECORD_SWITCH_CPU_WIDE
                   record  is generated, this bit indicates that the context
                   switch is away from the current process (instead of  into
                   the current process).
            In addition, the following bits can be set:
            PERF_RECORD_MISC_EXACT_IP
                   This  indicates that the content of PERF_SAMPLE_IP points
                   to the actual instruction that triggered the event.   See
                   also perf_event_attr.precise_ip.
            PERF_RECORD_MISC_EXT_RESERVED (since Linux 2.6.35)
                   This  indicates  there  is  extended data available (cur-
                   rently not used).
            PERF_RECORD_MISC_PROC_MAP_PARSE_TIMEOUT
                   This bit is not set by the kernel.  It  is  reserved  for
                   the    user-space   perf   utility   to   indicate   that
                   /proc/i[pid]/maps parsing was taking  too  long  and  was
                   stopped, and thus the mmap records may be truncated.
     type   The  type  value  is one of the below.  The values in the corre-
            sponding record (that follows the header)  depend  on  the  type
            selected as shown.
            PERF_RECORD_MMAP
                The MMAP events record the PROT_EXEC mappings so that we can
                correlate user-space IPs to code.  They have  the  following
                structure:
                    struct {
                        struct perf_event_header header;
                        u32    pid, tid;
                        u64    addr;
                        u64    len;
                        u64    pgoff;
                        char   filename[]; };
                pid    is the process ID.
                tid    is the thread ID.
                addr   is  the  address of the allocated memory.  len is the
                       length of the allocated memory.  pgoff  is  the  page
                       offset of the allocated memory.  filename is a string
                       describing the backing of the allocated memory.
            PERF_RECORD_LOST
                This record indicates when events are lost.
                    struct {
                        struct perf_event_header header;
                        u64    id;
                        u64    lost;
                        struct sample_id sample_id; };
                id     is the unique event ID  for  the  samples  that  were
                       lost.
                lost   is the number of events that were lost.
            PERF_RECORD_COMM
                This record indicates a change in the process name.
                    struct {
                        struct perf_event_header header;
                        u32    pid;
                        u32    tid;
                        char   comm[];
                        struct sample_id sample_id; };
                pid    is the process ID.
                tid    is the thread ID.
                comm   is a string containing the new name of the process.
            PERF_RECORD_EXIT
                This record indicates a process exit event.
                    struct {
                        struct perf_event_header header;
                        u32    pid, ppid;
                        u32    tid, ptid;
                        u64    time;
                        struct sample_id sample_id; };
            PERF_RECORD_THROTTLE, PERF_RECORD_UNTHROTTLE
                This record indicates a throttle/unthrottle event.
                    struct {
                        struct perf_event_header header;
                        u64    time;
                        u64    id;
                        u64    stream_id;
                        struct sample_id sample_id; };
            PERF_RECORD_FORK
                This record indicates a fork event.
                    struct {
                        struct perf_event_header header;
                        u32    pid, ppid;
                        u32    tid, ptid;
                        u64    time;
                        struct sample_id sample_id; };
            PERF_RECORD_READ
                This record indicates a read event.
                    struct {
                        struct perf_event_header header;
                        u32    pid, tid;
                        struct read_format values;
                        struct sample_id sample_id; };
            PERF_RECORD_SAMPLE
                This record indicates a sample.
                    struct {
                        struct perf_event_header header;
                        u64    sample_id;   /* if PERF_SAMPLE_IDENTIFIER */
                        u64    ip;          /* if PERF_SAMPLE_IP */
                        u32    pid, tid;    /* if PERF_SAMPLE_TID */
                        u64    time;        /* if PERF_SAMPLE_TIME */
                        u64    addr;        /* if PERF_SAMPLE_ADDR */
                        u64    id;          /* if PERF_SAMPLE_ID */
                        u64    stream_id;   /* if PERF_SAMPLE_STREAM_ID */
                        u32    cpu, res;    /* if PERF_SAMPLE_CPU */
                        u64    period;      /* if PERF_SAMPLE_PERIOD */
                        struct read_format v;
                                            /* if PERF_SAMPLE_READ */
                        u64    nr;          /* if PERF_SAMPLE_CALLCHAIN */
                        u64    ips[nr];     /* if PERF_SAMPLE_CALLCHAIN */
                        u32    size;        /* if PERF_SAMPLE_RAW */
                        char  data[size];   /* if PERF_SAMPLE_RAW */
                        u64     bnr;          /* if PERF_SAMPLE_BRANCH_STACK
                    */
                        struct perf_branch_entry lbr[bnr];
                                            /*  if  PERF_SAMPLE_BRANCH_STACK
                    */
                        u64    abi;         /* if PERF_SAMPLE_REGS_USER */
                        u64    regs[weight(mask)];
                                            /* if PERF_SAMPLE_REGS_USER */
                        u64    size;        /* if PERF_SAMPLE_STACK_USER */
                        char   data[size];  /* if PERF_SAMPLE_STACK_USER */
                        u64    dyn_size;    /* if PERF_SAMPLE_STACK_USER &&
                                               size != 0 */
                        u64    weight;      /* if PERF_SAMPLE_WEIGHT */
                        u64    data_src;    /* if PERF_SAMPLE_DATA_SRC */
                        u64    transaction; /* if PERF_SAMPLE_TRANSACTION */
                        u64    abi;         /* if PERF_SAMPLE_REGS_INTR */
                        u64    regs[weight(mask)];
                                            /* if  PERF_SAMPLE_REGS_INTR  */
                    };
                sample_id
                    If PERF_SAMPLE_IDENTIFIER is enabled, a 64-bit unique ID
                    is included.  This is a  duplication  of  the  PERF_SAM-
                    PLE_ID  id  value,  but included at the beginning of the
                    sample so parsers can easily obtain the value.
                ip  If PERF_SAMPLE_IP is enabled, then a 64-bit  instruction
                    pointer value is included.
                pid, tid
                    If  PERF_SAMPLE_TID is enabled, then a 32-bit process ID
                    and 32-bit thread ID are included.
                time
                    If PERF_SAMPLE_TIME is enabled, then a 64-bit  timestamp
                    is  included.   This is obtained via local_clock() which
                    is a hardware timestamp if  available  and  the  jiffies
                    value if not.
                addr
                    If PERF_SAMPLE_ADDR is enabled, then a 64-bit address is
                    included.  This is usually the address of a  tracepoint,
                    breakpoint, or software event; otherwise the value is 0.
                id  If PERF_SAMPLE_ID is enabled,  a  64-bit  unique  ID  is
                    included.   If  the event is a member of an event group,
                    the group leader ID is returned.  This ID is the same as
                    the one returned by PERF_FORMAT_ID.
                stream_id
                    If  PERF_SAMPLE_STREAM_ID is enabled, a 64-bit unique ID
                    is included.  Unlike PERF_SAMPLE_ID  the  actual  ID  is
                    returned,  not the group leader.  This ID is the same as
                    the one returned by PERF_FORMAT_ID.
                cpu, res
                    If PERF_SAMPLE_CPU is enabled, this is  a  32-bit  value
                    indicating  which  CPU  was being used, in addition to a
                    reserved (unused) 32-bit value.
                period
                    If PERF_SAMPLE_PERIOD is enabled, a 64-bit  value  indi-
                    cating the current sampling period is written.
                v   If  PERF_SAMPLE_READ  is  enabled,  a  structure of type
                    read_format is included which has values for all  events
                    in  the  event group.  The values included depend on the
                    read_format value used at perf_event_open() time.
                nr, ips[nr]
                    If PERF_SAMPLE_CALLCHAIN is enabled, then a 64-bit  num-
                    ber  is  included  which  indicates  how  many following
                    64-bit instruction pointers will follow.   This  is  the
                    current callchain.
                size, data[size]
                    If PERF_SAMPLE_RAW is enabled, then a 32-bit value indi-
                    cating size is included followed by an  array  of  8-bit
                    values  of length size.  The values are padded with 0 to
                    have 64-bit alignment.
                    This RAW record data is opaque with respect to the  ABI.
                    The  ABI  doesn't  make any promises with respect to the
                    stability of its  content,  it  may  vary  depending  on
                    event, hardware, and kernel version.
                bnr, lbr[bnr]
                    If  PERF_SAMPLE_BRANCH_STACK  is  enabled, then a 64-bit
                    value indicating the number of records is included, fol-
                    lowed  by  bnr  perf_branch_entry  structures which each
                    include the fields:
                    from   This indicates the source instruction (may not be
                           a branch).
                    to     The branch target.
                    mispred
                           The branch target was mispredicted.
                    predicted
                           The branch target was predicted.
                    in_tx (since Linux 3.11)
                           The branch was in a transactional memory transac-
                           tion.
                    abort (since Linux 3.11)
                           The branch was in an aborted transactional memory
                           transaction.
                    cycles (since Linux 4.3)
                           This  reports  the number of cycles elapsed since
                           the previous branch stack update.
                    The entries are from most to least recent, so the  first
                    entry has the most recent branch.
                    Support  for mispred, predicted, and cycles is optional;
                    if not supported, those values will be 0.
                    The type  of  branches  recorded  is  specified  by  the
                    branch_sample_type field.
                abi, regs[weight(mask)]
                    If  PERF_SAMPLE_REGS_USER  is enabled, then the user CPU
                    registers are recorded.
                    The  abi  field  is  one  of  PERF_SAMPLE_REGS_ABI_NONE,
                    PERF_SAMPLE_REGS_ABI_32 or PERF_SAMPLE_REGS_ABI_64.
                    The  regs  field  is  an array of the CPU registers that
                    were specified by the sample_regs_user attr field.   The
                    number  of  values is the number of bits set in the sam-
                    ple_regs_user bit mask.
                size, data[size], dyn_size
                    If PERF_SAMPLE_STACK_USER  is  enabled,  then  the  user
                    stack  is  recorded.  This can be used to generate stack
                    backtraces.  size is the size requested by the  user  in
                    sample_stack_user or else the maximum record size.  data
                    is the stack data (a raw dump of the memory  pointed  to
                    by the stack pointer at the time of sampling).  dyn_size
                    is the amount of data actually dumped (can be less  than
                    size).  Note that dyn_size is omitted if size is 0.
                weight
                    If  PERF_SAMPLE_WEIGHT  is  enabled, then a 64-bit value
                    provided by the hardware is recorded that indicates  how
                    costly  the  event was.  This allows expensive events to
                    stand out more clearly in profiles.
                data_src
                    If PERF_SAMPLE_DATA_SRC is enabled, then a 64-bit  value
                    is recorded that is made up of the following fields:
                    mem_op
                        Type of opcode, a bitwise combination of:
                        PERF_MEM_OP_NA          Not available
                        PERF_MEM_OP_LOAD        Load instruction
                        PERF_MEM_OP_STORE       Store instruction
                        PERF_MEM_OP_PFETCH      Prefetch
                        PERF_MEM_OP_EXEC        Executable code
                    mem_lvl
                        Memory hierarchy level hit or miss, a bitwise combi-
                        nation   of   the   following,   shifted   left   by
                        PERF_MEM_LVL_SHIFT:
                        PERF_MEM_LVL_NA         Not available
                        PERF_MEM_LVL_HIT        Hit
                        PERF_MEM_LVL_MISS       Miss
                        PERF_MEM_LVL_L1         Level 1 cache
                        PERF_MEM_LVL_LFB        Line fill buffer
                        PERF_MEM_LVL_L2         Level 2 cache
                        PERF_MEM_LVL_L3         Level 3 cache
                        PERF_MEM_LVL_LOC_RAM    Local DRAM
                        PERF_MEM_LVL_REM_RAM1   Remote DRAM 1 hop
                        PERF_MEM_LVL_REM_RAM2   Remote DRAM 2 hops
                        PERF_MEM_LVL_REM_CCE1   Remote cache 1 hop
                        PERF_MEM_LVL_REM_CCE2   Remote cache 2 hops
                        PERF_MEM_LVL_IO         I/O memory
                        PERF_MEM_LVL_UNC        Uncached memory
                    mem_snoop
                        Snoop  mode, a bitwise combination of the following,
                        shifted left by PERF_MEM_SNOOP_SHIFT:
                        PERF_MEM_SNOOP_NA       Not available
                        PERF_MEM_SNOOP_NONE     No snoop
                        PERF_MEM_SNOOP_HIT      Snoop hit
                        PERF_MEM_SNOOP_MISS     Snoop miss
                        PERF_MEM_SNOOP_HITM     Snoop hit modified
                    mem_lock
                        Lock instruction, a bitwise combination of the  fol-
                        lowing, shifted left by PERF_MEM_LOCK_SHIFT:
                        PERF_MEM_LOCK_NA        Not available
                        PERF_MEM_LOCK_LOCKED    Locked transaction
                    mem_dtlb
                        TLB access hit or miss, a bitwise combination of the
                        following, shifted left by PERF_MEM_TLB_SHIFT:
                        PERF_MEM_TLB_NA         Not available
                        PERF_MEM_TLB_HIT        Hit
                        PERF_MEM_TLB_MISS       Miss
                        PERF_MEM_TLB_L1         Level 1 TLB
                        PERF_MEM_TLB_L2         Level 2 TLB
                        PERF_MEM_TLB_WK         Hardware walker
                        PERF_MEM_TLB_OS         OS fault handler
                transaction
                    If the  PERF_SAMPLE_TRANSACTION  flag  is  set,  then  a
                    64-bit  field  is recorded describing the sources of any
                    transactional memory aborts.
                    The field is a bitwise combination of the following val-
                    ues:
                    PERF_TXN_ELISION
                           Abort  from  an  elision type transaction (Intel-
                           CPU-specific).
                    PERF_TXN_TRANSACTION
                           Abort from a generic transaction.
                    PERF_TXN_SYNC
                           Synchronous  abort  (related  to   the   reported
                           instruction).
                    PERF_TXN_ASYNC
                           Asynchronous  abort  (not related to the reported
                           instruction).
                    PERF_TXN_RETRY
                           Retryable abort  (retrying  the  transaction  may
                           have succeeded).
                    PERF_TXN_CONFLICT
                           Abort due to memory conflicts with other threads.
                    PERF_TXN_CAPACITY_WRITE
                           Abort due to write capacity overflow.
                    PERF_TXN_CAPACITY_READ
                           Abort due to read capacity overflow.
                    In addition, a user-specified abort code can be obtained
                    from  the high 32 bits of the field by shifting right by
                    PERF_TXN_ABORT_SHIFT  and   masking   with   the   value
                    PERF_TXN_ABORT_MASK.
                abi, regs[weight(mask)]
                    If  PERF_SAMPLE_REGS_INTR  is enabled, then the user CPU
                    registers are recorded.
                    The  abi  field  is  one  of  PERF_SAMPLE_REGS_ABI_NONE,
                    PERF_SAMPLE_REGS_ABI_32, or PERF_SAMPLE_REGS_ABI_64.
                    The  regs  field  is  an array of the CPU registers that
                    were specified by the sample_regs_intr attr field.   The
                    number  of  values is the number of bits set in the sam-
                    ple_regs_intr bit mask.
            PERF_RECORD_MMAP2
                This record includes extended information on  mmap(2)  calls
                returning  executable  mappings.   The  format is similar to
                that of the PERF_RECORD_MMAP record, but includes extra val-
                ues that allow uniquely identifying shared mappings.
                    struct {
                        struct perf_event_header header;
                        u32    pid;
                        u32    tid;
                        u64    addr;
                        u64    len;
                        u64    pgoff;
                        u32    maj;
                        u32    min;
                        u64    ino;
                        u64    ino_generation;
                        u32    prot;
                        u32    flags;
                        char   filename[];
                        struct sample_id sample_id; };
                pid    is the process ID.
                tid    is the thread ID.
                addr   is the address of the allocated memory.
                len    is the length of the allocated memory.
                pgoff  is the page offset of the allocated memory.
                maj    is the major ID of the underlying device.
                min    is the minor ID of the underlying device.
                ino    is the inode number.
                ino_generation
                       is the inode generation.
                prot   is the protection information.
                flags  is the flags information.
                filename
                       is  a  string describing the backing of the allocated
                       memory.
            PERF_RECORD_AUX (since Linux 4.1)
                This record reports that new data is available in the  sepa-
                rate AUX buffer region.
                    struct {
                        struct perf_event_header header;
                        u64    aux_offset;
                        u64    aux_size;
                        u64    flags;
                        struct sample_id sample_id; };
                aux_offset
                       offset  in  the  AUX  mmap  region where the new data
                       begins.
                aux_size
                       size of the data made available.
                flags  describes the AUX update.
                       PERF_AUX_FLAG_TRUNCATED
                              if set, then the data returned  was  truncated
                              to fit the available buffer size.
                       PERF_AUX_FLAG_OVERWRITE
                              if set, then the data returned has overwritten
                              previous data.
            PERF_RECORD_ITRACE_START (since Linux 4.1)
                This  record  indicates  which  process  has  initiated   an
                instruction  trace  event, allowing tools to properly corre-
                late the instruction addresses in the AUX  buffer  with  the
                proper executable.
                    struct {
                        struct perf_event_header header;
                        u32    pid;
                        u32    tid; };
                pid    process  ID  of  the  thread  starting an instruction
                       trace.
                tid    thread ID  of  the  thread  starting  an  instruction
                       trace.
            PERF_RECORD_LOST_SAMPLES (since Linux 4.2)
                When  using  hardware  sampling  (such  as  Intel PEBS) this
                record indicates some number of samples that may  have  been
                lost.
                    struct {
                        struct perf_event_header header;
                        u64    lost;
                        struct sample_id sample_id; };
                lost   the number of potentially lost samples.
            PERF_RECORD_SWITCH (since Linux 4.3)
                This  record  indicates  a context switch has happened.  The
                PERF_RECORD_MISC_SWITCH_OUT bit in the misc field  indicates
                whether  it  was a context switch into or away from the cur-
                rent process.
                    struct {
                        struct perf_event_header header;
                        struct sample_id sample_id; };
            PERF_RECORD_SWITCH_CPU_WIDE (since Linux 4.3)
                As with PERF_RECORD_SWITCH this record indicates  a  context
                switch  has  happened,  but  it only occurs when sampling in
                CPU-wide mode and provides  additional  information  on  the
                process       being       switched       to/from.        The
                PERF_RECORD_MISC_SWITCH_OUT bit in the misc field  indicates
                whether  it  was a context switch into or away from the cur-
                rent process.
                    struct {
                        struct perf_event_header header;
                        u32 next_prev_pid;
                        u32 next_prev_tid;
                        struct sample_id sample_id; };
                next_prev_pid
                       The process ID of the previous (if switching  in)  or
                       next (if switching out) process on the CPU.
                next_prev_tid
                       The  thread  ID  of the previous (if switching in) or
                       next (if switching out) thread on the CPU.
 Overflow handling
     Events can be set to notify when a threshold is crossed, indicating  an
     overflow.   Overflow conditions can be captured by monitoring the event
     file descriptor with poll(2), select(2), or  epoll(7).   Alternatively,
     the  overflow events can be captured via sa signal handler, by enabling
     I/O signaling on  the  file  descriptor;  see  the  discussion  of  the
     F_SETOWN and F_SETSIG operations in fcntl(2).
     Overflows  are  generated  only  by sampling events (sample_period must
     have a nonzero value).
     There are two ways to generate overflow notifications.
     The first is to set a wakeup_events or wakeup_watermark value that will
     trigger  if  a  certain number of samples or bytes have been written to
     the mmap ring buffer.  In this case, POLL_IN is indicated.
     The other way is by use  of  the  PERF_EVENT_IOC_REFRESH  ioctl.   This
     ioctl  adds to a counter that decrements each time the event overflows.
     When nonzero, POLL_IN is indicated, but  once  the  counter  reaches  0
     POLL_HUP is indicated and the underlying event is disabled.
     Refreshing  an event group leader refreshes all siblings and refreshing
     with a parameter of  0  currently  enables  infinite  refreshes;  these
     behaviors are unsupported and should not be relied on.
     Starting with Linux 3.18, POLL_HUP is indicated if the event being mon-
     itored is attached to a different process and that process exits.
 rdpmc instruction
     Starting with Linux 3.4 on x86, you can use the  rdpmc  instruction  to
     get  low-latency  reads  without having to enter the kernel.  Note that
     using rdpmc is not necessarily faster than other  methods  for  reading
     event values.
     Support  for  this  can be detected with the cap_usr_rdpmc field in the
     mmap page; documentation on how to calculate event values can be  found
     in that section.
     Originally,  when rdpmc support was enabled, any process (not just ones
     with an active perf event) could use the rdpmc  instruction  to  access
     the  counters.   Starting with Linux 4.0, rdpmc support is only allowed
     if an event is currently enabled in a process's  context.   To  restore
     the old behavior, write the value 2 to /sys/devices/cpu/rdpmc.
 perf_event ioctl calls
     Various ioctls act on perf_event_open() file descriptors:
     PERF_EVENT_IOC_ENABLE
            This  enables  the  individual event or event group specified by
            the file descriptor argument.
            If the PERF_IOC_FLAG_GROUP bit is set  in  the  ioctl  argument,
            then all events in a group are enabled, even if the event speci-
            fied is not the group leader (but see BUGS).
     PERF_EVENT_IOC_DISABLE
            This disables the individual counter or event group specified by
            the file descriptor argument.
            Enabling  or disabling the leader of a group enables or disables
            the entire group; that is, while the group leader  is  disabled,
            none  of the counters in the group will count.  Enabling or dis-
            abling a member of a group other than the  leader  affects  only
            that  counter;  disabling  a  non-leader stops that counter from
            counting but doesn't affect any other counter.
            If the PERF_IOC_FLAG_GROUP bit is set  in  the  ioctl  argument,
            then all events in a group are disabled, even if the event spec-
            ified is not the group leader (but see BUGS).
     PERF_EVENT_IOC_REFRESH
            Non-inherited overflow counters can use this to enable a counter
            for a number of overflows specified by the argument, after which
            it is disabled.  Subsequent calls of this ioctl add the argument
            value  to  the  current  count.   An  overflow notification with
            POLL_IN set will happen on each overflow until the count reaches
            0;  when  that  happens a notification with POLL_HUP set is sent
            and the event is disabled.  Using an argument of 0 is considered
            undefined behavior.
     PERF_EVENT_IOC_RESET
            Reset  the event count specified by the file descriptor argument
            to zero.  This resets only the counts; there is no way to  reset
            the multiplexing time_enabled or time_running values.
            If  the  PERF_IOC_FLAG_GROUP  bit  is set in the ioctl argument,
            then all events in a group are reset, even if the  event  speci-
            fied is not the group leader (but see BUGS).
     PERF_EVENT_IOC_PERIOD
            This updates the overflow period for the event.
            Since  Linux  3.7  (on  ARM) and Linux 3.14 (all other architec-
            tures), the new period takes effect immediately.  On older  ker-
            nels,  the  new  period did not take effect until after the next
            overflow.
            The argument is a pointer  to  a  64-bit  value  containing  the
            desired new period.
            Prior  to Linux 2.6.36, this ioctl always failed due to a bug in
            the kernel.
     PERF_EVENT_IOC_SET_OUTPUT
            This tells the kernel to report event notifications to the spec-
            ified  file  descriptor  rather  than the default one.  The file
            descriptors must all be on the same CPU.
            The argument specifies the desired file  descriptor,  or  -1  if
            output should be ignored.
     PERF_EVENT_IOC_SET_FILTER (since Linux 2.6.33)
            This adds an ftrace filter to this event.
            The argument is a pointer to the desired ftrace filter.
     PERF_EVENT_IOC_ID (since Linux 3.12)
            This  returns  the  event  ID  value  for  the  given event file
            descriptor.
            The argument is a pointer to a 64-bit unsigned integer  to  hold
            the result.
     PERF_EVENT_IOC_SET_BPF (since Linux 4.1)
            This  allows attaching a Berkeley Packet Filter (BPF) program to
            an existing kprobe tracepoint  event.   You  need  CAP_SYS_ADMIN
            privileges to use this ioctl.
            The  argument  is a BPF program file descriptor that was created
            by a previous bpf(2) system call.
 Using prctl(2)
     A process can enable or disable all the event groups that are  attached
     to    it    using    the    prctl(2)   PR_TASK_PERF_EVENTS_ENABLE   and
     PR_TASK_PERF_EVENTS_DISABLE operations.  This applies to  all  counters
     on  the calling process, whether created by this process or by another,
     and does not affect any counters that this process has created on other
     processes.   It  enables  or  disables  only the group leaders, not any
     other members in the groups.
 perf_event related configuration files
     Files in /proc/sys/kernel/
         /proc/sys/kernel/perf_event_paranoid
                The perf_event_paranoid file can be set to  restrict  access
                to the performance counters.
                2   allow  only user-space measurements (default since Linux
                    4.6).
                1   allow both kernel and user measurements (default  before
                    Linux 4.6).
                0   allow access to CPU-specific data but not raw tracepoint
                    samples.
                -1  no restrictions.
                The existence of the perf_event_paranoid file is  the  offi-
                cial   method   for   determining   if   a  kernel  supports
                perf_event_open().
         /proc/sys/kernel/perf_event_max_sample_rate
                This sets the maximum sample rate.  Setting  this  too  high
                can  allow  users  to  sample at a rate that impacts overall
                machine performance and potentially  lock  up  the  machine.
                The default value is 100000 (samples per second).
         /proc/sys/kernel/perf_event_max_stack
                This  file  sets  the  maximum  depth of stack frame entries
                reported when generating a call trace.
         /proc/sys/kernel/perf_event_mlock_kb
                Maximum number of pages an unprivileged user  can  mlock(2).
                The default is 516 (kB).
     Files in /sys/bus/event_source/devices/
         Since Linux 2.6.34, the kernel supports having multiple PMUs avail-
         able for monitoring.  Information on how to program these PMUs  can
         be  found  under /sys/bus/event_source/devices/.  Each subdirectory
         corresponds to a different PMU.
         /sys/bus/event_source/devices/*/type (since Linux 2.6.38)
                This contains an integer that can be used in the type  field
                of  perf_event_attr  to  indicate  that you wish to use this
                PMU.
         /sys/bus/event_source/devices/cpu/rdpmc (since Linux 3.4)
                If this file is 1, then direct user-space access to the per-
                formance counter registers is allowed via the rdpmc instruc-
                tion.  This can be disabled by echoing 0 to the file.
                As of Linux 4.0 the behavior has  changed,  so  that  1  now
                means  only  allow  access  to  processes  with  active perf
                events, with 2 indicating the old allow-anyone-access behav-
                ior.
         /sys/bus/event_source/devices/*/format/ (since Linux 3.4)
                This  subdirectory contains information on the architecture-
                specific subfields available  for  programming  the  various
                config fields in the perf_event_attr struct.
                The  content  of  each file is the name of the config field,
                followed by a colon, followed by a  series  of  integer  bit
                ranges separated by commas.  For example, the file event may
                contain the value  config1:1,6-10,44  which  indicates  that
                event  is  an attribute that occupies bits 1,6-10, and 44 of
                perf_event_attr::config1.
         /sys/bus/event_source/devices/*/events/ (since Linux 3.4)
                This subdirectory contains  files  with  predefined  events.
                The  contents  are  strings  describing  the  event settings
                expressed in terms of the fields  found  in  the  previously
                mentioned  ./format/  directory.   These are not necessarily
                complete lists of all events supported by a PMU, but usually
                a subset of events deemed useful or interesting.
                The  content of each file is a list of attribute names sepa-
                rated by commas.  Each entry has an optional  value  (either
                hex  or  decimal).   If  no  value  is specified, then it is
                assumed to be a single-bit field with  a  value  of  1.   An
                example entry may look like this: event=0x2,inv,ldlat=3.
         /sys/bus/event_source/devices/*/uevent
                This  file  is  the  standard  kernel  device  interface for
                injecting hotplug events.
         /sys/bus/event_source/devices/*/cpumask (since Linux 3.7)
                The cpumask file contains a comma-separated list of integers
                that  indicate  a  representative CPU number for each socket
                (package) on the motherboard.  This is needed  when  setting
                up  uncore  or  northbridge  events,  as  those PMUs present
                socket-wide events.

RETURN VALUE

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

ERRORS

     The  errors  returned by perf_event_open() can be inconsistent, and may
     vary across processor architectures and performance monitoring units.
     E2BIG  Returned if the perf_event_attr size value is too small (smaller
            than  PERF_ATTR_SIZE_VER0), too big (larger than the page size),
            or larger than the kernel supports and the extra bytes  are  not
            zero.  When E2BIG is returned, the perf_event_attr size field is
            overwritten by the kernel to be the size of the structure it was
            expecting.
     EACCES Returned when the requested event requires CAP_SYS_ADMIN permis-
            sions (or a more permissive perf_event paranoid setting).   Some
            common  cases  where  an unprivileged process may encounter this
            error: attaching to a process owned by a different  user;  moni-
            toring  all  processes  on a given CPU (i.e., specifying the pid
            argument as -1); and not setting exclude_kernel when  the  para-
            noid setting requires it.
     EBADF  Returned  if  the  group_fd file descriptor is not valid, or, if
            PERF_FLAG_PID_CGROUP is set, the cgroup file descriptor  in  pid
            is not valid.
     EBUSY (since Linux 4.1)
            Returned  if  another  event already has exclusive access to the
            PMU.
     EFAULT Returned if  the  attr  pointer  points  at  an  invalid  memory
            address.
     EINVAL Returned if the specified event is invalid.  There are many pos-
            sible reasons for this.  A not-exhaustive list:  sample_freq  is
            higher  than  the  maximum  setting; the cpu to monitor does not
            exist; read_format is out of range; sample_type is out of range;
            the flags value is out of range; exclusive or pinned set and the
            event is not a group leader; the event config values are out  of
            range  or  set  reserved bits; the generic event selected is not
            supported; or there is not  enough  room  to  add  the  selected
            event.
     EMFILE Each  opened  event uses one file descriptor.  If a large number
            of events are opened, the per-process limit  on  the  number  of
            open file descriptors will be reached, and no more events can be
            created.
     ENODEV Returned when the event involves a feature not supported by  the
            current CPU.
     ENOENT Returned  if  the type setting is not valid.  This error is also
            returned for some unsupported generic events.
     ENOSPC Prior to Linux 3.3, if there was not enough room for the  event,
            ENOSPC  was returned.  In Linux 3.3, this was changed to EINVAL.
            ENOSPC is still returned if  you  try  to  add  more  breakpoint
            events than supported by the hardware.
     ENOSYS Returned  if PERF_SAMPLE_STACK_USER is set in sample_type and it
            is not supported by hardware.
     EOPNOTSUPP
            Returned if an event requiring a specific  hardware  feature  is
            requested  but  there  is  no  hardware  support.  This includes
            requesting low-skid events if not supported, branch  tracing  if
            it  is not available, sampling if no PMU interrupt is available,
            and branch stacks for software events.
     EOVERFLOW (since Linux 4.8)
            Returned  if  PERF_SAMPLE_CALLCHAIN  is   requested   and   sam-
            ple_max_stack   is   larger   than   the  maximum  specified  in
            /proc/sys/kernel/perf_event_max_stack.
     EPERM  Returned on many (but not all) architectures when an unsupported
            exclude_hv,  exclude_idle,  exclude_user, or exclude_kernel set-
            ting is specified.
            It can also happen, as with EACCES,  when  the  requested  event
            requires   CAP_SYS_ADMIN   permissions  (or  a  more  permissive
            perf_event paranoid setting).  This includes  setting  a  break-
            point on a kernel address, and (since Linux 3.13) setting a ker-
            nel function-trace tracepoint.
     ESRCH  Returned if attempting to attach to  a  process  that  does  not
            exist.

VERSION

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

CONFORMING TO

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

NOTES

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

BUGS

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

EXAMPLE

     The following is a short example that measures  the  total  instruction
     count of a call to printf(3).
     #include  <stdlib.h>  #include  <stdio.h>  #include <unistd.h> #include
     <string.h>   #include   <sys/ioctl.h>   #include   <linux/perf_event.h>
     #include <asm/unistd.h>
     static  long  perf_event_open(struct  perf_event_attr  *hw_event, pid_t
     pid,
                     int cpu, int group_fd, unsigned long flags) {
         int ret;
         ret = syscall(__NR_perf_event_open, hw_event, pid, cpu,
                        group_fd, flags);
         return ret; }
     int main(int argc, char **argv) {
         struct perf_event_attr pe;
         long long count;
         int fd;
         memset(&pe, 0, sizeof(struct perf_event_attr));
         pe.type = PERF_TYPE_HARDWARE;
         pe.size = sizeof(struct perf_event_attr);
         pe.config = PERF_COUNT_HW_INSTRUCTIONS;
         pe.disabled = 1;
         pe.exclude_kernel = 1;
         pe.exclude_hv = 1;
         fd = perf_event_open(&pe, 0, -1, -1, 0);
         if (fd == -1) {
            fprintf(stderr, "Error opening leader %llx\n", pe.config);
            exit(EXIT_FAILURE);
         }
         ioctl(fd, PERF_EVENT_IOC_RESET, 0);
         ioctl(fd, PERF_EVENT_IOC_ENABLE, 0);
         printf("Measuring instruction count for this printf\n");
         ioctl(fd, PERF_EVENT_IOC_DISABLE, 0);
         read(fd, &count, sizeof(long long));
         printf("Used %lld instructions\n", count);
         close(fd); }

SEE ALSO

     perf(1), fcntl(2), mmap(2), open(2), prctl(2), read(2)

COLOPHON

     This page is part of release 4.16 of the Linux  man-pages  project.   A
     description  of  the project, information about reporting bugs, and the
     latest    version    of    this    page,    can     be     found     at
     https://www.kernel.org/doc/man-pages/.

Linux 2018-02-02 PERF_EVENT_OPEN(2)

/data/webs/external/dokuwiki/data/pages/man/perf_event_open.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1

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