perf_event_open(2) - Linux manual page (original) (raw)
perfeventopen(2) System Calls Manual perfeventopen(2)
NAME top
perf_event_open - set up performance monitoringLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <linux/perf_event.h>** /* Definition of **PERF_*** constants */
**#include <linux/hw_breakpoint.h>** /* Definition of **HW_*** constants */
**#include <sys/syscall.h>** /* Definition of **SYS_*** constants */
**#include <unistd.h>**
**int syscall(SYS_perf_event_open, struct perf_event_attr ***_attr_**,**
**pid_t** _pid_**, int** _cpu_**, int** _groupfd_**, unsigned long** _flags_**);**
_Note_: glibc provides no wrapper for **perf_event_open**(),
necessitating the use of [syscall(2)](../man2/syscall.2.html).DESCRIPTION top
Given a list of parameters, **perf_event_open**() returns a file
descriptor, for use in subsequent system calls ([read(2)](../man2/read.2.html), [mmap(2)](../man2/mmap.2.html),
[prctl(2)](../man2/prctl.2.html), [fcntl(2)](../man2/fcntl.2.html), etc.).
A call to **perf_event_open**() creates a file descriptor that allows
measuring 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)](../man2/ioctl.2.html) and
via [prctl(2)](../man2/prctl.2.html). 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)](../man2/read.2.html) call. A _sampling_ event periodically
writes measurements to a buffer that can then be accessed via
[mmap(2)](../man2/mmap.2.html).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_PERFMON** (since Linux 5.8) or
**CAP_SYS_ADMIN** capability or a
_/proc/sys/kernel/perfeventparanoid_ 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 **CAP_PERFMON** (since Linux 5.9) and a ptrace
access mode **PTRACE_MODE_READ_REALCREDS** check on older Linux
versions; see [ptrace(2)](../man2/ptrace.2.html).
The _groupfd_ argument allows event groups to be created. An event
group has one event which is the group leader. The leader is
created first, with _groupfd_ = -1. The rest of the group members
are created with subsequent **perf_event_open**() calls with _groupfd_
being set to the file descriptor of the group leader. (A single
event on its own is created with _groupfd_ = -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
following 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)](../man2/execve.2.html). Setting the close-on-
exec flags at creation time, rather than later with
[fcntl(2)](../man2/fcntl.2.html), avoids potential race conditions where the
calling thread invokes **perf_event_open**() and [fcntl(2)](../man2/fcntl.2.html) at
the same time as another thread calls [fork(2)](../man2/fork.2.html) then
[execve(2)](../man2/execve.2.html).
**PERF_FLAG_FD_NO_GROUP**
This flag tells the event to ignore the _groupfd_ 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
_groupfd_.
**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 monitor 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 _perfeventattr_ structure provides detailed configuration
information 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 */
write_backward : 1, /* Write ring buffer from end
to beginning */
namespaces : 1, /* include namespaces data */
ksymbol : 1, /* include ksymbol events */
bpf_event : 1, /* include bpf events */
aux_output : 1, /* generate AUX records
instead of events */
cgroup : 1, /* include cgroup events */
text_poke : 1, /* include text poke events */
build_id : 1, /* use build id in mmap2 events */
inherit_thread : 1, /* children only inherit */
/* if cloned with CLONE_THREAD */
remove_on_exec : 1, /* event is removed from task
on exec */
sigtrap : 1, /* send synchronous SIGTRAP
on event */
__reserved_1 : 26;
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 size */
__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 */
__u32 aux_sample_size; /* max aux sample size */
__u32 __reserved_3; /* align to u64 */
__u64 sig_data; /* user data for sigtrap */
};
The fields of the _perfeventattr_ 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
provided by the kernel (even if no hardware support
is available).
**PERF_TYPE_TRACEPOINT**
This indicates a tracepoint provided by the kernel
tracepoint infrastructure.
**PERF_TYPE_HW_CACHE**
This indicates a hardware cache event. This has a
special 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
multiple 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 filesystem: there is a subdirectory per
PMU instance under _/sys/bus/eventsource/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/eventsource/devices/cpu/type_ contains the
value for the core CPU PMU, which is usually 4.
**kprobe**
**uprobe** (both 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 _kprobefunc_, _uprobepath_, _kprobeaddr_,
and _probeoffset_ for more details.
_size_ The size of the _perfeventattr_ structure for
forward/backward compatibility. Set this using
_sizeof(struct perfeventattr)_ to allow the kernel to see
the struct size at the time of compilation.
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 corresponding to the
addition of _sampleregsuser_ and _samplestackuser_ in Linux
3.7. **PERF_ATTR_SIZE_VER4** is 104 corresponding to the
addition of _sampleregsintr_ in Linux 3.19.
**PERF_ATTR_SIZE_VER5** is 112 corresponding to the addition of
_auxwatermark_ 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
dependent 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
generalized 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 messages; 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 conjunction 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 negatively 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.
**PERF_COUNT_SW_BPF_OUTPUT** (since Linux 4.4)
This is used to generate raw sample data from
BPF. BPF programs can write to this event
using **bpf_perf_event_output** helper.
**PERF_COUNT_SW_CGROUP_SWITCHES** (since Linux 5.13)
This counts context switches to a task in a
different cgroup. In other words, if the next
task is in the same cgroup, it won't count the
switch.
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:
config = (perf_hw_cache_id) |
(perf_hw_cache_op_id << 8) |
(perf_hw_cache_op_result_id << 16);
where _perfhwcacheid_ 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 _perfhwcacheopid_ 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 _perfhwcacheopresultid_ 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 architectural 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/eventsource/devices/[k,u]probe/format/retprobe_)
for kretprobe/uretprobe. See fields _kprobefunc_,
_uprobepath_, _kprobeaddr_, and _probeoffset_ for more
details.
_kprobefunc_
_uprobepath_
_kprobeaddr_
_probeoffset_
These fields describe the kprobe/uprobe for dynamic PMUs
**kprobe** and **uprobe**. For **kprobe**: use _kprobefunc_ and
_probeoffset_, or use _kprobeaddr_ and leave _kprobefunc_ as
NULL. For **uprobe**: use _uprobepath_ and _probeoffset_.
_sampleperiod_
_samplefreq_
A "sampling" event is one that generates an overflow
notification every N events, where N is given by
_sampleperiod_. A sampling event has _sampleperiod_ > 0.
When an overflow occurs, requested data is recorded in the
mmap buffer. The _sampletype_ field controls what data is
recorded on each overflow.
_samplefreq_ 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.
_sampletype_
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)](../man2/mmap.2.html).
The order in which the values are saved in the sample are
documented in the MMAP Layout subsection below; it is not
the _enum perfeventsampleformat_ 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 _branchsampletype_ 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 hardware 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
different _sampletype_ settings. Parsing the event
stream properly 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 support).
The _preciseip_ 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 _sampleregsintr_. Unlike
**PERF_SAMPLE_REGS_USER** the register values will
return kernel register state if the overflow
happened while kernel code is running. If the CPU
supports hardware sampling of register state (i.e.,
PEBS on Intel x86) and _preciseip_ is set higher than
zero then the register values returned are those
captured by hardware at the time of the sampled
instruction's retirement.
**PERF_SAMPLE_PHYS_ADDR** (since Linux 4.13)
Records physical address of data like in
**PERF_SAMPLE_ADDR**.
**PERF_SAMPLE_CGROUP** (since Linux 5.7)
Records (perf_event) cgroup ID of the process. This
corresponds to the _id_ field in the
**PERF_RECORD_CGROUP** event.
**PERF_SAMPLE_DATA_PAGE_SIZE** (since Linux 5.11)
Records page size of data like in **PERF_SAMPLE_ADDR**.
**PERF_SAMPLE_CODE_PAGE_SIZE** (since Linux 5.11)
Records page size of ip like in **PERF_SAMPLE_IP**.
**PERF_SAMPLE_WEIGHT_STRUCT** (since Linux 5.12)
Records hardware provided weight values like in
**PERF_SAMPLE_WEIGHT**, but it can represent multiple
values in a struct. This shares the same space as
**PERF_SAMPLE_WEIGHT**, so users can apply either of
those, not both. It has the following format and
the meaning of each field is dependent on the
hardware implementation.
union perf_sample_weight {
u64 full; /* PERF_SAMPLE_WEIGHT */
struct { /* PERF_SAMPLE_WEIGHT_STRUCT */
u32 var1_dw;
u16 var2_w;
u16 var3_w;
};
};
_readformat_
This field specifies the format of the data returned by
[read(2)](../man2/read.2.html) on a **perf_event_open**() file descriptor.
**PERF_FORMAT_TOTAL_TIME_ENABLED**
Adds the 64-bit _timeenabled_ 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 _timerunning_ 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.
**PERF_FORMAT_LOST (since Linux 6.0)**
Adds a 64-bit value that is the number of lost
samples for this event. This would be only
meaningful when _sampleperiod_ or _samplefreq_ is set.
_disabled_
The _disabled_ bit specifies whether the counter starts out
disabled or enabled. If disabled, the event can later be
enabled by [ioctl(2)](../man2/ioctl.2.html), [prctl(2)](../man2/prctl.2.html), or _enableonexec_.
When creating an event group, typically the group leader is
initialized with _disabled_ set to 1 and any child events are
initialized 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 children).
Inherit does not work for some combinations of _readformat_
values, such as **PERF_FORMAT_GROUP**. Additionally, using it
together with _cpu == -1_ prevents the creation of the mmap
ring-buffer used for logging asynchronous events in sampled
mode.
_pinned_ The _pinned_ bit specifies that the counter should always be
on the CPU if at all possible. It applies only to hardware
counters 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)](../man2/read.2.html) returns 0)
until the counter is subsequently 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).
_excludeuser_
If this bit is set, the count excludes events that happen
in user space.
_excludekernel_
If this bit is set, the count excludes events that happen
in kernel space.
_excludehv_
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.
_excludeidle_
If set, don't count when the CPU is running the idle task.
While you can currently enable this for any event type, it
is ignored for all but software events.
_mmap_ The _mmap_ bit enables generation of **PERF_RECORD_MMAP** samples
for every [mmap(2)](../man2/mmap.2.html) 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
modified by the [execve(2)](../man2/execve.2.html) and **prctl**(PR_SET_NAME) system
calls as well as writing to _/proc/self/comm_. If the
_commexec_ 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 [execve(2)](../man2/execve.2.html) case from the
others.
_freq_ If this bit is set, then _samplefrequency_ not _sampleperiod_
is used when setting up the sampling interval.
_inheritstat_
This bit enables saving of event counts on context switch
for inherited tasks. This is meaningful only if the
_inherit_ field is set.
_enableonexec_
If this bit is set, a counter is automatically enabled
after a call to [execve(2)](../man2/execve.2.html).
_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 _wakeupwatermark_ boundary. Otherwise, overflow
notifications happen after _wakeupevents_ samples.
_preciseip_ (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**.
_mmapdata_ (since Linux 2.6.36)
This is the counterpart of the _mmap_ field. This enables
generation of **PERF_RECORD_MMAP** samples for [mmap(2)](../man2/mmap.2.html) calls
that do not have **PROT_EXEC** set (for example data and SysV
shared memory).
_sampleidall_ (since Linux 2.6.38)
If set, then TID, TIME, ID, STREAM_ID, and CPU can
additionally be included in non-**PERF_RECORD_SAMPLE**s if the
corresponding _sampletype_ 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 */
};
_excludehost_ (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 meaningful outside the guests; this setting does not
change counts gathered inside of a guest. Currently, this
functionality is x86 only.
_excludeguest_ (since Linux 3.2)
When conducting measurements that include processes running
VM instances (i.e., have executed a **KVM_RUN ioctl**(2)), do
not measure 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 functionality is x86 only.
_excludecallchainkernel_ (since Linux 3.7)
Do not include kernel callchains.
_excludecallchainuser_ (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.
_commexec_ (since Linux 3.16)
This is purely a feature-detection flag, it does not change
kernel 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
[execve(2)](../man2/execve.2.html). This allows tools to distinguish between the
various types of process renaming.
_useclockid_ (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.
_contextswitch_ (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 advantage of this method
is that it will give full information even with strict
_perfeventparanoid_ settings.
_writebackward_ (since Linux 4.6)
This causes the ring buffer to be written from the end to
the beginning. This is to support reading from
overwritable ring buffer.
_namespaces_ (since Linux 4.11)
This enables the generation of **PERF_RECORD_NAMESPACES**
records when a task enters a new namespace. Each namespace
has a combination of device and inode numbers.
_ksymbol_ (since Linux 5.0)
This enables the generation of **PERF_RECORD_KSYMBOL** records
when new kernel symbols are registered or unregistered.
This is analyzing dynamic kernel functions like eBPF.
_bpfevent_ (since Linux 5.0)
This enables the generation of **PERF_RECORD_BPF_EVENT**
records when an eBPF program is loaded or unloaded.
_auxoutput_ (since Linux 5.4)
This allows normal (non-AUX) events to generate data for
AUX events if the hardware supports it.
_cgroup_ (since Linux 5.7)
This enables the generation of **PERF_RECORD_CGROUP** records
when a new cgroup is created (and activated).
_textpoke_ (since Linux 5.8)
This enables the generation of **PERF_RECORD_TEXT_POKE**
records when there's a change to the kernel text (i.e.,
self-modifying code).
_buildid_ (since Linux 5.12)
This changes the contents in the **PERF_RECORD_MMAP2** to have
a build-id instead of device and inode numbers.
_inheritthread_ (since Linux 5.13)
This disables the inheritance of the event to a child
process. Only new threads in the same process (which is
cloned with **CLONE_THREAD**) will inherit the event.
_removeonexec_ (since Linux 5.13)
This closes the event when it starts a new process image by
[execve(2)](../man2/execve.2.html).
_sigtrap_ (since Linux 5.13)
This enables synchronous signal delivery of **SIGTRAP** on
event overflow.
_wakeupevents_
_wakeupwatermark_
This union sets how many samples (_wakeupevents_) or bytes
(_wakeupwatermark_) happen before an overflow notification
happens. Which one is used is selected by the _watermark_
bit flag.
_wakeupevents_ counts only **PERF_RECORD_SAMPLE** record types.
To receive overflow notification for all **PERF_RECORD** types
choose watermark and set _wakeupwatermark_ to 1.
Prior to Linux 3.0, setting _wakeupevents_ to 0 resulted in
no overflow notifications; more recent kernels treat 0 the
same as 1.
_bptype_ (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.
_bpaddr_ (since Linux 2.6.33)
This is the address of the breakpoint. For execution
breakpoints, this is the memory address of the instruction
of interest; 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 OFFCORE_EVENTS on Nehalem/Westmere/SandyBridge
use this field on Linux 3.3 and later kernels.
_bplen_ (since Linux 2.6.33)
_bplen_ is the size 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_BREAKPOINT_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.
_branchsampletype_ (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.
_sampleregsuser_ (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-specific and is described in the kernel header
file _arch/ARCH/include/uapi/asm/perfregs.h_.
_samplestackuser_ (since Linux 3.7)
This defines the size of the user stack to dump if
**PERF_SAMPLE_STACK_USER** is specified.
_clockid_ (since Linux 4.1)
If _useclockid_ 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_MONOTONIC_RAW**, **CLOCK_REALTIME**, **CLOCK_BOOTTIME**, and
**CLOCK_TAI** currently supported.
_auxwatermark_ (since Linux 4.1)
This specifies how much data is required to trigger a
**PERF_RECORD_AUX** sample.
_samplemaxstack_ (since Linux 4.8)
When _sampletype_ includes **PERF_SAMPLE_CALLCHAIN**, this field
specifies how many stack frames to report when generating
the callchain.
_auxsamplesize_ (since Linux 5.5)
When **PERF_SAMPLE_AUX** flag is set, specify the desired size
of AUX data. Note that it can get smaller data than the
specified size.
_sigdata_ (since Linux 5.13)
This data will be copied to user's signal handler (through
_siperf_ in the _siginfot_) to disambiguate which event
triggered the signal.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 readformat 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 */
u64 lost; /* if PERF_FORMAT_LOST */
} 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 */
u64 lost; /* if PERF_FORMAT_LOST */
};
The values read are as follows:
_nr_ The number of events in this file descriptor. Available
only if **PERF_FORMAT_GROUP** was specified.
_timeenabled_
_timerunning_
Total time the event was enabled and running. Normally
these values are the same. Multiplexing happens if the
number of events is more than the number of available PMU
counter slots. In that case the events run only part of
the time and the _timeenabled_ 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 _readformat_.
_lost_ The number of lost samples of this event; only present if
**PERF_FORMAT_LOST** was specified in _readformat_.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 perfeventmmappage_) that contains various
bits of information such as where the ring-buffer head is.
Before Linux 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
_perfeventmmappage_ structure in more detail:
_version_
Version number of this structure.
_compatversion_
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.
_timeenabled_
Time the event was active.
_timerunning_
Time the event was running.
_capusrtime_ / _capusrrdpmc_ / _capbit0_ (since Linux 3.4)
There was a bug in the definition of _capusrtime_ and
_capusrrdpmc_ 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 _capusrtime_ or _capusrrdpmc_ were
actually set.
Starting with Linux 3.12, these are renamed to _capbit0_ and
you should use the _capusertime_ and _capuserrdpmc_ fields
instead.
_capbit0isdeprecated_ (since Linux 3.12)
If set, this bit indicates that the kernel supports the
properly separated _capusertime_ and _capuserrdpmc_ bits.
If not-set, it indicates an older kernel where _capusrtime_
and _capusrrdpmc_ map to the same bit and thus both
features should be used with caution.
_capuserrdpmc_ (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);
_capusertime_ (since Linux 3.12)
This bit indicates the hardware has a constant, nonstop
timestamp counter (TSC on x86).
_capusertimezero_ (since Linux 3.12)
Indicates the presence of _timezero_ which allows mapping
timestamp values to the hardware clock.
_pmcwidth_
If _capusrrdpmc_, 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;
_timeshift_
_timemult_
_timeoffset_
If _capusrtime_, these fields can be used to compute the
time delta since _timeenabled_ (in nanoseconds) using rdtsc
or similar.
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 _timeoffset_, _timemult_, _timeshift_, 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;
_timezero_ (since Linux 3.12)
If _capusrtimezero_ is set, then the hardware clock (the
TSC timestamp counter on x86) can be calculated from the
_timezero_, _timemult_, and _timeshift_ 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);
_datahead_
This points to the head of the data section. The value
continuously increases, it does not wrap. The value needs
to be manually wrapped by the size of the mmap buffer
before accessing the samples.
On SMP-capable platforms, after reading the _datahead_
value, user space should issue an rmb().
_datatail_
When the mapping is **PROT_WRITE**, the _datatail_ value should
be written by user space to reflect the last read data. In
this case, the kernel will not overwrite unread data.
_dataoffset_ (since Linux 4.1)
Contains the offset of the location in the mmap buffer
where perf sample data begins.
_datasize_ (since Linux 4.1)
Contains the size of the perf sample region within the mmap
buffer.
_auxhead_
_auxtail_
_auxoffset_
_auxsize_ _(since Linux 4.1)_
The AUX region allows [mmap(2)](../man2/mmap.2.html)-ing 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 _auxoffset_ needs to be set
with an offset greater than _dataoffset_+_datasize_ and
_auxsize_ 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)](../man2/setrlimit.2.html)), and also as part of the
_perfeventmlockkb_ 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 overwrite 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 _auxhead_ and _auxtail_ ring buffer pointers have the
same behavior and ordering rules as the previous described
_datahead_ and _datatail_.
The following 2^n ring-buffer pages have the layout described
below.
If _perfeventattr.sampleidall_ 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 _perfeventheader_ 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 _perfeventheader_ 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 following (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 [execve(2)](../man2/execve.2.html) 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 _perfeventattr.preciseip_.
**PERF_RECORD_MISC_SWITCH_OUT_PREEMPT** (since Linux 4.17)
When a **PERF_RECORD_SWITCH** or
**PERF_RECORD_SWITCH_CPU_WIDE** record is generated,
this indicates the context switch was a preemption.
**PERF_RECORD_MISC_MMAP_BUILD_ID** (since Linux 5.12)
This indicates that the content of **PERF_SAMPLE_MMAP2**
contains build-ID data instead of device major and
minor numbers as well as the inode number.
**PERF_RECORD_MISC_EXT_RESERVED** (since Linux 2.6.35)
This indicates there is extended data available
(currently 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/_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
corresponding 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 size 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 */
union perf_sample_weight weight;
/* if PERF_SAMPLE_WEIGHT */
/* || PERF_SAMPLE_WEIGHT_STRUCT */
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 */
u64 phys_addr; /* if PERF_SAMPLE_PHYS_ADDR */
u64 cgroup; /* if PERF_SAMPLE_CGROUP */
u64 data_page_size;
/* if PERF_SAMPLE_DATA_PAGE_SIZE */
u64 code_page_size;
/* if PERF_SAMPLE_CODE_PAGE_SIZE */
u64 size; /* if PERF_SAMPLE_AUX */
char data[size]; /* if PERF_SAMPLE_AUX */
};
_sampleid_
If **PERF_SAMPLE_IDENTIFIER** is enabled, a 64-bit
unique ID is included. This is a duplication of
the **PERF_SAMPLE_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**.
_streamid_
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
indicating 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 _readformat_ value used at
**perf_event_open**() time.
_nr_
_ips[nr]_
If **PERF_SAMPLE_CALLCHAIN** is enabled, then a 64-bit
number 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
indicating size is included followed by an array of
8-bit values of size _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, followed by _bnr perfbranchentry_
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.
_intx_ (since Linux 3.11)
The branch was in a transactional memory
transaction.
_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
_branchsampletype_ 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 _sampleregsuser_ attr
field. The number of values is the number of bits
set in the _sampleregsuser_ bit mask.
_size_
_data[size]_
_dynsize_
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 _samplestackuser_ 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). _dynsize_ is the amount of data
actually dumped (can be less than _size_). Note that
_dynsize_ is omitted if _size_ is 0.
_weight_
If **PERF_SAMPLE_WEIGHT** or **PERF_SAMPLE_WEIGHT_STRUCT**
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.
_datasrc_
If **PERF_SAMPLE_DATA_SRC** is enabled, then a 64-bit
value is recorded that is made up of the following
fields:
_memop_
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
_memlvl_
Memory hierarchy level hit or miss, a bitwise
combination 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
_memsnoop_
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
_memlock_
Lock instruction, a bitwise combination of the
following, shifted left by **PERF_MEM_LOCK_SHIFT**:
**PERF_MEM_LOCK_NA**
Not available
**PERF_MEM_LOCK_LOCKED**
Locked transaction
_memdtlb_
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
values:
**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 _sampleregsintr_ attr
field. The number of values is the number of bits
set in the _sampleregsintr_ bit mask.
_physaddr_
If the **PERF_SAMPLE_PHYS_ADDR** flag is set, then the
64-bit physical address is recorded.
_cgroup_
If the **PERF_SAMPLE_CGROUP** flag is set, then the
64-bit cgroup ID (for the perf_event subsystem) is
recorded. To get the pathname of the cgroup, the
ID should match to one in a **PERF_RECORD_CGROUP**.
_datapagesize_
If the **PERF_SAMPLE_DATA_PAGE_SIZE** flag is set, then
the 64-bit page size value of the **data** address is
recorded.
_codepagesize_
If the **PERF_SAMPLE_CODE_PAGE_SIZE** flag is set, then
the 64-bit page size value of the **ip** address is
recorded.
_size_
_data_[_size_]
If **PERF_SAMPLE_AUX** is enabled, a snapshot of the
aux buffer is recorded.
**PERF_RECORD_MMAP2**
This record includes extended information on [mmap(2)](../man2/mmap.2.html)
calls returning executable mappings. The format is
similar to that of the **PERF_RECORD_MMAP** record, but
includes extra values that allow uniquely identifying
shared mappings. Depending on the
**PERF_RECORD_MISC_MMAP_BUILD_ID** bit in the header, the
extra values have different layout and meanings.
struct {
struct perf_event_header header;
u32 pid;
u32 tid;
u64 addr;
u64 len;
u64 pgoff;
union {
struct {
u32 maj;
u32 min;
u64 ino;
u64 ino_generation;
};
struct { /* if PERF_RECORD_MISC_MMAP_BUILD_ID */
u8 build_id_size;
u8 __reserved_1;
u16 __reserved_2;
u8 build_id[20];
};
};
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 size 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.
_inogeneration_
is the inode generation.
_buildidsize_
is the actual size of _buildid_ field (up to 20).
_buildid_
is a raw data to identify a binary.
_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
separate AUX buffer region.
struct {
struct perf_event_header header;
u64 aux_offset;
u64 aux_size;
u64 flags;
struct sample_id sample_id;
};
_auxoffset_
offset in the AUX mmap region where the new data
begins.
_auxsize_
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
correlate 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 current 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 current process.
struct {
struct perf_event_header header;
u32 next_prev_pid;
u32 next_prev_tid;
struct sample_id sample_id;
};
_nextprevpid_
The process ID of the previous (if switching in)
or next (if switching out) process on the CPU.
_nextprevtid_
The thread ID of the previous (if switching in)
or next (if switching out) thread on the CPU.
**PERF_RECORD_NAMESPACES** (since Linux 4.11)
This record includes various namespace information of a
process.
struct {
struct perf_event_header header;
u32 pid;
u32 tid;
u64 nr_namespaces;
struct { u64 dev, inode } [nr_namespaces];
struct sample_id sample_id;
};
_pid_ is the process ID
_tid_ is the thread ID
_nrnamespace_
is the number of namespaces in this record
Each namespace has _dev_ and _inode_ fields and is recorded
in the fixed position like below:
**NET_NS_INDEX**=**0**
Network namespace
**UTS_NS_INDEX**=**1**
UTS namespace
**IPC_NS_INDEX**=**2**
IPC namespace
**PID_NS_INDEX**=**3**
PID namespace
**USER_NS_INDEX**=**4**
User namespace
**MNT_NS_INDEX**=**5**
Mount namespace
**CGROUP_NS_INDEX**=**6**
Cgroup namespace
**PERF_RECORD_KSYMBOL** (since Linux 5.0)
This record indicates kernel symbol register/unregister
events.
struct {
struct perf_event_header header;
u64 addr;
u32 len;
u16 ksym_type;
u16 flags;
char name[];
struct sample_id sample_id;
};
_addr_ is the address of the kernel symbol.
_len_ is the size of the kernel symbol.
_ksymtype_
is the type of the kernel symbol. Currently the
following types are available:
**PERF_RECORD_KSYMBOL_TYPE_BPF**
The kernel symbol is a BPF function.
_flags_ If the **PERF_RECORD_KSYMBOL_FLAGS_UNREGISTER** is
set, then this event is for unregistering the
kernel symbol.
**PERF_RECORD_BPF_EVENT** (since Linux 5.0)
This record indicates BPF program is loaded or
unloaded.
struct {
struct perf_event_header header;
u16 type;
u16 flags;
u32 id;
u8 tag[BPF_TAG_SIZE];
struct sample_id sample_id;
};
_type_ is one of the following values:
**PERF_BPF_EVENT_PROG_LOAD**
A BPF program is loaded
**PERF_BPF_EVENT_PROG_UNLOAD**
A BPF program is unloaded
_id_ is the ID of the BPF program.
_tag_ is the tag of the BPF program. Currently,
**BPF_TAG_SIZE** is defined as 8.
**PERF_RECORD_CGROUP** (since Linux 5.7)
This record indicates a new cgroup is created and
activated.
struct {
struct perf_event_header header;
u64 id;
char path[];
struct sample_id sample_id;
};
_id_ is the cgroup identifier. This can be also
retrieved by [name_to_handle_at(2)](../man2/name%5Fto%5Fhandle%5Fat.2.html) on the cgroup
path (as a file handle).
_path_ is the path of the cgroup from the root.
**PERF_RECORD_TEXT_POKE** (since Linux 5.8)
This record indicates a change in the kernel text.
This includes addition and removal of the text and the
corresponding size is zero in this case.
struct {
struct perf_event_header header;
u64 addr;
u16 old_len;
u16 new_len;
u8 bytes[];
struct sample_id sample_id;
};
_addr_ is the address of the change
_oldlen_
is the old size
_newlen_
is the new size
_bytes_ contains old bytes immediately followed by new
bytes.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 (_sampleperiod_
must have a nonzero value).
There are two ways to generate overflow notifications.
The first is to set a _wakeupevents_ or _wakeupwatermark_ 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
monitored 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 _capusrrdpmc_ 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 specified 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 disabling 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 specified 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 _timeenabled_ or _timerunning_
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 specified 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
architectures), the new period takes effect immediately.
On older kernels, 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
specified 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_PERFMON** (since Linux 5.8) or **CAP_SYS_ADMIN** privileges
to use this ioctl.
The argument is a BPF program file descriptor that was
created by a previous [bpf(2)](../man2/bpf.2.html) system call.
**PERF_EVENT_IOC_PAUSE_OUTPUT** (since Linux 4.7)
This allows pausing and resuming the event's ring-buffer.
A paused ring-buffer does not prevent generation of
samples, but simply discards them. The discarded samples
are considered lost, and cause a **PERF_RECORD_LOST** sample to
be generated when possible. An overflow signal may still
be triggered by the discarded sample even though the ring-
buffer remains empty.
The argument is an unsigned 32-bit integer. A nonzero
value pauses the ring-buffer, while a zero value resumes
the ring-buffer.
**PERF_EVENT_MODIFY_ATTRIBUTES** (since Linux 4.17)
This allows modifying an existing event without the
overhead of closing and reopening a new event. Currently
this is supported only for breakpoint events.
The argument is a pointer to a _perfeventattr_ structure
containing the updated event settings.
**PERF_EVENT_IOC_QUERY_BPF** (since Linux 4.16)
This allows querying which Berkeley Packet Filter (BPF)
programs are attached to an existing kprobe tracepoint.
You can only attach one BPF program per event, but you can
have multiple events attached to a tracepoint. Querying
this value on one tracepoint event returns the ID of all
BPF programs in all events attached to the tracepoint. You
need **CAP_PERFMON** (since Linux 5.8) or **CAP_SYS_ADMIN**
privileges to use this ioctl.
The argument is a pointer to a structure
struct perf_event_query_bpf {
__u32 ids_len;
__u32 prog_cnt;
__u32 ids[0];
};
The _idslen_ field indicates the number of ids that can fit
in the provided _ids_ array. The _progcnt_ value is filled in
by the kernel with the number of attached BPF programs.
The _ids_ array is filled with the ID of each attached BPF
program. If there are more programs than will fit in the
array, then the kernel will return **ENOSPC** and _idslen_ will
indicate the number of program IDs that were successfully
copied.Using prctl(2) A process can enable or disable all currently open event groups using the prctl(2) PR_TASK_PERF_EVENTS_ENABLE and PR_TASK_PERF_EVENTS_DISABLE operations. This applies only to events created locally by the calling process. This does not apply to events created by other processes attached to the calling process or inherited events from a parent process. Only group leaders are enabled and disabled, not any other members of the groups.
perf_event related configuration files Files in /proc/sys/kernel/
_/proc/sys/kernel/perfeventparanoid_
The _perfeventparanoid_ 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 _perfeventparanoid_ file is the
official method for determining if a kernel supports
**perf_event_open**().
_/proc/sys/kernel/perfeventmaxsamplerate_
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/perfeventmaxstack_
This file sets the maximum depth of stack frame entries
reported when generating a call trace.
_/proc/sys/kernel/perfeventmlockkb_
Maximum number of pages an unprivileged user can
[mlock(2)](../man2/mlock.2.html). The default is 516 (kB).
Files in _/sys/bus/eventsource/devices/_
Since Linux 2.6.34, the kernel supports having multiple PMUs
available for monitoring. Information on how to program these
PMUs can be found under _/sys/bus/eventsource/devices/_. Each
subdirectory corresponds to a different PMU.
_/sys/bus/eventsource/devices/*/type_ (since Linux 2.6.38)
This contains an integer that can be used in the _type_
field of _perfeventattr_ to indicate that you wish to
use this PMU.
_/sys/bus/eventsource/devices/cpu/rdpmc_ (since Linux 3.4)
If this file is 1, then direct user-space access to the
performance counter registers is allowed via the rdpmc
instruction. 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
behavior.
_/sys/bus/eventsource/devices/*/format/_ (since Linux 3.4)
This subdirectory contains information on the
architecture-specific subfields available for
programming the various _config_ fields in the
_perfeventattr_ 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
_perfeventattr::config1_.
_/sys/bus/eventsource/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
separated 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/eventsource/devices/*/uevent_
This file is the standard kernel device interface for
injecting hotplug events.
_/sys/bus/eventsource/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 top
On success, **perf_event_open**() returns the new file descriptor. On
error, -1 is returned and _[errno](../man3/errno.3.html)_ is set to indicate the error.ERRORS top
The errors returned by **perf_event_open**() can be inconsistent, and
may vary across processor architectures and performance monitoring
units.
**E2BIG** Returned if the _perfeventattr 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
_perfeventattr 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_PERFMON**
(since Linux 5.8) or **CAP_SYS_ADMIN** permissions (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;
monitoring all processes on a given CPU (i.e., specifying
the _pid_ argument as -1); and not setting _excludekernel_
when the paranoid setting requires it.
**EBADF** Returned if the _groupfd_ 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.
**EINTR** Returned when trying to mix perf and ftrace handling for a
uprobe.
**EINVAL** Returned if the specified event is invalid. There are many
possible reasons for this. A not-exhaustive list:
_samplefreq_ is higher than the maximum setting; the _cpu_ to
monitor does not exist; _readformat_ is out of range;
_sampletype_ 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 _sampletype_
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
_samplemaxstack_ is larger than the maximum specified in
_/proc/sys/kernel/perfeventmaxstack_.
**EPERM** Returned on many (but not all) architectures when an
unsupported _excludehv_, _excludeidle_, _excludeuser_, or
_excludekernel_ setting is specified.
It can also happen, as with **EACCES**, when the requested
event requires **CAP_PERFMON** (since Linux 5.8) or
**CAP_SYS_ADMIN** permissions (or a more permissive perf_event
paranoid setting). This includes setting a breakpoint on a
kernel address, and (since Linux 3.13) setting a kernel
function-trace tracepoint.
**ESRCH** Returned if attempting to attach to a process that does not
exist.STANDARDS top
Linux.HISTORY top
**perf_event_open**() was introduced in Linux 2.6.31 but was called
**perf_counter_open**(). It was renamed in Linux 2.6.32.NOTES top
The official way of knowing if **perf_event_open**() support is
enabled is checking for the existence of the file
_/proc/sys/kernel/perfeventparanoid_.
**CAP_PERFMON** capability (since Linux 5.8) provides secure approach
to performance monitoring and observability operations in a system
according to the principal of least privilege (POSIX IEEE
1003.1e). Accessing system performance monitoring and
observability operations using **CAP_PERFMON** rather than the much
more powerful **CAP_SYS_ADMIN** excludes chances to misuse credentials
and makes operations more secure. **CAP_SYS_ADMIN** usage for secure
system performance monitoring and observability is discouraged in
favor of the **CAP_PERFMON** capability.BUGS top
The **F_SETOWN_EX** option to [fcntl(2)](../man2/fcntl.2.html) 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
kernel. 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 _capusrrdpmc_ and
_capusrtime_ bits mapped to the same location. Code should
migrate to the new _capuserrdpmc_ and _capusertime_ 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.EXAMPLES top
The following is a short example that measures the total
instruction count of a call to [printf(3)](../man3/printf.3.html).
#include <err.h>
#include <linux/perf_event.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <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(SYS_perf_event_open, hw_event, pid, cpu,
group_fd, flags);
return ret;
}
int
main(void)
{
int fd;
long long count;
struct perf_event_attr pe;
memset(&pe, 0, sizeof(pe));
pe.type = PERF_TYPE_HARDWARE;
pe.size = sizeof(pe);
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)
err(EXIT_FAILURE, "Error opening leader %llx\n", pe.config);
if (ioctl(fd, PERF_EVENT_IOC_RESET, 0) == -1)
err(EXIT_FAILURE, "PERF_EVENT_IOC_RESET");
if (ioctl(fd, PERF_EVENT_IOC_ENABLE, 0) == -1)
err(EXIT_FAILURE, "PERF_EVENT_IOC_ENABLE");
printf("Measuring instruction count for this printf\n");
if (ioctl(fd, PERF_EVENT_IOC_DISABLE, 0) == -1)
err(EXIT_FAILURE, "PERF_EVENT_IOC_DISABLE");
if (read(fd, &count, sizeof(count)) != sizeof(count))
err(EXIT_FAILURE, "read");
printf("Used %lld instructions\n", count);
if (close(fd) == -1)
err(EXIT_FAILURE, "close");
}SEE ALSO top
[perf(1)](../man1/perf.1.html), [fcntl(2)](../man2/fcntl.2.html), [mmap(2)](../man2/mmap.2.html), [open(2)](../man2/open.2.html), [prctl(2)](../man2/prctl.2.html), [read(2)](../man2/read.2.html)
_Documentation/admin-guide/perf-security.rst_ in the kernel source
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Pages that refer to this page:bpf(2), gettid(2), mount_setattr(2), openat2(2), syscalls(2), stapprobes(3stap), proc_pid_fd(5), systemd.exec(5), bpf-helpers(7), capabilities(7), cgroups(7)