NAME¶

perf-record - Run a command and record its profile into perf.data

SYNOPSIS¶

perf record [-e <EVENT> | --event=EVENT] [-a] <command>
perf record [-e <EVENT> | --event=EVENT] [-a] -- <command> [<options>]

DESCRIPTION¶

This command runs a command and gathers a performance counter profile from it, into perf.data - without displaying anything.

This file can then be inspected later on, using perf report.

OPTIONS¶

<command>...

-e, --event=

where M, N, K are numbers (in decimal, hex, octal format). Acceptable
values for each of 'config', 'config1' and 'config2' are defined by
corresponding entries in /sys/bus/event_source/devices/<pmu>/format/*
param1 and param2 are defined as formats for the PMU in:
/sys/bus/event_source/devices/<pmu>/format/*

There are also some parameters which are not defined in .../<pmu>/format/*.
These params can be used to overload default config values per event.
Here are some common parameters:
- 'period': Set event sampling period
- 'freq': Set event sampling frequency
- 'time': Disable/enable time stamping. Acceptable values are 1 for


   enabling time stamping. 0 for disabling time stamping.


   The default is 1.
- 'call-graph': Disable/enable callgraph. Acceptable str are "fp" for


 FP mode, "dwarf" for DWARF mode, "lbr" for LBR mode and


 "no" for disable callgraph.
- 'stack-size': user stack size for dwarf mode
- 'name' : User defined event name. Single quotes (') may be used to


   escape symbols in the name from parsing by shell and tool


   like this: name=\'CPU_CLK_UNHALTED.THREAD:cmask=0x1\'.
- 'aux-output': Generate AUX records instead of events. This requires


  that an AUX area event is also provided.
- 'aux-sample-size': Set sample size for AUX area sampling. If the
'--aux-sample' option has been used, set aux-sample-size=0 to disable
AUX area sampling for the event.

See the linkperf:perf-list[1] man page for more parameters.

Note: If user explicitly sets options which conflict with the params,
the value set by the parameters will be overridden.

Also not defined in .../<pmu>/format/* are PMU driver specific
configuration parameters.  Any configuration parameter preceded by
the letter '@' is not interpreted in user space and sent down directly
to the PMU driver.  For example:

perf record -e some_event/@cfg1,@cfg2=config/ ...

will see 'cfg1' and 'cfg2=config' pushed to the PMU driver associated
with the event for further processing.  There is no restriction on
what the configuration parameters are, as long as their semantic is
understood and supported by the PMU driver.

When processing a '.c' file, perf searches an installed LLVM to compile it
into an object file first. Optional clang options can be passed via the
'--clang-opt' command line option, e.g.:

perf record --clang-opt "-DLINUX_VERSION_CODE=0x50000" \


            -e tests/bpf-script-example.c

Note: '--clang-opt' must be placed before '--event/-e'.

--filter=<filter>

In the case of tracepoints, multiple '--filter' options are combined
using '&&'.

A hardware trace PMU advertises its ability to accept a number of
address filters        by specifying a non-zero value in
/sys/bus/event_source/devices/<pmu>/nr_addr_filters.

Address filters have the format:

filter|start|stop|tracestop <start> [/ <size>] [@<file name>]

Where:
- 'filter': defines a region that will be traced.
- 'start': defines an address at which tracing will begin.
- 'stop': defines an address at which tracing will stop.
- 'tracestop': defines a region in which tracing will stop.

<file name> is the name of the object file, <start> is the offset to the
code to trace in that file, and <size> is the size of the region to
trace. 'start' and 'stop' filters need not specify a <size>.

If no object file is specified then the kernel is assumed, in which case
the start address must be a current kernel memory address.

<start> can also be specified by providing the name of a symbol. If the
symbol name is not unique, it can be disambiguated by inserting #n where
'n' selects the n'th symbol in address order. Alternately #0, #g or #G
select only a global symbol. <size> can also be specified by providing
the name of a symbol, in which case the size is calculated to the end
of that symbol. For 'filter' and 'tracestop' filters, if <size> is
omitted and <start> is a symbol, then the size is calculated to the end
of that symbol.

If <size> is omitted and <start> is '*', then the start and size will
be calculated from the first and last symbols, i.e. to trace the whole
file.

If symbol names (or '*') are provided, they must be surrounded by white
space.

The filter passed to the kernel is not necessarily the same as entered.
To see the filter that is passed, use the -v option.

The kernel may not be able to configure a trace region if it is not
within a single mapping.  MMAP events (or /proc/<pid>/maps) can be
examined to determine if that is a possibility.

Multiple filters can be separated with space or comma.

--exclude-perf

-a, --all-cpus

-p, --pid=

-t, --tid=

-u, --uid=

-r, --realtime=

--no-buffering

-c, --count=

-o, --output=

-i, --no-inherit

-F, --freq=

--strict-freq

-m, --mmap-pages=

--group

-g

--call-graph

The unwinding method used for kernel space is dependent on the
unwinder used by the active kernel configuration, i.e
CONFIG_UNWINDER_FRAME_POINTER (fp) or CONFIG_UNWINDER_ORC (orc)

Any option specified here controls the method used for user space.

Valid options are "fp" (frame pointer), "dwarf" (DWARF's CFI -
Call Frame Information) or "lbr" (Hardware Last Branch Record
facility).

In some systems, where binaries are build with gcc
--fomit-frame-pointer, using the "fp" method will produce bogus
call graphs, using "dwarf", if available (perf tools linked to
the libunwind or libdw library) should be used instead.
Using the "lbr" method doesn't require any compiler options. It
will produce call graphs from the hardware LBR registers. The
main limitation is that it is only available on new Intel
platforms, such as Haswell. It can only get user call chain. It
doesn't work with branch stack sampling at the same time.

When "dwarf" recording is used, perf also records (user) stack dump
when sampled.  Default size of the stack dump is 8192 (bytes).
User can change the size by passing the size after comma like
"--call-graph dwarf,4096".

-q, --quiet

-v, --verbose

-s, --stat

-d, --data

--phys-data

--data-page-size

--code-page-size

-T, --timestamp

-P, --period

--sample-cpu

-n, --no-samples

-R, --raw-samples

-C, --cpu

-B, --no-buildid

-N, --no-buildid-cache

-G name,..., --cgroup name,...

If wanting to monitor, say, cycles for a cgroup and also for system wide, this command line can be used: perf stat -e cycles -G cgroup_name -a -e cycles.

-b, --branch-any

-j, --branch-filter

--weight

--namespaces

--all-cgroups

--transaction

--per-thread

-D, --delay=

-I, --intr-regs

--user-regs

--running-time

-k, --clockid

-S, --snapshot

In Snapshot Mode trace data is captured only when signal SIGUSR2 is received and on exit if the above e option is given.

--aux-sample[=OPTIONS]

--proc-map-timeout

--switch-events

--clang-path=PATH

--clang-opt=OPTIONS

--vmlinux=PATH

--buildid-all

--buildid-mmap

--aio[=n]

--affinity=mode

--mmap-flush=number

The maximal allowed value is a quarter of the size of mmaped data pages.

The default option value is 1 byte which means that every time that the output writing thread finds some new data in the mmaped buffer the data is extracted, possibly compressed (-z) and written to the output, perf.data or pipe.

Larger data chunks are compressed more effectively in comparison to smaller chunks so extraction of larger chunks from the mmap data pages is preferable from the perspective of output size reduction.

Also at some cases executing less output write syscalls with bigger data size can take less time than executing more output write syscalls with smaller data size thus lowering runtime profiling overhead.

-z, --compression-level[=n]

--all-kernel

--all-user

--kernel-callchains

--user-callchains

Don’t use both --kernel-callchains and --user-callchains at the same time or no callchains will be collected.

--timestamp-filename Append timestamp to output file name.

--timestamp-boundary

--switch-output[=mode]

Note: the precision of  the size  threshold  hugely depends
on your configuration  - the number and size of  your  ring
buffers (-m). It is generally more precise for higher sizes
(like >5M), for lower values expect different sizes.

A possible use case is to, given an external event, slice the perf.data file that gets then processed, possibly via a perf script, to decide if that particular perf.data snapshot should be kept or not.

Implies --timestamp-filename, --no-buildid and --no-buildid-cache. The reason for the latter two is to reduce the data file switching overhead. You can still switch them on with:

--switch-output --no-no-buildid  --no-no-buildid-cache

--switch-output-event

Uses the same syntax as --event, it will just not be recorded, serving only to switch the perf.data file as soon as the --switch-output event is processed by a separate sideband thread.

This sideband thread is also used to other purposes, like processing the PERF_RECORD_BPF_EVENT records as they happen, asking the kernel for extra BPF information, etc.

--switch-max-files=N

--dry-run

perf record --dry-run -e can act as a BPF script compiler if llvm.dump-obj in config file is set to true.

--synth=TYPE

Kernel (and some other) events are recorded regardless of the choice in this option. For example, --synth=no would have MMAP events for kernel and modules.

Available types are: task - synthesize FORK and COMM events for each task mmap - synthesize MMAP events for each process (implies task) cgroup - synthesize CGROUP events for each cgroup all - synthesize all events (default) no - do not synthesize any of the above events

--tail-synthesize

--overwrite

When --overwrite and --switch-output are used perf records and drops events until it receives a signal, meaning that something unusual was detected that warrants taking a snapshot of the most current events, those fitting in the ring buffer at that moment.

overwrite attribute can also be set or canceled for an event using config terms. For example: cycles/overwrite/ and instructions/no-overwrite/.

Implies --tail-synthesize.

--kcore

--max-size=<size>

--num-thread-synthesize

--control=fifo:ctl-fifo[,ack-fifo], --control=fd:ctl-fd[,ack-fd]

Available commands: enable : enable events disable : disable events enable name : enable event name disable name : disable event name snapshot : AUX area tracing snapshot). stop : stop perf record ping : ping

'evlist [-v|-g|-F] : display all events


                     -F  Show just the sample frequency used for each event.


                     -v  Show all fields.


                     -g  Show event group information.

Measurements can be started with events disabled using --delay=-1 option. Optionally send control command completion (ack\n) to ack-fd descriptor to synchronize with the controlling process. Example of bash shell script to enable and disable events during measurements:

#!/bin/bash

ctl_dir=/tmp/

ctl_fifo=${ctl_dir}perf_ctl.fifo
test -p ${ctl_fifo} && unlink ${ctl_fifo}
mkfifo ${ctl_fifo}
exec {ctl_fd}<>${ctl_fifo}

ctl_ack_fifo=${ctl_dir}perf_ctl_ack.fifo
test -p ${ctl_ack_fifo} && unlink ${ctl_ack_fifo}
mkfifo ${ctl_ack_fifo}
exec {ctl_fd_ack}<>${ctl_ack_fifo}

perf record -D -1 -e cpu-cycles -a               \


            --control fd:${ctl_fd},${ctl_fd_ack} \


            -- sleep 30 &
perf_pid=$!

sleep 5  && echo 'enable' >&${ctl_fd} && read -u ${ctl_fd_ack} e1 && echo "enabled(${e1})"
sleep 10 && echo 'disable' >&${ctl_fd} && read -u ${ctl_fd_ack} d1 && echo "disabled(${d1})"

exec {ctl_fd_ack}>&-
unlink ${ctl_ack_fifo}

exec {ctl_fd}>&-
unlink ${ctl_fifo}

wait -n ${perf_pid}
exit $?

INTEL HYBRID SUPPORT¶

Support for Intel hybrid events within perf tools.

For some Intel platforms, such as AlderLake, which is hybrid platform and it consists of atom cpu and core cpu. Each cpu has dedicated event list. Part of events are available on core cpu, part of events are available on atom cpu and even part of events are available on both.

Kernel exports two new cpu pmus via sysfs: /sys/devices/cpu_core /sys/devices/cpu_atom

The cpus files are created under the directories. For example,

cat /sys/devices/cpu_core/cpus 0-15

cat /sys/devices/cpu_atom/cpus 16-23

It indicates cpu0-cpu15 are core cpus and cpu16-cpu23 are atom cpus.

Quickstart

LIST HYBRID EVENT¶

As before, use perf-list to list the symbolic event.

perf list

inst_retired.any [Fixed Counter: Counts the number of instructions retired. Unit: cpu_atom] inst_retired.any [Number of instructions retired. Fixed Counter - architectural event. Unit: cpu_core]

The Unit: xxx is added to brief description to indicate which pmu the event is belong to. Same event name but with different pmu can be supported.

ENABLE HYBRID EVENT WITH A SPECIFIC PMU¶

To enable a core only event or atom only event, following syntax is supported:

        cpu_core/<event name>/
or


        cpu_atom/<event name>/

For example, count the cycles event on core cpus.

perf stat -e cpu_core/cycles/

CREATE TWO EVENTS FOR ONE HARDWARE EVENT AUTOMATICALLY¶

When creating one event and the event is available on both atom and core, two events are created automatically. One is for atom, the other is for core. Most of hardware events and cache events are available on both cpu_core and cpu_atom.

For hardware events, they have pre-defined configs (e.g. 0 for cycles). But on hybrid platform, kernel needs to know where the event comes from (from atom or from core). The original perf event type PERF_TYPE_HARDWARE can’t carry pmu information. So now this type is extended to be PMU aware type. The PMU type ID is stored at attr.config[63:32].

PMU type ID is retrieved from sysfs. /sys/devices/cpu_atom/type /sys/devices/cpu_core/type

The new attr.config layout for PERF_TYPE_HARDWARE:

PERF_TYPE_HARDWARE: 0xEEEEEEEE000000AA AA: hardware event ID EEEEEEEE: PMU type ID

Cache event is similar. The type PERF_TYPE_HW_CACHE is extended to be PMU aware type. The PMU type ID is stored at attr.config[63:32].

The new attr.config layout for PERF_TYPE_HW_CACHE:

PERF_TYPE_HW_CACHE: 0xEEEEEEEE00DDCCBB BB: hardware cache ID CC: hardware cache op ID DD: hardware cache op result ID EEEEEEEE: PMU type ID

When enabling a hardware event without specified pmu, such as, perf stat -e cycles -a (use system-wide in this example), two events are created automatically.

------------------------------------------------------------
perf_event_attr:


  size                             120


  config                           0x400000000


  sample_type                      IDENTIFIER


  read_format                      TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING


  disabled                         1


  inherit                          1


  exclude_guest                    1
------------------------------------------------------------

and

------------------------------------------------------------
perf_event_attr:


  size                             120


  config                           0x800000000


  sample_type                      IDENTIFIER


  read_format                      TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING


  disabled                         1


  inherit                          1


  exclude_guest                    1
------------------------------------------------------------

type 0 is PERF_TYPE_HARDWARE. 0x4 in 0x400000000 indicates it’s cpu_core pmu. 0x8 in 0x800000000 indicates it’s cpu_atom pmu (atom pmu type id is random).

The kernel creates cycles (0x400000000) on cpu0-cpu15 (core cpus), and create cycles (0x800000000) on cpu16-cpu23 (atom cpus).

For perf-stat result, it displays two events:

Performance counter stats for 'system wide':

6,744,979      cpu_core/cycles/
1,965,552      cpu_atom/cycles/

The first cycles is core event, the second cycles is atom event.

THREAD MODE EXAMPLE:¶

perf-stat reports the scaled counts for hybrid event and with a percentage displayed. The percentage is the event’s running time/enabling time.

One example, triad_loop runs on cpu16 (atom core), while we can see the scaled value for core cycles is 160,444,092 and the percentage is 0.47%.

perf stat -e cycles -- taskset -c 16 ./triad_loop

As previous, two events are created.

perf_event_attr:


  size                             120


  config                           0x400000000


  sample_type                      IDENTIFIER


  read_format                      TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING


  disabled                         1


  inherit                          1


  enable_on_exec                   1


  exclude_guest                    1

and

perf_event_attr:


  size                             120


  config                           0x800000000


  sample_type                      IDENTIFIER


  read_format                      TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING


  disabled                         1


  inherit                          1


  enable_on_exec                   1


  exclude_guest                    1

Performance counter stats for 'taskset -c 16 ./triad_loop':

233,066,666      cpu_core/cycles/                                              (0.43%)
604,097,080      cpu_atom/cycles/                                              (99.57%)

PERF_5.16-RECORD:¶

If there is no -e specified in perf record, on hybrid platform, it creates two default cycles and adds them to event list. One is for core, the other is for atom.

PERF_5.16-STAT:¶

If there is no -e specified in perf stat, on hybrid platform, besides of software events, following events are created and added to event list in order.

cpu_core/cycles/, cpu_atom/cycles/, cpu_core/instructions/, cpu_atom/instructions/, cpu_core/branches/, cpu_atom/branches/, cpu_core/branch-misses/, cpu_atom/branch-misses/

Of course, both perf-stat and perf-record support to enable hybrid event with a specific pmu.

e.g. perf stat -e cpu_core/cycles/ perf stat -e cpu_atom/cycles/ perf stat -e cpu_core/r1a/ perf stat -e cpu_atom/L1-icache-loads/ perf stat -e cpu_core/cycles/,cpu_atom/instructions/ perf stat -e {cpu_core/cycles/,cpu_core/instructions/}

But {cpu_core/cycles/,cpu_atom/instructions/} will return warning and disable grouping, because the pmus in group are not matched (cpu_core vs. cpu_atom).

SEE ALSO¶

perf-stat(1), perf-list(1), perf-intel-pt(1)