NAME¶

perf-stat - Run a command and gather performance counter statistics

SYNOPSIS¶

perf stat [-e <EVENT> | --event=EVENT] [-a] <command>
perf stat [-e <EVENT> | --event=EVENT] [-a] -- <command> [<options>]
perf stat [-e <EVENT> | --event=EVENT] [-a] record [-o file] -- <command> [<options>]
perf stat report [-i file]

DESCRIPTION¶

This command runs a command and gathers performance counter statistics from it.

OPTIONS¶

<command>...

record

report

-e, --event=

'percore' is a event qualifier that sums up the event counts for both
hardware threads in a core. For example:
perf stat -A -a -e cpu/event,percore=1/,otherevent ...

Note that the last two syntaxes support prefix and glob matching in
the PMU name to simplify creation of events across multiple instances
of the same type of PMU in large systems (e.g. memory controller PMUs).
Multiple PMU instances are typical for uncore PMUs, so the prefix
'uncore_' is also ignored when performing this match.

-i, --no-inherit

-p, --pid=<pid>

-t, --tid=<tid>

-b, --bpf-prog

# bpftool prog | head -n 1
17247: tracepoint  name sys_enter  tag 192d548b9d754067  gpl

# perf stat -e cycles,instructions --bpf-prog 17247 --timeout 1000

Performance counter stats for 'BPF program(s) 17247':

85,967      cycles
28,982      instructions              #    0.34  insn per cycle

1.102235068 seconds time elapsed

--bpf-counters

--bpf-attr-map

-a, --all-cpus

--no-scale

-d, --detailed

-d:          detailed events, L1 and LLC data cache


    -d -d:     more detailed events, dTLB and iTLB events


 -d -d -d:     very detailed events, adding prefetch events

-r, --repeat=<n>

-B, --big-num

-C, --cpu=

-A, --no-aggr

-n, --null

This can be useful to measure just elapsed wall-clock time - or to assess the raw overhead of perf stat itself, without running any counters.

-v, --verbose

-x SEP, --field-separator SEP

--table

$ perf stat --null -r 5 --table perf bench sched pipe

Performance counter stats for 'perf bench sched pipe' (5 runs):

# Table of individual measurements:
5.189 (-0.293) #
5.189 (-0.294) #
5.186 (-0.296) #
5.663 (+0.181) ##
6.186 (+0.703) ####

# Final result:
5.483 +- 0.198 seconds time elapsed  ( +-  3.62% )

-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.

--for-each-cgroup name

-o file, --output file

--append

--log-fd

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

#!/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 stat -D -1 -e cpu-cycles -a -I 1000       \


          --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 $?

--pre, --post

perf stat --repeat 10 --null --sync --pre make -s O=defconfig-build/clean -- make -s -j64 O=defconfig-build/ bzImage

-I msecs, --interval-print msecs

If the metric exists, it is calculated by the counts generated in this interval and the metric is printed after #.

--interval-count times

--interval-clear

--timeout msecs

--metric-only

--per-socket

--per-die

--per-cluster

--per-cache

--per-core

--per-thread

--per-node

-D msecs, --delay msecs

-T, --transaction

--metric-no-group

--metric-no-merge

--metric-no-threshold

--quiet

STAT RECORD¶

Stores stat data into perf data file.

-o file, --output file

STAT REPORT¶

Reads and reports stat data from perf data file.

-i file, --input file

--per-socket

--per-die

--per-cluster

--per-cache

--per-core

-M, --metrics

When threshold information is available for a metric, the
color red is used to signify a metric has exceeded a threshold
while green shows it hasn't. The default color means that
no threshold information was available or the threshold
couldn't be computed.

-A, --no-aggr, --no-merge

When multiple events are created from a single event specification, stat will, by default, aggregate the event counts and show the result in a single row. This option disables that behavior and shows the individual events and counts.

Multiple events are created from a single event specification when:

Frontend bound means that the CPU cannot fetch and decode instructions fast enough. Backend bound means that computation or memory access is the bottle neck. Bad Speculation means that the CPU wasted cycles due to branch mispredictions and similar issues. Retiring means that the CPU computed without an apparently bottleneck. The bottleneck is only the real bottleneck if the workload is actually bound by the CPU and not by something else.

For best results it is usually a good idea to use it with interval mode like -I 1000, as the bottleneck of workloads can change often.

This enables --metric-only, unless overridden with --no-metric-only.

The following restrictions only apply to older Intel CPUs and Atom, on newer CPUs (IceLake and later) TopDown can be collected for any thread:

The top down metrics are collected per core instead of per CPU thread. Per core mode is automatically enabled and -a (global monitoring) is needed, requiring root rights or perf.perf_event_paranoid=-1.

Topdown uses the full Performance Monitoring Unit, and needs disabling of the NMI watchdog (as root): echo 0 > /proc/sys/kernel/nmi_watchdog for best results. Otherwise the bottlenecks may be inconsistent on workload with changing phases.

To interpret the results it is usually needed to know on which CPUs the workload runs on. If needed the CPUs can be forced using taskset.

--td-level

As the higher levels gather more metrics and use more counters they will be less accurate. By convention a metric can be examined by appending _group to it and this will increase accuracy compared to gathering all metrics for a level. For example, level 1 analysis may highlight tma_frontend_bound. This metric may be drilled into with tma_frontend_bound_group with perf stat -M tma_frontend_bound_group....

Error out if the input is higher than the supported max level.

--smi-cost

During the measurement, the /sys/device/cpu/freeze_on_smi will be set to freeze core counters on SMI. The aperf counter will not be effected by the setting. The cost of SMI can be measured by (aperf - unhalted core cycles).

In practice, the percentages of SMI cycles is very useful for performance oriented analysis. --metric_only will be applied by default. The output is SMI cycles%, equals to (aperf - unhalted core cycles) / aperf

Users who wants to get the actual value can apply --no-metric-only.

--all-kernel

--all-user

--percore-show-thread

This option with event modifier "percore" enabled also sums up the event counts for all hardware threads in a core but show the sum counts per hardware thread. This is essentially a replacement for the any bit and convenient for post processing.

--summary

--no-csv-summary

This option can be enabled in perf config by setting the variable stat.no-csv-summary.

$ perf config stat.no-csv-summary=true

--cputype

EXAMPLES¶

$ perf stat -- make

Performance counter stats for 'make':

   83723.452481      task-clock:u (msec)       #    1.004 CPUs utilized


              0      context-switches:u        #    0.000 K/sec


              0      cpu-migrations:u          #    0.000 K/sec


      3,228,188      page-faults:u             #    0.039 M/sec
229,570,665,834      cycles:u                  #    2.742 GHz
313,163,853,778      instructions:u            #    1.36  insn per cycle


 69,704,684,856      branches:u                #  832.559 M/sec


  2,078,861,393      branch-misses:u           #    2.98% of all branches

83.409183620 seconds time elapsed

74.684747000 seconds user


 8.739217000 seconds sys

TIMINGS¶

As displayed in the example above we can display 3 types of timings. We always display the time the counters were enabled/alive:

83.409183620 seconds time elapsed

For workload sessions we also display time the workloads spent in user/system lands:

74.684747000 seconds user


 8.739217000 seconds sys

Those times are the very same as displayed by the time tool.

CSV FORMAT¶

With -x, perf stat is able to output a not-quite-CSV format output Commas in the output are not put into "". To make it easy to parse it is recommended to use a different character like -x \;

The fields are in this order:

Additional metrics may be printed with all earlier fields being empty.

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.

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-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-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).

JSON FORMAT¶

With -j, perf stat is able to print out a JSON format output that can be used for parsing.

SEE ALSO¶

perf-top(1), perf-list(1)