perf-stat.txt

perf-stat(1)
============

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

SYNOPSIS
--------
[verse]
'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>...::
	Any command you can specify in a shell.

record::
	See STAT RECORD.

report::
	See STAT REPORT.

-e::
--event=::
	Select the PMU event. Selection can be:

	- a symbolic event name (use 'perf list' to list all events)

	- a raw PMU event (eventsel+umask) in the form of rNNN where NNN is a
	  hexadecimal event descriptor.

	- a symbolically formed event like 'pmu/param1=0x3,param2/' where
	  param1 and param2 are defined as formats for the PMU in
	  /sys/bus/event_source/devices/<pmu>/format/*

	- a symbolically formed event like 'pmu/config=M,config1=N,config2=K/'
	  where M, N, K are numbers (in decimal, hex, octal format).
	  Acceptable values for each of 'config', 'config1' and 'config2'
	  parameters are defined by corresponding entries in
	  /sys/bus/event_source/devices/<pmu>/format/*

	Note that the last two syntaxes support prefix and glob matching in
	the PMU name to simplify creation of events accross 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::
        child tasks do not inherit counters
-p::
--pid=<pid>::
        stat events on existing process id (comma separated list)

-t::
--tid=<tid>::
        stat events on existing thread id (comma separated list)


-a::
--all-cpus::
        system-wide collection from all CPUs (default if no target is specified)

-c::
--scale::
	scale/normalize counter values

-d::
--detailed::
	print more detailed statistics, can be specified up to 3 times

	   -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>::
	repeat command and print average + stddev (max: 100). 0 means forever.

-B::
--big-num::
        print large numbers with thousands' separators according to locale

-C::
--cpu=::
Count only on the list of CPUs provided. Multiple CPUs can be provided as a
comma-separated list with no space: 0,1. Ranges of CPUs are specified with -: 0-2.
In per-thread mode, this option is ignored. The -a option is still necessary
to activate system-wide monitoring. Default is to count on all CPUs.

-A::
--no-aggr::
Do not aggregate counts across all monitored CPUs.

-n::
--null::
        null run - don't start any counters

-v::
--verbose::
        be more verbose (show counter open errors, etc)

-x SEP::
--field-separator SEP::
print counts using a CSV-style output to make it easy to import directly into
spreadsheets. Columns are separated by the string specified in SEP.

--table:: Display time for each run (-r option), in a table format, e.g.:

  $ 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::
monitor only in the container (cgroup) called "name". This option is available only
in per-cpu mode. The cgroup filesystem must be mounted. All threads belonging to
container "name" are monitored when they run on the monitored CPUs. Multiple cgroups
can be provided. Each cgroup is applied to the corresponding event, i.e., first cgroup
to first event, second cgroup to second event and so on. It is possible to provide
an empty cgroup (monitor all the time) using, e.g., -G foo,,bar. Cgroups must have
corresponding events, i.e., they always refer to events defined earlier on the command
line. If the user wants to track multiple events for a specific cgroup, the user can
use '-e e1 -e e2 -G foo,foo' or just use '-e e1 -e e2 -G foo'.

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'.

-o file::
--output file::
Print the output into the designated file.

--append::
Append to the output file designated with the -o option. Ignored if -o is not specified.

--log-fd::

Log output to fd, instead of stderr.  Complementary to --output, and mutually exclusive
with it.  --append may be used here.  Examples:
     3>results  perf stat --log-fd 3          -- $cmd
     3>>results perf stat --log-fd 3 --append -- $cmd

--pre::
--post::
	Pre and post measurement hooks, e.g.:

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::
Print count deltas every N milliseconds (minimum: 1ms)
The overhead percentage could be high in some cases, for instance with small, sub 100ms intervals.  Use with caution.
	example: 'perf stat -I 1000 -e cycles -a sleep 5'

--interval-count times::
Print count deltas for fixed number of times.
This option should be used together with "-I" option.
	example: 'perf stat -I 1000 --interval-count 2 -e cycles -a'

--interval-clear::
Clear the screen before next interval.

--timeout msecs::
Stop the 'perf stat' session and print count deltas after N milliseconds (minimum: 10 ms).
This option is not supported with the "-I" option.
	example: 'perf stat --time 2000 -e cycles -a'

--metric-only::
Only print computed metrics. Print them in a single line.
Don't show any raw values. Not supported with --per-thread.

--per-socket::
Aggregate counts per processor socket for system-wide mode measurements.  This
is a useful mode to detect imbalance between sockets.  To enable this mode,
use --per-socket in addition to -a. (system-wide).  The output includes the
socket number and the number of online processors on that socket. This is
useful to gauge the amount of aggregation.

--per-core::
Aggregate counts per physical processor for system-wide mode measurements.  This
is a useful mode to detect imbalance between physical cores.  To enable this mode,
use --per-core in addition to -a. (system-wide).  The output includes the
core number and the number of online logical processors on that physical processor.

--per-thread::
Aggregate counts per monitored threads, when monitoring threads (-t option)
or processes (-p option).

-D msecs::
--delay msecs::
After starting the program, wait msecs before measuring. This is useful to
filter out the startup phase of the program, which is often very different.

-T::
--transaction::

Print statistics of transactional execution if supported.

STAT RECORD
-----------
Stores stat data into perf data file.

-o file::
--output file::
Output file name.

STAT REPORT
-----------
Reads and reports stat data from perf data file.

-i file::
--input file::
Input file name.

--per-socket::
Aggregate counts per processor socket for system-wide mode measurements.

--per-core::
Aggregate counts per physical processor for system-wide mode measurements.

-M::
--metrics::
Print metrics or metricgroups specified in a comma separated list.
For a group all metrics from the group are added.
The events from the metrics are automatically measured.
See perf list output for the possble metrics and metricgroups.

-A::
--no-aggr::
Do not aggregate counts across all monitored CPUs.

--topdown::
Print top down level 1 metrics if supported by the CPU. This allows to
determine bottle necks in the CPU pipeline for CPU bound workloads,
by breaking the cycles consumed down into frontend bound, backend bound,
bad speculation and retiring.

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.

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.

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

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.

--no-merge::
Do not merge results from same PMUs.

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:
1. Prefix or glob matching is used for the PMU name.
2. Aliases, which are listed immediately after the Kernel PMU events
   by perf list, are used.

--smi-cost::
Measure SMI cost if msr/aperf/ and msr/smi/ events are supported.

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.

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:

	- optional usec time stamp in fractions of second (with -I xxx)
	- optional CPU, core, or socket identifier
	- optional number of logical CPUs aggregated
	- counter value
	- unit of the counter value or empty
	- event name
	- run time of counter
	- percentage of measurement time the counter was running
	- optional variance if multiple values are collected with -r
	- optional metric value
	- optional unit of metric

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

SEE ALSO
--------
linkperf:perf-top[1], linkperf:perf-list[1]