PERF-STAT(1)

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>...
    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/*

-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.

-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.

-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: 10ms) 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

--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.

-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.

--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 -j

    Performance counter stats for 'make -j':

    8117.370256  task clock ticks     #      11.281 CPU utilization factor
            678  context switches     #       0.000 M/sec
            133  CPU migrations       #       0.000 M/sec
         235724  pagefaults           #       0.029 M/sec
    24821162526  CPU cycles           #    3057.784 M/sec
    18687303457  instructions         #    2302.138 M/sec
      172158895  cache references     #      21.209 M/sec
       27075259  cache misses         #       3.335 M/sec

    Wall-clock time elapsed:   719.554352 msecs

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

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