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When measuring workloads the startup phase -- doing page faults, dynamic
linking, opening files -- is often very different from the rest of the
workload. Especially with smaller kernels and using counter
multiplexing this can give significant measurement errors.
Multiplexing assumes that the workload is mostly the same over longer
periods. But at startup there is typically some spike of activity which
is relatively short. If many groups are multiplexing the one group
seeing the spike, and which is then scaled up over the time to run all
groups, may see a significant error.
Also in general it's often not useful to measure the startup, because it
is so different from the rest.
One way around this is to use interval mode and discard the first
sample, but this can be awkward because interval mode doesn't support
intervals of less than 100ms, and also a useful interval is not
necessarily the same as a useful startup delay.
This patch adds a new --initial-delay / -D option to skip measuring for
the startup phase. The time can be specified in ms
Here's a simple example:
perf stat -e page-faults bash -c 'for i in $(seq 100000) ; do true ; done'
...
3,721 page-faults
...
If we just wait 20 ms the number of page faults is 1/3 less:
perf stat -D 20 -e page-faults bash -c 'for i in $(seq 100000) ; do true ; done'
...
2,823 page-faults
...
So we filtered out most of the startup noise from bash.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Reviewed-by: Jiri Olsa <jolsa@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1375490473-1503-4-git-send-email-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
161 lines
4.8 KiB
Plaintext
161 lines
4.8 KiB
Plaintext
perf-stat(1)
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============
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NAME
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----
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perf-stat - Run a command and gather performance counter statistics
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SYNOPSIS
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--------
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[verse]
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'perf stat' [-e <EVENT> | --event=EVENT] [-a] <command>
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'perf stat' [-e <EVENT> | --event=EVENT] [-a] -- <command> [<options>]
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DESCRIPTION
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-----------
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This command runs a command and gathers performance counter statistics
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from it.
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OPTIONS
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-------
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<command>...::
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Any command you can specify in a shell.
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-e::
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--event=::
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Select the PMU event. Selection can be a symbolic event name
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(use 'perf list' to list all events) or a raw PMU
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event (eventsel+umask) in the form of rNNN where NNN is a
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hexadecimal event descriptor.
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-i::
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--no-inherit::
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child tasks do not inherit counters
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-p::
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--pid=<pid>::
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stat events on existing process id (comma separated list)
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-t::
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--tid=<tid>::
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stat events on existing thread id (comma separated list)
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-a::
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--all-cpus::
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system-wide collection from all CPUs
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-c::
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--scale::
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scale/normalize counter values
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-r::
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--repeat=<n>::
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repeat command and print average + stddev (max: 100). 0 means forever.
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-B::
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--big-num::
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print large numbers with thousands' separators according to locale
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-C::
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--cpu=::
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Count only on the list of CPUs provided. Multiple CPUs can be provided as a
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comma-separated list with no space: 0,1. Ranges of CPUs are specified with -: 0-2.
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In per-thread mode, this option is ignored. The -a option is still necessary
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to activate system-wide monitoring. Default is to count on all CPUs.
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-A::
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--no-aggr::
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Do not aggregate counts across all monitored CPUs in system-wide mode (-a).
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This option is only valid in system-wide mode.
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-n::
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--null::
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null run - don't start any counters
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-v::
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--verbose::
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be more verbose (show counter open errors, etc)
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-x SEP::
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--field-separator SEP::
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print counts using a CSV-style output to make it easy to import directly into
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spreadsheets. Columns are separated by the string specified in SEP.
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-G name::
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--cgroup name::
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monitor only in the container (cgroup) called "name". This option is available only
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in per-cpu mode. The cgroup filesystem must be mounted. All threads belonging to
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container "name" are monitored when they run on the monitored CPUs. Multiple cgroups
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can be provided. Each cgroup is applied to the corresponding event, i.e., first cgroup
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to first event, second cgroup to second event and so on. It is possible to provide
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an empty cgroup (monitor all the time) using, e.g., -G foo,,bar. Cgroups must have
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corresponding events, i.e., they always refer to events defined earlier on the command
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line.
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-o file::
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--output file::
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Print the output into the designated file.
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--append::
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Append to the output file designated with the -o option. Ignored if -o is not specified.
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--log-fd::
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Log output to fd, instead of stderr. Complementary to --output, and mutually exclusive
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with it. --append may be used here. Examples:
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3>results perf stat --log-fd 3 -- $cmd
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3>>results perf stat --log-fd 3 --append -- $cmd
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--pre::
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--post::
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Pre and post measurement hooks, e.g.:
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perf stat --repeat 10 --null --sync --pre 'make -s O=defconfig-build/clean' -- make -s -j64 O=defconfig-build/ bzImage
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-I msecs::
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--interval-print msecs::
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Print count deltas every N milliseconds (minimum: 100ms)
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example: perf stat -I 1000 -e cycles -a sleep 5
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--per-socket::
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Aggregate counts per processor socket for system-wide mode measurements. This
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is a useful mode to detect imbalance between sockets. To enable this mode,
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use --per-socket in addition to -a. (system-wide). The output includes the
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socket number and the number of online processors on that socket. This is
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useful to gauge the amount of aggregation.
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--per-core::
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Aggregate counts per physical processor for system-wide mode measurements. This
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is a useful mode to detect imbalance between physical cores. To enable this mode,
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use --per-core in addition to -a. (system-wide). The output includes the
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core number and the number of online logical processors on that physical processor.
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-D msecs::
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--initial-delay msecs::
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After starting the program, wait msecs before measuring. This is useful to
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filter out the startup phase of the program, which is often very different.
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EXAMPLES
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--------
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$ perf stat -- make -j
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Performance counter stats for 'make -j':
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8117.370256 task clock ticks # 11.281 CPU utilization factor
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678 context switches # 0.000 M/sec
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133 CPU migrations # 0.000 M/sec
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235724 pagefaults # 0.029 M/sec
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24821162526 CPU cycles # 3057.784 M/sec
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18687303457 instructions # 2302.138 M/sec
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172158895 cache references # 21.209 M/sec
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27075259 cache misses # 3.335 M/sec
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Wall-clock time elapsed: 719.554352 msecs
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SEE ALSO
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--------
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linkperf:perf-top[1], linkperf:perf-list[1]
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