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
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_4.14-top(1), perf_4.14-list(1)
