PERF-TOP(1)                      perf Manual                     PERF-TOP(1)

NAME         top

       perf-top - System profiling tool.

SYNOPSIS         top

       perf top [-e <EVENT> | --event=EVENT] [<options>]

DESCRIPTION         top

       This command generates and displays a performance counter profile in
       real time.

OPTIONS         top

       -a, --all-cpus
           System-wide collection. (default)

       -c <count>, --count=<count>
           Event period to sample.

       -C <cpu-list>, --cpu=<cpu>
           Monitor 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. Default is to monitor all CPUS.

       -d <seconds>, --delay=<seconds>
           Number of seconds to delay between refreshes.

       -e <event>, --event=<event>
           Select the PMU event. Selection can be a symbolic event name (use
           perf list to list all events) or a raw PMU event (eventsel+umask)
           in the form of rNNN where NNN is a hexadecimal event descriptor.

       -E <entries>, --entries=<entries>
           Display this many functions.

       -f <count>, --count-filter=<count>
           Only display functions with more events than this.

           Put the counters into a counter group.

       -F <freq>, --freq=<freq>
           Profile at this frequency. Use max to use the currently maximum
           allowed frequency, i.e. the value in the
           kernel.perf_event_max_sample_rate sysctl.

       -i, --inherit
           Child tasks do not inherit counters.

       -k <path>, --vmlinux=<path>
           Path to vmlinux. Required for annotation functionality.

           Ignore vmlinux files.

           kallsyms pathname

       -m <pages>, --mmap-pages=<pages>
           Number of mmap data pages (must be a power of two) or size
           specification with appended unit character - B/K/M/G. The size is
           rounded up to have nearest pages power of two value.

       -p <pid>, --pid=<pid>
           Profile events on existing Process ID (comma separated list).

       -t <tid>, --tid=<tid>
           Profile events on existing thread ID (comma separated list).

       -u, --uid=
           Record events in threads owned by uid. Name or number.

       -r <priority>, --realtime=<priority>
           Collect data with this RT SCHED_FIFO priority.

           Annotate this symbol.

       -K, --hide_kernel_symbols
           Hide kernel symbols.

       -U, --hide_user_symbols
           Hide user symbols.

           Demangle kernel symbols.

       -D, --dump-symtab
           Dump the symbol table used for profiling.

       -v, --verbose
           Be more verbose (show counter open errors, etc).

       -z, --zero
           Zero history across display updates.

       -s, --sort
           Sort by key(s): pid, comm, dso, symbol, parent, srcline, weight,
           local_weight, abort, in_tx, transaction, overhead, sample,
           period. Please see description of --sort in the perf-report man

           Specify output field - multiple keys can be specified in CSV
           format. Following fields are available: overhead, overhead_sys,
           overhead_us, overhead_children, sample and period. Also it can
           contain any sort key(s).

               By default, every sort keys not specified in --field will be appended

       -n, --show-nr-samples
           Show a column with the number of samples.

           Show a column with the sum of periods.

           Only consider symbols in these dsos. This option will affect the
           percentage of the overhead column. See --percentage for more

           Only consider symbols in these comms. This option will affect the
           percentage of the overhead column. See --percentage for more

           Only consider these symbols. This option will affect the
           percentage of the overhead column. See --percentage for more

       -M, --disassembler-style=
           Set disassembler style for objdump.

       --prefix=PREFIX, --prefix-strip=N
           Remove first N entries from source file path names in executables
           and add PREFIX. This allows to display source code compiled on
           systems with different file system layout.

           Interleave source code with assembly code. Enabled by default,
           disable with --no-source.

           Show raw instruction encoding of assembly instructions.

           Enables call-graph (stack chain/backtrace) recording.

       --call-graph [mode,type,min[,limit],order[,key][,branch]]
           Setup and enable call-graph (stack chain/backtrace) recording,
           implies -g. See --call-graph section in perf-record and
           perf-report man pages for details.

           Accumulate callchain of children to parent entry so that then can
           show up in the output. The output will have a new "Children"
           column and will be sorted on the data. It requires
           -g/--call-graph option enabled. See the ‘overhead calculation’
           section for more details. Enabled by default, disable with

           Set the stack depth limit when parsing the callchain, anything
           beyond the specified depth will be ignored. This is a trade-off
           between information loss and faster processing especially for
           workloads that can have a very long callchain stack.

               Default: /proc/sys/kernel/perf_event_max_stack when present, 127 otherwise.

           Ignore callees of the function(s) matching the given regex. This
           has the effect of collecting the callers of each such function
           into one place in the call-graph tree.

           Do not show entries which have an overhead under that percent.
           (Default: 0).

           Determine how to display the overhead percentage of filtered
           entries. Filters can be applied by --comms, --dsos and/or
           --symbols options and Zoom operations on the TUI (thread, dso,

               "relative" means it's relative to filtered entries only so that the
               sum of shown entries will be always 100%. "absolute" means it retains
               the original value before and after the filter is applied.

       -w, --column-widths=<width[,width...]>
           Force each column width to the provided list, for large terminal
           readability. 0 means no limit (default behavior).

           When processing pre-existing threads /proc/XXX/mmap, it may take
           a long time, because the file may be huge. A time out is needed
           in such cases. This option sets the time out limit. The default
           value is 500 ms.

       -b, --branch-any
           Enable taken branch stack sampling. Any type of taken branch may
           be sampled. This is a shortcut for --branch-filter any. See
           --branch-filter for more infos.

       -j, --branch-filter
           Enable taken branch stack sampling. Each sample captures a series
           of consecutive taken branches. The number of branches captured
           with each sample depends on the underlying hardware, the type of
           branches of interest, and the executed code. It is possible to
           select the types of branches captured by enabling filters. For a
           full list of modifiers please see the perf record manpage.

               The option requires at least one branch type among any, any_call, any_ret, ind_call, cond.
               The privilege levels may be omitted, in which case, the privilege levels of the associated
               event are applied to the branch filter. Both kernel (k) and hypervisor (hv) privilege
               levels are subject to permissions.  When sampling on multiple events, branch stack sampling
               is enabled for all the sampling events. The sampled branch type is the same for all events.
               The various filters must be specified as a comma separated list: --branch-filter any_ret,u,k
               Note that this feature may not be available on all processors.

           When displaying traceevent output, do not use print fmt or

           Enable hierarchy output.

           Enable this to use just the most recent records, which helps in
           high core count machines such as Knights Landing/Mill, but right
           now is disabled by default as the pausing used in this technique
           is leading to loss of metadata events such as PERF_RECORD_MMAP
           which makes perf top unable to resolve samples, leading to lots
           of unknown samples appearing on the UI. Enable this if you are in
           such machines and profiling a workload that doesn’t creates short
           lived threads and/or doesn’t uses many executable mmap
           operations. Work is being planed to solve this situation, till
           then, this will remain disabled by default.

           Don’t do ownership validation.

           The number of threads to run when synthesizing events for
           existing processes. By default, the number of threads equals to
           the number of online CPUs.

           Record events of type PERF_RECORD_NAMESPACES and display it with
           the cgroup_id sort key.

       --switch-on EVENT_NAME
           Only consider events after this event is found.


               Find out where broadcast packets are handled

               perf probe -L icmp_rcv

               Insert a probe there:

               perf probe icmp_rcv:59

               Start perf top and ask it to only consider the cycles events when a
               broadcast packet arrives This will show a menu with two entries and
               will start counting when a broadcast packet arrives:

               perf top -e cycles,probe:icmp_rcv --switch-on=probe:icmp_rcv

               Alternatively one can ask for --group and then two overhead columns
               will appear, the first for cycles and the second for the switch-on event.

               perf top --group -e cycles,probe:icmp_rcv --switch-on=probe:icmp_rcv

               This may be interesting to measure a workload only after some initialization
               phase is over, i.e. insert a perf probe at that point and use the above
               examples replacing probe:icmp_rcv with the just-after-init probe.

       --switch-off EVENT_NAME
           Stop considering events after this event is found.

           Show the --switch-on/off events too. This has no effect in perf
           top now but probably we’ll make the default not to show the
           switch-on/off events on the --group mode and if there is only one
           event besides the off/on ones, go straight to the histogram
           browser, just like perf top with no events explicitely specified


           Display refresh delay.

           Number of entries to display.

           Event to display when multiple counters are active.

           Profile display filter (>= hit count).

           Annotation display filter (>= % of total).

           Annotate symbol.

           Stop annotation, return to full profile display.

           Hide kernel symbols.

           Hide user symbols.

           Toggle event count zeroing across display updates.


       Pressing any unmapped key displays a menu, and prompts for input.


       The overhead can be shown in two columns as Children and Self when
       perf collects callchains. The self overhead is simply calculated by
       adding all period values of the entry - usually a function (symbol).
       This is the value that perf shows traditionally and sum of all the
       self overhead values should be 100%.

       The children overhead is calculated by adding all period values of
       the child functions so that it can show the total overhead of the
       higher level functions even if they don’t directly execute much.
       Children here means functions that are called from another (parent)

       It might be confusing that the sum of all the children overhead
       values exceeds 100% since each of them is already an accumulation of
       self overhead of its child functions. But with this enabled, users
       can find which function has the most overhead even if samples are
       spread over the children.

       Consider the following example; there are three functions like below.

           .ft C
           void foo(void) {
               /* do something */

           void bar(void) {
               /* do something */

           int main(void) {
               return 0;

       In this case foo is a child of bar, and bar is an immediate child of
       main so foo also is a child of main. In other words, main is a parent
       of foo and bar, and bar is a parent of foo.

       Suppose all samples are recorded in foo and bar only. When it’s
       recorded with callchains the output will show something like below in
       the usual (self-overhead-only) output of perf report:

           .ft C
           Overhead  Symbol
           ........  .....................
             60.00%  foo
                     --- foo

             40.00%  bar
                     --- bar

       When the --children option is enabled, the self overhead values of
       child functions (i.e. foo and bar) are added to the parents to
       calculate the children overhead. In this case the report could be
       displayed as:

           .ft C
           Children      Self  Symbol
           ........  ........  ....................
            100.00%     0.00%  __libc_start_main
                     --- __libc_start_main

            100.00%     0.00%  main
                     --- main

            100.00%    40.00%  bar
                     --- bar

             60.00%    60.00%  foo
                     --- foo

       In the above output, the self overhead of foo (60%) was add to the
       children overhead of bar, main and __libc_start_main. Likewise, the
       self overhead of bar (40%) was added to the children overhead of main
       and \_\_libc_start_main.

       So \_\_libc_start_main and main are shown first since they have same
       (100%) children overhead (even though they have zero self overhead)
       and they are the parents of foo and bar.

       Since v3.16 the children overhead is shown by default and the output
       is sorted by its values. The children overhead is disabled by
       specifying --no-children option on the command line or by adding
       report.children = false or top.children = false in the perf config

SEE ALSO         top

       perf-stat(1), perf-list(1), perf-report(1)

COLOPHON         top

       This page is part of the perf (Performance analysis tools for Linux
       (in Linux source tree)) project.  Information about the project can
       be found at ⟨⟩.  If
       you have a bug report for this manual page, send it to  This page was obtained from the
       project's upstream Git repository
       ⟨⟩ on
       2020-02-08.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-02-07.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

perf                             01/30/2020                      PERF-TOP(1)

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