perf-top(1) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | INTERACTIVE PROMPTING KEYS | OVERHEAD CALCULATION | SEE ALSO | COLOPHON

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.

       --group
           Put the counters into a counter group.

       --group-sort-idx
           Sort the output by the event at the index n in group. If n is
           invalid, sort by the first event. It can support multiple
           groups with different amount of events. WARNING: This should
           be used on grouped events.

       -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
           Ignore vmlinux files.

       --kallsyms=<file>
           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.

       --sym-annotate=<symbol>
           Annotate this symbol.

       -K, --hide_kernel_symbols
           Hide kernel symbols.

       -U, --hide_user_symbols
           Hide user symbols.

       --demangle-kernel
           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 page.

       --fields=
           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
               automatically.

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

       --show-total-period
           Show a column with the sum of periods.

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

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

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

       -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.

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

       --asm-raw
           Show raw instruction encoding of assembly instructions.

       -g
           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.

       --children
           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 --no-children.

       --max-stack
           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=<regex>
           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.

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

       --percentage
           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, etc).

               "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).

       --proc-map-timeout
           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.

       --raw-trace
           When displaying traceevent output, do not use print fmt or
           plugins.

       --hierarchy
           Enable hierarchy output.

       --overwrite
           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.

       --force
           Don’t do ownership validation.

       --num-thread-synthesize
           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.

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

       -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.

       --all-cgroups
           Record events of type PERF_RECORD_CGROUP and display it with
           the cgroup sort key.

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

               E.g.:

               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-on-off-events
           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
           explicitly specified does.

       --stitch-lbr
           Show callgraph with stitched LBRs, which may have more
           complete callgraph. The option must be used with --call-graph
           lbr recording. Disabled by default. In common cases with call
           stack overflows, it can recreate better call stacks than the
           default lbr call stack output. But this approach is not full
           proof. There can be cases where it creates incorrect call
           stacks from incorrect matches. The known limitations include
           exception handing such as setjmp/longjmp will have
           calls/returns not match.

INTERACTIVE PROMPTING KEYS         top

       [d]
           Display refresh delay.

       [e]
           Number of entries to display.

       [E]
           Event to display when multiple counters are active.

       [f]
           Profile display filter (>= hit count).

       [F]
           Annotation display filter (>= % of total).

       [s]
           Annotate symbol.

       [S]
           Stop annotation, return to full profile display.

       [K]
           Hide kernel symbols.

       [U]
           Hide user symbols.

       [z]
           Toggle event count zeroing across display updates.

       [qQ]
           Quit.

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

OVERHEAD CALCULATION         top

       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) function.

       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 */
               foo();
           }

           int main(void) {
               bar()
               return 0;
           }
           .ft

       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
                         bar
                         main
                         __libc_start_main

             40.00%  bar
                     |
                     --- bar
                         main
                         __libc_start_main
           .ft

       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
                         __libc_start_main

            100.00%    40.00%  bar
                     |
                     --- bar
                         main
                         __libc_start_main

             60.00%    60.00%  foo
                     |
                     --- foo
                         bar
                         main
                         __libc_start_main
           .ft

       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 file.

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 
       ⟨https://perf.wiki.kernel.org/index.php/Main_Page⟩.  If you have a
       bug report for this manual page, send it to
       linux-kernel@vger.kernel.org.  This page was obtained from the
       project's upstream Git repository
       ⟨http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git⟩
       on 2021-08-27.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-08-26.)  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 man-pages@man7.org

perf                           2021-06-24                    PERF-TOP(1)

Pages that refer to this page: perf(1)perf-buildid-list(1)perf-kvm(1)perf-list(1)perf-stat(1)