PERF-TOP(1)

NAME
perf-top - System profiling tool.

SYNOPSIS

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

DESCRIPTION

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

OPTIONS

-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.

-F <freq>, --freq=<freq>
    Profile at this frequency.

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

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

-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.

--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
    Setup and enable call-graph (stack chain/backtrace) recording, implies -g.

--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.

--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: 127

--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.

INTERACTIVE PROMPTING KEYS

[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.

[z]
    Toggle event count zeroing across display updates.

[qQ]
    Quit.

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

OVERHEAD CALCULATION

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

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