NAME

       perf-stat-hist - histogram summary of tracepoint values. Uses Linux perf_events.

SYNOPSIS

       perf-stat-hist [-h] [-b buckets|-P power] [-m max] tracepoint variable [seconds]

DESCRIPTION

       This is a proof-of-concept showing in-kernel histograms using Linux perf_events (aka the "perf" command),
       on older kernels where perf_events does not have this native capability.

       These histograms show the distribution  of  variable,  allowing  details  including  multiple  modes  and
       outliers to be studied.

       This uses multiple counting tracepoints with different filters, one for each histogram bucket. While this
       is summarized in-kernel, the use of multiple tracepoints does add addiitonal overhead. Hopefully, in  the
       future  this  this  functionality  will be provided in an efficient way from perf_events itself, at which
       point this tool can be deleted or rewritten.

REQUIREMENTS

       Linux perf_events: add linux-tools-common, run "perf", then add any additional packages it requests. Also
       uses awk.

OPTIONS

       -h     Usage message.

       -b buckets
              Specify  a  list of bucket points for the histogram as a string (eg, "10 500 1000"). The histogram
              will include buckets for less-than the minimum, and greater-than-or-equal-to the  maximum.   If  a
              single  value  is specified, two statistics only are gathered: for less-than and for greater-than-
              or-equal-to.  The overhead is relative to the number of buckets, so only specifying a single value
              costs the lowest overhead.

       -P power
              Power  for  power-of  histogram.  By  default, a power-of-4 histogram is created.  This and the -b
              option are exclusive.

       -m max Max value for power-of histograms.

       tracepoint
              Tracepoint specification. Eg, syscalls:sys_enter_read.

       variable
              The tracepoint variable name to summarize. To see what are available, cat the  format  file  under
              /sys/kernel/debug/tracing/events/*/*/format.

       seconds
              Number of seconds to trace. If not specified, this runs until Ctrl-C.

EXAMPLES

       Trace read() syscalls until Ctrl-C, and show histogram of requested size:
              # perf-stat-hist syscalls:sys_enter_read count

       Trace read() syscall completions until Ctrl-C, and show histogram of successful returned size:
              # perf-stat-hist syscalls:sys_exit_read ret

       Trace read() return sizes for 10 seconds, showing histogram:
              # perf-stat-hist syscalls:sys_exit_read ret 10

       Trace network transmits until Ctrl-C, and show histogram of packet size:
              # perf-stat-hist net:net_dev_xmit len

       Trace read() return sizes, using a power-of-10 histogram:
              perf-stat-hist -P 10 syscalls:sys_exit_read ret

       Trace read() return sizes, using a power-of-2 histogram, and a max of 1024:
              perf-stat-hist -P 2 -m 1024 syscalls:sys_exit_read ret

       Trace read() return sizes, using the specified bucket points:
              perf-stat-hist -b "10 50 100 5000" syscalls:sys_exit_read ret

       Trace read() return sizes, and bifurcate statistics by the value 10:
              perf-stat-hist -b 10 syscalls:sys_exit_read ret

FIELDS

       Range  Range of the histogram bucket, in units of the variable specified.

       Count  Number of occurrences (tracepoint events) of the variable in this range.

       Distribution
              ASCII histogram representation of the Count column.

OVERHEAD

       While  the  counts  are  performed  in-kernel,  there is one tracepoint used per histogram bucket, so the
       overheads are higher than usual (relative to the number of buckets) than  function  counting  using  perf
       stat. The lowest overhead is when -b is used to specify one bucket only, bifurcating statistics.

SOURCE

       This is from the perf-tools collection.

              https://github.com/brendangregg/perf-tools

       Also  look  under the examples directory for a text file containing example usage, output, and commentary
       for this tool.

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Brendan Gregg

SEE ALSO

       perf(1)