NAME

       funclatency - Time functions and print latency as a histogram.

SYNOPSIS

       funclatency [-h] [-p PID] [-i INTERVAL] [-d DURATION] [-T] [-u] [-m] [-F] [-r] [-v] pattern

DESCRIPTION

       This tool traces function calls and times their duration (latency), and shows the latency distribution as
       a  histogram.  The time is measured from when the function is called to when it returns, and is inclusive
       of both on-CPU time and time spent blocked.

       This tool uses in-kernel eBPF maps for storing timestamps and the histogram, for efficiency.

       Currently nested or recursive functions are not supported properly, and timestamps will  be  overwritten,
       creating dubious output. Try to match single functions, or groups of functions that run at the same stack
       layer, and don't ultimately call each other.

       WARNING:  This  uses  dynamic tracing of (what can be many) functions, an activity that has had issues on
       some kernel versions (risk of panics or freezes). Test, and know what you are doing, before use.

       Since this uses BPF, only the root user can use this tool.

REQUIREMENTS

       CONFIG_BPF and bcc.

OPTIONS

       pattern Function name or search pattern. Supports "*" wildcards. See EXAMPLES.  You can also use  -r  for
       regular expressions.  -h Print usage message.

       -p PID Trace this process ID only.

       -i INTERVAL
              Print output every interval seconds.

       -d DURATION
              Total duration of trace, in seconds.

       -T     Include timestamps on output.

       -u     Output histogram in microseconds.

       -m     Output histogram in milliseconds.

       -F     Print a separate histogram per function matched.

       -r     Use regular expressions for the search pattern.

       -v     Print the BPF program (for debugging purposes).

EXAMPLES

       Time the do_sys_open() kernel function, and print the distribution as a histogram:
              # funclatency do_sys_open

       Time the read() function in libc across all processes on the system:
              # funclatency c:read

       Time vfs_read(), and print the histogram in units of microseconds:
              # funclatency -u vfs_read

       Time do_nanosleep(), and print the histogram in units of milliseconds:
              # funclatency -m do_nanosleep

       Time libc open(), and print output every 2 seconds, for duration 10 seconds:
              # funclatency -i 2 -d 10 c:read

       Time vfs_read(), and print output every 5 seconds, with timestamps:
              # funclatency -mTi 5 vfs_read

       Time vfs_read() for process ID 181 only:
              # funclatency -p 181 vfs_read:

       Time both vfs_fstat() and vfs_fstatat() calls, by use of a wildcard:
              # funclatency 'vfs_fstat*'

       Time both vfs_fstat* calls, and print a separate histogram for each:
              # funclatency -F 'vfs_fstat*'

FIELDS

       necs   Nanosecond range

       usecs  Microsecond range

       msecs  Millisecond range

       count  How many calls fell into this range

       distribution
              An ASCII bar chart to visualize the distribution (count column)

OVERHEAD

       This traces kernel functions and maintains in-kernel timestamps and a histogram, which are asynchronously
       copied  to user-space. While this method is very efficient, the rate of kernel functions can also be very
       high (>1M/sec), at which point the overhead is expected to be measurable. Measure in a  test  environment
       and  understand  overheads before use. You can also use funccount to measure the rate of kernel functions
       over a short duration, to set some expectations before use.

SOURCE

       This is from bcc.

              https://github.com/iovisor/bcc

       Also look in the bcc distribution for a companion _examples.txt file containing  example  usage,  output,
       and commentary for this tool.

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Brendan Gregg, Sasha Goldshtein

SEE ALSO

       funccount(8)

USER COMMANDS                                      2015-08-18                                     funclatency(8)