NAME

       funcinterval - Time interval between the same function, tracepoint as a histogram.

SYNOPSIS

       funcinterval [-h] [-p PID] [-i INTERVAL] [-d DURATION] [-T] [-u] [-m] [-v] pattern

DESCRIPTION

       This tool times interval between the same function as a histogram.

       eBPF/bcc is very suitable for platform performance tuning.  By funclatency, we can profile
       specific functions to know how latency this function costs. However, sometimes performance
       drop  is  not  about  the  latency  of  function  but the interval between function calls.
       funcinterval is born for this purpose.

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

       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.  -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.

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

EXAMPLES

       Time the interval of do_sys_open() kernel function as a histogram:
              # funcinterval do_sys_open

       Time the interval of xhci_ring_ep_doorbell(), in microseconds:
              # funcinterval -u xhci_ring_ep_doorbell

       Time the interval of do_nanosleep(), in milliseconds
              # funcinterval -m do_nanosleep

       Output every 5 seconds, with timestamps:
              # funcinterval -mTi 5 vfs_read

       Time process 181 only:
              # funcinterval -p 181 vfs_read

       Time the interval of mm_vmscan_direct_reclaim_begin tracepoint:
              # funcinterval t:vmscan:mm_vmscan_direct_reclaim_begin

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

       Edward Wu

SEE ALSO

       funclatency(8) funccount(8)