NAME

       runqlat.bt - CPU scheduler run queue latency as a histogram. Uses bpftrace/eBPF.

SYNOPSIS

       runqlat.bt

DESCRIPTION

       This  traces  time  spent  waiting  in the CPU scheduler for a turn on-CPU. This metric is
       often called run queue latency, or scheduler latency. This tool shows this  latency  as  a
       power-of-2  histogram  in nanoseconds, allowing multimodal distributions to be studied, as
       well as latency outliers.

       This tool uses the sched tracepoints.

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

REQUIREMENTS

       CONFIG_BPF and bpftrace.

EXAMPLES

       Trace CPU run queue latency system wide, printing a histogram on Ctrl-C:
              # runqlat.bt

FIELDS

       1st, 2nd
              This is a range of latency, in microseconds (shown in "[...)" set notation).

       3rd    A column showing the count of scheduler events in this range.

       4th    This is an ASCII histogram representing the count column.

OVERHEAD

       This traces scheduler functions, which can become very frequent. While eBPF has  very  low
       overhead,  and  this  tool  uses in-kernel maps for efficiency, the frequency of scheduler
       events for some workloads may be high enough  that  the  overhead  of  this  tool  becomes
       significant. Measure in a lab environment to quantify the overhead before use.

SOURCE

       This is from bpftrace.

              https://github.com/iovisor/bpftrace

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

       This is a bpftrace version of the bcc tool of the same name. The bcc tool may provide more
       options and customizations.

              https://github.com/iovisor/bcc

OS

       Linux

STABILITY

       Unstable - in development.

AUTHOR

       Brendan Gregg

SEE ALSO

       runqlen.bt(8), mpstat(1), pidstat(1), uptime(1)