runqslower_example.txt

Demonstrations of runqslower, the Linux eBPF/bcc version.


runqslower shows high latency scheduling times between tasks being
ready to run and them running on CPU after that. For example:

# runqslower

Note: Showing TID (thread id) in the report column. The smallest
execution unit becomes a TID when using the --pid flag as
in that case the tool reports not only the parent pid but
its children threads as well.

Tracing run queue latency higher than 10000 us.

TIME     COMM             TID           LAT(us)
04:16:32 cc1              12924           12739
04:16:32 sh               13640           12118
04:16:32 make             13639           12730
04:16:32 bash             13655           12047
04:16:32 bash             13657           12744
04:16:32 bash             13656           12880
04:16:32 sh               13660           10846
04:16:32 gcc              13663           12681
04:16:32 make             13668           10814
04:16:32 make             13670           12988
04:16:32 gcc              13677           11770
04:16:32 gcc              13678           23519
04:16:32 as               12999           20541
[...]

This shows various processes waiting for available CPU during a Linux kernel
build. By default the output contains delays for more than 10ms.

These delays can be analyzed in depth with "perf sched" tool, see:

* http://www.brendangregg.com/blog/2017-03-16/perf-sched.html

USAGE message:

# ./runqslower -h
usage: runqslower.py [-h] [-p PID | -t TID] [min_us]

Trace high run queue latency

positional arguments:
  min_us             minimum run queue latency to trace, in us (default 10000)

optional arguments:
  -h, --help         show this help message and exit
  -p PID, --pid PID  trace this PID only
  -t TID, --tid TID  trace this TID only
  -P, --previous     also show previous task name and TID

examples:
    ./runqslower         # trace run queue latency higher than 10000 us (default)
    ./runqslower 1000    # trace run queue latency higher than 1000 us
    ./runqslower -p 123  # trace pid 123
    ./runqslower -t 123  # trace tid 123 (use for threads only)
    ./runqslower -P      # also show previous task comm and TID