NAME¶

runqlen.bt - CPU scheduler run queue length as a histogram. Uses bpftrace/eBPF.

SYNOPSIS¶

runqlen.bt

DESCRIPTION¶

This program summarizes scheduler queue length as a histogram, and can also show run queue occupancy. It works by sampling the run queue length on all CPUs at 99 Hertz.

This tool can be used to identify imbalances, eg, when processes are bound to CPUs causing queueing, or interrupt mappings causing the same.

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

REQUIREMENTS¶

CONFIG_BPF and bpftrace.

EXAMPLES¶

Trace CPU run queue length system wide, printing a histogram on Ctrl-C:

# runqlen.bt

FIELDS¶

1st, 2nd

The run queue length is shown in the first field (after "[").

3rd

A column showing the count of samples in for that length.

4th

This is an ASCII histogram representing the count column.

OVERHEAD¶

This samples scheduler structs at 99 Hertz across all CPUs. Relatively, this is a low rate of events, and the overhead of this tool is expected to be near zero.

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¶

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