runqlen.bt(8) System Manager's Manual runqlen.bt(8)
NAME
runqlen.bt - CPU scheduler run queue length as a histogram. Uses bpf-
trace/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)
USER COMMANDS 2018-10-07 runqlen.bt(8)
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