runqlat.bt(8)

1runqlat.bt(8)               System Manager's Manual              runqlat.bt(8)
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NAME

6       runqlat.bt  - CPU scheduler run queue latency as a histogram. Uses bpf‐
7       trace/eBPF.
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SYNOPSIS

10       runqlat.bt
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DESCRIPTION

13       This traces time spent waiting in the CPU scheduler for a turn  on-CPU.
14       This  metric  is  often called run queue latency, or scheduler latency.
15       This tool shows this latency as a power-of-2 histogram in  nanoseconds,
16       allowing  multimodal  distributions  to  be studied, as well as latency
17       outliers.
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19       This tool uses the sched tracepoints.
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21       Since this uses BPF, only the root user can use this tool.
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REQUIREMENTS

24       CONFIG_BPF and bpftrace.
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EXAMPLES

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

32       1st, 2nd
33              This  is  a  range of latency, in microseconds (shown in "[...)"
34              set notation).
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36       3rd    A column showing the count of scheduler events in this range.
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38       4th    This is an ASCII histogram representing the count column.
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OVERHEAD

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

48       This is from bpftrace.
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50              https://github.com/iovisor/bpftrace
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52       Also look in the bpftrace distribution for  a  companion  _examples.txt
53       file containing example usage, output, and commentary for this tool.
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55       This  is  a  bpftrace version of the bcc tool of the same name. The bcc
56       tool may provide more options and customizations.
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58              https://github.com/iovisor/bcc
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OS

61       Linux
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STABILITY

64       Unstable - in development.
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AUTHOR

67       Brendan Gregg
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