bcc-cpudist(8)

1cpudist(8)                  System Manager's Manual                 cpudist(8)
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NAME

6       cpudist - On- and off-CPU task time as a histogram.
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SYNOPSIS

9       cpudist [-h] [-O] [-T] [-m] [-P] [-L] [-p PID] [interval] [count]
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DESCRIPTION

12       This  measures  the time a task spends on the CPU before being desched‐
13       uled, and shows the times as a histogram. Tasks that spend a very short
14       time  on  the  CPU  can be indicative of excessive context-switches and
15       poor workload distribution, and possibly point to a  shared  source  of
16       contention  that  keeps tasks switching in and out as it becomes avail‐
17       able (such as a mutex).
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19       Similarly, the tool can also measure the time  a  task  spends  off-CPU
20       before  it  is scheduled again. This can be helpful in identifying long
21       blocking and I/O operations, or alternatively very  short  descheduling
22       times due to short-lived locks or timers.
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24       This  tool uses in-kernel eBPF maps for storing timestamps and the his‐
25       togram, for efficiency. Despite this, the overhead  of  this  tool  may
26       become significant for some workloads: see the OVERHEAD section.
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28       Since this uses BPF, only the root user can use this tool.
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REQUIREMENTS

31       CONFIG_BPF and bcc.
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OPTIONS

34       -h     Print usage message.
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36       -O     Measure off-CPU time instead of on-CPU time.
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38       -T     Include timestamps on output.
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40       -m     Output histogram in milliseconds.
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42       -P     Print  a histogram for each PID (tgid from the kernel's perspec‐
43              tive).
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45       -L     Print a histogram for each TID (pid from the  kernel's  perspec‐
46              tive).
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48       -p PID Only show this PID (filtered in kernel for efficiency).
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50       interval
51              Output interval, in seconds.
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53       count  Number of outputs.
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EXAMPLES

56       Summarize task on-CPU time as a histogram:
57              # cpudist
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59       Summarize task off-CPU time as a histogram:
60              # cpudist -O
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62       Print 1 second summaries, 10 times:
63              # cpudist 1 10
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65       Print  1  second  summaries,  using  milliseconds as units for the his‐
66       togram, and include timestamps on output:
67              # cpudist -mT 1
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69       Trace PID 186 only, 1 second summaries:
70              # cpudist -P 185 1
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FIELDS

73       usecs  Microsecond range
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75       msecs  Millisecond range
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77       count  How many times a task event fell into this range
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79       distribution
80              An ASCII bar chart to visualize the distribution (count column)
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OVERHEAD

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

90       This is from bcc.
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92              https://github.com/iovisor/bcc
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94       Also look in the bcc distribution for  a  companion  _example.txt  file
95       containing example usage, output, and commentary for this tool.
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OS

98       Linux
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STABILITY

101       Unstable - in development.
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AUTHOR

104       Sasha Goldshtein
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