bcc-dcstat(8)

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

6       dcstat - Directory entry cache (dcache) stats. Uses Linux eBPF/bcc.
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SYNOPSIS

9       dcstat [interval [count]]
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DESCRIPTION

12       The  Linux  directory  entry cache (dcache) improves the performance of
13       file and directory name lookups. This tool provides per-second  summary
14       statistics of dcache performance.
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16       This uses kernel dynamic tracing of kernel functions, lookup_fast() and
17       d_lookup(), which will need to be modified to match kernel changes.
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19       Since this uses BPF, only the root user can use this tool.
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REQUIREMENTS

22       CONFIG_BPF and bcc.
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EXAMPLES

25       Print summaries each second:
26              # dcstat
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28       Print output every five seconds, three times:
29              # dcstat 5 3
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FIELDS

32       REFS/s Number dcache lookups (references) per second.
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34       SLOW/s Number of dcache lookups that failed the lookup_fast() path  and
35              executed the lookup_slow() path instead.
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37       MISS/s Number of dcache misses (failed both fast and slow lookups).
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39       HIT%   Percentage of dcache hits over total references.
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OVERHEAD

42       The  overhead  depends  on  the  frequency  of  file and directory name
43       lookups.  While the per-event overhead is low,  some  applications  may
44       make  over 100k lookups per second, and the low per-event overhead will
45       begin to add up, and could begin to be measurable (over 10% CPU usage).
46       Measure in a test environment.
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SOURCE

49       This is from bcc.
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51              https://github.com/iovisor/bcc
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53       Also  look  in  the bcc distribution for a companion _examples.txt file
54       containing example usage, output, and commentary for this tool.
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OS

57       Linux
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STABILITY

60       Unstable - in development.
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AUTHOR

63       Brendan Gregg
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