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62 lines
1.6 KiB
62 lines
1.6 KiB
4 months ago
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.TH dcstat 8 "2016-02-09" "USER COMMANDS"
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.SH NAME
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dcstat \- Directory entry cache (dcache) stats. Uses Linux eBPF/bcc.
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.SH SYNOPSIS
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.B dcstat
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[interval [count]]
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.SH DESCRIPTION
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The Linux directory entry cache (dcache) improves the performance of file and
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directory name lookups. This tool provides per-second summary statistics of
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dcache performance.
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This uses kernel dynamic tracing of kernel functions, lookup_fast() and
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d_lookup(), which will need to be modified to match kernel changes.
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Since this uses BPF, only the root user can use this tool.
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.SH REQUIREMENTS
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CONFIG_BPF and bcc.
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.SH EXAMPLES
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.TP
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Print summaries each second:
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#
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.B dcstat
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.TP
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Print output every five seconds, three times:
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#
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.B dcstat 5 3
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.SH FIELDS
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.TP
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REFS/s
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Number dcache lookups (references) per second.
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.TP
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SLOW/s
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Number of dcache lookups that failed the lookup_fast() path and executed the
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lookup_slow() path instead.
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.TP
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MISS/s
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Number of dcache misses (failed both fast and slow lookups).
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.TP
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HIT%
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Percentage of dcache hits over total references.
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.SH OVERHEAD
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The overhead depends on the frequency of file and directory name lookups.
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While the per-event overhead is low, some applications may make over 100k
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lookups per second, and the low per-event overhead will begin to add up, and
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could begin to be measurable (over 10% CPU usage). Measure in a test
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environment.
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.SH SOURCE
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This is from bcc.
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.IP
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https://github.com/iovisor/bcc
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.PP
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Also look in the bcc distribution for a companion _examples.txt file containing
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example usage, output, and commentary for this tool.
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.SH OS
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Linux
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.SH STABILITY
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Unstable - in development.
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.SH AUTHOR
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Brendan Gregg
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.SH SEE ALSO
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dcsnoop(8)
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