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86 lines
2.1 KiB
86 lines
2.1 KiB
4 months ago
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.TH cachestat 8 "2016-01-30" "USER COMMANDS"
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.SH NAME
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cachestat \- Statistics for linux page cache hit/miss ratios. Uses Linux eBPF/bcc.
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.SH SYNOPSIS
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.B cachestat
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[-T] [interval [count]]
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.SH DESCRIPTION
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This traces four kernel functions and prints per-second summaries. This can
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be useful for general workload characterization, and looking for patterns
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in operation usage over time.
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This works by tracing kernel page cache functions using dynamic tracing, and will
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need updating to match any changes to these functions. Edit the script to
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customize which functions are traced.
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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 every five second:
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#
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.B cachestat
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.TP
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Print summaries every five seconds with timestamp:
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#
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.B cachestat -T
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.TP
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Print summaries each second:
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#
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.B cachestat 1
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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 cachestat 5 3
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.TP
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Print output with timestamp every five seconds, three times:
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#
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.B cachestat -T 5 3
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.SH FIELDS
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.TP
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TIME
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Timestamp.
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.TP
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HITS
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Number of page cache hits.
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.TP
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MISSES
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Number of page cache misses.
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.TP
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DIRTIES
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Number of dirty pages added to the page cache.
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.TP
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READ_HIT%
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Read hit percent of page cache usage.
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.TP
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WRITE_HIT%
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Write hit percent of page cache usage.
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.TP
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BUFFERS_MB
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Buffers size taken from /proc/meminfo.
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.TP
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CACHED_MB
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Cached amount of data in current page cache taken from /proc/meminfo.
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.SH OVERHEAD
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This traces various kernel page cache functions and maintains in-kernel counts, which
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are asynchronously copied to user-space. While the rate of operations can
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be very high (>1G/sec) we can have up to 34% overhead, this is still a relatively efficient way to trace
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these events, and so the overhead is expected to be small for normal workloads.
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Measure in a test 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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Allan McAleavy
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.SH SEE ALSO
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https://github.com/brendangregg/perf-tools/blob/master/fs/cachestat
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