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