dcstat.8

.TH dcstat 8  "2016-02-09" "USER COMMANDS"
.SH NAME
dcstat \- Directory entry cache (dcache) stats. Uses Linux eBPF/bcc.
.SH SYNOPSIS
.B dcstat
[interval [count]]
.SH 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.
.SH REQUIREMENTS
CONFIG_BPF and bcc.
.SH EXAMPLES
.TP
Print summaries each second:
#
.B dcstat
.TP
Print output every five seconds, three times:
#
.B dcstat 5 3
.SH FIELDS
.TP
REFS/s
Number dcache lookups (references) per second.
.TP
SLOW/s
Number of dcache lookups that failed the lookup_fast() path and executed the
lookup_slow() path instead.
.TP
MISS/s
Number of dcache misses (failed both fast and slow lookups).
.TP
HIT%
Percentage of dcache hits over total references.
.SH 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.
.SH SOURCE
This is from bcc.
.IP
https://github.com/iovisor/bcc
.PP
Also look in the bcc distribution for a companion _examples.txt file containing
example usage, output, and commentary for this tool.
.SH OS
Linux
.SH STABILITY
Unstable - in development.
.SH AUTHOR
Brendan Gregg
.SH SEE ALSO
dcsnoop(8)