Manual: dcstat-bpfcc

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 over‐
       head 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 envi‐
       ronment.

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,	out‐
       put, 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)