bionic (8) dcstat-bpfcc.8.gz

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)