dcstat - Directory entry cache (dcache) stats. Uses Linux eBPF/bcc.
The Linux directory entry cache (dcache) improves the performance of file and
directory name lookups. This tool provides per-second summary statistics of
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.
CONFIG_BPF and bcc.
- Print summaries each second:
- # dcstat
- Print output every five seconds, three times:
- # dcstat 5 3
- Number dcache lookups (references) per second.
- Number of dcache lookups that failed the lookup_fast() path
and executed the lookup_slow() path instead.
- Number of dcache misses (failed both fast and slow
- Percentage of dcache hits over total references.
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.
This is from bcc.
Also look in the bcc distribution for a companion _examples.txt file containing
example usage, output, and commentary for this tool.
Unstable - in development.