dcstat [interval [count]]
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.
CONFIG_BPF and bcc.
- Print summaries each second:
- 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 lookups).
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.