dcstat - Directory entry cache (dcache) stats. Uses Linux eBPF/bcc. 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: # dcstat

Print output every five seconds, three times: # dcstat 5 3

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.

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. 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.

Linux Unstable - in development. Brendan Gregg dcsnoop(8)