bcc-dcstat man page

dcstat ā€” 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)

Info

2016-02-09 USER COMMANDS