dcstat(8) System Manager's Manual dcstat(8)

# [NAME](#NAME)

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

# [SYNOPSIS](#SYNOPSIS)

**dcstat** \[interval \[count]]

# [DESCRIPTION](#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](#REQUIREMENTS)

CONFIG\_BPF and bcc.

# [EXAMPLES](#EXAMPLES)

[Print summaries each second:](#Print)

\# **dcstat**

[Print output every five seconds, three times:](#Print~2)

\# **dcstat 5 3**

# [FIELDS](#FIELDS)

[REFS/s](#REFS/s)

Number dcache lookups (references) per second.

[SLOW/s](#SLOW/s)

Number of dcache lookups that failed the lookup\_fast() path and executed the lookup\_slow() path instead.

[MISS/s](#MISS/s)

Number of dcache misses (failed both fast and slow lookups).

[HIT%](#HIT_)

Percentage of dcache hits over total references.

# [OVERHEAD](#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](#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](#OS)

Linux

# [STABILITY](#STABILITY)

Unstable - in development.

# [AUTHOR](#AUTHOR)

Brendan Gregg

# [SEE ALSO](#SEE_ALSO)

[dcsnoop(8)](/man/enterprise-packages/bcc/dcsnoop.8)

2016-02-09 USER COMMANDS

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Document: dcstat(8) from bcc 0.37.0-r3 (Chainguard OS)
Source: https://github.com/iovisor/bcc