---
name: "wqlat-bpfcc"
section: "8"
platform: "linux"
package: "bpfcc-tools"
version: "0.31.0+ds-7"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/wqlat-bpfcc"
---

# wqlat-bpfcc(8)

Summarize kernel workqueue latency as a histogram.

## NAME

wqlat - Summarize kernel workqueue latency as a histogram.

## SYNOPSIS

**wqlat \[-h\] \[-T\] \[-N\] \[-W\] \[-w WQNAME\] \[interval \[count\]\]**

## DESCRIPTION

wqlat traces  work's waiting on workqueue, and records the distribution of work's queuing latency (time). This is printed as a histogram  either on Ctrl-C, or after a given interval in seconds.

This tool uses in-kernel eBPF maps for storing timestamps and the histogram, for efficiency.

This tool uses the workqueue:workqueue\_queue\_work and workqueue:workqueue\_execute\_start kernel tracepoints, which is a stable tracing mechanism. Please note BPF programs can  attach to tracepoints from Linux 4.7 only, so this tools can only support kernel 4.7 or later version.

Since this uses BPF, only the root user can use this tool.

## REQUIREMENTS

CONFIG\_BPF and bcc.

## OPTIONS

\-h Print usage message.

- \-T

  Include timestamps on output.

- \-N

  Output histogram in nanoseconds.

- \-W

  Print a histogram per workqueue.

- \-w WQNAME

  Trace this workqueue only

- interval

  Output interval, in seconds.

- count

  Number of outputs.

## EXAMPLES

- Summarize kernel workqueue latency as a histogram:

  \# **wqlat**

- Print 1 second summaries, 10 times:

  \# **wqlat 1 10**

- Print 1 second summaries, using nanoseconds as units for the histogram, and

  include timestamps on output: # **wqlat -NT 1**

- Print 1 second summaries, 10 times per workqueue:

  \# **wqlat -W 1 10**

- Print 1 second summaries for workqueue nvmet\_tcp\_wq:

  \# **wqlat -w nvmet\_tcp\_wq 1**

## FIELDS

- usecs

  Microsecond range

- nsecs

  Nanosecond range

- count

  How many works into this range

- distribution

  An ASCII bar chart to visualize the distribution (count column)

## OVERHEAD

This traces kernel functions and maintains in-kernel timestamps and a histogram, which are asynchronously copied to user-space. This method is very efficient, and the overhead for most workqueue scheduling rates (\< 100k) should be  negligible.If you have a higher workqueue scheduling, please test and quantify  the overhead before use.

## 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

Ping Gan

## SEE ALSO

biolatency