Manual: wqlat-bpfcc

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

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

USER COMMANDS						 2024-01-29						    wqlat(8)