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)