Provided by: bpfcc-tools_0.29.1+ds-1ubuntu7_all bug

NAME

       runqslower - Trace long process scheduling delays.

SYNOPSIS

       runqslower [-p PID] [-t TID] [-P] [min_us]

DESCRIPTION

       This  measures the time a task spends waiting on a run queue (or equivalent scheduler data structure) for
       a turn on-CPU, and shows occurrences of time exceeding passed threshold. This time should be small, but a
       task may need to wait its turn due to CPU load. The higher the CPU load, the longer a task will generally
       need to wait its turn.

       This tool measures two types of run queue latency:

       1. The time from a task being enqueued on a run queue to its context switch and  execution.  This  traces
       ttwu_do_wakeup(),  wake_up_new_task()  -> finish_task_switch() with either raw tracepoints (if supported)
       or kprobes and instruments the run queue latency after a voluntary context switch.

       2. The time from when a task was involuntary context switched and still in the runnable state, to when it
       next executed. This is instrumented from finish_task_switch() alone.

       The overhead of this tool may become significant for some workloads: see the OVERHEAD section.

       This works by tracing various kernel scheduler functions using dynamic tracing, and will need updating to
       match any changes to these functions.

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

REQUIREMENTS

       CONFIG_BPF and bcc.

OPTIONS

       -h     Print usage message.

       -p PID Only show this PID (filtered in kernel for efficiency).

       -t TID Only show this TID (filtered in kernel for efficiency).

       min_us Minimum scheduling delay in microseconds to output.

       -P     Also show previous task comm and TID.

EXAMPLES

       Show scheduling delays longer than 10ms:
              # runqslower

       Show scheduling delays longer than 1ms for process with PID 123:
              # runqslower -p 123 1000

FIELDS

       TIME   Time of when scheduling event occurred.

       COMM   Process name.

       PID    Process ID.

       LAT(us)
              Scheduling latency from time when task was ready to run to the time it was assigned to  a  CPU  to
              run.

OVERHEAD

       This  traces  scheduler  functions, which can become very frequent. While eBPF has very low overhead, and
       this tool uses in-kernel maps for efficiency, the frequency of scheduler events for some workloads may be
       high  enough that the overhead of this tool becomes significant. Measure in a lab environment to 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

       Ivan Babrou, original BCC Python version Andrii Nakryiko, CO-RE version

SEE ALSO

       runqlen(8), runqlat(8), pidstat(1)