runqslower(8) System Manager's Manual runqslower(8)
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 equiva-
lent 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 func-
tions.
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 effi-
ciency, 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)
USER COMMANDS 2016-02-07 runqslower(8)
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