Re: [RFC PATCH v1 1/1] perf test: Increase load in lock contention test on low-activity systems

[Namhyung Kim <namhyung@kernel.org>]

Hello,

On Wed, Jul 09, 2025 at 10:38:09PM +0200, Jan Polensky wrote:
> On low-activity systems, the 'kernel lock contention analysis test'
> often fails due to insufficient system load. To address this, the test
> now increases load by using multiple groups and threads in 'perf bench
> sched messaging', scaled to the number of available CPUs.
> 
> Signed-off-by: Jan Polensky <japo@linux.ibm.com>
> ---
>  tools/perf/tests/shell/lock_contention.sh | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/tests/shell/lock_contention.sh b/tools/perf/tests/shell/lock_contention.sh
> index 30d195d4c62f..e859e1503b5c 100755
> --- a/tools/perf/tests/shell/lock_contention.sh
> +++ b/tools/perf/tests/shell/lock_contention.sh
> @@ -44,7 +44,8 @@ check() {
>  test_record()
>  {
>  	echo "Testing perf lock record and perf lock contention"
> -	perf lock record -o ${perfdata} -- perf bench sched messaging > /dev/null 2>&1
> +	perf lock record -o ${perfdata} -- perf bench sched messaging \
> +		--group "$(nproc)" --thread "$(nproc)" > /dev/null 2>&1

  $ perf bench sched messaging -h
  # Running 'sched/messaging' benchmark:
  
   Usage: perf bench sched messaging <options>
  
      -g, --group <n>       Specify number of groups
      -l, --nr_loops <n>    Specify the number of loops to run (default: 100)
      -p, --pipe            Use pipe() instead of socketpair()
      -t, --thread          Be multi thread instead of multi process

The default value of --group option is 10 so it can be smaller on tiny
systems.  Note that it'd create 20 tasks for each group (I don't think
we have an option to control this).

Also --thread option doesn't take an argument so the number will be
ignored.

More importantly, there are several instances of this workload.
Probably we want to change all of them by introducing a shell variable.
But I'm a bit afraid how much overhead it'd bring up.

Thanks,
Namhyung


>  	# the output goes to the stderr and we expect only 1 output (-E 1)
>  	perf lock contention -i ${perfdata} -E 1 -q 2> ${result}
>  	if [ "$(cat "${result}" | wc -l)" != "1" ]; then
> --
> 2.48.1
>