Re: [PATCH v1 10/12] perf tests: Speed up off-cpu profiling tests

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Scaling down the off-cpu threshold margin to 20ms in the below-threshold test introduces severe test flakiness due to scheduling latencies.
--

commit 9a01b97619e9e9de7c1d6aeb44a8dcd7c6b1f2b5
Author: Ian Rogers <irogers@google.com>

perf tests: Speed up off-cpu profiling tests
    
This commit speeds up the off-cpu profiling tests by scaling down workload
durations and thresholds by a factor of 10. The sleep time is reduced from
1 second to 0.1 seconds, decreasing the total test sleep overhead from 3.0
seconds to 0.3 seconds.

> diff --git a/tools/perf/tests/shell/record_offcpu.sh b/tools/perf/tests/shell/record_offcpu.sh
> --- a/tools/perf/tests/shell/record_offcpu.sh
> +++ b/tools/perf/tests/shell/record_offcpu.sh

[ ... ]

> @@ -128,8 +128,8 @@ test_offcpu_above_thresh() {
>  test_offcpu_below_thresh() {
>    echo "${test_below_thresh}"
>  
> -  # collect direct off-cpu samples for tasks blocked for more than 1.2s
> -  if ! perf record -e dummy --off-cpu --off-cpu-thresh 1200 -o ${perfdata} -- sleep 1 2> /dev/null
> +  # collect direct off-cpu samples for tasks blocked for more than 120ms
> +  if ! perf record -e dummy --off-cpu --off-cpu-thresh 120 -o ${perfdata} -- sleep 0.1 2> /dev/null

[Severity: Medium]
Will this tight 20ms margin cause test flakiness on busy systems or CI
environments?

In test_offcpu_below_thresh(), the test asserts that no direct off-cpu
samples are generated, requiring the total off-cpu time to remain strictly
below the 120ms threshold. Since sleep 0.1 guarantees a minimum of 100ms
off-cpu time, this leaves only 20ms for system scheduling overhead such as
timer granularity, wake-up latency, and runqueue wait time.

If scheduling latency pushes the total off-cpu time over 120ms, the BPF
program will emit a direct sample, causing the test to falsely fail. The
previous configuration of a 1000ms sleep versus a 1200ms threshold provided
a much more resilient 200ms margin.

>    then
>      echo "${test_below_thresh} [Failed record]"
>      err=1

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260616012744.4049193-1-irogers@google.com?part=10