linux-kernel - Re: [PATCH v2] perf test: Allow tolerance for leader sampling test

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Message-ID: <CAJpZYjUCwZDDL-19nGwZNgo1X9o3sTJoL2NeR__CxrTXTB4V4Q@mail.gmail.com>
Date: Wed, 9 Apr 2025 16:19:38 -0700
From: Chun-Tse Shao <ctshao@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: Ian Rogers <irogers@...gle.com>, Thomas Richter <tmricht@...ux.ibm.com>, peterz@...radead.org, 
	mingo@...hat.com, acme@...nel.org, namhyung@...nel.org, mark.rutland@....com, 
	alexander.shishkin@...ux.intel.com, jolsa@...nel.org, adrian.hunter@...el.com, 
	kan.liang@...ux.intel.com, james.clark@...aro.org, dapeng1.mi@...ux.intel.com, 
	vmolnaro@...hat.com, linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v2] perf test: Allow tolerance for leader sampling test

Please ignore this since Thomas Richter already submitted the fix [1]
with bc invocation.

[1] lore.kernel.org/20250408074641.1471473-1-tmricht@...ux.ibm.com/

Thanks,
CT

On Wed, Apr 9, 2025 at 4:12 PM Chun-Tse Shao <ctshao@...gle.com> wrote:
>
> There is a known issue that the leader sampling is inconsistent, since
> throttle only affect leader, not the slave. The detail is in [1]. To
> maintain test coverage, this patch sets a tolerance rate of 80% to
> accommodate the throttled samples and prevent test failures due to
> throttling.
>
> [1] lore.kernel.org/20250328182752.769662-1-ctshao@...gle.com
>
> Signed-off-by: Chun-Tse Shao <ctshao@...gle.com>
> Suggested-by: Ian Rogers <irogers@...gle.com>
> Suggested-by: Thomas Richter <tmricht@...ux.ibm.com>
> Tested-by: Thomas Richter <tmricht@...ux.ibm.com>
> ---
>  tools/perf/tests/shell/record.sh | 28 ++++++++++++++++++++++++----
>  1 file changed, 24 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/tests/shell/record.sh b/tools/perf/tests/shell/record.sh
> index ba8d873d3ca7..06a718e80121 100755
> --- a/tools/perf/tests/shell/record.sh
> +++ b/tools/perf/tests/shell/record.sh
> @@ -240,19 +240,39 @@ test_leader_sampling() {
>    fi
>    index=0
>    perf script -i "${perfdata}" > $script_output
> +  # Check if the two instruction counts are equal in each record.
> +  # However, the throttling code doesn't consider event grouping. During throttling, only the
> +  # leader is stopped, causing the slave's counts significantly higher. To temporarily solve this,
> +  # let's set the tolerance rate to 80%.
> +  # TODO: Revert the code for tolerance once the throttling mechanism is fixed.
> +  valid_counts=0
> +  invalid_counts=0
> +  tolerance_rate=0.8
>    while IFS= read -r line
>    do
> -    # Check if the two instruction counts are equal in each record
>      cycles=$(echo $line | awk '{for(i=1;i<=NF;i++) if($i=="cycles:") print $(i-1)}')
>      if [ $(($index%2)) -ne 0 ] && [ ${cycles}x != ${prev_cycles}x ]
>      then
> -      echo "Leader sampling [Failed inconsistent cycles count]"
> -      err=1
> -      return
> +      invalid_counts=$(($invalid_counts+1))
> +    else
> +      valid_counts=$(($valid_counts+1))
>      fi
>      index=$(($index+1))
>      prev_cycles=$cycles
>    done < $script_output
> +  total_counts=$(bc <<< "$invalid_counts+$valid_counts")
> +  if (( $(bc <<< "$total_counts <= 0") ))
> +  then
> +      echo "Leader sampling [No sample generated]"
> +      err=1
> +      return
> +  fi
> +  if (( $(bc <<< "scale=3; $invalid_counts/$total_counts > 1-$tolerance_rate") ))
> +  then
> +      echo "Leader sampling [Failed inconsistent cycles count]"
> +      err=1
> +      return
> +  fi
>    echo "Basic leader sampling test [Success]"
>  }
>
> --
> 2.49.0.504.g3bcea36a83-goog
>