linux-kernel - Re: [PATCH v15 10/10] perf test: Add direct off-cpu test

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Message-ID: <CAH0uvohY6fBaJvMZNi-fcHEW1Dw7Zp5Q_+ZxNgcaaFary-3sWw@mail.gmail.com>
Date: Thu, 13 Feb 2025 15:04:10 -0800
From: Howard Chu <howardchu95@...il.com>
To: acme@...nel.org
Cc: namhyung@...nel.org, jolsa@...nel.org, irogers@...gle.com, 
	adrian.hunter@...el.com, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>, 
	James Clark <james.clark@...aro.org>, Kan Liang <kan.liang@...ux.intel.com>, 
	Mark Rutland <mark.rutland@....com>, Peter Zijlstra <peterz@...radead.org>, 
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH v15 10/10] perf test: Add direct off-cpu test

Hello,

On Thu, Feb 13, 2025 at 3:00 PM Howard Chu <howardchu95@...il.com> wrote:
>
> Why is there a --off-cpu-thresh 2000?
>
> We collect an off-cpu period __ONLY ONCE__, either in direct sample form,
> or in accumulated form (in BPF stack trace map).
>
> If I don't add --off-cpu-thresh 2000, the sample in the original test
> goes into the ring buffer instead of the BPF stack trace map.
>
> Additionally, when using -e dummy, the ring buffer is not open, causing
> us to lose a sample.

Just noticed that this commit message is wrong, should be:
"""
Add tests for direct off-cpu samples and --off-cpu-thresh option.
"""

Sorry.

Thanks,
Howard

>
> Signed-off-by: Howard Chu <howardchu95@...il.com>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Cc: Ian Rogers <irogers@...gle.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: James Clark <james.clark@...aro.org>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Kan Liang <kan.liang@...ux.intel.com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Link: https://lore.kernel.org/r/20241108204137.2444151-11-howardchu95@gmail.com
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> ---
>  tools/perf/tests/shell/record_offcpu.sh | 71 +++++++++++++++++++++++++
>  1 file changed, 71 insertions(+)
>
> diff --git a/tools/perf/tests/shell/record_offcpu.sh b/tools/perf/tests/shell/record_offcpu.sh
> index 678947fe69ee..c5d6cae94c65 100755
> --- a/tools/perf/tests/shell/record_offcpu.sh
> +++ b/tools/perf/tests/shell/record_offcpu.sh
> @@ -7,6 +7,9 @@ set -e
>  err=0
>  perfdata=$(mktemp /tmp/__perf_test.perf.data.XXXXX)
>
> +ts=$(printf "%u" $((~0 << 32))) # OFF_CPU_TIMESTAMP
> +dummy_timestamp=${ts%???} # remove the last 3 digits to match perf script
> +
>  cleanup() {
>    rm -f ${perfdata}
>    rm -f ${perfdata}.old
> @@ -19,6 +22,9 @@ trap_cleanup() {
>  }
>  trap trap_cleanup EXIT TERM INT
>
> +test_over_thresh="Threshold test (over threshold)"
> +test_below_thresh="Threshold test (below threshold)"
> +
>  test_offcpu_priv() {
>    echo "Checking off-cpu privilege"
>
> @@ -88,6 +94,63 @@ test_offcpu_child() {
>    echo "Child task off-cpu test [Success]"
>  }
>
> +# task blocks longer than the --off-cpu-thresh, perf should collect a direct sample
> +test_offcpu_over_thresh() {
> +  echo "${test_over_thresh}"
> +
> +  # collect direct off-cpu samples for tasks blocked for more than 999ms
> +  if ! perf record -e dummy --off-cpu --off-cpu-thresh 999 -o ${perfdata} -- sleep 1 2> /dev/null
> +  then
> +    echo "${test_over_thresh} [Failed record]"
> +    err=1
> +    return
> +  fi
> +  # direct sample's timestamp should be lower than the dummy_timestamp of the at-the-end sample
> +  # check if a direct sample exists
> +  if ! perf script --time "0, ${dummy_timestamp}" -i ${perfdata} -F event | grep -q "offcpu-time"
> +  then
> +    echo "${test_over_thresh} [Failed missing direct samples]"
> +    err=1
> +    return
> +  fi
> +  # there should only be one direct sample, and its period should be higher than off-cpu-thresh
> +  if ! perf script --time "0, ${dummy_timestamp}" -i ${perfdata} -F period | \
> +       awk '{ if (int($1) > 999000000) exit 0; else exit 1; }'
> +  then
> +    echo "${test_over_thresh} [Failed off-cpu time too short]"
> +    err=1
> +    return
> +  fi
> +  echo "${test_over_thresh} [Success]"
> +}
> +
> +# task blocks shorter than the --off-cpu-thresh, perf should collect an at-the-end sample
> +test_offcpu_below_thresh() {
> +  echo "${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 12000 -o ${perfdata} -- sleep 1 2> /dev/null
> +  then
> +    echo "${test_below_thresh} [Failed record]"
> +    err=1
> +    return
> +  fi
> +  # see if there's an at-the-end sample
> +  if ! perf script --time "${dummy_timestamp}," -i ${perfdata} -F event | grep -q 'offcpu-time'
> +  then
> +    echo "${test_below_thresh} [Failed at-the-end samples cannot be found]"
> +    err=1
> +    return
> +  fi
> +  # plus there shouldn't be any direct samples
> +  if perf script --time "0, ${dummy_timestamp}" -i ${perfdata} -F event | grep -q 'offcpu-time'
> +  then
> +    echo "${test_below_thresh} [Failed direct samples are found when they shouldn't be]"
> +    err=1
> +    return
> +  fi
> +  echo "${test_below_thresh} [Success]"
> +}
>
>  test_offcpu_priv
>
> @@ -99,5 +162,13 @@ if [ $err = 0 ]; then
>    test_offcpu_child
>  fi
>
> +if [ $err = 0 ]; then
> +  test_offcpu_over_thresh
> +fi
> +
> +if [ $err = 0 ]; then
> +  test_offcpu_below_thresh
> +fi
> +
>  cleanup
>  exit $err
> --
> 2.45.2
>