[PATCH 1/2] perf test: Fix LBR test by ignoring idle task

[PATCH 1/2] perf test: Fix LBR test by ignoring idle task

[Namhyung Kim]

I found 'perf record LBR tests' failing due to empty branch stacks.

  $ perf test -v LBR
  ...
  LBR system wide any branch test
  Lowering default frequency rate from 4000 to 1000.
  Please consider tweaking /proc/sys/kernel/perf_event_max_sample_rate.
  [ perf record: Woken up 8 times to write data ]
  [ perf record: Captured and wrote 3.142 MB /tmp/__perf_test.perf.data.dgSBl (3572 samples) ]
  LBR system wide any branch test: 3572 samples
  LBR system wide any branch test [Failed empty br stack ratio exceed 2%: 3%]
  LBR system wide any call test
  Lowering default frequency rate from 4000 to 1000.
  Please consider tweaking /proc/sys/kernel/perf_event_max_sample_rate.
  [ perf record: Woken up 8 times to write data ]
  [ perf record: Captured and wrote 3.337 MB /tmp/__perf_test.perf.data.dgSBl (3967 samples) ]
  LBR system wide any call test: 3967 samples
  LBR system wide any call test [Failed empty br stack ratio exceed 2%: 9%]
  ...

The failing cases were in system-wide mode and I realized that the
samples were from the idle tasks (swapper).  I suspect going to/from
idle state may affect the LBR contents.

If we can skip empty branch stacks from the idle tasks, the failure
should go away.  I can see the following output in perf report -D.

  $ perf report -D | grep -m5 -A3 'branch stack: nr:0'
  ...
  --
  ... branch stack: nr:0
   ... thread: swapper:0
   ...... dso: /proc/kcore

  --
  ... branch stack: nr:0
   ... thread: swapper:0
   ...... dso: /proc/kcore

  --
  ... branch stack: nr:0
   ... thread: DefaultEventMan:10282
   ...... dso: /proc/kcore

  --
  ... branch stack: nr:0
   ... thread: swapper:0
   ...... dso: /proc/kcore

  --
  ... branch stack: nr:0
   ... thread: swapper:0
   ...... dso: /proc/kcore

  $ perf report -D | grep -c 'branch stack: nr:0'
  145

  $ perf report -D | grep -A3 'branch stack: nr:0' | grep thread | grep -c swapper
  i36

  $ perf report -D | grep -A3 'branch stack: nr:0' | grep thread | grep -cv swapper
  9

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/tests/shell/record_lbr.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/tests/shell/record_lbr.sh b/tools/perf/tests/shell/record_lbr.sh
index 8d750ee631f877fd..afad02d0180e023c 100755
--- a/tools/perf/tests/shell/record_lbr.sh
+++ b/tools/perf/tests/shell/record_lbr.sh
@@ -93,7 +93,7 @@ lbr_test() {
     return
   fi
 
-  zero_nr=$(echo "$out" | grep -c 'branch stack: nr:0' || true)
+  zero_nr=$(echo "$out" | grep -A3 'branch stack: nr:0' | grep thread | grep -cv swapper || true)
   r=$(($zero_nr * 100 / $bs_nr))
   if [ $r -gt $threshold ]; then
     echo "$test [Failed empty br stack ratio exceed $threshold%: $r%]"
-- 
2.49.0.1015.ga840276032-goog

[PATCH 2/2] perf test: Update sysfs path for core PMU caps

[Namhyung Kim]

While cpu is a system device, it'd be better to use a path for
event_source devices when it checks PMU capability.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/tests/shell/record_lbr.sh | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/tests/shell/record_lbr.sh b/tools/perf/tests/shell/record_lbr.sh
index afad02d0180e023c..6fcb5e52b9b4fcf6 100755
--- a/tools/perf/tests/shell/record_lbr.sh
+++ b/tools/perf/tests/shell/record_lbr.sh
@@ -4,7 +4,8 @@
 
 set -e
 
-if [ ! -f /sys/devices/cpu/caps/branches ] && [ ! -f /sys/devices/cpu_core/caps/branches ]
+if [ ! -f /sys/bus/event_source/devices/cpu/caps/branches ] &&
+   [ ! -f /sys/bus/event_source/devices/cpu_core/caps/branches ]
 then
   echo "Skip: only x86 CPUs support LBR"
   exit 2
-- 
2.49.0.1015.ga840276032-goog

Re: [PATCH 1/2] perf test: Fix LBR test by ignoring idle task

[Ian Rogers]

On Fri, May 9, 2025 at 2:30 PM Namhyung Kim <namhyung@kernel.org> wrote:
>
> I found 'perf record LBR tests' failing due to empty branch stacks.
>
>   $ perf test -v LBR
>   ...
>   LBR system wide any branch test
>   Lowering default frequency rate from 4000 to 1000.
>   Please consider tweaking /proc/sys/kernel/perf_event_max_sample_rate.
>   [ perf record: Woken up 8 times to write data ]
>   [ perf record: Captured and wrote 3.142 MB /tmp/__perf_test.perf.data.dgSBl (3572 samples) ]
>   LBR system wide any branch test: 3572 samples
>   LBR system wide any branch test [Failed empty br stack ratio exceed 2%: 3%]
>   LBR system wide any call test
>   Lowering default frequency rate from 4000 to 1000.
>   Please consider tweaking /proc/sys/kernel/perf_event_max_sample_rate.
>   [ perf record: Woken up 8 times to write data ]
>   [ perf record: Captured and wrote 3.337 MB /tmp/__perf_test.perf.data.dgSBl (3967 samples) ]
>   LBR system wide any call test: 3967 samples
>   LBR system wide any call test [Failed empty br stack ratio exceed 2%: 9%]
>   ...
>
> The failing cases were in system-wide mode and I realized that the
> samples were from the idle tasks (swapper).  I suspect going to/from
> idle state may affect the LBR contents.
>
> If we can skip empty branch stacks from the idle tasks, the failure
> should go away.  I can see the following output in perf report -D.
>
>   $ perf report -D | grep -m5 -A3 'branch stack: nr:0'
>   ...
>   --
>   ... branch stack: nr:0
>    ... thread: swapper:0
>    ...... dso: /proc/kcore
>
>   --
>   ... branch stack: nr:0
>    ... thread: swapper:0
>    ...... dso: /proc/kcore
>
>   --
>   ... branch stack: nr:0
>    ... thread: DefaultEventMan:10282
>    ...... dso: /proc/kcore
>
>   --
>   ... branch stack: nr:0
>    ... thread: swapper:0
>    ...... dso: /proc/kcore
>
>   --
>   ... branch stack: nr:0
>    ... thread: swapper:0
>    ...... dso: /proc/kcore
>
>   $ perf report -D | grep -c 'branch stack: nr:0'
>   145
>
>   $ perf report -D | grep -A3 'branch stack: nr:0' | grep thread | grep -c swapper
>   i36
>
>   $ perf report -D | grep -A3 'branch stack: nr:0' | grep thread | grep -cv swapper
>   9
>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Reviewed-by: Ian Rogers <irogers@google.com>

Thanks,
Ian

> ---
>  tools/perf/tests/shell/record_lbr.sh | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/tests/shell/record_lbr.sh b/tools/perf/tests/shell/record_lbr.sh
> index 8d750ee631f877fd..afad02d0180e023c 100755
> --- a/tools/perf/tests/shell/record_lbr.sh
> +++ b/tools/perf/tests/shell/record_lbr.sh
> @@ -93,7 +93,7 @@ lbr_test() {
>      return
>    fi
>
> -  zero_nr=$(echo "$out" | grep -c 'branch stack: nr:0' || true)
> +  zero_nr=$(echo "$out" | grep -A3 'branch stack: nr:0' | grep thread | grep -cv swapper || true)
>    r=$(($zero_nr * 100 / $bs_nr))
>    if [ $r -gt $threshold ]; then
>      echo "$test [Failed empty br stack ratio exceed $threshold%: $r%]"
> --
> 2.49.0.1015.ga840276032-goog
>

Re: [PATCH 2/2] perf test: Update sysfs path for core PMU caps

[Ian Rogers]

On Fri, May 9, 2025 at 2:30 PM Namhyung Kim <namhyung@kernel.org> wrote:
>
> While cpu is a system device, it'd be better to use a path for
> event_source devices when it checks PMU capability.
>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Reviewed-by: Ian Rogers <irogers@google.com>

Thanks,
Ian

> ---
>  tools/perf/tests/shell/record_lbr.sh | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/tests/shell/record_lbr.sh b/tools/perf/tests/shell/record_lbr.sh
> index afad02d0180e023c..6fcb5e52b9b4fcf6 100755
> --- a/tools/perf/tests/shell/record_lbr.sh
> +++ b/tools/perf/tests/shell/record_lbr.sh
> @@ -4,7 +4,8 @@
>
>  set -e
>
> -if [ ! -f /sys/devices/cpu/caps/branches ] && [ ! -f /sys/devices/cpu_core/caps/branches ]
> +if [ ! -f /sys/bus/event_source/devices/cpu/caps/branches ] &&
> +   [ ! -f /sys/bus/event_source/devices/cpu_core/caps/branches ]
>  then
>    echo "Skip: only x86 CPUs support LBR"
>    exit 2
> --
> 2.49.0.1015.ga840276032-goog
>

Re: [PATCH 2/2] perf test: Update sysfs path for core PMU caps

[Arnaldo Carvalho de Melo]

On Tue, May 13, 2025 at 07:58:40AM -0700, Ian Rogers wrote:
> On Fri, May 9, 2025 at 2:30 PM Namhyung Kim <namhyung@kernel.org> wrote:
> >
> > While cpu is a system device, it'd be better to use a path for
> > event_source devices when it checks PMU capability.
> >
> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> 
> Reviewed-by: Ian Rogers <irogers@google.com>

Thanks, applied to perf-tools-next,

- Arnaldo

Re: [PATCH 1/2] perf test: Fix LBR test by ignoring idle task

[Arnaldo Carvalho de Melo]

On Tue, May 13, 2025 at 07:58:07AM -0700, Ian Rogers wrote:
> On Fri, May 9, 2025 at 2:30 PM Namhyung Kim <namhyung@kernel.org> wrote:
> > I found 'perf record LBR tests' failing due to empty branch stacks.

<SNIP>

> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
 
> Reviewed-by: Ian Rogers <irogers@google.com>

Thanks, applied to perf-tools-next,

- Arnaldo