Re: [PATCH] perf stat: Fix aggregation of cgroup events

[Chun-Tse Shao]

On Thu, Oct 1, 2026 at 10:48 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> I got a report that perf stat with BPF and cgroup is broken with
> aggregation like per-socket or node.  On my machine, running the
> following command shows the problem.
>
>   $ sudo perf stat -a --bpf-counters --per-socket -e cycles \
>     --for-each-cgroup /user.slice,/system.slice  sleep 1
>
>    Performance counter stats for 'system wide':
>
>   S0       12      <not counted>      cpu_atom/cycles/                 user.slice
>   S0       16      <not counted>      cpu_core/cycles/                 user.slice
>   S0       12      <not counted>      cpu_atom/cycles/                 system.slice
>   S0       16      <not counted>      cpu_core/cycles/                 system.slice
>
>          1.002798147 seconds time elapsed
>
> That's because there's a logic to make the whole event failed if result
> from any CPU looks bad when aggregation is enabled.  Normally it
> considers bad when an event has no enabled and running time.  But it's
> possible for a cgroup event to have no chance to run on some CPU during
> the window and then it will have 0 enabled and running time.  Let's not
> treat them as errors.
>
> After the fix, the same command produces:
>
>    Performance counter stats for 'system wide':
>
>   S0       12          5,094,112      cpu_atom/cycles/                 user.slice
>   S0       16         28,075,944      cpu_core/cycles/                 user.slice
>   S0       12          1,516,568      cpu_atom/cycles/                 system.slice
>   S0       16          5,569,575      cpu_core/cycles/                 system.slice
>
>          1.003231856 seconds time elapsed
>
> Reported-by: Chun-Tse Shao <ctshao@xxxxxxxxxx>
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Tested-by: Chun-Tse Shao <ctshao@xxxxxxxxxx>

Thanks for the fix!


-CT

> ---
>  tools/perf/util/stat.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/tools/perf/util/stat.c b/tools/perf/util/stat.c
> index 25f31a17436828aa..6da3dbbde0e2ad8d 100644
> --- a/tools/perf/util/stat.c
> +++ b/tools/perf/util/stat.c
> @@ -381,6 +381,10 @@ static bool evsel__count_has_error(struct evsel *evsel,
>         if (config->aggr_mode == AGGR_GLOBAL)
>                 return false;
>
> +       /* cgroup events may not be scheduled on some CPUs */
> +       if (evsel->cgrp)
> +               return false;
> +
>         /* it's considered ok when it actually ran */
>         if (count->ena != 0 && count->run != 0)
>                 return false;
> --
> 2.55.0
>