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

[Namhyung Kim <namhyung@kernel.org>]

On Fri, Oct 02, 2026 at 10:13:29AM -0700, Chun-Tse Shao wrote:
> On Thu, Oct 1, 2026 at 10:48 PM Namhyung Kim <namhyung@kernel.org> 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@google.com>
> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> 
> Tested-by: Chun-Tse Shao <ctshao@google.com>

Thanks for the test!

Arnaldo, can you please take this?

Thanks,
Namhyung