Re: [PATCH v1 1/5] perf stat: Better hybrid support for the NMI watchdog warning

Ian Rogers
2025-04-02T15:49:29Z

On Wed, Apr 2, 2025 at 8:23 AM Liang, Kan <kan.liang@linux.intel.com> wrote:
>
>
>
> On 2025-03-18 12:14 a.m., Ian Rogers wrote:
> > Prior to this patch evlist__has_hybrid would return false if the
> > processor wasn't hybrid or the evlist didn't contain any core
> > events. If the only PMU used by events was cpu_core then it would
> > true even though there are no cpu_atom events. For example:
> >
> > ```
> > $ perf stat --cputype=cpu_core -e '{cycles,cycles,cycles,cycles,cycles,cycles,cycles,cycles,cycles}' true
> >
> > Performance counter stats for 'true':
> >
> > <not counted> cpu_core/cycles/ (0.00%)
> > <not counted> cpu_core/cycles/ (0.00%)
> > <not counted> cpu_core/cycles/ (0.00%)
> > <not counted> cpu_core/cycles/ (0.00%)
> > <not counted> cpu_core/cycles/ (0.00%)
> > <not counted> cpu_core/cycles/ (0.00%)
> > <not counted> cpu_core/cycles/ (0.00%)
> > <not counted> cpu_core/cycles/ (0.00%)
> > <not counted> cpu_core/cycles/ (0.00%)
> >
> > 0.001981900 seconds time elapsed
> >
> > 0.002311000 seconds user
> > 0.000000000 seconds sys
> > ```
> >
> > This patch changes evlist__has_hybrid to return true only if the
> > evlist contains events from >1 core PMU. This means the NMI watchdog
> > warning is shown for the case above.
>
> Nit:
> The function name may still bring confusions.
> It may be better to change the function name as well, e.g.,
> evlist__has_hybrid_pmus()? It implies more than one PMU.

Thanks, I'll change in v2.

Ian

> Thanks,
> Kan>
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> > tools/perf/util/stat-display.c | 14 +++++++++++++-
> > 1 file changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/perf/util/stat-display.c b/tools/perf/util/stat-display.c
> > index e852ac0d9847..f311f1960e29 100644
> > --- a/tools/perf/util/stat-display.c
> > +++ b/tools/perf/util/stat-display.c
> > @@ -825,13 +825,25 @@ static bool is_mixed_hw_group(struct evsel *counter)
> > static bool evlist__has_hybrid(struct evlist *evlist)
> > {
> > struct evsel *evsel;
> > + struct perf_pmu *last_core_pmu = NULL;
> >
> > if (perf_pmus__num_core_pmus() == 1)
> > return false;
> >
> > evlist__for_each_entry(evlist, evsel) {
> > - if (evsel->core.is_pmu_core)
> > + if (evsel->core.is_pmu_core) {
> > + struct perf_pmu *pmu = evsel__find_pmu(evsel);
> > +
> > + if (pmu == last_core_pmu)
> > + continue;
> > +
> > + if (last_core_pmu == NULL) {
> > + last_core_pmu = pmu;
> > + continue;
> > + }
> > + /* A distinct core PMU. */
> > return true;
> > + }
> > }
> >
> > return false;
>