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

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Message-ID: <CAP-5=fXJ9pi+B_ppA93mE6gd8XYP4TDJThUreZeZxQtGwQ7Fug@mail.gmail.com>
Date: Wed, 2 Apr 2025 08:49:17 -0700
From: Ian Rogers <irogers@...gle.com>
To: "Liang, Kan" <kan.liang@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Howard Chu <howardchu95@...il.com>, 
	Weilin Wang <weilin.wang@...el.com>, Levi Yun <yeoreum.yun@....com>, 
	"Dr. David Alan Gilbert" <linux@...blig.org>, Andi Kleen <ak@...ux.intel.com>, 
	James Clark <james.clark@...aro.org>, Dominique Martinet <asmadeus@...ewreck.org>, 
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/5] perf stat: Better hybrid support for the NMI
 watchdog warning

On Wed, Apr 2, 2025 at 8:23 AM Liang, Kan <kan.liang@...ux.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@...gle.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;
>