linux-kernel - Re: [PATCH 2/2] perf pmu: Fix num

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Date: Thu, 9 May 2024 23:16:40 -0700
From: Ian Rogers <irogers@...gle.com>
To: Jia He <justin.he@....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>, Kan Liang <kan.liang@...ux.intel.com>, 
	James Clark <james.clark@....com>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] perf pmu: Fix num_events calculation

On Thu, May 9, 2024 at 7:47 PM Jia He <justin.he@....com> wrote:
>
> When pe is NULL in the function perf_pmu__new_alias(), the total number
> of events is added to loaded_json_aliases. However, if pmu->events_table
> is NULL and cpu_aliases_added is false, the calculation for the events
> number in perf_pmu__num_events() is incorrect.
>
> Then cause the error report after "perf list":
> Unexpected event smmuv3_pmcg_3f062/smmuv3_pmcg_3f062/transaction//
>
> Fix it by adding loaded_json_aliases in the calculation under the
> mentioned conditions.
>
> Test it also with "perf bench internals pmu-scan" and there is no
> regression.
>
> Fixes: e6ff1eed3584 ("perf pmu: Lazily add JSON events")
> Signed-off-by: Jia He <justin.he@....com>
> ---
>  tools/perf/util/pmu.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
> index a1eef7b2e389..a53224e2ce7e 100644
> --- a/tools/perf/util/pmu.c
> +++ b/tools/perf/util/pmu.c
> @@ -1639,6 +1639,8 @@ size_t perf_pmu__num_events(struct perf_pmu *pmu)
>                  nr += pmu->loaded_json_aliases;
>         else if (pmu->events_table)
>                 nr += pmu_events_table__num_events(pmu->events_table, pmu) - pmu->loaded_json_aliases;
> +       else
> +               nr += pmu->loaded_json_aliases;

Thanks for working on this! The "struct pmu_event *pe" in new_alias is
an entry from the json data, and "pmu->events_table" should NULL if
there is no json data. I believe the code is assuming that these lines
aren't necessary as it shouldn't be possible to load json data if the
json events table doesn't exist for the PMU - if there is no json data
then loaded_json_aliases should be 0 and no addition is necessary. I'm
wondering why this case isn't true for you.

Thanks,
Ian

>
>         return pmu->selectable ? nr + 1 : nr;
>  }
> --
> 2.34.1
>