Re: [PATCH v1] perf metricgroup: Avoid scanning unnecessary PMUs for identifier match

[Ian Rogers]

On Mon, Mar 30, 2026 at 11:30 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> On Mon, Mar 30, 2026 at 03:44:21PM +0100, James Clark wrote:
> >
> >
> > On 26/03/2026 10:44 pm, Ian Rogers wrote:
> > > Only uncore PMUs can have an identifier, so add an optimized
> > > perf_pmus__scan routine for that case to avoid all PMU types being
> > > created.
> > >
> > > Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> >
> > Reviewed-by: James Clark <james.clark@xxxxxxxxxx>
> >
> > > ---
> > >   tools/perf/util/metricgroup.c |  8 ++------
> > >   tools/perf/util/pmus.c        | 18 +++++++++++++++++-
> > >   tools/perf/util/pmus.h        |  1 +
> > >   3 files changed, 20 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/tools/perf/util/metricgroup.c b/tools/perf/util/metricgroup.c
> > > index 7e39d469111b..769b38400832 100644
> > > --- a/tools/perf/util/metricgroup.c
> > > +++ b/tools/perf/util/metricgroup.c
> > > @@ -410,13 +410,9 @@ static int metricgroup__sys_event_iter(const struct pmu_metric *pm,
> > >     if (!pm->metric_expr || !pm->compat)
> > >             return 0;
> > > -   while ((pmu = perf_pmus__scan(pmu))) {
> > > -
> > > -           if (!pmu->id || !pmu_uncore_identifier_match(pm->compat, pmu->id))
> > > -                   continue;
> > > -
> > > +   while ((pmu = perf_pmus__scan_for_uncore_id(pmu, pm->compat)))
> > >             return d->fn(pm, table, d->data);
>
> Sashiko review: it's natural to convert it to 'if'.

Yeah, I saw and disagreed. The pattern with the  "while ((pmu =
perf_pmus__scan...(pmu)))" functions is for them to be a while loop.
With an "if" it would read:
```
pmu = perf_pmus__scan...(pmu);
if (pmu)
   return ...
```
and we lose the consistency of having while loops in the code.

Thanks,
Ian

> Thanks,
> Namhyung
>
>
> > > -   }
> > > +
> > >     return 0;
> > >   }
> > > diff --git a/tools/perf/util/pmus.c b/tools/perf/util/pmus.c
> > > index 98be2eb8f1f0..9859d7056fb7 100644
> > > --- a/tools/perf/util/pmus.c
> > > +++ b/tools/perf/util/pmus.c
> > > @@ -409,7 +409,7 @@ struct perf_pmu *perf_pmus__scan_matching_wildcard(struct perf_pmu *pmu, const c
> > >     if (!pmu) {
> > >             /*
> > >              * Core PMUs, other sysfs PMUs and tool PMU can have any name or
> > > -            * aren't wother optimizing for.
> > > +            * aren't worth optimizing for.
> > >              */
> > >             unsigned int to_read_pmus =  PERF_TOOL_PMU_TYPE_PE_CORE_MASK |
> > >                     PERF_TOOL_PMU_TYPE_PE_OTHER_MASK |
> > > @@ -486,6 +486,22 @@ static struct perf_pmu *perf_pmus__scan_skip_duplicates(struct perf_pmu *pmu)
> > >     return NULL;
> > >   }
> > > +struct perf_pmu *perf_pmus__scan_for_uncore_id(struct perf_pmu *pmu, const char *compat)
> > > +{
> > > +   if (!pmu) {
> > > +           /* Only uncore PMUs can have identifiers. */
> > > +           unsigned int to_read_pmus = PERF_TOOL_PMU_TYPE_PE_OTHER_MASK;
> > > +
> > > +           pmu_read_sysfs(to_read_pmus);
> > > +           pmu = list_prepare_entry(pmu, &other_pmus, list);
> > > +   }
> > > +   list_for_each_entry_continue(pmu, &other_pmus, list) {
> > > +           if (pmu->id && pmu_uncore_identifier_match(compat, pmu->id))
> > > +                   return pmu;
> > > +   }
> > > +   return NULL;
> > > +}
> > > +
> > >   const struct perf_pmu *perf_pmus__pmu_for_pmu_filter(const char *str)
> > >   {
> > >     struct perf_pmu *pmu = NULL;
> > > diff --git a/tools/perf/util/pmus.h b/tools/perf/util/pmus.h
> > > index 7cb36863711a..0d55edb3f2fc 100644
> > > --- a/tools/perf/util/pmus.h
> > > +++ b/tools/perf/util/pmus.h
> > > @@ -23,6 +23,7 @@ struct perf_pmu *perf_pmus__scan(struct perf_pmu *pmu);
> > >   struct perf_pmu *perf_pmus__scan_core(struct perf_pmu *pmu);
> > >   struct perf_pmu *perf_pmus__scan_for_event(struct perf_pmu *pmu, const char *event);
> > >   struct perf_pmu *perf_pmus__scan_matching_wildcard(struct perf_pmu *pmu, const char *wildcard);
> > > +struct perf_pmu *perf_pmus__scan_for_uncore_id(struct perf_pmu *pmu, const char *compat);
> > >   const struct perf_pmu *perf_pmus__pmu_for_pmu_filter(const char *str);
> >