linux-kernel - Re: [PATCH v1 6/7] perf pmu-events: Remember the events and metrics table

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Date:   Sat, 7 Oct 2023 22:49:25 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Yang Jihong <yangjihong1@...wei.com>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        James Clark <james.clark@....com>,
        Leo Yan <leo.yan@...aro.org>,
        John Garry <john.g.garry@...cle.com>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Thomas Richter <tmricht@...ux.ibm.com>,
        Ravi Bangoria <ravi.bangoria@....com>,
        Kajol Jain <kjain@...ux.ibm.com>,
        Jing Zhang <renyu.zj@...ux.alibaba.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 6/7] perf pmu-events: Remember the events and metrics table

On Sat, Oct 7, 2023 at 8:39 PM Yang Jihong <yangjihong1@...wei.com> wrote:
>
> Hello,
>
> On 2023/10/7 10:13, Ian Rogers wrote:
> > strcmp_cpuid_str performs regular expression comparisons. Avoid
> > repeated computation of the table by remembering the table in a
> > static.
> >
> > Signed-off-by: Ian Rogers <irogers@...gle.com>
> > ---
> >   tools/perf/pmu-events/jevents.py | 48 +++++++++++++++++++-------------
> >   1 file changed, 28 insertions(+), 20 deletions(-)
> >
> > diff --git a/tools/perf/pmu-events/jevents.py b/tools/perf/pmu-events/jevents.py
> > index fd009752b427..8d8d5088c53c 100755
> > --- a/tools/perf/pmu-events/jevents.py
> > +++ b/tools/perf/pmu-events/jevents.py
> > @@ -978,28 +978,32 @@ int pmu_metrics_table__for_each_metric(const struct pmu_metrics_table *table,
> >
> >   const struct pmu_events_table *perf_pmu__find_events_table(struct perf_pmu *pmu)
> >   {
> > -        const struct pmu_events_table *table = NULL;
> > -        char *cpuid = perf_pmu__getcpuid(pmu);
> > +        static const struct pmu_events_table *table;
> >           size_t i;
> >
> > -        /* on some platforms which uses cpus map, cpuid can be NULL for
> > -         * PMUs other than CORE PMUs.
> > -         */
> > -        if (!cpuid)
> > -                return NULL;
> > -
> > -        i = 0;
> > -        for (;;) {
> > -                const struct pmu_events_map *map = &pmu_events_map[i++];
> > -                if (!map->arch)
> > -                        break;
> > -
> > -                if (!strcmp_cpuid_str(map->cpuid, cpuid)) {
> > -                        table = &map->event_table;
> > -                        break;
> > +        if (!table) {
> If there is no matched table in pmu_events_map,
> perf_pmu__find_events_table() will enter this branch for repeated search
> each time.
> Or do we need to use another variable to indicate whether the search has
> been performed?

Agreed, the behavior will match the existing behavior. Longer term I
want to remove this code. Do you have a scenario we should optimize
for here?

Thanks,
Ian

> Thanks,
> Yang