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

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Date:   Sun, 8 Oct 2023 11:39:20 +0800
From:   Yang Jihong <yangjihong1@...wei.com>
To:     Ian Rogers <irogers@...gle.com>,
        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

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?

Thanks,
Yang