linux-kernel - Re: [PATCH v5 10/15] perf jevents: Generate metrics and events as separate tables

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Message-ID: <8f53bb96-8213-12f1-f91c-7fb311e4c9a4@oracle.com>
Date:   Mon, 30 Jan 2023 16:07:02 +0000
From:   John Garry <john.g.garry@...cle.com>
To:     Ian Rogers <irogers@...gle.com>, Will Deacon <will@...nel.org>,
        James Clark <james.clark@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.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>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Kim Phillips <kim.phillips@....com>,
        Florian Fischer <florian.fischer@...q.space>,
        Ravi Bangoria <ravi.bangoria@....com>,
        Xing Zhengjun <zhengjun.xing@...ux.intel.com>,
        Rob Herring <robh@...nel.org>,
        Kang Minchul <tegongkang@...il.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sandipan Das <sandipan.das@....com>,
        Jing Zhang <renyu.zj@...ux.alibaba.com>,
        linuxppc-dev@...ts.ozlabs.org, Kajol Jain <kjain@...ux.ibm.com>
Cc:     Stephane Eranian <eranian@...gle.com>,
        Perry Taylor <perry.taylor@...el.com>,
        Caleb Biggers <caleb.biggers@...el.com>
Subject: Re: [PATCH v5 10/15] perf jevents: Generate metrics and events as
 separate tables

On 26/01/2023 23:36, Ian Rogers wrote:
> @@ -660,7 +763,29 @@ const struct pmu_events_table *perf_pmu__find_events_table(struct perf_pmu *pmu)
>   
>   const struct pmu_metrics_table *perf_pmu__find_metrics_table(struct perf_pmu *pmu)
>   {
> -        return (struct pmu_metrics_table *)perf_pmu__find_events_table(pmu);
> +        const struct pmu_metrics_table *table = NULL;
> +        char *cpuid = perf_pmu__getcpuid(pmu);
> +        int 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->metric_table;
> +                        break;
> +                }
> +        }
> +        free(cpuid);
> +        return table;
>   }

This is almost identical to generated perf_pmu__find_events_table(), 
except we return a pmu_metrics_table * (instead of a pmu_events_table *) 
and also return the metric table member (instead of event table). But 
the definitions are:

/* Struct used to make the PMU event table implementation opaque to 
callers. */
struct pmu_events_table {
         const struct compact_pmu_event *entries;
         size_t length;
};

/* Struct used to make the PMU metric table implementation opaque to 
callers. */
struct pmu_metrics_table {
         const struct compact_pmu_event *entries;
         size_t length;
};

Those structs are defined to be the same thing, so I am failing to see 
the point in a) separate structure types b) why so much duplication

As for b), I know that they are generated and the python code may be 
simpler this way (is it?), but still...

Thanks,
John