linux-kernel - Re: [PATCH 3/4] arm_pmu: Remove unused PERF_PMU_CAP_HETEROGENEOUS

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Date:   Mon, 10 Jul 2023 09:08:17 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     James Clark <james.clark@....com>
Cc:     linux-perf-users@...r.kernel.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 Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Will Deacon <will@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/4] arm_pmu: Remove unused PERF_PMU_CAP_HETEROGENEOUS_CPUS
 capability

On Mon, Jul 10, 2023 at 5:22 AM James Clark <james.clark@....com> wrote:
>
> Since commit bd2756811766 ("perf: Rewrite core context handling") the
> relationship between perf_event_context and PMUs has changed so that
> the error scenario that PERF_PMU_CAP_HETEROGENEOUS_CPUS originally
> silenced no longer exists.
>
> Remove the capability and associated comment to avoid confusion that it
> actually influences any perf core behavior. This change should be a
> no-op.
>
> Signed-off-by: James Clark <james.clark@....com>

Acked-by: Ian Rogers <irogers@...gle.com>

Thanks,
Ian

> ---
>  drivers/perf/arm_pmu.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> index d8844a9461a2..297906df6628 100644
> --- a/drivers/perf/arm_pmu.c
> +++ b/drivers/perf/arm_pmu.c
> @@ -872,15 +872,12 @@ struct arm_pmu *armpmu_alloc(void)
>                 .attr_groups    = pmu->attr_groups,
>                 /*
>                  * This is a CPU PMU potentially in a heterogeneous
> -                * configuration (e.g. big.LITTLE). This is not an uncore PMU,
> -                * and we have taken ctx sharing into account (e.g. with our
> -                * pmu::filter callback and pmu::event_init group validation).
> -                *
> +                * configuration (e.g. big.LITTLE) so
>                  * PERF_PMU_CAP_EXTENDED_HW_TYPE is required to open the legacy
>                  * PERF_TYPE_HARDWARE and PERF_TYPE_HW_CACHE events on a
>                  * specific PMU.
>                  */
> -               .capabilities   = PERF_PMU_CAP_HETEROGENEOUS_CPUS | PERF_PMU_CAP_EXTENDED_REGS |
> +               .capabilities   = PERF_PMU_CAP_EXTENDED_REGS |
>                                   PERF_PMU_CAP_EXTENDED_HW_TYPE,
>         };
>
> --
> 2.34.1
>