linux-kernel - Re: [PATCH v6 01/10] arm64: pmu: Add function implementation to update event index in userpage

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Message-ID: <20210330153036.GA6567@willie-the-truck>
Date:   Tue, 30 Mar 2021 16:30:37 +0100
From:   Will Deacon <will@...nel.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Ian Rogers <irogers@...gle.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        honnappa.nagarahalli@....com, Zachary.Leaf@....com,
        Raphael Gault <raphael.gault@....com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Itaru Kitayama <itaru.kitayama@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 01/10] arm64: pmu: Add function implementation to
 update event index in userpage

On Wed, Mar 10, 2021 at 05:08:28PM -0700, Rob Herring wrote:
> From: Raphael Gault <raphael.gault@....com>
> 
> In order to be able to access the counter directly for userspace,
> we need to provide the index of the counter using the userpage.
> We thus need to override the event_idx function to retrieve and
> convert the perf_event index to armv8 hardware index.
> 
> Since the arm_pmu driver can be used by any implementation, even
> if not armv8, two components play a role into making sure the
> behaviour is correct and consistent with the PMU capabilities:
> 
> * the ARMPMU_EL0_RD_CNTR flag which denotes the capability to access
> counter from userspace.
> * the event_idx call back, which is implemented and initialized by
> the PMU implementation: if no callback is provided, the default
> behaviour applies, returning 0 as index value.
> 
> Signed-off-by: Raphael Gault <raphael.gault@....com>
> Signed-off-by: Rob Herring <robh@...nel.org>
> ---
>  arch/arm64/kernel/perf_event.c | 18 ++++++++++++++++++
>  include/linux/perf/arm_pmu.h   |  2 ++
>  2 files changed, 20 insertions(+)

Acked-by: Will Deacon <will@...nel.org>

Will