linux-kernel - Re: [PATCH V13 03/10] arm64/perf: Add branch stack support in struct arm

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Date:   Fri, 23 Jun 2023 16:21:12 -0700
From:   Namhyung Kim <namhyung@...il.com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        will@...nel.org, catalin.marinas@....com, mark.rutland@....com,
        Mark Brown <broonie@...nel.org>,
        James Clark <james.clark@....com>,
        Rob Herring <robh@...nel.org>, Marc Zyngier <maz@...nel.org>,
        Suzuki Poulose <suzuki.poulose@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH V13 03/10] arm64/perf: Add branch stack support in struct arm_pmu

Hello,

On Wed, Jun 21, 2023 at 11:55 PM Anshuman Khandual
<anshuman.khandual@....com> wrote:
>
> This updates 'struct arm_pmu' for branch stack sampling support being added
> later. This adds an element 'reg_trbidr' to capture BRBE attribute details.

reg_brbidr, right?

Thanks,
Namhyung


> These updates here will help in tracking any branch stack sampling support.
>
> This also enables perf branch stack sampling event on all 'struct arm pmu',
> supporting the feature but after removing the current gate that blocks such
> events unconditionally in armpmu_event_init(). Instead a quick probe can be
> initiated via arm_pmu->has_branch_stack to ascertain the support.
>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Tested-by: James Clark <james.clark@....com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
>  drivers/perf/arm_pmu.c       | 3 +--
>  include/linux/perf/arm_pmu.h | 9 ++++++++-
>  2 files changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> index aada47e3b126..d9ffe9e56e74 100644
> --- a/drivers/perf/arm_pmu.c
> +++ b/drivers/perf/arm_pmu.c
> @@ -510,8 +510,7 @@ static int armpmu_event_init(struct perf_event *event)
>                 !cpumask_test_cpu(event->cpu, &armpmu->supported_cpus))
>                 return -ENOENT;
>
> -       /* does not support taken branch sampling */
> -       if (has_branch_stack(event))
> +       if (has_branch_stack(event) && !armpmu->has_branch_stack)
>                 return -EOPNOTSUPP;
>
>         return __hw_perf_event_init(event);
> diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
> index f7fbd162ca4c..ba4204bdcebf 100644
> --- a/include/linux/perf/arm_pmu.h
> +++ b/include/linux/perf/arm_pmu.h
> @@ -102,7 +102,9 @@ struct arm_pmu {
>         int             (*map_event)(struct perf_event *event);
>         void            (*sched_task)(struct perf_event_pmu_context *pmu_ctx, bool sched_in);
>         int             num_events;
> -       bool            secure_access; /* 32-bit ARM only */
> +       unsigned int    secure_access   : 1, /* 32-bit ARM only */
> +                       has_branch_stack: 1, /* 64-bit ARM only */
> +                       reserved        : 30;
>  #define ARMV8_PMUV3_MAX_COMMON_EVENTS          0x40
>         DECLARE_BITMAP(pmceid_bitmap, ARMV8_PMUV3_MAX_COMMON_EVENTS);
>  #define ARMV8_PMUV3_EXT_COMMON_EVENT_BASE      0x4000
> @@ -118,6 +120,11 @@ struct arm_pmu {
>
>         /* Only to be used by ACPI probing code */
>         unsigned long acpi_cpuid;
> +
> +       /* Implementation specific attributes */
> +#ifdef CONFIG_ARM64_BRBE
> +       u64             reg_brbidr;
> +#endif
>  };
>
>  #define to_arm_pmu(p) (container_of(p, struct arm_pmu, pmu))
> --
> 2.25.1
>