linux-kernel - Re: [PATCH V7 4/6] arm64/perf: Add branch stack support in struct pmu_hw

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Date:   Thu, 12 Jan 2023 13:59:54 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH V7 4/6] arm64/perf: Add branch stack support in struct
 pmu_hw_events

On Thu, Jan 05, 2023 at 08:40:37AM +0530, Anshuman Khandual wrote:
> This adds branch records buffer pointer in 'struct pmu_hw_events' which can
> be used to capture branch records during PMU interrupt. This percpu pointer
> here needs to be allocated first before usage.
> 
> 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
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>

This looks fine, but it's difficult to review this without seeing how its
lifetime is managed, and it feels like this should be folded into a subsequent
patch which manages that.

Thanks,
Mark.

> ---
>  include/linux/perf/arm_pmu.h | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/include/linux/perf/arm_pmu.h b/include/linux/perf/arm_pmu.h
> index 64e1b2594025..9184f9b33740 100644
> --- a/include/linux/perf/arm_pmu.h
> +++ b/include/linux/perf/arm_pmu.h
> @@ -44,6 +44,13 @@ static_assert((PERF_EVENT_FLAG_ARCH & ARMPMU_EVT_47BIT) == ARMPMU_EVT_47BIT);
>  	},								\
>  }
>  
> +#define MAX_BRANCH_RECORDS 64
> +
> +struct branch_records {
> +	struct perf_branch_stack	branch_stack;
> +	struct perf_branch_entry	branch_entries[MAX_BRANCH_RECORDS];
> +};
> +
>  /* The events for a given PMU register set. */
>  struct pmu_hw_events {
>  	/*
> @@ -70,6 +77,8 @@ struct pmu_hw_events {
>  	struct arm_pmu		*percpu_pmu;
>  
>  	int irq;
> +
> +	struct branch_records	*branches;
>  };
>  
>  enum armpmu_attr_groups {
> -- 
> 2.25.1
>