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SubjectRe: [RFC V1 06/11] arm64/perf: Drive BRBE from perf event states
On Mon, Jan 24, 2022 at 10:00:48AM +0530, Anshuman Khandual wrote:
> Branch stack sampling rides along the normal perf event and all the branch
> records get captured during the PMU interrupt. This just changes perf event
> handling on the arm64 platform to accommodate required BRBE operations that
> will enable branch stack sampling support.
>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: linux-perf-users@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-arm-kernel@lists.infradead.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> arch/arm64/kernel/perf_event.c | 6 +++++
> drivers/perf/arm_pmu.c | 40 ++++++++++++++++++++++++++++++++++
> 2 files changed, 46 insertions(+)
>
> diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
> index f6a47036b0b4..11c82c8f2eec 100644
> --- a/arch/arm64/kernel/perf_event.c
> +++ b/arch/arm64/kernel/perf_event.c
> @@ -864,6 +864,12 @@ static irqreturn_t armv8pmu_handle_irq(struct arm_pmu *cpu_pmu)
> if (!armpmu_event_set_period(event))
> continue;
>
> + if (has_branch_stack(event)) {
> + cpu_pmu->brbe_read(cpuc, event);

Is has_branch_stack() guaranteed to be false on arm32? If not, this will
be a NULL function ptr.

To add to my other comments, this patch is where I would add
brbe_read(), etc. to arm_pmu.

Rob

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