linux-kernel - Re: [PATCH v5] arm64: pmuv3: dynamically map PERF_COUNT_HW_BRANCH

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Date:   Thu, 6 Apr 2023 16:10:23 +0100
From:   Will Deacon <will@...nel.org>
To:     Peter Newman <peternewman@...gle.com>
Cc:     mark.rutland@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        acme@...nel.org, adrian.hunter@...el.com,
        alexander.shishkin@...ux.intel.com, catalin.marinas@....com,
        eranian@...gle.com, irogers@...gle.com, jolsa@...nel.org,
        mingo@...hat.com, namhyung@...nel.org, peterz@...radead.org
Subject: Re: [PATCH v5] arm64: pmuv3: dynamically map
 PERF_COUNT_HW_BRANCH_INSTRUCTIONS

Hi Peter,

On Mon, Apr 03, 2023 at 11:15:47AM +0200, Peter Newman wrote:
> From: Stephane Eranian <eranian@...gle.com>
> 
> The mapping of perf_events generic hardware events to actual PMU events on
> ARM PMUv3 may not always be correct. This is in particular true for the
> PERF_COUNT_HW_BRANCH_INSTRUCTIONS event. Although the mapping points to an
> architected event, it may not always be available. This can be seen with a
> simple:
> 
> $ perf stat -e branches sleep 0
>  Performance counter stats for 'sleep 0':
> 
>    <not supported>      branches
> 
>        0.001401081 seconds time elapsed
> 
> Yet the hardware does have an event that could be used for branches.
> 
> Dynamically check for a supported hardware event which can be used for
> PERF_COUNT_HW_BRANCH_INSTRUCTIONS at mapping time.
> 
> And with that:
> 
> $ perf stat -e branches sleep 0
> 
>  Performance counter stats for 'sleep 0':
> 
>            166,739      branches
> 
>        0.000832163 seconds time elapsed
> 
> Co-Developed-by: Stephane Eranian <eranian@...gle.com>
> Signed-off-by: Stephane Eranian <eranian@...gle.com>
> Co-Developed-by: Mark Rutland <mark.rutland@....com>
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Co-Developed-by: Peter Newman <peternewman@...gle.com>
> Signed-off-by: Peter Newman <peternewman@...gle.com>
> Link: https://lore.kernel.org/all/YvunKCJHSXKz%2FkZB@FVFF77S0Q05N
> ---
> v4->v5:
>  - update changelog tags

Thanks, this looks good to me.

Please can you rebase it on my for-next/perf branch so that I can queue it
up? More of the PMU code has moved out into drivers/perf/.

Cheers,

Will

[1] https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/log/?h=for-next/perf