linux-kernel - Re: [PATCH 00/20] perf vendors events arm64: Multiple Arm CPUs

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Date:   Thu, 19 May 2022 14:50:03 +0100
From:   Nick Forrington <nick.forrington@....com>
To:     John Garry <john.garry@...wei.com>,
        Robin Murphy <robin.murphy@....com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        acme@...nel.org
Cc:     Will Deacon <will@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kajol Jain <kjain@...ux.ibm.com>,
        James Clark <james.clark@....com>,
        Andrew Kilroy <andrew.kilroy@....com>
Subject: Re: [PATCH 00/20] perf vendors events arm64: Multiple Arm CPUs


On 19/05/2022 08:59, John Garry wrote:
> On 18/05/2022 15:14, Robin Murphy wrote:
>>> Sure, we should have these 32b cores supported for ARCH=arm if they 
>>> are supported for ARCH=arm64. But then does it even make sense to 
>>> have A7 support in arch/arm64?
>>
>> That's what I'm getting at. If it is tied to the build target as 
>> you've said above, then there is no point in an AArch64 perf tool 
>> including data for CPUs on which that tool cannot possibly run; it's 
>> simply a waste of space.
>>
>> If there is interest in plumbing in support on AArch32 builds as 
>> well, then I'd still be inclined to have a single arch/arm events 
>> directory, and either do some build-time path munging or just symlink 
>> an arch/arm64 sibling back to it. Yes, technically there are 
>> AArch64-only CPUs whose data would then be redundant when building 
>> for AArch32, 
>
> If size is an issue then we have ways to cut this down, like doing the 
> arch standard events fixup dynamically when running perf tool, or even 
> not describing those events in the JSONs and rely on reading the CPU 
> PMU events folder to learn which of those events are supported.
>
> > but those are
> > such a minority that it seems like an entirely reasonable compromise.
>
> @Nick, Can you drop the 32b core support for arm64? Or, if you really 
> want them, look into ARCH=arm pmu-events support?

No problem - I'll resubmit without the 32b-only CPUs.

Thanks,
Nick