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

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Message-ID: <5773b630-8159-1eba-481a-1bf3c406c055@arm.com>
Date:   Wed, 18 May 2022 13:32:26 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     John Garry <john.garry@...wei.com>,
        Nick Forrington <nick.forrington@....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 2022-05-18 09:15, John Garry wrote:
> On 17/05/2022 15:32, Robin Murphy wrote:
>>
>> On 2022-05-10 11:47, Nick Forrington wrote:
>>> Add Performance Monitoring Unit event data for the Arm CPUs listed
>>> below.
>>>
>>> Changesets are dependent due to incremental updates to the common events
>>> file and mapfile.csv.
>>>
>>> Data is sourced from https://github.com/ARM-software/data
>>>
>>> Nick Forrington (20):
>>>    perf vendors events arm64: Arm Cortex-A5
>>>    perf vendors events arm64: Arm Cortex-A7
>>>    perf vendors events arm64: Arm Cortex-A8
>>>    perf vendors events arm64: Arm Cortex-A9
>>>    perf vendors events arm64: Arm Cortex-A15
>>>    perf vendors events arm64: Arm Cortex-A17
>>>    perf vendors events arm64: Arm Cortex-A32
>>
>> Obligatory question over anything relating to the above CPUs being in 
>> an "arch/arm64" directory... ;)
> 
> If we were to add to arm32/arm then the common event numbers and maybe 
> other JSONs in future would need to be duplicated.
> 
> Would there be any reason to add to arm32/arm apart to from being 
> strictly proper? Maybe if lots of other 32b support for other vendors 
> came along then it could make sense (to separate them out).

That's the heart of the question, really. At best it seems unnecessarily 
confusing as-is. AFAICS either the naming isn't functional, wherein it 
would potentially make the most sense to rename the whole thing 
"pmu-events/arch/arm" if it's merely for categorising Arm architectures 
in general, or it is actually tied to the host triplet, in which case 
the above patches are most likely useless.

I'd agree that there doesn't seem much point in trying to separate 
things along relatively arbitrary lines if it *isn't* functionally 
necessary - the PMUv2 common events look to be a straightforward subset 
of the PMUv3 ones, but then there's Cortex-A32 anyway, plus most of the 
already-supported CPUs could equally run an AArch32 perf tool as well.

Thanks,
Robin.