linux-kernel - Re: [RFC/PATCH 1/1] tools headers arm64: Sync arm64's cputype.h with the kernel sources

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Date: Tue, 4 Jun 2024 21:01:41 +0100
From: Leo Yan <niayan01@...s.arm.com>
To: Mark Rutland <mark.rutland@....com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
 Besar Wicaksono <bwicaksono@...dia.com>, Will Deacon <will@...nel.org>,
 Adrian Hunter <adrian.hunter@...el.com>, Ian Rogers <irogers@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Kan Liang <kan.liang@...ux.intel.com>,
 Namhyung Kim <namhyung@...nel.org>,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 linux-perf-users@...r.kernel.org, James Clark <james.clark@....com>
Subject: Re: [RFC/PATCH 1/1] tools headers arm64: Sync arm64's cputype.h with
 the kernel sources

On 6/4/24 19:55, Mark Rutland wrote:

[...]

>> Now more and more Arm CPUs support the data source in SPE and share the same
>> data source format. It's not scalable for us to adding every CPU variant
>> into the file util/arm-spe.c.
>>
>> I would like to expose the PMSIDR_EL1.LDS bit (Data source indicator for
>> sampled load instructions) via the 'cap' folder, and then we can save this
>> info into the perf meta data during record phase.
> 
> I'd be happy to expose fields from PMSIDR_EL1.
> 
>> In the perf report, we can parse the meta data and if the
>> PMSIDR_EL1.LDS bit is set, the tool will parse the data source packet
>> based on the common format.
> 
> I don't believe that's right.
> 
> PMSIDR_EL1.LDS indicates that the loaded data source field is
> implemented, but even when it is implemented, the format is
> IMPLEMENTATION DEFINED.

Thanks for correction. PMSIDR_EL1.LDS bit is necessary but not 
sufficient for using the common data source format.

> Today, Arm Ltd implementations happen to share a format, but that isn't
> implied by PMSIDR_EL1.LDS, and there's no guarantee that future CPUs
> will all use the same format.
> 
> For the moment we'll have to keep adding to this list.

I would like to use an opposite way - we can only maintain CPU variants 
with special data source format, otherwise, all other CPUs use the 
common format.

Thanks,
Leo