linux-kernel - Re: [PATCH 07/10] perf: arm_spe: Add support for filtering on data source

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Message-ID: <5752f039-51c1-4452-b5df-03ff06da7be3@linaro.org>
Date: Wed, 21 May 2025 09:54:48 +0100
From: James Clark <james.clark@...aro.org>
To: Leo Yan <leo.yan@....com>
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Mark Rutland <mark.rutland@....com>, Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...hat.com>, Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>, Jonathan Corbet <corbet@....net>,
 Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
 Joey Gouly <joey.gouly@....com>, Suzuki K Poulose <suzuki.poulose@....com>,
 Zenghui Yu <yuzenghui@...wei.com>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
 linux-doc@...r.kernel.org, kvmarm@...ts.linux.dev
Subject: Re: [PATCH 07/10] perf: arm_spe: Add support for filtering on data
 source



On 20/05/2025 5:22 pm, Leo Yan wrote:
> On Tue, May 20, 2025 at 05:10:03PM +0100, Leo Yan wrote:
> 
> [...]
> 
>> If 'PMSFCR_EL1.FDS == 0 and PMSDSFR_EL1 == 0x0' is the init state, as
>> you said, when user passed 0xFFFF,FFFF,FFFF,FFFF for data filter, we
>> cannot distinguish it from the init state, as a result, we will fail
>> to handle this case.
> 
> Correct a typo. The case above, it means "when a user passes 0x0 for
> data source filter ....".
> 
> Sorry for spamming.
> 
> Leo

I'm thinking I'd rather leave it consistent with PMSFCR_EL1.FT and 
automatically enable PMSFCR_EL1.FDS for any non zero data-source filter.

This means we don't need a tool change to set some other flag when a 
filter is provided (even if it's zero) and it's much simpler. It also 
doesn't prevent the possibility of adding the enable flag in the future 
if someone comes out with a need for it, but I don't think it needs to 
be done now. TBH I can't imagine a case where someone would want to 
filter out any samples that have any data source. Surely you'd only be 
looking for a selected set of data sources, or no filtering at all.