linux-kernel - Re: [PATCH v5 00/17] perf c2c: Support data source and display for Arm64

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Date:   Fri, 12 Aug 2022 23:20:10 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        John Garry <john.garry@...wei.com>,
        Will Deacon <will@...nel.org>,
        James Clark <james.clark@....com>,
        German Gomez <german.gomez@....com>,
        Ali Saidi <alisaidi@...zon.com>, Joe Mario <jmario@...hat.com>,
        Adam Li <adam.li@...erecomputing.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v5 00/17] perf c2c: Support data source and display for
 Arm64

On Fri, Aug 12, 2022 at 09:43:07AM -0300, Arnaldo Carvalho de Melo wrote:

[...]

> > One question: should I later continue to upstream the first patch for
> > syncing the kernel header perf_event.h after Peter.Z comes back?
> 
> yes, and we may have to backtrack and find some other way to implement
> this if he is opposed, as he in the past didn't like
> perf_event_attr.type namespace being used by userspace only records such
> as PERF_RECORD_FINISHED_ROUND, PERF_RECORD_COMPRESSED, etc.
> 
> In this case its different, I think its ok as we already have
> PERF_MEM_SNOOPX_FWD and PERF_MEM_SNOOPX_PEER probably will be emitted by
> the some of the architectures, from the kernel, right?

Yes, as I know x86 generates memory samples from kernel, and SNOOPX_PEER
can be a useful snooping flag for other archs.

As a last resort if SNOOPX_PEER is rejected, we can rollback to use
existed flag (like reusing PERF_MEM_SNOOPX_FWD), though this would be
ambiguous for expressing the memory operations on Arm64.

Thanks,
Leo