Re: [PATCH v6 12/13] alpha/perf: sample only retired instructions for precise events

[sashiko-bot@kernel.org]

> ProfileMe samples include instructions killed on a wrong path, which
> show up as hot spots in perf report although they did no work. On an
> EV7 loop with a randomly mispredicted branch, 19% of the samples were
> killed before being mapped and another 48% later.
> 
> PEBS and AMD IBS op samples are of retired instructions only, so make
> precise_ip imply the retired filter, unless filters are given. The
> profileme bit still selects every sample. With cycles:p, both kinds of
> killed sample went to 0%.
> 
> DTB miss samples, whose instruction is aborted, are then dropped too:
> cycles:p reports DTB hits only, and the misses need cpu/cycles,trapped/p.
> 
> The kept samples carry the full period, as do those AMD IBS keeps when
> its swfilt discards others. So in frequency mode the sample rate, and
> the event count perf report estimates from the periods, fall by the
> share of killed instructions: to about a third on that loop.
> 
> Suggested-by: Ian Rogers <irogers@google.com>
> Assisted-by: Claude:claude-opus-5-5
> Signed-off-by: Matt Turner <mattst88@gmail.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261104-alpha-profileme-v6-0-63362e9290a3@gmail.com?part=12