linux-kernel - Re: [PATCH] perf/bpf: Don't call bpf_overflow

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Message-ID: <CAP045Apu6Sb=eKLXkZ5TWitWbmGHMDArD1++81vdN2_NqeFTyw@mail.gmail.com>
Date: Mon, 15 Jul 2024 09:48:58 -0700
From: Kyle Huey <me@...ehuey.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Jiri Olsa <olsajiri@...il.com>, khuey@...ehuey.com, Ingo Molnar <mingo@...hat.com>, 
	Namhyung Kim <namhyung@...nel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	robert@...llahan.org, Joe Damato <jdamato@...tly.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Ian Rogers <irogers@...gle.com>, 
	Adrian Hunter <adrian.hunter@...el.com>, "Liang, Kan" <kan.liang@...ux.intel.com>, 
	Andrii Nakryiko <andrii@...nel.org>, Song Liu <song@...nel.org>, linux-perf-users@...r.kernel.org, 
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH] perf/bpf: Don't call bpf_overflow_handler() for tracing events

On Mon, Jul 15, 2024 at 9:30 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Mon, Jul 15, 2024 at 08:19:44AM -0700, Kyle Huey wrote:
>
> > I think this would probably work but stealing the bit seems far more
> > complicated than just gating on perf_event_is_tracing().
>
> perf_event_is_tracing() is something like 3 branches. It is not a simple
> conditional. Combined with that re-load and the wrong return value, this
> all wants a cleanup.
>
> Using that LSB works, it's just that the code aint pretty.

Maybe we could gate on !event->tp_event instead. Somebody who is more
familiar with this code than me should probably confirm that tp_event
being non-null and perf_event_is_tracing() being true are equivalent
though.

- Kyle