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

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Message-ID: <20240715163003.GK14400@noisy.programming.kicks-ass.net>
Date: Mon, 15 Jul 2024 18:30:03 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Kyle Huey <me@...ehuey.com>
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 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.