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

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Message-ID: <ZpYgYaKKbw3FPUpv@krava>
Date: Tue, 16 Jul 2024 09:25:21 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Kyle Huey <me@...ehuey.com>, Masami Hiramatsu <mhiramat@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, 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 09:48:58AM -0700, Kyle Huey wrote:
> 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.
> 

it looks like that's the case, AFAICS tracepoint/kprobe/uprobe events
are the only ones having the tp_event pointer set, Masami?

fwiw I tried to run bpf selftests with that and it's fine

jirka