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

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Message-Id: <20240721010304.bf426eafee8e3745ce21f6c3@kernel.org>
Date: Sun, 21 Jul 2024 01:03:04 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Jiri Olsa <olsajiri@...il.com>
Cc: Kyle Huey <me@...ehuey.com>, Peter Zijlstra <peterz@...radead.org>,
 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 Tue, 16 Jul 2024 09:25:21 +0200
Jiri Olsa <olsajiri@...il.com> wrote:

> 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?

Hmm, I think any dynamic_events has tp_event (is struct trace_event_call *)
because it represents the event itself. But yes, if the event is working
like a trace-event, it should have tp_event. So you can use it instead
perf_event_is_tracing().

Thank you,

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


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>