linux-kernel - Re: [PATCH v5 13/17] perf: Support deferred user callchains

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Message-ID: <20250424131644.51bc747c@gandalf.local.home>
Date: Thu, 24 Apr 2025 13:16:44 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, Masami
 Hiramatsu <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Josh Poimboeuf <jpoimboe@...nel.org>,
 x86@...nel.org, Ingo Molnar <mingo@...nel.org>, Arnaldo Carvalho de Melo
 <acme@...nel.org>, Indu Bhagat <indu.bhagat@...cle.com>, Alexander Shishkin
 <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>, Adrian
 Hunter <adrian.hunter@...el.com>, linux-perf-users@...r.kernel.org, Mark
 Brown <broonie@...nel.org>, linux-toolchains@...r.kernel.org, Jordan Rome
 <jordalgo@...a.com>, Sam James <sam@...too.org>, Andrii Nakryiko
 <andrii.nakryiko@...il.com>, Jens Remus <jremus@...ux.ibm.com>, Florian
 Weimer <fweimer@...hat.com>, Andy Lutomirski <luto@...nel.org>, Weinan Liu
 <wnliu@...gle.com>, Blake Jones <blakejones@...gle.com>, Beau Belgrave
 <beaub@...ux.microsoft.com>, "Jose E. Marchesi" <jemarch@....org>
Subject: Re: [PATCH v5 13/17] perf: Support deferred user callchains

On Thu, 24 Apr 2025 18:38:45 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> > +	guard(irqsave)();
> > +
> > +        /* callback already pending? */
> > +        pending = READ_ONCE(event->pending_unwind_callback);
> > +        if (pending)
> > +                return 1;
> > +
> > +        /* Claim the work unless an NMI just now swooped in to do so. */
> > +        if (!try_cmpxchg(&event->pending_unwind_callback, &pending, 1))
> > +                return 1;
> > +
> > +        /* The work has been claimed, now schedule it. */
> > +        ret = task_work_add(current, work, TWA_RESUME);
> > +        if (WARN_ON_ONCE(ret)) {
> > +                WRITE_ONCE(event->pending_unwind_callback, 0);
> > +                return ret;
> > +        }
> > +	return 0;
> > +}  
> 
> You have whitespace issues ...

Bah, that may have been due to cut and paste to fix up things during the
multiple rebases I did.

Thanks!

-- Steve