linux-kernel - Re: [PATCH 19/20] perf tools: Reference count struct thread

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Date:	Tue, 3 Mar 2015 10:57:25 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	Borislav Petkov <bp@...e.de>, David Ahern <dsahern@...il.com>,
	Don Zickus <dzickus@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 19/20] perf tools: Reference count struct thread

Em Tue, Mar 03, 2015 at 10:42:14PM +0900, Namhyung Kim escreveu:
> On Tue, Mar 03, 2015 at 12:26:08AM -0300, Arnaldo Carvalho de Melo wrote:
> > +++ b/tools/perf/util/thread.c
> > @@ -82,6 +82,20 @@ void thread__delete(struct thread *thread)

> > +struct thread *thread__get(struct thread *thread)
> > +{
> > +	++thread->refcnt;
> > +	return thread;
> > +}

> > +void thread__put(struct thread *thread)
> > +{
> > +	if (thread && --thread->refcnt == 0) {
> > +		list_del_init(&thread->node);
> > +		thread__delete(thread);
> > +	}
> > +}
 
> I think we need to protect refcnt from concurrent accesses from
> multiple threads.  Not to mention my multi-thread work, perf top
> already uses two threads.

Sure
 
> For perf top case, hist_entry__new() will be called from main thread
> and hist_entry__delete() might be called from display thread.

Reference counting is a step in that direction, as to if the integer
inc/dec is enough or is already surrounded by existing serialization
needs to be checked.

- Arnaldo
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