Re: [BUG] segfault in perf-top -- thread refcnt

From: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>, David Ahern <dsahern@gmail.com>,
	Jiri Olsa <jolsa@kernel.org>,
	Stephane Eranian <eranian@google.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [BUG] segfault in perf-top -- thread refcnt
Date: Mon, 30 Mar 2015 21:46:35 -0300	[thread overview]
Message-ID: <20150331004635.GB9438@kernel.org> (raw)
In-Reply-To: <20150331002730.GE32033@sejong>

Em Tue, Mar 31, 2015 at 09:27:30AM +0900, Namhyung Kim escreveu:
> On Mon, Mar 30, 2015 at 12:13:03PM -0300, Arnaldo Carvalho de Melo wrote:
> > Em Mon, Mar 30, 2015 at 11:58:05AM -0300, Arnaldo Carvalho de Melo escreveu:
> > > Em Mon, Mar 30, 2015 at 09:48:52PM +0900, Namhyung Kim escreveu:
> > > > But this makes every sample processing grabs and releases the lock so
> > > > might cause high overhead.  It can be a problem if such processing is
> > > > done parallelly like my multi-thread work. :-/
> > > 
> > > Still untested, using rw lock, next step is auditing the
> > > machine__findnew_thread users that really should be using
> > > machine__find_thread, i.e. grabbing just the reader lock, and measuring
> > > the overhead of using a pthread rw lock instead of pthread_mutex_t as
> > > Jiri is doing.
> > 
> > Don't bother trying it, doesn't even compile ;-\
> 
> OK. :)
> 
> But I think rw lock still has not-so-low overhead as it involves
> atomic operations and cache misses.

But we will have to serialize access to the data structure at some
point...

- Arnaldo