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

From: Namhyung Kim <namhyung@kernel.org>
To: Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
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: Tue, 31 Mar 2015 09:27:30 +0900	[thread overview]
Message-ID: <20150331002730.GE32033@sejong> (raw)
In-Reply-To: <20150330151303.GD32560@kernel.org>

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.

Thanks,
Namhyung