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 16:21:02 +0900 [thread overview]
Message-ID: <20150331072102.GA20651@sejong> (raw)
In-Reply-To: <20150331004635.GB9438@kernel.org>
On Mon, Mar 30, 2015 at 09:46:35PM -0300, Arnaldo Carvalho de Melo wrote:
> 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...
Yes, as long as we keep ref-counting.
I'm guessing if we only focus on the perf top case, there might be a
way to cleanup dead threads without ref-counting (i.e. w/o affecting
fastpath on the perf report).
Thanks,
Namhyung
next prev parent reply other threads:[~2015-03-31 7:27 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-27 17:31 [BUG] segfault in perf-top -- thread refcnt David Ahern
2015-03-27 19:51 ` Arnaldo Carvalho de Melo
2015-03-27 20:11 ` Arnaldo Carvalho de Melo
2015-03-27 20:13 ` David Ahern
2015-03-30 8:07 ` Jiri Olsa
2015-03-30 10:22 ` Jiri Olsa
2015-03-30 11:21 ` Jiri Olsa
2015-03-30 11:49 ` Jiri Olsa
2015-03-30 12:48 ` Namhyung Kim
2015-03-30 12:56 ` Jiri Olsa
2015-03-30 13:06 ` Namhyung Kim
2015-03-30 14:02 ` Arnaldo Carvalho de Melo
2015-03-31 0:15 ` Namhyung Kim
2015-03-30 13:07 ` Arnaldo Carvalho de Melo
2015-03-30 13:20 ` Jiri Olsa
2015-03-30 13:59 ` Arnaldo Carvalho de Melo
2015-03-30 14:58 ` Arnaldo Carvalho de Melo
2015-03-30 15:13 ` Arnaldo Carvalho de Melo
2015-03-31 0:27 ` Namhyung Kim
2015-03-31 0:46 ` Arnaldo Carvalho de Melo
2015-03-31 7:21 ` Namhyung Kim [this message]
2015-03-30 13:22 ` Arnaldo Carvalho de Melo
2015-03-30 13:09 ` Arnaldo Carvalho de Melo
2015-03-30 13:17 ` Arnaldo Carvalho de Melo
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