Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753701Ab3JBQB0 (ORCPT ); Wed, 2 Oct 2013 12:01:26 -0400 Received: from mail-wg0-f42.google.com ([74.125.82.42]:65258 "EHLO mail-wg0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753046Ab3JBQBW (ORCPT ); Wed, 2 Oct 2013 12:01:22 -0400 Date: Wed, 2 Oct 2013 18:01:18 +0200 From: Frederic Weisbecker To: Arjan van de Ven Cc: Peter Zijlstra , Oleg Nesterov , Fernando Luis =?iso-8859-1?Q?V=E1zquez?= Cao , Ingo Molnar , Thomas Gleixner , LKML , Tetsuo Handa , Andrew Morton Subject: Re: [PATCH 2/4] nohz: Synchronize sleep time stats with seqlock Message-ID: <20131002160116.GG7941@localhost.localdomain> References: <20130821113551.GA1472@redhat.com> <20130821123311.GA31370@twins.programming.kicks-ass.net> <20130821142356.GC31370@twins.programming.kicks-ass.net> <20130821164146.GA15194@redhat.com> <20131001140525.GE24825@localhost.localdomain> <20131001155633.GR3657@laptop.programming.kicks-ass.net> <20131001164708.GG24825@localhost.localdomain> <20131001165957.GT3657@laptop.programming.kicks-ass.net> <20131002124539.GF7941@localhost.localdomain> <524C2F45.4040401@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <524C2F45.4040401@linux.intel.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1036 Lines: 24 On Wed, Oct 02, 2013 at 07:35:49AM -0700, Arjan van de Ven wrote: > On 10/2/2013 5:45 AM, Frederic Weisbecker wrote: > >On Tue, Oct 01, 2013 at 06:59:57PM +0200, Peter Zijlstra wrote: > >>On Tue, Oct 01, 2013 at 06:47:10PM +0200, Frederic Weisbecker wrote: > >>>Yeah thinking more about it, the preempt disable was probably not > >>>necessary. Now that's trading 2 atomics + 1 Lock/Unlock with 2 Lock/Unlock. > >> > >>It trades the current 2 atomics for 2 LOCK/UNLOCK. And on x86_64 that's > >>2 atomics. > > > >Do you mean 2 atomics for LOCK/UNLOCK? Or is that pair optimized somehow > >in x86? > > unlock is not actually an atomic. > > and on some modern machines, neither is the lock, for the uncontended case ;-) > Yeah, we are never getting short on black magic as the time goes :) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/