From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756599AbZBRTSz (ORCPT ); Wed, 18 Feb 2009 14:18:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754540AbZBRTSi (ORCPT ); Wed, 18 Feb 2009 14:18:38 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:38597 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754089AbZBRTSh (ORCPT ); Wed, 18 Feb 2009 14:18:37 -0500 Date: Wed, 18 Feb 2009 20:17:57 +0100 From: Ingo Molnar To: Suresh Siddha Cc: Nick Piggin , Peter Zijlstra , Oleg Nesterov , Jens Axboe , Linus Torvalds , "Paul E. McKenney" , Rusty Russell , Steven Rostedt , "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" Subject: Re: smp.c && barriers (Was: [PATCH 1/4] generic-smp: remove single ipi fallback for smp_call_function_many()) Message-ID: <20090218191757.GD8889@elte.hu> References: <20090216220214.GA10093@redhat.com> <1234823097.30178.406.camel@laptop> <20090216231946.GA12009@redhat.com> <1234862974.4744.31.camel@laptop> <20090217101130.GA8660@wotan.suse.de> <1234866453.4744.58.camel@laptop> <20090217112657.GE26402@wotan.suse.de> <1234923702.29823.7.camel@vayu> <20090218135945.GC23125@wotan.suse.de> <1234982620.29823.22.camel@vayu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1234982620.29823.22.camel@vayu> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Suresh Siddha wrote: > On Wed, 2009-02-18 at 05:59 -0800, Nick Piggin wrote: > > You're saying the problem is in generic_exec_single because I've > > removed the smp_mb that inadvertently also serialises memory with > > the x2apic on x86? > > yes. > > > > > Indeed that could cause problems on some architectures which I > > had hoped to avoid. So the patch is probably better off to first > > add the smp_mb() to arch_send_call_function_xxx arch code, unless > > it is immediately obvious or confirmed by arch maintainer that > > such barrier is not required. > > For x2apic specific operations we should add the smp_mb() sequence. But > we need to make sure that we don't end up doing it twice (once in > generic code and another in arch code) for all the ipi paths. right now we do have an smp_mb() due to your fix in November. So what should happen is to move that smp_mb() from the x86 generic IPI path to the x86 x2apic IPI path. (and turn it into an smp_wmb() - that should be enough - we dont care about future reads being done sooner than this point.) Ingo