From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753437Ab0AGSkY (ORCPT ); Thu, 7 Jan 2010 13:40:24 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751612Ab0AGSkW (ORCPT ); Thu, 7 Jan 2010 13:40:22 -0500 Received: from e6.ny.us.ibm.com ([32.97.182.146]:40944 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751460Ab0AGSkV (ORCPT ); Thu, 7 Jan 2010 13:40:21 -0500 Date: Thu, 7 Jan 2010 10:40:16 -0800 From: "Paul E. McKenney" To: Steven Rostedt Cc: Peter Zijlstra , Josh Triplett , Mathieu Desnoyers , linux-kernel@vger.kernel.org, Ingo Molnar , akpm@linux-foundation.org, tglx@linutronix.de, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, laijs@cn.fujitsu.com, dipankar@in.ibm.com Subject: Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier Message-ID: <20100107184016.GM6764@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1262842854.28171.3710.camel@gandalf.stny.rr.com> <20100107061955.GC25786@Krystal> <20100107063558.GC12939@feather> <1262853855.4049.86.camel@laptop> <20100107165249.GE6764@linux.vnet.ibm.com> <1262884716.4049.103.camel@laptop> <20100107173118.GG6764@linux.vnet.ibm.com> <1262886277.28171.3734.camel@gandalf.stny.rr.com> <20100107175637.GI6764@linux.vnet.ibm.com> <1262887447.28171.3736.camel@gandalf.stny.rr.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1262887447.28171.3736.camel@gandalf.stny.rr.com> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 07, 2010 at 01:04:07PM -0500, Steven Rostedt wrote: > On Thu, 2010-01-07 at 09:56 -0800, Paul E. McKenney wrote: > > On Thu, Jan 07, 2010 at 12:44:37PM -0500, Steven Rostedt wrote: > > > On Thu, 2010-01-07 at 09:31 -0800, Paul E. McKenney wrote: > > > > > > > Something like the following for sys_membarrier(), then? > > > > > > > > smp_mb(); > > > > for_each_cpu(cpu, current->mm->cpu_vm_mask) { > > > > if (cpu_curr(cpu)->mm == current->mm) > > > > smp_call_function_single(cpu, func, NULL, 1); > > > > } > > > > > > > > Then the code changing ->mm on the other CPU also needs to have a > > > > full smp_mb() somewhere after the change to ->mm, but before starting > > > > user-space execution. Which it might well just due to overhead, but > > > > we need to make sure that someone doesn't optimize us out of existence. > > > > > > To change the mm requires things like flushing the TLB. I'd be surprised > > > if the change of the mm does not already do a smp_mb() somewhere. > > > > Agreed, but "somewhere" does not fill me with warm fuzzies. ;-) > > Another question would be, does flushing the TLB imply a mb()? I do not believe that it is guaranteed to on all architectures. Thanx, Paul