From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753327Ab0AGQwy (ORCPT ); Thu, 7 Jan 2010 11:52:54 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752382Ab0AGQwx (ORCPT ); Thu, 7 Jan 2010 11:52:53 -0500 Received: from e8.ny.us.ibm.com ([32.97.182.138]:57983 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752141Ab0AGQww (ORCPT ); Thu, 7 Jan 2010 11:52:52 -0500 Date: Thu, 7 Jan 2010 08:52:49 -0800 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Josh Triplett , Mathieu Desnoyers , Steven Rostedt , 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: <20100107165249.GE6764@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20100107044007.GA22863@Krystal> <1262842854.28171.3710.camel@gandalf.stny.rr.com> <20100107061955.GC25786@Krystal> <20100107063558.GC12939@feather> <1262853855.4049.86.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1262853855.4049.86.camel@laptop> 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 09:44:15AM +0100, Peter Zijlstra wrote: > On Wed, 2010-01-06 at 22:35 -0800, Josh Triplett wrote: > > > > The number of threads doesn't matter nearly as much as the number of > > threads typically running at a time compared to the number of > > processors. Of course, we can't measure that as easily, but I don't > > know that your proposed heuristic would approximate it well. > > Quite agreed, and not disturbing RT tasks is even more important. OK, so I stand un-Reviewed-by twice in one morning. ;-) > A simple: > > for_each_cpu(cpu, current->mm->cpu_vm_mask) { > if (cpu_curr(cpu)->mm == current->mm) > smp_call_function_single(cpu, func, NULL, 1); > } > > seems far preferable over anything else, if you really want you can use > a cpumask to copy cpu_vm_mask in and unset bits and use the mask with > smp_call_function_any(), but that includes having to allocate the > cpumask, which might or might not be too expensive for Mathieu. This would be vulnerable to the sys_membarrier() CPU seeing an old value of cpu_curr(cpu)->mm, and that other task seeing the old value of the pointer we are trying to RCU-destroy, right? Thanx, Paul