From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752781Ab0AGO1n (ORCPT ); Thu, 7 Jan 2010 09:27:43 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752216Ab0AGO1n (ORCPT ); Thu, 7 Jan 2010 09:27:43 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:32970 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750951Ab0AGO1m (ORCPT ); Thu, 7 Jan 2010 09:27:42 -0500 X-Authority-Analysis: v=1.0 c=1 a=r_nf4N-T2GkA:10 a=7U3hwN5JcxgA:10 a=NxCurGSypRDGMPjQZM8A:9 a=EFXI3Qub4OP4sP8HFX8A:7 a=aa3d6ZXQn8yc7yoFLHHNtdqhbtQA:4 a=A0X8C_FPr_91ywAm:21 a=6eHwggJ0t_Z9e5q0:21 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.89.75 Subject: Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier From: Steven Rostedt Reply-To: rostedt@goodmis.org To: Mathieu Desnoyers Cc: linux-kernel@vger.kernel.org, "Paul E. McKenney" , Ingo Molnar , akpm@linux-foundation.org, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, laijs@cn.fujitsu.com, dipankar@in.ibm.com In-Reply-To: <20100107061955.GC25786@Krystal> References: <20100107044007.GA22863@Krystal> <1262842854.28171.3710.camel@gandalf.stny.rr.com> <20100107061955.GC25786@Krystal> Content-Type: text/plain; charset="ISO-8859-15" Organization: Kihon Technologies Inc. Date: Thu, 07 Jan 2010 09:27:38 -0500 Message-ID: <1262874458.28171.3728.camel@gandalf.stny.rr.com> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2010-01-07 at 01:19 -0500, Mathieu Desnoyers wrote: > I see your point. Actually you are missing the point ;-) > > This would probably be good for machines with very large number of cpus > and without IPI broadcast support, running processes with only few > threads. I really start to think that we should have some way to compare > the number of threads belonging to a process and choose between the > broadcast IPI and the per-cpu IPI depending if we are over or under an > arbitrary threshold. This has nothing to do with performance. It has to do with a thread should not interfere with a thread belonging to another process. We really don't care how long the sys_membarrier() takes (it's the slow path anyway). We do care that a critical RT task is being interrupted by some java thread sending thousands of IPIs. -- Steve