From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932715Ab0AGIc7 (ORCPT ); Thu, 7 Jan 2010 03:32:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932562Ab0AGIc6 (ORCPT ); Thu, 7 Jan 2010 03:32:58 -0500 Received: from casper.infradead.org ([85.118.1.10]:57024 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932467Ab0AGIc5 (ORCPT ); Thu, 7 Jan 2010 03:32:57 -0500 Subject: Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier From: Peter Zijlstra To: paulmck@linux.vnet.ibm.com Cc: Mathieu Desnoyers , linux-kernel@vger.kernel.org, Ingo Molnar , akpm@linux-foundation.org, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, laijs@cn.fujitsu.com, dipankar@in.ibm.com In-Reply-To: <20100107050248.GA6803@linux.vnet.ibm.com> References: <20100107044007.GA22863@Krystal> <20100107050248.GA6803@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" Date: Thu, 07 Jan 2010 09:32:16 +0100 Message-ID: <1262853136.4049.81.camel@laptop> 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 Wed, 2010-01-06 at 21:02 -0800, Paul E. McKenney wrote: > > Beats the heck out of user-mode signal handlers!!! And it is hard > to imagine groveling through runqueues ever being a win, even on very > large systems. The only reasonable optimization I can imagine is to > turn this into a no-op for a single-threaded process, but there are > other ways to do that optimization. > > Reviewed-by: "Paul E. McKenney" Then imagine someone doing: while (1) sys_membarrier(); on your multi node machine, see how happy you are then.