From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757627AbYJGVK1 (ORCPT ); Tue, 7 Oct 2008 17:10:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757418AbYJGVJe (ORCPT ); Tue, 7 Oct 2008 17:09:34 -0400 Received: from terminus.zytor.com ([198.137.202.10]:55367 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757411AbYJGVJd (ORCPT ); Tue, 7 Oct 2008 17:09:33 -0400 Message-ID: <48EBCFF8.6050500@zytor.com> Date: Tue, 07 Oct 2008 14:09:12 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Venki Pallipadi CC: Ingo Molnar , Thomas Gleixner , linux-kernel Subject: Re: [PATCH] x86: Add clflush before monitor for Intel 7400 series References: <20081007210056.GA5802@linux-os.sc.intel.com> In-Reply-To: <20081007210056.GA5802@linux-os.sc.intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Venki Pallipadi wrote: > For Intel 7400 series CPUs, the recommendation is to use a clflush on the > monitored address just before monitor and mwait pair [1]. This clflush makes > sure that there are no false wakeups from mwait when the monitored address > was recently written to. > > [1] "MONITOR/MWAIT Recommendations for Intel Xeon Processor 7400 series" > section in specification update document of 7400 series > http://download.intel.com/design/xeon/specupdt/32033601.pdf > > Signed-off-by: Venkatesh Pallipadi This seems very expensive. It really makes me wonder if it wouldn't just be better to either declare monitor/mwait non-functional on this chip, or make sure that mwaits can handle false wakeups. -hpa