From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758157AbYJQUNt (ORCPT ); Fri, 17 Oct 2008 16:13:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755710AbYJQUNm (ORCPT ); Fri, 17 Oct 2008 16:13:42 -0400 Received: from terminus.zytor.com ([198.137.202.10]:39147 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755497AbYJQUNl (ORCPT ); Fri, 17 Oct 2008 16:13:41 -0400 Message-ID: <48F8F1DB.9030202@zytor.com> Date: Fri, 17 Oct 2008 13:13:15 -0700 From: "H. Peter Anvin" User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: "Pallipadi, Venkatesh" 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> <48EBCFF8.6050500@zytor.com> <20081007214920.GA17439@linux-os.sc.intel.com> <48EBEA97.9020404@zytor.com> <7E82351C108FA840AB1866AC776AEC4637B798D6@orsmsx505.amr.corp.intel.com> In-Reply-To: <7E82351C108FA840AB1866AC776AEC4637B798D6@orsmsx505.amr.corp.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 Pallipadi, Venkatesh wrote: > > hpa, > > Do you still have reservations about this being expensive. > Note that this is only done when a CPU is about to go idle and > The cost of clflush itself will be minimal compared to idle > entry + idle exit latency. > I guess I'm a bit confused about the tradeoff of CLFLUSH versus simply disabling MWAIT. This is a relatively recent processor and so optimizing matters (if this was a P4 I would be more worried about what has least impact on the kernel as a whole.) Entry and exit latency do matter (specifically, exit latency matters for longer waits and the combined entry+exit latency matters for short waits.) On the other hand, perhaps what we need to do is to get the fix in and worry about performance later. -hpa