From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752276AbYJRHPx (ORCPT ); Sat, 18 Oct 2008 03:15:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751212AbYJRHPo (ORCPT ); Sat, 18 Oct 2008 03:15:44 -0400 Received: from one.firstfloor.org ([213.235.205.2]:48087 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750871AbYJRHPo (ORCPT ); Sat, 18 Oct 2008 03:15:44 -0400 To: "H. Peter Anvin" Cc: "Pallipadi, Venkatesh" , Ingo Molnar , Thomas Gleixner , linux-kernel Subject: Re: [PATCH] x86: Add clflush before monitor for Intel 7400 series From: Andi Kleen 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> <48F8F1DB.9030202@zytor.com> <7E82351C108FA840AB1866AC776AEC4637B799FB@orsmsx505.amr.corp.intel.com> <48F91673.6090901@zytor.com> Date: Sat, 18 Oct 2008 09:15:39 +0200 In-Reply-To: <48F91673.6090901@zytor.com> (H. Peter Anvin's message of "Fri, 17 Oct 2008 15:49:23 -0700") Message-ID: <87vdvqjrvo.fsf@basil.nowhere.org> User-Agent: Gnus/5.1008 (Gnus v5.10.8) Emacs/21.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "H. Peter Anvin" writes: > Pallipadi, Venkatesh wrote: >>>> >>> 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.) >> As of now this is only for a limited models of CPUs (MP CPUs) >> and not a norm. It is a errata on this CPU and not >> something that is going to become architectural. >> > > Yes, I understand. However, there is still the option to disable > MWAIT, and the question is still open if it makes sense. This would mean falling back to the IO port interface for deeper C states. Even with the CLFLUSH MWAIT is a much better (and I believe faster) interface. -Andi -- ak@linux.intel.com