From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752766Ab0HPH2b (ORCPT ); Mon, 16 Aug 2010 03:28:31 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:37632 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751339Ab0HPH2a (ORCPT ); Mon, 16 Aug 2010 03:28:30 -0400 Date: Mon, 16 Aug 2010 09:28:05 +0200 From: Ingo Molnar To: "Eric W. Biederman" Cc: Yinghai Lu , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Andrew Morton , linux-kernel@vger.kernel.org, Suresh Siddha Subject: Re: [PATCH] x86: Don't write io_apic ID if it is not changed Message-ID: <20100816072805.GA22479@elte.hu> References: <4C66FEA9.3040303@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: 0.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=0.5 required=5.9 tests=BAYES_40 autolearn=no SpamAssassin version=3.2.5 0.5 BAYES_40 BODY: Bayesian spam probability is 20 to 40% [score: 0.2916] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Eric W. Biederman wrote: > Yinghai Lu writes: > > > For 32bit mptable path, setup_ids_from_mpc() always write io apic id > > register, even there is no change needed. > > > > So try to do that when they are different bewteen reading out and > > mptable > > What is the advantage of not writing the value? Just guessing, but if other OSs dont do it we might surprise buggy hardware [and trigger erratas in them], so this would be a standard 'dont touch the hw unless necessary' defensive move. Similar bugs are not unprecedented. Thanks, Ingo