From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758073AbZBTNAA (ORCPT ); Fri, 20 Feb 2009 08:00:00 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754352AbZBTM7p (ORCPT ); Fri, 20 Feb 2009 07:59:45 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:39036 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754283AbZBTM7o (ORCPT ); Fri, 20 Feb 2009 07:59:44 -0500 Date: Fri, 20 Feb 2009 13:59:19 +0100 From: Ingo Molnar To: Gleb Natapov Cc: Suresh Siddha , Yinghai Lu , Thomas Gleixner , "H. Peter Anvin" , Andrew Morton , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] x86: enable x2apic early at the first point Message-ID: <20090220125919.GE26418@elte.hu> References: <499DD40F.40102@kernel.org> <1235081612.14523.23.camel@vayu> <499DE05A.40804@kernel.org> <1235086118.14523.40.camel@vayu> <20090220083528.GB24555@elte.hu> <20090220090912.GA4632@redhat.com> <20090220094123.GJ24555@elte.hu> <20090220105804.GA24826@redhat.com> <20090220110651.GH28581@elte.hu> <20090220123328.GC24826@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090220123328.GC24826@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Gleb Natapov wrote: > On Fri, Feb 20, 2009 at 12:06:51PM +0100, Ingo Molnar wrote: > > > > > If you'll revert my patch it will not be possible to use > > > > > x2apic in KVM (at least without KVM implementing interrupt > > > > > remapping which is unneeded otherwise) and x2apic interface is > > > > > much better for vitalization. Instead of reverting the patch > > > > > it will be better to add check if x2apic can be used without > > > > > intr-remmaping (all CPUs belong to cluster 0) or allow > > > > > enabling of x2apic without IR if running as a guest. > > > > > > > > yep, that would be required - because your patch can break real > > > > systems right now. Mind sending me a fix for it? > > > > > > > > I've applied Yinghai's fix as well, so please base it on latest > > > > tip:master. > > > > > > > OK. Will send next week. > > > > ok, that's too long of a breakage window - i'll revert it then, > > please send a new version once you have it. > > > > What approach you actually prefer? Enable x2apic without > intr-remapping only when running in KVM, or even if running on > real HW but all CPUs are in cluster 0? If former then below is > updated patch (tested only in KVM) if later then it's > definitely for next week :) The latter would be the ideal solution - i.e. next week :) x2apic is a rare feature, and the more exposure we give it the more tested it becomes. It's also obviously good for general code structure if core CPU features are separated from chipset/iommu features. Plus, x2apic accesses could actually be faster than UC accesses to the lapic, so whenever we can we should enter x2apic mode - even if intr-remap is not turned on (because not needed). Ingo