From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754839AbZESMgF (ORCPT ); Tue, 19 May 2009 08:36:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753776AbZESMf5 (ORCPT ); Tue, 19 May 2009 08:35:57 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:48276 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753372AbZESMf4 (ORCPT ); Tue, 19 May 2009 08:35:56 -0400 Date: Tue, 19 May 2009 14:35:48 +0200 From: Ingo Molnar To: Jeremy Fitzhardinge Cc: the arch/x86 maintainers , Linux Kernel Mailing List , Xen-devel Subject: Re: [GIT PULL] Xen APIC hooks (with io_apic_ops) Message-ID: <20090519123548.GA26439@elte.hu> References: <1242170724-13349-1-git-send-email-jeremy@goop.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1242170724-13349-1-git-send-email-jeremy@goop.org> User-Agent: Mutt/1.5.18 (2008-05-17) 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=3.2.5 -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 * Jeremy Fitzhardinge wrote: > Hi Ingo, > > Here's a revised set of the Xen APIC changes which adds > io_apic_ops to allow Xen to intercept IO APIC access operations. In a previous discussion you said: > IO APIC operations are not even slightly performance critical? Are > they ever used on the interrupt delivery path? Since they are not performance critical, then why doesnt Xen catch the IO-APIC accesses, and virtualizes the device? If you want to hook into the IO-APIC code at such a low level, why dont you hook into the _hardware_ API - i.e. catch those setup/routing modifications to the IO-APIC space. No Linux changes are needed in that case. Ingo