From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752435AbaLSL7o (ORCPT ); Fri, 19 Dec 2014 06:59:44 -0500 Received: from mail-wi0-f172.google.com ([209.85.212.172]:44882 "EHLO mail-wi0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752329AbaLSL7l (ORCPT ); Fri, 19 Dec 2014 06:59:41 -0500 Message-ID: <54941326.4080405@redhat.com> Date: Fri, 19 Dec 2014 12:59:34 +0100 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Yang Zhang , "Wu, Feng" , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "x86@kernel.org" , Gleb Natapov , Paolo Bonzini , "dwmw2@infradead.org" , "joro@8bytes.org" , Alex Williamson , Jiang Liu CC: "iommu@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" , KVM list , Eric Auger Subject: Re: [v3 06/26] iommu, x86: No need to migrating irq for VT-d Posted-Interrupts References: <1418397300-10870-1-git-send-email-feng.wu@intel.com> <1418397300-10870-7-git-send-email-feng.wu@intel.com> In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/12/2014 02:46, Zhang, Yang Z wrote: >> If the IRQ is posted, its affinity is controlled by guest (irq <---> >> vCPU <----> pCPU), it has no effect when host changes its affinity. > > That's the problem: User is able to changes it in host but it never > takes effect since it is actually controlled by guest. I guess it > will break the IRQ balance too. I don't think that's a problem. Controlling the affinity in the host affects which CPU in the host takes care of signaling the guest. If this signaling is done directly by the chipset, there is no need to do anything in the host and thus the host affinity can be bypassed. Paolo From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [v3 06/26] iommu, x86: No need to migrating irq for VT-d Posted-Interrupts Date: Fri, 19 Dec 2014 12:59:34 +0100 Message-ID: <54941326.4080405@redhat.com> References: <1418397300-10870-1-git-send-email-feng.wu@intel.com> <1418397300-10870-7-git-send-email-feng.wu@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , KVM list , Eric Auger To: Yang Zhang , "Wu, Feng" , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org" , Gleb Natapov , Paolo Bonzini , "dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org" , "joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org" , Alex Williamson , Jiang Liu Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org List-Id: kvm.vger.kernel.org On 19/12/2014 02:46, Zhang, Yang Z wrote: >> If the IRQ is posted, its affinity is controlled by guest (irq <---> >> vCPU <----> pCPU), it has no effect when host changes its affinity. > > That's the problem: User is able to changes it in host but it never > takes effect since it is actually controlled by guest. I guess it > will break the IRQ balance too. I don't think that's a problem. Controlling the affinity in the host affects which CPU in the host takes care of signaling the guest. If this signaling is done directly by the chipset, there is no need to do anything in the host and thus the host affinity can be bypassed. Paolo