From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751682Ab2IFLqg (ORCPT ); Thu, 6 Sep 2012 07:46:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:11230 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750852Ab2IFLqf (ORCPT ); Thu, 6 Sep 2012 07:46:35 -0400 Message-ID: <50488D14.4010304@redhat.com> Date: Thu, 06 Sep 2012 14:46:28 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Tomoki Sekiyama CC: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, yrl.pp-manager.tt@hitachi.com Subject: Re: [RFC v2 PATCH 00/21] KVM: x86: CPU isolation and direct interrupts delivery to guests References: <20120906112718.13320.8231.stgit@kvmdev> In-Reply-To: <20120906112718.13320.8231.stgit@kvmdev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/06/2012 02:27 PM, Tomoki Sekiyama wrote: > This RFC patch series provides facility to dedicate CPUs to KVM guests > and enable the guests to handle interrupts from passed-through PCI devices > directly (without VM exit and relay by the host). > > With this feature, we can improve throughput and response time of the device > and the host's CPU usage by reducing the overhead of interrupt handling. > This is good for the application using very high throughput/frequent > interrupt device (e.g. 10GbE NIC). > Real-time applicatoins also gets benefit from CPU isolation feature, which > reduces interfare from host kernel tasks and scheduling delay. > > The overview of this patch series is presented in CloudOpen 2012. > The slides are available at: > http://events.linuxfoundation.org/images/stories/pdf/lcna_co2012_sekiyama.pdf During Plumbers 2012, both Intel and AMD disclosed upcoming features to their processors (APIC-V and AVIC) that allow directing device interrupts to guest vcpus without host kernel involvement. This works without pinning, dedicating a core to a guest, or any special measures beyond support for the feature. CPU isolation is still useful to improve real-time latency further, but this is really independent of kvm. I am inclined to reject this feature in favour of the new hardware support. Sorry, I know this isn't nice to hear, but the extra maintenance burden cannot be justified for a niche use case with special limitations when generally useful feature exploiting proper hardware support provides the same functionality. -- error compiling committee.c: too many arguments to function