From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752655AbbAIPNn (ORCPT ); Fri, 9 Jan 2015 10:13:43 -0500 Received: from mx1.redhat.com ([209.132.183.28]:50978 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752060AbbAIPNl (ORCPT ); Fri, 9 Jan 2015 10:13:41 -0500 Date: Fri, 9 Jan 2015 16:12:59 +0100 From: Radim =?utf-8?B?S3LEjW3DocWZ?= To: Paolo Bonzini Cc: Feng Wu , tglx@linutronix.de, mingo@redhat.com, hpa@zytor.com, x86@kernel.org, gleb@kernel.org, dwmw2@infradead.org, joro@8bytes.org, alex.williamson@redhat.com, jiang.liu@linux.intel.com, eric.auger@linaro.org, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, kvm@vger.kernel.org Subject: Re: [v3 13/26] KVM: Define a new interface kvm_find_dest_vcpu() for VT-d PI Message-ID: <20150109151258.GC9877@potion.brq.redhat.com> References: <1418397300-10870-1-git-send-email-feng.wu@intel.com> <1418397300-10870-14-git-send-email-feng.wu@intel.com> <20150109145435.GA22469@potion.brq.redhat.com> <54AFEC00.80507@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <54AFEC00.80507@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2015-01-09 15:56+0100, Paolo Bonzini: > > > On 09/01/2015 15:54, Radim Krčmář wrote: > > There are two points relevant to this patch in new KVM's implementation, > > ("KVM: x86: amend APIC lowest priority arbitration", > > https://lkml.org/lkml/2015/1/9/362) > > > > 1) lowest priority depends on TPR > > 2) there is no need for balancing > > > > (1) has to be considered with PI as well. > > The chipset doesn't support it. :( I meant that we need to recompute PI entries for lowest priority interrupts every time guest's TPR changes. Luckily, Linux doesn't use TPR, but other OS might be a reason to drop lowest priority from PI optimizations. (Or make it more complicated.) > > I kept (2) to avoid whining from people building on that behaviour, but > > lowest priority backed by PI could be transparent without it. > > > > Patch below removes the balancing, but I am not sure this is a price we > > allowed ourselves to pay ... what are your opinions? > > I wouldn't mind, but it requires a lot of benchmarking. (I was afraid it would come to that.)