From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [v3 13/26] KVM: Define a new interface kvm_find_dest_vcpu() for VT-d PI Date: Thu, 18 Dec 2014 17:58:13 +0100 Message-ID: <549307A5.3060305@redhat.com> References: <1418397300-10870-1-git-send-email-feng.wu@intel.com> <1418397300-10870-14-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-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "eric.auger-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org" To: "Zhang, Yang Z" , "Wu, Feng" , "tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org" , "mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org" , "hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org" , "x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org" , "gleb-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org" , "dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org" , "joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org" , "alex.williamson-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org" , "jiang.liu-VuQAYsv1563Yd54FQh9/CA@public.gmane.org" 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 18/12/2014 15:49, Zhang, Yang Z wrote: >>> Here, we introduce a similar way with 'apic_arb_prio' to handle >>> guest lowest priority interrtups when VT-d PI is used. Here is >>> the ideas: - Each vCPU has a counter 'round_robin_counter'. - >>> When guests sets an interrupts to lowest priority, we choose the >>> vCPU with smallest 'round_robin_counter' as the destination, then >>> increase it. > > How this can work well? All subsequent interrupts are delivered to > one vCPU? It shouldn't be the best solution, need more consideration. Well, it's a hardware limitation. The alternative (which is easy to implement) is to only do PI for single-CPU interrupts. This should work well for multiqueue NICs (and of course for UP guests :)), so perhaps it's a good idea to only support that as a first attempt. Paolo > Also, I think you should take the apic_arb_prio into consider since > the priority is for the whole vCPU not for one interrupt.