From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] KVM: x86: Add lowest-priority support for vt-d posted-interrupts Date: Tue, 24 Nov 2015 15:38:26 +0100 Message-ID: <56547662.7020804@redhat.com> References: <1447037208-75615-1-git-send-email-feng.wu@intel.com> <20151116190314.GA12245@potion.brq.redhat.com> <564AF645.5010506@redhat.com> <20151124143557.GA24676@potion.brq.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" To: =?UTF-8?Q?Radim_Krcm=c3=a1r?= , "Wu, Feng" Return-path: In-Reply-To: <20151124143557.GA24676@potion.brq.redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 24/11/2015 15:35, Radim Krcm=C3=A1r wrote: > > Thanks for your guys' review. Yes, we can introduce a module option > > for it. According to Radim's comments above, we need use the > > same policy for PI and non-PI lowest-priority interrupts, so here i= s the > > question: for vector hashing, it is easy to apply it for both non-P= I and PI > > case, however, for Round-Robin, in non-PI case, the round robin cou= nter > > is used and updated when the interrupt is injected to guest, but fo= r > > PI case, the interrupt is injected to guest totally by hardware, so= ftware > > cannot control it while interrupt delivery, we can only decide the > > destination vCPU for the PI interrupt in the initial configuration > > time (guest update vMSI -> QEMU -> KVM). Do you guys have any good > > suggestion to do round robin for PI lowest-priority? Seems Round ro= bin > > is not a good way for PI lowest-priority interrupts. Any comments > > are appreciated! > > It's meaningless to try dynamic algorithms with PI so if we allow bot= h > lowest priority algorithms, I'd let PI handle any lowest priority onl= y > with vector hashing. (It's an ugly compromise.) =46or now, I would just keep the 4.4 behavior, i.e. disable PI unless there is a single destination || vector hashing is enabled. We can fli= p the switch later. Paolo