From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 0/1] x2apic implementation for kvm Date: Mon, 25 May 2009 13:49:04 +0300 Message-ID: <4A1A77A0.7040207@redhat.com> References: <1242927475-6140-1-git-send-email-gleb@redhat.com> <200905251719.16009.sheng@linux.intel.com> <4A1A635A.1000000@redhat.com> <200905251759.08421.sheng@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Gleb Natapov , kvm@vger.kernel.org To: Sheng Yang Return-path: Received: from mx2.redhat.com ([66.187.237.31]:50171 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753309AbZEYKtG (ORCPT ); Mon, 25 May 2009 06:49:06 -0400 In-Reply-To: <200905251759.08421.sheng@linux.intel.com> Sender: kvm-owner@vger.kernel.org List-ID: Sheng Yang wrote: > On Monday 25 May 2009 17:22:34 Avi Kivity wrote: > >> Sheng Yang wrote: >> >>> I think that means the PV interface for lapic. And yes, we can support it >>> follow MS's interface, but x2apic still seems another story as you >>> noted... I still don't think support x2apic here would bring us more >>> benefits. >>> >> x2apic has the following benefit: >> >> - msr exits are faster than mmio (no page table walk, emulation) >> > > Need PV(at least part of). I don't think Hyper-V considered this, and not sure > the community's aptitude. > Hyper-V does define MSRs for local apic access, as far as I can tell they're identical to x2apic except for the msr index. >> - potential to support large guests once we add interrupt remapping >> > > Then it can be added before we have it. Compared to the workload, x2apic is > not the problem, interrupt remapping/VT-d is. > I'd like to have the benefit sooner. x2apic provides two user-visible benefits: performance and large guests. I don't want performance to wait for large guests. >> - shared code with the Hyper-V paravirt interface >> > > So I think the key thing are ICR related(and seems no data available > currently). Compare the benefit of ICR improve(can it improved in another way? > Does Hyper-V interface has related things?), and the workload of x2apic > virtualization as well as guest OS support, well, I don't know, but not > optimistic x2apic, without interrupt remapping, is fairly simple. -- error compiling committee.c: too many arguments to function