From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Nakajima, Jun" Subject: Re: QEMU PIC indirection patch for in-kernel APIC work Date: Wed, 4 Apr 2007 09:20:57 -0700 Message-ID: <8FFF7E42E93CC646B632AB40643802A8025B962E@scsmsx412.amr.corp.intel.com> References: <4613CCD1.2070702@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: "Avi Kivity" , "Anthony Liguori" Return-path: Content-class: urn:content-classes:message In-Reply-To: <4613CCD1.2070702-atKUWr5tajBWk0Htik3J/w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Avi Kivity wrote: > Anthony Liguori wrote: >> >>> >>> This pushes towards in kernel apic too. Can't see how we avoid it. >>> >> >> Does it really? IIUC, we would avoid TPR traps entirely and would >> just need to synchronize the TPR whenever we go down to userspace. >> > > It's a bit more complex than that, as userspace would need to tell the > kernel the highest priority pending interrupt so that it can program > the hardware to exit when an interrupt is ready. However I agree > with you that in principle we could split the apic emulation between > kvm and qemu, even with this featurette. Most of H/W-virtualization capable processors out there don't support that feature today. I think the decision (kvm or qemu) should be done based on performance data. I'm not worried about maintenance issues; the APIC code is not expected to change frequently. I'm a bit worried about extra complexity caused by such split, though. BTW, I see CPU utilization of qemu is almost always 99% in the top command when I run kernel build in an x86-64 Linux guest. Jun --- Intel Open Source Technology Center ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV