From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Dor Laor" Subject: Re: QEMU PIC indirection patch for in-kernel APIC work Date: Wed, 4 Apr 2007 09:27:28 -0700 Message-ID: <64F9B87B6B770947A9F8391472E032160B318EDB@ehost011-8.exch011.intermedia.net> References: <4613CCD1.2070702@qumranet.com> <8FFF7E42E93CC646B632AB40643802A8025B962E@scsmsx412.amr.corp.intel.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: "Nakajima, Jun" , "Avi Kivity" , "Anthony Liguori" Return-path: Content-class: urn:content-classes:message In-Reply-To: <8FFF7E42E93CC646B632AB40643802A8025B962E-1a9uaKK1+wJcIJlls4ac1rfspsVTdybXVpNB7YpNyf8@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 >>>> >>>> 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. > I had an in-kernel-apic implementation for KVM and the performance improvement was insignificant. It is mainly a software engineering thing. PV drivers can benefit from APIC in the kernel but again just a mere improvement. >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. What does qemu do? Idle guest hardly consume cpu, especially KVM powered. >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