From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: QEMU PIC indirection patch for in-kernel APIC work Date: Thu, 05 Apr 2007 16:59:17 +0300 Message-ID: <461500B5.4080102@qumranet.com> References: <0E6FE5D295DE5B4B8D9070C26A227987E0D1EC@pdsmsx411.ccr.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: "Dong, Eddie" Return-path: In-Reply-To: <0E6FE5D295DE5B4B8D9070C26A227987E0D1EC-wq7ZOvIWXbNpB2pF5aRoyrfspsVTdybXVpNB7YpNyf8@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 Dong, Eddie wrote: > Dor Laor wrote: > >> Do you know why Xen guy choose of implementing it in Xen? Why didn't >> they rip Qemu implementation? >> >> > With PIC in Xen, CPU2K gets 6.5% performance gain in old 1000HZ linux > kernel, KB gets 14% gain. We also did a shared PIC model which share > PIC state among Qemu & VMM with less LOC in VMM, it can get > similar performance gain (5.8% in my test). > BTW, at that time, PIT is in VMM already. > I expect that the gain in kvm will be smaller. Xen has to schedule dom0 to process the event channel (possibly on another cpu), dom0 has to schedule qemu-dm (again, possibly on another cpu), qemu does its thing, and then Xen has to schedule domU again. With kvm, we are always on the same cpu, and the only overhead is the system call, which is a few hundred nanoseconds. I expect with current hardware that it will be negligible (as a vmexit is measured in microseconds), but to become measurable as hardware improves. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- 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