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 14:33:42 -0700 Message-ID: <64F9B87B6B770947A9F8391472E032160B319171@ehost011-8.exch011.intermedia.net> References: <4613D93A.5020902@qumranet.com> <8FFF7E42E93CC646B632AB40643802A8025B970D@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" Return-path: Content-class: urn:content-classes:message In-Reply-To: <8FFF7E42E93CC646B632AB40643802A8025B970D-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 >Avi Kivity wrote: >> Nakajima, Jun wrote: >>> I compared the performance on Xen and KVM for kernel build using the >>> same guest image. Looks like KVM was (kvm-17) three times slower as >>> far as we tested, and that high load of qemu was one of the >>> symptoms. We are looking at the shadow code, but the load of qemu >>> looks very high. I remember we had similar problems in Xen before, >>> but those were fixed. Someone should take a look at the qemu side. >>> >> >> I'd expect the following issues to dominate: >> >> - the shadow cache is quite small at 256 pages. Increasing it may >> increase performance. > >Yes, we are aware of this. > >> >> - we haven't yet taught the scheduler that migrating vcpus is >> expensive due to the IPI needed to fetch the vmcs. Maybe running >> with 'taskset 1' would help >> >> - shadow eviction policy is FIFO, not LRU, which probably causes many >> page faults. > >This may explain that the performance gets worse as we repeat kernel >build, at least, the second run is slower than the first one. > >> >> Running kvm_stat can help show what's going on. > >Thanks for the good insights. We'll come back with some analysis. Maybe you can come up with a patch ;) If you touch those areas anyway and run several benchmarks, writing a small piece of code is neglectable effort. > >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