From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: KVM performance Date: Tue, 30 Jan 2007 14:56:34 +0200 Message-ID: <45BF4082.3010803@qumranet.com> References: <1169857267.30807.44.camel@localhost.localdomain> <45BB0E85.9060303@qumranet.com> <1169902138.32208.25.camel@localhost.localdomain> <45BC6F98.908@qumranet.com> <1170161536.17669.10.camel@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, tim.c.chen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org To: Rusty Russell Return-path: In-Reply-To: <1170161536.17669.10.camel-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@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 Rusty Russell wrote: >> The clever guest kernel will set the accessed bit (and the dirty bit on >> writable ptes) to avoid an rmw cycle by the hardware pagetable walker. >> >> [two instrumented runs later] >> >> Both Linux and Windows seem to do this optimization. >> > > Right. This (trivial!) optimization wins lguest a good 10%: > > Before: > Time for one Copy-on-Write fault: 13622 nsec > Time to exec client once: 1085481 nsec > Time for one fork/exit/wait: 700796 nsec > After: > Time for one Copy-on-Write fault: 12036 nsec > Time to exec client once: 969899 nsec > Time for one fork/exit/wait: 664601 nsec > > Another optimization is that we can stop having two parallel implementations of the same code. I suggest we start thinking how to merge. -- 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