From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: Floating point vs Integer performance Date: Tue, 13 Mar 2007 10:03:20 +0200 Message-ID: <45F65AC8.2000605@qumranet.com> References: <1173730724.7220.5.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Benjamin Prosnitz Return-path: In-reply-to: <1173730724.7220.5.camel@localhost> 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 Benjamin Prosnitz wrote: > I ran some benchmarks inside of KVM-12 on my system and outside of KVM > (no virtualization on my system). I found that floating point > performance when running both with and without KVM was approximately the > same, but integer performance in KVM was about 25% of what I get when > running the test outside of KVM. These were tests using Dhrystone 2 and > Double Precision Whetstone on a Core 2 Duo T7200 processor. > > Any thoughts on why the integer and floating point performance appears > to differ so much? > > Perhaps the integer benchmarks thrash the mmu cache. Try raising KVM_NUM_MMU_PAGES to 1024. 4MB per VM lowmem is a lot, but if it helps many workloads, it's worth it. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. ------------------------------------------------------------------------- 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