From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: 64 bit guest much faster ? Date: Mon, 26 Oct 2009 12:12:13 +0200 Message-ID: <4AE575FD.6010801@redhat.com> References: <4AE1D1A4.6050001@pms.ifi.lmu.de> <4AE564C6.3040605@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: Stefan , kvm@vger.kernel.org To: Gerd Hoffmann Return-path: Received: from mx1.redhat.com ([209.132.183.28]:64903 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755480AbZJZKMM (ORCPT ); Mon, 26 Oct 2009 06:12:12 -0400 In-Reply-To: <4AE564C6.3040605@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 10/26/2009 10:58 AM, Gerd Hoffmann wrote: > On 10/23/09 17:54, Stefan wrote: >> >> Hello, >> >> I have a simple question (sorry I'm a kvm beginner): >> Is it right that a 64bit guest (8 CPUs, 16GB) is >> much faster than a 32bit guest (8 CPUs, 16GB PAE). > ^^^^ > Yes. With *that* much memory the 32bit guest struggles with address > space limitations (32bit -> 4G), whereas the 64bit guest doesn't. > > With up to 1G you shouldn't see a noticable difference. But the more > highmem the 32bit guest uses the higher is the penalty. Especially > without ept/npt as every kmap() of a high page is a roundtrip to the > hypervisor then. > Oh yes, without ept/npt the slowdown should indeed be significant with this much memory. -- error compiling committee.c: too many arguments to function