From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gerd Hoffmann Subject: Re: 64 bit guest much faster ? Date: Mon, 26 Oct 2009 09:58:46 +0100 Message-ID: <4AE564C6.3040605@redhat.com> References: <4AE1D1A4.6050001@pms.ifi.lmu.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Stefan Return-path: Received: from mx1.redhat.com ([209.132.183.28]:40910 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755353AbZJZI6r (ORCPT ); Mon, 26 Oct 2009 04:58:47 -0400 In-Reply-To: <4AE1D1A4.6050001@pms.ifi.lmu.de> Sender: kvm-owner@vger.kernel.org List-ID: 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. cheers, Gerd