From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751594AbZLMS3z (ORCPT ); Sun, 13 Dec 2009 13:29:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750900AbZLMS3y (ORCPT ); Sun, 13 Dec 2009 13:29:54 -0500 Received: from claw.goop.org ([74.207.240.146]:60598 "HELO claw.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1750832AbZLMS3x convert rfc822-to-8bit (ORCPT ); Sun, 13 Dec 2009 13:29:53 -0500 Message-ID: <4B2532A0.2070001@goop.org> Date: Sun, 13 Dec 2009 10:29:52 -0800 From: Jeremy Fitzhardinge User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.5) Gecko/20091203 Fedora/3.0-3.13.rc2.fc12 Thunderbird/3.0 MIME-Version: 1.0 To: =?UTF-8?B?T3phbiDDh2HEn2xheWFu?= CC: "linux-kernel@vger.kernel.org" Subject: Re: Poor KVM guest performance on an HP rack server References: <4B243B2B.806@pardus.org.tr> <4B24856A.4020507@goop.org> <4B24BE17.805@pardus.org.tr> In-Reply-To: <4B24BE17.805@pardus.org.tr> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/13/09 02:12, Ozan Çağlayan wrote: > Hmm, that's because we're using/developing a Linux distribution which > doesn't have 64-bit support yet. But since the guest will be a > compile-farm for our needs, it's worth trying to run an 64-bit distro on > the host to see the difference, thanks for the tip but how much should > this affect the performance? 32-bit PAE is marginal above 4G of memory and the limit is at about 8G. Above that, so much lowmem (<~1GB) is occupied by page and other kernel structures that there's barely any memory to do any real work. If this is what's happening, you'd expect to see poor host performance, and slow guest performance would be secondary to that. With 64-bit, all the memory can be directly addressed so none of this applies. I would expect to see significant performance gains. There's nothing to stop you from running 32-bit PAE guests, so you can do your distro development that way (at least in part). J