From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dor Laor Subject: Re: virtio disk slower than IDE? Date: Sun, 15 Nov 2009 15:15:57 +0200 Message-ID: <4AFFFF0D.3090608@redhat.com> References: <4AFEBD59.2090002@bobich.net> <4AFFCF18.1080509@redhat.com> <4AFFED49.9010305@bobich.net> Reply-To: dlaor@redhat.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Gordan Bobic Return-path: Received: from mx1.redhat.com ([209.132.183.28]:59324 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752836AbZKONQE (ORCPT ); Sun, 15 Nov 2009 08:16:04 -0500 In-Reply-To: <4AFFED49.9010305@bobich.net> Sender: kvm-owner@vger.kernel.org List-ID: On 11/15/2009 02:00 PM, Gordan Bobic wrote: > Dor Laor wrote: >> On 11/14/2009 04:23 PM, Gordan Bobic wrote: >>> I just tried paravirtualized virtio block devices, and my tests show >>> that they are approximately 30% slower than emulated IDE devices. I'm >>> guessing this isn't normal. Is this a known issue or am I likely to have >>> mosconfigured something? I'm using 64-bit RHEL/CentOS 5 (both host and >>> guest). >> >> Please try to change the io scheduler on the host to io scheduler, it >> should boost your performance back. > > I presume you mean the deadline io scheduler. I tried that (kernel > parameter elevator=deadline) and it made no measurable difference > compared to the cfq scheduler. What version of kvm do you use? Is it rhel5.4? Can you post the qemu cmdline and the perf test in the guest? Lastly, do you use cache=wb on qemu? it's just a fun mode, we use cache=off only. > > Gordan > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html