From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Hajnoczi Subject: Re: vhost-blk development Date: Wed, 11 Apr 2012 11:19:48 +0100 Message-ID: References: <24144665.60022.1334078743662.JavaMail.root@zimbra.liquidweb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: kvm@vger.kernel.org To: Michael Baysek Return-path: Received: from mail-lpp01m010-f46.google.com ([209.85.215.46]:60374 "EHLO mail-lpp01m010-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755163Ab2DKKTu convert rfc822-to-8bit (ORCPT ); Wed, 11 Apr 2012 06:19:50 -0400 Received: by lahj13 with SMTP id j13so565951lah.19 for ; Wed, 11 Apr 2012 03:19:48 -0700 (PDT) In-Reply-To: <24144665.60022.1334078743662.JavaMail.root@zimbra.liquidweb.com> Sender: kvm-owner@vger.kernel.org List-ID: On Tue, Apr 10, 2012 at 6:25 PM, Michael Baysek = wrote: > Well, I'm trying to determine which I/O method currently has the very= least performance overhead and gives the best performance for both rea= ds and writes. > > I am doing my testing by putting the entire guest onto a ramdisk. =A0= I'm working on an i5-760 with 16GB RAM with VT-d enabled. =A0I am runni= ng the standard Centos 6 kernel with 0.12.1.2 release of qemu-kvm that = comes stock on Centos 6. =A0The guest is configured with 512 MB RAM, us= ing, 4 cpu cores with it's /dev/vda being the ramdisk on the host. Results collected for ramdisk usually do not reflect the performance you get with a real disk or SSD. I suggest using the host/guest configuration you want to deploy. > I've been using iozone 3.98 with -O -l32 -i0 -i1 -i2 -e -+n -r4K -s25= 0M to measure performance. I haven't looked up the options but I think you need -I to use O_DIRECT and bypass the guest page cache - otherwise you are not benchmarking I/O performance but overall file system/page cache performance. Stefan