From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: KVM Test report, kernel 647e9e... qemu 7811d4... Date: Fri, 26 Mar 2010 12:54:13 +0300 Message-ID: <4BAC8445.4000205@redhat.com> References: <4BAA2D0E.1010606@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: "kvm@vger.kernel.org" To: "Hao, Xudong" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:24995 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752780Ab0CZJyR (ORCPT ); Fri, 26 Mar 2010 05:54:17 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 03/26/2010 11:39 AM, Hao, Xudong wrote: > > I checked cache=writeback parameter, the diotest performance is much worse than "no this parameter"(about 20 times). > > Followed qemu help, my command is "qemu-system-x86_64 -m 512 -smp 4 -net nic,macaddr=00:16:3e:79:0c:db,model=rtl8139 -net tap,script=/etc/kvm/qemu-ifup -hda /share/ltp_guest.img -drive cache=writeback", is it right? > > When booting guest with cache=writeback, there are some hdb drive Error printed in guest, and guest booting very slow. > > You need to fold the -hda parameter into -driver, so the whole command line becomes qemu-system-x86_64 -m 512 -smp 4 -net nic,macaddr=00:16:3e:79:0c:db,model=rtl8139 -net tap,script=/etc/kvm/qemu-ifup -drive file=/share/ltp_guest.img,cache=writeback -hda is deprecated, it forces cache=writethrough. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic.