From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: sync guest calls made async on host - SQLite performance Date: Thu, 24 Sep 2009 14:44:45 +0300 Message-ID: <4ABB5BAD.3000007@redhat.com> References: <4ABA45BE.1080008@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org To: Matthew Tippett Return-path: Received: from mx1.redhat.com ([209.132.183.28]:59600 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751457AbZIXLoq (ORCPT ); Thu, 24 Sep 2009 07:44:46 -0400 In-Reply-To: <4ABA45BE.1080008@gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: On 09/23/2009 06:58 PM, Matthew Tippett wrote: > Hi, > > I would like to call attention to the SQLite performance under KVM in > the current Ubuntu Alpha. > > http://www.phoronix.com/scan.php?page=article&item=linux_2631_kvm&num=3 > > SQLite's benchmark as part of the Phoronix Test Suite is typically IO > limited and is affected by both disk and filesystem performance. > > When comparing SQLite under the host against the guest OS, there is > an order of magnitude _IMPROVEMENT_ in the measured performance of > the guest. > > I am expecting that the host is doing synchronous IO operations but > somewhere in the stack the calls are ultimately being made > asynchronous or at the very least batched for writing. > > On the surface, this represents a data integrity issue and I am > interested in the KVM communities thoughts on this behaviour. Is it > expected? Is it acceptable? Is it safe? qemu defaults to write-through caching, so there is no data integrity concern. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic.