From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754709Ab2GROoC (ORCPT ); Wed, 18 Jul 2012 10:44:02 -0400 Received: from mx1.redhat.com ([209.132.183.28]:31653 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753179Ab2GROn7 (ORCPT ); Wed, 18 Jul 2012 10:43:59 -0400 Message-ID: <5006CC26.20203@redhat.com> Date: Wed, 18 Jul 2012 22:45:58 +0800 From: Asias He User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120615 Thunderbird/13.0.1 MIME-Version: 1.0 To: Jeff Moyer CC: linux-kernel@vger.kernel.org, "Michael S. Tsirkin" , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH RESEND 5/5] vhost-blk: Add vhost-blk support References: <1342169711-12386-1-git-send-email-asias@redhat.com> <1342169711-12386-6-git-send-email-asias@redhat.com> <50060FE8.4040607@redhat.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/18/2012 10:31 PM, Jeff Moyer wrote: > Asias He writes: > >> On 07/18/2012 03:10 AM, Jeff Moyer wrote: >>> Asias He writes: >>> >>>> vhost-blk is a in kernel virito-blk device accelerator. >>>> >>>> This patch is based on Liu Yuan's implementation with various >>>> improvements and bug fixes. Notably, this patch makes guest notify and >>>> host completion processing in parallel which gives about 60% performance >>>> improvement compared to Liu Yuan's implementation. >>> >>> So, first off, some basic questions. Is it correct to assume that you >>> tested this with buffered I/O (files opened *without* O_DIRECT)? >>> I'm pretty sure that if you used O_DIRECT, you'd run into problems (which >>> are solved by the patch set posted by Shaggy, based on Zach Brown's work >>> of many moons ago). Note that, with buffered I/O, the submission path >>> is NOT asynchronous. So, any speedups you've reported are extremely >>> suspect. ;-) >> >> I always used O_DIRECT to test this patchset. And I mostly used raw >> block device as guest image. Is this the reason why I did not hit the >> problem you mentioned. Btw, I do have run this patchset on image based >> file. I still do not see problems like IO hangs. > > Hmm, so do the iovec's passed in point to buffers in userspace? I > thought they were kernel buffers, which would have blown up in > get_user_pages_fast. Yes. The iovec's passed in point to userspace buffers. ;-) -- Asias