From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Moyer Subject: Re: [PATCH RESEND 5/5] vhost-blk: Add vhost-blk support Date: Wed, 18 Jul 2012 10:31:28 -0400 Message-ID: References: <1342169711-12386-1-git-send-email-asias@redhat.com> <1342169711-12386-6-git-send-email-asias@redhat.com> <50060FE8.4040607@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, "Michael S. Tsirkin" , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org To: Asias He Return-path: Received: from mx1.redhat.com ([209.132.183.28]:30140 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754601Ab2GROba (ORCPT ); Wed, 18 Jul 2012 10:31:30 -0400 In-Reply-To: <50060FE8.4040607@redhat.com> (Asias He's message of "Wed, 18 Jul 2012 09:22:48 +0800") Sender: kvm-owner@vger.kernel.org List-ID: 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. Cheers, Jeff