From mboxrd@z Thu Jan 1 00:00:00 1970 From: Asias He Subject: Re: [PATCH RESEND 5/5] vhost-blk: Add vhost-blk support Date: Wed, 18 Jul 2012 22:45:58 +0800 Message-ID: <5006CC26.20203@redhat.com> 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"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Jeff Moyer Cc: virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, "Michael S. Tsirkin" List-Id: virtualization@lists.linuxfoundation.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