From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH 0/5] Add vhost-blk support Date: Tue, 17 Jul 2012 15:02:45 +0200 Message-ID: <50056275.6000407@redhat.com> References: <1342107302-28116-1-git-send-email-asias@redhat.com> <50052276.2080906@redhat.com> <500527BA.9000001@redhat.com> <50052E7E.6020100@redhat.com> <20120717112645.GA9363@redhat.com> <20120717115450.GA9796@redhat.com> <20120717124859.GA9883@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: linux-aio@kvack.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Benjamin LaHaise , Alexander Viro , linux-fsdevel@vger.kernel.org To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20120717124859.GA9883@redhat.com> 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 List-Id: linux-fsdevel.vger.kernel.org Il 17/07/2012 14:48, Michael S. Tsirkin ha scritto: > On Tue, Jul 17, 2012 at 01:03:39PM +0100, Stefan Hajnoczi wrote: >> On Tue, Jul 17, 2012 at 12:54 PM, Michael S. Tsirkin wrote: >>>> Knowing the answer to that is important before anyone can say whether >>>> this approach is good or not. >>>> >>>> Stefan >>> >>> Why is it? >> >> Because there might be a fix to kvmtool which closes the gap. It >> would be embarassing if vhost-blk was pushed just because no one >> looked into what is actually going on. > > Embarrasing to whom? Is someone working on an optimization that > makes the work in question redundant, with posting just around > the corner? Then maybe the thing to do is just wait a bit. Of course there is work going on to make QEMU perform better. Not sure about lkvm. >> And on the flipside, hard evidence of an overhead that cannot be >> resolved could be good reason to do more vhost devices in the future. > > How can one have hard evidence of an overhead that cannot be resolved? Since we do have two completely independent userspaces (lkvm and data-plane QEMU), you can build up some compelling evidence of an overhead that cannot be resolved in user space. >> Either way, it's useful to do this before going further. > > I think each work should be discussed on its own merits. Maybe > vhost-blk is just well written. So? What is your conclusion? If it's just that vhost-blk is written well, my conclusion is that lkvm people should look into improving their virtio-blk userspace. We take hints from each other all the time, for example virtio-scsi will have unlocked kick in 3.6. Why can't vhost-* just get into staging, and we call it a day? Paolo