From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: virtio specification: OOO completion of the xmit buffers in the networking device Date: Wed, 4 Jun 2014 21:54:17 +0300 Message-ID: <20140604185417.GD11756@redhat.com> References: <538C7D2D.8080508@cloudius-systems.com> <871tv549gu.fsf@rustcorp.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Vlad Zolotarov , kvm@vger.kernel.org To: Rusty Russell Return-path: Received: from mx1.redhat.com ([209.132.183.28]:22411 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750742AbaFDSxx (ORCPT ); Wed, 4 Jun 2014 14:53:53 -0400 Content-Disposition: inline In-Reply-To: <871tv549gu.fsf@rustcorp.com.au> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, Jun 04, 2014 at 01:22:49PM +0930, Rusty Russell wrote: > Vlad Zolotarov writes: > > Rusty, hi! > > I'd like to ask for a small clarification about the virtio spec. > > The virtio specification is put the way that it allows the out-of-order > > completions in general. Although it states that it's mostly relevant to > > the virtio-blk it doesn't explicitly bans it for virtio networking > > devices (for generality?). > > Indeed. > > > (AFAICS the current virtio HV implementations make sure there is no OOO > > Tx buffers completions). > > > > I wonder if this feature (OOO Tx buffers completions) seems practical to > > u and if not can I hope that it could be clearly stated in the future > > virtio specification releases that it's forbidden? > > Are you sure that vhost-net doesn't allow async completion already? > I can't immediately see why it can't happen, but MST is CC'd. > > Cheers, > Rusty. vhost-net completes in order but this is just an implementation detail: this allows keeping a couple of indexes for head/tail instead of tracking requests individually. We can change this in the future and guest must allow out of order completions. -- MST