From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CF9EEC76186 for ; Wed, 17 Jul 2019 10:35:52 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A79F4217F9 for ; Wed, 17 Jul 2019 10:35:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A79F4217F9 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:55766 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hnhHr-0001Vj-L6 for qemu-devel@archiver.kernel.org; Wed, 17 Jul 2019 06:35:51 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:55736) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hnhHc-00013i-OU for qemu-devel@nongnu.org; Wed, 17 Jul 2019 06:35:37 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hnhHb-0001Ky-Mf for qemu-devel@nongnu.org; Wed, 17 Jul 2019 06:35:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:35825) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hnhHb-0001KH-Ef for qemu-devel@nongnu.org; Wed, 17 Jul 2019 06:35:35 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2142E285AE; Wed, 17 Jul 2019 10:35:34 +0000 (UTC) Received: from redhat.com (ovpn-120-247.rdu2.redhat.com [10.10.120.247]) by smtp.corp.redhat.com (Postfix) with SMTP id E43015D71D; Wed, 17 Jul 2019 10:35:27 +0000 (UTC) Date: Wed, 17 Jul 2019 06:35:21 -0400 From: "Michael S. Tsirkin" To: Stefan Hajnoczi Message-ID: <20190717063514-mutt-send-email-mst@kernel.org> References: <20190624091304.666-1-stefanha@redhat.com> <20190717101453.GE7341@stefanha-x1.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190717101453.GE7341@stefanha-x1.localdomain> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Wed, 17 Jul 2019 10:35:34 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH] docs: clarify multiqueue vs multiple virtqueues X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , Sebastien Boeuf , qemu-devel@nongnu.org, Cathy Zhang Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Jul 17, 2019 at 11:14:53AM +0100, Stefan Hajnoczi wrote: > On Mon, Jun 24, 2019 at 10:13:04AM +0100, Stefan Hajnoczi wrote: > > The vhost-user specification does not explain when > > VHOST_USER_PROTOCOL_F_MQ must be implemented. This may lead > > implementors of vhost-user masters to believe that this protocol feature > > is required for any device that has multiple virtqueues. That would be > > a mistake since existing vhost-user slaves offer multiple virtqueues but > > do not advertise VHOST_USER_PROTOCOL_F_MQ. > > > > For example, a vhost-net device with one rx/tx queue pair is not > > multiqueue. The slave does not need to advertise > > VHOST_USER_PROTOCOL_F_MQ. Therefore the master must assume it has these > > virtqueues and cannot rely on askingt the slave how many virtqueues > > exist. > > > > Extend the specification to explain the different between true > > multiqueue and regular devices with a fixed virtqueue layout. > > > > Signed-off-by: Stefan Hajnoczi > > --- > > Based-on: <20190621094005.4134-1-stefanha@redhat.com> > > --- > > docs/interop/vhost-user.rst | 17 +++++++++++++++++ > > 1 file changed, 17 insertions(+) > > Ping? queued, thanks! > > > > diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst > > index 5750668aba..7827b710aa 100644 > > --- a/docs/interop/vhost-user.rst > > +++ b/docs/interop/vhost-user.rst > > @@ -324,6 +324,15 @@ must support changing some configuration aspects on the fly. > > Multiple queue support > > ---------------------- > > > > +Many devices have a fixed number of virtqueues. In this case the master > > +already knows the number of available virtqueues without communicating with the > > +slave. > > + > > +Some devices do not have a fixed number of virtqueues. Instead the maximum > > +number of virtqueues is chosen by the slave. The number can depend on host > > +resource availability or slave implementation details. Such devices are called > > +multiple queue devices. > > + > > Multiple queue support allows the slave to advertise the maximum number of > > queues. This is treated as a protocol extension, hence the slave has to > > implement protocol features first. The multiple queues feature is supported > > @@ -339,6 +348,14 @@ queue in the sent message to identify a specified queue. > > The master enables queues by sending message ``VHOST_USER_SET_VRING_ENABLE``. > > vhost-user-net has historically automatically enabled the first queue pair. > > > > +Slaves should always implement the ``VHOST_USER_PROTOCOL_F_MQ`` protocol > > +feature, even for devices with a fixed number of virtqueues, since it is simple > > +to implement and offers a degree of introspection. > > + > > +Masters must not rely on the ``VHOST_USER_PROTOCOL_F_MQ`` protocol feature for > > +devices with a fixed number of virtqueues. Only true multiqueue devices > > +require this protocol feature. > > + > > Migration > > --------- > > > > -- > > 2.21.0 > >