From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:59320)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1V2DxG-0007y1-7Y
	for qemu-devel@nongnu.org; Thu, 25 Jul 2013 01:19:13 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1V2DxD-00008P-NV
	for qemu-devel@nongnu.org; Thu, 25 Jul 2013 01:19:10 -0400
Received: from mx1.redhat.com ([209.132.183.28]:57106)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <mst@redhat.com>) id 1V2DxD-000084-GS
	for qemu-devel@nongnu.org; Thu, 25 Jul 2013 01:19:07 -0400
Date: Thu, 25 Jul 2013 08:20:26 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20130725052026.GA21106@redhat.com>
References: <87li4v8ktz.fsf@rustcorp.com.au>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <87li4v8ktz.fsf@rustcorp.com.au>
Subject: Re: [Qemu-devel] vhost acceleration broken?
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>

On Thu, Jul 25, 2013 at 11:25:20AM +0930, Rusty Russell wrote:
> Hi all,
> 
>         Using latest kernel and master qemu, the following doesn't use
> vhost acceleration:
> 
> sudo qemu-system-x86_64 -machine pc,accel=kvm $ARGS -m 1024 -net tap,script=/home/rusty/bin/kvm-ifup,downscript=no,vhost=on -net nic,model=virtio -drive file=$QEMUIMAGE,index=0,media=disk,if=virtio -kernel arch/x86/boot/bzImage -append "root=/dev/vda1 $KARGS $*"
> 
> Culprit is here:
> 
> hw/net/virtio-net.c:virtio_net_vhost_status():
>     if (nc->peer->info->type != NET_CLIENT_OPTIONS_KIND_TAP) {
>         return;
>     }
> 
> info->type is NET_CLIENT_OPTIONS_KIND_HUBPORT.
> 
> At a glance, it seems like vlan is always enabled, and that means a hub,
> so that change silently disabled vhost acceleration.
> 
> It's quite possible that I've screwed up qemu's impenetrable command
> line (-net or -netdev, who knows what's better?).
> 
> Frustrated,
> Rusty.

That's just it.
Replace -net with -netdev, and things will work.