From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:45881)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1S10j3-00083D-Ej
	for qemu-devel@nongnu.org; Fri, 24 Feb 2012 14:22:43 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1S10j1-00013Y-Mm
	for qemu-devel@nongnu.org; Fri, 24 Feb 2012 14:22:41 -0500
Received: from mail-pz0-f45.google.com ([209.85.210.45]:43899)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <anthony@codemonkey.ws>) id 1S10j1-00013M-Gh
	for qemu-devel@nongnu.org; Fri, 24 Feb 2012 14:22:39 -0500
Received: by dadp14 with SMTP id p14so3370337dad.4
	for <qemu-devel@nongnu.org>; Fri, 24 Feb 2012 11:22:38 -0800 (PST)
Message-ID: <4F47E37A.6000702@codemonkey.ws>
Date: Fri, 24 Feb 2012 13:22:34 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
References: <4F47DEB1.7080009@redhat.com>
In-Reply-To: <4F47DEB1.7080009@redhat.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] converting the block layer from coroutines to
	threads
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: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>, qemu-devel <qemu-devel@nongnu.org>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

On 02/24/2012 01:02 PM, Paolo Bonzini wrote:
> Hi all,
>
> a few weeks ago Stefan Hajnoczi pointed me to his work on virtio-blk
> performance.
>
> Stefan's work had two sides.  First, he captured very nice performance
> data of the block layer at
> http://www.linux-kvm.org/page/Virtio/Block/Latency; second, in order to
> measure peak performance, he basically implemented "vhost-blk" in
> userspace.

I don't think the improvements here have anything to do with the block layer.

We've done the same thing with virtio-net and saw impressive performance results 
as a consequence.  Conversely, we see a similar improvement by applying the same 
technique to vhost-net.

Virtio really wants each virtqueue to be processed in a separate thread.  On a 
multicore system, there's considerable improvement doing this.

I think that's where we ought to start.  We really just need the block layer to 
be re-entrant, we don't actually need qcow2 or anything else that uses 
coroutines to use full threads.

Or at least, as far as I know, we don't have any performance data to suggest 
that we do.

Regards,

Anthony Liguori