From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1Lz7hL-0001vM-FR
	for qemu-devel@nongnu.org; Wed, 29 Apr 2009 07:11:31 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1Lz7hG-0001tn-Pj
	for qemu-devel@nongnu.org; Wed, 29 Apr 2009 07:11:31 -0400
Received: from [199.232.76.173] (port=36035 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1Lz7hG-0001th-JL
	for qemu-devel@nongnu.org; Wed, 29 Apr 2009 07:11:26 -0400
Received: from mx20.gnu.org ([199.232.41.8]:34954)
	by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32)
	(Exim 4.60) (envelope-from <paul@codesourcery.com>)
	id 1Lz7hG-0006Xg-9u
	for qemu-devel@nongnu.org; Wed, 29 Apr 2009 07:11:26 -0400
Received: from mail.codesourcery.com ([65.74.133.4])
	by mx20.gnu.org with esmtp (Exim 4.60)
	(envelope-from <paul@codesourcery.com>) id 1Lz7hD-0006Nn-2j
	for qemu-devel@nongnu.org; Wed, 29 Apr 2009 07:11:23 -0400
From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] Re: [PATCH] virtio-blk: add SGI_IO passthru support
Date: Wed, 29 Apr 2009 12:11:19 +0100
References: <20090427082606.GA32604@lst.de> <49F730AD.8090705@codemonkey.ws>
	<20090429104854.GA7846@lst.de>
In-Reply-To: <20090429104854.GA7846@lst.de>
MIME-Version: 1.0
Content-Type: text/plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
Message-Id: <200904291211.20374.paul@codesourcery.com>
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-devel@nongnu.org
Cc: kvm@vger.kernel.org, Rusty Russell <rusty@rustcorp.com.au>, Christian Borntraeger <borntraeger@de.ibm.com>, Hannes Reinecke <hare@suse.de>, Christoph Hellwig <hch@lst.de>

On Wednesday 29 April 2009, Christoph Hellwig wrote:
> On Tue, Apr 28, 2009 at 11:37:01AM -0500, Anthony Liguori wrote:
> > Ah, excellent.  I think that's a great thing to do.  So do you think
> > virtio-scsi would deprecate virtio-blk?
>
> I don't think so.  If you have an image format or a non-scsi blockdevice
> underneath virtio-block avoids the encoding into SCSI CDBs and back and
> should be faster.

Is this actually measurably faster, or just infinitesimally faster in theory?

I can maybe see that virtio-blk is slightly simpler for dumb drivers, though 
even then a basic scsi host is pretty straightforward and I find it hard to 
believe there's much real benefit.

Paul