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Date: Wed, 29 Jun 2011 11:46:19 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] virtio scsi host draft specification, v3
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To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Christoph Hellwig <chellwig@redhat.com>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>, Rusty Russell <rusty@rustcorp.com.au>, qemu-devel <qemu-devel@nongnu.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Hannes Reinecke <hare@suse.de>, Linux Virtualization <virtualization@lists.linux-foundation.org>

On Wed, Jun 29, 2011 at 10:23:26AM +0200, Paolo Bonzini wrote:
> On 06/12/2011 09:51 AM, Michael S. Tsirkin wrote:
> >>>
> >>>  If a device uses more than one queue it is the responsibility of the
> >>>  device to ensure strict request ordering.
> >Maybe I misunderstand - how can this be the responsibility of
> >the device if the device does not get the information about
> >the original ordering of the requests?
> >
> >For example, if the driver is crazy enough to put
> >all write requests on one queue and all barriers
> >on another one, how is the device supposed to ensure
> >ordering?
> 
> I agree here, in fact I misread Hannes's comment as "if a driver
> uses more than one queue it is responsibility of the driver to
> ensure strict request ordering".  If you send requests to different
> queues, you know that those requests are independent.  I don't think
> anything else is feasible in the virtio framework.
> 
> Paolo

Like this then?

  If a driver uses more than one queue it is the responsibility of the
  driver to ensure strict request ordering: the device does not
  supply any guarantees about the ordering of requests between different
  virtqueues.