linux-kernel - Re: virtio scsi host draft specification, v3

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

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.


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