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Date: Wed, 29 Jun 2011 12:06:29 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] virtio scsi host draft specification, v3
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To: Christoph Hellwig <hch@infradead.org>
Cc: Christoph Hellwig <chellwig@redhat.com>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>, "Michael S. Tsirkin" <mst@redhat.com>, 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 06/29/2011 12:03 PM, Christoph Hellwig wrote:
> >  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.
>
> That doesn't really fit very well with the SAM model.  If we want
> to use multiple queues for a single LUN it has to be transparent to
> the SCSI command stream.  Then again I don't quite see the use for
> that anyway.

Agreed, I see a use for multiple queues (MSI-X), but not for multiple 
queues shared by a single LUN.

Paolo