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

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Message-ID: <4E0B0007.3050901@redhat.com>
Date:	Wed, 29 Jun 2011 12:35:51 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Christoph Hellwig <hch@...radead.org>,
	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 06/29/2011 12:31 PM, Michael S. Tsirkin wrote:
> On Wed, Jun 29, 2011 at 12:06:29PM +0200, Paolo Bonzini wrote:
>> 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.
>
> Then let's make it explicit in the spec?

What, forbid it or say ordering is not guaranteed?  The latter is 
already explicit with the wording suggested in the thread.

Paolo
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