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Date: Wed, 29 Jun 2011 12:35:51 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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To: "Michael S. Tsirkin" <mst@redhat.com>
CC: Christoph Hellwig <hch@infradead.org>, Hannes Reinecke <hare@suse.de>,
        Linux Virtualization <virtualization@lists.linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        qemu-devel <qemu-devel@nongnu.org>,
        Rusty Russell <rusty@rustcorp.com.au>,
        Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>,
        Christoph Hellwig <chellwig@redhat.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>
Subject: Re: virtio scsi host draft specification, v3
References: <4DEE2B15.4090809@redhat.com> <4DF21447.6090005@suse.de> <20110612075140.GB11941@redhat.com> <4E0AE0FE.2090905@redhat.com> <20110629100341.GC22900@infradead.org> <4E0AF925.2050707@redhat.com> <20110629103139.GC16757@redhat.com>
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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