[virtio-comment] Question regarding packed ring Virtio 1.1 feature

[virtio-comment] Question regarding packed ring Virtio 1.1 feature

[Yuri Benditovich]

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Hi, 

From the spec it looks like the device must maintain backward compatibility with Virt 1.0 split queue implementation and use the packed one only when negotiated. 
What is the rational of such limitation, especially in case of true hardware device? 

Thanks, 
Yuri Benditovich 


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Re: [virtio-comment] Question regarding packed ring Virtio 1.1 feature

[Michael S. Tsirkin]

On Thu, Nov 21, 2019 at 08:40:29AM -0500, Yuri Benditovich wrote:
> Hi,
> 
> From the spec it looks like the device must maintain backward compatibility
> with Virt 1.0 split queue implementation and use the packed one only when
> negotiated.
> What is the rational of such limitation, especially in case of true hardware
> device?
> 
> Thanks,
> Yuri Benditovich


I don't think that's intentional. Any device without a split queue
implementation will fail negotiation if PACKED_RING has not been
negotiated. It's more of a SHOULD since split ring support
allows backwards compatibility with deployed software.

-- 
MST


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