Re: [virtio-dev] RFC: Doorbell suppression, packed-ring mode and hardware offload

[Jason Wang <jasowang@redhat.com>]

On 2019/2/14 äå11:41, Michael S. Tsirkin wrote:
> > I think it's as simple as increase the avail idx by X? Since descriptor were
> > used in order, device can just read the next X-1 descriptors in this case.
> >
> > Thanks
> Right so a spec change would be needed, it's not transparent to guest.


With the change, IN_ORDER + split_ring becomes something like submission 
queue (descriptor ring) + completion queue (used ring). And used ring 
access could be eliminated sometime, e.g for net for TX, we don't care 
about used len.

What's more interesting is, this avail idx optimization is not required 
for out of order completion which means it could be used for e.g block 
or SCSI device.

Thanks