Re: [Qemu-devel] question on virtio

[Jamie Lokier]

Michael S. Tsirkin wrote:
> Hi!
> I see this in virtio_ring.c:
> 
>         /* Put entry in available array (but don't update avail->idx *
>          until they do sync). */
> 
> Why is it done this way?
> It seems that updating the index straight away would be simpler, while
> this might allow the host to specilatively look up the buffer and handle
> it, without waiting for the kick.

Even better, if the host updates a location containing which index it
has seen recently, you can avoid the kick entirely during sustained
flows - just like your recent patch to avoid sending irqs to the
guest.

-- Jamie