[Qemu-devel] Re: [PATCHv2-RFC 0/2] virtio: put last seen used index into ring itself

[Avi Kivity <avi@redhat.com>]

On 05/26/2010 10:50 PM, Michael S. Tsirkin wrote:
> Here's a rewrite of the original patch with a new layout.
> I haven't tested it yet so no idea how this performs, but
> I think this addresses the cache bounce issue raised by Avi.
> Posting for early flames/comments.
>
> Generally, the Host end of the virtio ring doesn't need to see where
> Guest is up to in consuming the ring.  However, to completely understand
> what's going on from the outside, this information must be exposed.
> For example, host can reduce the number of interrupts by detecting
> that the guest is currently handling previous buffers.
>
> We add a feature bit so the guest can tell the host that it's writing
> out the current value there, if it wants to use that.
>
> This differs from original approach in that the used index
> is put after avail index (they are typically written out together).
> To avoid cache bounces on descriptor access,
> and make future extensions easier, we put the ring itself at start of
> page, and move the control after it.
>    

I missed the spec patch, can you repost it?

-- 
error compiling committee.c: too many arguments to function