Re: [RFC 7/11] virtio_pci: new, capability-aware driver.

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Jan 12, 2012 at 08:02:06AM +1100, Benjamin Herrenschmidt wrote:
> On Wed, 2012-01-11 at 14:26 -0600, Anthony Liguori wrote:
> > 
> > I'd say that's a special case but I see what you're getting at here.
> > 
> > So what about keeping the config space read-only and using control
> > queues for 
> > everything else?
> 
> Which is exactly what Rusty and I are proposing :-)
> I would go further
> and eliminate the idea of a seqlock and instead of a status queue with
> precise messages indicating what changed.
>
> I would couple that with the new queue format allowing immediate data in
> the descriptor to avoid having to use indirect buffers for these, which
> means no allocation, no buffer pool etc... which makes everything a lot
> easier to deal with as well.

We just need a couple of buffers outstanding. It can't be easier,
and a single buf descriptors already do not use indirection.

> We could probably have a helper library for sending control messages
> which could handle waiting for a ring slot to be free (practically
> always the case on control queues), writing the message, sending it and
> waiting for a status queue confirmation message.
> 
> Cheers,
> Ben.
> 

Look, we have a race currently. Let us not tie a bug fix to a huge
rewrite with unclear performance benefits, please.

-- 
MST