From mboxrd@z Thu Jan  1 00:00:00 1970
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [RFC 7/11] virtio_pci: new, capability-aware driver.
Date: Thu, 12 Jan 2012 09:16:25 +1100
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Pawel Moll <pawel.moll@arm.com>, virtualization <virtualization@lists.linux-foundation.org>, Christian Borntraeger <borntraeger@de.ibm.com>, Sasha Levin <levinsasha928@gmail.com>, Anthony Liguori <anthony@codemonkey.ws>
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On Thu, 2012-01-12 at 00:02 +0200, Michael S. Tsirkin wrote:
> > 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.

Well, if we change endian, change the way config works, I think we are
doing enough dramatic changes to go all the way and change the ring
format too.

I don't think there's anything "unclear" about improving the rings in
the direction that all network cards have been chosing so far :-) But
for the control ring, performance is clearly not an issue.

I also like the simplicity of immediate data, it limits the failure
path, no allocation -does- make it easier, not having to wait for the
previous buffer to be complete if you pre-allocate etc...

In any case, if we do a lot of changes at the same time, we are probably
better off cutting the cord and making an incompatible vfio v2 with a
new set of drivers.

Having to deal with all the variants in a single driver will result in
unmaintainable drivers imho.

Cheers,
Ben.