Re: [virtio-comment] Re: [PATCH 0/3] Rename queue index to queue number

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

On Thu, Mar 02, 2023 at 04:06:52PM +0100, Cornelia Huck wrote:
> On Wed, Mar 01 2023, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Wed, Mar 01, 2023 at 06:22:07PM +0100, Halil Pasic wrote:
> >> On Mon, 27 Feb 2023 09:45:31 +0100
> >> Cornelia Huck <cohuck@redhat.com> wrote:
> >> 
> >> > For the vq index/number, I'm not that sure that "virtqueue number" is
> >> > better that "virtqueue index" -- actually, I'd prefer the latter. We'd
> >> > need some renaming either way.
> >> 
> >> I prefer index as well. Especially that we start indexing with 0. Also
> >> seems to be the more common term for such stuff in both Mathematics and
> >> CS.
> >> 
> >> Regards,
> >> Halil 
> >
> >
> > Basically I am saying that this:
> >
> > /* Queue size for the currently selected queue - Write Only */
> > #define VIRTIO_MMIO_QUEUE_NUM           0x038
> >
> > is a bad name because queue number seems to be ambiguous.
> >
> > Maybe start with just getting rid of uses of QUEUE_NUM meaning size?
> 
> Nod, that seems to be uncontroversial.
> 
> >
> >
> > If we want to use queue index we need to fix RSS spec in networking
> > since that seems to want to use queue index in a very weird way:
> > networking has this idea of calling queues like this:
> > receiveq1 receiveq2 ....
> > why 1-based? I guess we wanted this to be clear even to a 5 year olds ;)
> >
> > And then for extra fun, in the RSS section we say "0 based index" where we
> > seem to mean "this number in the queue name, but subtract 1 in your head".
> > Why subtract 1? I guess we wanted these 5 year olds to practice math ...
> 
> Heh :)
> 
> Yeah, that looks like a mess... I don't think we should use a weird
> substraction scheme. I haven't looked at the RSS stuff much, would it be
> hard to fix it up?

We can't change the ABI, I guess we can say that it's bits 1 to 15
of the VQ number or equivalently VQ number divided
by 2 (it's always an even number for any receiveq).

-- 
MST