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

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

On Fri, Mar 03, 2023 at 10:49:37PM +0100, Halil Pasic wrote:
> On Fri, 3 Mar 2023 02:42:49 -0500
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > > >
> > > > 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).
> 
> I don't think it would require an ABI change. We could just change the
> queue names. AFAIK those are not part of the ABI. I don't think it would
> be hard.

Well at the moment this is the mapping:

RSS index -  queue name - virtio pci vqn

0		receiveq1	0
1		receiveq2	2
2		receiveq3	4
3		receiveq4	6




> BTW what speaks for "VQ number" over "VQ index"?
> 
> Regards,
> Halil

We use "vq index" when referring to queue_select.

But, we use "vq number" when talking about notifications.

For fun MMIO calls the queue size field QueueNum


So both number and index are taken by things other than the number,
changing the meaning can confuse existing users.  Ideally we'd use some
other new term to avoid confusion but I could not come up with one so
far.  I feel there's less of a chance of a confusion between VQ size and
its number. But it's not a strong prefrence, RSS is relatively young
and it's the only incompatible user of index so far.


-- 
MST