Linux Virtualization - Apr 2023 - [PATCH net] virtio-net: reject small vring sizes

> > So, what do you think, we should fix virtio-net to work with smaller
rings? we should fail probe?
> >
> > I think that since this never came up until now, there is no big
demand to such small rings.
> 
> The worry is that once we start failing probe there's just a tiny
chance
> hosts begin to rely on us failing probe then we won't be able to fix
it.
> So it depends on the size of the patch I think. So far it seems small
enough
> that wasting code on failing probe isn't worth it.
> 
I see your point.
Regardless, we'll need to fail probe in some cases.
ring size of 1 for example (if I'm not mistaken)
control vq even needs a bigger ring.

Maybe we can fix virtnet to allow smaller rings + fail probe in some cases, all
in the same patch/patchset.

On Mon, Apr 17, 2023 at 10:04:56AM +0000, Alvaro Karsz
wrote:
> > > So, what do you think, we should fix virtio-net to work with
smaller rings? we should fail probe?
> > >
> > > I think that since this never came up until now, there is no big
demand to such small rings.
> > 
> > The worry is that once we start failing probe there's just a tiny
chance
> > hosts begin to rely on us failing probe then we won't be able to
fix it.
> > So it depends on the size of the patch I think. So far it seems small
enough
> > that wasting code on failing probe isn't worth it.
> > 
> 
> I see your point.
> Regardless, we'll need to fail probe in some cases.
> ring size of 1 for example (if I'm not mistaken)
Hmm. We can make it work if we increase hard header size, then
there will always be room for vnet header.
> control vq even needs a bigger ring.
Why does it?
> Maybe we can fix virtnet to allow smaller rings + fail probe in some cases,
all in the same patch/patchset.
If we can't make it work then yes.

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MST