Re: [PATCH net-next v5 3/5] veth: implement Byte Queue Limits (BQL) for latency reduction

[Jesper Dangaard Brouer]

On 09/05/2026 04.06, Jakub Kicinski wrote:
> On Thu, 7 May 2026 21:09:09 +0200 Jesper Dangaard Brouer wrote:
> > > > > I still think first that adding an option to modify the hard-coded
> > > > > VETH_RING_SIZE is the way to go.
> >
> > Not against being able to modify VETH_RING_SIZE, but I don't think it is
> > the solution here.
>
> Was it evaluated, tho?
>
> It's obviously super easy these days have AI spew no end of complex
> code. So it'd be great to have some solid, ideally production-like
> data to back this all up.
>
> VETH_RING_SIZE seems trivial, ethtool set ringparam

No, unfortunately we cannot just decrease the VETH_RING_SIZE.  The
reason is that XDP-redirect into veth don't have any back-pressure and
would simply drop packets if queue size becomes less than the NAPI
budget (64). (Yes, we use both normal path and XDP-redirect in
production).  My benchmarking shows that an optimal BQL limit is
dynamically adjusted between 17-55 depending on veth consumer namespace
overhead/speed, when balancing throughput and latency.

--Jesper