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

From: Jakub Kicinski <[email-masked]>
Date: Sun, 10 May 2026 08:56:02 -0700

On Sat, 9 May 2026 11:09:51 +0200 Jesper Dangaard Brouer wrote:
> On 09/05/2026 04.06, Jakub Kicinski wrote:
> > On Thu, 7 May 2026 21:09:09 +0200 Jesper Dangaard Brouer wrote:  
> >> 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. 

To be clear - I said may it configurable with ethtool -G
not change the default.

> 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). 

Doesn't this mean you have a queue which is not under BQL control?

> 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.

Testing with prod-approximating traffic pattern and load would be great.