Re: [PATCH net V3 1/2] veth: enable dev_watchdog for detecting stalled TXQs

[Jesper Dangaard Brouer]

On 08/11/2025 02.54, Jakub Kicinski wrote:
> On Fri, 7 Nov 2025 14:42:58 +0100 Jesper Dangaard Brouer wrote:
> > > I think this belongs in net-next.. Fail safe is not really a bug fix.
> > > I'm slightly worried we're missing a corner case and will cause
> > > timeouts to get printed for someone's config.
> >
> > This is a recovery fix.  If the race condition fix isn't 100% then this
> > patch will allow veth to recover.  Thus, to me it makes sense to group
> > these two patches together.
> >
> > I'm more worried that we we're missing a corner case that we cannot
> > recover from. Than triggering timeouts to get printed, for a config
> > where NAPI consumer veth_poll() takes more that 5 seconds to run (budget
> > max 64 packets this needs to consume packets at a rate less than 12.8
> > pps). It might be good to get some warnings if the system is operating
> > this slow.
> >
> > Also remember this is not the default config that most people use.
> > The code is only activated if attaching a qdisc to veth, which isn't
> > default. Plus, NAPI mode need to be activated, where in normal NAPI mode
> > the producer and consumer usually runs on the same CPU, which makes it
> > impossible to overflow the ptr_ring.  The veth backpressure is primarily
> > needed when running with threaded-NAPI, where it is natural that
> > producer and consumer runs on different CPUs. In our production setup
> > the consumer is always slower than the producer (as the product inside
> > the namespace have installed too many nftables rules).
>
> I understand all of this, but IMO the fix is in patch 2.
> This is a resiliency improvement, not a fix.

As maintainer you have the final say, so I send a [V4]. Notice that
doing it this way will cause a merge conflict once net and net-next gets
merged.

[V4] 
https://lore.kernel.org/all/176295319819.307447.6162285688886096284.stgit@firesoul/

--Jesper