Re: [RFC PATCH net-next] veth: apply qdisc backpressure on full ptr_ring to reduce TX drops

["Toke Høiland-Jørgensen" <toke@redhat.com>]

David Ahern <dsahern@kernel.org> writes:

> On 4/7/25 3:15 AM, Toke Høiland-Jørgensen wrote:
>>> +static inline bool txq_has_qdisc(struct netdev_queue *txq)
>>> +{
>>> +	struct Qdisc *q;
>>> +
>>> +	q = rcu_dereference(txq->qdisc);
>>> +	if (q->enqueue)
>>> +		return true;
>>> +	else
>>> +		return false;
>>> +}
>> 
>> This seems like a pretty ugly layering violation, inspecting the qdisc
>> like this in the driver?
>
> vrf driver has something very similar - been there since March 2017.

Doesn't make it any less ugly, though ;)

And AFAICT, vrf is doing more with the information; basically picking a
whole different TX path? Can you elaborate on the reasoning for this (do
people actually install qdiscs on VRF devices in practice)?

-Toke