On 5/13/20 4:43 AM, Toke Høiland-Jørgensen wrote: > I don't like this. I makes the egress hook asymmetrical with the ingress > hook (ingress hook sees all traffic, egress only some of it). If the > performance hit of disabling GSO is the concern, maybe it's better to > wait until we figure out how to deal with that (presumably by > multi-buffer XDP)?
XDP is for accelerated networking. Disabling a h/w offload feature to use a s/w feature is just wrong. But it is more than just disabling GSO, and multi-buffer support for XDP is still not going to solve the problem. XDP is free form allowing any packet modifications - pushing and popping headers - and, for example, that blows up all of the skb markers for mac, network, transport and their inner versions. Walking the skb after an XDP program has run to reset the markers does not make sense. Combine this with the generic xdp overhead (e.g., handling skb clone and linearize), and the whole thing just does not make sense. We have to accept there a lot of use cases / code paths that simply can not be converted to work with both skbs and xdp_frames. The qdisc code is one example. This is another. Requiring a tc program for the skb path is an acceptable trade off.
