On Fri, Sep 03, 2021 at 04:44:04PM +0200, Toke Høiland-Jørgensen wrote: > Martin KaFai Lau <kafai@xxxxxx> writes: > > > On Fri, Sep 03, 2021 at 12:27:52AM +0200, Toke Høiland-Jørgensen wrote: > >> >> The question is if it's useful to provide the full struct_ops for > >> >> qdiscs? Having it would allow a BPF program to implement that interface > >> >> towards userspace (things like statistics, classes etc), but the > >> >> question is if anyone is going to bother with that given the wealth of > >> >> BPF-specific introspection tools already available? > > Instead of bpftool can only introspect bpf qdisc and the existing tc > > can only introspect kernel qdisc, it will be nice to have bpf > > qdisc work as other qdisc and showing details together with others > > in tc. e.g. a bpf qdisc export its data/stats with its btf-id > > to tc and have tc print it out in a generic way? > > I'm not opposed to the idea, certainly. I just wonder if people who go > to the trouble of writing a custom qdisc in BPF will feel it's worth it > to do the extra work to make this available via a second API. We could > certainly encourage it, and some things are easy (drop and pkt counters, > etc), but other things (like class stats) will depend on the semantics > of the qdisc being implemented, so will require extra work from the BPF > qdisc developer... Right, different qdisc has different stats, I think it is currently stored in qdisc_priv()? When a qdisc is created, a separate priv is created together. Yes, the bpf qdisc prog can store its stats to a bpf map, but then when the same prog attached to different qdiscs, it has to create different stats maps? Also, instead of ->enqueue() itself is a bpf prog, having an ->enqueue() preparing a bpf ctx (zeroing, assigning...etc) and then make another call to a bpf prog will all add some costs. That said, I still think it needs a bpf skb map that can queue/dequeue skb first. Then it will become possible to prototype different interface ideas.
