netdev - Re: [RFC Patch net-next] net_sched: introduce eBPF based Qdisc

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Date:   Fri, 03 Sep 2021 16:44:04 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     John Fastabend <john.fastabend@...il.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Cong Wang <cong.wang@...edance.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [RFC Patch net-next] net_sched: introduce eBPF based Qdisc

Martin KaFai Lau <kafai@...com> 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...

-Toke