netdev - Re: [RFC PATCH v8 18/20] selftests: Add a bpf fq qdisc to selftest

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Date: Fri, 24 May 2024 12:33:47 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Martin KaFai Lau <martin.lau@...ux.dev>
Cc: Amery Hung <ameryhung@...il.com>, Network Development <netdev@...r.kernel.org>, 
	bpf <bpf@...r.kernel.org>, yangpeihao@...u.edu.cn, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...nel.org>, Kui-Feng Lee <sinquersw@...il.com>, 
	Toke Høiland-Jørgensen <toke@...hat.com>, 
	Jamal Hadi Salim <jhs@...atatu.com>, Jiri Pirko <jiri@...nulli.us>, Stanislav Fomichev <sdf@...gle.com>, 
	Cong Wang <xiyou.wangcong@...il.com>, Peilin Ye <yepeilin.cs@...il.com>
Subject: Re: [RFC PATCH v8 18/20] selftests: Add a bpf fq qdisc to selftest

On Thu, May 23, 2024 at 11:25 PM Martin KaFai Lau <martin.lau@...ux.dev> wrote:
>
> > +
> > +unsigned long time_next_delayed_flow = ~0ULL;
> > +unsigned long unthrottle_latency_ns = 0ULL;
> > +unsigned long ktime_cache = 0;
> > +unsigned long dequeue_now;
> > +unsigned int fq_qlen = 0;
>
> I suspect some of these globals may be more natural if it is stored private to
> an individual Qdisc instance. i.e. qdisc_priv(). e.g. in the sch_mq setup.
>
> A high level idea is to allow the SEC(".struct_ops.link") to specify its own
> Qdisc_ops.priv_size.
>
> The bpf prog could use it as a simple u8 array memory area to write anything but
> the verifier can't learn a lot from it. It will be more useful if it can work
> like map_value(s) to the verifier such that the verifier can also see the
> bpf_rb_root/bpf_list_head/bpf_spin_lock...etc.

Qdisc_ops.priv_size is too qdsic specific.
imo using globals here is fine. bpf prog can use hash map or arena
to store per-netdev or per-qdisc data.
The less custom things the better.