netdev - Re: [PATCH bpf-next 0/7] bpf: Propagate cn to TCP

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Date:   Tue, 26 Mar 2019 08:43:11 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     brakmo <brakmo@...com>, netdev <netdev@...r.kernel.org>,
        Martin Lau <kafai@...com>, Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next 0/7] bpf: Propagate cn to TCP

On 03/26/2019 08:07 AM, Alexei Starovoitov wrote:

> so after 20+ years linux qdisc design is wrong?

Yes it is how it is, return values can not be propagated back to the TCP stack in all cases.

When a packet is queued to Qdisc 1, there is no way we can return
a value that can represent what the packet becomes when dequeued later and queued into Qdisc 2.

Also some qdisc take their drop decision later (eg : codel and fq_codel), so ->enqueue() will
return a success which might be a lie.

> bpf is about choice. We have to give people tools to experiment even
> when we philosophically disagree on the design.

Maybe, but I feel that for the moment, the choice is only for FB, and rest
of the world has to re-invent private ebpf code in order to benefit from all of this.

I doubt many TCP users will have the skills/money to benefit from this.

Meanwhile, we as a community have to maintain a TCP/IP stack with added hooks and complexity.

It seems TCP stack became a playground for experiments.