netdev - Re: [PATCH net v4 2/3] tcp_cubic: fix to match Reno additive increment

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Message-ID: <CANn89iKPnJzZA3NopjpVE_5wiJtxf6q2Run8G2S8Q4kvwPT-QA@mail.gmail.com>
Date: Mon, 19 Aug 2024 10:22:39 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Mingrui Zhang <mrzhang97@...il.com>
Cc: davem@...emloft.net, ncardwell@...gle.com, netdev@...r.kernel.org, 
	Lisong Xu <xu@....edu>
Subject: Re: [PATCH net v4 2/3] tcp_cubic: fix to match Reno additive increment

On Sat, Aug 17, 2024 at 6:35 PM Mingrui Zhang <mrzhang97@...il.com> wrote:
>
> The original code follows RFC 8312 (obsoleted CUBIC RFC).
>
> The patched code follows RFC 9438 (new CUBIC RFC):

Please give the precise location in the RFC (4.3 Reno-Friendly Region)

> "Once _W_est_ has grown to reach the _cwnd_ at the time of most
> recently setting _ssthresh_ -- that is, _W_est_ >= _cwnd_prior_ --
> the sender SHOULD set α__cubic_ to 1 to ensure that it can achieve
> the same congestion window increment rate as Reno, which uses AIMD
> (1,0.5)."
>
> Add new field 'cwnd_prior' in bictcp to hold cwnd before a loss event
>
> Fixes: 89b3d9aaf467 ("[TCP] cubic: precompute constants")

RFC 9438 is brand new, I think we should not backport this patch to
stable linux versions.

This would target net-next, unless there is clear evidence that it is
absolutely safe.

Note the existence of tools/testing/selftests/bpf/progs/bpf_cc_cubic.c
and tools/testing/selftests/bpf/progs/bpf_cubic.c

If this patch was a fix, I presume we would need to fix these files ?