netdev - Re: [PATCH v9 net-next 14/15] tcp: accecn: try to fit AccECN option with SACK

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Message-ID: <CANn89iJQJbggfu63j7cLH1Fr5jPwEh2yP05dZn5pQ=zpk3iXmA@mail.gmail.com>
Date: Wed, 25 Jun 2025 02:33:01 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: chia-yu.chang@...ia-bell-labs.com
Cc: pabeni@...hat.com, linux-doc@...r.kernel.org, corbet@....net, 
	horms@...nel.org, dsahern@...nel.org, kuniyu@...zon.com, bpf@...r.kernel.org, 
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	kuba@...nel.org, stephen@...workplumber.org, xiyou.wangcong@...il.com, 
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	mirja.kuehlewind@...csson.com, cheshire@...le.com, rs.ietf@....at, 
	Jason_Livingood@...cast.com, vidhi_goel@...le.com
Subject: Re: [PATCH v9 net-next 14/15] tcp: accecn: try to fit AccECN option
 with SACK

On Sat, Jun 21, 2025 at 12:38 PM <chia-yu.chang@...ia-bell-labs.com> wrote:
>
> From: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
>
> As SACK blocks tend to eat all option space when there are
> many holes, it is useful to compromise on sending many SACK
> blocks in every ACK and attempt to fit the AccECN option
> there by reducing the number of SACK blocks. However, it will
> never go below two SACK blocks because of the AccECN option.
>
> As the AccECN option is often not put to every ACK, the space
> hijack is usually only temporary. Depending on the length of
> AccECN option (can be either 11, 8, 5, or 2 bytes, cf. Table
> 5 in AccECN spec) and the NOPs used for alignment of other
> TCP options, up to two SACK blocks will be reduced.

I think it would be nice to study how AccECN and SACK compression play
together ?