netdev - Re: [PATCH v13 net-next 12/15] tcp: accecn: detect loss ACK w/ AccECN option and add TCP_ACCECN_OPTION

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Message-ID: <CANn89i+8vG=DiXrd9tbv2PCH_ALpDYUKsj5jm4Jk+G7Qp+2EPQ@mail.gmail.com>
Date: Sun, 1 Feb 2026 11:24:46 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: chia-yu.chang@...ia-bell-labs.com
Cc: pabeni@...hat.com, parav@...dia.com, linux-doc@...r.kernel.org, 
	corbet@....net, horms@...nel.org, dsahern@...nel.org, kuniyu@...gle.com, 
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Subject: Re: [PATCH v13 net-next 12/15] tcp: accecn: detect loss ACK w/ AccECN
 option and add TCP_ACCECN_OPTION_PERSIST

On Sat, Jan 31, 2026 at 11:26 PM <chia-yu.chang@...ia-bell-labs.com> wrote:
>
> From: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
>
> Detect spurious retransmission of a previously sent ACK carrying the
> AccECN option after the second retransmission. Since this might be caused
> by the middlebox dropping ACK with options it does not recognize, disable
> the sending of the AccECN option in all subsequent ACKs. This patch
> follows Section 3.2.3.2.2 of AccECN spec (RFC9768), and a new field
> (accecn_opt_sent_w_dsack) is added to indicate that an AccECN option was
> sent with duplicate SACK info.
>
> Also, a new AccECN option sending mode is added to tcp_ecn_option sysctl:
> (TCP_ECN_OPTION_PERSIST), which ignores the AccECN fallback policy and
> persistently sends AccECN option once it fits into TCP option space.
>
> Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
> Acked-by: Paolo Abeni <pabeni@...hat.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>