netdev - Re: [PATCH v2 net-next 13/14] tcp: accecn: stop sending AccECN opt when loss ACK w/ option

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Message-ID: <b2a0cbdc-776a-42c8-8e19-051a12a1a7bc@redhat.com>
Date: Thu, 25 Sep 2025 17:46:30 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: "Chia-Yu Chang (Nokia)" <chia-yu.chang@...ia-bell-labs.com>,
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Subject: Re: [PATCH v2 net-next 13/14] tcp: accecn: stop sending AccECN opt
 when loss ACK w/ option

On 9/25/25 4:46 PM, Chia-Yu Chang (Nokia) wrote:
>From: Paolo Abeni <pabeni@...hat.com> Sent: Tuesday, September 23, 2025 12:52 PM
>> On 9/18/25 6:21 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).
>>
>> Is this really useful/triggers in practice?
>>
>> AFAICS it will take effect only it the retransmission happens just after an egress AccECN packet, i.e. will not trigger if the there are more later non AccECN packets pending.
> 
> Hi Paolo,
> 
> This is a simplied implementation than what is mentieond in the RFC9768: 
> "Such a host detect loss of ACKs carrying the AccECN Option by detecting whether the acknowledged data alwaysreappears as a retransmission. In such cases, the host disable the sending of the AccECN Option for this half-connection."
> 
> However, to implement the case that not that just after egressing the ACK with AccECN, I was thinking to modify struct tcp_sack_block but that maybe an over engineering.

I agree touching tcp_sack_block looks overkill. I think that the
simplified implementation is a bit too far from the RFC specification
and too simplistic to be effective. I suggest dropping this change.

Thanks,

Paolo