netdev - Re: [PATCH net-next 2/2] tcp: change data receiver flowlabel after one dup

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Date: Fri, 29 Sep 2023 02:54:44 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: David Morley <morleyd.kernel@...il.com>
Cc: David Miller <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org, 
	David Morley <morleyd@...gle.com>, Neal Cardwell <ncardwell@...gle.com>, 
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH net-next 2/2] tcp: change data receiver flowlabel after
 one dup

On Wed, Sep 27, 2023 at 8:28 PM David Morley <morleyd.kernel@...il.com> wrote:
>
> From: David Morley <morleyd@...gle.com>
>
> This commit changes the data receiver repath behavior to occur after
> receiving a single duplicate. This can help recover ACK connectivity
> quicker if a TLP was sent along a nonworking path.
>
> For instance, consider the case where we have an initially nonworking
> forward path and reverse path and subsequently switch to only working
> forward paths. Before this patch we would have the following behavior.
>
> +---------+--------+--------+----------+----------+----------+
> | Event   | For FL | Rev FL | FP Works | RP Works | Data Del |
> +---------+--------+--------+----------+----------+----------+
> | Initial | A      | 1      | N        | N        | 0        |
> +---------+--------+--------+----------+----------+----------+
> | TLP     | A      | 1      | N        | N        | 0        |
> +---------+--------+--------+----------+----------+----------+
> | RTO 1   | B      | 1      | Y        | N        | 1        |
> +---------+--------+--------+----------+----------+----------+
> | RTO 2   | C      | 1      | Y        | N        | 2        |
> +---------+--------+--------+----------+----------+----------+
> | RTO 3   | D      | 2      | Y        | Y        | 3        |
> +---------+--------+--------+----------+----------+----------+
>
> This patch gets rid of at least RTO 3, avoiding additional unnecessary
> repaths of a working forward path to a (potentially) nonworking one.
>
> In addition, this commit changes the behavior to avoid repathing upon
> rx of duplicate data if the local endpoint is in CA_Loss (in which
> case the RTOs will already be changing the outgoing flowlabel).
>
> Signed-off-by: David Morley <morleyd@...gle.com>
> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> Tested-by: David Morley <morleyd@...gle.com>

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