netdev - Re: [PATCH net] tcp: reduce tcp_comp_sack_slack

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Message-ID: <CANn89iLp_7voEq8SryQXUFhDDTPaRosryNtHersRD6RM49Kh0g@mail.gmail.com>
Date: Fri, 14 Nov 2025 06:08:58 -0800
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Neal Cardwell <ncardwell@...gle.com>, 
	Kuniyuki Iwashima <kuniyu@...gle.com>, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net] tcp: reduce tcp_comp_sack_slack_ns default value to
 10 usec

On Fri, Nov 14, 2025 at 5:51 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> net.ipv4.tcp_comp_sack_slack_ns current default value is too high.
>
> When a flow has many drops (1 % or more), and small RTT, adding 100 usec
> before sending SACK stalls the sender relying on getting SACK
> fast enough to keep the pipe busy.
>
> Decrease the default to 10 usec.
>
> This is orthogonal to Congestion Control heuristics to determine
> if drops are caused by congestion or not.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

This was meant for net-next, but applying this to net tree should be
fine as well.

No need for backports though.