netdev - Re: [PATCH v1 net-next 6/6] selftest: packetdrill: Add max RTO test for SYN+ACK.

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Message-ID: <CANn89iJ9ED4WwnmnWM5ehMb9J=tMYK0Fh15Q2B2y=E6K=KbM7A@mail.gmail.com>
Date: Fri, 7 Nov 2025 00:43:17 -0800
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...gle.com>
Cc: Neal Cardwell <ncardwell@...gle.com>, "David S . Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Yuchung Cheng <ycheng@...gle.com>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v1 net-next 6/6] selftest: packetdrill: Add max RTO test
 for SYN+ACK.

On Wed, Nov 5, 2025 at 4:34 PM Kuniyuki Iwashima <kuniyu@...gle.com> wrote:
>
> This script sets net.ipv4.tcp_rto_max_ms to 1000 and checks
> if SYN+ACK RTO is capped at 1s for TFO and non-TFO.
>
> Without the previous patch, the max RTO is applied to TFO
> SYN+ACK only, and non-TFO SYN+ACK RTO increases exponentially.
>
>   # selftests: net/packetdrill: tcp_rto_synack_rto_max.pkt
>   # TAP version 13
>   # 1..2
>   # tcp_rto_synack_rto_max.pkt:46: error handling packet: timing error:
>      expected outbound packet at 5.091936 sec but happened at 6.107826 sec; tolerance 0.127974 sec
>   # script packet:  5.091936 S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
>   # actual packet:  6.107826 S. 0:0(0) ack 1 win 65535 <mss 1460,nop,nop,sackOK>
>   # not ok 1 ipv4
>   # tcp_rto_synack_rto_max.pkt:46: error handling packet: timing error:
>      expected outbound packet at 5.075901 sec but happened at 6.091841 sec; tolerance 0.127976 sec
>   # script packet:  5.075901 S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK>
>   # actual packet:  6.091841 S. 0:0(0) ack 1 win 65535 <mss 1460,nop,nop,sackOK>
>   # not ok 2 ipv6
>   # # Totals: pass:0 fail:2 xfail:0 xpass:0 skip:0 error:0
>   not ok 49 selftests: net/packetdrill: tcp_rto_synack_rto_max.pkt # exit=1
>
> With the previous patch, all SYN+ACKs are retransmitted
> after 1s.
>
>   # selftests: net/packetdrill: tcp_rto_synack_rto_max.pkt
>   # TAP version 13
>   # 1..2
>   # ok 1 ipv4
>   # ok 2 ipv6
>   # # Totals: pass:2 fail:0 xfail:0 xpass:0 skip:0 error:0
>   ok 49 selftests: net/packetdrill: tcp_rto_synack_rto_max.pkt
>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>

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