netdev - Re: [PATCH net-next] tcp: better handle TCP_TX

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Message-ID: <3b20bfde-1a99-4018-a8d9-bb7323b33285@redhat.com>
Date: Tue, 14 Oct 2025 10:22:51 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Eric Dumazet <edumazet@...gle.com>, "David S . Miller"
 <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>
Cc: Simon Horman <horms@...nel.org>, Neal Cardwell <ncardwell@...gle.com>,
 Willem de Bruijn <willemb@...gle.com>, Kuniyuki Iwashima
 <kuniyu@...gle.com>, netdev@...r.kernel.org, eric.dumazet@...il.com
Subject: Re: [PATCH net-next] tcp: better handle TCP_TX_DELAY on established
 flows

On 10/13/25 4:59 PM, Eric Dumazet wrote:
> Some applications uses TCP_TX_DELAY socket option after TCP flow
> is established.
> 
> Some metrics need to be updated, otherwise TCP might take time to
> adapt to the new (emulated) RTT.
> 
> This patch adjusts tp->srtt_us, tp->rtt_min, icsk_rto
> and sk->sk_pacing_rate.
> 
> This is best effort, and for instance icsk_rto is reset
> without taking backoff into account.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

The CI is consistently reporting pktdrill failures on top of this patch:

# selftests: net/packetdrill: tcp_user_timeout_user-timeout-probe.pkt
# TAP version 13
# 1..2
# tcp_user_timeout_user-timeout-probe.pkt:35: error in Python code
# Traceback (most recent call last):
#   File "/tmp/code_T7S7S4", line 202, in <module>
#     assert tcpi_probes == 6, tcpi_probes; \
# AssertionError: 0
# tcp_user_timeout_user-timeout-probe.pkt: error executing code:
'python3' returned non-zero status 1

To be accurate, the patches batch under tests also includes:

https://patchwork.kernel.org/project/netdevbpf/list/?series=1010780

but the latter looks even more unlikely to cause the reported issues?!?

Tentatively setting this patch to changes request, to for CI's sake.

/P