-----Original Message-----
From: Paolo Abeni <pabeni@redhat.com> 
Sent: Thursday, November 6, 2025 12:39 PM
To: Chia-Yu Chang (Nokia) <redacted>; edumazet@google.com; parav@nvidia.com; linux-doc@vger.kernel.org; corbet@lwn.net; horms@kernel.org; dsahern@kernel.org; kuniyu@google.com; bpf@vger.kernel.org; netdev@vger.kernel.org; dave.taht@gmail.com; jhs@mojatatu.com; kuba@kernel.org; stephen@networkplumber.org; xiyou.wangcong@gmail.com; jiri@resnulli.us; davem@davemloft.net; andrew+netdev@lunn.ch; donald.hunter@gmail.com; ast@fiberby.net; liuhangbin@gmail.com; shuah@kernel.org; linux-kselftest@vger.kernel.org; ij@kernel.org; ncardwell@google.com; Koen De Schepper (Nokia) <redacted>; g.white@cablelabs.com; ingemar.s.johansson@ericsson.com; mirja.kuehlewind@ericsson.com; cheshire <redacted>; rs.ietf@gmx.at; Jason_Livingood@comcast.com; Vidhi Goel <redacted>
Cc: Olivier Tilmans (Nokia) <redacted>
Subject: Re: [PATCH v5 net-next 05/14] tcp: L4S ECT(1) identifier and NEEDS_ACCECN for CC modules


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On 10/30/25 3:34 PM, chia-yu.chang@nokia-bell-labs.com wrote:

quoted

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 

7f5df7a71f62..d475f80b2248 100644

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c

@@ -328,12 +328,17 @@ static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
                       struct tcphdr *th, int tcp_header_len)  {
      struct tcp_sock *tp = tcp_sk(sk);
+     bool ecn_ect_1;

      if (!tcp_ecn_mode_any(tp))
              return;

+     ecn_ect_1 = tp->ecn_flags & TCP_ECN_ECT_1;
+     if (ecn_ect_1 && !tcp_accecn_ace_fail_recv(tp))
+             __INET_ECN_xmit(sk, true);

I'm possibly lost, but I can't find ecn_flags TCP_ECN_ECT_1 bit being
set here or elsewhere in this series.

Also why isn't this chunk under `if (tcp_ecn_mode_accecn(tp))` ?

/P

Hi Paolo,

This bit will be set by congestion control (TCP Prague, which will be submitted after AccECN patch series).

It is intended to use ECT-1 rather than ECT-0, and we were thinking this flag can be irrespective to AccECN negotiation.

Shall I put in the Prague patch series?

Chia-Yu