netdev - Re: [PATCH v6 net-next 04/15] tcp: AccECN core

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Message-ID: <39e06f51-621a-4d17-a4dd-17287e260e18@redhat.com>
Date: Tue, 13 May 2025 15:55:14 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: chia-yu.chang@...ia-bell-labs.com, horms@...nel.org, dsahern@...nel.org,
 kuniyu@...zon.com, bpf@...r.kernel.org, netdev@...r.kernel.org,
 dave.taht@...il.com, jhs@...atatu.com, kuba@...nel.org,
 stephen@...workplumber.org, xiyou.wangcong@...il.com, jiri@...nulli.us,
 davem@...emloft.net, edumazet@...gle.com, andrew+netdev@...n.ch,
 donald.hunter@...il.com, ast@...erby.net, liuhangbin@...il.com,
 shuah@...nel.org, linux-kselftest@...r.kernel.org, ij@...nel.org,
 ncardwell@...gle.com, koen.de_schepper@...ia-bell-labs.com,
 g.white@...lelabs.com, ingemar.s.johansson@...csson.com,
 mirja.kuehlewind@...csson.com, cheshire@...le.com, rs.ietf@....at,
 Jason_Livingood@...cast.com, vidhi_goel@...le.com
Cc: Olivier Tilmans <olivier.tilmans@...ia.com>
Subject: Re: [PATCH v6 net-next 04/15] tcp: AccECN core

On 5/9/25 11:18 PM, chia-yu.chang@...ia-bell-labs.com wrote:
> @@ -5098,7 +5100,8 @@ static void __init tcp_struct_check(void)
>  	/* 32bit arches with 8byte alignment on u64 fields might need padding
>  	 * before tcp_clock_cache.
>  	 */
> -	CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_txrx, 92 + 4);
> +	CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_txrx, 96 + 4);

This looks inconsistent with the pahole output in the commit message
(the groups looks 95 bytes wide, comprising the holes)

[...]
> @@ -382,11 +393,17 @@ static void tcp_ecn_send(struct sock *sk, struct sk_buff *skb,
>  {
>  	struct tcp_sock *tp = tcp_sk(sk);
>  
> -	if (tcp_ecn_mode_rfc3168(tp)) {
> +	if (!tcp_ecn_mode_any(tp))
> +		return;
> +
> +	INET_ECN_xmit(sk);
> +	if (tcp_ecn_mode_accecn(tp)) {
> +		tcp_accecn_set_ace(th, tp);
> +		skb_shinfo(skb)->gso_type |= SKB_GSO_TCP_ACCECN;
> +	} else {
>  		/* Not-retransmitted data segment: set ECT and inject CWR. */
>  		if (skb->len != tcp_header_len &&
>  		    !before(TCP_SKB_CB(skb)->seq, tp->snd_nxt)) {
> -			INET_ECN_xmit(sk);

The above chunk apparently changes the current behaviour for
!tcp_ecn_mode_accecn(), unconditionally setting ECN, while before ECN
was set only for non retrans segments.

/P