netdev - Re: [PATCH v12 net-next 12/15] tcp: accecn: AccECN option send control

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Message-ID: <b2c0653e-077f-4609-922e-777f1d868dd0@redhat.com>
Date: Mon, 14 Jul 2025 16:54:59 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: chia-yu.chang@...ia-bell-labs.com, edumazet@...gle.com,
 linux-doc@...r.kernel.org, corbet@....net, 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, 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
Subject: Re: [PATCH v12 net-next 12/15] tcp: accecn: AccECN option send
 control

On 7/4/25 10:53 AM, chia-yu.chang@...ia-bell-labs.com wrote:
> @@ -285,9 +297,33 @@ static inline void tcp_ecn_received_counters(struct sock *sk,
>  
>  		if (len > 0) {
>  			u8 minlen = tcp_ecnfield_to_accecn_optfield(ecnfield);
> +			u32 oldbytes = tp->received_ecn_bytes[ecnfield - 1];
> +
>  			tp->received_ecn_bytes[ecnfield - 1] += len;
>  			tp->accecn_minlen = max_t(u8, tp->accecn_minlen,
>  						  minlen);
> +
> +			/* Demand AccECN option at least every 2^22 bytes to
> +			 * avoid overflowing the ECN byte counters.
> +			 */
> +			if ((tp->received_ecn_bytes[ecnfield - 1] ^ oldbytes) &
> +			    ~((1 << 22) - 1)) {

I don't understand the above statement, I don't think it yield the
result expected according to the above comment.

> @@ -365,6 +401,7 @@ static inline void tcp_accecn_init_counters(struct tcp_sock *tp)
>  	__tcp_accecn_init_bytes_counters(tp->received_ecn_bytes);
>  	__tcp_accecn_init_bytes_counters(tp->delivered_ecn_bytes);
>  	tp->accecn_minlen = 0;
> +	tp->accecn_opt_demand = 0;
>  	tp->est_ecnfield = 0;
>  }
>  
> @@ -447,6 +484,7 @@ static inline void tcp_ecn_rcv_synack(struct sock *sk, const struct tcphdr *th,
>  	default:
>  		tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
>  		tp->syn_ect_rcv = ip_dsfield & INET_ECN_MASK;
> +		tp->accecn_opt_demand = 2;
>  		if (INET_ECN_is_ce(ip_dsfield) &&
>  		    tcp_accecn_validate_syn_feedback(sk, ace,
>  						     tp->syn_ect_snt)) {
> @@ -467,6 +505,7 @@ static inline void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th,
>  		} else {
>  			tp->syn_ect_rcv = TCP_SKB_CB(skb)->ip_dsfield &
>  					  INET_ECN_MASK;
> +			tp->prev_ecnfield = tp->syn_ect_rcv;
>  			tcp_ecn_mode_set(tp, TCP_ECN_MODE_ACCECN);
>  		}
>  	}
> @@ -565,4 +604,16 @@ tcp_ecn_make_synack(const struct request_sock *req, struct tcphdr *th)
>  		th->ece = 1;
>  }
>  
> +static inline bool tcp_accecn_option_beacon_check(const struct sock *sk)
> +{
> +	const struct tcp_sock *tp = tcp_sk(sk);
> +
> +	if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option_beacon))
> +		return false;
> +
> +	return tcp_stamp_us_delta(tp->tcp_mstamp, tp->accecn_opt_tstamp) *
> +	       READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option_beacon) >=
> +	       (tp->srtt_us >> 3);

To be consistent:

	u32 ecn_beacon =
READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_ecn_option_beacon);

	if (!ecn_beacon)
		return false;

	return tcp_stamp_us_delta(tp->tcp_mstamp, tp->accecn_opt_tstamp) *
ecn_beacon // ...

/P