netdev - [PATCH v6 net-next 13/15] tcp: accecn: AccECN ACE field multi-wrap heuristic

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Message-Id: <20250509211820.36880-14-chia-yu.chang@nokia-bell-labs.com>
Date: Fri,  9 May 2025 23:18:18 +0200
From: chia-yu.chang@...ia-bell-labs.com
To: horms@...nel.org,
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Cc: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
Subject: [PATCH v6 net-next 13/15] tcp: accecn: AccECN ACE field multi-wrap heuristic

From: Ilpo Järvinen <ij@...nel.org>

Armed with ceb delta from option, delivered bytes, and
delivered packets it is possible to estimate how many times
ACE field wrapped.

This calculation is necessary only if more than one wrap
is possible. Without SACK, delivered bytes and packets are
not always trustworthy in which case TCP falls back to the
simpler no-or-all wraps ceb algorithm.

Signed-off-by: Ilpo Järvinen <ij@...nel.org>
Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
---
 net/ipv4/tcp_input.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index f206c1a93a56..deced87f31f8 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -748,6 +748,24 @@ static u32 __tcp_accecn_process(struct sock *sk, const struct sk_buff *skb,
 		d_ceb = tp->delivered_ecn_bytes[INET_ECN_CE - 1] - old_ceb;
 		if (!d_ceb)
 			return delta;
+
+		if ((delivered_pkts >= (TCP_ACCECN_CEP_ACE_MASK + 1) * 2) &&
+		    (tcp_is_sack(tp) ||
+		     ((1 << inet_csk(sk)->icsk_ca_state) &
+		      (TCPF_CA_Open | TCPF_CA_CWR)))) {
+			u32 est_d_cep;
+
+			if (delivered_bytes <= d_ceb)
+				return safe_delta;
+
+			est_d_cep = DIV_ROUND_UP_ULL((u64)d_ceb *
+						     delivered_pkts,
+						     delivered_bytes);
+			return min(safe_delta,
+				   delta +
+				   (est_d_cep & ~TCP_ACCECN_CEP_ACE_MASK));
+		}
+
 		if (d_ceb > delta * tp->mss_cache)
 			return safe_delta;
 		if (d_ceb <
-- 
2.34.1