tcp: try to avoid safer when ACKs are thinned

minuscat · Jul 16, 2024 · 11bba80 · 11bba80
1 parent 79efc31
commit 11bba80
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Showing 3 changed files with 21 additions and 1 deletion.
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
@@ -345,6 +345,7 @@ struct tcp_sock {
 		prev_ecnfield:2,/* ECN bits from the previous segment */
 		accecn_opt_demand:2,/* Demand AccECN option for n next ACKs */
 		estimate_ecnfield:2;/* ECN field for AccECN delivered estimates */
+	u16	pkts_acked_ewma;/* EWMA of packets acked for AccECN cep heuristic */
 	u64     accecn_opt_tstamp;      /* Last AccECN option sent timestamp */
 	u32	lost;		/* Total data packets lost incl. rexmits */
 	u32	app_limited;	/* limited until "delivered" reaches this val */

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
@@ -3057,6 +3057,7 @@ int tcp_disconnect(struct sock *sk, int flags)
 	tcp_accecn_init_counters(tp);
 	tp->prev_ecnfield = 0;
 	tp->accecn_opt_tstamp = 0;
+	tp->pkts_acked_ewma = 0;
 	if (icsk->icsk_ca_ops->release)
 		icsk->icsk_ca_ops->release(sk);
 	memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
@@ -685,6 +685,10 @@ static void tcp_count_delivered(struct tcp_sock *tp, u32 delivered,
 		tcp_count_delivered_ce(tp, delivered);
 }
 
+#define PKTS_ACKED_WEIGHT	6
+#define PKTS_ACKED_PREC		6
+#define ACK_COMP_THRESH		4
+
 /* Returns the ECN CE delta */
 static u32 __tcp_accecn_process(struct sock *sk, const struct sk_buff *skb,
 				u32 delivered_pkts, u32 delivered_bytes, int flag)
@@ -701,6 +705,19 @@ static u32 __tcp_accecn_process(struct sock *sk, const struct sk_buff *skb,
 
 	opt_deltas_valid = tcp_accecn_process_option(tp, skb, delivered_bytes, flag);
 
+	if (delivered_pkts) {
+		if (!tp->pkts_acked_ewma) {
+			tp->pkts_acked_ewma = delivered_pkts << PKTS_ACKED_PREC;
+		} else {
+			u32 ewma = tp->pkts_acked_ewma;
+
+			ewma = (((ewma << PKTS_ACKED_WEIGHT) - ewma) +
+				(delivered_pkts << PKTS_ACKED_PREC)) >>
+				PKTS_ACKED_WEIGHT;
+			tp->pkts_acked_ewma = min_t(u32, ewma, 0xFFFFU);
+		}
+	}
+
 	if (!(flag & FLAG_SLOWPATH)) {
 		/* AccECN counter might overflow on large ACKs */
 		if (delivered_pkts <= TCP_ACCECN_CEP_ACE_MASK)
@@ -752,7 +769,8 @@ static u32 __tcp_accecn_process(struct sock *sk, const struct sk_buff *skb,
 			return safe_delta;
 		if (d_ceb < safe_delta * tp->mss_cache >> TCP_ACCECN_SAFETY_SHIFT)
 			return delta;
-	}
+	} else if (tp->pkts_acked_ewma > (ACK_COMP_THRESH << PKTS_ACKED_PREC))
+		return delta;
 
 	return safe_delta;
 }