Re: [PATCH/RFC] [v2] TCP: use non-delayed ACK for congestion control RTT

[Gavin McCullagh <Gavin.McCullagh@nuim.ie>]

The last attempt didn't take account of the situation where a timestamp
wasn't available and tcp_clean_rtx_queue() has to feed both the RTO and the
congestion avoidance.  This updated patch stores both RTTs, making the
delayed one available for the RTO and the other (ca_seq_rtt) available for
congestion control.


Signed-off-by: Gavin McCullagh <gavin.mccullagh@nuim.ie> 


diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 889c893..6fb7989 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2651,6 +2651,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, s32 *seq_rtt_p,
 	u32 cnt = 0;
 	u32 reord = tp->packets_out;
 	s32 seq_rtt = -1;
+	s32 ca_seq_rtt = -1;
 	ktime_t last_ackt = net_invalid_timestamp();
 
 	while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {
@@ -2686,13 +2687,15 @@ static int tcp_clean_rtx_queue(struct sock *sk, s32 *seq_rtt_p,
 				if (sacked & TCPCB_SACKED_RETRANS)
 					tp->retrans_out -= packets_acked;
 				flag |= FLAG_RETRANS_DATA_ACKED;
+				ca_seq_rtt = -1;
 				seq_rtt = -1;
 				if ((flag & FLAG_DATA_ACKED) ||
 				    (packets_acked > 1))
 					flag |= FLAG_NONHEAD_RETRANS_ACKED;
 			} else {
+				ca_seq_rtt = now - scb->when;
 				if (seq_rtt < 0) {
-					seq_rtt = now - scb->when;
+					seq_rtt = ca_seq_rtt;
 					if (fully_acked)
 						last_ackt = skb->tstamp;
 				}
@@ -2709,8 +2712,9 @@ static int tcp_clean_rtx_queue(struct sock *sk, s32 *seq_rtt_p,
 			    !before(end_seq, tp->snd_up))
 				tp->urg_mode = 0;
 		} else {
+			ca_seq_rtt = now - scb->when;
 			if (seq_rtt < 0) {
-				seq_rtt = now - scb->when;
+				seq_rtt = ca_seq_rtt;
 				if (fully_acked)
 					last_ackt = skb->tstamp;
 			}
@@ -2772,8 +2776,8 @@ static int tcp_clean_rtx_queue(struct sock *sk, s32 *seq_rtt_p,
 						 net_invalid_timestamp()))
 					rtt_us = ktime_us_delta(ktime_get_real(),
 								last_ackt);
-				else if (seq_rtt > 0)
-					rtt_us = jiffies_to_usecs(seq_rtt);
+				else if (ca_seq_rtt > 0)
+					rtt_us = jiffies_to_usecs(ca_seq_rtt);
 			}
 
 			ca_ops->pkts_acked(sk, pkts_acked, rtt_us);