Index: sys/netinet/cc/cc.h
===================================================================
--- sys/netinet/cc/cc.h
+++ sys/netinet/cc/cc.h
@@ -81,6 +81,7 @@
 	int		bytes_this_ack; /* # bytes acked by the current ACK. */
 	tcp_seq		curack; /* Most recent ACK. */
 	uint32_t	flags; /* Flags for cc_var (see below) */
+	int32_t		sample_rtt_us;	/* RTT as measured by this ack in us */
 	int		type; /* Indicates which ptr is valid in ccvc. */
 	union ccv_container {
 		struct tcpcb		*tcp;
Index: sys/netinet/tcp_input.c
===================================================================
--- sys/netinet/tcp_input.c
+++ sys/netinet/tcp_input.c
@@ -304,9 +304,10 @@
  * CC wrapper hook functions
  */
 void
-cc_ack_received(struct tcpcb *tp, struct tcphdr *th, uint16_t nsegs,
-    uint16_t type)
+cc_ack_received(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to,
+    uint16_t nsegs, uint16_t type)
 {
+	int ts;
 	INP_WLOCK_ASSERT(tp->t_inpcb);
 
 	tp->ccv->nsegs = nsegs;
@@ -333,6 +334,12 @@
 	if (CC_ALGO(tp)->ack_received != NULL) {
 		/* XXXLAS: Find a way to live without this */
 		tp->ccv->curack = th->th_ack;
+		ts = tcp_ts_getticks();
+		if (to->to_tsecr && TSTMP_LT(to->to_tsecr, ts))
+			tp->ccv->sample_rtt_us =
+			    (ts - to->to_tsecr)*(1000000/*USEC_PER_SEC*//hz);
+		else
+			tp->ccv->sample_rtt_us = -1;
 		CC_ALGO(tp)->ack_received(tp->ccv, type);
 	}
 }
@@ -642,6 +649,7 @@
 	m = *mp;
 	*mp = NULL;
 	to.to_flags = 0;
+	to.to_tsecr = 0;
 	TCPSTAT_INC(tcps_rcvtotal);
 
 #ifdef INET6
@@ -1781,7 +1789,7 @@
 				 * typically means increasing the congestion
 				 * window.
 				 */
-				cc_ack_received(tp, th, nsegs, CC_ACK);
+				cc_ack_received(tp, th, &to, nsegs, CC_ACK);
 
 				tp->snd_una = th->th_ack;
 				/*
@@ -2581,7 +2589,7 @@
 					tp->t_dupacks = 0;
 				else if (++tp->t_dupacks > tcprexmtthresh ||
 				     IN_FASTRECOVERY(tp->t_flags)) {
-					cc_ack_received(tp, th, nsegs,
+					cc_ack_received(tp, th, &to, nsegs,
 					    CC_DUPACK);
 					if ((tp->t_flags & TF_SACK_PERMIT) &&
 					    IN_FASTRECOVERY(tp->t_flags)) {
@@ -2641,7 +2649,7 @@
 					}
 					/* Congestion signal before ack. */
 					cc_cong_signal(tp, th, CC_NDUPACK);
-					cc_ack_received(tp, th, nsegs,
+					cc_ack_received(tp, th, &to, nsegs,
 					    CC_DUPACK);
 					tcp_timer_activate(tp, TT_REXMT, 0);
 					tp->t_rtttime = 0;
@@ -2679,7 +2687,7 @@
 					 * segment. Restore the original
 					 * snd_cwnd after packet transmission.
 					 */
-					cc_ack_received(tp, th, nsegs,
+					cc_ack_received(tp, th, &to, nsegs,
 					    CC_DUPACK);
 					uint32_t oldcwnd = tp->snd_cwnd;
 					tcp_seq oldsndmax = tp->snd_max;
@@ -2847,7 +2855,7 @@
 		 * control related information. This typically means increasing
 		 * the congestion window.
 		 */
-		cc_ack_received(tp, th, nsegs, CC_ACK);
+		cc_ack_received(tp, th, &to, nsegs, CC_ACK);
 
 		SOCKBUF_LOCK(&so->so_snd);
 		if (acked > sbavail(&so->so_snd)) {
Index: sys/netinet/tcp_stacks/fastpath.c
===================================================================
--- sys/netinet/tcp_stacks/fastpath.c
+++ sys/netinet/tcp_stacks/fastpath.c
@@ -285,7 +285,7 @@
 		 * typically means increasing the congestion
 		 * window.
 		 */
-		cc_ack_received(tp, th, nsegs, CC_ACK);
+		cc_ack_received(tp, th, &to, nsegs, CC_ACK);
 
 		tp->snd_una = th->th_ack;
 		/*
@@ -1097,7 +1097,7 @@
 					tp->t_dupacks = 0;
 				else if (++tp->t_dupacks > tcprexmtthresh ||
 				     IN_FASTRECOVERY(tp->t_flags)) {
-					cc_ack_received(tp, th, nsegs,
+					cc_ack_received(tp, th, &to, nsegs,
 					    CC_DUPACK);
 					if ((tp->t_flags & TF_SACK_PERMIT) &&
 					    IN_FASTRECOVERY(tp->t_flags)) {
@@ -1148,7 +1148,7 @@
 					}
 					/* Congestion signal before ack. */
 					cc_cong_signal(tp, th, CC_NDUPACK);
-					cc_ack_received(tp, th, nsegs,
+					cc_ack_received(tp, th, &to, nsegs,
 					    CC_DUPACK);
 					tcp_timer_activate(tp, TT_REXMT, 0);
 					tp->t_rtttime = 0;
@@ -1183,7 +1183,7 @@
 					 * segment. Restore the original
 					 * snd_cwnd after packet transmission.
 					 */
-					cc_ack_received(tp, th, nsegs,
+					cc_ack_received(tp, th, &to, nsegs,
 					    CC_DUPACK);
 					uint32_t oldcwnd = tp->snd_cwnd;
 					tcp_seq oldsndmax = tp->snd_max;
@@ -1338,7 +1338,7 @@
 		 * control related information. This typically means increasing
 		 * the congestion window.
 		 */
-		cc_ack_received(tp, th, nsegs, CC_ACK);
+		cc_ack_received(tp, th, &to, nsegs, CC_ACK);
 
 		SOCKBUF_LOCK(&so->so_snd);
 		if (acked > sbavail(&so->so_snd)) {
@@ -2150,7 +2150,7 @@
 		 * typically means increasing the congestion
 		 * window.
 		 */
-		cc_ack_received(tp, th, nsegs, CC_ACK);
+		cc_ack_received(tp, th, &to, nsegs, CC_ACK);
 
 		tp->snd_una = th->th_ack;
 		tp->t_dupacks = 0;
Index: sys/netinet/tcp_var.h
===================================================================
--- sys/netinet/tcp_var.h
+++ sys/netinet/tcp_var.h
@@ -785,7 +785,7 @@
 		     struct tcphdr *, struct mbuf *, int);
 void	tcp_xmit_timer(struct tcpcb *, int);
 void	tcp_newreno_partial_ack(struct tcpcb *, struct tcphdr *);
-void	cc_ack_received(struct tcpcb *tp, struct tcphdr *th,
+void	cc_ack_received(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to,
 			    uint16_t nsegs, uint16_t type);
 void 	cc_conn_init(struct tcpcb *tp);
 void 	cc_post_recovery(struct tcpcb *tp, struct tcphdr *th);