tcp: Rename rfc6675_pipe to sack.revised, and enable by default

As full support of RFC6675 is in place, deprecating
net.inet.tcp.rfc6675_pipe and enabling by default
net.inet.tcp.sack.revised.

Reviewed By: #transport, kbowling, rrs
Sponsored by: NetApp, Inc.
Differential Revision: https://reviews.freebsd.org/D28702

7 files changed, 31 insertions, 27 deletions

diff --git a/share/man/man4/tcp.4 b/share/man/man4/tcp.4
index d01505e58427..cbb8021226fe 100644
--- a/share/man/man4/tcp.4
+++ b/share/man/man4/tcp.4
@@ -34,7 +34,7 @@
 .\"     From: @(#)tcp.4	8.1 (Berkeley) 6/5/93
 .\" $FreeBSD$
 .\"
-.Dd April 8, 2021
+.Dd April 17, 2021
 .Dt TCP 4
 .Os
 .Sh NAME
@@ -558,16 +558,8 @@ Helpful when a misconfigured token bucket traffic policer causes persistent
 high losses leading to RTO, but reduces PRR effectiveness in more common settings
 (default is false).
 .It Va rfc6675_pipe
-Calculate the bytes in flight using the algorithm described in RFC 6675, and
-is also an improvement when Proportional Rate Reduction is enabled.
-Also enables two other mechanisms from RFC6675.
-Rescue Retransmission helps timely loss recovery, when the trailing segments
-of a transmission are lost, while no additional data is ready to be sent.
-In case a partial ACK without a SACK block is received during SACK loss
-recovery, the trailing segment is immediately resent, rather than waiting
-for a Retransmission timeout.
-SACK loss recovery is also engaged, once two segments plus one byte are
-SACKed - even if no traditional duplicate ACKs were seen.
+Deprecated and superseded by
+.Va sack.revised
 .It Va rfc3042
 Enable the Limited Transmit algorithm as described in RFC 3042.
 It helps avoid timeouts on lossy links and also when the congestion window
@@ -584,6 +576,17 @@ Enable support for RFC 2018, TCP Selective Acknowledgment option,
 which allows the receiver to inform the sender about all successfully
 arrived segments, allowing the sender to retransmit the missing segments
 only.
+.It Va sack.revised
+Enables three updated mechanisms from RFC6675 (default is true).
+Calculate the bytes in flight using the algorithm described in RFC 6675, and
+is also an improvement when Proportional Rate Reduction is enabled.
+Next, Rescue Retransmission helps timely loss recovery, when the trailing segments
+of a transmission are lost, while no additional data is ready to be sent.
+In case a partial ACK without a SACK block is received during SACK loss
+recovery, the trailing segment is immediately resent, rather than waiting
+for a Retransmission timeout.
+Finally, SACK loss recovery is also engaged, once two segments plus one byte are
+SACKed - even if no traditional duplicate ACKs were observed.
 .It Va sack.maxholes
 Maximum number of SACK holes per connection.
 Defaults to 128.
diff --git a/sys/netinet/cc/cc_cubic.c b/sys/netinet/cc/cc_cubic.c
index 210806c2f4f7..56b87ba4089b 100644
--- a/sys/netinet/cc/cc_cubic.c
+++ b/sys/netinet/cc/cc_cubic.c
@@ -373,7 +373,7 @@ cubic_post_recovery(struct cc_var *ccv)
 		 *
 		 * XXXLAS: Find a way to do this without needing curack
 		 */
-		if (V_tcp_do_rfc6675_pipe)
+		if (V_tcp_do_newsack)
 			pipe = tcp_compute_pipe(ccv->ccvc.tcp);
 		else
 			pipe = CCV(ccv, snd_max) - ccv->curack;
diff --git a/sys/netinet/cc/cc_htcp.c b/sys/netinet/cc/cc_htcp.c
index b5739142c9e5..d109f2c4af4a 100644
--- a/sys/netinet/cc/cc_htcp.c
+++ b/sys/netinet/cc/cc_htcp.c
@@ -366,7 +366,7 @@ htcp_post_recovery(struct cc_var *ccv)
 		 *
 		 * XXXLAS: Find a way to do this without needing curack
 		 */
-		if (V_tcp_do_rfc6675_pipe)
+		if (V_tcp_do_newsack)
 			pipe = tcp_compute_pipe(ccv->ccvc.tcp);
 		else
 			pipe = CCV(ccv, snd_max) - ccv->curack;
diff --git a/sys/netinet/cc/cc_newreno.c b/sys/netinet/cc/cc_newreno.c
index 84f8b6a5eb1a..daf4e3351ffa 100644
--- a/sys/netinet/cc/cc_newreno.c
+++ b/sys/netinet/cc/cc_newreno.c
@@ -302,7 +302,7 @@ newreno_post_recovery(struct cc_var *ccv)
 		 *
 		 * XXXLAS: Find a way to do this without needing curack
 		 */
-		if (V_tcp_do_rfc6675_pipe)
+		if (V_tcp_do_newsack)
 			pipe = tcp_compute_pipe(ccv->ccvc.tcp);
 		else
 			pipe = CCV(ccv, snd_max) - ccv->curack;
diff --git a/sys/netinet/tcp_input.c b/sys/netinet/tcp_input.c
index cfb0989a7203..ed184de4a4bf 100644
--- a/sys/netinet/tcp_input.c
+++ b/sys/netinet/tcp_input.c
@@ -168,11 +168,6 @@ SYSCTL_INT(_net_inet_tcp, OID_AUTO, newcwv, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_do_newcwv), 0,
     "Enable New Congestion Window Validation per RFC7661");
 
-VNET_DEFINE(int, tcp_do_rfc6675_pipe) = 0;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc6675_pipe, CTLFLAG_VNET | CTLFLAG_RW,
-    &VNET_NAME(tcp_do_rfc6675_pipe), 0,
-    "Use calculated pipe/in-flight bytes per RFC 6675");
-
 VNET_DEFINE(int, tcp_do_rfc3042) = 1;
 SYSCTL_INT(_net_inet_tcp, OID_AUTO, rfc3042, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_do_rfc3042), 0,
@@ -2595,7 +2590,7 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 						 * we have less than 1/2 the original window's
 						 * worth of data in flight.
 						 */
-						if (V_tcp_do_rfc6675_pipe)
+						if (V_tcp_do_newsack)
 							awnd = tcp_compute_pipe(tp);
 						else
 							awnd = (tp->snd_nxt - tp->snd_fack) +
@@ -2612,7 +2607,7 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
 					goto drop;
 				} else if (tp->t_dupacks == tcprexmtthresh ||
 					    (tp->t_flags & TF_SACK_PERMIT &&
-					     V_tcp_do_rfc6675_pipe &&
+					     V_tcp_do_newsack &&
 					     tp->sackhint.sacked_bytes >
 					     (tcprexmtthresh - 1) * maxseg)) {
 enter_recovery:
@@ -3940,7 +3935,7 @@ tcp_do_prr_ack(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
 	 * network.
 	 */
 	del_data = tp->sackhint.delivered_data;
-	if (V_tcp_do_rfc6675_pipe)
+	if (V_tcp_do_newsack)
 		pipe = tcp_compute_pipe(tp);
 	else
 		pipe = (tp->snd_nxt - tp->snd_fack) + tp->sackhint.sack_bytes_rexmit;
diff --git a/sys/netinet/tcp_sack.c b/sys/netinet/tcp_sack.c
index f8d983da723b..a28bb40a8332 100644
--- a/sys/netinet/tcp_sack.c
+++ b/sys/netinet/tcp_sack.c
@@ -130,10 +130,16 @@ VNET_DECLARE(struct uma_zone *, sack_hole_zone);
 
 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
     "TCP SACK");
+
 VNET_DEFINE(int, tcp_do_sack) = 1;
-#define	V_tcp_do_sack			VNET(tcp_do_sack)
 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_VNET | CTLFLAG_RW,
-    &VNET_NAME(tcp_do_sack), 0, "Enable/Disable TCP SACK support");
+    &VNET_NAME(tcp_do_sack), 0,
+    "Enable/Disable TCP SACK support");
+
+VNET_DEFINE(int, tcp_do_newsack) = 1;
+SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, revised, CTLFLAG_VNET | CTLFLAG_RW,
+    &VNET_NAME(tcp_do_newsack), 0,
+    "Use revised SACK loss recovery per RFC 6675");
 
 VNET_DEFINE(int, tcp_sack_maxholes) = 128;
 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_VNET | CTLFLAG_RW,
@@ -826,7 +832,7 @@ tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
 	 * the trailing packets of a window are lost and no further data
 	 * is available for sending.
 	 */
-	if ((V_tcp_do_rfc6675_pipe) &&
+	if ((V_tcp_do_newsack) &&
 	    SEQ_LT(th->th_ack, tp->snd_recover) &&
 	    (tp->snd_recover == tp->snd_max) &&
 	    TAILQ_EMPTY(&tp->snd_holes) &&
diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
index 48e4c5c8e89a..4d28cab80d89 100644
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -846,7 +846,7 @@ VNET_DECLARE(int, tcp_tolerate_missing_ts);
 VNET_DECLARE(int, tcp_do_rfc3042);
 VNET_DECLARE(int, tcp_do_rfc3390);
 VNET_DECLARE(int, tcp_do_rfc3465);
-VNET_DECLARE(int, tcp_do_rfc6675_pipe);
+VNET_DECLARE(int, tcp_do_newsack);
 VNET_DECLARE(int, tcp_do_sack);
 VNET_DECLARE(int, tcp_do_tso);
 VNET_DECLARE(int, tcp_ecn_maxretries);
@@ -891,7 +891,7 @@ VNET_DECLARE(struct inpcbinfo, tcbinfo);
 #define	V_tcp_do_rfc3042		VNET(tcp_do_rfc3042)
 #define	V_tcp_do_rfc3390		VNET(tcp_do_rfc3390)
 #define	V_tcp_do_rfc3465		VNET(tcp_do_rfc3465)
-#define	V_tcp_do_rfc6675_pipe		VNET(tcp_do_rfc6675_pipe)
+#define	V_tcp_do_newsack		VNET(tcp_do_newsack)
 #define	V_tcp_do_sack			VNET(tcp_do_sack)
 #define	V_tcp_do_tso			VNET(tcp_do_tso)
 #define	V_tcp_ecn_maxretries		VNET(tcp_ecn_maxretries)