tcp: retire do_newsack - always adhere to RFC6675 SACK

Depreciation notice for net.inet.tcp.newsack is in 15.0.
Remove this tunable for HEAD, streamlining the code slightly.

Reviewed by:    tuexen, cc, nickbanks_netflix.com, #transport
Sponsored by:   NetApp, Inc.
Differential Revision: https://reviews.freebsd.org/D54072

sys/netinet/tcp_input.c

@@ -2535,8 +2535,7 @@ tcp_do_segment(struct tcpcb *tp, struct mbuf *m, struct tcphdr *th,
 		}
 		if (th->th_ack == tp->snd_una) {
 			/* Check if this is a duplicate ACK. */
-			if ((tp->t_flags & TF_SACK_PERMIT) &&
-			    V_tcp_do_newsack) {
+			if (tp->t_flags & TF_SACK_PERMIT) {
 				/*
 				 * If SEG.ACK == SND.UNA, RFC 6675 requires a
 				 * duplicate ACK to selectively acknowledge
@@ -2613,7 +2612,6 @@ tcp_do_segment(struct tcpcb *tp, struct mbuf *m, struct tcphdr *th,
 				goto drop;
 			} else if (tp->t_dupacks == tcprexmtthresh ||
 				    (tp->t_flags & TF_SACK_PERMIT &&
-				     V_tcp_do_newsack &&
 				     tp->sackhint.sacked_bytes >
 				     (tcprexmtthresh - 1) * maxseg)) {
 enter_recovery:
@@ -2780,8 +2778,7 @@ tcp_do_segment(struct tcpcb *tp, struct mbuf *m, struct tcphdr *th,
 		 * from the left side. Such partial ACKs should not be
 		 * counted as dupacks here.
 		 */
-		if (V_tcp_do_newsack &&
-		    tcp_is_sack_recovery(tp, &to) &&
+		if (tcp_is_sack_recovery(tp, &to) &&
 		    (((tp->t_rxtshift == 0) && (sack_changed != SACK_NOCHANGE)) ||
 		     ((tp->t_rxtshift > 0) && (sack_changed == SACK_NEWLOSS))) &&
 		    (tp->snd_nxt == tp->snd_max)) {
@@ -4120,13 +4117,11 @@ tcp_compute_pipe(struct tcpcb *tp)
 
 	if (tp->t_fb->tfb_compute_pipe != NULL) {
 		pipe = (*tp->t_fb->tfb_compute_pipe)(tp);
-	} else if (V_tcp_do_newsack) {
+	} else {
 		pipe = tp->snd_max - tp->snd_una +
 			tp->sackhint.sack_bytes_rexmit -
 			tp->sackhint.sacked_bytes -
 			tp->sackhint.lost_bytes;
-	} else {
-		pipe = tp->snd_nxt - tp->snd_fack + tp->sackhint.sack_bytes_rexmit;
 	}
 	return (imax(pipe, 0));
 }

sys/netinet/tcp_sack.c

@@ -126,28 +126,6 @@ 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_DEFINE(int, tcp_do_newsack) = 1;
-
-static int
-sysctl_net_inet_tcp_sack_revised(SYSCTL_HANDLER_ARGS)
-{
-	int error;
-	int new;
-
-	new = V_tcp_do_newsack;
-	error = sysctl_handle_int(oidp, &new, 0, req);
-	if (error == 0 && req->newptr) {
-		V_tcp_do_newsack = new;
-		gone_in(16, "net.inet.tcp.sack.revised will be deprecated."
-		    " net.inet.tcp.sack.enable will always follow RFC6675 SACK.\n");
-	}
-	return (error);
-}
-
-SYSCTL_PROC(_net_inet_tcp_sack, OID_AUTO, revised, CTLFLAG_VNET | CTLFLAG_RW | CTLTYPE_INT,
-    &VNET_NAME(tcp_do_newsack), 0, sysctl_net_inet_tcp_sack_revised, "CU",
-    "Use revised SACK loss recovery per RFC 6675");
-
 VNET_DEFINE(int, tcp_do_lrd) = 1;
 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, lrd, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_do_lrd), 1,
@@ -1013,8 +991,7 @@ tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th, u_int *maxsegp)
 	 * the trailing packets of a window are lost and no further data
 	 * is available for sending.
 	 */
-	if ((V_tcp_do_newsack) &&
-	    SEQ_LT(th->th_ack, tp->snd_recover) &&
+	if (SEQ_LT(th->th_ack, tp->snd_recover) &&
 	    TAILQ_EMPTY(&tp->snd_holes) &&
 	    (tp->sackhint.delivered_data > 0)) {
 		/*
@@ -1079,22 +1056,6 @@ tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
 	}
 	KASSERT(SEQ_LT(hole->start, hole->end),
 	    ("%s: SEQ_GEQ(hole.start, hole.end)", __func__));
-	if (!(V_tcp_do_newsack)) {
-		KASSERT(SEQ_LT(hole->start, tp->snd_fack),
-		    ("%s: SEG_GEQ(hole.start, snd.fack)", __func__));
-		KASSERT(SEQ_LT(hole->end, tp->snd_fack),
-		    ("%s: SEG_GEQ(hole.end, snd.fack)", __func__));
-		KASSERT(SEQ_LT(hole->rxmit, tp->snd_fack),
-		    ("%s: SEQ_GEQ(hole.rxmit, snd.fack)", __func__));
-		if (SEQ_GEQ(hole->start, hole->end) ||
-		    SEQ_GEQ(hole->start, tp->snd_fack) ||
-		    SEQ_GEQ(hole->end, tp->snd_fack) ||
-		    SEQ_GEQ(hole->rxmit, tp->snd_fack)) {
-			log(LOG_CRIT,"tcp: invalid SACK hole (%u-%u,%u) vs fwd ack %u, ignoring.\n",
-					hole->start, hole->end, hole->rxmit, tp->snd_fack);
-			return (NULL);
-		}
-	}
 	return (hole);
 }
 

sys/netinet/tcp_stacks/rack.c

@@ -5393,7 +5393,7 @@ rack_ack_received(struct tcpcb *tp, struct tcp_rack *rack, uint32_t th_ack, uint
 		log.u_bbr.flex4 = tp->t_ccv.nsegs;
 		log.u_bbr.flex5 = labc_to_use;
 		log.u_bbr.flex6 = prior_cwnd;
-		log.u_bbr.flex7 = V_tcp_do_newsack;
+		log.u_bbr.flex7 = 1;  /* always doing RFC6675 SACK */
 		log.u_bbr.flex8 = 1;
 		lgb = tcp_log_event(tp, NULL, NULL, NULL, BBR_LOG_CWND, 0,
 				     0, &log, false, NULL, __func__, __LINE__,&tv);
@@ -5508,7 +5508,7 @@ rack_post_recovery(struct tcpcb *tp, uint32_t th_ack)
 		log.u_bbr.flex4 = tp->t_ccv.nsegs;
 		log.u_bbr.flex5 = V_tcp_abc_l_var;
 		log.u_bbr.flex6 = orig_cwnd;
-		log.u_bbr.flex7 = V_tcp_do_newsack;
+		log.u_bbr.flex7 = 1;  /* always doing RFC6675 SACK */
 		log.u_bbr.pkts_out = rack->r_ctl.rc_prr_sndcnt;
 		log.u_bbr.flex8 = 2;
 		tcp_log_event(tp, NULL, NULL, NULL, BBR_LOG_CWND, 0,

sys/netinet/tcp_var.h

@@ -1308,7 +1308,6 @@ 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_newsack);
 VNET_DECLARE(int, tcp_do_sack);
 VNET_DECLARE(int, tcp_do_tso);
 VNET_DECLARE(int, tcp_ecn_maxretries);
@@ -1359,7 +1358,6 @@ 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_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)