Merge branch 'sctp-RFC-4960-Errata-fixes'

Marcelo Ricardo Leitner says:

====================
sctp: RFC 4960 Errata fixes

This patchset contains fixes for 4 Errata topics from
https://tools.ietf.org/html/draft-ietf-tsvwg-rfc4960-errata-01
Namely, sections:
 3.12. Order of Adjustments of partial_bytes_acked and cwnd
 3.22. Increase of partial_bytes_acked in Congestion Avoidance
 3.26. CWND Increase in Congestion Avoidance Phase
 3.27. Refresh of cwnd and ssthresh after Idle Period

Tests performed with netperf using net namespaces, with drop rates at
0%, 0.5% and 1% by netem, IPv4 and IPv6, 10 runs for each combination.
I couldn't spot differences on the stats. With and without these patches
the results vary in a similar way in terms of throughput and
retransmissions.

Tests with 20ms delay and 20ms delay + drops at 0.5% and 1% also had
results in a similar way, no noticeable difference.

Looking at cwnd, it was possible to notice slightly lower values being
used while still sustaining same throughput profile.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

net/sctp/transport.c

@@ -405,14 +405,6 @@ void sctp_transport_raise_cwnd(struct sctp_transport *transport,
 	    TSN_lte(asoc->fast_recovery_exit, sack_ctsn))
 		asoc->fast_recovery = 0;
 
-	/* The appropriate cwnd increase algorithm is performed if, and only
-	 * if the cumulative TSN whould advanced and the congestion window is
-	 * being fully utilized.
-	 */
-	if (TSN_lte(sack_ctsn, transport->asoc->ctsn_ack_point) ||
-	    (flight_size < cwnd))
-		return;
-
 	ssthresh = transport->ssthresh;
 	pba = transport->partial_bytes_acked;
 	pmtu = transport->asoc->pathmtu;
@@ -435,6 +427,14 @@ void sctp_transport_raise_cwnd(struct sctp_transport *transport,
 		if (asoc->fast_recovery)
 			return;
 
+		/* The appropriate cwnd increase algorithm is performed
+		 * if, and only if the congestion window is being fully
+		 * utilized.  Note that RFC4960 Errata 3.22 removed the
+		 * other condition on ctsn moving.
+		 */
+		if (flight_size < cwnd)
+			return;
+
 		if (bytes_acked > pmtu)
 			cwnd += pmtu;
 		else
@@ -446,23 +446,33 @@ void sctp_transport_raise_cwnd(struct sctp_transport *transport,
 			 flight_size, pba);
 	} else {
 		/* RFC 2960 7.2.2 Whenever cwnd is greater than ssthresh,
-		 * upon each SACK arrival that advances the Cumulative TSN Ack
-		 * Point, increase partial_bytes_acked by the total number of
-		 * bytes of all new chunks acknowledged in that SACK including
-		 * chunks acknowledged by the new Cumulative TSN Ack and by
-		 * Gap Ack Blocks.
+		 * upon each SACK arrival, increase partial_bytes_acked
+		 * by the total number of bytes of all new chunks
+		 * acknowledged in that SACK including chunks
+		 * acknowledged by the new Cumulative TSN Ack and by Gap
+		 * Ack Blocks. (updated by RFC4960 Errata 3.22)
 		 *
-		 * When partial_bytes_acked is equal to or greater than cwnd
-		 * and before the arrival of the SACK the sender had cwnd or
-		 * more bytes of data outstanding (i.e., before arrival of the
-		 * SACK, flightsize was greater than or equal to cwnd),
-		 * increase cwnd by MTU, and reset partial_bytes_acked to
-		 * (partial_bytes_acked - cwnd).
+		 * When partial_bytes_acked is greater than cwnd and
+		 * before the arrival of the SACK the sender had less
+		 * bytes of data outstanding than cwnd (i.e., before
+		 * arrival of the SACK, flightsize was less than cwnd),
+		 * reset partial_bytes_acked to cwnd. (RFC 4960 Errata
+		 * 3.26)
+		 *
+		 * When partial_bytes_acked is equal to or greater than
+		 * cwnd and before the arrival of the SACK the sender
+		 * had cwnd or more bytes of data outstanding (i.e.,
+		 * before arrival of the SACK, flightsize was greater
+		 * than or equal to cwnd), partial_bytes_acked is reset
+		 * to (partial_bytes_acked - cwnd). Next, cwnd is
+		 * increased by MTU. (RFC 4960 Errata 3.12)
 		 */
 		pba += bytes_acked;
-		if (pba >= cwnd) {
+		if (pba > cwnd && flight_size < cwnd)
+			pba = cwnd;
+		if (pba >= cwnd && flight_size >= cwnd) {
+			pba = pba - cwnd;
 			cwnd += pmtu;
-			pba = ((cwnd < pba) ? (pba - cwnd) : 0);
 		}
 
 		pr_debug("%s: congestion avoidance: transport:%p, "
@@ -559,6 +569,8 @@ void sctp_transport_lower_cwnd(struct sctp_transport *transport,
 		 */
 		transport->cwnd = max(transport->cwnd/2,
 					 4*asoc->pathmtu);
+		/* RFC 4960 Errata 3.27.2: also adjust sshthresh */
+		transport->ssthresh = transport->cwnd;
 		break;
 	}