svn commit: r186171 - projects/tcp_ffcaia2008_8.x/sys/netinet

[Lawrence Stewart]

Author: lstewart
Date: Tue Dec 16 07:08:35 2008
New Revision: 186171
URL: http://svn.freebsd.org/changeset/base/186171

Log:
  More work on TCP ABC support.

Modified:
  projects/tcp_ffcaia2008_8.x/sys/netinet/tcp_input.c
  projects/tcp_ffcaia2008_8.x/sys/netinet/tcp_var.h

Modified: projects/tcp_ffcaia2008_8.x/sys/netinet/tcp_input.c
==============================================================================
--- projects/tcp_ffcaia2008_8.x/sys/netinet/tcp_input.c	Tue Dec 16 06:01:08 2008	(r186170)
+++ projects/tcp_ffcaia2008_8.x/sys/netinet/tcp_input.c	Tue Dec 16 07:08:35 2008	(r186171)
@@ -137,7 +137,7 @@ SYSCTL_V_INT(V_NET, vnet_inet, _net_inet
     "Enable RFC 3465 (Appropriate Byte Counting)");
 SYSCTL_V_INT(V_NET, vnet_inet, _net_inet_tcp, OID_AUTO, abc_l_var, CTLFLAG_RW,
     tcp_abc_l_var, 1,
-    "Max # segments)");
+    "Cap the max cwnd increment during slow-start to this number of segments");
 
 int	tcp_do_ecn = 0;
 int	tcp_ecn_maxretries = 1;
@@ -2111,23 +2111,53 @@ process_ACK:
 
 		/*
 		 * When new data is acked, open the congestion window.
-		 * If the window gives us less than ssthresh packets
-		 * in flight, open exponentially (maxseg per packet).
-		 * Otherwise open linearly: maxseg per window
-		 * (maxseg^2 / cwnd per packet).
-		 * If cwnd > maxseg^2, fix the cwnd increment at 1 byte
-		 * to avoid capping cwnd (as suggested in RFC2581).
+		 * Method depends on which congestion control state we're
+		 * in (slow start or cong avoid) and if ABC (RFC 3465) is
+		 * enabled.
+		 *
+		 * slow start: cwnd <= ssthresh
+		 * cong avoid: cwnd > ssthresh
+		 *
+		 * slow start and ABC (RFC 3465):
+		 *   Grow cwnd exponentially by the amount of data
+		 *   ACKed capping the max increment per ACK to
+		 *   (abc_l_var * maxseg) bytes.
+		 *
+		 * slow start without ABC (RFC 2581):
+		 *   Grow cwnd exponentially by maxseg per ACK.
+		 *
+		 * cong avoid and ABC (RFC 3465):
+		 *   Grow cwnd linearly by maxseg per RTT for each
+		 *   cwnd worth of ACKed data.
+		 *
+		 * cong avoid without ABC (RFC 2581):
+		 *   Grow cwnd linearly by approximately maxseg per RTT using
+		 *   maxseg^2 / cwnd per ACK as the increment.
+		 *   If cwnd > maxseg^2, fix the cwnd increment at 1 byte to
+		 *   avoid capping cwnd (as suggested in RFC 2581).
 		 */
 		if ((!V_tcp_do_newreno && !(tp->t_flags & TF_SACK_PERMIT)) ||
 		    !IN_FASTRECOVERY(tp)) {
 			u_int cw = tp->snd_cwnd;
 			u_int incr = tp->t_maxseg;
-			if (V_tcp_do_rfc3465)
+			/* In congestion avoidance? */
+			if (cw > tp->snd_ssthresh) {
+				if (V_tcp_do_rfc3465) {
+					tp->t_bytes_acked += acked;
+					if (tp->t_bytes_acked >= tp->snd_cwnd)
+						tp->t_bytes_acked -= cw;
+					else
+						incr = 0;
+				}
+				else
+					incr = max((incr * incr / cw), 1);
+			/* In slow-start with ABC enabled? */
+			} else if (V_tcp_do_rfc3465)
 				incr = min(acked,
 				    V_tcp_abc_l_var * tp->t_maxseg);
-			else if (cw > tp->snd_ssthresh)
-				incr = max((incr * incr / cw), 1);
-			tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
+			/* ABC is on by default, so (incr == 0) frequently. */
+			if (incr > 0)
+				tp->snd_cwnd = min(cw+incr, TCP_MAXWIN<<tp->snd_scale);
 		}
 		SOCKBUF_LOCK(&so->so_snd);
 		if (acked > so->so_snd.sb_cc) {

Modified: projects/tcp_ffcaia2008_8.x/sys/netinet/tcp_var.h
==============================================================================
--- projects/tcp_ffcaia2008_8.x/sys/netinet/tcp_var.h	Tue Dec 16 06:01:08 2008	(r186170)
+++ projects/tcp_ffcaia2008_8.x/sys/netinet/tcp_var.h	Tue Dec 16 07:08:35 2008	(r186171)
@@ -213,6 +213,7 @@ struct tcpcb {
 	void	*t_pspare[3];		/* toe usrreqs / toepcb * / congestion algo / vimage / 1 general use */
 	struct toe_usrreqs *t_tu;       /* offload operations vector */
 	void	*t_toe;			/* TOE pcb pointer */
+	int	t_bytes_acked;		/* # bytes acked during current RTT */
 };
 
 #define IN_FASTRECOVERY(tp)	(tp->t_flags & TF_FASTRECOVERY)