From ce40806e29c94d9ef49c4fa072726d5ef4868fe2 Mon Sep 17 00:00:00 2001
From: thorpej <thorpej@NetBSD.org>
Date: Thu, 30 Apr 1998 18:27:20 +0000
Subject: [PATCH] In the CWM code, don't use the Floyd initial window
 computation as the burst size allowed, but rather a fixed number of packets,
 as described in the Internet Draft.  Default allowed burst is 4 packets, per
 the Draft.

Make the use of CWM and the allowed burst size tunable via sysctl.
---
 sys/netinet/tcp_output.c | 13 ++++++-------
 sys/netinet/tcp_var.h    | 12 ++++++++++--
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/sys/netinet/tcp_output.c b/sys/netinet/tcp_output.c
index 207b38bd9151..34d3676bda26 100644
--- a/sys/netinet/tcp_output.c
+++ b/sys/netinet/tcp_output.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: tcp_output.c,v 1.35 1998/04/29 03:44:12 kml Exp $	*/
+/*	$NetBSD: tcp_output.c,v 1.36 1998/04/30 18:27:20 thorpej Exp $	*/
 
 /*-
  * Copyright (c) 1997, 1998 The NetBSD Foundation, Inc.
@@ -110,13 +110,12 @@ extern struct mbuf *m_copypack();
 #define MAX_TCPOPTLEN	32	/* max # bytes that go in options */
 
 /*
- * Knob to enable Congestion Window Monitoring.
+ * Knob to enable Congestion Window Monitoring, and control the
+ * the burst size it allows.  Default burst is 4 packets, per
+ * the Internet draft.
  */
-#ifdef TCP_CWM
-int	tcp_cwm = 1;
-#else
 int	tcp_cwm = 0;
-#endif
+int	tcp_cwm_burstsize = 4;
 
 static __inline void tcp_segsize __P((struct tcpcb *, int *, int *));
 static __inline void
@@ -199,7 +198,7 @@ tcp_output(tp)
 		 * been acknowledged (i.e. transmission is idle).
 		 */
 		tp->snd_cwnd = min(tp->snd_cwnd,
-		    TCP_INITIAL_WINDOW(tcp_init_win, txsegsize) +
+		    (tcp_cwm_burstsize * txsegsize) +
 		    (tp->snd_nxt - tp->snd_una));
 	} else {
 		if (idle && tp->t_idle >= tp->t_rxtcur) {
diff --git a/sys/netinet/tcp_var.h b/sys/netinet/tcp_var.h
index feb2edfc30c6..2ca952d6f37d 100644
--- a/sys/netinet/tcp_var.h
+++ b/sys/netinet/tcp_var.h
@@ -1,4 +1,4 @@
-/*	$NetBSD: tcp_var.h,v 1.44 1998/04/30 17:55:27 thorpej Exp $	*/
+/*	$NetBSD: tcp_var.h,v 1.45 1998/04/30 18:27:21 thorpej Exp $	*/
 
 /*-
  * Copyright (c) 1997, 1998 The NetBSD Foundation, Inc.
@@ -384,7 +384,9 @@ struct	tcpstat {
 #define	TCPCTL_WSCALE		11	/* RFC1323 window scaling */
 #define	TCPCTL_TSTAMP		12	/* RFC1323 timestamps */
 #define	TCPCTL_COMPAT_42	13	/* 4.2BSD TCP bug work-arounds */
-#define	TCPCTL_MAXID		14
+#define	TCPCTL_CWM		14	/* Congestion Window Monitoring */
+#define	TCPCTL_CWM_BURSTSIZE	15	/* burst size allowed by CWM */
+#define	TCPCTL_MAXID		16
 
 #define	TCPCTL_NAMES { \
 	{ 0, 0 }, \
@@ -401,6 +403,8 @@ struct	tcpstat {
 	{ "win_scale", CTLTYPE_INT }, \
 	{ "timestamps", CTLTYPE_INT }, \
 	{ "compat_42", CTLTYPE_INT }, \
+	{ "cwm", CTLTYPE_INT }, \
+	{ "cwm_burstsize", CTLTYPE_INT }, \
 }
 
 #ifdef _KERNEL
@@ -415,6 +419,8 @@ extern	int tcp_mssdflt;	/* default seg size */
 extern	int tcp_init_win;	/* initial window */
 extern	int tcp_mss_ifmtu;	/* take MSS from interface, not in_maxmtu */
 extern	int tcp_compat_42;	/* work around ancient broken TCP peers */
+extern	int tcp_cwm;		/* enable Congestion Window Monitoring */
+extern	int tcp_cwm_burstsize;	/* burst size allowed by CWM */
 extern	int tcp_syn_cache_limit; /* max entries for compressed state engine */
 extern	int tcp_syn_bucket_limit;/* max entries per hash bucket */
 extern	int tcp_syn_cache_interval; /* compressed state timer */
@@ -439,6 +445,8 @@ extern	u_long syn_cache_count;
 	&tcp_do_win_scale, \
 	&tcp_do_timestamps, \
 	&tcp_compat_42, \
+	&tcp_cwm, \
+	&tcp_cwm_burstsize, \
 }
 
 int	 tcp_attach __P((struct socket *));