Index: netinet/tcp_output.c
===================================================================
RCS file: /home/ncvs/src/sys/netinet/tcp_output.c,v
retrieving revision 1.121
diff -u -p -r1.121 tcp_output.c
--- netinet/tcp_output.c	22 Oct 2006 11:52:16 -0000	1.121
+++ netinet/tcp_output.c	16 Nov 2006 22:39:18 -0000
@@ -48,6 +48,7 @@
 #include <sys/socket.h>
 #include <sys/socketvar.h>
 #include <sys/sysctl.h>
+#include <sys/syslog.h>
 
 #include <net/route.h>
 
@@ -103,13 +104,26 @@ SYSCTL_INT(_net_inet_tcp, OID_AUTO, loca
 	&ss_fltsz_local, 1, "Slow start flight size for local networks");
 
 int     tcp_do_newreno = 1;
-SYSCTL_INT(_net_inet_tcp, OID_AUTO, newreno, CTLFLAG_RW, &tcp_do_newreno,
-	0, "Enable NewReno Algorithms");
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, newreno, CTLFLAG_RW,
+	&tcp_do_newreno, 0, "Enable NewReno Algorithms");
 
 int	tcp_do_tso = 1;
 SYSCTL_INT(_net_inet_tcp, OID_AUTO, tso, CTLFLAG_RW,
 	&tcp_do_tso, 0, "Enable TCP Segmentation Offload");
 
+int	tcp_do_autosndbuf = 1;
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, sndbuf_auto, CTLFLAG_RW,
+	&tcp_do_autosndbuf, 0, "Enable automatic send buffers");
+
+int	tcp_autosndbuf_inc = 8*1024;
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, sndbuf_inc, CTLFLAG_RW,
+	&tcp_autosndbuf_inc, 0, "Incrementor step size of automatic send buffer");
+
+int	tcp_autosndbuf_max = 256*1024;
+SYSCTL_INT(_net_inet_tcp, OID_AUTO, sndbuf_max, CTLFLAG_RW,
+	&tcp_autosndbuf_max, 0, "Max size of automatic send buffer");
+
+
 /*
  * Tcp output routine: figure out what should be sent and send it.
  */
@@ -380,11 +394,58 @@ after_sack_rexmit:
 		}
 	}
 
+	/* len will be >= 0 after this point. */
+	KASSERT(len >= 0, ("%s: len < 0", __func__));
+
 	/*
-	 * len will be >= 0 after this point.  Truncate to the maximum
-	 * segment length or enable TCP Segmentation Offloading (if supported
-	 * by hardware) and ensure that FIN is removed if the length no longer
-	 * contains the last data byte.
+	 * Automatic sizing of send socket buffer.  Often the send buffer
+	 * size is not optimally adjusted to the actual network conditions
+	 * at hand (delay bandwidth product).  Setting the buffer size too
+	 * small limits throughput on links with high bandwidth and high
+	 * delay (eg. trans-continental/oceanic links).  Setting the
+	 * buffer size too big consumes too much real kernel memory,
+	 * especially with many connections on busy servers.
+	 *
+	 * The criteria to step up the send buffer one notch are:
+	 *  1. receive window of remote host is larger than send buffer
+	 *     (with a fudge factor of 5/4th);
+	 *  2. send buffer is filled to 7/8th with data (so we actually
+	 *     have data to make use of it);
+	 *  3. send buffer fill has not hit maximal automatic size;
+	 *  4. our send window (slow start and cogestion controlled) is
+	 *     larger than sent but unacknowledged data in send buffer.
+	 *
+	 * The remote host receive window scaling factor may limit the
+	 * growing of the send buffer before it reaches its allowed
+	 * maximum.
+	 *
+	 * Optional: Shrink send buffer during idle periods together
+	 * with congestion window.  Requires another timer.  Has to
+	 * wait for upcoming tcp timer rewrite.
+	 */
+	if (tcp_do_autosndbuf && so->so_snd.sb_flags & SB_AUTOSIZE) {
+		if ((tp->snd_wnd / 4 * 5) >= so->so_snd.sb_hiwat &&
+		    so->so_snd.sb_cc >= (so->so_snd.sb_hiwat / 8 * 7) &&
+		    so->so_snd.sb_cc < tcp_autosndbuf_max &&
+		    sendwin >= (so->so_snd.sb_cc - (tp->snd_nxt - tp->snd_una))) {
+#if 1
+			log(LOG_DEBUG, "%s: inc sockbuf, old %i, new %i, "
+			    "sb_cc %i, snd_wnd %i, sendwnd %i\n",
+			    __func__, so->so_snd.sb_hiwat,
+			    so->so_snd.sb_hiwat + tcp_autosndbuf_inc,
+			    so->so_snd.sb_cc, (int)tp->snd_wnd, (int)sendwin);
+#endif
+			(void)sbreserve_locked(&so->so_snd,
+			    min(so->so_snd.sb_hiwat + tcp_autosndbuf_inc,
+				tcp_autosndbuf_max),
+			    so, curthread);
+		}
+	}
+
+	/*
+	 * Truncate to the maximum segment length or enable TCP Segmentation
+	 * Offloading (if supported by hardware) and ensure that FIN is removed
+	 * if the length no longer contains the last data byte.
 	 *
 	 * TSO may only be used if we are in a pure bulk sending state.  The
 	 * presence of TCP-MD5, SACK retransmits, SACK advertizements and
Index: netinet/tcp_usrreq.c
===================================================================
RCS file: /home/ncvs/src/sys/netinet/tcp_usrreq.c,v
retrieving revision 1.141
diff -u -p -r1.141 tcp_usrreq.c
--- netinet/tcp_usrreq.c	17 Sep 2006 13:39:35 -0000	1.141
+++ netinet/tcp_usrreq.c	16 Nov 2006 22:39:19 -0000
@@ -1441,6 +1444,8 @@ tcp_attach(so)
 		if (error)
 			return (error);
 	}
+	so->so_rcv.sb_flags |= SB_AUTOSIZE;
+	so->so_snd.sb_flags |= SB_AUTOSIZE;
 	INP_INFO_WLOCK(&tcbinfo);
 	error = in_pcballoc(so, &tcbinfo);
 	if (error) {
Index: sys/socketvar.h
===================================================================
RCS file: /home/ncvs/src/sys/sys/socketvar.h,v
retrieving revision 1.154
diff -u -p -r1.154 socketvar.h
--- sys/socketvar.h	1 Aug 2006 10:30:26 -0000	1.154
+++ sys/socketvar.h	16 Nov 2006 22:41:18 -0000
@@ -128,6 +128,7 @@ struct socket {
 #define	SB_NOINTR	0x40		/* operations not interruptible */
 #define SB_AIO		0x80		/* AIO operations queued */
 #define SB_KNOTE	0x100		/* kernel note attached */
+#define SB_AUTOSIZE	0x800		/* automatically size socket buffer */
 
 	void	(*so_upcall)(struct socket *, void *, int);
 	void	*so_upcallarg;