svn commit: r232345 - user/andre/tcp_workqueue/sys/netinet

[Andre Oppermann]

Author: andre
Date: Thu Mar  1 16:18:39 2012
New Revision: 232345
URL: http://svn.freebsd.org/changeset/base/232345

Log:
  Increase the initial CWND to 10 segments as defined in IETF TCPM
  draft-ietf-tcpm-initcwnd-03 discussing why the higher initial window
  improves the overall performance of many web services without risking
  congestion collapse.
  
  As long as it remains a draft it is not enabled by default and placed
  under a sysctl marking it clearly as experimental:
   net.inet.tcp.exprimental.initcwnd10
  
  Linux as of kernel 3.0 has enabled it by default.

Modified:
  user/andre/tcp_workqueue/sys/netinet/tcp_input.c
  user/andre/tcp_workqueue/sys/netinet/tcp_var.h

Modified: user/andre/tcp_workqueue/sys/netinet/tcp_input.c
==============================================================================
--- user/andre/tcp_workqueue/sys/netinet/tcp_input.c	Thu Mar  1 16:04:25 2012	(r232344)
+++ user/andre/tcp_workqueue/sys/netinet/tcp_input.c	Thu Mar  1 16:18:39 2012	(r232345)
@@ -155,6 +155,14 @@ SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO,
     &VNET_NAME(tcp_do_rfc3390), 0,
     "Enable RFC 3390 (Increasing TCP's Initial Congestion Window)");
 
+SYSCTL_NODE(_net_inet_tcp, OID_AUTO, experimental, CTLFLAG_RW, 0,
+    "Experimental TCP extensions");
+
+VNET_DEFINE(int, tcp_do_initcwnd10) = 0;
+SYSCTL_VNET_INT(_net_inet_tcp_experimental, OID_AUTO, initcwnd10, CTLFLAG_RW,
+    &VNET_NAME(tcp_do_initcwnd10), 0,
+    "Enable draft-ietf-tcpm-initcwnd-03 (Increasing initial CWND to 10)");
+
 VNET_DEFINE(int, tcp_do_rfc3465) = 1;
 SYSCTL_VNET_INT(_net_inet_tcp, OID_AUTO, rfc3465, CTLFLAG_RW,
     &VNET_NAME(tcp_do_rfc3465), 0,
@@ -343,6 +351,7 @@ cc_conn_init(struct tcpcb *tp)
 	 *
 	 * RFC5681 Section 3.1 specifies the default conservative values.
 	 * RFC3390 specifies slightly more aggressive values.
+	 * draft-ietf-tcpm-initcwnd-03 increases it to ten segments.
 	 *
 	 * If a SYN or SYN/ACK was lost and retransmitted, we have to
 	 * reduce the initial CWND to one segment as congestion is likely
@@ -350,6 +359,9 @@ cc_conn_init(struct tcpcb *tp)
 	 */
 	if (tp->snd_cwnd == 1)
 		tp->snd_cwnd = tp->t_maxseg;		/* SYN(-ACK) lost */
+	else if (V_tcp_do_initcwnd10)
+		tp->snd_cwnd = min(10 * tp->t_maxseg,
+		    max(2 * tp->t_maxseg, 14600));
 	else if (V_tcp_do_rfc3390)
 		tp->snd_cwnd = min(4 * tp->t_maxseg,
 		    max(2 * tp->t_maxseg, 4380));

Modified: user/andre/tcp_workqueue/sys/netinet/tcp_var.h
==============================================================================
--- user/andre/tcp_workqueue/sys/netinet/tcp_var.h	Thu Mar  1 16:04:25 2012	(r232344)
+++ user/andre/tcp_workqueue/sys/netinet/tcp_var.h	Thu Mar  1 16:18:39 2012	(r232345)
@@ -611,6 +611,7 @@ VNET_DECLARE(int, tcp_mssdflt);	/* XXX *
 VNET_DECLARE(int, tcp_minmss);
 VNET_DECLARE(int, tcp_delack_enabled);
 VNET_DECLARE(int, tcp_do_rfc3390);
+VNET_DECLARE(int, tcp_do_initcwnd10);
 VNET_DECLARE(int, tcp_sendspace);
 VNET_DECLARE(int, tcp_recvspace);
 VNET_DECLARE(int, path_mtu_discovery);
@@ -623,6 +624,7 @@ VNET_DECLARE(int, tcp_abc_l_var);
 #define	V_tcp_minmss		VNET(tcp_minmss)
 #define	V_tcp_delack_enabled	VNET(tcp_delack_enabled)
 #define	V_tcp_do_rfc3390	VNET(tcp_do_rfc3390)
+#define	V_tcp_do_initcwnd10	VNET(tcp_do_initcwnd10)
 #define	V_tcp_sendspace		VNET(tcp_sendspace)
 #define	V_tcp_recvspace		VNET(tcp_recvspace)
 #define	V_path_mtu_discovery	VNET(path_mtu_discovery)