[TCP]: More sysctl tweakings for rcvbuf stuff.

1) Add sysctl to control rcvbuf moderation, off for now.
2) Set default winscale to zero.

include/linux/sysctl.h

@@ -337,6 +337,7 @@ enum
  	NET_TCP_BIC_FAST_CONVERGENCE=103,
 	NET_TCP_BIC_LOW_WINDOW=104,
 	NET_TCP_DEFAULT_WIN_SCALE=105,
+	NET_TCP_MODERATE_RCVBUF=106,
 };
 
 enum {

include/net/tcp.h

@@ -611,6 +611,7 @@ extern int sysctl_tcp_bic;
 extern int sysctl_tcp_bic_fast_convergence;
 extern int sysctl_tcp_bic_low_window;
 extern int sysctl_tcp_default_win_scale;
+extern int sysctl_tcp_moderate_rcvbuf;
 
 extern atomic_t tcp_memory_allocated;
 extern atomic_t tcp_sockets_allocated;

net/ipv4/sysctl_net_ipv4.c

@@ -673,6 +673,14 @@ ctl_table ipv4_table[] = {
 		.mode		= 0644,
 		.proc_handler	= &proc_dointvec,
 	},
+	{
+		.ctl_name	= NET_TCP_MODERATE_RCVBUF,
+		.procname	= "tcp_moderate_rcvbuf",
+		.data		= &sysctl_tcp_moderate_rcvbuf,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec,
+	},
 	{ .ctl_name = 0 }
 };
 

net/ipv4/tcp.c

@@ -276,7 +276,7 @@ kmem_cache_t *tcp_timewait_cachep;
 
 atomic_t tcp_orphan_count = ATOMIC_INIT(0);
 
-int sysctl_tcp_default_win_scale = 7;
+int sysctl_tcp_default_win_scale;
 
 int sysctl_tcp_mem[3];
 int sysctl_tcp_wmem[3] = { 4 * 1024, 16 * 1024, 128 * 1024 };

net/ipv4/tcp_input.c

@@ -90,6 +90,8 @@ int sysctl_tcp_nometrics_save;
 int sysctl_tcp_westwood;
 int sysctl_tcp_vegas_cong_avoid;
 
+int sysctl_tcp_moderate_rcvbuf;
+
 /* Default values of the Vegas variables, in fixed-point representation
  * with V_PARAM_SHIFT bits to the right of the binary point.
  */
@@ -460,19 +462,21 @@ void tcp_rcv_space_adjust(struct sock *sk)
 
 		tp->rcvq_space.space = space;
 
-		/* Receive space grows, normalize in order to
-		 * take into account packet headers and sk_buff
-		 * structure overhead.
-		 */
-		space /= tp->advmss;
-		if (!space)
-			space = 1;
-		rcvmem = (tp->advmss + MAX_TCP_HEADER +
-			  16 + sizeof(struct sk_buff));
-		space *= rcvmem;
-		space = min(space, sysctl_tcp_rmem[2]);
-		if (space > sk->sk_rcvbuf)
-			sk->sk_rcvbuf = space;
+		if (sysctl_tcp_moderate_rcvbuf) {
+			/* Receive space grows, normalize in order to
+			 * take into account packet headers and sk_buff
+			 * structure overhead.
+			 */
+			space /= tp->advmss;
+			if (!space)
+				space = 1;
+			rcvmem = (tp->advmss + MAX_TCP_HEADER +
+				  16 + sizeof(struct sk_buff));
+			space *= rcvmem;
+			space = min(space, sysctl_tcp_rmem[2]);
+			if (space > sk->sk_rcvbuf)
+				sk->sk_rcvbuf = space;
+		}
 	}
 	
 new_measure: