[RFC PATCH 3/5] Adjust alpha to 2*(1-beta)

[Baruch Even <baruch@xxxxxxxxx>]

Update alpha to be related to beta so that fairness between flows will
be preserved. See article for details.

Signed-Off-By: Douglas Leith <doug.leith@xxxxxxx>
Signed-Off-By: Baruch Even <baruch@xxxxxxxxx>

Index: 2.6.12-rc/net/ipv4/tcp_input.c
===================================================================
--- 2.6.12-rc.orig/net/ipv4/tcp_input.c
+++ 2.6.12-rc/net/ipv4/tcp_input.c
@@ -106,6 +106,7 @@ int sysctl_tcp_bic_beta = 819;              /* = 819
 int sysctl_tcp_htcp = 1;
 int sysctl_tcp_htcp_modeswitch = 1;
 int sysctl_tcp_htcp_alpha_func = 1;
+int sysctl_tcp_htcp_alpha_adjust = 1;
 
 #define FLAG_DATA              0x01 /* Incoming frame contained data.          
*/
 #define FLAG_WIN_UPDATE                0x02 /* Incoming ACK was a window 
update.       */
@@ -2131,7 +2132,15 @@ static inline void reno_cong_avoid(struc
                                }
                        }
 
-                       tp->htcp.snd_alpha = alpha;
+                       if (sysctl_tcp_htcp_alpha_adjust) {
+                               alpha = alpha*2*((1<<7)-tp->htcp.snd_beta);
+                               if (!alpha)
+                                       alpha = 1<<7;
+                       }
+                       else
+                               alpha <<= 7;
+
+                       tp->htcp.snd_alpha = alpha>>7;
 
                        tp->snd_cwnd_cnt++;
                        if ((tp->snd_cwnd_cnt*alpha)>>7 > tp->snd_cwnd) {
Index: 2.6.12-rc/include/net/tcp.h
===================================================================
--- 2.6.12-rc.orig/include/net/tcp.h
+++ 2.6.12-rc/include/net/tcp.h
@@ -615,6 +615,7 @@ extern int sysctl_tcp_tso_win_divisor;
 extern int sysctl_tcp_htcp;
 extern int sysctl_tcp_htcp_modeswitch;
 extern int sysctl_tcp_htcp_alpha_func;
+extern int sysctl_tcp_htcp_alpha_adjust;
 
 extern atomic_t tcp_memory_allocated;
 extern atomic_t tcp_sockets_allocated;
Index: 2.6.12-rc/net/ipv4/sysctl_net_ipv4.c
===================================================================
--- 2.6.12-rc.orig/net/ipv4/sysctl_net_ipv4.c
+++ 2.6.12-rc/net/ipv4/sysctl_net_ipv4.c
@@ -714,6 +714,14 @@ ctl_table ipv4_table[] = {
                .mode           = 0644,
                .proc_handler   = &proc_dointvec,
        },
+       {
+               .ctl_name       = NET_TCP_HTCP_ALPHA_ADJUST,
+               .procname       = "tcp_htcp_alpha_adjust",
+               .data           = &sysctl_tcp_htcp_alpha_adjust,
+               .maxlen         = sizeof(int),
+               .mode           = 0644,
+               .proc_handler   = &proc_dointvec,
+       },
        { .ctl_name = 0 }
 };
 
Index: 2.6.12-rc/include/linux/sysctl.h
===================================================================
--- 2.6.12-rc.orig/include/linux/sysctl.h
+++ 2.6.12-rc/include/linux/sysctl.h
@@ -349,6 +349,7 @@ enum
        NET_TCP_HTCP=109,
        NET_TCP_HTCP_MODESWITCH=110,
        NET_TCP_HTCP_ALPHA_FUNC=111,
+       NET_TCP_HTCP_ALPHA_ADJUST=112,
 };
 
 enum {