[RFC PATCH 2/5] Adjust alpha according to a function defined in HTCP

[Baruch Even <baruch@xxxxxxxxx>]

Modify alpha as a function of the time since last backoff.

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
@@ -105,6 +105,7 @@ int sysctl_tcp_bic_low_window = 14;
 int sysctl_tcp_bic_beta = 819;         /* = 819/1024 (BICTCP_BETA_SCALE) */
 int sysctl_tcp_htcp = 1;
 int sysctl_tcp_htcp_modeswitch = 1;
+int sysctl_tcp_htcp_alpha_func = 1;
 
 #define FLAG_DATA              0x01 /* Incoming frame contained data.          
*/
 #define FLAG_WIN_UPDATE                0x02 /* Incoming ACK was a window 
update.       */
@@ -2120,6 +2121,16 @@ static inline void reno_cong_avoid(struc
                        measure_minRTT(tp);
 
                        /* calculate increase rate - alpha is number of packets 
added to cwnd per RTT */
+                       if (sysctl_tcp_htcp_alpha_func) {
+                               /* time since last backoff */
+                               __u32 diff = tp->htcp.snd_ccount * 
tp->htcp.snd_minRTT;
+
+                               if (diff > HZ) {
+                                       diff -= HZ;
+                                       alpha += ( 
10*diff+((diff>>1)*(diff>>1)/HZ) )/HZ;
+                               }
+                       }
+
                        tp->htcp.snd_alpha = alpha;
 
                        tp->snd_cwnd_cnt++;
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
@@ -614,6 +614,7 @@ extern int sysctl_tcp_moderate_rcvbuf;
 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 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
@@ -706,6 +706,14 @@ ctl_table ipv4_table[] = {
                .mode           = 0644,
                .proc_handler   = &proc_dointvec,
        },
+       {
+               .ctl_name       = NET_TCP_HTCP_ALPHA_FUNC,
+               .procname       = "tcp_htcp_alpha_func",
+               .data           = &sysctl_tcp_htcp_alpha_func,
+               .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
@@ -348,6 +348,7 @@ enum
        NET_TCP_BIC_BETA=108,
        NET_TCP_HTCP=109,
        NET_TCP_HTCP_MODESWITCH=110,
+       NET_TCP_HTCP_ALPHA_FUNC=111,
 };
 
 enum {