[PATCH TCP 3/4] Adjust alpha according to RTT timing

[Baruch Even <baruch@xxxxxxxxx>]

This is another H-TCP layer patch. This patch adds an rtt scaling to the alpha
parameter. This increases alpha for large distance networks.

Signed-Off-By: Baruch Even <baruch@xxxxxxxxx>

---
 net/ipv4/tcp_htcp.c |   13 +++++++++++++
 1 files changed, 13 insertions(+)

Index: 2.6.11-stephen-htcp/net/ipv4/tcp_htcp.c
===================================================================
--- 2.6.11-stephen-htcp.orig/net/ipv4/tcp_htcp.c
+++ 2.6.11-stephen-htcp/net/ipv4/tcp_htcp.c
@@ -12,6 +12,10 @@
 #define BETA_MIN       (1<<6)  /* 0.5 with shift << 7 */
 #define BETA_MAX       102     /* 0.8 with shift << 7 */
 
+static int use_rtt_scaling = 1;
+module_param(use_rtt_scaling, int, 0644);
+MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling");
+
 struct htcp_ca {
        u32     alpha;          /* Fixed point arith, << 7 */
        u32     beta;           /* Fixed point arith, << 7 */
@@ -85,6 +89,15 @@ static inline void htcp_alpha_update(str
        ca->alpha = 2*factor*((1<<7)-ca->beta);
        if (!ca->alpha)
                ca->alpha = 1<<7;
+
+       if (use_rtt_scaling && minRTT) {
+               u32 scale;
+               scale = (HZ<<3)/(10*minRTT);
+               scale = min(max(scale, 1U<<2), 10U<<3); /* clamping ratio to 
interval [0.5,10]<<3 */
+               ca->alpha = (ca->alpha<<3)/scale;
+               if (!ca->alpha)
+                       ca->alpha = 1<<7;
+       }
 }
 
 /* After we have the rtt data to calculate beta, we'd still prefer to wait one