From: Sangtae Ha <sangtae.ha@gmail.com>
Date: Mon, 14 Mar 2011 07:52:18 +0000 (+0000)
Subject: tcp_cubic: fix low utilization of CUBIC with HyStart
X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=b5ccd07337489fa9c9d32e0b628a2168b7953adf;p=openwrt%2Fstaging%2Fblogic.git

tcp_cubic: fix low utilization of CUBIC with HyStart

HyStart sets the initial exit point of slow start.
Suppose that HyStart exits at 0.5BDP in a BDP network and no history exists.
If the BDP of a network is large, CUBIC's initial cwnd growth may be
too conservative to utilize the link.
CUBIC increases the cwnd 20% per RTT in this case.

Signed-off-by: Sangtae Ha <sangtae.ha@gmail.com>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---

diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 7172c129ff19..90d92dd4cf13 100644
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -270,6 +270,13 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
 		ca->cnt = 100 * cwnd;              /* very small increment*/
 	}
 
+	/*
+	 * The initial growth of cubic function may be too conservative
+	 * when the available bandwidth is still unknown.
+	 */
+	if (ca->loss_cwnd == 0 && ca->cnt > 20)
+		ca->cnt = 20;	/* increase cwnd 5% per RTT */
+
 	/* TCP Friendly */
 	if (tcp_friendliness) {
 		u32 scale = beta_scale;