From b5ccd07337489fa9c9d32e0b628a2168b7953adf Mon Sep 17 00:00:00 2001 From: Sangtae Ha Date: Mon, 14 Mar 2011 07:52:18 +0000 Subject: [PATCH] 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 Acked-by: Stephen Hemminger Signed-off-by: David S. Miller --- net/ipv4/tcp_cubic.c | 7 +++++++ 1 file changed, 7 insertions(+) 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;