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tcp_cubic: fix low utilization of CUBIC with HyStart

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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>
This commit is contained in:
Sangtae Ha 2011-03-14 07:52:18 +00:00 committed by David S. Miller
parent 2b4636a5f8
commit b5ccd07337
1 changed files with 7 additions and 0 deletions
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7
net/ipv4/tcp_cubic.c
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@ -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;