[TCP] tcp_highspeed: Fix problem observed by Xiaoliang (David) Wei

When snd_cwnd is smaller than 38 and the connection is in
congestion avoidance phase (snd_cwnd > snd_ssthresh), the snd_cwnd
seems to stop growing.

The additive increase was confused because C array's are 0 based.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/ipv4/tcp_highspeed.c b/net/ipv4/tcp_highspeed.c
index b72fa55dfb84..ba7c63ca5bb1 100644
--- a/net/ipv4/tcp_highspeed.c
+++ b/net/ipv4/tcp_highspeed.c
@@ -135,7 +135,8 @@ static void hstcp_cong_avoid(struct sock *sk, u32 adk, u32 rtt,
 
                 /* Do additive increase */
                 if (tp->snd_cwnd < tp->snd_cwnd_clamp) {
-                        tp->snd_cwnd_cnt += ca->ai;
+                        /* cwnd = cwnd + a(w) / cwnd */
+                        tp->snd_cwnd_cnt += ca->ai + 1;
                         if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
                                 tp->snd_cwnd_cnt -= tp->snd_cwnd;
                                 tp->snd_cwnd++;