From 814d488c61260521b1b3cc97063700a5a6667c8f Mon Sep 17 00:00:00 2001 From: Neal Cardwell Date: Wed, 28 Jan 2015 20:01:36 -0500 Subject: [PATCH] tcp: fix the timid additive increase on stretch ACKs tcp_cong_avoid_ai() was too timid (snd_cwnd increased too slowly) on "stretch ACKs" -- cases where the receiver ACKed more than 1 packet in a single ACK. For example, suppose w is 10 and we get a stretch ACK for 20 packets, so acked is 20. We ought to increase snd_cwnd by 2 (since acked/w = 20/10 = 2), but instead we were only increasing cwnd by 1. This patch fixes that behavior. Reported-by: Eyal Perry Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/tcp_cong.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c index 6826017c12d1..faaee5338bea 100644 --- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c @@ -304,16 +304,19 @@ u32 tcp_slow_start(struct tcp_sock *tp, u32 acked) } EXPORT_SYMBOL_GPL(tcp_slow_start); -/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */ +/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w), + * for every packet that was ACKed. + */ void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked) { + tp->snd_cwnd_cnt += acked; if (tp->snd_cwnd_cnt >= w) { - if (tp->snd_cwnd < tp->snd_cwnd_clamp) - tp->snd_cwnd++; - tp->snd_cwnd_cnt = 0; - } else { - tp->snd_cwnd_cnt += acked; + u32 delta = tp->snd_cwnd_cnt / w; + + tp->snd_cwnd_cnt -= delta * w; + tp->snd_cwnd += delta; } + tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp); } EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);