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Commit 814d488c authored by Neal Cardwell's avatar Neal Cardwell Committed by David S. Miller
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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: default avatarEyal Perry <eyalpe@mellanox.com>
Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent e73ebb08

net/ipv4/tcp_cong.c

+9 −6
Original line number Original line Diff line number Diff line
@@ -304,16 +304,19 @@ u32 tcp_slow_start(struct tcp_sock *tp, u32 acked) 
}

}

EXPORT_SYMBOL_GPL(tcp_slow_start);

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)

void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 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;

	tp->snd_cwnd_cnt += acked;

	if (tp->snd_cwnd_cnt >= w) {

		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);

EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);