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tcp: fix the timid additive increase on stretch ACKs

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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 <eyalpe@mellanox.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Neal Cardwell 2015-01-28 20:01:36 -05:00 committed by David S. Miller
parent e73ebb0881
commit 814d488c61
1 changed files with 9 additions and 6 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

15
net/ipv4/tcp_cong.c
View file

@ -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);