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tcp: fix ABC in tcp_slow_start() 

When/if sysctl_tcp_abc > 1, we expect to increase cwnd by 2 if the
received ACK acknowledges more than 2*MSS bytes, in tcp_slow_start()

Problem is this RFC 3465 statement is not correctly coded, as
the while () loop increases snd_cwnd one by one.

Add a new variable to avoid this off-by one error.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Nandita Dukkipati <nanditad@google.com>
Cc: John Heffner <johnwheffner@gmail.com>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2012-07-20 05:02:33 +00:00 committed by David S. Miller
parent 5815d5e7aa
commit 9dc274151a
1 changed files with 3 additions and 2 deletions
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5
net/ipv4/tcp_cong.c
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@ -307,6 +307,7 @@ EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
void tcp_slow_start(struct tcp_sock *tp)
{
int cnt; /* increase in packets */
unsigned int delta = 0;
/* RFC3465: ABC Slow start
* Increase only after a full MSS of bytes is acked
@ -333,9 +334,9 @@ void tcp_slow_start(struct tcp_sock *tp)
tp->snd_cwnd_cnt += cnt;
while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
tp->snd_cwnd_cnt -= tp->snd_cwnd;
if (tp->snd_cwnd < tp->snd_cwnd_clamp)
tp->snd_cwnd++;
delta++;
}
tp->snd_cwnd = min(tp->snd_cwnd + delta, tp->snd_cwnd_clamp);
}
EXPORT_SYMBOL_GPL(tcp_slow_start);