tcp: fix ABC in tcp_slow_start() (9dc27415) · Commits · 戴 / test

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>

net/ipv4/tcp_cong.c

+3 −2

Original line number	Original line	Diff line number	Diff line
	@@ -307,6 +307,7 @@ EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
	void tcp_slow_start(struct tcp_sock *tp)		void tcp_slow_start(struct tcp_sock *tp)
	{		{
	int cnt; /* increase in packets */		int cnt; /* increase in packets */
			unsigned int delta = 0;

	/* RFC3465: ABC Slow start		/* RFC3465: ABC Slow start
	* Increase only after a full MSS of bytes is acked		* 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;		tp->snd_cwnd_cnt += cnt;
	while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {		while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
	tp->snd_cwnd_cnt -= tp->snd_cwnd;		tp->snd_cwnd_cnt -= tp->snd_cwnd;
	if (tp->snd_cwnd < tp->snd_cwnd_clamp)		delta++;
	tp->snd_cwnd++;
	}		}
			tp->snd_cwnd = min(tp->snd_cwnd + delta, tp->snd_cwnd_clamp);
	}		}
	EXPORT_SYMBOL_GPL(tcp_slow_start);		EXPORT_SYMBOL_GPL(tcp_slow_start);

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