Commit c940587b authored Oct 29, 2007 by Xiaoliang (David) Wei Committed by David S. Miller Oct 29, 2007

[TCP] vegas: Fix a bug in disabling slow start by gamma parameter.

TCP Vegas implementation has a bug in the process of disabling
slow-start with gamma parameter. The bug may lead to extreme
unfairness in the presence of early packet loss. See details in:
http://www.cs.caltech.edu/~weixl/technical/ns2linux/known_linux/index.html#vegas

Switch the order of "if (tp->snd_cwnd <= tp->snd_ssthresh)" statement
and "if (diff > gamma)" statement to eliminate the problem.

Signed-off-by: Xiaoliang (David) Wei <davidwei79@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 5c81833c

net/ipv4/tcp_vegas.c

+18 −19

Original line number	Diff line number	Diff line
		@@ -266,9 +266,7 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack,
		*/
		diff = (old_wnd << V_PARAM_SHIFT) - target_cwnd;

		if (tp->snd_cwnd <= tp->snd_ssthresh) {
		/* Slow start. */
		if (diff > gamma) {
		if (diff > gamma && tp->snd_ssthresh > 2 ) {
		/* Going too fast. Time to slow down
		* and switch to congestion avoidance.
		*/
		@@ -285,7 +283,8 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack,
		(target_cwnd >>
		V_PARAM_SHIFT)+1);

		}
		} else if (tp->snd_cwnd <= tp->snd_ssthresh) {
		/* Slow start. */
		tcp_slow_start(tp);
		} else {
		/* Congestion avoidance. */