Commit c940587b authored by Xiaoliang (David) Wei's avatar Xiaoliang (David) Wei Committed by David S. Miller

[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: default avatarXiaoliang (David) Wei <davidwei79@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 5c81833c
...@@ -266,9 +266,7 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, ...@@ -266,9 +266,7 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack,
*/ */
diff = (old_wnd << V_PARAM_SHIFT) - target_cwnd; diff = (old_wnd << V_PARAM_SHIFT) - target_cwnd;
if (tp->snd_cwnd <= tp->snd_ssthresh) { if (diff > gamma && tp->snd_ssthresh > 2 ) {
/* Slow start. */
if (diff > gamma) {
/* Going too fast. Time to slow down /* Going too fast. Time to slow down
* and switch to congestion avoidance. * and switch to congestion avoidance.
*/ */
...@@ -285,7 +283,8 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, ...@@ -285,7 +283,8 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack,
(target_cwnd >> (target_cwnd >>
V_PARAM_SHIFT)+1); V_PARAM_SHIFT)+1);
} } else if (tp->snd_cwnd <= tp->snd_ssthresh) {
/* Slow start. */
tcp_slow_start(tp); tcp_slow_start(tp);
} else { } else {
/* Congestion avoidance. */ /* Congestion avoidance. */
......
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