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| author | Xiaoliang (David) Wei <davidwei79@gmail.com> | 2007-10-29 20:24:36 -0700 |
|---|---|---|
| committer | David S. Miller <davem@sunset.davemloft.net> | 2007-10-29 22:37:25 -0700 |
| commit | c940587bf603b4295a7f5e9ff8fed123368a1ef7 (patch) | |
| tree | eb442c1632039667cdad235cdcc29cb5ca2976fc /net/ipv4/tcp_vegas.c | |
| parent | 5c81833c2f74304142be6dde5688bf444316da21 (diff) | |
| download | lwn-c940587bf603b4295a7f5e9ff8fed123368a1ef7.tar.gz lwn-c940587bf603b4295a7f5e9ff8fed123368a1ef7.zip | |
[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>
Diffstat (limited to 'net/ipv4/tcp_vegas.c')
| -rw-r--r-- | net/ipv4/tcp_vegas.c | 37 |
1 files changed, 18 insertions, 19 deletions
diff --git a/net/ipv4/tcp_vegas.c b/net/ipv4/tcp_vegas.c index b49dedcda52d..007304e99842 100644 --- a/net/ipv4/tcp_vegas.c +++ b/net/ipv4/tcp_vegas.c @@ -266,26 +266,25 @@ 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) { - /* Going too fast. Time to slow down - * and switch to congestion avoidance. - */ - tp->snd_ssthresh = 2; - - /* Set cwnd to match the actual rate - * exactly: - * cwnd = (actual rate) * baseRTT - * Then we add 1 because the integer - * truncation robs us of full link - * utilization. - */ - tp->snd_cwnd = min(tp->snd_cwnd, - (target_cwnd >> - V_PARAM_SHIFT)+1); + if (diff > gamma && tp->snd_ssthresh > 2 ) { + /* Going too fast. Time to slow down + * and switch to congestion avoidance. + */ + tp->snd_ssthresh = 2; + + /* Set cwnd to match the actual rate + * exactly: + * cwnd = (actual rate) * baseRTT + * Then we add 1 because the integer + * truncation robs us of full link + * utilization. + */ + tp->snd_cwnd = min(tp->snd_cwnd, + (target_cwnd >> + V_PARAM_SHIFT)+1); - } + } else if (tp->snd_cwnd <= tp->snd_ssthresh) { + /* Slow start. */ tcp_slow_start(tp); } else { /* Congestion avoidance. */ |