From a357dde9df33f28611e6a3d4f88265e39bcc8880 Mon Sep 17 00:00:00 2001 From: Stephen Hemminger Date: Fri, 30 Nov 2007 01:10:55 +1100 Subject: [PATCH] [TCP] illinois: Incorrect beta usage Lachlan Andrew observed that my TCP-Illinois implementation uses the beta value incorrectly: The parameter beta in the paper specifies the amount to decrease *by*: that is, on loss, W <- W - beta*W but in tcp_illinois_ssthresh() uses beta as the amount to decrease *to*: W <- beta*W This bug makes the Linux TCP-Illinois get less-aggressive on uncongested network, hurting performance. Note: since the base beta value is .5, it has no impact on a congested network. Signed-off-by: Stephen Hemminger Signed-off-by: Herbert Xu --- net/ipv4/tcp_illinois.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/ipv4/tcp_illinois.c b/net/ipv4/tcp_illinois.c index 64f1cbaf96e..5aa5f5496d6 100644 --- a/net/ipv4/tcp_illinois.c +++ b/net/ipv4/tcp_illinois.c @@ -298,7 +298,7 @@ static u32 tcp_illinois_ssthresh(struct sock *sk) struct illinois *ca = inet_csk_ca(sk); /* Multiplicative decrease */ - return max((tp->snd_cwnd * ca->beta) >> BETA_SHIFT, 2U); + return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->beta) >> BETA_SHIFT), 2U); }