From: Stephen Hemminger Date: Tue, 11 Dec 2007 01:39:37 +0000 (+0800) Subject: TCP: illinois: Incorrect beta usage X-Git-Tag: v2.6.23.10~8 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=931c8cbed400a72c0da0756594154504b4634a2a;p=thirdparty%2Fkernel%2Fstable.git TCP: illinois: Incorrect beta usage [TCP] illinois: Incorrect beta usage [ Upstream commit: a357dde9df33f28611e6a3d4f88265e39bcc8880 ] 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 Signed-off-by: Greg Kroah-Hartman --- diff --git a/net/ipv4/tcp_illinois.c b/net/ipv4/tcp_illinois.c index 64f1cbaf96e8a..5aa5f5496d6d7 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); }