Messages in this thread Patch in this message | | | Date | Wed, 12 Dec 2007 22:53:32 -0800 | From | Greg KH <> | Subject | [patch 53/60] TCP: illinois: Incorrect beta usage |
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2.6.23-stable review patch. If anyone has any objections, please let us know.
------------------ From: Stephen Hemminger <shemminger@linux-foundation.org>
[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 <shemminger@linux-foundation.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- net/ipv4/tcp_illinois.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/net/ipv4/tcp_illinois.c +++ b/net/ipv4/tcp_illinois.c @@ -298,7 +298,7 @@ static u32 tcp_illinois_ssthresh(struct 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); } --
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