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 <[EMAIL PROTECTED]>
--- a/net/ipv4/tcp_illinois.c 2007-08-18 07:50:15.000000000 -0700
+++ b/net/ipv4/tcp_illinois.c 2007-11-28 15:39:04.000000000 -0800
@@ -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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