[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 <shemminger@linux-foundation.org> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
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@ -298,7 +298,7 @@ static u32 tcp_illinois_ssthresh(struct sock *sk)
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struct illinois *ca = inet_csk_ca(sk);
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struct illinois *ca = inet_csk_ca(sk);
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/* Multiplicative decrease */
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/* Multiplicative decrease */
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return max((tp->snd_cwnd * ca->beta) >> BETA_SHIFT, 2U);
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return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->beta) >> BETA_SHIFT), 2U);
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}
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}
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