releases/2.6.22.15/tcp-illinois-incorrect-beta-usage.patch

   1 From stable-bounces@linux.kernel.org Mon Dec 10 20:32:29 2007
   2 From: Stephen Hemminger <shemminger@linux-foundation.org>
   3 Date: Tue, 11 Dec 2007 09:39:37 +0800
   4 Subject: TCP: illinois: Incorrect beta usage
   5 To: stable@kernel.org, <davem@davemloft.net>
   6 Message-ID: <E1J1u5x-0002LB-00@gondolin.me.apana.org.au>
   7
   8
   9 From: Stephen Hemminger <shemminger@linux-foundation.org>
  10
  11 [TCP] illinois: Incorrect beta usage
  12
  13 [ Upstream commit: a357dde9df33f28611e6a3d4f88265e39bcc8880 ]
  14
  15 Lachlan Andrew observed that my TCP-Illinois implementation uses the
  16 beta value incorrectly:
  17 The parameter  beta  in the paper specifies the amount to decrease
  18 *by*:  that is, on loss,
  19  W <-  W -  beta*W
  20 but in   tcp_illinois_ssthresh() uses  beta  as the amount
  21 to decrease  *to*: W <- beta*W
  22
  23 This bug makes the Linux TCP-Illinois get less-aggressive on uncongested network,
  24 hurting performance. Note: since the base beta value is .5, it has no
  25 impact on a congested network.
  26
  27 Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
  28 Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
  29 Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
  30
  31 ---
  32  net/ipv4/tcp_illinois.c |    2 +-
  33  1 file changed, 1 insertion(+), 1 deletion(-)
  34
  35 --- a/net/ipv4/tcp_illinois.c
  36 +++ b/net/ipv4/tcp_illinois.c
  37 @@ -300,7 +300,7 @@ static u32 tcp_illinois_ssthresh(struct
  38         struct illinois *ca = inet_csk_ca(sk);
  39
  40         /* Multiplicative decrease */
  41 -       return max((tp->snd_cwnd * ca->beta) >> BETA_SHIFT, 2U);
  42 +       return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->beta) >> BETA_SHIFT), 2U);
  43  }
  44
  45