Gitweb:     
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=1e757f9996114f713a79d3fbcd08739efcfc5c34
Commit:     1e757f9996114f713a79d3fbcd08739efcfc5c34
Parent:     143cf35324548df54563b19d0444e0fe170027f8
Author:     Ilpo Järvinen <[EMAIL PROTECTED]>
AuthorDate: Mon Jul 30 19:48:37 2007 -0700
Committer:  David S. Miller <[EMAIL PROTECTED]>
CommitDate: Tue Jul 31 02:28:30 2007 -0700

    [TCP]: Fix ratehalving with bidirectional flows
    
    Actually, the ratehalving seems to work too well, as cwnd is
    reduced on every second ACK even though the packets in flight
    remains unchanged. Recoveries in a bidirectional flows suffer
    quite badly because of this, both NewReno and SACK are affected.
    
    After this patch, rate halving is performed for ACK only if
    packets in flight was supposedly changed too.
    
    Signed-off-by: Ilpo Järvinen <[EMAIL PROTECTED]>
    Signed-off-by: David S. Miller <[EMAIL PROTECTED]>
---
 net/ipv4/tcp_input.c |   21 ++++++++++++---------
 1 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 4b255fe..41163dd 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1851,19 +1851,22 @@ static inline u32 tcp_cwnd_min(const struct sock *sk)
 }
 
 /* Decrease cwnd each second ack. */
-static void tcp_cwnd_down(struct sock *sk)
+static void tcp_cwnd_down(struct sock *sk, int flag)
 {
        struct tcp_sock *tp = tcp_sk(sk);
        int decr = tp->snd_cwnd_cnt + 1;
 
-       tp->snd_cwnd_cnt = decr&1;
-       decr >>= 1;
+       if ((flag&FLAG_FORWARD_PROGRESS) ||
+           (IsReno(tp) && !(flag&FLAG_NOT_DUP))) {
+               tp->snd_cwnd_cnt = decr&1;
+               decr >>= 1;
 
-       if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
-               tp->snd_cwnd -= decr;
+               if (decr && tp->snd_cwnd > tcp_cwnd_min(sk))
+                       tp->snd_cwnd -= decr;
 
-       tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
-       tp->snd_cwnd_stamp = tcp_time_stamp;
+               tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp)+1);
+               tp->snd_cwnd_stamp = tcp_time_stamp;
+       }
 }
 
 /* Nothing was retransmitted or returned timestamp is less
@@ -2060,7 +2063,7 @@ static void tcp_try_to_open(struct sock *sk, int flag)
                }
                tcp_moderate_cwnd(tp);
        } else {
-               tcp_cwnd_down(sk);
+               tcp_cwnd_down(sk, flag);
        }
 }
 
@@ -2260,7 +2263,7 @@ tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
 
        if (is_dupack || tcp_head_timedout(sk))
                tcp_update_scoreboard(sk);
-       tcp_cwnd_down(sk);
+       tcp_cwnd_down(sk, flag);
        tcp_xmit_retransmit_queue(sk);
 }
 
-
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