| From stable-bounces@linux.kernel.org Wed Mar 23 10:50:18 2005 |
| Date: Wed, 23 Mar 2005 10:48:24 -0800 |
| From: "David S. Miller" <davem@davemloft.net> |
| To: stable@kernel.org |
| Subject: [PATCH][TCP] Fix BIC congestion avoidance algorithm error |
| |
| Since BIC is the default congestion control algorithm |
| enabled in every 2.6.x kernel out there, fixing errors |
| in it becomes quite critical. |
| |
| A flaw in the loss handling caused it to not perform |
| the binary search regimen of the BIC algorithm |
| properly. |
| |
| The fix below from Stephen Hemminger has been heavily |
| verified. |
| |
| [TCP]: BIC not binary searching correctly |
| |
| While redoing BIC for the split up version, I discovered that the existing |
| 2.6.11 code doesn't really do binary search. It ends up being just a slightly |
| modified version of Reno. See attached graphs to see the effect over simulated |
| 1mbit environment. |
| |
| The problem is that BIC is supposed to reset the cwnd to the last loss value |
| rather than ssthresh when loss is detected. The correct code (from the BIC |
| TCP code for Web100) is in this patch. |
| |
| Signed-off-by: Stephen Hemminger <shemminger@osdl.org> |
| Signed-off-by: David S. Miller <davem@davemloft.net> |
| Signed-off-by: Chris Wright <chrisw@osdl.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> |
| |
| --- 1.92/net/ipv4/tcp_input.c 2005-02-22 10:45:31 -08:00 |
| +++ edited/net/ipv4/tcp_input.c 2005-03-23 10:55:18 -08:00 |
| @@ -1653,7 +1653,10 @@ |
| static void tcp_undo_cwr(struct tcp_sock *tp, int undo) |
| { |
| if (tp->prior_ssthresh) { |
| - tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1); |
| + if (tcp_is_bic(tp)) |
| + tp->snd_cwnd = max(tp->snd_cwnd, tp->bictcp.last_max_cwnd); |
| + else |
| + tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh<<1); |
| |
| if (undo && tp->prior_ssthresh > tp->snd_ssthresh) { |
| tp->snd_ssthresh = tp->prior_ssthresh; |
| |
