Messages in this thread Patch in this message | | | Date | Tue, 5 Apr 2005 09:47:59 -0700 | From | Greg KH <> | Subject | [07/08] [TCP] Fix BIC congestion avoidance algorithm error |
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-stable review patch. If anyone has any objections, please let us know.
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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; - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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