Commit 5628adf1 authored Nov 16, 2011 by Neal Cardwell Committed by David S. Miller Nov 27, 2011

tcp: use DSACKs that arrive when packets_out is 0



The bug: Senders ignored DSACKs after recovery when there were no
outstanding packets (a common scenario for HTTP servers).

The change: when there are no outstanding packets (the "no_queue" goto
label), call tcp_fastretrans_alert() in order to use DSACKs to undo
congestion window reductions.

Other patches in this series will provide other changes that are
necessary to fully fix this problem.

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 7d2b55f8

net/ipv4/tcp_input.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -3788,6 +3788,10 @@ static int tcp_ack(struct sock sk, const struct sk_buff skb, int flag)
		return 1;

		no_queue:
		/* If data was DSACKed, see if we can undo a cwnd reduction. */
		if (flag & FLAG_DSACKING_ACK)
		tcp_fastretrans_alert(sk, pkts_acked, newly_acked_sacked,
		is_dupack, flag);
		/* If this ack opens up a zero window, clear backoff. It was
		* being used to time the probes, and is probably far higher than
		* it needs to be for normal retransmission.