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Commit 7363a5b2 authored by Ilpo Järvinen's avatar Ilpo Järvinen Committed by David S. Miller
Browse files

tcp: separate timeout marking loop to it's own function 



Some comment about its current state added. So far I have
seen very few cases where the thing is actually useful,
usually just marginally (though admittedly I don't usually
see top of window losses where it seems possible that there
could be some gain), instead, more often the cases suffer
from L-marking spike which is certainly not desirable
(I'll bury improving it to my todo list, but on a low
prio position).

Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent d0af4160

net/ipv4/tcp_input.c

+39 −24
Original line number Diff line number Diff line
@@ -2461,6 +2461,44 @@ static int tcp_time_to_recover(struct sock *sk) 
	return 0;

}



/* New heuristics: it is possible only after we switched to restart timer

 * each time when something is ACKed. Hence, we can detect timed out packets

 * during fast retransmit without falling to slow start.

 *

 * Usefulness of this as is very questionable, since we should know which of

 * the segments is the next to timeout which is relatively expensive to find

 * in general case unless we add some data structure just for that. The

 * current approach certainly won't find the right one too often and when it

 * finally does find _something_ it usually marks large part of the window

 * right away (because a retransmission with a larger timestamp blocks the

 * loop from advancing). -ij

 */

static void tcp_timeout_skbs(struct sock *sk)

{

	struct tcp_sock *tp = tcp_sk(sk);

	struct sk_buff *skb;



	if (!tcp_is_fack(tp) || !tcp_head_timedout(sk))

		return;



	skb = tp->scoreboard_skb_hint;

	if (tp->scoreboard_skb_hint == NULL)

		skb = tcp_write_queue_head(sk);



	tcp_for_write_queue_from(skb, sk) {

		if (skb == tcp_send_head(sk))

			break;

		if (!tcp_skb_timedout(sk, skb))

			break;



		tcp_skb_mark_lost(tp, skb);

	}



	tp->scoreboard_skb_hint = skb;



	tcp_verify_left_out(tp);

}



/* Mark head of queue up as lost. With RFC3517 SACK, the packets is

 * is against sacked "cnt", otherwise it's against facked "cnt"

 */
@@ -2533,30 +2571,7 @@ static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit) 
		tcp_mark_head_lost(sk, sacked_upto);

	}



	/* New heuristics: it is possible only after we switched

	 * to restart timer each time when something is ACKed.

	 * Hence, we can detect timed out packets during fast

	 * retransmit without falling to slow start.

	 */

	if (tcp_is_fack(tp) && tcp_head_timedout(sk)) {

		struct sk_buff *skb;



		skb = tp->scoreboard_skb_hint ? tp->scoreboard_skb_hint

			: tcp_write_queue_head(sk);



		tcp_for_write_queue_from(skb, sk) {

			if (skb == tcp_send_head(sk))

				break;

			if (!tcp_skb_timedout(sk, skb))

				break;



			tcp_skb_mark_lost(tp, skb);

		}



		tp->scoreboard_skb_hint = skb;



		tcp_verify_left_out(tp);

	}

	tcp_timeout_skbs(sk);

}



/* CWND moderation, preventing bursts due to too big ACKs