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

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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: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Ilpo Järvinen 2009-02-28 04:44:33 +00:00 committed by David S. Miller
parent d0af4160d1
commit 7363a5b233
1 changed files with 39 additions and 24 deletions
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63
net/ipv4/tcp_input.c
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@ -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