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[TCP] FRTO: Reverse RETRANS bit clearing logic 

Previously RETRANS bits were cleared on the entry to FRTO. We
postpone that into tcp_enter_frto_loss, which is really the
place were the clearing should be done anyway. This allows
simplification of the logic from a clearing loop to the head skb
clearing only.

Besides, the other changes made in the previous patches to
tcp_use_frto made it impossible for the non-SACKed FRTO to be
entered if other than the head has been rexmitted.

With SACK-enhanced FRTO (and Appendix B), however, there can be
a number retransmissions in flight when RTO expires (same thing
could happen before this patchset also with non-SACK FRTO). To
not introduce any jumpiness into the packet counting during FRTO,
instead of clearing RETRANS bits from skbs during entry, do it
later on.

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 2007-02-21 23:11:57 -08:00 committed by David S. Miller
parent 46d0de4ed9
commit d1a54c6a0a
1 changed files with 23 additions and 12 deletions
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35
net/ipv4/tcp_input.c
View File

@ -1268,7 +1268,11 @@ int tcp_use_frto(struct sock *sk)
/* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
* recovery a bit and use heuristics in tcp_process_frto() to detect if
* the RTO was spurious.
* the RTO was spurious. Only clear SACKED_RETRANS of the head here to
* keep retrans_out counting accurate (with SACK F-RTO, other than head
* may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
* bits are handled if the Loss state is really to be entered (in
* tcp_enter_frto_loss).
*
* Do like tcp_enter_loss() would; when RTO expires the second time it
* does:
@ -1289,17 +1293,13 @@ void tcp_enter_frto(struct sock *sk)
tcp_ca_event(sk, CA_EVENT_FRTO);
}
/* Have to clear retransmission markers here to keep the bookkeeping
* in shape, even though we are not yet in Loss state.
* If something was really lost, it is eventually caught up
* in tcp_enter_frto_loss.
*/
tp->retrans_out = 0;
tp->undo_marker = tp->snd_una;
tp->undo_retrans = 0;
sk_stream_for_retrans_queue(skb, sk) {
skb = skb_peek(&sk->sk_write_queue);
if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
tp->retrans_out -= tcp_skb_pcount(skb);
}
tcp_sync_left_out(tp);
@ -1313,7 +1313,7 @@ void tcp_enter_frto(struct sock *sk)
* which indicates that we should follow the traditional RTO recovery,
* i.e. mark everything lost and do go-back-N retransmission.
*/
static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments)
static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
@ -1322,10 +1322,21 @@ static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments)
tp->sacked_out = 0;
tp->lost_out = 0;
tp->fackets_out = 0;
tp->retrans_out = 0;
sk_stream_for_retrans_queue(skb, sk) {
cnt += tcp_skb_pcount(skb);
TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
/*
* Count the retransmission made on RTO correctly (only when
* waiting for the first ACK and did not get it)...
*/
if ((tp->frto_counter == 1) && !(flag&FLAG_DATA_ACKED)) {
tp->retrans_out += tcp_skb_pcount(skb);
/* ...enter this if branch just for the first segment */
flag |= FLAG_DATA_ACKED;
} else {
TCP_SKB_CB(skb)->sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
}
if (!(TCP_SKB_CB(skb)->sacked&TCPCB_SACKED_ACKED)) {
/* Do not mark those segments lost that were
@ -2550,7 +2561,7 @@ static int tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)
inet_csk(sk)->icsk_retransmits = 0;
if (!before(tp->snd_una, tp->frto_highmark)) {
tcp_enter_frto_loss(sk, tp->frto_counter + 1);
tcp_enter_frto_loss(sk, tp->frto_counter + 1, flag);
return 1;
}
@ -2562,7 +2573,7 @@ static int tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)
return 1;
if (!(flag&FLAG_DATA_ACKED)) {
tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3));
tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3), flag);
return 1;
}