Commit d1a54c6a authored by Ilpo Järvinen's avatar Ilpo Järvinen Committed by David S. Miller
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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: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 46d0de4e

net/ipv4/tcp_input.c

+23 −12
Original line number Diff line number Diff line
@@ -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;

	}

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