Commit 7487c48c authored by Ilpo Järvinen's avatar Ilpo Järvinen Committed by David S. Miller
Browse files

[TCP] FRTO: Consecutive RTOs keep prior_ssthresh and ssthresh 



In case a latency spike causes more than one RTO, the later should not
cause the already reduced ssthresh to propagate into the prior_ssthresh
since FRTO declares all such RTOs spurious at once or none of them. In
treating of ssthresh, we mimic what tcp_enter_loss() does.

The previous state (in frto_counter) must be available until we have
checked it in tcp_enter_frto(), and also ACK information flag in
process_frto().

Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 30935cf4

net/ipv4/tcp_input.c

+14 −6
Original line number Diff line number Diff line
@@ -1252,6 +1252,10 @@ int tcp_use_frto(const 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.

 *

 * Do like tcp_enter_loss() would; when RTO expires the second time it

 * does:

 *  "Reduce ssthresh if it has not yet been made inside this window."

 */

void tcp_enter_frto(struct sock *sk)

{
@@ -1259,11 +1263,10 @@ void tcp_enter_frto(struct sock *sk) 
	struct tcp_sock *tp = tcp_sk(sk);

	struct sk_buff *skb;



	tp->frto_counter = 1;



	if (icsk->icsk_ca_state <= TCP_CA_Disorder ||

	if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||

	    tp->snd_una == tp->high_seq ||

	    (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {

	    ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&

	     !icsk->icsk_retransmits)) {

		tp->prior_ssthresh = tcp_current_ssthresh(sk);

		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);

		tcp_ca_event(sk, CA_EVENT_FRTO);
@@ -1285,6 +1288,7 @@ void tcp_enter_frto(struct sock *sk) 


	tcp_set_ca_state(sk, TCP_CA_Open);

	tp->frto_highmark = tp->snd_nxt;

	tp->frto_counter = 1;

}



/* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
@@ -2513,12 +2517,16 @@ static void tcp_conservative_spur_to_response(struct tcp_sock *tp) 
 *     to prove that the RTO is indeed spurious. It transfers the control

 *     from F-RTO to the conventional RTO recovery

 */

static void tcp_process_frto(struct sock *sk, u32 prior_snd_una)

static void tcp_process_frto(struct sock *sk, u32 prior_snd_una, int flag)

{

	struct tcp_sock *tp = tcp_sk(sk);



	tcp_sync_left_out(tp);



	/* Duplicate the behavior from Loss state (fastretrans_alert) */

	if (flag&FLAG_DATA_ACKED)

		inet_csk(sk)->icsk_retransmits = 0;



	if (tp->snd_una == prior_snd_una ||

	    !before(tp->snd_una, tp->frto_highmark)) {

		tcp_enter_frto_loss(sk);
@@ -2607,7 +2615,7 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag) 
	flag |= tcp_clean_rtx_queue(sk, &seq_rtt);



	if (tp->frto_counter)

		tcp_process_frto(sk, prior_snd_una);

		tcp_process_frto(sk, prior_snd_una, flag);



	if (tcp_ack_is_dubious(sk, flag)) {

		/* Advance CWND, if state allows this. */

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