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[TCP] FRTO: Consecutive RTOs keep prior_ssthresh and ssthresh

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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: 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 23:02:30 -08:00 committed by David S. Miller
parent 30935cf4f9
commit 7487c48c4f
1 changed files with 14 additions and 6 deletions
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20
net/ipv4/tcp_input.c
View file

@ -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. */