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tcp: remove early retransmit
This patch removes the support of RFC5827 early retransmit (i.e., fast recovery on small inflight with <3 dupacks) because it is subsumed by the new RACK loss detection. More specifically when RACK receives DUPACKs, it'll arm a reordering timer to start fast recovery after a quarter of (min)RTT, hence it covers the early retransmit except RACK does not limit itself to specific inflight or dupack numbers. Signed-off-by: Yuchung Cheng <ycheng@google.com> Signed-off-by: Neal Cardwell <ncardwell@google.com> Acked-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Yuchung Cheng
David S. Miller
parent
840a3cbe89
commit
bec41a11dd
@ -246,21 +246,12 @@ tcp_dsack - BOOLEAN
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Allows TCP to send "duplicate" SACKs.
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tcp_early_retrans - INTEGER
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Enable Early Retransmit (ER), per RFC 5827. ER lowers the threshold
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for triggering fast retransmit when the amount of outstanding data is
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small and when no previously unsent data can be transmitted (such
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that limited transmit could be used). Also controls the use of
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Tail loss probe (TLP) that converts RTOs occurring due to tail
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losses into fast recovery (draft-dukkipati-tcpm-tcp-loss-probe-01).
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Tail loss probe (TLP) converts RTOs occurring due to tail
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losses into fast recovery (draft-ietf-tcpm-rack). Note that
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TLP requires RACK to function properly (see tcp_recovery below)
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Possible values:
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0 disables ER
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1 enables ER
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2 enables ER but delays fast recovery and fast retransmit
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by a fourth of RTT. This mitigates connection falsely
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recovers when network has a small degree of reordering
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(less than 3 packets).
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3 enables delayed ER and TLP.
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4 enables TLP only.
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0 disables TLP
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3 or 4 enables TLP
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Default: 3
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tcp_ecn - INTEGER
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@ -224,8 +224,7 @@ struct tcp_sock {
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repair : 1,
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frto : 1;/* F-RTO (RFC5682) activated in CA_Loss */
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u8 repair_queue;
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u8 do_early_retrans:1,/* Enable RFC5827 early-retransmit */
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syn_data:1, /* SYN includes data */
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u8 syn_data:1, /* SYN includes data */
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syn_fastopen:1, /* SYN includes Fast Open option */
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syn_fastopen_exp:1,/* SYN includes Fast Open exp. option */
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syn_data_acked:1,/* data in SYN is acked by SYN-ACK */
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@ -565,7 +565,6 @@ void tcp_skb_collapse_tstamp(struct sk_buff *skb,
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const struct sk_buff *next_skb);
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/* tcp_input.c */
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void tcp_resume_early_retransmit(struct sock *sk);
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void tcp_rearm_rto(struct sock *sk);
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void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req);
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void tcp_reset(struct sock *sk);
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@ -1037,24 +1036,6 @@ static inline void tcp_enable_fack(struct tcp_sock *tp)
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tp->rx_opt.sack_ok |= TCP_FACK_ENABLED;
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}
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/* TCP early-retransmit (ER) is similar to but more conservative than
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* the thin-dupack feature. Enable ER only if thin-dupack is disabled.
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*/
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static inline void tcp_enable_early_retrans(struct tcp_sock *tp)
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{
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struct net *net = sock_net((struct sock *)tp);
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tp->do_early_retrans = sysctl_tcp_early_retrans &&
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sysctl_tcp_early_retrans < 4 && !sysctl_tcp_thin_dupack &&
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!(sysctl_tcp_recovery & TCP_RACK_LOSS_DETECTION) &&
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net->ipv4.sysctl_tcp_reordering == 3;
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}
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static inline void tcp_disable_early_retrans(struct tcp_sock *tp)
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{
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tp->do_early_retrans = 0;
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}
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static inline unsigned int tcp_left_out(const struct tcp_sock *tp)
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{
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return tp->sacked_out + tp->lost_out;
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@ -215,7 +215,6 @@ int inet_sk_diag_fill(struct sock *sk, struct inet_connection_sock *icsk,
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}
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if (icsk->icsk_pending == ICSK_TIME_RETRANS ||
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icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
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icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
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icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
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r->idiag_timer = 1;
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@ -406,7 +406,6 @@ void tcp_init_sock(struct sock *sk)
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tp->mss_cache = TCP_MSS_DEFAULT;
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tp->reordering = sock_net(sk)->ipv4.sysctl_tcp_reordering;
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tcp_enable_early_retrans(tp);
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tcp_assign_congestion_control(sk);
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tp->tsoffset = 0;
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@ -2477,8 +2476,6 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
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err = -EINVAL;
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else {
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tp->thin_dupack = val;
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if (tp->thin_dupack)
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tcp_disable_early_retrans(tp);
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}
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break;
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@ -904,8 +904,6 @@ static void tcp_update_reordering(struct sock *sk, const int metric,
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tcp_disable_fack(tp);
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}
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if (metric > 0)
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tcp_disable_early_retrans(tp);
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tp->rack.reord = 1;
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}
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@ -2054,30 +2052,6 @@ static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
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return tcp_is_fack(tp) ? tp->fackets_out : tp->sacked_out + 1;
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}
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static bool tcp_pause_early_retransmit(struct sock *sk, int flag)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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unsigned long delay;
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/* Delay early retransmit and entering fast recovery for
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* max(RTT/4, 2msec) unless ack has ECE mark, no RTT samples
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* available, or RTO is scheduled to fire first.
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*/
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if (sysctl_tcp_early_retrans < 2 || sysctl_tcp_early_retrans > 3 ||
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(flag & FLAG_ECE) || !tp->srtt_us)
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return false;
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delay = max(usecs_to_jiffies(tp->srtt_us >> 5),
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msecs_to_jiffies(2));
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if (!time_after(inet_csk(sk)->icsk_timeout, (jiffies + delay)))
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return false;
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inet_csk_reset_xmit_timer(sk, ICSK_TIME_EARLY_RETRANS, delay,
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TCP_RTO_MAX);
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return true;
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}
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/* Linux NewReno/SACK/FACK/ECN state machine.
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* --------------------------------------
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*
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@ -2221,16 +2195,6 @@ static bool tcp_time_to_recover(struct sock *sk, int flag)
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tcp_is_sack(tp) && !tcp_send_head(sk))
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return true;
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/* Trick#6: TCP early retransmit, per RFC5827. To avoid spurious
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* retransmissions due to small network reorderings, we implement
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* Mitigation A.3 in the RFC and delay the retransmission for a short
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* interval if appropriate.
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*/
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if (tp->do_early_retrans && !tp->retrans_out && tp->sacked_out &&
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(tp->packets_out >= (tp->sacked_out + 1) && tp->packets_out < 4) &&
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!tcp_may_send_now(sk))
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return !tcp_pause_early_retransmit(sk, flag);
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return false;
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}
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@ -3050,8 +3014,7 @@ void tcp_rearm_rto(struct sock *sk)
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} else {
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u32 rto = inet_csk(sk)->icsk_rto;
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/* Offset the time elapsed after installing regular RTO */
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if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
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icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
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if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
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icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
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struct sk_buff *skb = tcp_write_queue_head(sk);
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const u32 rto_time_stamp =
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@ -3068,24 +3031,6 @@ void tcp_rearm_rto(struct sock *sk)
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}
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}
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/* This function is called when the delayed ER timer fires. TCP enters
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* fast recovery and performs fast-retransmit.
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*/
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void tcp_resume_early_retransmit(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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tcp_rearm_rto(sk);
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/* Stop if ER is disabled after the delayed ER timer is scheduled */
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if (!tp->do_early_retrans)
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return;
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tcp_enter_recovery(sk, false);
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tcp_update_scoreboard(sk, 1);
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tcp_xmit_retransmit_queue(sk);
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}
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/* If we get here, the whole TSO packet has not been acked. */
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static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
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{
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@ -3651,8 +3596,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
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skb_mstamp_get(&sack_state.ack_time);
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if (icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
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icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
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if (icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
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tcp_rearm_rto(sk);
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if (after(ack, prior_snd_una)) {
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@ -2229,7 +2229,6 @@ static void get_tcp4_sock(struct sock *sk, struct seq_file *f, int i)
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int state;
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if (icsk->icsk_pending == ICSK_TIME_RETRANS ||
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icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
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icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
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icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
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timer_active = 1;
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@ -522,7 +522,6 @@ void tcp_init_metrics(struct sock *sk)
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val = tcp_metric_get(tm, TCP_METRIC_REORDERING);
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if (val && tp->reordering != val) {
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tcp_disable_fack(tp);
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tcp_disable_early_retrans(tp);
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tp->reordering = val;
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}
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@ -468,7 +468,6 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
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newtp->sacked_out = 0;
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newtp->fackets_out = 0;
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newtp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
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tcp_enable_early_retrans(newtp);
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newtp->tlp_high_seq = 0;
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newtp->lsndtime = treq->snt_synack.stamp_jiffies;
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newsk->sk_txhash = treq->txhash;
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@ -76,10 +76,8 @@ static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
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tp->snd_nxt = TCP_SKB_CB(skb)->end_seq;
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tp->packets_out += tcp_skb_pcount(skb);
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if (!prior_packets || icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
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icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
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if (!prior_packets || icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)
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tcp_rearm_rto(sk);
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}
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NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPORIGDATASENT,
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tcp_skb_pcount(skb));
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@ -2289,8 +2287,6 @@ bool tcp_schedule_loss_probe(struct sock *sk)
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u32 timeout, tlp_time_stamp, rto_time_stamp;
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u32 rtt = usecs_to_jiffies(tp->srtt_us >> 3);
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if (WARN_ON(icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS))
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return false;
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/* No consecutive loss probes. */
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if (WARN_ON(icsk->icsk_pending == ICSK_TIME_LOSS_PROBE)) {
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tcp_rearm_rto(sk);
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@ -2309,8 +2305,9 @@ bool tcp_schedule_loss_probe(struct sock *sk)
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/* Schedule a loss probe in 2*RTT for SACK capable connections
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* in Open state, that are either limited by cwnd or application.
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*/
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if (sysctl_tcp_early_retrans < 3 || !tp->packets_out ||
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!tcp_is_sack(tp) || inet_csk(sk)->icsk_ca_state != TCP_CA_Open)
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if ((sysctl_tcp_early_retrans != 3 && sysctl_tcp_early_retrans != 4) ||
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!tp->packets_out || !tcp_is_sack(tp) ||
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icsk->icsk_ca_state != TCP_CA_Open)
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return false;
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if ((tp->snd_cwnd > tcp_packets_in_flight(tp)) &&
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@ -566,9 +566,6 @@ void tcp_write_timer_handler(struct sock *sk)
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case ICSK_TIME_REO_TIMEOUT:
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tcp_rack_reo_timeout(sk);
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break;
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case ICSK_TIME_EARLY_RETRANS:
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tcp_resume_early_retransmit(sk);
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break;
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case ICSK_TIME_LOSS_PROBE:
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tcp_send_loss_probe(sk);
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break;
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@ -1745,7 +1745,6 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
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srcp = ntohs(inet->inet_sport);
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if (icsk->icsk_pending == ICSK_TIME_RETRANS ||
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icsk->icsk_pending == ICSK_TIME_EARLY_RETRANS ||
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icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
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icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
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timer_active = 1;
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