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tcp: do not purge SACK scoreboard on first RTO
Keeping the SACK scoreboard intact after the first RTO and retransmitting all data anew only on subsequent RTOs allows a more timely and efficient loss recovery under many adverse cirumstances. Reviewed By: tuexen, #transport MFC after: 10 weeks Sponsored by: NetApp, Inc. Differential Revision: https://reviews.freebsd.org/D42906
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@ -439,7 +439,10 @@ cc_cong_signal(struct tcpcb *tp, struct tcphdr *th, uint32_t type)
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case CC_RTO:
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tp->t_dupacks = 0;
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tp->t_bytes_acked = 0;
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EXIT_RECOVERY(tp->t_flags);
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if ((tp->t_rxtshift > 1) ||
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!((tp->t_flags & TF_SACK_PERMIT) &&
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(!TAILQ_EMPTY(&tp->snd_holes))))
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EXIT_RECOVERY(tp->t_flags);
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if (tp->t_flags2 & TF2_ECN_PERMIT)
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tp->t_flags2 |= TF2_ECN_SND_CWR;
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break;
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@ -908,6 +908,25 @@ tcp_free_sackholes(struct tcpcb *tp)
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("tp->sackhint.nexthole == NULL"));
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}
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/*
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* Resend all the currently existing SACK holes of
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* the scoreboard. This is in line with the Errata to
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* RFC 2018, which allows the use of SACK data past
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* an RTO to good effect typically.
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*/
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void
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tcp_resend_sackholes(struct tcpcb *tp)
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{
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struct sackhole *p;
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INP_WLOCK_ASSERT(tptoinpcb(tp));
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TAILQ_FOREACH(p, &tp->snd_holes, scblink) {
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p->rxmit = p->start;
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}
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tp->sackhint.nexthole = TAILQ_FIRST(&tp->snd_holes);
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tp->sackhint.sack_bytes_rexmit = 0;
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}
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/*
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* Partial ack handling within a sack recovery episode. Keeping this very
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* simple for now. When a partial ack is received, force snd_cwnd to a value
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@ -559,7 +559,6 @@ tcp_timer_rexmt(struct tcpcb *tp)
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TCP_PROBE2(debug__user, tp, PRU_SLOWTIMO);
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CURVNET_SET(inp->inp_vnet);
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tcp_free_sackholes(tp);
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if (tp->t_fb->tfb_tcp_rexmit_tmr) {
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/* The stack has a timer action too. */
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(*tp->t_fb->tfb_tcp_rexmit_tmr)(tp);
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@ -619,8 +618,11 @@ tcp_timer_rexmt(struct tcpcb *tp)
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* the retransmitted packet's to_tsval to by tcp_output
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*/
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tp->t_flags |= TF_PREVVALID;
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} else
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tcp_resend_sackholes(tp);
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} else {
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tp->t_flags &= ~TF_PREVVALID;
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tcp_free_sackholes(tp);
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}
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TCPSTAT_INC(tcps_rexmttimeo);
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if ((tp->t_state == TCPS_SYN_SENT) ||
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(tp->t_state == TCPS_SYN_RECEIVED))
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@ -1499,6 +1499,7 @@ struct sackhole *tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt);
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void tcp_do_prr_ack(struct tcpcb *, struct tcphdr *, struct tcpopt *, sackstatus_t);
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void tcp_lost_retransmission(struct tcpcb *, struct tcphdr *);
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void tcp_sack_partialack(struct tcpcb *, struct tcphdr *);
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void tcp_resend_sackholes(struct tcpcb *tp);
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void tcp_free_sackholes(struct tcpcb *tp);
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void tcp_sack_lost_retransmission(struct tcpcb *, struct tcphdr *);
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int tcp_newreno(struct tcpcb *, struct tcphdr *);
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