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When SYN or SYN/ACK had to be retransmitted RFC5681 requires us to
reduce the initial CWND to one segment. This reduction got lost some time ago due to a change in initialization ordering. Additionally in tcp_timer_rexmt() avoid entering fast recovery when we're still in TCPS_SYN_SENT state. MFC after: 2 weeks
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=242250
@ -345,10 +345,16 @@ cc_conn_init(struct tcpcb *tp)
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/*
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* Set the initial slow-start flight size.
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*
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* RFC3390 says only do this if SYN or SYN/ACK didn't got lost.
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* XXX: We currently check only in syncache_socket for that.
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* RFC5681 Section 3.1 specifies the default conservative values.
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* RFC3390 specifies slightly more aggressive values.
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*
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* If a SYN or SYN/ACK was lost and retransmitted, we have to
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* reduce the initial CWND to one segment as congestion is likely
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* requiring us to be cautious.
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*/
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if (V_tcp_do_rfc3390)
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if (tp->snd_cwnd == 1)
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tp->snd_cwnd = tp->t_maxseg; /* SYN(-ACK) lost */
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else if (V_tcp_do_rfc3390)
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tp->snd_cwnd = min(4 * tp->t_maxseg,
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max(2 * tp->t_maxseg, 4380));
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else {
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@ -852,11 +852,12 @@ syncache_socket(struct syncache *sc, struct socket *lso, struct mbuf *m)
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tcp_mss(tp, sc->sc_peer_mss);
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/*
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* If the SYN,ACK was retransmitted, reset cwnd to 1 segment.
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* If the SYN,ACK was retransmitted, indicate that CWND to be
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* limited to one segment in cc_conn_init().
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* NB: sc_rxmits counts all SYN,ACK transmits, not just retransmits.
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*/
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if (sc->sc_rxmits > 1)
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tp->snd_cwnd = tp->t_maxseg;
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tp->snd_cwnd = 1;
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#ifdef TCP_OFFLOAD
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/*
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@ -539,7 +539,13 @@ tcp_timer_rexmt(void * xtp)
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}
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INP_INFO_RUNLOCK(&V_tcbinfo);
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headlocked = 0;
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if (tp->t_rxtshift == 1) {
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if (tp->t_state == TCPS_SYN_SENT) {
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/*
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* If the SYN was retransmitted, indicate CWND to be
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* limited to 1 segment in cc_conn_init().
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*/
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tp->snd_cwnd = 1;
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} else if (tp->t_rxtshift == 1) {
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/*
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* first retransmit; record ssthresh and cwnd so they can
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* be recovered if this turns out to be a "bad" retransmit.
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