> Author: mmacy > Date: Tue May 8 02:22:34 2018 > New Revision: 333346 > URL: https://svnweb.freebsd.org/changeset/base/333346 > > Log: > Fix spurious retransmit recovery on low latency networks
Your commit message quality is defanitly much much better!! Just one little nit... > > TCP's smoothed RTT (SRTT) can be much larger than an actual observed RTT. > This can be either because of hz restricting the calculable RTT to 10ms in > VMs or 1ms using the default 1000hz or simply because SRTT recently > incorporated a larger value. Can you wrap lines at 80 characters please. Thanks, > If an ACK arrives before the calculated badrxtwin (now + SRTT): > tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1)); > > We'll erroneously reset snd_una to snd_max. If multiple segments were > dropped and this happens repeatedly the transmit rate will be limited to 1MSS > per RTO until we've retransmitted all drops. > > Reported by: rstone > Reviewed by: hiren, transport > Approved by: sbruno > MFC after: 1 month > Differential Revision: https://reviews.freebsd.org/D8556 > > Modified: > head/sys/netinet/tcp_input.c > head/sys/netinet/tcp_output.c > head/sys/netinet/tcp_timer.c > > Modified: head/sys/netinet/tcp_input.c > ============================================================================== > --- head/sys/netinet/tcp_input.c Tue May 8 01:39:45 2018 > (r333345) > +++ head/sys/netinet/tcp_input.c Tue May 8 02:22:34 2018 > (r333346) > @@ -1682,6 +1682,9 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru > to.to_tsecr -= tp->ts_offset; > if (TSTMP_GT(to.to_tsecr, tcp_ts_getticks())) > to.to_tsecr = 0; > + else if (tp->t_flags & TF_PREVVALID && > + tp->t_badrxtwin != 0 && SEQ_LT(to.to_tsecr, > tp->t_badrxtwin)) > + cc_cong_signal(tp, th, CC_RTO_ERR); > } > /* > * Process options only when we get SYN/ACK back. The SYN case > @@ -1794,9 +1797,10 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru > TCPSTAT_INC(tcps_predack); > > /* > - * "bad retransmit" recovery. > + * "bad retransmit" recovery without timestamps. > */ > - if (tp->t_rxtshift == 1 && > + if ((to.to_flags & TOF_TS) == 0 && > + tp->t_rxtshift == 1 && > tp->t_flags & TF_PREVVALID && > (int)(ticks - tp->t_badrxtwin) < 0) { > cc_cong_signal(tp, th, CC_RTO_ERR); > @@ -2787,8 +2791,10 @@ process_ACK: > * original cwnd and ssthresh, and proceed to transmit where > * we left off. > */ > - if (tp->t_rxtshift == 1 && tp->t_flags & TF_PREVVALID && > - (int)(ticks - tp->t_badrxtwin) < 0) > + if (tp->t_rxtshift == 1 && > + tp->t_flags & TF_PREVVALID && > + tp->t_badrxtwin && > + SEQ_LT(to.to_tsecr, tp->t_badrxtwin)) > cc_cong_signal(tp, th, CC_RTO_ERR); > > /* > > Modified: head/sys/netinet/tcp_output.c > ============================================================================== > --- head/sys/netinet/tcp_output.c Tue May 8 01:39:45 2018 > (r333345) > +++ head/sys/netinet/tcp_output.c Tue May 8 02:22:34 2018 > (r333346) > @@ -206,7 +206,7 @@ tcp_output(struct tcpcb *tp) > #if defined(IPSEC) || defined(IPSEC_SUPPORT) > unsigned ipsec_optlen = 0; > #endif > - int idle, sendalot; > + int idle, sendalot, curticks; > int sack_rxmit, sack_bytes_rxmt; > struct sackhole *p; > int tso, mtu; > @@ -808,9 +808,12 @@ send: > /* Timestamps. */ > if ((tp->t_flags & TF_RCVD_TSTMP) || > ((flags & TH_SYN) && (tp->t_flags & TF_REQ_TSTMP))) { > - to.to_tsval = tcp_ts_getticks() + tp->ts_offset; > + curticks = tcp_ts_getticks(); > + to.to_tsval = curticks + tp->ts_offset; > to.to_tsecr = tp->ts_recent; > to.to_flags |= TOF_TS; > + if (tp->t_rxtshift == 1) > + tp->t_badrxtwin = curticks; > } > > /* Set receive buffer autosizing timestamp. */ > > Modified: head/sys/netinet/tcp_timer.c > ============================================================================== > --- head/sys/netinet/tcp_timer.c Tue May 8 01:39:45 2018 > (r333345) > +++ head/sys/netinet/tcp_timer.c Tue May 8 02:22:34 2018 > (r333346) > @@ -693,7 +693,12 @@ tcp_timer_rexmt(void * xtp) > tp->t_flags |= TF_WASCRECOVERY; > else > tp->t_flags &= ~TF_WASCRECOVERY; > - tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT + 1)); > + if ((tp->t_flags & TF_RCVD_TSTMP) == 0) > + tp->t_badrxtwin = ticks + (tp->t_srtt >> (TCP_RTT_SHIFT > + 1)); > + /* In the event that we've negotiated timestamps > + * badrxtwin will be set to the value that we set > + * the retransmitted packet's to_tsval to by tcp_output > + */ > tp->t_flags |= TF_PREVVALID; > } else > tp->t_flags &= ~TF_PREVVALID; > > -- Rod Grimes rgri...@freebsd.org _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
