tcp: allow packets to be marked as ECT1 instead of ECT0
This adds the capability for a modular congestion control to select which variant of ECN-capable-transport it wants to use when sending out elegible segments. As an initial CC to utilize this, DCTCP was selected. Event: IETF 115 Hackathon Reviewed By: tuexen, #transport Sponsored by: NetApp, Inc. Differential Revision: https://reviews.freebsd.org/D24869
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@ -28,7 +28,7 @@
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 13, 2021
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.Dd November 8, 2022
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.Dt CC_DCTCP 4
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.Os
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.Sh NAME
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@ -91,6 +91,11 @@ gain of 1 / ( 2 ^
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.It Va slowstart
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A flag if the congestion window should be reduced by one half after slow start.
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Valid settings 0 and 1, default 0.
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.It Va ect1
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Controls if a DCTCP session should use IP ECT(0) marking when sending out
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segments (default), or ECT(1) marking making use of L4S infrastructure.
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Changes to this setting will only affect new sessions, existing sessions will
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retain their previous marking value.
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.El
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.Sh SEE ALSO
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.Xr cc_cdg 4 ,
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@ -68,6 +68,8 @@ VNET_DEFINE_STATIC(uint32_t, dctcp_shift_g) = 4;
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#define V_dctcp_shift_g VNET(dctcp_shift_g)
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VNET_DEFINE_STATIC(uint32_t, dctcp_slowstart) = 0;
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#define V_dctcp_slowstart VNET(dctcp_slowstart)
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VNET_DEFINE_STATIC(uint32_t, dctcp_ect1) = 0;
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#define V_dctcp_ect1 VNET(dctcp_ect1)
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struct dctcp {
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uint32_t bytes_ecn; /* # of marked bytes during a RTT */
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@ -313,8 +315,11 @@ dctcp_conn_init(struct cc_var *ccv)
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dctcp_data = ccv->cc_data;
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if (CCV(ccv, t_flags2) & TF2_ECN_PERMIT)
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if (CCV(ccv, t_flags2) & TF2_ECN_PERMIT) {
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dctcp_data->save_sndnxt = CCV(ccv, snd_nxt);
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if (V_dctcp_ect1)
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CCV(ccv, t_flags2) |= TF2_ECN_USE_ECT1;
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}
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}
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/*
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@ -478,5 +483,10 @@ SYSCTL_PROC(_net_inet_tcp_cc_dctcp, OID_AUTO, slowstart,
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&VNET_NAME(dctcp_slowstart), 0, &dctcp_slowstart_handler, "IU",
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"half CWND reduction after the first slow start");
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SYSCTL_UINT(_net_inet_tcp_cc_dctcp, OID_AUTO, ect1,
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CTLFLAG_VNET | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
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&VNET_NAME(dctcp_ect1), 0,
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"Send DCTCP segments with ÍP ECT(0) or ECT(1)");
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DECLARE_CC_MODULE(dctcp, &dctcp_cc_algo);
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MODULE_VERSION(dctcp, 2);
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@ -411,9 +411,14 @@ tcp_ecn_output_established(struct tcpcb *tp, uint16_t *thflags, int len, bool rx
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!((tp->t_flags & TF_FORCEDATA) && len == 1));
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/* RFC3168 ECN marking, only new data segments */
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if (newdata) {
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if (tp->t_flags2 & TF2_ECN_USE_ECT1) {
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ipecn = IPTOS_ECN_ECT1;
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TCPSTAT_INC(tcps_ecn_ect1);
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} else {
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ipecn = IPTOS_ECN_ECT0;
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TCPSTAT_INC(tcps_ecn_ect0);
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}
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}
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/*
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* Reply with proper ECN notifications.
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*/
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@ -578,6 +578,8 @@ tcp_packets_this_ack(struct tcpcb *tp, tcp_seq ack)
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#define TF2_ECN_SND_ECE 0x00000080 /* ECN ECE in queue */
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#define TF2_ACE_PERMIT 0x00000100 /* Accurate ECN mode */
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#define TF2_FBYTES_COMPLETE 0x00000400 /* We have first bytes in and out */
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#define TF2_ECN_USE_ECT1 0x00000800 /* Use ECT(1) marking on session */
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/*
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* Structure to hold TCP options that are only used during segment
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* processing (in tcp_input), but not held in the tcpcb.
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