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tcp: allow packets to be marked as ECT1 instead of ECT0

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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
This commit is contained in:
Richard Scheffenegger 2022-11-08 18:35:58 +01:00
parent d6273acf56
commit dc9daa04fb
4 changed files with 27 additions and 5 deletions
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7
share/man/man4/cc_dctcp.4
View File

@ -28,7 +28,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd May 13, 2021
.Dd November 8, 2022
.Dt CC_DCTCP 4
.Os
.Sh NAME
@ -91,6 +91,11 @@ gain of 1 / ( 2 ^
.It Va slowstart
A flag if the congestion window should be reduced by one half after slow start.
Valid settings 0 and 1, default 0.
.It Va ect1
Controls if a DCTCP session should use IP ECT(0) marking when sending out
segments (default), or ECT(1) marking making use of L4S infrastructure.
Changes to this setting will only affect new sessions, existing sessions will
retain their previous marking value.
.El
.Sh SEE ALSO
.Xr cc_cdg 4 ,

12
sys/netinet/cc/cc_dctcp.c
View File

@ -68,6 +68,8 @@ VNET_DEFINE_STATIC(uint32_t, dctcp_shift_g) = 4;
#define V_dctcp_shift_g VNET(dctcp_shift_g)
VNET_DEFINE_STATIC(uint32_t, dctcp_slowstart) = 0;
#define V_dctcp_slowstart VNET(dctcp_slowstart)
VNET_DEFINE_STATIC(uint32_t, dctcp_ect1) = 0;
#define V_dctcp_ect1 VNET(dctcp_ect1)
struct dctcp {
uint32_t bytes_ecn; /* # of marked bytes during a RTT */
@ -313,8 +315,11 @@ dctcp_conn_init(struct cc_var *ccv)
dctcp_data = ccv->cc_data;
if (CCV(ccv, t_flags2) & TF2_ECN_PERMIT)
if (CCV(ccv, t_flags2) & TF2_ECN_PERMIT) {
dctcp_data->save_sndnxt = CCV(ccv, snd_nxt);
if (V_dctcp_ect1)
CCV(ccv, t_flags2) |= TF2_ECN_USE_ECT1;
}
}
/*
@ -478,5 +483,10 @@ SYSCTL_PROC(_net_inet_tcp_cc_dctcp, OID_AUTO, slowstart,
&VNET_NAME(dctcp_slowstart), 0, &dctcp_slowstart_handler, "IU",
"half CWND reduction after the first slow start");
SYSCTL_UINT(_net_inet_tcp_cc_dctcp, OID_AUTO, ect1,
CTLFLAG_VNET | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
&VNET_NAME(dctcp_ect1), 0,
"Send DCTCP segments with ÍP ECT(0) or ECT(1)");
DECLARE_CC_MODULE(dctcp, &dctcp_cc_algo);
MODULE_VERSION(dctcp, 2);

9
sys/netinet/tcp_ecn.c
View File

@ -411,8 +411,13 @@ tcp_ecn_output_established(struct tcpcb *tp, uint16_t *thflags, int len, bool rx
!((tp->t_flags & TF_FORCEDATA) && len == 1));
/* RFC3168 ECN marking, only new data segments */
if (newdata) {
ipecn = IPTOS_ECN_ECT0;
TCPSTAT_INC(tcps_ecn_ect0);
if (tp->t_flags2 & TF2_ECN_USE_ECT1) {
ipecn = IPTOS_ECN_ECT1;
TCPSTAT_INC(tcps_ecn_ect1);
} else {
ipecn = IPTOS_ECN_ECT0;
TCPSTAT_INC(tcps_ecn_ect0);
}
}
/*
* Reply with proper ECN notifications.

4
sys/netinet/tcp_var.h
View File

@ -577,7 +577,9 @@ tcp_packets_this_ack(struct tcpcb *tp, tcp_seq ack)
#define TF2_ECN_SND_CWR 0x00000040 /* ECN CWR in queue */
#define TF2_ECN_SND_ECE 0x00000080 /* ECN ECE in queue */
#define TF2_ACE_PERMIT 0x00000100 /* Accurate ECN mode */
#define TF2_FBYTES_COMPLETE 0x00000400 /* We have first bytes in and out */
#define TF2_FBYTES_COMPLETE 0x00000400 /* We have first bytes in and out */
#define TF2_ECN_USE_ECT1 0x00000800 /* Use ECT(1) marking on session */
/*
* Structure to hold TCP options that are only used during segment
* processing (in tcp_input), but not held in the tcpcb.