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tcp: add conservative d.cep accounting algorithm

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Accurate ECN asks to conservatively estimate, when the
ACE counter may have wrapped due to a single ACK covering a larger
number of segments. This is described in Annex A.2 of the
accurate-ecn draft.

Event:			IETF 115 Hackathon
Reviewed By:		tuexen, #transport
Sponsored by:		NetApp, Inc.
Differential Revision:	https://reviews.freebsd.org/D37281
This commit is contained in:
Richard Scheffenegger 2022-11-06 11:59:55 +01:00
parent 22c81cc516
commit b1258b7643
5 changed files with 27 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
sys/netinet/tcp_ecn.c
View File

@ -271,9 +271,9 @@ tcp_ecn_input_parallel_syn(struct tcpcb *tp, uint16_t thflags, int iptos)
* TCP ECN processing.
*/
int
tcp_ecn_input_segment(struct tcpcb *tp, uint16_t thflags, int iptos)
tcp_ecn_input_segment(struct tcpcb *tp, uint16_t thflags, int tlen, int pkts, int iptos)
{
int delta_ace = 0;
int delta_cep = 0;
if (tp->t_flags2 & (TF2_ECN_PERMIT | TF2_ACE_PERMIT)) {
switch (iptos & IPTOS_ECN_MASK) {
@ -292,9 +292,12 @@ tcp_ecn_input_segment(struct tcpcb *tp, uint16_t thflags, int iptos)
if ((iptos & IPTOS_ECN_MASK) == IPTOS_ECN_CE)
tp->t_rcep += 1;
if (tp->t_flags2 & TF2_ECN_PERMIT) {
delta_ace = (tcp_ecn_get_ace(thflags) + 8 -
(tp->t_scep & 0x07)) & 0x07;
tp->t_scep += delta_ace;
delta_cep = (tcp_ecn_get_ace(thflags) + 8 -
(tp->t_scep & 7)) & 7;
if (delta_cep < pkts)
delta_cep = pkts -
((pkts - delta_cep) & 7);
tp->t_scep += delta_cep;
} else {
/*
* process the final ACK of the 3WHS
@ -326,7 +329,7 @@ tcp_ecn_input_segment(struct tcpcb *tp, uint16_t thflags, int iptos)
} else {
/* RFC3168 ECN handling */
if ((thflags & (TH_SYN | TH_ECE)) == TH_ECE) {
delta_ace = 1;
delta_cep = 1;
tp->t_scep++;
}
if (thflags & TH_CWR) {
@ -341,7 +344,7 @@ tcp_ecn_input_segment(struct tcpcb *tp, uint16_t thflags, int iptos)
cc_ecnpkt_handler_flags(tp, thflags, iptos);
}
return delta_ace;
return delta_cep;
}
/*

2
sys/netinet/tcp_ecn.h
View File

@ -43,7 +43,7 @@
void tcp_ecn_input_syn_sent(struct tcpcb *, uint16_t, int);
void tcp_ecn_input_parallel_syn(struct tcpcb *, uint16_t, int);
int tcp_ecn_input_segment(struct tcpcb *, uint16_t, int);
int tcp_ecn_input_segment(struct tcpcb *, uint16_t, int, int, int);
uint16_t tcp_ecn_output_syn_sent(struct tcpcb *);
int tcp_ecn_output_established(struct tcpcb *, uint16_t *, int, bool);
void tcp_ecn_syncache_socket(struct tcpcb *, struct syncache *);

4
sys/netinet/tcp_input.c
View File

@ -1627,7 +1627,9 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
/*
* TCP ECN processing.
*/
if (tcp_ecn_input_segment(tp, thflags, iptos))
if (tcp_ecn_input_segment(tp, thflags, tlen,
tcp_packets_this_ack(tp, th->th_ack),
iptos))
cc_cong_signal(tp, th, CC_ECN);
/*

10
sys/netinet/tcp_stacks/rack.c
View File

@ -13528,8 +13528,10 @@ rack_do_compressed_ack_processing(struct tcpcb *tp, struct socket *so, struct mb
rack_cc_after_idle(rack, tp);
}
tp->t_rcvtime = ticks;
/* Now what about ECN? */
if (tcp_ecn_input_segment(tp, ae->flags, ae->codepoint))
/* Now what about ECN of a chain of pure ACKs? */
if (tcp_ecn_input_segment(tp, ae->flags, 0,
tcp_packets_this_ack(tp, ae->ack),
ae->codepoint))
rack_cong_signal(tp, CC_ECN, ae->ack, __LINE__);
#ifdef TCP_ACCOUNTING
/* Count for the specific type of ack in */
@ -14320,7 +14322,9 @@ rack_do_segment_nounlock(struct mbuf *m, struct tcphdr *th, struct socket *so,
* TCP ECN processing. XXXJTL: If we ever use ECN, we need to move
* this to occur after we've validated the segment.
*/
if (tcp_ecn_input_segment(tp, thflags, iptos))
if (tcp_ecn_input_segment(tp, thflags, tlen,
tcp_packets_this_ack(tp, th->th_ack),
iptos))
rack_cong_signal(tp, CC_ECN, th->th_ack, __LINE__);
/*

6
sys/netinet/tcp_var.h
View File

@ -551,6 +551,12 @@ tcp_unlock_or_drop(struct tcpcb *tp, int tcp_output_retval)
#endif
#define BYTES_THIS_ACK(tp, th) (th->th_ack - tp->snd_una)
static int inline
tcp_packets_this_ack(struct tcpcb *tp, tcp_seq ack)
{
return ((ack - tp->snd_una) / tp->t_maxseg +
((((ack - tp->snd_una) % tp->t_maxseg) != 0) ? 1 : 0));
}
/*
* Flags for the t_oobflags field.