Date: Fri, 4 Dec 2020 11:29:27 +0000 (UTC) From: Richard Scheffenegger <rscheff@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r368327 - head/sys/netinet Message-ID: <202012041129.0B4BTRPF098802@repo.freebsd.org>
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Author: rscheff Date: Fri Dec 4 11:29:27 2020 New Revision: 368327 URL: https://svnweb.freebsd.org/changeset/base/368327 Log: Add TCP feature Proportional Rate Reduction (PRR) - RFC6937 PRR improves loss recovery and avoids RTOs in a wide range of scenarios (ACK thinning) over regular SACK loss recovery. PRR is disabled by default, enable by net.inet.tcp.do_prr = 1. Performance may be impeded by token bucket rate policers at the bottleneck, where net.inet.tcp.do_prr_conservate = 1 should be enabled in addition. Submitted by: Aris Angelogiannopoulos Sponsored by: NetApp, Inc. Differential Revision: https://reviews.freebsd.org/D18892 Modified: head/sys/netinet/tcp_input.c head/sys/netinet/tcp_var.h Modified: head/sys/netinet/tcp_input.c ============================================================================== --- head/sys/netinet/tcp_input.c Fri Dec 4 04:39:48 2020 (r368326) +++ head/sys/netinet/tcp_input.c Fri Dec 4 11:29:27 2020 (r368327) @@ -153,6 +153,16 @@ SYSCTL_INT(_net_inet_tcp, OID_AUTO, drop_synfin, CTLFL &VNET_NAME(drop_synfin), 0, "Drop TCP packets with SYN+FIN set"); +VNET_DEFINE(int, tcp_do_prr_conservative) = 0; +SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_prr_conservative, CTLFLAG_VNET | CTLFLAG_RW, + &VNET_NAME(tcp_do_prr_conservative), 0, + "Do conservative Proportional Rate Reduction"); + +VNET_DEFINE(int, tcp_do_prr) = 1; +SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_prr, CTLFLAG_VNET | CTLFLAG_RW, + &VNET_NAME(tcp_do_prr), 1, + "Enable Proportional Rate Reduction per RFC 6937"); + VNET_DEFINE(int, tcp_do_newcwv) = 0; SYSCTL_INT(_net_inet_tcp, OID_AUTO, newcwv, CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(tcp_do_newcwv), 0, @@ -2554,7 +2564,55 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru IN_FASTRECOVERY(tp->t_flags)) { cc_ack_received(tp, th, nsegs, CC_DUPACK); - if ((tp->t_flags & TF_SACK_PERMIT) && + if (V_tcp_do_prr && + IN_FASTRECOVERY(tp->t_flags) && + (tp->t_flags & TF_SACK_PERMIT)) { + long snd_cnt = 0, limit = 0; + long del_data = 0, pipe = 0; + /* + * In a duplicate ACK del_data is only the + * diff_in_sack. If no SACK is used del_data + * will be 0. Pipe is the amount of data we + * estimate to be in the network. + */ + del_data = tp->sackhint.delivered_data; + pipe = (tp->snd_nxt - tp->snd_fack) + + tp->sackhint.sack_bytes_rexmit; + tp->sackhint.prr_delivered += del_data; + if (pipe > tp->snd_ssthresh) { + snd_cnt = (tp->sackhint.prr_delivered * + tp->snd_ssthresh / + tp->sackhint.recover_fs) + + 1 - tp->sackhint.sack_bytes_rexmit; + } else { + if (V_tcp_do_prr_conservative) + limit = tp->sackhint.prr_delivered - + tp->sackhint.sack_bytes_rexmit; + else + if ((tp->sackhint.prr_delivered - + tp->sackhint.sack_bytes_rexmit) > + del_data) + limit = tp->sackhint.prr_delivered - + tp->sackhint.sack_bytes_rexmit + + maxseg; + else + limit = del_data + maxseg; + if ((tp->snd_ssthresh - pipe) < limit) + snd_cnt = tp->snd_ssthresh - pipe; + else + snd_cnt = limit; + } + snd_cnt = max((snd_cnt / maxseg), 0); + /* + * Send snd_cnt new data into the network in + * response to this ACK. If there is a going + * to be a SACK retransmission, adjust snd_cwnd + * accordingly. + */ + tp->snd_cwnd = tp->snd_nxt - tp->snd_recover + + tp->sackhint.sack_bytes_rexmit + + (snd_cnt * maxseg); + } else if ((tp->t_flags & TF_SACK_PERMIT) && IN_FASTRECOVERY(tp->t_flags)) { int awnd; @@ -2583,13 +2641,14 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru tcp_seq onxt = tp->snd_nxt; /* - * If we're doing sack, check to - * see if we're already in sack + * If we're doing sack, or prr, check + * to see if we're already in sack * recovery. If we're not doing sack, * check to see if we're in newreno * recovery. */ - if (tp->t_flags & TF_SACK_PERMIT) { + if (V_tcp_do_prr || + (tp->t_flags & TF_SACK_PERMIT)) { if (IN_FASTRECOVERY(tp->t_flags)) { tp->t_dupacks = 0; break; @@ -2607,6 +2666,16 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru CC_DUPACK); tcp_timer_activate(tp, TT_REXMT, 0); tp->t_rtttime = 0; + if (V_tcp_do_prr) { + /* + * snd_ssthresh is already updated by + * cc_cong_signal. + */ + tp->sackhint.prr_delivered = 0; + tp->sackhint.sack_bytes_rexmit = 0; + if (!(tp->sackhint.recover_fs = tp->snd_nxt - tp->snd_una)) + tp->sackhint.recover_fs = 1; + } if (tp->t_flags & TF_SACK_PERMIT) { TCPSTAT_INC( tcps_sack_recovery_episode); @@ -2713,7 +2782,10 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, stru if (IN_FASTRECOVERY(tp->t_flags)) { if (SEQ_LT(th->th_ack, tp->snd_recover)) { if (tp->t_flags & TF_SACK_PERMIT) - tcp_sack_partialack(tp, th); + if (V_tcp_do_prr) + tcp_prr_partialack(tp, th); + else + tcp_sack_partialack(tp, th); else tcp_newreno_partial_ack(tp, th); } else @@ -3837,6 +3909,54 @@ tcp_mssopt(struct in_conninfo *inc) mss = max(maxmtu, thcmtu) - min_protoh; return (mss); +} + +void +tcp_prr_partialack(struct tcpcb *tp, struct tcphdr *th) +{ + long snd_cnt = 0, limit = 0, del_data = 0, pipe = 0; + int maxseg = tcp_maxseg(tp); + + INP_WLOCK_ASSERT(tp->t_inpcb); + + tcp_timer_activate(tp, TT_REXMT, 0); + tp->t_rtttime = 0; + /* + * Compute the amount of data that this ACK is indicating + * (del_data) and an estimate of how many bytes are in the + * network. + */ + if (SEQ_GEQ(th->th_ack, tp->snd_una)) + del_data = BYTES_THIS_ACK(tp, th); + del_data += tp->sackhint.delivered_data; + pipe = (tp->snd_nxt - tp->snd_fack) + tp->sackhint.sack_bytes_rexmit; + tp->sackhint.prr_delivered += del_data; + /* + * Proportional Rate Reduction + */ + if (pipe > tp->snd_ssthresh) + snd_cnt = (tp->sackhint.prr_delivered * tp->snd_ssthresh / tp->sackhint.recover_fs) - + tp->sackhint.sack_bytes_rexmit; + else { + if (V_tcp_do_prr_conservative) + limit = tp->sackhint.prr_delivered - tp->sackhint.sack_bytes_rexmit; + else + if ((tp->sackhint.prr_delivered - tp->sackhint.sack_bytes_rexmit) > del_data) + limit = tp->sackhint.prr_delivered - tp->sackhint.sack_bytes_rexmit + maxseg; + else + limit = del_data + maxseg; + snd_cnt = min((tp->snd_ssthresh - pipe), limit); + } + snd_cnt = max((snd_cnt / maxseg), 0); + /* + * Send snd_cnt new data into the network in response to this ack. + * If there is going to be a SACK retransmission, adjust snd_cwnd + * accordingly. + */ + tp->snd_cwnd = tp->snd_nxt - tp->snd_recover + + tp->sackhint.sack_bytes_rexmit + (snd_cnt * maxseg); + tp->t_flags |= TF_ACKNOW; + (void) tcp_output(tp); } /* Modified: head/sys/netinet/tcp_var.h ============================================================================== --- head/sys/netinet/tcp_var.h Fri Dec 4 04:39:48 2020 (r368326) +++ head/sys/netinet/tcp_var.h Fri Dec 4 11:29:27 2020 (r368327) @@ -113,8 +113,9 @@ struct sackhint { int32_t sacked_bytes; /* Total sacked bytes reported by the * receiver via sack option */ - uint32_t _pad1[1]; /* TBD */ - uint64_t _pad[1]; /* TBD */ + uint32_t recover_fs; /* Flight Size at the start of Loss recovery */ + uint32_t prr_delivered; /* Total bytes delivered using PRR */ + uint32_t _pad[1]; /* TBD */ }; #define SEGQ_EMPTY(tp) TAILQ_EMPTY(&(tp)->t_segq) @@ -866,6 +867,8 @@ VNET_DECLARE(int, tcp_sendspace); VNET_DECLARE(struct inpcbhead, tcb); VNET_DECLARE(struct inpcbinfo, tcbinfo); +#define V_tcp_do_prr VNET(tcp_do_prr) +#define V_tcp_do_prr_conservative VNET(tcp_do_prr_conservative) #define V_tcp_do_newcwv VNET(tcp_do_newcwv) #define V_drop_synfin VNET(drop_synfin) #define V_path_mtu_discovery VNET(path_mtu_discovery) @@ -1051,6 +1054,7 @@ void tcp_clean_dsack_blocks(struct tcpcb *tp); void tcp_clean_sackreport(struct tcpcb *tp); void tcp_sack_adjust(struct tcpcb *tp); struct sackhole *tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt); +void tcp_prr_partialack(struct tcpcb *, struct tcphdr *); void tcp_sack_partialack(struct tcpcb *, struct tcphdr *); void tcp_free_sackholes(struct tcpcb *tp); int tcp_newreno(struct tcpcb *, struct tcphdr *);
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