Dear all,
This patch builds upon the work shared in the following email. Mike's
patch is a prerequisite to apply this patch.
Date: Tue, 24 Oct 2017 15:21:08 +0200
From: Mike Belopuhov <m...@belopuhov.com>
Subject: Re: Refactor TCP partial ACK handling
TCP_FACK was disabled by provos@ in June 1999. This patch removes
the TCP_FACK option and associated #if{,n}def code.
TCP_FACK is an algorithm that decides that when something is lost, all
not SACKed packets until the most forward SACK are lost. It may be a
correct estimate, if network does not reorder packets.
The algorithm described in RFC 6675 may be a better replacement. This
culling patch can provide guidance how and where to implement 6675.
Kind regards,
Job
share/man/man4/options.4 | 5 ---
sys/conf/GENERIC | 1 -
sys/netinet/tcp_input.c | 111 +----------------------------------------------
sys/netinet/tcp_output.c | 42 ------------------
sys/netinet/tcp_timer.c | 5 ---
sys/netinet/tcp_usrreq.c | 5 ---
sys/netinet/tcp_var.h | 6 ---
usr.bin/netstat/inet.c | 3 --
8 files changed, 1 insertion(+), 177 deletions(-)
diff --git share/man/man4/options.4 share/man/man4/options.4
index c28d4e27896..737dc29efea 100644
--- share/man/man4/options.4
+++ share/man/man4/options.4
@@ -445,11 +445,6 @@ TCP to adjust the transmission rate using this signal.
Both communication endpoints negotiate enabling
.Em ECN
functionality at the TCP connection establishment.
-.It Cd option TCP_FACK
-Turns on forward acknowledgements allowing a more precise estimate of
-outstanding data during the fast recovery phase by using
-.Em SACK
-information.
.It Cd option TCP_SIGNATURE
Turns on support for the TCP MD5 Signature option (RFC 2385).
This is used by
diff --git sys/conf/GENERIC sys/conf/GENERIC
index 6df800175ed..e385b45785c 100644
--- sys/conf/GENERIC
+++ sys/conf/GENERIC
@@ -47,7 +47,6 @@ option FUSE # FUSE
option SOCKET_SPLICE # Socket Splicing for TCP and UDP
option TCP_ECN # Explicit Congestion Notification for TCP
option TCP_SIGNATURE # TCP MD5 Signatures, for BGP routing sessions
-#option TCP_FACK # Forward Acknowledgements for TCP
option INET6 # IPv6
option IPSEC # IPsec
diff --git sys/netinet/tcp_input.c sys/netinet/tcp_input.c
index 8d172e2905c..4321d85854c 100644
--- sys/netinet/tcp_input.c
+++ sys/netinet/tcp_input.c
@@ -974,10 +974,6 @@ findpcb:
if (SEQ_GT(tp->snd_una, tp->snd_last))
#endif
tp->snd_last = tp->snd_una;
-#ifdef TCP_FACK
- tp->snd_fack = tp->snd_una;
- tp->retran_data = 0;
-#endif
m_freem(m);
/*
@@ -1566,18 +1562,7 @@ trimthenstep6:
*/
if (TCP_TIMER_ISARMED(tp, TCPT_REXMT) == 0)
tp->t_dupacks = 0;
-#ifdef TCP_FACK
- /*
- * In FACK, can enter fast rec. if the receiver
- * reports a reass. queue longer than 3 segs.
- */
- else if (++tp->t_dupacks == tcprexmtthresh ||
- ((SEQ_GT(tp->snd_fack, tcprexmtthresh *
- tp->t_maxseg + tp->snd_una)) &&
- SEQ_GT(tp->snd_una, tp->snd_last))) {
-#else
else if (++tp->t_dupacks == tcprexmtthresh) {
-#endif /* TCP_FACK */
tcp_seq onxt = tp->snd_nxt;
u_long win =
ulmin(tp->snd_wnd, tp->snd_cwnd) /
@@ -1603,15 +1588,6 @@ trimthenstep6:
#endif
tcpstat_inc(tcps_cwr_frecovery);
tcpstat_inc(tcps_sack_recovery_episode);
-#ifdef TCP_FACK
- tp->t_dupacks = tcprexmtthresh;
- (void) tcp_output(tp);
- /*
- * During FR, snd_cwnd is held
- * constant for FACK.
- */
- tp->snd_cwnd = tp->snd_ssthresh;
-#else
/*
* tcp_output() will send
* oldest SACK-eligible rtx.
@@ -1619,7 +1595,6 @@ trimthenstep6:
(void) tcp_output(tp);
tp->snd_cwnd = tp->snd_ssthresh+
tp->t_maxseg * tp->t_dupacks;
-#endif /* TCP_FACK */
goto drop;
}
TCP_TIMER_DISARM(tp, TCPT_REXMT);
@@ -1639,17 +1614,6 @@ trimthenstep6:
tp->snd_nxt = onxt;
goto drop;
} else if (tp->t_dupacks > tcprexmtthresh) {
-#ifdef TCP_FACK
- /*
- * while (awnd < cwnd)
- * sendsomething();
- */
- if (tp->sack_enable) {
- if (tp->snd_awnd < tp->snd_cwnd)
- tcp_output(tp);
- goto drop;
- }
-#endif /* TCP_FACK */
tp->snd_cwnd += tp->t_maxseg;
(void) tcp_output(tp);
goto drop;
@@ -1685,11 +1649,6 @@ trimthenstep6:
tcp_seq_subtract(tp->snd_max,
th->th_ack);
tp->t_dupacks = 0;
-#ifdef TCP_FACK
- if (tp->sack_enable &&
- SEQ_GT(th->th_ack, tp->snd_fack))
- tp->snd_fack = th->th_ack;
-#endif
}
} else {
/*
@@ -1789,16 +1748,6 @@ trimthenstep6:
#endif
if (SEQ_LT(tp->snd_nxt, tp->snd_una))
tp->snd_nxt = tp->snd_una;
-#ifdef TCP_FACK
- if (SEQ_GT(tp->snd_una, tp->snd_fack)) {
- tp->snd_fack = tp->snd_una;
- /* Update snd_awnd for partial ACK
- * without any SACK blocks.
- */
- tp->snd_awnd = tcp_seq_subtract(tp->snd_nxt,
- tp->snd_fack) + tp->retran_data;
- }
-#endif
switch (tp->t_state) {
@@ -2467,11 +2416,6 @@ tcp_sack_option(struct tcpcb *tp, struct tcphdr *th,
u_char *cp, int optlen)
continue; /* bad SACK fields */
if (SEQ_LEQ(sack.end, tp->snd_una))
continue; /* old block */
-#ifdef TCP_FACK
- /* Updates snd_fack. */
- if (SEQ_GT(sack.end, tp->snd_fack))
- tp->snd_fack = sack.end;
-#endif
if (SEQ_GT(th->th_ack, tp->snd_una)) {
if (SEQ_LT(sack.start, th->th_ack))
continue;
@@ -2520,16 +2464,6 @@ tcp_sack_option(struct tcpcb *tp, struct tcphdr *th,
u_char *cp, int optlen)
}
if (SEQ_LEQ(sack.start, cur->start)) {
/* Data acks at least the beginning of hole */
-#ifdef TCP_FACK
- if (SEQ_GT(sack.end, cur->rxmit))
- tp->retran_data -=
- tcp_seq_subtract(cur->rxmit,
- cur->start);
- else
- tp->retran_data -=
- tcp_seq_subtract(sack.end,
- cur->start);
-#endif
if (SEQ_GEQ(sack.end, cur->end)) {
/* Acks entire hole, so delete hole */
if (p != cur) {
@@ -2554,12 +2488,6 @@ tcp_sack_option(struct tcpcb *tp, struct tcphdr *th,
u_char *cp, int optlen)
}
/* move end of hole backward */
if (SEQ_GEQ(sack.end, cur->end)) {
-#ifdef TCP_FACK
- if (SEQ_GT(cur->rxmit, sack.start))
- tp->retran_data -=
- tcp_seq_subtract(cur->rxmit,
- sack.start);
-#endif
cur->end = sack.start;
cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
cur->dups++;
@@ -2580,16 +2508,6 @@ tcp_sack_option(struct tcpcb *tp, struct tcphdr *th,
u_char *cp, int optlen)
pool_get(&sackhl_pool, PR_NOWAIT);
if (temp == NULL)
goto done; /* ENOBUFS */
-#ifdef TCP_FACK
- if (SEQ_GT(cur->rxmit, sack.end))
- tp->retran_data -=
- tcp_seq_subtract(sack.end,
- sack.start);
- else if (SEQ_GT(cur->rxmit, sack.start))
- tp->retran_data -=
- tcp_seq_subtract(cur->rxmit,
- sack.start);
-#endif
temp->next = cur->next;
temp->start = sack.end;
temp->end = cur->end;
@@ -2631,21 +2549,6 @@ tcp_sack_option(struct tcpcb *tp, struct tcphdr *th,
u_char *cp, int optlen)
}
}
done:
-#ifdef TCP_FACK
- /*
- * Update retran_data and snd_awnd. Go through the list of
- * holes. Increment retran_data by (hole->rxmit - hole->start).
- */
- tp->retran_data = 0;
- cur = tp->snd_holes;
- while (cur) {
- tp->retran_data += cur->rxmit - cur->start;
- cur = cur->next;
- }
- tp->snd_awnd = tcp_seq_subtract(tp->snd_nxt, tp->snd_fack) +
- tp->retran_data;
-#endif
-
return;
}
@@ -2705,11 +2608,9 @@ tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
/* Turn off retx. timer (will start again next segment) */
TCP_TIMER_DISARM(tp, TCPT_REXMT);
tp->t_rtttime = 0;
-#ifndef TCP_FACK
/*
* Partial window deflation. This statement relies on the
- * fact that tp->snd_una has not been updated yet. In FACK
- * hold snd_cwnd constant during fast recovery.
+ * fact that tp->snd_una has not been updated yet.
*/
if (tp->snd_cwnd > (th->th_ack - tp->snd_una)) {
tp->snd_cwnd -= th->th_ack - tp->snd_una;
@@ -2718,11 +2619,6 @@ tcp_sack_partialack(struct tcpcb *tp, struct tcphdr *th)
tp->snd_cwnd = tp->t_maxseg;
tp->snd_cwnd += tp->t_maxseg;
tp->t_flags |= TF_NEEDOUTPUT;
-#else
- /* Force call to tcp_output */
- if (tp->snd_awnd < tp->snd_cwnd)
- tp->t_flags |= TF_NEEDOUTPUT;
-#endif
}
/*
@@ -3703,11 +3599,6 @@ syn_cache_get(struct sockaddr *src, struct sockaddr
*dst, struct tcphdr *th,
tp->irs = sc->sc_irs;
tcp_sendseqinit(tp);
tp->snd_last = tp->snd_una;
-#ifdef TCP_FACK
- tp->snd_fack = tp->snd_una;
- tp->retran_data = 0;
- tp->snd_awnd = 0;
-#endif
#ifdef TCP_ECN
if (sc->sc_flags & SCF_ECN_PERMIT) {
tp->t_flags |= TF_ECN_PERMIT;
diff --git sys/netinet/tcp_output.c sys/netinet/tcp_output.c
index a0a88b5ec3d..a652ad1d80d 100644
--- sys/netinet/tcp_output.c
+++ sys/netinet/tcp_output.c
@@ -130,17 +130,7 @@ tcp_sack_output(struct tcpcb *tp)
return (NULL);
p = tp->snd_holes;
while (p) {
-#ifndef TCP_FACK
if (p->dups >= tcprexmtthresh && SEQ_LT(p->rxmit, p->end)) {
-#else
- /* In FACK, if p->dups is less than tcprexmtthresh, but
- * snd_fack advances more than tcprextmtthresh * tp->t_maxseg,
- * tcp_input() will try fast retransmit. This forces output.
- */
- if ((p->dups >= tcprexmtthresh ||
- tp->t_dupacks == tcprexmtthresh) &&
- SEQ_LT(p->rxmit, p->end)) {
-#endif /* TCP_FACK */
if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */
p = p->next;
continue;
@@ -258,15 +248,6 @@ again:
if (tp->sack_enable && SEQ_LT(tp->snd_nxt, tp->snd_max))
tcp_sack_adjust(tp);
off = tp->snd_nxt - tp->snd_una;
-#ifdef TCP_FACK
- /* Normally, sendable data is limited by off < tp->snd_cwnd.
- * But in FACK, sendable data is limited by snd_awnd < snd_cwnd,
- * regardless of offset.
- */
- if (tp->sack_enable && (tp->t_dupacks > tcprexmtthresh))
- win = tp->snd_wnd;
- else
-#endif
win = ulmin(tp->snd_wnd, tp->snd_cwnd);
flags = tcp_outflags[tp->t_state];
@@ -285,11 +266,8 @@ again:
sack_rxmit = 1;
/* Coalesce holes into a single retransmission */
len = min(tp->t_maxseg, p->end - p->rxmit);
-#ifndef TCP_FACK
- /* in FACK, hold snd_cwnd constant during recovery */
if (SEQ_LT(tp->snd_una, tp->snd_last))
tp->snd_cwnd -= tp->t_maxseg;
-#endif
}
}
@@ -329,17 +307,6 @@ again:
if (!sack_rxmit) {
len = ulmin(so->so_snd.sb_cc, win) - off;
-
-#ifdef TCP_FACK
- /*
- * If we're in fast recovery (SEQ_GT(tp->snd_last,
tp->snd_una)),
- * and amount of outstanding data (snd_awnd) is >= snd_cwnd,
then
- * do not send data (like zero window conditions)
- */
- if (tp->sack_enable && SEQ_GT(tp->snd_last, tp->snd_una) &&
- len && (tp->snd_awnd >= tp->snd_cwnd))
- len = 0;
-#endif /* TCP_FACK */
}
if (len < 0) {
@@ -794,9 +761,6 @@ send:
sendalot = 0;
th->th_seq = htonl(p->rxmit);
p->rxmit += len;
-#ifdef TCP_FACK
- tp->retran_data += len;
-#endif
tcpstat_pkt(tcps_sack_rexmits, tcps_sack_rexmit_bytes, len);
}
@@ -1096,12 +1060,6 @@ send:
#endif /* INET6 */
}
-#ifdef TCP_FACK
- /* Update snd_awnd to reflect the new data that was sent. */
- tp->snd_awnd = tcp_seq_subtract(tp->snd_max, tp->snd_fack) +
- tp->retran_data;
-#endif
-
if (error) {
out:
if (error == ENOBUFS) {
diff --git sys/netinet/tcp_timer.c sys/netinet/tcp_timer.c
index 9d2e75942cd..3452121da6d 100644
--- sys/netinet/tcp_timer.c
+++ sys/netinet/tcp_timer.c
@@ -172,11 +172,6 @@ tcp_timer_freesack(struct tcpcb *tp)
pool_put(&sackhl_pool, p);
}
tp->snd_holes = 0;
-#ifdef TCP_FACK
- tp->snd_fack = tp->snd_una;
- tp->retran_data = 0;
- tp->snd_awnd = 0;
-#endif
}
void
diff --git sys/netinet/tcp_usrreq.c sys/netinet/tcp_usrreq.c
index d7ee1ecc517..549149a0531 100644
--- sys/netinet/tcp_usrreq.c
+++ sys/netinet/tcp_usrreq.c
@@ -269,11 +269,6 @@ tcp_usrreq(struct socket *so, int req, struct mbuf *m,
struct mbuf *nam,
tcp_set_iss_tsm(tp);
tcp_sendseqinit(tp);
tp->snd_last = tp->snd_una;
-#ifdef TCP_FACK
- tp->snd_fack = tp->snd_una;
- tp->retran_data = 0;
- tp->snd_awnd = 0;
-#endif
error = tcp_output(tp);
break;
diff --git sys/netinet/tcp_var.h sys/netinet/tcp_var.h
index 4c1b37b2b68..4ca5fc0afe4 100644
--- sys/netinet/tcp_var.h
+++ sys/netinet/tcp_var.h
@@ -119,12 +119,6 @@ struct tcpcb {
int sack_enable; /* enable SACK for this connection */
int snd_numholes; /* number of holes seen by sender */
struct sackhole *snd_holes; /* linked list of holes (sorted) */
-#if 1 /*defined(TCP_FACK)*/
- tcp_seq snd_fack; /* for FACK congestion control */
- u_long snd_awnd; /* snd_nxt - snd_fack + */
- /* retransmitted data */
- int retran_data; /* amount of outstanding retx. data */
-#endif /* TCP_FACK */
tcp_seq snd_last; /* for use in fast recovery */
/* receive sequence variables */
u_long rcv_wnd; /* receive window */
diff --git usr.bin/netstat/inet.c usr.bin/netstat/inet.c
index 468d514a22e..4cb82ea7379 100644
--- usr.bin/netstat/inet.c
+++ usr.bin/netstat/inet.c
@@ -1496,9 +1496,6 @@ tcpcb_dump(u_long off)
p("%lu", snd_wnd, "\n ");
p("%d", sack_enable, ", ");
p("%d", snd_numholes, ", ");
- p("%u", snd_fack, ", ");
- p("%lu",snd_awnd, "\n ");
- p("%u", retran_data, ", ");
p("%u", snd_last, "\n ");
p("%u", irs, "\n ");
p("%u", rcv_nxt, ", ");
