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29 * @(#)tcp_sack.c 8.12 (Berkeley) 5/24/95
34 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994
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97 * Research Laboratory (NRL).
100 #include "opt_inet6.h"
101 #include "opt_tcpdebug.h"
102 #include "opt_tcp_input.h"
103 #include "opt_tcp_sack.h"
105 #include <sys/param.h>
106 #include <sys/systm.h>
107 #include <sys/kernel.h>
108 #include <sys/sysctl.h>
109 #include <sys/malloc.h>
110 #include <sys/mbuf.h>
111 #include <sys/proc.h> /* for proc0 declaration */
112 #include <sys/protosw.h>
113 #include <sys/socket.h>
114 #include <sys/socketvar.h>
115 #include <sys/syslog.h>
116 #include <sys/systm.h>
118 #include <machine/cpu.h> /* before tcp_seq.h, for tcp_random18() */
123 #include <net/route.h>
125 #include <netinet/in.h>
126 #include <netinet/in_systm.h>
127 #include <netinet/ip.h>
128 #include <netinet/in_var.h>
129 #include <netinet/in_pcb.h>
130 #include <netinet/ip_var.h>
131 #include <netinet/ip6.h>
132 #include <netinet/icmp6.h>
133 #include <netinet6/nd6.h>
134 #include <netinet6/ip6_var.h>
135 #include <netinet6/in6_pcb.h>
136 #include <netinet/tcp.h>
137 #include <netinet/tcp_fsm.h>
138 #include <netinet/tcp_seq.h>
139 #include <netinet/tcp_timer.h>
140 #include <netinet/tcp_var.h>
141 #include <netinet6/tcp6_var.h>
142 #include <netinet/tcpip.h>
144 #include <netinet/tcp_debug.h>
145 #endif /* TCPDEBUG */
147 #include <machine/in_cksum.h>
149 extern struct uma_zone *sack_hole_zone;
151 SYSCTL_NODE(_net_inet_tcp, OID_AUTO, sack, CTLFLAG_RW, 0, "TCP SACK");
153 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, enable, CTLFLAG_RW,
154 &tcp_do_sack, 0, "Enable/Disable TCP SACK support");
155 TUNABLE_INT("net.inet.tcp.sack.enable", &tcp_do_sack);
157 static int tcp_sack_maxholes = 128;
158 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, maxholes, CTLFLAG_RW,
159 &tcp_sack_maxholes, 0,
160 "Maximum number of TCP SACK holes allowed per connection");
162 static int tcp_sack_globalmaxholes = 65536;
163 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalmaxholes, CTLFLAG_RW,
164 &tcp_sack_globalmaxholes, 0,
165 "Global maximum number of TCP SACK holes");
167 static int tcp_sack_globalholes = 0;
168 SYSCTL_INT(_net_inet_tcp_sack, OID_AUTO, globalholes, CTLFLAG_RD,
169 &tcp_sack_globalholes, 0,
170 "Global number of TCP SACK holes currently allocated");
173 * This function is called upon receipt of new valid data (while not in header
174 * prediction mode), and it updates the ordered list of sacks.
177 tcp_update_sack_list(struct tcpcb *tp, tcp_seq rcv_start, tcp_seq rcv_end)
180 * First reported block MUST be the most recent one. Subsequent
181 * blocks SHOULD be in the order in which they arrived at the
182 * receiver. These two conditions make the implementation fully
183 * compliant with RFC 2018.
185 struct sackblk head_blk, saved_blks[MAX_SACK_BLKS];
186 int num_head, num_saved, i;
188 INP_LOCK_ASSERT(tp->t_inpcb);
190 /* Check arguments */
191 KASSERT(SEQ_LT(rcv_start, rcv_end), ("rcv_start < rcv_end"));
193 /* SACK block for the received segment. */
194 head_blk.start = rcv_start;
195 head_blk.end = rcv_end;
198 * Merge updated SACK blocks into head_blk, and
199 * save unchanged SACK blocks into saved_blks[].
200 * num_saved will have the number of the saved SACK blocks.
203 for (i = 0; i < tp->rcv_numsacks; i++) {
204 tcp_seq start = tp->sackblks[i].start;
205 tcp_seq end = tp->sackblks[i].end;
206 if (SEQ_GEQ(start, end) || SEQ_LEQ(start, tp->rcv_nxt)) {
208 * Discard this SACK block.
210 } else if (SEQ_LEQ(head_blk.start, end) &&
211 SEQ_GEQ(head_blk.end, start)) {
213 * Merge this SACK block into head_blk.
214 * This SACK block itself will be discarded.
216 if (SEQ_GT(head_blk.start, start))
217 head_blk.start = start;
218 if (SEQ_LT(head_blk.end, end))
222 * Save this SACK block.
224 saved_blks[num_saved].start = start;
225 saved_blks[num_saved].end = end;
231 * Update SACK list in tp->sackblks[].
234 if (SEQ_GT(head_blk.start, tp->rcv_nxt)) {
236 * The received data segment is an out-of-order segment.
237 * Put head_blk at the top of SACK list.
239 tp->sackblks[0] = head_blk;
242 * If the number of saved SACK blocks exceeds its limit,
243 * discard the last SACK block.
245 if (num_saved >= MAX_SACK_BLKS)
250 * Copy the saved SACK blocks back.
252 bcopy(saved_blks, &tp->sackblks[num_head],
253 sizeof(struct sackblk) * num_saved);
256 /* Save the number of SACK blocks. */
257 tp->rcv_numsacks = num_head + num_saved;
261 * Delete all receiver-side SACK information.
264 tcp_clean_sackreport(tp)
269 INP_LOCK_ASSERT(tp->t_inpcb);
270 tp->rcv_numsacks = 0;
271 for (i = 0; i < MAX_SACK_BLKS; i++)
272 tp->sackblks[i].start = tp->sackblks[i].end=0;
276 * Allocate struct sackhole.
278 static struct sackhole *
279 tcp_sackhole_alloc(struct tcpcb *tp, tcp_seq start, tcp_seq end)
281 struct sackhole *hole;
283 if (tp->snd_numholes >= tcp_sack_maxholes ||
284 tcp_sack_globalholes >= tcp_sack_globalmaxholes) {
285 tcpstat.tcps_sack_sboverflow++;
289 hole = (struct sackhole *)uma_zalloc(sack_hole_zone, M_NOWAIT);
298 tcp_sack_globalholes++;
304 * Free struct sackhole.
307 tcp_sackhole_free(struct tcpcb *tp, struct sackhole *hole)
309 uma_zfree(sack_hole_zone, hole);
312 tcp_sack_globalholes--;
314 KASSERT(tp->snd_numholes >= 0, ("tp->snd_numholes >= 0"));
315 KASSERT(tcp_sack_globalholes >= 0, ("tcp_sack_globalholes >= 0"));
319 * Insert new SACK hole into scoreboard.
321 static struct sackhole *
322 tcp_sackhole_insert(struct tcpcb *tp, tcp_seq start, tcp_seq end,
323 struct sackhole *after)
325 struct sackhole *hole;
327 /* Allocate a new SACK hole. */
328 hole = tcp_sackhole_alloc(tp, start, end);
332 /* Insert the new SACK hole into scoreboard */
334 TAILQ_INSERT_AFTER(&tp->snd_holes, after, hole, scblink);
336 TAILQ_INSERT_TAIL(&tp->snd_holes, hole, scblink);
338 /* Update SACK hint. */
339 if (tp->sackhint.nexthole == NULL)
340 tp->sackhint.nexthole = hole;
346 * Remove SACK hole from scoreboard.
349 tcp_sackhole_remove(struct tcpcb *tp, struct sackhole *hole)
351 /* Update SACK hint. */
352 if (tp->sackhint.nexthole == hole)
353 tp->sackhint.nexthole = TAILQ_NEXT(hole, scblink);
355 /* Remove this SACK hole. */
356 TAILQ_REMOVE(&tp->snd_holes, hole, scblink);
358 /* Free this SACK hole. */
359 tcp_sackhole_free(tp, hole);
363 * Process cumulative ACK and the TCP SACK option to update the scoreboard.
364 * tp->snd_holes is an ordered list of holes (oldest to newest, in terms of
365 * the sequence space).
368 tcp_sack_doack(struct tcpcb *tp, struct tcpopt *to, tcp_seq th_ack)
370 struct sackhole *cur, *temp;
371 struct sackblk sack, sack_blocks[TCP_MAX_SACK + 1], *sblkp;
372 int i, j, num_sack_blks;
374 INP_LOCK_ASSERT(tp->t_inpcb);
378 * If SND.UNA will be advanced by SEG.ACK, and if SACK holes exist,
379 * treat [SND.UNA, SEG.ACK) as if it is a SACK block.
381 if (SEQ_LT(tp->snd_una, th_ack) && !TAILQ_EMPTY(&tp->snd_holes)) {
382 sack_blocks[num_sack_blks].start = tp->snd_una;
383 sack_blocks[num_sack_blks++].end = th_ack;
386 * Append received valid SACK blocks to sack_blocks[].
388 for (i = 0; i < to->to_nsacks; i++) {
389 bcopy((to->to_sacks + i * TCPOLEN_SACK), &sack, sizeof(sack));
390 sack.start = ntohl(sack.start);
391 sack.end = ntohl(sack.end);
392 if (SEQ_GT(sack.end, sack.start) &&
393 SEQ_GT(sack.start, tp->snd_una) &&
394 SEQ_GT(sack.start, th_ack) &&
395 SEQ_LT(sack.start, tp->snd_max) &&
396 SEQ_GT(sack.end, tp->snd_una) &&
397 SEQ_LEQ(sack.end, tp->snd_max))
398 sack_blocks[num_sack_blks++] = sack;
402 * Return if SND.UNA is not advanced and no valid SACK block
405 if (num_sack_blks == 0)
409 * Sort the SACK blocks so we can update the scoreboard
410 * with just one pass. The overhead of sorting upto 4+1 elements
411 * is less than making upto 4+1 passes over the scoreboard.
413 for (i = 0; i < num_sack_blks; i++) {
414 for (j = i + 1; j < num_sack_blks; j++) {
415 if (SEQ_GT(sack_blocks[i].end, sack_blocks[j].end)) {
416 sack = sack_blocks[i];
417 sack_blocks[i] = sack_blocks[j];
418 sack_blocks[j] = sack;
422 if (TAILQ_EMPTY(&tp->snd_holes))
424 * Empty scoreboard. Need to initialize snd_fack (it may be
425 * uninitialized or have a bogus value). Scoreboard holes
426 * (from the sack blocks received) are created later below (in
427 * the logic that adds holes to the tail of the scoreboard).
429 tp->snd_fack = SEQ_MAX(tp->snd_una, th_ack);
431 * In the while-loop below, incoming SACK blocks (sack_blocks[])
432 * and SACK holes (snd_holes) are traversed from their tails with
433 * just one pass in order to reduce the number of compares especially
434 * when the bandwidth-delay product is large.
435 * Note: Typically, in the first RTT of SACK recovery, the highest
436 * three or four SACK blocks with the same ack number are received.
437 * In the second RTT, if retransmitted data segments are not lost,
438 * the highest three or four SACK blocks with ack number advancing
441 sblkp = &sack_blocks[num_sack_blks - 1]; /* Last SACK block */
442 if (SEQ_LT(tp->snd_fack, sblkp->start)) {
444 * The highest SACK block is beyond fack.
445 * Append new SACK hole at the tail.
446 * If the second or later highest SACK blocks are also
447 * beyond the current fack, they will be inserted by
448 * way of hole splitting in the while-loop below.
450 temp = tcp_sackhole_insert(tp, tp->snd_fack,sblkp->start,NULL);
452 tp->snd_fack = sblkp->end;
453 /* Go to the previous sack block. */
457 * We failed to add a new hole based on the current
458 * sack block. Skip over all the sack blocks that
459 * fall completely to the right of snd_fack and proceed
460 * to trim the scoreboard based on the remaining sack
461 * blocks. This also trims the scoreboard for th_ack
462 * (which is sack_blocks[0]).
464 while (sblkp >= sack_blocks &&
465 SEQ_LT(tp->snd_fack, sblkp->start))
467 if (sblkp >= sack_blocks &&
468 SEQ_LT(tp->snd_fack, sblkp->end))
469 tp->snd_fack = sblkp->end;
471 } else if (SEQ_LT(tp->snd_fack, sblkp->end))
472 /* fack is advanced. */
473 tp->snd_fack = sblkp->end;
474 /* We must have at least one SACK hole in scoreboard */
475 KASSERT(!TAILQ_EMPTY(&tp->snd_holes), ("SACK scoreboard must not be empty"));
476 cur = TAILQ_LAST(&tp->snd_holes, sackhole_head); /* Last SACK hole */
478 * Since the incoming sack blocks are sorted, we can process them
479 * making one sweep of the scoreboard.
481 while (sblkp >= sack_blocks && cur != NULL) {
482 if (SEQ_GEQ(sblkp->start, cur->end)) {
484 * SACKs data beyond the current hole.
485 * Go to the previous sack block.
490 if (SEQ_LEQ(sblkp->end, cur->start)) {
492 * SACKs data before the current hole.
493 * Go to the previous hole.
495 cur = TAILQ_PREV(cur, sackhole_head, scblink);
498 tp->sackhint.sack_bytes_rexmit -= (cur->rxmit - cur->start);
499 KASSERT(tp->sackhint.sack_bytes_rexmit >= 0,
500 ("sackhint bytes rtx >= 0"));
501 if (SEQ_LEQ(sblkp->start, cur->start)) {
502 /* Data acks at least the beginning of hole */
503 if (SEQ_GEQ(sblkp->end, cur->end)) {
504 /* Acks entire hole, so delete hole */
506 cur = TAILQ_PREV(cur, sackhole_head, scblink);
507 tcp_sackhole_remove(tp, temp);
509 * The sack block may ack all or part of the next
510 * hole too, so continue onto the next hole.
514 /* Move start of hole forward */
515 cur->start = sblkp->end;
516 cur->rxmit = SEQ_MAX(cur->rxmit, cur->start);
519 /* Data acks at least the end of hole */
520 if (SEQ_GEQ(sblkp->end, cur->end)) {
521 /* Move end of hole backward */
522 cur->end = sblkp->start;
523 cur->rxmit = SEQ_MIN(cur->rxmit, cur->end);
526 * ACKs some data in middle of a hole; need to
529 temp = tcp_sackhole_insert(tp, sblkp->end,
532 if (SEQ_GT(cur->rxmit, temp->rxmit)) {
533 temp->rxmit = cur->rxmit;
534 tp->sackhint.sack_bytes_rexmit
538 cur->end = sblkp->start;
539 cur->rxmit = SEQ_MIN(cur->rxmit,
544 tp->sackhint.sack_bytes_rexmit += (cur->rxmit - cur->start);
546 * Testing sblkp->start against cur->start tells us whether
547 * we're done with the sack block or the sack hole.
548 * Accordingly, we advance one or the other.
550 if (SEQ_LEQ(sblkp->start, cur->start))
551 cur = TAILQ_PREV(cur, sackhole_head, scblink);
558 * Free all SACK holes to clear the scoreboard.
561 tcp_free_sackholes(struct tcpcb *tp)
565 INP_LOCK_ASSERT(tp->t_inpcb);
566 while ((q = TAILQ_FIRST(&tp->snd_holes)) != NULL)
567 tcp_sackhole_remove(tp, q);
568 tp->sackhint.sack_bytes_rexmit = 0;
570 KASSERT(tp->snd_numholes == 0, ("tp->snd_numholes == 0"));
571 KASSERT(tp->sackhint.nexthole == NULL,
572 ("tp->sackhint.nexthole == NULL"));
576 * Partial ack handling within a sack recovery episode.
577 * Keeping this very simple for now. When a partial ack
578 * is received, force snd_cwnd to a value that will allow
579 * the sender to transmit no more than 2 segments.
580 * If necessary, a better scheme can be adopted at a
581 * later point, but for now, the goal is to prevent the
582 * sender from bursting a large amount of data in the midst
586 tcp_sack_partialack(tp, th)
592 INP_LOCK_ASSERT(tp->t_inpcb);
593 callout_stop(tp->tt_rexmt);
595 /* send one or 2 segments based on how much new data was acked */
596 if (((th->th_ack - tp->snd_una) / tp->t_maxseg) > 2)
598 tp->snd_cwnd = (tp->sackhint.sack_bytes_rexmit +
599 (tp->snd_nxt - tp->sack_newdata) +
600 num_segs * tp->t_maxseg);
601 if (tp->snd_cwnd > tp->snd_ssthresh)
602 tp->snd_cwnd = tp->snd_ssthresh;
603 tp->t_flags |= TF_ACKNOW;
604 (void) tcp_output(tp);
609 * Debug version of tcp_sack_output() that walks the scoreboard. Used for
610 * now to sanity check the hint.
612 static struct sackhole *
613 tcp_sack_output_debug(struct tcpcb *tp, int *sack_bytes_rexmt)
617 INP_LOCK_ASSERT(tp->t_inpcb);
618 *sack_bytes_rexmt = 0;
619 TAILQ_FOREACH(p, &tp->snd_holes, scblink) {
620 if (SEQ_LT(p->rxmit, p->end)) {
621 if (SEQ_LT(p->rxmit, tp->snd_una)) {/* old SACK hole */
624 *sack_bytes_rexmt += (p->rxmit - p->start);
627 *sack_bytes_rexmt += (p->rxmit - p->start);
634 * Returns the next hole to retransmit and the number of retransmitted bytes
635 * from the scoreboard. We store both the next hole and the number of
636 * retransmitted bytes as hints (and recompute these on the fly upon SACK/ACK
637 * reception). This avoids scoreboard traversals completely.
639 * The loop here will traverse *at most* one link. Here's the argument.
640 * For the loop to traverse more than 1 link before finding the next hole to
641 * retransmit, we would need to have at least 1 node following the current hint
642 * with (rxmit == end). But, for all holes following the current hint,
643 * (start == rxmit), since we have not yet retransmitted from them. Therefore,
644 * in order to traverse more 1 link in the loop below, we need to have at least
645 * one node following the current hint with (start == rxmit == end).
646 * But that can't happen, (start == end) means that all the data in that hole
647 * has been sacked, in which case, the hole would have been removed from the
651 tcp_sack_output(struct tcpcb *tp, int *sack_bytes_rexmt)
653 struct sackhole *hole = NULL;
655 INP_LOCK_ASSERT(tp->t_inpcb);
656 *sack_bytes_rexmt = tp->sackhint.sack_bytes_rexmit;
657 hole = tp->sackhint.nexthole;
658 if (hole == NULL || SEQ_LT(hole->rxmit, hole->end))
660 while ((hole = TAILQ_NEXT(hole, scblink)) != NULL) {
661 if (SEQ_LT(hole->rxmit, hole->end)) {
662 tp->sackhint.nexthole = hole;
671 * After a timeout, the SACK list may be rebuilt. This SACK information
672 * should be used to avoid retransmitting SACKed data. This function
673 * traverses the SACK list to see if snd_nxt should be moved forward.
676 tcp_sack_adjust(struct tcpcb *tp)
678 struct sackhole *p, *cur = TAILQ_FIRST(&tp->snd_holes);
680 INP_LOCK_ASSERT(tp->t_inpcb);
682 return; /* No holes */
683 if (SEQ_GEQ(tp->snd_nxt, tp->snd_fack))
684 return; /* We're already beyond any SACKed blocks */
686 * Two cases for which we want to advance snd_nxt:
687 * i) snd_nxt lies between end of one hole and beginning of another
688 * ii) snd_nxt lies between end of last hole and snd_fack
690 while ((p = TAILQ_NEXT(cur, scblink)) != NULL) {
691 if (SEQ_LT(tp->snd_nxt, cur->end))
693 if (SEQ_GEQ(tp->snd_nxt, p->start))
696 tp->snd_nxt = p->start;
700 if (SEQ_LT(tp->snd_nxt, cur->end))
702 tp->snd_nxt = tp->snd_fack;