1 /*
2 * Copyright (c) 2013-2021 Apple Inc. All rights reserved.
3 *
4 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
5 *
6 * This file contains Original Code and/or Modifications of Original Code
7 * as defined in and that are subject to the Apple Public Source License
8 * Version 2.0 (the 'License'). You may not use this file except in
9 * compliance with the License. The rights granted to you under the License
10 * may not be used to create, or enable the creation or redistribution of,
11 * unlawful or unlicensed copies of an Apple operating system, or to
12 * circumvent, violate, or enable the circumvention or violation of, any
13 * terms of an Apple operating system software license agreement.
14 *
15 * Please obtain a copy of the License at
16 * http://www.opensource.apple.com/apsl/ and read it before using this file.
17 *
18 * The Original Code and all software distributed under the License are
19 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
20 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
21 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
22 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
23 * Please see the License for the specific language governing rights and
24 * limitations under the License.
25 *
26 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
27 */
28
29 #include "tcp_includes.h"
30
31 #include <sys/param.h>
32 #include <sys/kernel.h>
33 #include <sys/syslog.h>
34
35 #include <netinet/in.h>
36 #include <netinet/in_systm.h>
37 #include <netinet/ip.h>
38 #include <netinet/ip6.h>
39 #include <netinet/ip_var.h>
40
41 static int tcp_cubic_init(struct tcpcb *tp);
42 static int tcp_cubic_cleanup(struct tcpcb *tp);
43 static void tcp_cubic_cwnd_init_or_reset(struct tcpcb *tp);
44 static void tcp_cubic_congestion_avd(struct tcpcb *tp, struct tcphdr *th);
45 static void tcp_cubic_ack_rcvd(struct tcpcb *tp, struct tcphdr *th);
46 static void tcp_cubic_pre_fr(struct tcpcb *tp);
47 static void tcp_cubic_post_fr(struct tcpcb *tp, struct tcphdr *th);
48 static void tcp_cubic_after_timeout(struct tcpcb *tp);
49 static int tcp_cubic_delay_ack(struct tcpcb *tp, struct tcphdr *th);
50 static void tcp_cubic_switch_cc(struct tcpcb *tp);
51 static uint32_t tcp_cubic_update(struct tcpcb *tp, uint32_t rtt);
52 static inline void tcp_cubic_clear_state(struct tcpcb *tp);
53
54 extern float cbrtf(float x);
55
56 struct tcp_cc_algo tcp_cc_cubic = {
57 .name = "cubic",
58 .init = tcp_cubic_init,
59 .cleanup = tcp_cubic_cleanup,
60 .cwnd_init = tcp_cubic_cwnd_init_or_reset,
61 .congestion_avd = tcp_cubic_congestion_avd,
62 .ack_rcvd = tcp_cubic_ack_rcvd,
63 .pre_fr = tcp_cubic_pre_fr,
64 .post_fr = tcp_cubic_post_fr,
65 .after_idle = tcp_cubic_cwnd_init_or_reset,
66 .after_timeout = tcp_cubic_after_timeout,
67 .delay_ack = tcp_cubic_delay_ack,
68 .switch_to = tcp_cubic_switch_cc
69 };
70
71 static float tcp_cubic_backoff = 0.2f; /* multiplicative decrease factor */
72 static float tcp_cubic_coeff = 0.4f;
73 static float tcp_cubic_fast_convergence_factor = 0.875f;
74
75 static float tcp_cubic_beta = 0.8f;
76
77 static int
tcp_cubic_init(struct tcpcb * tp)78 tcp_cubic_init(struct tcpcb *tp)
79 {
80 os_atomic_inc(&tcp_cc_cubic.num_sockets, relaxed);
81
82 if (tcp_cubic_rfc_compliant) {
83 tcp_cubic_backoff = 0.3f; /* multiplicative decrease factor */
84 tcp_cubic_fast_convergence_factor = 0.85f;
85 tcp_cubic_beta = 0.7f;
86 } else {
87 tcp_cubic_backoff = 0.2f; /* multiplicative decrease factor */
88 tcp_cubic_fast_convergence_factor = 0.875f;
89 tcp_cubic_beta = 0.8f;
90 }
91
92 VERIFY(tp->t_ccstate != NULL);
93 tcp_cubic_clear_state(tp);
94 return 0;
95 }
96
97 static int
tcp_cubic_cleanup(struct tcpcb * tp)98 tcp_cubic_cleanup(struct tcpcb *tp)
99 {
100 #pragma unused(tp)
101 os_atomic_dec(&tcp_cc_cubic.num_sockets, relaxed);
102 return 0;
103 }
104
105 /*
106 * Initialize the congestion window at the beginning of a connection or
107 * after idle time
108 */
109 static void
tcp_cubic_cwnd_init_or_reset(struct tcpcb * tp)110 tcp_cubic_cwnd_init_or_reset(struct tcpcb *tp)
111 {
112 VERIFY(tp->t_ccstate != NULL);
113
114 tcp_cubic_clear_state(tp);
115 tcp_cc_cwnd_init_or_reset(tp);
116 tp->t_pipeack = 0;
117 tcp_clear_pipeack_state(tp);
118
119 /* Start counting bytes for RFC 3465 again */
120 tp->t_bytes_acked = 0;
121
122 /*
123 * slow start threshold could get initialized to a lower value
124 * when there is a cached value in the route metrics. In this case,
125 * the connection can enter congestion avoidance without any packet
126 * loss and Cubic will enter steady-state too early. It is better
127 * to always probe to find the initial slow-start threshold.
128 */
129 if (tp->t_inpcb->inp_stat->txbytes <= tcp_initial_cwnd(tp) &&
130 tp->snd_ssthresh < (TCP_MAXWIN << TCP_MAX_WINSHIFT)) {
131 tp->snd_ssthresh = TCP_MAXWIN << TCP_MAX_WINSHIFT;
132 }
133
134 /* Initialize cubic last max to be same as ssthresh */
135 tp->t_ccstate->cub_last_max = tp->snd_ssthresh;
136 }
137
138 /*
139 * Compute the target congestion window for the next RTT according to
140 * cubic equation when an ack is received.
141 *
142 * W(t) = C(t-K)^3 + W(last_max)
143 */
144 static uint32_t
tcp_cubic_update(struct tcpcb * tp,uint32_t rtt)145 tcp_cubic_update(struct tcpcb *tp, uint32_t rtt)
146 {
147 struct tcp_globals *globals = tcp_get_globals(tp);
148 float K, var;
149 uint32_t elapsed_time, win;
150
151 win = min(tp->snd_cwnd, tp->snd_wnd);
152 if (tp->t_ccstate->cub_last_max == 0) {
153 tp->t_ccstate->cub_last_max = tp->snd_ssthresh;
154 }
155
156 if (tp->t_ccstate->cub_epoch_start == 0) {
157 /*
158 * This is the beginning of a new epoch, initialize some of
159 * the variables that we need to use for computing the
160 * congestion window later.
161 */
162 tp->t_ccstate->cub_epoch_start = tcp_globals_now(globals);
163 if (tp->t_ccstate->cub_epoch_start == 0) {
164 tp->t_ccstate->cub_epoch_start = 1;
165 }
166 if (win < tp->t_ccstate->cub_last_max) {
167 /*
168 * Compute cubic epoch period, this is the time
169 * period that the window will take to increase to
170 * last_max again after backoff due to loss.
171 */
172 if (tcp_cubic_minor_fixes) {
173 K = ((float)tp->t_ccstate->cub_last_max - win) / tp->t_maxseg / tcp_cubic_coeff;
174 } else {
175 K = (tp->t_ccstate->cub_last_max - win) / tp->t_maxseg / tcp_cubic_coeff;
176 }
177 K = cbrtf(K);
178 tp->t_ccstate->cub_epoch_period = K * TCP_RETRANSHZ;
179 /* Origin point */
180 tp->t_ccstate->cub_origin_point = tp->t_ccstate->cub_last_max;
181 } else {
182 tp->t_ccstate->cub_epoch_period = 0;
183 tp->t_ccstate->cub_origin_point = win;
184 }
185 }
186
187 VERIFY(tp->t_ccstate->cub_origin_point > 0);
188 /*
189 * Compute the target window for the next RTT using smoothed RTT
190 * as an estimate for next RTT.
191 */
192 elapsed_time = timer_diff(tcp_globals_now(globals), 0, tp->t_ccstate->cub_epoch_start, 0);
193
194 if (tcp_cubic_use_minrtt) {
195 elapsed_time += max(tcp_cubic_use_minrtt, rtt);
196 } else {
197 elapsed_time += rtt;
198 }
199 var = (elapsed_time - tp->t_ccstate->cub_epoch_period) / TCP_RETRANSHZ;
200 var = var * var * var * (tcp_cubic_coeff * tp->t_maxseg);
201
202 return (uint32_t)(tp->t_ccstate->cub_origin_point + var);
203 }
204
205 /*
206 * Standard TCP utilizes bandwidth well in low RTT and low BDP connections
207 * even when there is some packet loss. Enabling TCP mode will help Cubic
208 * to achieve this kind of utilization.
209 *
210 * But if there is a bottleneck link in the path with a fixed size queue
211 * and fixed bandwidth, TCP Cubic will help to reduce packet loss at this
212 * link because of the steady-state behavior. Using average and mean
213 * absolute deviation of W(lastmax), we try to detect if the congestion
214 * window is close to the bottleneck bandwidth. In that case, disabling
215 * TCP mode will help to minimize packet loss at this link.
216 *
217 * Disable TCP mode if the W(lastmax) (the window where previous packet
218 * loss happened) is within a small range from the average last max
219 * calculated.
220 */
221 #define TCP_CUBIC_ENABLE_TCPMODE(_tp_) \
222 ((!soissrcrealtime((_tp_)->t_inpcb->inp_socket) && \
223 (_tp_)->t_ccstate->cub_mean_dev > (tp->t_maxseg << 1)) ? 1 : 0)
224
225 /*
226 * Compute the window growth if standard TCP (AIMD) was used with
227 * a backoff of 0.5 and additive increase of 1 packet per RTT.
228 *
229 * TCP window at time t can be calculated using the following equation
230 * with tcp_beta_cubic
231 *
232 * W(t) <- Wmax * tcp_beta_cubic + 3 * ((1 - tcp_beta_cubic)/(1 + tcp_beta_cubic)) * t/RTT
233 *
234 */
235 static uint32_t
tcp_cubic_tcpwin(struct tcpcb * tp,struct tcphdr * th)236 tcp_cubic_tcpwin(struct tcpcb *tp, struct tcphdr *th)
237 {
238 if (tp->t_ccstate->cub_tcp_win == 0) {
239 /* Start of the epoch, we set the tcp_win to whatever Cubic decided
240 * at the beginning of the epoch.
241 */
242 tp->t_ccstate->cub_tcp_win = min(tp->snd_cwnd, tp->snd_wnd);
243 if (tcp_cubic_minor_fixes) {
244 tp->t_ccstate->cub_tcp_bytes_acked = BYTES_ACKED(th, tp);
245 } else {
246 tp->t_ccstate->cub_tcp_bytes_acked = 0;
247 }
248 } else {
249 tp->t_ccstate->cub_tcp_bytes_acked += BYTES_ACKED(th, tp);
250
251 if (tcp_cubic_minor_fixes) {
252 /*
253 * Increase by ai_factor * MSS, once per RTT. Counting bytes_acked
254 * against the snd_cwnd represents exactly one RTT at full rate.
255 */
256 while (tp->t_ccstate->cub_tcp_bytes_acked >= tp->snd_cwnd) {
257 /* Enough bytes have been ACK'd for TCP to do AIMD*/
258 tp->t_ccstate->cub_tcp_bytes_acked -= tp->snd_cwnd;
259
260 if (tp->snd_cwnd >= tp->t_ccstate->cub_last_max || !tcp_cubic_rfc_compliant) {
261 tp->t_ccstate->cub_tcp_win += tp->t_maxseg;
262 } else {
263 /* Increase-rate from Section 4.2, RFC 8312 */
264 float ai_factor = (float)3 * (1 - tcp_cubic_beta) / (1 + tcp_cubic_beta);
265
266 tp->t_ccstate->cub_tcp_win += (uint32_t)(tp->t_maxseg * ai_factor);
267 }
268 }
269 } else {
270 if (tp->t_ccstate->cub_tcp_bytes_acked >= tp->t_ccstate->cub_tcp_win) {
271 tp->t_ccstate->cub_tcp_bytes_acked -= tp->t_ccstate->cub_tcp_win;
272 tp->t_ccstate->cub_tcp_win += tp->t_maxseg;
273 }
274 }
275 }
276 return tp->t_ccstate->cub_tcp_win;
277 }
278
279 /*
280 * Handle an in-sequence ack during congestion avoidance phase.
281 */
282 static void
tcp_cubic_congestion_avd(struct tcpcb * tp,struct tcphdr * th)283 tcp_cubic_congestion_avd(struct tcpcb *tp, struct tcphdr *th)
284 {
285 uint32_t cubic_target_win, tcp_win, rtt;
286 uint64_t incr_win = UINT32_MAX;
287
288 /* Do not increase congestion window in non-validated phase */
289 if (tcp_cc_is_cwnd_nonvalidated(tp) != 0) {
290 return;
291 }
292
293 tp->t_bytes_acked += BYTES_ACKED(th, tp);
294
295 rtt = get_base_rtt(tp);
296 /*
297 * First compute cubic window. If cubic variables are not
298 * initialized (after coming out of recovery), this call will
299 * initialize them.
300 */
301 cubic_target_win = tcp_cubic_update(tp, rtt);
302
303 /* Compute TCP window if a multiplicative decrease of 0.2 is used */
304 tcp_win = tcp_cubic_tcpwin(tp, th);
305
306 if (tp->snd_cwnd < tcp_win && tcp_cubic_minor_fixes == 0 && TCP_CUBIC_ENABLE_TCPMODE(tp)) {
307 /* this connection is in TCP-friendly region */
308 if (tp->t_bytes_acked >= tp->snd_cwnd) {
309 tp->t_bytes_acked -= tp->snd_cwnd;
310 tp->snd_cwnd = min(tcp_win, TCP_MAXWIN << tp->snd_scale);
311 }
312 } else {
313 if (cubic_target_win > tp->snd_cwnd) {
314 /*
315 * The target win is computed for the next RTT.
316 * To reach this value, cwnd will have to be updated
317 * one segment at a time. Compute how many bytes
318 * need to be acknowledged before we can increase
319 * the cwnd by one segment.
320 */
321 incr_win = (uint64_t)tp->snd_cwnd * tp->t_maxseg;
322 incr_win /= (cubic_target_win - tp->snd_cwnd);
323 if (!tcp_cubic_minor_fixes) {
324 if (incr_win > 0 && tp->t_bytes_acked >= incr_win) {
325 tp->t_bytes_acked -= incr_win;
326 tp->snd_cwnd =
327 min((tp->snd_cwnd + tp->t_maxseg),
328 TCP_MAXWIN << tp->snd_scale);
329 }
330 }
331 }
332 }
333
334 if (tcp_cubic_minor_fixes) {
335 tcp_win = tcp_round_to(tcp_win, tp->t_maxseg);
336
337 if (tp->snd_cwnd < tcp_win) {
338 uint64_t tcp_incr_win;
339
340 tcp_incr_win = (uint64_t)tp->snd_cwnd * tp->t_maxseg;
341 tcp_incr_win /= (tcp_win - tp->snd_cwnd);
342
343 if (tcp_incr_win < incr_win) {
344 /* this connection is in TCP-friendly region */
345 incr_win = tcp_incr_win;
346 }
347 }
348
349 if (incr_win > 0 && tp->t_bytes_acked >= incr_win) {
350 tp->t_bytes_acked -= incr_win;
351 tp->snd_cwnd = min(tp->snd_cwnd + tp->t_maxseg, TCP_MAXWIN << tp->snd_scale);
352 }
353 }
354 }
355
356 static void
tcp_cubic_ack_rcvd(struct tcpcb * tp,struct tcphdr * th)357 tcp_cubic_ack_rcvd(struct tcpcb *tp, struct tcphdr *th)
358 {
359 /* Do not increase the congestion window in non-validated phase */
360 if (tcp_cc_is_cwnd_nonvalidated(tp) != 0) {
361 return;
362 }
363
364 if (tp->snd_cwnd >= tp->snd_ssthresh) {
365 /* Congestion avoidance phase */
366 tcp_cubic_congestion_avd(tp, th);
367 } else {
368 /*
369 * Use 2*SMSS as limit on increment as suggested
370 * by RFC 3465 section 2.3
371 */
372 uint32_t acked, abc_lim, incr;
373
374 acked = BYTES_ACKED(th, tp);
375 if (tcp_cubic_minor_fixes) {
376 /*
377 * Maximum burst-size is limited to the initial congestion-window.
378 * We know that the network can survive this kind of burst.
379 */
380 abc_lim = tcp_initial_cwnd(tp);
381 } else {
382 abc_lim = (tp->snd_nxt == tp->snd_max) ? 2 * tp->t_maxseg : tp->t_maxseg;
383 }
384 incr = min(acked, abc_lim);
385
386 tp->snd_cwnd += incr;
387 tp->snd_cwnd = min(tp->snd_cwnd, TCP_MAXWIN << tp->snd_scale);
388 }
389 }
390
391 static void
tcp_cubic_pre_fr(struct tcpcb * tp)392 tcp_cubic_pre_fr(struct tcpcb *tp)
393 {
394 uint32_t win, avg;
395 int32_t dev;
396 tp->t_ccstate->cub_epoch_start = 0;
397 tp->t_ccstate->cub_tcp_win = 0;
398 tp->t_ccstate->cub_tcp_bytes_acked = 0;
399
400 win = min(tp->snd_cwnd, tp->snd_wnd);
401 if (tp->t_flagsext & TF_CWND_NONVALIDATED) {
402 tp->t_lossflightsize = tp->snd_max - tp->snd_una;
403 if (tcp_flow_control_response) {
404 win = max(tp->t_pipeack, tp->t_lossflightsize);
405 } else {
406 win = (max(tp->t_pipeack, tp->t_lossflightsize)) >> 1;
407 }
408 } else {
409 tp->t_lossflightsize = 0;
410 }
411 /*
412 * Note the congestion window at which packet loss occurred as
413 * cub_last_max.
414 *
415 * If the congestion window is less than the last max window when
416 * loss occurred, it indicates that capacity available in the
417 * network has gone down. This can happen if a new flow has started
418 * and it is capturing some of the bandwidth. To reach convergence
419 * quickly, backoff a little more.
420 */
421 if (win < tp->t_ccstate->cub_last_max && tcp_cubic_minor_fixes) {
422 tp->t_ccstate->cub_last_max = (uint32_t)((float)win * tcp_cubic_fast_convergence_factor);
423 } else {
424 tp->t_ccstate->cub_last_max = win;
425 }
426
427 if (tp->t_ccstate->cub_last_max == 0) {
428 /*
429 * If last_max is zero because snd_wnd is zero or for
430 * any other reason, initialize it to the amount of data
431 * in flight
432 */
433 tp->t_ccstate->cub_last_max = tp->snd_max - tp->snd_una;
434 }
435
436 /*
437 * Compute average and mean absolute deviation of the
438 * window at which packet loss occurred.
439 */
440 if (tp->t_ccstate->cub_avg_lastmax == 0) {
441 tp->t_ccstate->cub_avg_lastmax = tp->t_ccstate->cub_last_max;
442 } else {
443 /*
444 * Average is computed by taking 63 parts of
445 * history and one part of the most recent value
446 */
447 avg = tp->t_ccstate->cub_avg_lastmax;
448 avg = (avg << 6) - avg;
449 tp->t_ccstate->cub_avg_lastmax =
450 (avg + tp->t_ccstate->cub_last_max) >> 6;
451 }
452
453 /* caluclate deviation from average */
454 dev = tp->t_ccstate->cub_avg_lastmax - tp->t_ccstate->cub_last_max;
455
456 /* Take the absolute value */
457 if (dev < 0) {
458 dev = -dev;
459 }
460
461 if (tp->t_ccstate->cub_mean_dev == 0) {
462 tp->t_ccstate->cub_mean_dev = dev;
463 } else {
464 dev = dev + ((tp->t_ccstate->cub_mean_dev << 4)
465 - tp->t_ccstate->cub_mean_dev);
466 tp->t_ccstate->cub_mean_dev = dev >> 4;
467 }
468
469 /* Backoff congestion window by tcp_cubic_backoff factor */
470 win = (uint32_t)(win - (win * tcp_cubic_backoff));
471 win = tcp_round_to(win, tp->t_maxseg);
472 if (win < 2 * tp->t_maxseg) {
473 win = 2 * tp->t_maxseg;
474 }
475 tp->snd_ssthresh = win;
476 tcp_cc_resize_sndbuf(tp);
477 }
478
479 static void
tcp_cubic_post_fr(struct tcpcb * tp,struct tcphdr * th)480 tcp_cubic_post_fr(struct tcpcb *tp, struct tcphdr *th)
481 {
482 uint32_t flight_size = 0;
483 uint32_t ack;
484
485 if (th != NULL) {
486 ack = th->th_ack;
487 } else {
488 ack = tp->snd_una;
489 }
490
491 if (SEQ_LEQ(ack, tp->snd_max) && (!tcp_cubic_minor_fixes || tcp_flow_control_response)) {
492 flight_size = tp->snd_max - ack;
493 } else if (tcp_cubic_minor_fixes) {
494 /*
495 * Cubic Minor Fixes: snd_max - th_ack is a very very bad estimate
496 * of the flight size. Either the app is sending at full speed and
497 * flight_size *is* snd_sshtresh, or the app is not sending at full
498 * speed and congestion-window validation would have kicked in earlier.
499 *
500 * Except that for the latter, snd_ssthresh is way too high.
501 * When we exit recovery we will burst a lot of data out...
502 *
503 * So, tcp_flow_control_response brings us back to the old behavior.
504 * Too many feature-flags...
505 */
506 flight_size = tp->snd_ssthresh;
507 }
508
509 /*
510 * Cubic Minor Fixes: t_lossflightsize is always 0, because of
511 * EXIT_FASTRECOVERY. This here is basically dead code...
512 */
513 if (SACK_ENABLED(tp) && tp->t_lossflightsize > 0 && !tcp_cubic_minor_fixes) {
514 uint32_t total_rxt_size = 0, ncwnd;
515 /*
516 * When SACK is enabled, the number of retransmitted bytes
517 * can be counted more accurately.
518 */
519 total_rxt_size = tcp_rxtseg_total_size(tp);
520 ncwnd = max(tp->t_pipeack, tp->t_lossflightsize);
521 if (total_rxt_size <= ncwnd) {
522 ncwnd = ncwnd - total_rxt_size;
523 }
524
525 /*
526 * To avoid sending a large burst at the end of recovery
527 * set a max limit on ncwnd
528 */
529 ncwnd = min(ncwnd, (tp->t_maxseg << 6));
530 ncwnd = ncwnd >> 1;
531 flight_size = max(ncwnd, flight_size);
532 }
533 /*
534 * Complete ack. The current window was inflated for fast recovery.
535 * It has to be deflated post recovery.
536 *
537 * Window inflation should have left us with approx snd_ssthresh
538 * outstanding data. If the flight size is zero or one segment,
539 * make congestion window to be at least as big as 2 segments to
540 * avoid delayed acknowledgements. This is according to RFC 6582.
541 */
542 if (flight_size < tp->snd_ssthresh) {
543 tp->snd_cwnd = max(flight_size, tp->t_maxseg) + tp->t_maxseg;
544 } else {
545 tp->snd_cwnd = tp->snd_ssthresh;
546 }
547
548 tp->t_ccstate->cub_tcp_win = 0;
549 tp->t_ccstate->cub_tcp_bytes_acked = 0;
550 }
551
552 static void
tcp_cubic_after_timeout(struct tcpcb * tp)553 tcp_cubic_after_timeout(struct tcpcb *tp)
554 {
555 VERIFY(tp->t_ccstate != NULL);
556
557 /*
558 * Avoid adjusting congestion window due to SYN retransmissions.
559 * If more than one byte (SYN) is outstanding then it is still
560 * needed to adjust the window.
561 */
562 if (tp->t_state < TCPS_ESTABLISHED &&
563 ((int)(tp->snd_max - tp->snd_una) <= 1)) {
564 return;
565 }
566
567 if (!IN_FASTRECOVERY(tp)) {
568 tcp_cubic_clear_state(tp);
569 tcp_cubic_pre_fr(tp);
570 }
571
572 /*
573 * Close the congestion window down to one segment as a retransmit
574 * timeout might indicate severe congestion.
575 */
576 tp->snd_cwnd = tp->t_maxseg;
577 }
578
579 static int
tcp_cubic_delay_ack(struct tcpcb * tp,struct tcphdr * th)580 tcp_cubic_delay_ack(struct tcpcb *tp, struct tcphdr *th)
581 {
582 return tcp_cc_delay_ack(tp, th);
583 }
584
585 /*
586 * When switching from a different CC it is better for Cubic to start
587 * fresh. The state required for Cubic calculation might be stale and it
588 * might not represent the current state of the network. If it starts as
589 * a new connection it will probe and learn the existing network conditions.
590 */
591 static void
tcp_cubic_switch_cc(struct tcpcb * tp)592 tcp_cubic_switch_cc(struct tcpcb *tp)
593 {
594 tcp_cubic_cwnd_init_or_reset(tp);
595
596 os_atomic_inc(&tcp_cc_cubic.num_sockets, relaxed);
597 }
598
599 static inline void
tcp_cubic_clear_state(struct tcpcb * tp)600 tcp_cubic_clear_state(struct tcpcb *tp)
601 {
602 tp->t_ccstate->cub_last_max = 0;
603 tp->t_ccstate->cub_epoch_start = 0;
604 tp->t_ccstate->cub_origin_point = 0;
605 tp->t_ccstate->cub_tcp_win = 0;
606 tp->t_ccstate->cub_tcp_bytes_acked = 0;
607 tp->t_ccstate->cub_epoch_period = 0;
608 }
609