1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 2009-2010
5 * Swinburne University of Technology, Melbourne, Australia
6 * Copyright (c) 2010-2011 The FreeBSD Foundation
7 * All rights reserved.
8 *
9 * This software was developed at the Centre for Advanced Internet
10 * Architectures, Swinburne University of Technology, by David Hayes and
11 * Lawrence Stewart, made possible in part by a grant from the Cisco University
12 * Research Program Fund at Community Foundation Silicon Valley.
13 *
14 * Portions of this software were developed at the Centre for Advanced Internet
15 * Architectures, Swinburne University of Technology, Melbourne, Australia by
16 * David Hayes under sponsorship from the FreeBSD Foundation.
17 *
18 * Redistribution and use in source and binary forms, with or without
19 * modification, are permitted provided that the following conditions
20 * are met:
21 * 1. Redistributions of source code must retain the above copyright
22 * notice, this list of conditions and the following disclaimer.
23 * 2. Redistributions in binary form must reproduce the above copyright
24 * notice, this list of conditions and the following disclaimer in the
25 * documentation and/or other materials provided with the distribution.
26 *
27 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
28 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
29 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
30 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
31 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
32 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
33 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
34 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
35 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
36 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
37 * SUCH DAMAGE.
38 */
39
40 /*
41 * An implementation of the CAIA-Hamilton delay based congestion control
42 * algorithm, based on "Improved coexistence and loss tolerance for delay based
43 * TCP congestion control" by D. A. Hayes and G. Armitage., in 35th Annual IEEE
44 * Conference on Local Computer Networks (LCN 2010), Denver, Colorado, USA,
45 * 11-14 October 2010.
46 *
47 * Originally released as part of the NewTCP research project at Swinburne
48 * University of Technology's Centre for Advanced Internet Architectures,
49 * Melbourne, Australia, which was made possible in part by a grant from the
50 * Cisco University Research Program Fund at Community Foundation Silicon
51 * Valley. More details are available at:
52 * http://caia.swin.edu.au/urp/newtcp/
53 */
54
55 #include <sys/cdefs.h>
56 __FBSDID("$FreeBSD$");
57
58 #include <sys/param.h>
59 #include <sys/kernel.h>
60 #include <sys/khelp.h>
61 #include <sys/limits.h>
62 #include <sys/malloc.h>
63 #include <sys/module.h>
64 #include <sys/queue.h>
65 #include <sys/socket.h>
66 #include <sys/socketvar.h>
67 #include <sys/sysctl.h>
68 #include <sys/systm.h>
69
70 #include <net/vnet.h>
71
72 #include <netinet/tcp.h>
73 #include <netinet/tcp_seq.h>
74 #include <netinet/tcp_timer.h>
75 #include <netinet/tcp_var.h>
76 #include <netinet/cc/cc.h>
77 #include <netinet/cc/cc_module.h>
78
79 #include <netinet/khelp/h_ertt.h>
80
81 /*
82 * Private signal type for rate based congestion signal.
83 * See <netinet/cc.h> for appropriate bit-range to use for private signals.
84 */
85 #define CC_CHD_DELAY 0x02000000
86
87 /* Largest possible number returned by random(). */
88 #define RANDOM_MAX INT_MAX
89
90 static void chd_ack_received(struct cc_var *ccv, uint16_t ack_type);
91 static void chd_cb_destroy(struct cc_var *ccv);
92 static int chd_cb_init(struct cc_var *ccv);
93 static void chd_cong_signal(struct cc_var *ccv, uint32_t signal_type);
94 static void chd_conn_init(struct cc_var *ccv);
95 static int chd_mod_init(void);
96
97 struct chd {
98 /*
99 * Shadow window - keeps track of what the NewReno congestion window
100 * would have been if delay-based cwnd backoffs had not been made. This
101 * functionality aids coexistence with loss-based TCP flows which may be
102 * sharing links along the path.
103 */
104 unsigned long shadow_w;
105 /*
106 * Loss-based TCP compatibility flag - When set, it turns on the shadow
107 * window functionality.
108 */
109 int loss_compete;
110 /* The maximum round trip time seen within a measured rtt period. */
111 int maxrtt_in_rtt;
112 /* The previous qdly that caused cwnd to backoff. */
113 int prev_backoff_qdly;
114 };
115
116 static int ertt_id;
117
118 VNET_DEFINE_STATIC(uint32_t, chd_qmin) = 5;
119 VNET_DEFINE_STATIC(uint32_t, chd_pmax) = 50;
120 VNET_DEFINE_STATIC(uint32_t, chd_loss_fair) = 1;
121 VNET_DEFINE_STATIC(uint32_t, chd_use_max) = 1;
122 VNET_DEFINE_STATIC(uint32_t, chd_qthresh) = 20;
123 #define V_chd_qthresh VNET(chd_qthresh)
124 #define V_chd_qmin VNET(chd_qmin)
125 #define V_chd_pmax VNET(chd_pmax)
126 #define V_chd_loss_fair VNET(chd_loss_fair)
127 #define V_chd_use_max VNET(chd_use_max)
128
129 static MALLOC_DEFINE(M_CHD, "chd data",
130 "Per connection data required for the CHD congestion control algorithm");
131
132 struct cc_algo chd_cc_algo = {
133 .name = "chd",
134 .ack_received = chd_ack_received,
135 .cb_destroy = chd_cb_destroy,
136 .cb_init = chd_cb_init,
137 .cong_signal = chd_cong_signal,
138 .conn_init = chd_conn_init,
139 .mod_init = chd_mod_init
140 };
141
142 static __inline void
chd_window_decrease(struct cc_var * ccv)143 chd_window_decrease(struct cc_var *ccv)
144 {
145 unsigned long win;
146
147 win = min(CCV(ccv, snd_wnd), CCV(ccv, snd_cwnd)) / CCV(ccv, t_maxseg);
148 win -= max((win / 2), 1);
149 CCV(ccv, snd_ssthresh) = max(win, 2) * CCV(ccv, t_maxseg);
150 }
151
152 /*
153 * Probabilistic backoff function. Returns 1 if we should backoff or 0
154 * otherwise. The calculation of p is similar to the calculation of p in cc_hd.
155 */
156 static __inline int
should_backoff(int qdly,int maxqdly,struct chd * chd_data)157 should_backoff(int qdly, int maxqdly, struct chd *chd_data)
158 {
159 unsigned long p, rand;
160
161 rand = random();
162
163 if (qdly < V_chd_qthresh) {
164 chd_data->loss_compete = 0;
165 p = (((RANDOM_MAX / 100) * V_chd_pmax) /
166 (V_chd_qthresh - V_chd_qmin)) *
167 (qdly - V_chd_qmin);
168 } else {
169 if (qdly > V_chd_qthresh) {
170 p = (((RANDOM_MAX / 100) * V_chd_pmax) /
171 (maxqdly - V_chd_qthresh)) *
172 (maxqdly - qdly);
173 if (V_chd_loss_fair && rand < p)
174 chd_data->loss_compete = 1;
175 } else {
176 p = (RANDOM_MAX / 100) * V_chd_pmax;
177 chd_data->loss_compete = 0;
178 }
179 }
180
181 return (rand < p);
182 }
183
184 static __inline void
chd_window_increase(struct cc_var * ccv,int new_measurement)185 chd_window_increase(struct cc_var *ccv, int new_measurement)
186 {
187 struct chd *chd_data;
188 int incr;
189
190 chd_data = ccv->cc_data;
191 incr = 0;
192
193 if (CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh)) {
194 /* Adapted from NewReno slow start. */
195 if (V_tcp_do_rfc3465) {
196 /* In slow-start with ABC enabled. */
197 if (CCV(ccv, snd_nxt) == CCV(ccv, snd_max)) {
198 /* Not due to RTO. */
199 incr = min(ccv->bytes_this_ack,
200 V_tcp_abc_l_var * CCV(ccv, t_maxseg));
201 } else {
202 /* Due to RTO. */
203 incr = min(ccv->bytes_this_ack,
204 CCV(ccv, t_maxseg));
205 }
206 } else
207 incr = CCV(ccv, t_maxseg);
208
209 } else { /* Congestion avoidance. */
210 if (V_tcp_do_rfc3465) {
211 if (ccv->flags & CCF_ABC_SENTAWND) {
212 ccv->flags &= ~CCF_ABC_SENTAWND;
213 incr = CCV(ccv, t_maxseg);
214 }
215 } else if (new_measurement)
216 incr = CCV(ccv, t_maxseg);
217 }
218
219 if (chd_data->shadow_w > 0) {
220 /* Track NewReno window. */
221 chd_data->shadow_w = min(chd_data->shadow_w + incr,
222 TCP_MAXWIN << CCV(ccv, snd_scale));
223 }
224
225 CCV(ccv,snd_cwnd) = min(CCV(ccv, snd_cwnd) + incr,
226 TCP_MAXWIN << CCV(ccv, snd_scale));
227 }
228
229 /*
230 * All ACK signals are used for timing measurements to determine delay-based
231 * congestion. However, window increases are only performed when
232 * ack_type == CC_ACK.
233 */
234 static void
chd_ack_received(struct cc_var * ccv,uint16_t ack_type)235 chd_ack_received(struct cc_var *ccv, uint16_t ack_type)
236 {
237 struct chd *chd_data;
238 struct ertt *e_t;
239 int backoff, new_measurement, qdly, rtt;
240
241 e_t = khelp_get_osd(CCV(ccv, osd), ertt_id);
242 chd_data = ccv->cc_data;
243 new_measurement = e_t->flags & ERTT_NEW_MEASUREMENT;
244 backoff = qdly = 0;
245
246 chd_data->maxrtt_in_rtt = imax(e_t->rtt, chd_data->maxrtt_in_rtt);
247
248 if (new_measurement) {
249 /*
250 * There is a new per RTT measurement, so check to see if there
251 * is delay based congestion.
252 */
253 rtt = V_chd_use_max ? chd_data->maxrtt_in_rtt : e_t->rtt;
254 chd_data->maxrtt_in_rtt = 0;
255
256 if (rtt && e_t->minrtt && !IN_RECOVERY(CCV(ccv, t_flags))) {
257 qdly = rtt - e_t->minrtt;
258 if (qdly > V_chd_qmin) {
259 /*
260 * Probabilistic delay based congestion
261 * indication.
262 */
263 backoff = should_backoff(qdly,
264 e_t->maxrtt - e_t->minrtt, chd_data);
265 } else
266 chd_data->loss_compete = 0;
267 }
268 /* Reset per RTT measurement flag to start a new measurement. */
269 e_t->flags &= ~ERTT_NEW_MEASUREMENT;
270 }
271
272 if (backoff) {
273 /*
274 * Update shadow_w before delay based backoff.
275 */
276 if (chd_data->loss_compete ||
277 qdly > chd_data->prev_backoff_qdly) {
278 /*
279 * Delay is higher than when we backed off previously,
280 * so it is possible that this flow is competing with
281 * loss based flows.
282 */
283 chd_data->shadow_w = max(CCV(ccv, snd_cwnd),
284 chd_data->shadow_w);
285 } else {
286 /*
287 * Reset shadow_w, as it is probable that this flow is
288 * not competing with loss based flows at the moment.
289 */
290 chd_data->shadow_w = 0;
291 }
292
293 chd_data->prev_backoff_qdly = qdly;
294 /*
295 * Send delay-based congestion signal to the congestion signal
296 * handler.
297 */
298 chd_cong_signal(ccv, CC_CHD_DELAY);
299
300 } else if (ack_type == CC_ACK)
301 chd_window_increase(ccv, new_measurement);
302 }
303
304 static void
chd_cb_destroy(struct cc_var * ccv)305 chd_cb_destroy(struct cc_var *ccv)
306 {
307
308 free(ccv->cc_data, M_CHD);
309 }
310
311 static int
chd_cb_init(struct cc_var * ccv)312 chd_cb_init(struct cc_var *ccv)
313 {
314 struct chd *chd_data;
315
316 chd_data = malloc(sizeof(struct chd), M_CHD, M_NOWAIT);
317 if (chd_data == NULL)
318 return (ENOMEM);
319
320 chd_data->shadow_w = 0;
321 ccv->cc_data = chd_data;
322
323 return (0);
324 }
325
326 static void
chd_cong_signal(struct cc_var * ccv,uint32_t signal_type)327 chd_cong_signal(struct cc_var *ccv, uint32_t signal_type)
328 {
329 struct ertt *e_t;
330 struct chd *chd_data;
331 int qdly;
332
333 e_t = khelp_get_osd(CCV(ccv, osd), ertt_id);
334 chd_data = ccv->cc_data;
335 qdly = imax(e_t->rtt, chd_data->maxrtt_in_rtt) - e_t->minrtt;
336
337 switch(signal_type) {
338 case CC_CHD_DELAY:
339 chd_window_decrease(ccv); /* Set new ssthresh. */
340 CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
341 CCV(ccv, snd_recover) = CCV(ccv, snd_max);
342 ENTER_CONGRECOVERY(CCV(ccv, t_flags));
343 break;
344
345 case CC_NDUPACK: /* Packet loss. */
346 /*
347 * Only react to loss as a congestion signal if qdly >
348 * V_chd_qthresh. If qdly is less than qthresh, presume that
349 * this is a non congestion related loss. If qdly is greater
350 * than qthresh, assume that we are competing with loss based
351 * tcp flows and restore window from any unnecessary backoffs,
352 * before the decrease.
353 */
354 if (!IN_RECOVERY(CCV(ccv, t_flags)) && qdly > V_chd_qthresh) {
355 if (chd_data->loss_compete) {
356 CCV(ccv, snd_cwnd) = max(CCV(ccv, snd_cwnd),
357 chd_data->shadow_w);
358 }
359 chd_window_decrease(ccv);
360 } else {
361 /*
362 * This loss isn't congestion related, or already
363 * recovering from congestion.
364 */
365 CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd);
366 CCV(ccv, snd_recover) = CCV(ccv, snd_max);
367 }
368
369 if (chd_data->shadow_w > 0) {
370 chd_data->shadow_w = max(chd_data->shadow_w /
371 CCV(ccv, t_maxseg) / 2, 2) * CCV(ccv, t_maxseg);
372 }
373 ENTER_FASTRECOVERY(CCV(ccv, t_flags));
374 break;
375
376 default:
377 newreno_cc_algo.cong_signal(ccv, signal_type);
378 }
379 }
380
381 static void
chd_conn_init(struct cc_var * ccv)382 chd_conn_init(struct cc_var *ccv)
383 {
384 struct chd *chd_data;
385
386 chd_data = ccv->cc_data;
387 chd_data->prev_backoff_qdly = 0;
388 chd_data->maxrtt_in_rtt = 0;
389 chd_data->loss_compete = 0;
390 /*
391 * Initialise the shadow_cwnd to be equal to snd_cwnd in case we are
392 * competing with loss based flows from the start.
393 */
394 chd_data->shadow_w = CCV(ccv, snd_cwnd);
395 }
396
397 static int
chd_mod_init(void)398 chd_mod_init(void)
399 {
400
401 ertt_id = khelp_get_id("ertt");
402 if (ertt_id <= 0) {
403 printf("%s: h_ertt module not found\n", __func__);
404 return (ENOENT);
405 }
406
407 chd_cc_algo.after_idle = newreno_cc_algo.after_idle;
408 chd_cc_algo.post_recovery = newreno_cc_algo.post_recovery;
409
410 return (0);
411 }
412
413 static int
chd_loss_fair_handler(SYSCTL_HANDLER_ARGS)414 chd_loss_fair_handler(SYSCTL_HANDLER_ARGS)
415 {
416 int error;
417 uint32_t new;
418
419 new = V_chd_loss_fair;
420 error = sysctl_handle_int(oidp, &new, 0, req);
421 if (error == 0 && req->newptr != NULL) {
422 if (new > 1)
423 error = EINVAL;
424 else
425 V_chd_loss_fair = new;
426 }
427
428 return (error);
429 }
430
431 static int
chd_pmax_handler(SYSCTL_HANDLER_ARGS)432 chd_pmax_handler(SYSCTL_HANDLER_ARGS)
433 {
434 int error;
435 uint32_t new;
436
437 new = V_chd_pmax;
438 error = sysctl_handle_int(oidp, &new, 0, req);
439 if (error == 0 && req->newptr != NULL) {
440 if (new == 0 || new > 100)
441 error = EINVAL;
442 else
443 V_chd_pmax = new;
444 }
445
446 return (error);
447 }
448
449 static int
chd_qthresh_handler(SYSCTL_HANDLER_ARGS)450 chd_qthresh_handler(SYSCTL_HANDLER_ARGS)
451 {
452 int error;
453 uint32_t new;
454
455 new = V_chd_qthresh;
456 error = sysctl_handle_int(oidp, &new, 0, req);
457 if (error == 0 && req->newptr != NULL) {
458 if (new <= V_chd_qmin)
459 error = EINVAL;
460 else
461 V_chd_qthresh = new;
462 }
463
464 return (error);
465 }
466
467 SYSCTL_DECL(_net_inet_tcp_cc_chd);
468 SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, chd, CTLFLAG_RW | CTLFLAG_MPSAFE, NULL,
469 "CAIA Hamilton delay-based congestion control related settings");
470
471 SYSCTL_PROC(_net_inet_tcp_cc_chd, OID_AUTO, loss_fair,
472 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
473 &VNET_NAME(chd_loss_fair), 1, &chd_loss_fair_handler,
474 "IU", "Flag to enable shadow window functionality.");
475
476 SYSCTL_PROC(_net_inet_tcp_cc_chd, OID_AUTO, pmax,
477 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
478 &VNET_NAME(chd_pmax), 5, &chd_pmax_handler,
479 "IU", "Per RTT maximum backoff probability as a percentage");
480
481 SYSCTL_PROC(_net_inet_tcp_cc_chd, OID_AUTO, queue_threshold,
482 CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
483 &VNET_NAME(chd_qthresh), 20, &chd_qthresh_handler,
484 "IU", "Queueing congestion threshold in ticks");
485
486 SYSCTL_UINT(_net_inet_tcp_cc_chd, OID_AUTO, queue_min,
487 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(chd_qmin), 5,
488 "Minimum queueing delay threshold in ticks");
489
490 SYSCTL_UINT(_net_inet_tcp_cc_chd, OID_AUTO, use_max,
491 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(chd_use_max), 1,
492 "Use the maximum RTT seen within the measurement period (RTT) "
493 "as the basic delay measurement for the algorithm.");
494
495 DECLARE_CC_MODULE(chd, &chd_cc_algo);
496 MODULE_VERSION(chd, 1);
497 MODULE_DEPEND(chd, ertt, 1, 1, 1);
498