1 | /* |
2 | * TCP CUBIC: Binary Increase Congestion control for TCP v2.3 |
3 | * Home page: |
4 | * http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC |
5 | * This is from the implementation of CUBIC TCP in |
6 | * Sangtae Ha, Injong Rhee and Lisong Xu, |
7 | * "CUBIC: A New TCP-Friendly High-Speed TCP Variant" |
8 | * in ACM SIGOPS Operating System Review, July 2008. |
9 | * Available from: |
10 | * http://netsrv.csc.ncsu.edu/export/cubic_a_new_tcp_2008.pdf |
11 | * |
12 | * CUBIC integrates a new slow start algorithm, called HyStart. |
13 | * The details of HyStart are presented in |
14 | * Sangtae Ha and Injong Rhee, |
15 | * "Taming the Elephants: New TCP Slow Start", NCSU TechReport 2008. |
16 | * Available from: |
17 | * http://netsrv.csc.ncsu.edu/export/hystart_techreport_2008.pdf |
18 | * |
19 | * All testing results are available from: |
20 | * http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_Testing |
21 | * |
22 | * Unless CUBIC is enabled and congestion window is large |
23 | * this behaves the same as the original Reno. |
24 | */ |
25 | |
26 | #include <linux/mm.h> |
27 | #include <linux/module.h> |
28 | #include <linux/math64.h> |
29 | #include <net/tcp.h> |
30 | |
31 | #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation |
32 | * max_cwnd = snd_cwnd * beta |
33 | */ |
34 | #define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */ |
35 | |
36 | /* Two methods of hybrid slow start */ |
37 | #define HYSTART_ACK_TRAIN 0x1 |
38 | #define HYSTART_DELAY 0x2 |
39 | |
40 | /* Number of delay samples for detecting the increase of delay */ |
41 | #define HYSTART_MIN_SAMPLES 8 |
42 | #define HYSTART_DELAY_MIN (4U<<3) |
43 | #define HYSTART_DELAY_MAX (16U<<3) |
44 | #define HYSTART_DELAY_THRESH(x) clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX) |
45 | |
46 | static int fast_convergence __read_mostly = 1; |
47 | static int beta __read_mostly = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */ |
48 | static int initial_ssthresh __read_mostly; |
49 | static int bic_scale __read_mostly = 41; |
50 | static int tcp_friendliness __read_mostly = 1; |
51 | |
52 | static int hystart __read_mostly = 1; |
53 | static int hystart_detect __read_mostly = HYSTART_ACK_TRAIN | HYSTART_DELAY; |
54 | static int hystart_low_window __read_mostly = 16; |
55 | static int hystart_ack_delta __read_mostly = 2; |
56 | |
57 | static u32 cube_rtt_scale __read_mostly; |
58 | static u32 beta_scale __read_mostly; |
59 | static u64 cube_factor __read_mostly; |
60 | |
61 | /* Note parameters that are used for precomputing scale factors are read-only */ |
62 | module_param(fast_convergence, int, 0644); |
63 | MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence" ); |
64 | module_param(beta, int, 0644); |
65 | MODULE_PARM_DESC(beta, "beta for multiplicative increase" ); |
66 | module_param(initial_ssthresh, int, 0644); |
67 | MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold" ); |
68 | module_param(bic_scale, int, 0444); |
69 | MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)" ); |
70 | module_param(tcp_friendliness, int, 0644); |
71 | MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness" ); |
72 | module_param(hystart, int, 0644); |
73 | MODULE_PARM_DESC(hystart, "turn on/off hybrid slow start algorithm" ); |
74 | module_param(hystart_detect, int, 0644); |
75 | MODULE_PARM_DESC(hystart_detect, "hybrid slow start detection mechanisms" |
76 | " 1: packet-train 2: delay 3: both packet-train and delay" ); |
77 | module_param(hystart_low_window, int, 0644); |
78 | MODULE_PARM_DESC(hystart_low_window, "lower bound cwnd for hybrid slow start" ); |
79 | module_param(hystart_ack_delta, int, 0644); |
80 | MODULE_PARM_DESC(hystart_ack_delta, "spacing between ack's indicating train (msecs)" ); |
81 | |
82 | /* BIC TCP Parameters */ |
83 | struct bictcp { |
84 | u32 cnt; /* increase cwnd by 1 after ACKs */ |
85 | u32 last_max_cwnd; /* last maximum snd_cwnd */ |
86 | u32 last_cwnd; /* the last snd_cwnd */ |
87 | u32 last_time; /* time when updated last_cwnd */ |
88 | u32 bic_origin_point;/* origin point of bic function */ |
89 | u32 bic_K; /* time to origin point |
90 | from the beginning of the current epoch */ |
91 | u32 delay_min; /* min delay (msec << 3) */ |
92 | u32 epoch_start; /* beginning of an epoch */ |
93 | u32 ack_cnt; /* number of acks */ |
94 | u32 tcp_cwnd; /* estimated tcp cwnd */ |
95 | u16 unused; |
96 | u8 sample_cnt; /* number of samples to decide curr_rtt */ |
97 | u8 found; /* the exit point is found? */ |
98 | u32 round_start; /* beginning of each round */ |
99 | u32 end_seq; /* end_seq of the round */ |
100 | u32 last_ack; /* last time when the ACK spacing is close */ |
101 | u32 curr_rtt; /* the minimum rtt of current round */ |
102 | }; |
103 | |
104 | static inline void bictcp_reset(struct bictcp *ca) |
105 | { |
106 | ca->cnt = 0; |
107 | ca->last_max_cwnd = 0; |
108 | ca->last_cwnd = 0; |
109 | ca->last_time = 0; |
110 | ca->bic_origin_point = 0; |
111 | ca->bic_K = 0; |
112 | ca->delay_min = 0; |
113 | ca->epoch_start = 0; |
114 | ca->ack_cnt = 0; |
115 | ca->tcp_cwnd = 0; |
116 | ca->found = 0; |
117 | } |
118 | |
119 | static inline u32 bictcp_clock(void) |
120 | { |
121 | #if HZ < 1000 |
122 | return ktime_to_ms(ktime_get_real()); |
123 | #else |
124 | return jiffies_to_msecs(jiffies); |
125 | #endif |
126 | } |
127 | |
128 | static inline void bictcp_hystart_reset(struct sock *sk) |
129 | { |
130 | struct tcp_sock *tp = tcp_sk(sk); |
131 | struct bictcp *ca = inet_csk_ca(sk); |
132 | |
133 | ca->round_start = ca->last_ack = bictcp_clock(); |
134 | ca->end_seq = tp->snd_nxt; |
135 | ca->curr_rtt = 0; |
136 | ca->sample_cnt = 0; |
137 | } |
138 | |
139 | static void bictcp_init(struct sock *sk) |
140 | { |
141 | struct bictcp *ca = inet_csk_ca(sk); |
142 | |
143 | bictcp_reset(ca); |
144 | |
145 | if (hystart) |
146 | bictcp_hystart_reset(sk); |
147 | |
148 | if (!hystart && initial_ssthresh) |
149 | tcp_sk(sk)->snd_ssthresh = initial_ssthresh; |
150 | } |
151 | |
152 | static void bictcp_cwnd_event(struct sock *sk, enum tcp_ca_event event) |
153 | { |
154 | if (event == CA_EVENT_TX_START) { |
155 | struct bictcp *ca = inet_csk_ca(sk); |
156 | u32 now = tcp_jiffies32; |
157 | s32 delta; |
158 | |
159 | delta = now - tcp_sk(sk)->lsndtime; |
160 | |
161 | /* We were application limited (idle) for a while. |
162 | * Shift epoch_start to keep cwnd growth to cubic curve. |
163 | */ |
164 | if (ca->epoch_start && delta > 0) { |
165 | ca->epoch_start += delta; |
166 | if (after(ca->epoch_start, now)) |
167 | ca->epoch_start = now; |
168 | } |
169 | return; |
170 | } |
171 | } |
172 | |
173 | /* calculate the cubic root of x using a table lookup followed by one |
174 | * Newton-Raphson iteration. |
175 | * Avg err ~= 0.195% |
176 | */ |
177 | static u32 cubic_root(u64 a) |
178 | { |
179 | u32 x, b, shift; |
180 | /* |
181 | * cbrt(x) MSB values for x MSB values in [0..63]. |
182 | * Precomputed then refined by hand - Willy Tarreau |
183 | * |
184 | * For x in [0..63], |
185 | * v = cbrt(x << 18) - 1 |
186 | * cbrt(x) = (v[x] + 10) >> 6 |
187 | */ |
188 | static const u8 v[] = { |
189 | /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118, |
190 | /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156, |
191 | /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179, |
192 | /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199, |
193 | /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215, |
194 | /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229, |
195 | /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242, |
196 | /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254, |
197 | }; |
198 | |
199 | b = fls64(a); |
200 | if (b < 7) { |
201 | /* a in [0..63] */ |
202 | return ((u32)v[(u32)a] + 35) >> 6; |
203 | } |
204 | |
205 | b = ((b * 84) >> 8) - 1; |
206 | shift = (a >> (b * 3)); |
207 | |
208 | x = ((u32)(((u32)v[shift] + 10) << b)) >> 6; |
209 | |
210 | /* |
211 | * Newton-Raphson iteration |
212 | * 2 |
213 | * x = ( 2 * x + a / x ) / 3 |
214 | * k+1 k k |
215 | */ |
216 | x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1))); |
217 | x = ((x * 341) >> 10); |
218 | return x; |
219 | } |
220 | |
221 | /* |
222 | * Compute congestion window to use. |
223 | */ |
224 | static inline void bictcp_update(struct bictcp *ca, u32 cwnd, u32 acked) |
225 | { |
226 | u32 delta, bic_target, max_cnt; |
227 | u64 offs, t; |
228 | |
229 | ca->ack_cnt += acked; /* count the number of ACKed packets */ |
230 | |
231 | if (ca->last_cwnd == cwnd && |
232 | (s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32) |
233 | return; |
234 | |
235 | /* The CUBIC function can update ca->cnt at most once per jiffy. |
236 | * On all cwnd reduction events, ca->epoch_start is set to 0, |
237 | * which will force a recalculation of ca->cnt. |
238 | */ |
239 | if (ca->epoch_start && tcp_jiffies32 == ca->last_time) |
240 | goto tcp_friendliness; |
241 | |
242 | ca->last_cwnd = cwnd; |
243 | ca->last_time = tcp_jiffies32; |
244 | |
245 | if (ca->epoch_start == 0) { |
246 | ca->epoch_start = tcp_jiffies32; /* record beginning */ |
247 | ca->ack_cnt = acked; /* start counting */ |
248 | ca->tcp_cwnd = cwnd; /* syn with cubic */ |
249 | |
250 | if (ca->last_max_cwnd <= cwnd) { |
251 | ca->bic_K = 0; |
252 | ca->bic_origin_point = cwnd; |
253 | } else { |
254 | /* Compute new K based on |
255 | * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ) |
256 | */ |
257 | ca->bic_K = cubic_root(cube_factor |
258 | * (ca->last_max_cwnd - cwnd)); |
259 | ca->bic_origin_point = ca->last_max_cwnd; |
260 | } |
261 | } |
262 | |
263 | /* cubic function - calc*/ |
264 | /* calculate c * time^3 / rtt, |
265 | * while considering overflow in calculation of time^3 |
266 | * (so time^3 is done by using 64 bit) |
267 | * and without the support of division of 64bit numbers |
268 | * (so all divisions are done by using 32 bit) |
269 | * also NOTE the unit of those veriables |
270 | * time = (t - K) / 2^bictcp_HZ |
271 | * c = bic_scale >> 10 |
272 | * rtt = (srtt >> 3) / HZ |
273 | * !!! The following code does not have overflow problems, |
274 | * if the cwnd < 1 million packets !!! |
275 | */ |
276 | |
277 | t = (s32)(tcp_jiffies32 - ca->epoch_start); |
278 | t += msecs_to_jiffies(ca->delay_min >> 3); |
279 | /* change the unit from HZ to bictcp_HZ */ |
280 | t <<= BICTCP_HZ; |
281 | do_div(t, HZ); |
282 | |
283 | if (t < ca->bic_K) /* t - K */ |
284 | offs = ca->bic_K - t; |
285 | else |
286 | offs = t - ca->bic_K; |
287 | |
288 | /* c/rtt * (t-K)^3 */ |
289 | delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ); |
290 | if (t < ca->bic_K) /* below origin*/ |
291 | bic_target = ca->bic_origin_point - delta; |
292 | else /* above origin*/ |
293 | bic_target = ca->bic_origin_point + delta; |
294 | |
295 | /* cubic function - calc bictcp_cnt*/ |
296 | if (bic_target > cwnd) { |
297 | ca->cnt = cwnd / (bic_target - cwnd); |
298 | } else { |
299 | ca->cnt = 100 * cwnd; /* very small increment*/ |
300 | } |
301 | |
302 | /* |
303 | * The initial growth of cubic function may be too conservative |
304 | * when the available bandwidth is still unknown. |
305 | */ |
306 | if (ca->last_max_cwnd == 0 && ca->cnt > 20) |
307 | ca->cnt = 20; /* increase cwnd 5% per RTT */ |
308 | |
309 | tcp_friendliness: |
310 | /* TCP Friendly */ |
311 | if (tcp_friendliness) { |
312 | u32 scale = beta_scale; |
313 | |
314 | delta = (cwnd * scale) >> 3; |
315 | while (ca->ack_cnt > delta) { /* update tcp cwnd */ |
316 | ca->ack_cnt -= delta; |
317 | ca->tcp_cwnd++; |
318 | } |
319 | |
320 | if (ca->tcp_cwnd > cwnd) { /* if bic is slower than tcp */ |
321 | delta = ca->tcp_cwnd - cwnd; |
322 | max_cnt = cwnd / delta; |
323 | if (ca->cnt > max_cnt) |
324 | ca->cnt = max_cnt; |
325 | } |
326 | } |
327 | |
328 | /* The maximum rate of cwnd increase CUBIC allows is 1 packet per |
329 | * 2 packets ACKed, meaning cwnd grows at 1.5x per RTT. |
330 | */ |
331 | ca->cnt = max(ca->cnt, 2U); |
332 | } |
333 | |
334 | static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked) |
335 | { |
336 | struct tcp_sock *tp = tcp_sk(sk); |
337 | struct bictcp *ca = inet_csk_ca(sk); |
338 | |
339 | if (!tcp_is_cwnd_limited(sk)) |
340 | return; |
341 | |
342 | if (tcp_in_slow_start(tp)) { |
343 | if (hystart && after(ack, ca->end_seq)) |
344 | bictcp_hystart_reset(sk); |
345 | acked = tcp_slow_start(tp, acked); |
346 | if (!acked) |
347 | return; |
348 | } |
349 | bictcp_update(ca, tp->snd_cwnd, acked); |
350 | tcp_cong_avoid_ai(tp, ca->cnt, acked); |
351 | } |
352 | |
353 | static u32 bictcp_recalc_ssthresh(struct sock *sk) |
354 | { |
355 | const struct tcp_sock *tp = tcp_sk(sk); |
356 | struct bictcp *ca = inet_csk_ca(sk); |
357 | |
358 | ca->epoch_start = 0; /* end of epoch */ |
359 | |
360 | /* Wmax and fast convergence */ |
361 | if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence) |
362 | ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta)) |
363 | / (2 * BICTCP_BETA_SCALE); |
364 | else |
365 | ca->last_max_cwnd = tp->snd_cwnd; |
366 | |
367 | return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); |
368 | } |
369 | |
370 | static void bictcp_state(struct sock *sk, u8 new_state) |
371 | { |
372 | if (new_state == TCP_CA_Loss) { |
373 | bictcp_reset(inet_csk_ca(sk)); |
374 | bictcp_hystart_reset(sk); |
375 | } |
376 | } |
377 | |
378 | static void hystart_update(struct sock *sk, u32 delay) |
379 | { |
380 | struct tcp_sock *tp = tcp_sk(sk); |
381 | struct bictcp *ca = inet_csk_ca(sk); |
382 | |
383 | if (ca->found & hystart_detect) |
384 | return; |
385 | |
386 | if (hystart_detect & HYSTART_ACK_TRAIN) { |
387 | u32 now = bictcp_clock(); |
388 | |
389 | /* first detection parameter - ack-train detection */ |
390 | if ((s32)(now - ca->last_ack) <= hystart_ack_delta) { |
391 | ca->last_ack = now; |
392 | if ((s32)(now - ca->round_start) > ca->delay_min >> 4) { |
393 | ca->found |= HYSTART_ACK_TRAIN; |
394 | NET_INC_STATS(sock_net(sk), |
395 | LINUX_MIB_TCPHYSTARTTRAINDETECT); |
396 | NET_ADD_STATS(sock_net(sk), |
397 | LINUX_MIB_TCPHYSTARTTRAINCWND, |
398 | tp->snd_cwnd); |
399 | tp->snd_ssthresh = tp->snd_cwnd; |
400 | } |
401 | } |
402 | } |
403 | |
404 | if (hystart_detect & HYSTART_DELAY) { |
405 | /* obtain the minimum delay of more than sampling packets */ |
406 | if (ca->sample_cnt < HYSTART_MIN_SAMPLES) { |
407 | if (ca->curr_rtt == 0 || ca->curr_rtt > delay) |
408 | ca->curr_rtt = delay; |
409 | |
410 | ca->sample_cnt++; |
411 | } else { |
412 | if (ca->curr_rtt > ca->delay_min + |
413 | HYSTART_DELAY_THRESH(ca->delay_min >> 3)) { |
414 | ca->found |= HYSTART_DELAY; |
415 | NET_INC_STATS(sock_net(sk), |
416 | LINUX_MIB_TCPHYSTARTDELAYDETECT); |
417 | NET_ADD_STATS(sock_net(sk), |
418 | LINUX_MIB_TCPHYSTARTDELAYCWND, |
419 | tp->snd_cwnd); |
420 | tp->snd_ssthresh = tp->snd_cwnd; |
421 | } |
422 | } |
423 | } |
424 | } |
425 | |
426 | /* Track delayed acknowledgment ratio using sliding window |
427 | * ratio = (15*ratio + sample) / 16 |
428 | */ |
429 | static void bictcp_acked(struct sock *sk, const struct ack_sample *sample) |
430 | { |
431 | const struct tcp_sock *tp = tcp_sk(sk); |
432 | struct bictcp *ca = inet_csk_ca(sk); |
433 | u32 delay; |
434 | |
435 | /* Some calls are for duplicates without timetamps */ |
436 | if (sample->rtt_us < 0) |
437 | return; |
438 | |
439 | /* Discard delay samples right after fast recovery */ |
440 | if (ca->epoch_start && (s32)(tcp_jiffies32 - ca->epoch_start) < HZ) |
441 | return; |
442 | |
443 | delay = (sample->rtt_us << 3) / USEC_PER_MSEC; |
444 | if (delay == 0) |
445 | delay = 1; |
446 | |
447 | /* first time call or link delay decreases */ |
448 | if (ca->delay_min == 0 || ca->delay_min > delay) |
449 | ca->delay_min = delay; |
450 | |
451 | /* hystart triggers when cwnd is larger than some threshold */ |
452 | if (hystart && tcp_in_slow_start(tp) && |
453 | tp->snd_cwnd >= hystart_low_window) |
454 | hystart_update(sk, delay); |
455 | } |
456 | |
457 | static struct tcp_congestion_ops cubictcp __read_mostly = { |
458 | .init = bictcp_init, |
459 | .ssthresh = bictcp_recalc_ssthresh, |
460 | .cong_avoid = bictcp_cong_avoid, |
461 | .set_state = bictcp_state, |
462 | .undo_cwnd = tcp_reno_undo_cwnd, |
463 | .cwnd_event = bictcp_cwnd_event, |
464 | .pkts_acked = bictcp_acked, |
465 | .owner = THIS_MODULE, |
466 | .name = "cubic" , |
467 | }; |
468 | |
469 | static int __init cubictcp_register(void) |
470 | { |
471 | BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); |
472 | |
473 | /* Precompute a bunch of the scaling factors that are used per-packet |
474 | * based on SRTT of 100ms |
475 | */ |
476 | |
477 | beta_scale = 8*(BICTCP_BETA_SCALE+beta) / 3 |
478 | / (BICTCP_BETA_SCALE - beta); |
479 | |
480 | cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */ |
481 | |
482 | /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3 |
483 | * so K = cubic_root( (wmax-cwnd)*rtt/c ) |
484 | * the unit of K is bictcp_HZ=2^10, not HZ |
485 | * |
486 | * c = bic_scale >> 10 |
487 | * rtt = 100ms |
488 | * |
489 | * the following code has been designed and tested for |
490 | * cwnd < 1 million packets |
491 | * RTT < 100 seconds |
492 | * HZ < 1,000,00 (corresponding to 10 nano-second) |
493 | */ |
494 | |
495 | /* 1/c * 2^2*bictcp_HZ * srtt */ |
496 | cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */ |
497 | |
498 | /* divide by bic_scale and by constant Srtt (100ms) */ |
499 | do_div(cube_factor, bic_scale * 10); |
500 | |
501 | return tcp_register_congestion_control(&cubictcp); |
502 | } |
503 | |
504 | static void __exit cubictcp_unregister(void) |
505 | { |
506 | tcp_unregister_congestion_control(&cubictcp); |
507 | } |
508 | |
509 | module_init(cubictcp_register); |
510 | module_exit(cubictcp_unregister); |
511 | |
512 | MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger" ); |
513 | MODULE_LICENSE("GPL" ); |
514 | MODULE_DESCRIPTION("CUBIC TCP" ); |
515 | MODULE_VERSION("2.3" ); |
516 | |