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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 (2U<<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 | |
56 | static u32 cube_rtt_scale __read_mostly; |
57 | static u32 beta_scale __read_mostly; |
58 | static u64 cube_factor __read_mostly; |
59 | |
60 | /* Note parameters that are used for precomputing scale factors are read-only */ |
61 | module_param(fast_convergence, int, 0644); |
62 | MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence"); |
63 | module_param(beta, int, 0644); |
64 | MODULE_PARM_DESC(beta, "beta for multiplicative increase"); |
65 | module_param(initial_ssthresh, int, 0644); |
66 | MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold"); |
67 | module_param(bic_scale, int, 0444); |
68 | MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)"); |
69 | module_param(tcp_friendliness, int, 0644); |
70 | MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness"); |
71 | module_param(hystart, int, 0644); |
72 | MODULE_PARM_DESC(hystart, "turn on/off hybrid slow start algorithm"); |
73 | module_param(hystart_detect, int, 0644); |
74 | MODULE_PARM_DESC(hystart_detect, "hyrbrid slow start detection mechanisms" |
75 | " 1: packet-train 2: delay 3: both packet-train and delay"); |
76 | module_param(hystart_low_window, int, 0644); |
77 | MODULE_PARM_DESC(hystart_low_window, "lower bound cwnd for hybrid slow start"); |
78 | |
79 | /* BIC TCP Parameters */ |
80 | struct bictcp { |
81 | u32 cnt; /* increase cwnd by 1 after ACKs */ |
82 | u32 last_max_cwnd; /* last maximum snd_cwnd */ |
83 | u32 loss_cwnd; /* congestion window at last loss */ |
84 | u32 last_cwnd; /* the last snd_cwnd */ |
85 | u32 last_time; /* time when updated last_cwnd */ |
86 | u32 bic_origin_point;/* origin point of bic function */ |
87 | u32 bic_K; /* time to origin point from the beginning of the current epoch */ |
88 | u32 delay_min; /* min delay */ |
89 | u32 epoch_start; /* beginning of an epoch */ |
90 | u32 ack_cnt; /* number of acks */ |
91 | u32 tcp_cwnd; /* estimated tcp cwnd */ |
92 | #define ACK_RATIO_SHIFT 4 |
93 | u16 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */ |
94 | u8 sample_cnt; /* number of samples to decide curr_rtt */ |
95 | u8 found; /* the exit point is found? */ |
96 | u32 round_start; /* beginning of each round */ |
97 | u32 end_seq; /* end_seq of the round */ |
98 | u32 last_jiffies; /* last time when the ACK spacing is close */ |
99 | u32 curr_rtt; /* the minimum rtt of current round */ |
100 | }; |
101 | |
102 | static inline void bictcp_reset(struct bictcp *ca) |
103 | { |
104 | ca->cnt = 0; |
105 | ca->last_max_cwnd = 0; |
106 | ca->loss_cwnd = 0; |
107 | ca->last_cwnd = 0; |
108 | ca->last_time = 0; |
109 | ca->bic_origin_point = 0; |
110 | ca->bic_K = 0; |
111 | ca->delay_min = 0; |
112 | ca->epoch_start = 0; |
113 | ca->delayed_ack = 2 << ACK_RATIO_SHIFT; |
114 | ca->ack_cnt = 0; |
115 | ca->tcp_cwnd = 0; |
116 | ca->found = 0; |
117 | } |
118 | |
119 | static inline void bictcp_hystart_reset(struct sock *sk) |
120 | { |
121 | struct tcp_sock *tp = tcp_sk(sk); |
122 | struct bictcp *ca = inet_csk_ca(sk); |
123 | |
124 | ca->round_start = ca->last_jiffies = jiffies; |
125 | ca->end_seq = tp->snd_nxt; |
126 | ca->curr_rtt = 0; |
127 | ca->sample_cnt = 0; |
128 | } |
129 | |
130 | static void bictcp_init(struct sock *sk) |
131 | { |
132 | bictcp_reset(inet_csk_ca(sk)); |
133 | |
134 | if (hystart) |
135 | bictcp_hystart_reset(sk); |
136 | |
137 | if (!hystart && initial_ssthresh) |
138 | tcp_sk(sk)->snd_ssthresh = initial_ssthresh; |
139 | } |
140 | |
141 | /* calculate the cubic root of x using a table lookup followed by one |
142 | * Newton-Raphson iteration. |
143 | * Avg err ~= 0.195% |
144 | */ |
145 | static u32 cubic_root(u64 a) |
146 | { |
147 | u32 x, b, shift; |
148 | /* |
149 | * cbrt(x) MSB values for x MSB values in [0..63]. |
150 | * Precomputed then refined by hand - Willy Tarreau |
151 | * |
152 | * For x in [0..63], |
153 | * v = cbrt(x << 18) - 1 |
154 | * cbrt(x) = (v[x] + 10) >> 6 |
155 | */ |
156 | static const u8 v[] = { |
157 | /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118, |
158 | /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156, |
159 | /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179, |
160 | /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199, |
161 | /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215, |
162 | /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229, |
163 | /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242, |
164 | /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254, |
165 | }; |
166 | |
167 | b = fls64(a); |
168 | if (b < 7) { |
169 | /* a in [0..63] */ |
170 | return ((u32)v[(u32)a] + 35) >> 6; |
171 | } |
172 | |
173 | b = ((b * 84) >> 8) - 1; |
174 | shift = (a >> (b * 3)); |
175 | |
176 | x = ((u32)(((u32)v[shift] + 10) << b)) >> 6; |
177 | |
178 | /* |
179 | * Newton-Raphson iteration |
180 | * 2 |
181 | * x = ( 2 * x + a / x ) / 3 |
182 | * k+1 k k |
183 | */ |
184 | x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1))); |
185 | x = ((x * 341) >> 10); |
186 | return x; |
187 | } |
188 | |
189 | /* |
190 | * Compute congestion window to use. |
191 | */ |
192 | static inline void bictcp_update(struct bictcp *ca, u32 cwnd) |
193 | { |
194 | u64 offs; |
195 | u32 delta, t, bic_target, max_cnt; |
196 | |
197 | ca->ack_cnt++; /* count the number of ACKs */ |
198 | |
199 | if (ca->last_cwnd == cwnd && |
200 | (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32) |
201 | return; |
202 | |
203 | ca->last_cwnd = cwnd; |
204 | ca->last_time = tcp_time_stamp; |
205 | |
206 | if (ca->epoch_start == 0) { |
207 | ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */ |
208 | ca->ack_cnt = 1; /* start counting */ |
209 | ca->tcp_cwnd = cwnd; /* syn with cubic */ |
210 | |
211 | if (ca->last_max_cwnd <= cwnd) { |
212 | ca->bic_K = 0; |
213 | ca->bic_origin_point = cwnd; |
214 | } else { |
215 | /* Compute new K based on |
216 | * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ) |
217 | */ |
218 | ca->bic_K = cubic_root(cube_factor |
219 | * (ca->last_max_cwnd - cwnd)); |
220 | ca->bic_origin_point = ca->last_max_cwnd; |
221 | } |
222 | } |
223 | |
224 | /* cubic function - calc*/ |
225 | /* calculate c * time^3 / rtt, |
226 | * while considering overflow in calculation of time^3 |
227 | * (so time^3 is done by using 64 bit) |
228 | * and without the support of division of 64bit numbers |
229 | * (so all divisions are done by using 32 bit) |
230 | * also NOTE the unit of those veriables |
231 | * time = (t - K) / 2^bictcp_HZ |
232 | * c = bic_scale >> 10 |
233 | * rtt = (srtt >> 3) / HZ |
234 | * !!! The following code does not have overflow problems, |
235 | * if the cwnd < 1 million packets !!! |
236 | */ |
237 | |
238 | /* change the unit from HZ to bictcp_HZ */ |
239 | t = ((tcp_time_stamp + (ca->delay_min>>3) - ca->epoch_start) |
240 | << BICTCP_HZ) / HZ; |
241 | |
242 | if (t < ca->bic_K) /* t - K */ |
243 | offs = ca->bic_K - t; |
244 | else |
245 | offs = t - ca->bic_K; |
246 | |
247 | /* c/rtt * (t-K)^3 */ |
248 | delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ); |
249 | if (t < ca->bic_K) /* below origin*/ |
250 | bic_target = ca->bic_origin_point - delta; |
251 | else /* above origin*/ |
252 | bic_target = ca->bic_origin_point + delta; |
253 | |
254 | /* cubic function - calc bictcp_cnt*/ |
255 | if (bic_target > cwnd) { |
256 | ca->cnt = cwnd / (bic_target - cwnd); |
257 | } else { |
258 | ca->cnt = 100 * cwnd; /* very small increment*/ |
259 | } |
260 | |
261 | /* TCP Friendly */ |
262 | if (tcp_friendliness) { |
263 | u32 scale = beta_scale; |
264 | delta = (cwnd * scale) >> 3; |
265 | while (ca->ack_cnt > delta) { /* update tcp cwnd */ |
266 | ca->ack_cnt -= delta; |
267 | ca->tcp_cwnd++; |
268 | } |
269 | |
270 | if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */ |
271 | delta = ca->tcp_cwnd - cwnd; |
272 | max_cnt = cwnd / delta; |
273 | if (ca->cnt > max_cnt) |
274 | ca->cnt = max_cnt; |
275 | } |
276 | } |
277 | |
278 | ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack; |
279 | if (ca->cnt == 0) /* cannot be zero */ |
280 | ca->cnt = 1; |
281 | } |
282 | |
283 | static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight) |
284 | { |
285 | struct tcp_sock *tp = tcp_sk(sk); |
286 | struct bictcp *ca = inet_csk_ca(sk); |
287 | |
288 | if (!tcp_is_cwnd_limited(sk, in_flight)) |
289 | return; |
290 | |
291 | if (tp->snd_cwnd <= tp->snd_ssthresh) { |
292 | if (hystart && after(ack, ca->end_seq)) |
293 | bictcp_hystart_reset(sk); |
294 | tcp_slow_start(tp); |
295 | } else { |
296 | bictcp_update(ca, tp->snd_cwnd); |
297 | tcp_cong_avoid_ai(tp, ca->cnt); |
298 | } |
299 | |
300 | } |
301 | |
302 | static u32 bictcp_recalc_ssthresh(struct sock *sk) |
303 | { |
304 | const struct tcp_sock *tp = tcp_sk(sk); |
305 | struct bictcp *ca = inet_csk_ca(sk); |
306 | |
307 | ca->epoch_start = 0; /* end of epoch */ |
308 | |
309 | /* Wmax and fast convergence */ |
310 | if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence) |
311 | ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta)) |
312 | / (2 * BICTCP_BETA_SCALE); |
313 | else |
314 | ca->last_max_cwnd = tp->snd_cwnd; |
315 | |
316 | ca->loss_cwnd = tp->snd_cwnd; |
317 | |
318 | return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); |
319 | } |
320 | |
321 | static u32 bictcp_undo_cwnd(struct sock *sk) |
322 | { |
323 | struct bictcp *ca = inet_csk_ca(sk); |
324 | |
325 | return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd); |
326 | } |
327 | |
328 | static void bictcp_state(struct sock *sk, u8 new_state) |
329 | { |
330 | if (new_state == TCP_CA_Loss) { |
331 | bictcp_reset(inet_csk_ca(sk)); |
332 | bictcp_hystart_reset(sk); |
333 | } |
334 | } |
335 | |
336 | static void hystart_update(struct sock *sk, u32 delay) |
337 | { |
338 | struct tcp_sock *tp = tcp_sk(sk); |
339 | struct bictcp *ca = inet_csk_ca(sk); |
340 | |
341 | if (!(ca->found & hystart_detect)) { |
342 | u32 curr_jiffies = jiffies; |
343 | |
344 | /* first detection parameter - ack-train detection */ |
345 | if (curr_jiffies - ca->last_jiffies <= msecs_to_jiffies(2)) { |
346 | ca->last_jiffies = curr_jiffies; |
347 | if (curr_jiffies - ca->round_start >= ca->delay_min>>4) |
348 | ca->found |= HYSTART_ACK_TRAIN; |
349 | } |
350 | |
351 | /* obtain the minimum delay of more than sampling packets */ |
352 | if (ca->sample_cnt < HYSTART_MIN_SAMPLES) { |
353 | if (ca->curr_rtt == 0 || ca->curr_rtt > delay) |
354 | ca->curr_rtt = delay; |
355 | |
356 | ca->sample_cnt++; |
357 | } else { |
358 | if (ca->curr_rtt > ca->delay_min + |
359 | HYSTART_DELAY_THRESH(ca->delay_min>>4)) |
360 | ca->found |= HYSTART_DELAY; |
361 | } |
362 | /* |
363 | * Either one of two conditions are met, |
364 | * we exit from slow start immediately. |
365 | */ |
366 | if (ca->found & hystart_detect) |
367 | tp->snd_ssthresh = tp->snd_cwnd; |
368 | } |
369 | } |
370 | |
371 | /* Track delayed acknowledgment ratio using sliding window |
372 | * ratio = (15*ratio + sample) / 16 |
373 | */ |
374 | static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us) |
375 | { |
376 | const struct inet_connection_sock *icsk = inet_csk(sk); |
377 | const struct tcp_sock *tp = tcp_sk(sk); |
378 | struct bictcp *ca = inet_csk_ca(sk); |
379 | u32 delay; |
380 | |
381 | if (icsk->icsk_ca_state == TCP_CA_Open) { |
382 | cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT; |
383 | ca->delayed_ack += cnt; |
384 | } |
385 | |
386 | /* Some calls are for duplicates without timetamps */ |
387 | if (rtt_us < 0) |
388 | return; |
389 | |
390 | /* Discard delay samples right after fast recovery */ |
391 | if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ) |
392 | return; |
393 | |
394 | delay = usecs_to_jiffies(rtt_us) << 3; |
395 | if (delay == 0) |
396 | delay = 1; |
397 | |
398 | /* first time call or link delay decreases */ |
399 | if (ca->delay_min == 0 || ca->delay_min > delay) |
400 | ca->delay_min = delay; |
401 | |
402 | /* hystart triggers when cwnd is larger than some threshold */ |
403 | if (hystart && tp->snd_cwnd <= tp->snd_ssthresh && |
404 | tp->snd_cwnd >= hystart_low_window) |
405 | hystart_update(sk, delay); |
406 | } |
407 | |
408 | static struct tcp_congestion_ops cubictcp = { |
409 | .init = bictcp_init, |
410 | .ssthresh = bictcp_recalc_ssthresh, |
411 | .cong_avoid = bictcp_cong_avoid, |
412 | .set_state = bictcp_state, |
413 | .undo_cwnd = bictcp_undo_cwnd, |
414 | .pkts_acked = bictcp_acked, |
415 | .owner = THIS_MODULE, |
416 | .name = "cubic", |
417 | }; |
418 | |
419 | static int __init cubictcp_register(void) |
420 | { |
421 | BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); |
422 | |
423 | /* Precompute a bunch of the scaling factors that are used per-packet |
424 | * based on SRTT of 100ms |
425 | */ |
426 | |
427 | beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta); |
428 | |
429 | cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */ |
430 | |
431 | /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3 |
432 | * so K = cubic_root( (wmax-cwnd)*rtt/c ) |
433 | * the unit of K is bictcp_HZ=2^10, not HZ |
434 | * |
435 | * c = bic_scale >> 10 |
436 | * rtt = 100ms |
437 | * |
438 | * the following code has been designed and tested for |
439 | * cwnd < 1 million packets |
440 | * RTT < 100 seconds |
441 | * HZ < 1,000,00 (corresponding to 10 nano-second) |
442 | */ |
443 | |
444 | /* 1/c * 2^2*bictcp_HZ * srtt */ |
445 | cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */ |
446 | |
447 | /* divide by bic_scale and by constant Srtt (100ms) */ |
448 | do_div(cube_factor, bic_scale * 10); |
449 | |
450 | return tcp_register_congestion_control(&cubictcp); |
451 | } |
452 | |
453 | static void __exit cubictcp_unregister(void) |
454 | { |
455 | tcp_unregister_congestion_control(&cubictcp); |
456 | } |
457 | |
458 | module_init(cubictcp_register); |
459 | module_exit(cubictcp_unregister); |
460 | |
461 | MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger"); |
462 | MODULE_LICENSE("GPL"); |
463 | MODULE_DESCRIPTION("CUBIC TCP"); |
464 | MODULE_VERSION("2.3"); |
465 |
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