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df3271f3 SH |
1 | /* |
2 | * TCP CUBIC: Binary Increase Congestion control for TCP v2.0 | |
3 | * | |
4 | * This is from the implementation of CUBIC TCP in | |
5 | * Injong Rhee, Lisong Xu. | |
6 | * "CUBIC: A New TCP-Friendly High-Speed TCP Variant | |
7 | * in PFLDnet 2005 | |
8 | * Available from: | |
9 | * http://www.csc.ncsu.edu/faculty/rhee/export/bitcp/cubic-paper.pdf | |
10 | * | |
11 | * Unless CUBIC is enabled and congestion window is large | |
12 | * this behaves the same as the original Reno. | |
13 | */ | |
14 | ||
15 | #include <linux/config.h> | |
16 | #include <linux/mm.h> | |
17 | #include <linux/module.h> | |
18 | #include <net/tcp.h> | |
19 | ||
20 | ||
21 | #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation | |
22 | * max_cwnd = snd_cwnd * beta | |
23 | */ | |
24 | #define BICTCP_B 4 /* | |
25 | * In binary search, | |
26 | * go to point (max+min)/N | |
27 | */ | |
28 | #define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */ | |
29 | ||
30 | static int fast_convergence = 1; | |
31 | static int max_increment = 16; | |
32 | static int beta = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */ | |
33 | static int initial_ssthresh = 100; | |
34 | static int bic_scale = 41; | |
35 | static int tcp_friendliness = 1; | |
36 | ||
37 | module_param(fast_convergence, int, 0644); | |
38 | MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence"); | |
39 | module_param(max_increment, int, 0644); | |
40 | MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search"); | |
41 | module_param(beta, int, 0644); | |
42 | MODULE_PARM_DESC(beta, "beta for multiplicative increase"); | |
43 | module_param(initial_ssthresh, int, 0644); | |
44 | MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold"); | |
45 | module_param(bic_scale, int, 0644); | |
46 | MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)"); | |
47 | module_param(tcp_friendliness, int, 0644); | |
48 | MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness"); | |
49 | ||
50 | ||
51 | /* BIC TCP Parameters */ | |
52 | struct bictcp { | |
53 | u32 cnt; /* increase cwnd by 1 after ACKs */ | |
54 | u32 last_max_cwnd; /* last maximum snd_cwnd */ | |
55 | u32 loss_cwnd; /* congestion window at last loss */ | |
56 | u32 last_cwnd; /* the last snd_cwnd */ | |
57 | u32 last_time; /* time when updated last_cwnd */ | |
58 | u32 bic_origin_point;/* origin point of bic function */ | |
59 | u32 bic_K; /* time to origin point from the beginning of the current epoch */ | |
60 | u32 delay_min; /* min delay */ | |
61 | u32 epoch_start; /* beginning of an epoch */ | |
62 | u32 ack_cnt; /* number of acks */ | |
63 | u32 tcp_cwnd; /* estimated tcp cwnd */ | |
64 | #define ACK_RATIO_SHIFT 4 | |
65 | u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */ | |
66 | }; | |
67 | ||
68 | static inline void bictcp_reset(struct bictcp *ca) | |
69 | { | |
70 | ca->cnt = 0; | |
71 | ca->last_max_cwnd = 0; | |
72 | ca->loss_cwnd = 0; | |
73 | ca->last_cwnd = 0; | |
74 | ca->last_time = 0; | |
75 | ca->bic_origin_point = 0; | |
76 | ca->bic_K = 0; | |
77 | ca->delay_min = 0; | |
78 | ca->epoch_start = 0; | |
79 | ca->delayed_ack = 2 << ACK_RATIO_SHIFT; | |
80 | ca->ack_cnt = 0; | |
81 | ca->tcp_cwnd = 0; | |
82 | } | |
83 | ||
84 | static void bictcp_init(struct sock *sk) | |
85 | { | |
86 | bictcp_reset(inet_csk_ca(sk)); | |
87 | if (initial_ssthresh) | |
88 | tcp_sk(sk)->snd_ssthresh = initial_ssthresh; | |
89 | } | |
90 | ||
91 | /* 65536 times the cubic root */ | |
92 | static const u64 cubic_table[8] | |
93 | = {0, 65536, 82570, 94519, 104030, 112063, 119087, 125367}; | |
94 | ||
95 | /* | |
96 | * calculate the cubic root of x | |
97 | * the basic idea is that x can be expressed as i*8^j | |
98 | * so cubic_root(x) = cubic_root(i)*2^j | |
99 | * in the following code, x is i, and y is 2^j | |
100 | * because of integer calculation, there are errors in calculation | |
101 | * so finally use binary search to find out the exact solution | |
102 | */ | |
103 | static u32 cubic_root(u64 x) | |
104 | { | |
105 | u64 y, app, target, start, end, mid, start_diff, end_diff; | |
106 | ||
107 | if (x == 0) | |
108 | return 0; | |
109 | ||
110 | target = x; | |
111 | ||
112 | /* first estimate lower and upper bound */ | |
113 | y = 1; | |
114 | while (x >= 8){ | |
115 | x = (x >> 3); | |
116 | y = (y << 1); | |
117 | } | |
118 | start = (y*cubic_table[x])>>16; | |
119 | if (x==7) | |
120 | end = (y<<1); | |
121 | else | |
122 | end = (y*cubic_table[x+1]+65535)>>16; | |
123 | ||
124 | /* binary search for more accurate one */ | |
125 | while (start < end-1) { | |
126 | mid = (start+end) >> 1; | |
127 | app = mid*mid*mid; | |
128 | if (app < target) | |
129 | start = mid; | |
130 | else if (app > target) | |
131 | end = mid; | |
132 | else | |
133 | return mid; | |
134 | } | |
135 | ||
136 | /* find the most accurate one from start and end */ | |
137 | app = start*start*start; | |
138 | if (app < target) | |
139 | start_diff = target - app; | |
140 | else | |
141 | start_diff = app - target; | |
142 | app = end*end*end; | |
143 | if (app < target) | |
144 | end_diff = target - app; | |
145 | else | |
146 | end_diff = app - target; | |
147 | ||
148 | if (start_diff < end_diff) | |
149 | return (u32)start; | |
150 | else | |
151 | return (u32)end; | |
152 | } | |
153 | ||
154 | static inline u32 bictcp_K(u32 dist, u32 srtt) | |
155 | { | |
156 | u64 d64; | |
157 | u32 d32; | |
158 | u32 count; | |
159 | u32 result; | |
160 | ||
161 | /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3 | |
162 | so K = cubic_root( (wmax-cwnd)*rtt/c ) | |
163 | the unit of K is bictcp_HZ=2^10, not HZ | |
164 | ||
165 | c = bic_scale >> 10 | |
166 | rtt = (tp->srtt >> 3 ) / HZ | |
167 | ||
168 | the following code has been designed and tested for | |
169 | cwnd < 1 million packets | |
170 | RTT < 100 seconds | |
171 | HZ < 1,000,00 (corresponding to 10 nano-second) | |
172 | ||
173 | */ | |
174 | ||
175 | /* 1/c * 2^2*bictcp_HZ */ | |
176 | d32 = (1 << (10+2*BICTCP_HZ)) / bic_scale; | |
177 | d64 = (__u64)d32; | |
178 | ||
179 | /* srtt * 2^count / HZ | |
180 | 1) to get a better accuracy of the following d32, | |
181 | the larger the "count", the better the accuracy | |
182 | 2) and avoid overflow of the following d64 | |
183 | the larger the "count", the high possibility of overflow | |
184 | 3) so find a "count" between bictcp_hz-3 and bictcp_hz | |
185 | "count" may be less than bictcp_HZ, | |
186 | then d64 becomes 0. that is OK | |
187 | */ | |
188 | d32 = srtt; | |
189 | count = 0; | |
190 | while (((d32 & 0x80000000)==0) && (count < BICTCP_HZ)){ | |
191 | d32 = d32 << 1; | |
192 | count++; | |
193 | } | |
194 | d32 = d32 / HZ; | |
195 | ||
196 | /* (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ) */ | |
197 | d64 = (d64 * dist * d32) >> (count+3-BICTCP_HZ); | |
198 | ||
199 | /* cubic root */ | |
200 | d64 = cubic_root(d64); | |
201 | ||
202 | result = (u32)d64; | |
203 | return result; | |
204 | } | |
205 | ||
206 | /* | |
207 | * Compute congestion window to use. | |
208 | */ | |
209 | static inline void bictcp_update(struct bictcp *ca, u32 cwnd) | |
210 | { | |
211 | u64 d64; | |
212 | u32 d32, t, srtt, bic_target, min_cnt, max_cnt; | |
213 | ||
214 | ca->ack_cnt++; /* count the number of ACKs */ | |
215 | ||
216 | if (ca->last_cwnd == cwnd && | |
217 | (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32) | |
218 | return; | |
219 | ||
220 | ca->last_cwnd = cwnd; | |
221 | ca->last_time = tcp_time_stamp; | |
222 | ||
223 | srtt = (HZ << 3)/10; /* use real time-based growth function */ | |
224 | ||
225 | if (ca->epoch_start == 0) { | |
226 | ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */ | |
227 | ca->ack_cnt = 1; /* start counting */ | |
228 | ca->tcp_cwnd = cwnd; /* syn with cubic */ | |
229 | ||
230 | if (ca->last_max_cwnd <= cwnd) { | |
231 | ca->bic_K = 0; | |
232 | ca->bic_origin_point = cwnd; | |
233 | } else { | |
234 | ca->bic_K = bictcp_K(ca->last_max_cwnd-cwnd, srtt); | |
235 | ca->bic_origin_point = ca->last_max_cwnd; | |
236 | } | |
237 | } | |
238 | ||
239 | /* cubic function - calc*/ | |
240 | /* calculate c * time^3 / rtt, | |
241 | * while considering overflow in calculation of time^3 | |
242 | * (so time^3 is done by using d64) | |
243 | * and without the support of division of 64bit numbers | |
244 | * (so all divisions are done by using d32) | |
245 | * also NOTE the unit of those veriables | |
246 | * time = (t - K) / 2^bictcp_HZ | |
247 | * c = bic_scale >> 10 | |
248 | * rtt = (srtt >> 3) / HZ | |
249 | * !!! The following code does not have overflow problems, | |
250 | * if the cwnd < 1 million packets !!! | |
251 | */ | |
252 | ||
253 | /* change the unit from HZ to bictcp_HZ */ | |
254 | t = ((tcp_time_stamp + ca->delay_min - ca->epoch_start) | |
255 | << BICTCP_HZ) / HZ; | |
256 | ||
257 | if (t < ca->bic_K) /* t - K */ | |
258 | d32 = ca->bic_K - t; | |
259 | else | |
260 | d32 = t - ca->bic_K; | |
261 | ||
262 | d64 = (u64)d32; | |
263 | d32 = (bic_scale << 3) * HZ / srtt; /* 1024*c/rtt */ | |
264 | d64 = (d32 * d64 * d64 * d64) >> (10+3*BICTCP_HZ); /* c/rtt * (t-K)^3 */ | |
265 | d32 = (u32)d64; | |
266 | if (t < ca->bic_K) /* below origin*/ | |
267 | bic_target = ca->bic_origin_point - d32; | |
268 | else /* above origin*/ | |
269 | bic_target = ca->bic_origin_point + d32; | |
270 | ||
271 | /* cubic function - calc bictcp_cnt*/ | |
272 | if (bic_target > cwnd) { | |
273 | ca->cnt = cwnd / (bic_target - cwnd); | |
274 | } else { | |
275 | ca->cnt = 100 * cwnd; /* very small increment*/ | |
276 | } | |
277 | ||
278 | if (ca->delay_min > 0) { | |
279 | /* max increment = Smax * rtt / 0.1 */ | |
280 | min_cnt = (cwnd * HZ * 8)/(10 * max_increment * ca->delay_min); | |
281 | if (ca->cnt < min_cnt) | |
282 | ca->cnt = min_cnt; | |
283 | } | |
284 | ||
285 | /* slow start and low utilization */ | |
286 | if (ca->loss_cwnd == 0) /* could be aggressive in slow start */ | |
287 | ca->cnt = 50; | |
288 | ||
289 | /* TCP Friendly */ | |
290 | if (tcp_friendliness) { | |
291 | u32 scale = 8*(BICTCP_BETA_SCALE+beta)/3/(BICTCP_BETA_SCALE-beta); | |
292 | d32 = (cwnd * scale) >> 3; | |
293 | while (ca->ack_cnt > d32) { /* update tcp cwnd */ | |
294 | ca->ack_cnt -= d32; | |
295 | ca->tcp_cwnd++; | |
296 | } | |
297 | ||
298 | if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */ | |
299 | d32 = ca->tcp_cwnd - cwnd; | |
300 | max_cnt = cwnd / d32; | |
301 | if (ca->cnt > max_cnt) | |
302 | ca->cnt = max_cnt; | |
303 | } | |
304 | } | |
305 | ||
306 | ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack; | |
307 | if (ca->cnt == 0) /* cannot be zero */ | |
308 | ca->cnt = 1; | |
309 | } | |
310 | ||
311 | ||
312 | /* Keep track of minimum rtt */ | |
313 | static inline void measure_delay(struct sock *sk) | |
314 | { | |
315 | const struct tcp_sock *tp = tcp_sk(sk); | |
316 | struct bictcp *ca = inet_csk_ca(sk); | |
317 | u32 delay; | |
318 | ||
319 | /* No time stamp */ | |
320 | if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) || | |
321 | /* Discard delay samples right after fast recovery */ | |
322 | (s32)(tcp_time_stamp - ca->epoch_start) < HZ) | |
323 | return; | |
324 | ||
325 | delay = tcp_time_stamp - tp->rx_opt.rcv_tsecr; | |
326 | if (delay == 0) | |
327 | delay = 1; | |
328 | ||
329 | /* first time call or link delay decreases */ | |
330 | if (ca->delay_min == 0 || ca->delay_min > delay) | |
331 | ca->delay_min = delay; | |
332 | } | |
333 | ||
334 | static void bictcp_cong_avoid(struct sock *sk, u32 ack, | |
335 | u32 seq_rtt, u32 in_flight, int data_acked) | |
336 | { | |
337 | struct tcp_sock *tp = tcp_sk(sk); | |
338 | struct bictcp *ca = inet_csk_ca(sk); | |
339 | ||
340 | if (data_acked) | |
341 | measure_delay(sk); | |
342 | ||
343 | if (!tcp_is_cwnd_limited(sk, in_flight)) | |
344 | return; | |
345 | ||
346 | if (tp->snd_cwnd <= tp->snd_ssthresh) | |
347 | tcp_slow_start(tp); | |
348 | else { | |
349 | bictcp_update(ca, tp->snd_cwnd); | |
350 | ||
351 | /* In dangerous area, increase slowly. | |
352 | * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd | |
353 | */ | |
354 | if (tp->snd_cwnd_cnt >= ca->cnt) { | |
355 | if (tp->snd_cwnd < tp->snd_cwnd_clamp) | |
356 | tp->snd_cwnd++; | |
357 | tp->snd_cwnd_cnt = 0; | |
358 | } else | |
359 | tp->snd_cwnd_cnt++; | |
360 | } | |
361 | ||
362 | } | |
363 | ||
364 | static u32 bictcp_recalc_ssthresh(struct sock *sk) | |
365 | { | |
366 | const struct tcp_sock *tp = tcp_sk(sk); | |
367 | struct bictcp *ca = inet_csk_ca(sk); | |
368 | ||
369 | ca->epoch_start = 0; /* end of epoch */ | |
370 | ||
371 | /* Wmax and fast convergence */ | |
372 | if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence) | |
373 | ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta)) | |
374 | / (2 * BICTCP_BETA_SCALE); | |
375 | else | |
376 | ca->last_max_cwnd = tp->snd_cwnd; | |
377 | ||
378 | ca->loss_cwnd = tp->snd_cwnd; | |
379 | ||
380 | return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); | |
381 | } | |
382 | ||
383 | static u32 bictcp_undo_cwnd(struct sock *sk) | |
384 | { | |
385 | struct bictcp *ca = inet_csk_ca(sk); | |
386 | ||
387 | return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd); | |
388 | } | |
389 | ||
390 | static u32 bictcp_min_cwnd(struct sock *sk) | |
391 | { | |
392 | return tcp_sk(sk)->snd_ssthresh; | |
393 | } | |
394 | ||
395 | static void bictcp_state(struct sock *sk, u8 new_state) | |
396 | { | |
397 | if (new_state == TCP_CA_Loss) | |
398 | bictcp_reset(inet_csk_ca(sk)); | |
399 | } | |
400 | ||
401 | /* Track delayed acknowledgment ratio using sliding window | |
402 | * ratio = (15*ratio + sample) / 16 | |
403 | */ | |
404 | static void bictcp_acked(struct sock *sk, u32 cnt) | |
405 | { | |
406 | const struct inet_connection_sock *icsk = inet_csk(sk); | |
407 | ||
408 | if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) { | |
409 | struct bictcp *ca = inet_csk_ca(sk); | |
410 | cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT; | |
411 | ca->delayed_ack += cnt; | |
412 | } | |
413 | } | |
414 | ||
415 | ||
416 | static struct tcp_congestion_ops cubictcp = { | |
417 | .init = bictcp_init, | |
418 | .ssthresh = bictcp_recalc_ssthresh, | |
419 | .cong_avoid = bictcp_cong_avoid, | |
420 | .set_state = bictcp_state, | |
421 | .undo_cwnd = bictcp_undo_cwnd, | |
422 | .min_cwnd = bictcp_min_cwnd, | |
423 | .pkts_acked = bictcp_acked, | |
424 | .owner = THIS_MODULE, | |
425 | .name = "cubic", | |
426 | }; | |
427 | ||
428 | static int __init cubictcp_register(void) | |
429 | { | |
430 | BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); | |
431 | return tcp_register_congestion_control(&cubictcp); | |
432 | } | |
433 | ||
434 | static void __exit cubictcp_unregister(void) | |
435 | { | |
436 | tcp_unregister_congestion_control(&cubictcp); | |
437 | } | |
438 | ||
439 | module_init(cubictcp_register); | |
440 | module_exit(cubictcp_unregister); | |
441 | ||
442 | MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger"); | |
443 | MODULE_LICENSE("GPL"); | |
444 | MODULE_DESCRIPTION("CUBIC TCP"); | |
445 | MODULE_VERSION("2.0"); |