Commit | Line | Data |
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df3271f3 | 1 | /* |
ae27e98a | 2 | * TCP CUBIC: Binary Increase Congestion control for TCP v2.3 |
6b3d6263 SH |
3 | * Home page: |
4 | * http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC | |
df3271f3 | 5 | * This is from the implementation of CUBIC TCP in |
ae27e98a SH |
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. | |
df3271f3 | 9 | * Available from: |
ae27e98a SH |
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 | |
df3271f3 SH |
21 | * |
22 | * Unless CUBIC is enabled and congestion window is large | |
23 | * this behaves the same as the original Reno. | |
24 | */ | |
25 | ||
df3271f3 SH |
26 | #include <linux/mm.h> |
27 | #include <linux/module.h> | |
6f6d6a1a | 28 | #include <linux/math64.h> |
df3271f3 | 29 | #include <net/tcp.h> |
df3271f3 SH |
30 | |
31 | #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation | |
32 | * max_cwnd = snd_cwnd * beta | |
33 | */ | |
df3271f3 SH |
34 | #define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */ |
35 | ||
ae27e98a SH |
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 | ||
59758f44 | 46 | static int fast_convergence __read_mostly = 1; |
6b3d6263 | 47 | static int beta __read_mostly = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */ |
66e1e3b2 | 48 | static int initial_ssthresh __read_mostly; |
59758f44 SH |
49 | static int bic_scale __read_mostly = 41; |
50 | static int tcp_friendliness __read_mostly = 1; | |
df3271f3 | 51 | |
ae27e98a SH |
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; | |
aac46324 | 55 | static int hystart_ack_delta __read_mostly = 2; |
ae27e98a | 56 | |
59758f44 SH |
57 | static u32 cube_rtt_scale __read_mostly; |
58 | static u32 beta_scale __read_mostly; | |
59 | static u64 cube_factor __read_mostly; | |
89b3d9aa SH |
60 | |
61 | /* Note parameters that are used for precomputing scale factors are read-only */ | |
df3271f3 SH |
62 | module_param(fast_convergence, int, 0644); |
63 | MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence"); | |
6b3d6263 | 64 | module_param(beta, int, 0644); |
df3271f3 SH |
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"); | |
89b3d9aa | 68 | module_param(bic_scale, int, 0444); |
df3271f3 SH |
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"); | |
ae27e98a SH |
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, "hyrbrid 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"); | |
aac46324 | 79 | module_param(hystart_ack_delta, int, 0644); |
80 | MODULE_PARM_DESC(hystart_ack_delta, "spacing between ack's indicating train (msecs)"); | |
df3271f3 | 81 | |
df3271f3 SH |
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 loss_cwnd; /* congestion window at last loss */ | |
87 | u32 last_cwnd; /* the last snd_cwnd */ | |
88 | u32 last_time; /* time when updated last_cwnd */ | |
89 | u32 bic_origin_point;/* origin point of bic function */ | |
90 | u32 bic_K; /* time to origin point from the beginning of the current epoch */ | |
17a6e9f1 | 91 | u32 delay_min; /* min delay (msec << 3) */ |
df3271f3 SH |
92 | u32 epoch_start; /* beginning of an epoch */ |
93 | u32 ack_cnt; /* number of acks */ | |
94 | u32 tcp_cwnd; /* estimated tcp cwnd */ | |
95 | #define ACK_RATIO_SHIFT 4 | |
ae27e98a SH |
96 | u16 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */ |
97 | u8 sample_cnt; /* number of samples to decide curr_rtt */ | |
98 | u8 found; /* the exit point is found? */ | |
99 | u32 round_start; /* beginning of each round */ | |
100 | u32 end_seq; /* end_seq of the round */ | |
17a6e9f1 | 101 | u32 last_ack; /* last time when the ACK spacing is close */ |
ae27e98a | 102 | u32 curr_rtt; /* the minimum rtt of current round */ |
df3271f3 SH |
103 | }; |
104 | ||
105 | static inline void bictcp_reset(struct bictcp *ca) | |
106 | { | |
107 | ca->cnt = 0; | |
108 | ca->last_max_cwnd = 0; | |
109 | ca->loss_cwnd = 0; | |
110 | ca->last_cwnd = 0; | |
111 | ca->last_time = 0; | |
112 | ca->bic_origin_point = 0; | |
113 | ca->bic_K = 0; | |
114 | ca->delay_min = 0; | |
115 | ca->epoch_start = 0; | |
116 | ca->delayed_ack = 2 << ACK_RATIO_SHIFT; | |
117 | ca->ack_cnt = 0; | |
118 | ca->tcp_cwnd = 0; | |
ae27e98a SH |
119 | ca->found = 0; |
120 | } | |
121 | ||
17a6e9f1 | 122 | static inline u32 bictcp_clock(void) |
123 | { | |
124 | #if HZ < 1000 | |
125 | return ktime_to_ms(ktime_get_real()); | |
126 | #else | |
127 | return jiffies_to_msecs(jiffies); | |
128 | #endif | |
129 | } | |
130 | ||
ae27e98a SH |
131 | static inline void bictcp_hystart_reset(struct sock *sk) |
132 | { | |
133 | struct tcp_sock *tp = tcp_sk(sk); | |
134 | struct bictcp *ca = inet_csk_ca(sk); | |
135 | ||
17a6e9f1 | 136 | ca->round_start = ca->last_ack = bictcp_clock(); |
ae27e98a SH |
137 | ca->end_seq = tp->snd_nxt; |
138 | ca->curr_rtt = 0; | |
139 | ca->sample_cnt = 0; | |
df3271f3 SH |
140 | } |
141 | ||
142 | static void bictcp_init(struct sock *sk) | |
143 | { | |
144 | bictcp_reset(inet_csk_ca(sk)); | |
ae27e98a SH |
145 | |
146 | if (hystart) | |
147 | bictcp_hystart_reset(sk); | |
148 | ||
149 | if (!hystart && initial_ssthresh) | |
df3271f3 SH |
150 | tcp_sk(sk)->snd_ssthresh = initial_ssthresh; |
151 | } | |
152 | ||
7e58886b SH |
153 | /* calculate the cubic root of x using a table lookup followed by one |
154 | * Newton-Raphson iteration. | |
155 | * Avg err ~= 0.195% | |
df3271f3 | 156 | */ |
9eb2d627 | 157 | static u32 cubic_root(u64 a) |
df3271f3 | 158 | { |
7e58886b SH |
159 | u32 x, b, shift; |
160 | /* | |
161 | * cbrt(x) MSB values for x MSB values in [0..63]. | |
162 | * Precomputed then refined by hand - Willy Tarreau | |
163 | * | |
164 | * For x in [0..63], | |
165 | * v = cbrt(x << 18) - 1 | |
166 | * cbrt(x) = (v[x] + 10) >> 6 | |
9eb2d627 | 167 | */ |
7e58886b SH |
168 | static const u8 v[] = { |
169 | /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118, | |
170 | /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156, | |
171 | /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179, | |
172 | /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199, | |
173 | /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215, | |
174 | /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229, | |
175 | /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242, | |
176 | /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254, | |
177 | }; | |
178 | ||
179 | b = fls64(a); | |
180 | if (b < 7) { | |
181 | /* a in [0..63] */ | |
182 | return ((u32)v[(u32)a] + 35) >> 6; | |
183 | } | |
184 | ||
185 | b = ((b * 84) >> 8) - 1; | |
186 | shift = (a >> (b * 3)); | |
187 | ||
188 | x = ((u32)(((u32)v[shift] + 10) << b)) >> 6; | |
189 | ||
190 | /* | |
191 | * Newton-Raphson iteration | |
192 | * 2 | |
193 | * x = ( 2 * x + a / x ) / 3 | |
194 | * k+1 k k | |
195 | */ | |
6f6d6a1a | 196 | x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1))); |
7e58886b | 197 | x = ((x * 341) >> 10); |
9eb2d627 | 198 | return x; |
df3271f3 SH |
199 | } |
200 | ||
df3271f3 SH |
201 | /* |
202 | * Compute congestion window to use. | |
203 | */ | |
204 | static inline void bictcp_update(struct bictcp *ca, u32 cwnd) | |
205 | { | |
89b3d9aa | 206 | u64 offs; |
6b3d6263 | 207 | u32 delta, t, bic_target, max_cnt; |
df3271f3 SH |
208 | |
209 | ca->ack_cnt++; /* count the number of ACKs */ | |
210 | ||
211 | if (ca->last_cwnd == cwnd && | |
212 | (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32) | |
213 | return; | |
214 | ||
215 | ca->last_cwnd = cwnd; | |
216 | ca->last_time = tcp_time_stamp; | |
217 | ||
df3271f3 SH |
218 | if (ca->epoch_start == 0) { |
219 | ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */ | |
220 | ca->ack_cnt = 1; /* start counting */ | |
221 | ca->tcp_cwnd = cwnd; /* syn with cubic */ | |
222 | ||
223 | if (ca->last_max_cwnd <= cwnd) { | |
224 | ca->bic_K = 0; | |
225 | ca->bic_origin_point = cwnd; | |
226 | } else { | |
89b3d9aa SH |
227 | /* Compute new K based on |
228 | * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ) | |
229 | */ | |
230 | ca->bic_K = cubic_root(cube_factor | |
231 | * (ca->last_max_cwnd - cwnd)); | |
df3271f3 SH |
232 | ca->bic_origin_point = ca->last_max_cwnd; |
233 | } | |
234 | } | |
235 | ||
e905a9ed YH |
236 | /* cubic function - calc*/ |
237 | /* calculate c * time^3 / rtt, | |
238 | * while considering overflow in calculation of time^3 | |
89b3d9aa | 239 | * (so time^3 is done by using 64 bit) |
df3271f3 | 240 | * and without the support of division of 64bit numbers |
89b3d9aa | 241 | * (so all divisions are done by using 32 bit) |
e905a9ed YH |
242 | * also NOTE the unit of those veriables |
243 | * time = (t - K) / 2^bictcp_HZ | |
244 | * c = bic_scale >> 10 | |
df3271f3 SH |
245 | * rtt = (srtt >> 3) / HZ |
246 | * !!! The following code does not have overflow problems, | |
247 | * if the cwnd < 1 million packets !!! | |
e905a9ed | 248 | */ |
df3271f3 SH |
249 | |
250 | /* change the unit from HZ to bictcp_HZ */ | |
17a6e9f1 | 251 | t = ((tcp_time_stamp + msecs_to_jiffies(ca->delay_min>>3) |
252 | - ca->epoch_start) << BICTCP_HZ) / HZ; | |
df3271f3 | 253 | |
e905a9ed | 254 | if (t < ca->bic_K) /* t - K */ |
89b3d9aa | 255 | offs = ca->bic_K - t; |
e905a9ed YH |
256 | else |
257 | offs = t - ca->bic_K; | |
df3271f3 | 258 | |
89b3d9aa SH |
259 | /* c/rtt * (t-K)^3 */ |
260 | delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ); | |
e905a9ed YH |
261 | if (t < ca->bic_K) /* below origin*/ |
262 | bic_target = ca->bic_origin_point - delta; | |
263 | else /* above origin*/ | |
264 | bic_target = ca->bic_origin_point + delta; | |
df3271f3 | 265 | |
e905a9ed YH |
266 | /* cubic function - calc bictcp_cnt*/ |
267 | if (bic_target > cwnd) { | |
df3271f3 | 268 | ca->cnt = cwnd / (bic_target - cwnd); |
e905a9ed YH |
269 | } else { |
270 | ca->cnt = 100 * cwnd; /* very small increment*/ | |
271 | } | |
df3271f3 | 272 | |
df3271f3 SH |
273 | /* TCP Friendly */ |
274 | if (tcp_friendliness) { | |
89b3d9aa SH |
275 | u32 scale = beta_scale; |
276 | delta = (cwnd * scale) >> 3; | |
e905a9ed YH |
277 | while (ca->ack_cnt > delta) { /* update tcp cwnd */ |
278 | ca->ack_cnt -= delta; | |
279 | ca->tcp_cwnd++; | |
df3271f3 SH |
280 | } |
281 | ||
282 | if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */ | |
89b3d9aa SH |
283 | delta = ca->tcp_cwnd - cwnd; |
284 | max_cnt = cwnd / delta; | |
df3271f3 SH |
285 | if (ca->cnt > max_cnt) |
286 | ca->cnt = max_cnt; | |
287 | } | |
e905a9ed | 288 | } |
df3271f3 SH |
289 | |
290 | ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack; | |
291 | if (ca->cnt == 0) /* cannot be zero */ | |
292 | ca->cnt = 1; | |
293 | } | |
294 | ||
c3a05c60 | 295 | static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight) |
df3271f3 SH |
296 | { |
297 | struct tcp_sock *tp = tcp_sk(sk); | |
298 | struct bictcp *ca = inet_csk_ca(sk); | |
299 | ||
df3271f3 SH |
300 | if (!tcp_is_cwnd_limited(sk, in_flight)) |
301 | return; | |
302 | ||
ae27e98a SH |
303 | if (tp->snd_cwnd <= tp->snd_ssthresh) { |
304 | if (hystart && after(ack, ca->end_seq)) | |
305 | bictcp_hystart_reset(sk); | |
df3271f3 | 306 | tcp_slow_start(tp); |
ae27e98a | 307 | } else { |
df3271f3 | 308 | bictcp_update(ca, tp->snd_cwnd); |
758ce5c8 | 309 | tcp_cong_avoid_ai(tp, ca->cnt); |
df3271f3 SH |
310 | } |
311 | ||
312 | } | |
313 | ||
314 | static u32 bictcp_recalc_ssthresh(struct sock *sk) | |
315 | { | |
316 | const struct tcp_sock *tp = tcp_sk(sk); | |
317 | struct bictcp *ca = inet_csk_ca(sk); | |
318 | ||
319 | ca->epoch_start = 0; /* end of epoch */ | |
320 | ||
321 | /* Wmax and fast convergence */ | |
322 | if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence) | |
323 | ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta)) | |
324 | / (2 * BICTCP_BETA_SCALE); | |
325 | else | |
326 | ca->last_max_cwnd = tp->snd_cwnd; | |
327 | ||
328 | ca->loss_cwnd = tp->snd_cwnd; | |
329 | ||
330 | return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); | |
331 | } | |
332 | ||
333 | static u32 bictcp_undo_cwnd(struct sock *sk) | |
334 | { | |
335 | struct bictcp *ca = inet_csk_ca(sk); | |
336 | ||
337 | return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd); | |
338 | } | |
339 | ||
df3271f3 SH |
340 | static void bictcp_state(struct sock *sk, u8 new_state) |
341 | { | |
ae27e98a | 342 | if (new_state == TCP_CA_Loss) { |
df3271f3 | 343 | bictcp_reset(inet_csk_ca(sk)); |
ae27e98a SH |
344 | bictcp_hystart_reset(sk); |
345 | } | |
346 | } | |
347 | ||
348 | static void hystart_update(struct sock *sk, u32 delay) | |
349 | { | |
350 | struct tcp_sock *tp = tcp_sk(sk); | |
351 | struct bictcp *ca = inet_csk_ca(sk); | |
352 | ||
353 | if (!(ca->found & hystart_detect)) { | |
17a6e9f1 | 354 | u32 now = bictcp_clock(); |
ae27e98a SH |
355 | |
356 | /* first detection parameter - ack-train detection */ | |
17a6e9f1 | 357 | if ((s32)(now - ca->last_ack) <= hystart_ack_delta) { |
358 | ca->last_ack = now; | |
359 | if ((s32)(now - ca->round_start) > ca->delay_min >> 4) | |
ae27e98a SH |
360 | ca->found |= HYSTART_ACK_TRAIN; |
361 | } | |
362 | ||
363 | /* obtain the minimum delay of more than sampling packets */ | |
364 | if (ca->sample_cnt < HYSTART_MIN_SAMPLES) { | |
365 | if (ca->curr_rtt == 0 || ca->curr_rtt > delay) | |
366 | ca->curr_rtt = delay; | |
367 | ||
368 | ca->sample_cnt++; | |
369 | } else { | |
370 | if (ca->curr_rtt > ca->delay_min + | |
371 | HYSTART_DELAY_THRESH(ca->delay_min>>4)) | |
372 | ca->found |= HYSTART_DELAY; | |
373 | } | |
374 | /* | |
375 | * Either one of two conditions are met, | |
376 | * we exit from slow start immediately. | |
377 | */ | |
378 | if (ca->found & hystart_detect) | |
379 | tp->snd_ssthresh = tp->snd_cwnd; | |
380 | } | |
df3271f3 SH |
381 | } |
382 | ||
383 | /* Track delayed acknowledgment ratio using sliding window | |
384 | * ratio = (15*ratio + sample) / 16 | |
385 | */ | |
30cfd0ba | 386 | static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us) |
df3271f3 SH |
387 | { |
388 | const struct inet_connection_sock *icsk = inet_csk(sk); | |
ae27e98a | 389 | const struct tcp_sock *tp = tcp_sk(sk); |
e7d0c885 SH |
390 | struct bictcp *ca = inet_csk_ca(sk); |
391 | u32 delay; | |
df3271f3 | 392 | |
35e86941 | 393 | if (icsk->icsk_ca_state == TCP_CA_Open) { |
df3271f3 SH |
394 | cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT; |
395 | ca->delayed_ack += cnt; | |
396 | } | |
df3271f3 | 397 | |
e7d0c885 SH |
398 | /* Some calls are for duplicates without timetamps */ |
399 | if (rtt_us < 0) | |
400 | return; | |
401 | ||
402 | /* Discard delay samples right after fast recovery */ | |
403 | if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ) | |
404 | return; | |
405 | ||
17a6e9f1 | 406 | delay = (rtt_us << 3) / USEC_PER_MSEC; |
e7d0c885 SH |
407 | if (delay == 0) |
408 | delay = 1; | |
409 | ||
410 | /* first time call or link delay decreases */ | |
411 | if (ca->delay_min == 0 || ca->delay_min > delay) | |
412 | ca->delay_min = delay; | |
ae27e98a SH |
413 | |
414 | /* hystart triggers when cwnd is larger than some threshold */ | |
415 | if (hystart && tp->snd_cwnd <= tp->snd_ssthresh && | |
416 | tp->snd_cwnd >= hystart_low_window) | |
417 | hystart_update(sk, delay); | |
e7d0c885 | 418 | } |
df3271f3 SH |
419 | |
420 | static struct tcp_congestion_ops cubictcp = { | |
421 | .init = bictcp_init, | |
422 | .ssthresh = bictcp_recalc_ssthresh, | |
423 | .cong_avoid = bictcp_cong_avoid, | |
424 | .set_state = bictcp_state, | |
425 | .undo_cwnd = bictcp_undo_cwnd, | |
df3271f3 SH |
426 | .pkts_acked = bictcp_acked, |
427 | .owner = THIS_MODULE, | |
428 | .name = "cubic", | |
429 | }; | |
430 | ||
431 | static int __init cubictcp_register(void) | |
432 | { | |
74975d40 | 433 | BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); |
89b3d9aa SH |
434 | |
435 | /* Precompute a bunch of the scaling factors that are used per-packet | |
436 | * based on SRTT of 100ms | |
437 | */ | |
438 | ||
439 | beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta); | |
440 | ||
22119240 | 441 | cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */ |
89b3d9aa SH |
442 | |
443 | /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3 | |
444 | * so K = cubic_root( (wmax-cwnd)*rtt/c ) | |
445 | * the unit of K is bictcp_HZ=2^10, not HZ | |
446 | * | |
447 | * c = bic_scale >> 10 | |
448 | * rtt = 100ms | |
449 | * | |
450 | * the following code has been designed and tested for | |
451 | * cwnd < 1 million packets | |
452 | * RTT < 100 seconds | |
453 | * HZ < 1,000,00 (corresponding to 10 nano-second) | |
454 | */ | |
455 | ||
456 | /* 1/c * 2^2*bictcp_HZ * srtt */ | |
457 | cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */ | |
458 | ||
459 | /* divide by bic_scale and by constant Srtt (100ms) */ | |
460 | do_div(cube_factor, bic_scale * 10); | |
461 | ||
3b585b34 | 462 | /* hystart needs ms clock resolution */ |
463 | if (hystart && HZ < 1000) | |
464 | cubictcp.flags |= TCP_CONG_RTT_STAMP; | |
465 | ||
df3271f3 SH |
466 | return tcp_register_congestion_control(&cubictcp); |
467 | } | |
468 | ||
469 | static void __exit cubictcp_unregister(void) | |
470 | { | |
471 | tcp_unregister_congestion_control(&cubictcp); | |
472 | } | |
473 | ||
474 | module_init(cubictcp_register); | |
475 | module_exit(cubictcp_unregister); | |
476 | ||
477 | MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger"); | |
478 | MODULE_LICENSE("GPL"); | |
479 | MODULE_DESCRIPTION("CUBIC TCP"); | |
ae27e98a | 480 | MODULE_VERSION("2.3"); |