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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 (4U<<3)
43#define HYSTART_DELAY_MAX (16U<<3)
44#define HYSTART_DELAY_THRESH(x) clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX)
45
46static int fast_convergence __read_mostly = 1;
47static int beta __read_mostly = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */
48static int initial_ssthresh __read_mostly;
49static int bic_scale __read_mostly = 41;
50static int tcp_friendliness __read_mostly = 1;
51
52static int hystart __read_mostly = 1;
53static int hystart_detect __read_mostly = HYSTART_ACK_TRAIN | HYSTART_DELAY;
54static int hystart_low_window __read_mostly = 16;
55static int hystart_ack_delta __read_mostly = 2;
56
57static u32 cube_rtt_scale __read_mostly;
58static u32 beta_scale __read_mostly;
59static u64 cube_factor __read_mostly;
60
61/* Note parameters that are used for precomputing scale factors are read-only */
62module_param(fast_convergence, int, 0644);
63MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
64module_param(beta, int, 0644);
65MODULE_PARM_DESC(beta, "beta for multiplicative increase");
66module_param(initial_ssthresh, int, 0644);
67MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
68module_param(bic_scale, int, 0444);
69MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
70module_param(tcp_friendliness, int, 0644);
71MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
72module_param(hystart, int, 0644);
73MODULE_PARM_DESC(hystart, "turn on/off hybrid slow start algorithm");
74module_param(hystart_detect, int, 0644);
75MODULE_PARM_DESC(hystart_detect, "hyrbrid slow start detection mechanisms"
76 " 1: packet-train 2: delay 3: both packet-train and delay");
77module_param(hystart_low_window, int, 0644);
78MODULE_PARM_DESC(hystart_low_window, "lower bound cwnd for hybrid slow start");
79module_param(hystart_ack_delta, int, 0644);
80MODULE_PARM_DESC(hystart_ack_delta, "spacing between ack's indicating train (msecs)");
81
82/* BIC TCP Parameters */
83struct 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 */
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#define ACK_RATIO_SHIFT 4
96#define ACK_RATIO_LIMIT (32u << ACK_RATIO_SHIFT)
97 u16 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
98 u8 sample_cnt; /* number of samples to decide curr_rtt */
99 u8 found; /* the exit point is found? */
100 u32 round_start; /* beginning of each round */
101 u32 end_seq; /* end_seq of the round */
102 u32 last_ack; /* last time when the ACK spacing is close */
103 u32 curr_rtt; /* the minimum rtt of current round */
104};
105
106static inline void bictcp_reset(struct bictcp *ca)
107{
108 ca->cnt = 0;
109 ca->last_max_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;
119 ca->found = 0;
120}
121
122static 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
131static 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
136 ca->round_start = ca->last_ack = bictcp_clock();
137 ca->end_seq = tp->snd_nxt;
138 ca->curr_rtt = 0;
139 ca->sample_cnt = 0;
140}
141
142static void bictcp_init(struct sock *sk)
143{
144 struct bictcp *ca = inet_csk_ca(sk);
145
146 bictcp_reset(ca);
147 ca->loss_cwnd = 0;
148
149 if (hystart)
150 bictcp_hystart_reset(sk);
151
152 if (!hystart && initial_ssthresh)
153 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
154}
155
156/* calculate the cubic root of x using a table lookup followed by one
157 * Newton-Raphson iteration.
158 * Avg err ~= 0.195%
159 */
160static u32 cubic_root(u64 a)
161{
162 u32 x, b, shift;
163 /*
164 * cbrt(x) MSB values for x MSB values in [0..63].
165 * Precomputed then refined by hand - Willy Tarreau
166 *
167 * For x in [0..63],
168 * v = cbrt(x << 18) - 1
169 * cbrt(x) = (v[x] + 10) >> 6
170 */
171 static const u8 v[] = {
172 /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118,
173 /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156,
174 /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179,
175 /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199,
176 /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215,
177 /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229,
178 /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242,
179 /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254,
180 };
181
182 b = fls64(a);
183 if (b < 7) {
184 /* a in [0..63] */
185 return ((u32)v[(u32)a] + 35) >> 6;
186 }
187
188 b = ((b * 84) >> 8) - 1;
189 shift = (a >> (b * 3));
190
191 x = ((u32)(((u32)v[shift] + 10) << b)) >> 6;
192
193 /*
194 * Newton-Raphson iteration
195 * 2
196 * x = ( 2 * x + a / x ) / 3
197 * k+1 k k
198 */
199 x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1)));
200 x = ((x * 341) >> 10);
201 return x;
202}
203
204/*
205 * Compute congestion window to use.
206 */
207static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
208{
209 u64 offs;
210 u32 delta, t, bic_target, max_cnt;
211
212 ca->ack_cnt++; /* count the number of ACKs */
213
214 if (ca->last_cwnd == cwnd &&
215 (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
216 return;
217
218 ca->last_cwnd = cwnd;
219 ca->last_time = tcp_time_stamp;
220
221 if (ca->epoch_start == 0) {
222 ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */
223 ca->ack_cnt = 1; /* start counting */
224 ca->tcp_cwnd = cwnd; /* syn with cubic */
225
226 if (ca->last_max_cwnd <= cwnd) {
227 ca->bic_K = 0;
228 ca->bic_origin_point = cwnd;
229 } else {
230 /* Compute new K based on
231 * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
232 */
233 ca->bic_K = cubic_root(cube_factor
234 * (ca->last_max_cwnd - cwnd));
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 64 bit)
243 * and without the support of division of 64bit numbers
244 * (so all divisions are done by using 32 bit)
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 + msecs_to_jiffies(ca->delay_min>>3)
255 - ca->epoch_start) << BICTCP_HZ) / HZ;
256
257 if (t < ca->bic_K) /* t - K */
258 offs = ca->bic_K - t;
259 else
260 offs = t - ca->bic_K;
261
262 /* c/rtt * (t-K)^3 */
263 delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
264 if (t < ca->bic_K) /* below origin*/
265 bic_target = ca->bic_origin_point - delta;
266 else /* above origin*/
267 bic_target = ca->bic_origin_point + delta;
268
269 /* cubic function - calc bictcp_cnt*/
270 if (bic_target > cwnd) {
271 ca->cnt = cwnd / (bic_target - cwnd);
272 } else {
273 ca->cnt = 100 * cwnd; /* very small increment*/
274 }
275
276 /*
277 * The initial growth of cubic function may be too conservative
278 * when the available bandwidth is still unknown.
279 */
280 if (ca->last_max_cwnd == 0 && ca->cnt > 20)
281 ca->cnt = 20; /* increase cwnd 5% per RTT */
282
283 /* TCP Friendly */
284 if (tcp_friendliness) {
285 u32 scale = beta_scale;
286 delta = (cwnd * scale) >> 3;
287 while (ca->ack_cnt > delta) { /* update tcp cwnd */
288 ca->ack_cnt -= delta;
289 ca->tcp_cwnd++;
290 }
291
292 if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */
293 delta = ca->tcp_cwnd - cwnd;
294 max_cnt = cwnd / delta;
295 if (ca->cnt > max_cnt)
296 ca->cnt = max_cnt;
297 }
298 }
299
300 ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
301 if (ca->cnt == 0) /* cannot be zero */
302 ca->cnt = 1;
303}
304
305static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
306{
307 struct tcp_sock *tp = tcp_sk(sk);
308 struct bictcp *ca = inet_csk_ca(sk);
309
310 if (!tcp_is_cwnd_limited(sk, in_flight))
311 return;
312
313 if (tp->snd_cwnd <= tp->snd_ssthresh) {
314 if (hystart && after(ack, ca->end_seq))
315 bictcp_hystart_reset(sk);
316 tcp_slow_start(tp);
317 } else {
318 bictcp_update(ca, tp->snd_cwnd);
319 tcp_cong_avoid_ai(tp, ca->cnt);
320 }
321
322}
323
324static u32 bictcp_recalc_ssthresh(struct sock *sk)
325{
326 const struct tcp_sock *tp = tcp_sk(sk);
327 struct bictcp *ca = inet_csk_ca(sk);
328
329 ca->epoch_start = 0; /* end of epoch */
330
331 /* Wmax and fast convergence */
332 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
333 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
334 / (2 * BICTCP_BETA_SCALE);
335 else
336 ca->last_max_cwnd = tp->snd_cwnd;
337
338 ca->loss_cwnd = tp->snd_cwnd;
339
340 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
341}
342
343static u32 bictcp_undo_cwnd(struct sock *sk)
344{
345 struct bictcp *ca = inet_csk_ca(sk);
346
347 return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
348}
349
350static void bictcp_state(struct sock *sk, u8 new_state)
351{
352 if (new_state == TCP_CA_Loss) {
353 bictcp_reset(inet_csk_ca(sk));
354 bictcp_hystart_reset(sk);
355 }
356}
357
358static void hystart_update(struct sock *sk, u32 delay)
359{
360 struct tcp_sock *tp = tcp_sk(sk);
361 struct bictcp *ca = inet_csk_ca(sk);
362
363 if (!(ca->found & hystart_detect)) {
364 u32 now = bictcp_clock();
365
366 /* first detection parameter - ack-train detection */
367 if ((s32)(now - ca->last_ack) <= hystart_ack_delta) {
368 ca->last_ack = now;
369 if ((s32)(now - ca->round_start) > ca->delay_min >> 4)
370 ca->found |= HYSTART_ACK_TRAIN;
371 }
372
373 /* obtain the minimum delay of more than sampling packets */
374 if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
375 if (ca->curr_rtt == 0 || ca->curr_rtt > delay)
376 ca->curr_rtt = delay;
377
378 ca->sample_cnt++;
379 } else {
380 if (ca->curr_rtt > ca->delay_min +
381 HYSTART_DELAY_THRESH(ca->delay_min>>4))
382 ca->found |= HYSTART_DELAY;
383 }
384 /*
385 * Either one of two conditions are met,
386 * we exit from slow start immediately.
387 */
388 if (ca->found & hystart_detect)
389 tp->snd_ssthresh = tp->snd_cwnd;
390 }
391}
392
393/* Track delayed acknowledgment ratio using sliding window
394 * ratio = (15*ratio + sample) / 16
395 */
396static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
397{
398 const struct inet_connection_sock *icsk = inet_csk(sk);
399 const struct tcp_sock *tp = tcp_sk(sk);
400 struct bictcp *ca = inet_csk_ca(sk);
401 u32 delay;
402
403 if (icsk->icsk_ca_state == TCP_CA_Open) {
404 u32 ratio = ca->delayed_ack;
405
406 ratio -= ca->delayed_ack >> ACK_RATIO_SHIFT;
407 ratio += cnt;
408
409 ca->delayed_ack = min(ratio, ACK_RATIO_LIMIT);
410 }
411
412 /* Some calls are for duplicates without timetamps */
413 if (rtt_us < 0)
414 return;
415
416 /* Discard delay samples right after fast recovery */
417 if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ)
418 return;
419
420 delay = (rtt_us << 3) / USEC_PER_MSEC;
421 if (delay == 0)
422 delay = 1;
423
424 /* first time call or link delay decreases */
425 if (ca->delay_min == 0 || ca->delay_min > delay)
426 ca->delay_min = delay;
427
428 /* hystart triggers when cwnd is larger than some threshold */
429 if (hystart && tp->snd_cwnd <= tp->snd_ssthresh &&
430 tp->snd_cwnd >= hystart_low_window)
431 hystart_update(sk, delay);
432}
433
434static struct tcp_congestion_ops cubictcp __read_mostly = {
435 .init = bictcp_init,
436 .ssthresh = bictcp_recalc_ssthresh,
437 .cong_avoid = bictcp_cong_avoid,
438 .set_state = bictcp_state,
439 .undo_cwnd = bictcp_undo_cwnd,
440 .pkts_acked = bictcp_acked,
441 .owner = THIS_MODULE,
442 .name = "cubic",
443};
444
445static int __init cubictcp_register(void)
446{
447 BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
448
449 /* Precompute a bunch of the scaling factors that are used per-packet
450 * based on SRTT of 100ms
451 */
452
453 beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta);
454
455 cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */
456
457 /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
458 * so K = cubic_root( (wmax-cwnd)*rtt/c )
459 * the unit of K is bictcp_HZ=2^10, not HZ
460 *
461 * c = bic_scale >> 10
462 * rtt = 100ms
463 *
464 * the following code has been designed and tested for
465 * cwnd < 1 million packets
466 * RTT < 100 seconds
467 * HZ < 1,000,00 (corresponding to 10 nano-second)
468 */
469
470 /* 1/c * 2^2*bictcp_HZ * srtt */
471 cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */
472
473 /* divide by bic_scale and by constant Srtt (100ms) */
474 do_div(cube_factor, bic_scale * 10);
475
476 /* hystart needs ms clock resolution */
477 if (hystart && HZ < 1000)
478 cubictcp.flags |= TCP_CONG_RTT_STAMP;
479
480 return tcp_register_congestion_control(&cubictcp);
481}
482
483static void __exit cubictcp_unregister(void)
484{
485 tcp_unregister_congestion_control(&cubictcp);
486}
487
488module_init(cubictcp_register);
489module_exit(cubictcp_unregister);
490
491MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
492MODULE_LICENSE("GPL");
493MODULE_DESCRIPTION("CUBIC TCP");
494MODULE_VERSION("2.3");
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
46static int fast_convergence __read_mostly = 1;
47static int beta __read_mostly = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */
48static int initial_ssthresh __read_mostly;
49static int bic_scale __read_mostly = 41;
50static int tcp_friendliness __read_mostly = 1;
51
52static int hystart __read_mostly = 1;
53static int hystart_detect __read_mostly = HYSTART_ACK_TRAIN | HYSTART_DELAY;
54static int hystart_low_window __read_mostly = 16;
55static int hystart_ack_delta __read_mostly = 2;
56
57static u32 cube_rtt_scale __read_mostly;
58static u32 beta_scale __read_mostly;
59static u64 cube_factor __read_mostly;
60
61/* Note parameters that are used for precomputing scale factors are read-only */
62module_param(fast_convergence, int, 0644);
63MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
64module_param(beta, int, 0644);
65MODULE_PARM_DESC(beta, "beta for multiplicative increase");
66module_param(initial_ssthresh, int, 0644);
67MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
68module_param(bic_scale, int, 0444);
69MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
70module_param(tcp_friendliness, int, 0644);
71MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
72module_param(hystart, int, 0644);
73MODULE_PARM_DESC(hystart, "turn on/off hybrid slow start algorithm");
74module_param(hystart_detect, int, 0644);
75MODULE_PARM_DESC(hystart_detect, "hyrbrid slow start detection mechanisms"
76 " 1: packet-train 2: delay 3: both packet-train and delay");
77module_param(hystart_low_window, int, 0644);
78MODULE_PARM_DESC(hystart_low_window, "lower bound cwnd for hybrid slow start");
79module_param(hystart_ack_delta, int, 0644);
80MODULE_PARM_DESC(hystart_ack_delta, "spacing between ack's indicating train (msecs)");
81
82/* BIC TCP Parameters */
83struct 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
91 from the beginning of the current epoch */
92 u32 delay_min; /* min delay (msec << 3) */
93 u32 epoch_start; /* beginning of an epoch */
94 u32 ack_cnt; /* number of acks */
95 u32 tcp_cwnd; /* estimated tcp cwnd */
96 u16 unused;
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 */
101 u32 last_ack; /* last time when the ACK spacing is close */
102 u32 curr_rtt; /* the minimum rtt of current round */
103};
104
105static inline void bictcp_reset(struct bictcp *ca)
106{
107 ca->cnt = 0;
108 ca->last_max_cwnd = 0;
109 ca->last_cwnd = 0;
110 ca->last_time = 0;
111 ca->bic_origin_point = 0;
112 ca->bic_K = 0;
113 ca->delay_min = 0;
114 ca->epoch_start = 0;
115 ca->ack_cnt = 0;
116 ca->tcp_cwnd = 0;
117 ca->found = 0;
118}
119
120static inline u32 bictcp_clock(void)
121{
122#if HZ < 1000
123 return ktime_to_ms(ktime_get_real());
124#else
125 return jiffies_to_msecs(jiffies);
126#endif
127}
128
129static inline void bictcp_hystart_reset(struct sock *sk)
130{
131 struct tcp_sock *tp = tcp_sk(sk);
132 struct bictcp *ca = inet_csk_ca(sk);
133
134 ca->round_start = ca->last_ack = bictcp_clock();
135 ca->end_seq = tp->snd_nxt;
136 ca->curr_rtt = 0;
137 ca->sample_cnt = 0;
138}
139
140static void bictcp_init(struct sock *sk)
141{
142 struct bictcp *ca = inet_csk_ca(sk);
143
144 bictcp_reset(ca);
145 ca->loss_cwnd = 0;
146
147 if (hystart)
148 bictcp_hystart_reset(sk);
149
150 if (!hystart && initial_ssthresh)
151 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
152}
153
154static void bictcp_cwnd_event(struct sock *sk, enum tcp_ca_event event)
155{
156 if (event == CA_EVENT_TX_START) {
157 struct bictcp *ca = inet_csk_ca(sk);
158 u32 now = tcp_time_stamp;
159 s32 delta;
160
161 delta = now - tcp_sk(sk)->lsndtime;
162
163 /* We were application limited (idle) for a while.
164 * Shift epoch_start to keep cwnd growth to cubic curve.
165 */
166 if (ca->epoch_start && delta > 0) {
167 ca->epoch_start += delta;
168 if (after(ca->epoch_start, now))
169 ca->epoch_start = now;
170 }
171 return;
172 }
173}
174
175/* calculate the cubic root of x using a table lookup followed by one
176 * Newton-Raphson iteration.
177 * Avg err ~= 0.195%
178 */
179static u32 cubic_root(u64 a)
180{
181 u32 x, b, shift;
182 /*
183 * cbrt(x) MSB values for x MSB values in [0..63].
184 * Precomputed then refined by hand - Willy Tarreau
185 *
186 * For x in [0..63],
187 * v = cbrt(x << 18) - 1
188 * cbrt(x) = (v[x] + 10) >> 6
189 */
190 static const u8 v[] = {
191 /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118,
192 /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156,
193 /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179,
194 /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199,
195 /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215,
196 /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229,
197 /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242,
198 /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254,
199 };
200
201 b = fls64(a);
202 if (b < 7) {
203 /* a in [0..63] */
204 return ((u32)v[(u32)a] + 35) >> 6;
205 }
206
207 b = ((b * 84) >> 8) - 1;
208 shift = (a >> (b * 3));
209
210 x = ((u32)(((u32)v[shift] + 10) << b)) >> 6;
211
212 /*
213 * Newton-Raphson iteration
214 * 2
215 * x = ( 2 * x + a / x ) / 3
216 * k+1 k k
217 */
218 x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1)));
219 x = ((x * 341) >> 10);
220 return x;
221}
222
223/*
224 * Compute congestion window to use.
225 */
226static inline void bictcp_update(struct bictcp *ca, u32 cwnd, u32 acked)
227{
228 u32 delta, bic_target, max_cnt;
229 u64 offs, t;
230
231 ca->ack_cnt += acked; /* count the number of ACKed packets */
232
233 if (ca->last_cwnd == cwnd &&
234 (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
235 return;
236
237 /* The CUBIC function can update ca->cnt at most once per jiffy.
238 * On all cwnd reduction events, ca->epoch_start is set to 0,
239 * which will force a recalculation of ca->cnt.
240 */
241 if (ca->epoch_start && tcp_time_stamp == ca->last_time)
242 goto tcp_friendliness;
243
244 ca->last_cwnd = cwnd;
245 ca->last_time = tcp_time_stamp;
246
247 if (ca->epoch_start == 0) {
248 ca->epoch_start = tcp_time_stamp; /* record beginning */
249 ca->ack_cnt = acked; /* start counting */
250 ca->tcp_cwnd = cwnd; /* syn with cubic */
251
252 if (ca->last_max_cwnd <= cwnd) {
253 ca->bic_K = 0;
254 ca->bic_origin_point = cwnd;
255 } else {
256 /* Compute new K based on
257 * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
258 */
259 ca->bic_K = cubic_root(cube_factor
260 * (ca->last_max_cwnd - cwnd));
261 ca->bic_origin_point = ca->last_max_cwnd;
262 }
263 }
264
265 /* cubic function - calc*/
266 /* calculate c * time^3 / rtt,
267 * while considering overflow in calculation of time^3
268 * (so time^3 is done by using 64 bit)
269 * and without the support of division of 64bit numbers
270 * (so all divisions are done by using 32 bit)
271 * also NOTE the unit of those veriables
272 * time = (t - K) / 2^bictcp_HZ
273 * c = bic_scale >> 10
274 * rtt = (srtt >> 3) / HZ
275 * !!! The following code does not have overflow problems,
276 * if the cwnd < 1 million packets !!!
277 */
278
279 t = (s32)(tcp_time_stamp - ca->epoch_start);
280 t += msecs_to_jiffies(ca->delay_min >> 3);
281 /* change the unit from HZ to bictcp_HZ */
282 t <<= BICTCP_HZ;
283 do_div(t, HZ);
284
285 if (t < ca->bic_K) /* t - K */
286 offs = ca->bic_K - t;
287 else
288 offs = t - ca->bic_K;
289
290 /* c/rtt * (t-K)^3 */
291 delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
292 if (t < ca->bic_K) /* below origin*/
293 bic_target = ca->bic_origin_point - delta;
294 else /* above origin*/
295 bic_target = ca->bic_origin_point + delta;
296
297 /* cubic function - calc bictcp_cnt*/
298 if (bic_target > cwnd) {
299 ca->cnt = cwnd / (bic_target - cwnd);
300 } else {
301 ca->cnt = 100 * cwnd; /* very small increment*/
302 }
303
304 /*
305 * The initial growth of cubic function may be too conservative
306 * when the available bandwidth is still unknown.
307 */
308 if (ca->last_max_cwnd == 0 && ca->cnt > 20)
309 ca->cnt = 20; /* increase cwnd 5% per RTT */
310
311tcp_friendliness:
312 /* TCP Friendly */
313 if (tcp_friendliness) {
314 u32 scale = beta_scale;
315
316 delta = (cwnd * scale) >> 3;
317 while (ca->ack_cnt > delta) { /* update tcp cwnd */
318 ca->ack_cnt -= delta;
319 ca->tcp_cwnd++;
320 }
321
322 if (ca->tcp_cwnd > cwnd) { /* if bic is slower than tcp */
323 delta = ca->tcp_cwnd - cwnd;
324 max_cnt = cwnd / delta;
325 if (ca->cnt > max_cnt)
326 ca->cnt = max_cnt;
327 }
328 }
329
330 /* The maximum rate of cwnd increase CUBIC allows is 1 packet per
331 * 2 packets ACKed, meaning cwnd grows at 1.5x per RTT.
332 */
333 ca->cnt = max(ca->cnt, 2U);
334}
335
336static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
337{
338 struct tcp_sock *tp = tcp_sk(sk);
339 struct bictcp *ca = inet_csk_ca(sk);
340
341 if (!tcp_is_cwnd_limited(sk))
342 return;
343
344 if (tcp_in_slow_start(tp)) {
345 if (hystart && after(ack, ca->end_seq))
346 bictcp_hystart_reset(sk);
347 acked = tcp_slow_start(tp, acked);
348 if (!acked)
349 return;
350 }
351 bictcp_update(ca, tp->snd_cwnd, acked);
352 tcp_cong_avoid_ai(tp, ca->cnt, acked);
353}
354
355static u32 bictcp_recalc_ssthresh(struct sock *sk)
356{
357 const struct tcp_sock *tp = tcp_sk(sk);
358 struct bictcp *ca = inet_csk_ca(sk);
359
360 ca->epoch_start = 0; /* end of epoch */
361
362 /* Wmax and fast convergence */
363 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
364 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
365 / (2 * BICTCP_BETA_SCALE);
366 else
367 ca->last_max_cwnd = tp->snd_cwnd;
368
369 ca->loss_cwnd = tp->snd_cwnd;
370
371 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
372}
373
374static u32 bictcp_undo_cwnd(struct sock *sk)
375{
376 struct bictcp *ca = inet_csk_ca(sk);
377
378 return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
379}
380
381static void bictcp_state(struct sock *sk, u8 new_state)
382{
383 if (new_state == TCP_CA_Loss) {
384 bictcp_reset(inet_csk_ca(sk));
385 bictcp_hystart_reset(sk);
386 }
387}
388
389static void hystart_update(struct sock *sk, u32 delay)
390{
391 struct tcp_sock *tp = tcp_sk(sk);
392 struct bictcp *ca = inet_csk_ca(sk);
393
394 if (ca->found & hystart_detect)
395 return;
396
397 if (hystart_detect & HYSTART_ACK_TRAIN) {
398 u32 now = bictcp_clock();
399
400 /* first detection parameter - ack-train detection */
401 if ((s32)(now - ca->last_ack) <= hystart_ack_delta) {
402 ca->last_ack = now;
403 if ((s32)(now - ca->round_start) > ca->delay_min >> 4) {
404 ca->found |= HYSTART_ACK_TRAIN;
405 NET_INC_STATS_BH(sock_net(sk),
406 LINUX_MIB_TCPHYSTARTTRAINDETECT);
407 NET_ADD_STATS_BH(sock_net(sk),
408 LINUX_MIB_TCPHYSTARTTRAINCWND,
409 tp->snd_cwnd);
410 tp->snd_ssthresh = tp->snd_cwnd;
411 }
412 }
413 }
414
415 if (hystart_detect & HYSTART_DELAY) {
416 /* obtain the minimum delay of more than sampling packets */
417 if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
418 if (ca->curr_rtt == 0 || ca->curr_rtt > delay)
419 ca->curr_rtt = delay;
420
421 ca->sample_cnt++;
422 } else {
423 if (ca->curr_rtt > ca->delay_min +
424 HYSTART_DELAY_THRESH(ca->delay_min >> 3)) {
425 ca->found |= HYSTART_DELAY;
426 NET_INC_STATS_BH(sock_net(sk),
427 LINUX_MIB_TCPHYSTARTDELAYDETECT);
428 NET_ADD_STATS_BH(sock_net(sk),
429 LINUX_MIB_TCPHYSTARTDELAYCWND,
430 tp->snd_cwnd);
431 tp->snd_ssthresh = tp->snd_cwnd;
432 }
433 }
434 }
435}
436
437/* Track delayed acknowledgment ratio using sliding window
438 * ratio = (15*ratio + sample) / 16
439 */
440static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
441{
442 const struct tcp_sock *tp = tcp_sk(sk);
443 struct bictcp *ca = inet_csk_ca(sk);
444 u32 delay;
445
446 /* Some calls are for duplicates without timetamps */
447 if (rtt_us < 0)
448 return;
449
450 /* Discard delay samples right after fast recovery */
451 if (ca->epoch_start && (s32)(tcp_time_stamp - ca->epoch_start) < HZ)
452 return;
453
454 delay = (rtt_us << 3) / USEC_PER_MSEC;
455 if (delay == 0)
456 delay = 1;
457
458 /* first time call or link delay decreases */
459 if (ca->delay_min == 0 || ca->delay_min > delay)
460 ca->delay_min = delay;
461
462 /* hystart triggers when cwnd is larger than some threshold */
463 if (hystart && tcp_in_slow_start(tp) &&
464 tp->snd_cwnd >= hystart_low_window)
465 hystart_update(sk, delay);
466}
467
468static struct tcp_congestion_ops cubictcp __read_mostly = {
469 .init = bictcp_init,
470 .ssthresh = bictcp_recalc_ssthresh,
471 .cong_avoid = bictcp_cong_avoid,
472 .set_state = bictcp_state,
473 .undo_cwnd = bictcp_undo_cwnd,
474 .cwnd_event = bictcp_cwnd_event,
475 .pkts_acked = bictcp_acked,
476 .owner = THIS_MODULE,
477 .name = "cubic",
478};
479
480static int __init cubictcp_register(void)
481{
482 BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
483
484 /* Precompute a bunch of the scaling factors that are used per-packet
485 * based on SRTT of 100ms
486 */
487
488 beta_scale = 8*(BICTCP_BETA_SCALE+beta) / 3
489 / (BICTCP_BETA_SCALE - beta);
490
491 cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */
492
493 /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
494 * so K = cubic_root( (wmax-cwnd)*rtt/c )
495 * the unit of K is bictcp_HZ=2^10, not HZ
496 *
497 * c = bic_scale >> 10
498 * rtt = 100ms
499 *
500 * the following code has been designed and tested for
501 * cwnd < 1 million packets
502 * RTT < 100 seconds
503 * HZ < 1,000,00 (corresponding to 10 nano-second)
504 */
505
506 /* 1/c * 2^2*bictcp_HZ * srtt */
507 cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */
508
509 /* divide by bic_scale and by constant Srtt (100ms) */
510 do_div(cube_factor, bic_scale * 10);
511
512 return tcp_register_congestion_control(&cubictcp);
513}
514
515static void __exit cubictcp_unregister(void)
516{
517 tcp_unregister_congestion_control(&cubictcp);
518}
519
520module_init(cubictcp_register);
521module_exit(cubictcp_unregister);
522
523MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
524MODULE_LICENSE("GPL");
525MODULE_DESCRIPTION("CUBIC TCP");
526MODULE_VERSION("2.3");