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Stephen Hemmingerdf3271f2005-12-13 23:13:28 -08001/*
Stephen Hemmingere1c3e7a2007-03-24 21:34:38 -07002 * TCP CUBIC: Binary Increase Congestion control for TCP v2.1
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -08003 *
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
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080015#include <linux/mm.h>
16#include <linux/module.h>
17#include <net/tcp.h>
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -080018#include <asm/div64.h>
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080019
20#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
21 * max_cwnd = snd_cwnd * beta
22 */
23#define BICTCP_B 4 /*
24 * In binary search,
25 * go to point (max+min)/N
26 */
27#define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */
28
Stephen Hemminger59758f42007-02-12 13:15:20 -080029static int fast_convergence __read_mostly = 1;
30static int max_increment __read_mostly = 16;
31static int beta __read_mostly = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */
David S. Miller66e1e3b2007-06-13 01:03:53 -070032static int initial_ssthresh __read_mostly;
Stephen Hemminger59758f42007-02-12 13:15:20 -080033static int bic_scale __read_mostly = 41;
34static int tcp_friendliness __read_mostly = 1;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080035
Stephen Hemminger59758f42007-02-12 13:15:20 -080036static u32 cube_rtt_scale __read_mostly;
37static u32 beta_scale __read_mostly;
38static u64 cube_factor __read_mostly;
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -080039
40/* Note parameters that are used for precomputing scale factors are read-only */
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080041module_param(fast_convergence, int, 0644);
42MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
43module_param(max_increment, int, 0644);
44MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search");
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -080045module_param(beta, int, 0444);
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080046MODULE_PARM_DESC(beta, "beta for multiplicative increase");
47module_param(initial_ssthresh, int, 0644);
48MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -080049module_param(bic_scale, int, 0444);
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080050MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
51module_param(tcp_friendliness, int, 0644);
52MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
53
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080054/* BIC TCP Parameters */
55struct bictcp {
56 u32 cnt; /* increase cwnd by 1 after ACKs */
57 u32 last_max_cwnd; /* last maximum snd_cwnd */
58 u32 loss_cwnd; /* congestion window at last loss */
59 u32 last_cwnd; /* the last snd_cwnd */
60 u32 last_time; /* time when updated last_cwnd */
61 u32 bic_origin_point;/* origin point of bic function */
62 u32 bic_K; /* time to origin point from the beginning of the current epoch */
63 u32 delay_min; /* min delay */
64 u32 epoch_start; /* beginning of an epoch */
65 u32 ack_cnt; /* number of acks */
66 u32 tcp_cwnd; /* estimated tcp cwnd */
67#define ACK_RATIO_SHIFT 4
68 u32 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
69};
70
71static inline void bictcp_reset(struct bictcp *ca)
72{
73 ca->cnt = 0;
74 ca->last_max_cwnd = 0;
75 ca->loss_cwnd = 0;
76 ca->last_cwnd = 0;
77 ca->last_time = 0;
78 ca->bic_origin_point = 0;
79 ca->bic_K = 0;
80 ca->delay_min = 0;
81 ca->epoch_start = 0;
82 ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
83 ca->ack_cnt = 0;
84 ca->tcp_cwnd = 0;
85}
86
87static void bictcp_init(struct sock *sk)
88{
89 bictcp_reset(inet_csk_ca(sk));
90 if (initial_ssthresh)
91 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
92}
93
Stephen Hemminger7e588862007-03-22 12:10:58 -070094/* calculate the cubic root of x using a table lookup followed by one
95 * Newton-Raphson iteration.
96 * Avg err ~= 0.195%
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080097 */
Stephen Hemminger9eb2d622005-12-21 19:32:36 -080098static u32 cubic_root(u64 a)
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080099{
Stephen Hemminger7e588862007-03-22 12:10:58 -0700100 u32 x, b, shift;
101 /*
102 * cbrt(x) MSB values for x MSB values in [0..63].
103 * Precomputed then refined by hand - Willy Tarreau
104 *
105 * For x in [0..63],
106 * v = cbrt(x << 18) - 1
107 * cbrt(x) = (v[x] + 10) >> 6
Stephen Hemminger9eb2d622005-12-21 19:32:36 -0800108 */
Stephen Hemminger7e588862007-03-22 12:10:58 -0700109 static const u8 v[] = {
110 /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118,
111 /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156,
112 /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179,
113 /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199,
114 /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215,
115 /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229,
116 /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242,
117 /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254,
118 };
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800119
Stephen Hemminger7e588862007-03-22 12:10:58 -0700120 b = fls64(a);
121 if (b < 7) {
122 /* a in [0..63] */
123 return ((u32)v[(u32)a] + 35) >> 6;
124 }
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800125
Stephen Hemminger7e588862007-03-22 12:10:58 -0700126 b = ((b * 84) >> 8) - 1;
127 shift = (a >> (b * 3));
128
129 x = ((u32)(((u32)v[shift] + 10) << b)) >> 6;
130
131 /*
132 * Newton-Raphson iteration
133 * 2
134 * x = ( 2 * x + a / x ) / 3
135 * k+1 k k
136 */
137 x = (2 * x + (u32)div64_64(a, (u64)x * (u64)(x - 1)));
138 x = ((x * 341) >> 10);
Stephen Hemminger9eb2d622005-12-21 19:32:36 -0800139 return x;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800140}
141
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800142/*
143 * Compute congestion window to use.
144 */
145static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
146{
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800147 u64 offs;
148 u32 delta, t, bic_target, min_cnt, max_cnt;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800149
150 ca->ack_cnt++; /* count the number of ACKs */
151
152 if (ca->last_cwnd == cwnd &&
153 (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
154 return;
155
156 ca->last_cwnd = cwnd;
157 ca->last_time = tcp_time_stamp;
158
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800159 if (ca->epoch_start == 0) {
160 ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */
161 ca->ack_cnt = 1; /* start counting */
162 ca->tcp_cwnd = cwnd; /* syn with cubic */
163
164 if (ca->last_max_cwnd <= cwnd) {
165 ca->bic_K = 0;
166 ca->bic_origin_point = cwnd;
167 } else {
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800168 /* Compute new K based on
169 * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
170 */
171 ca->bic_K = cubic_root(cube_factor
172 * (ca->last_max_cwnd - cwnd));
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800173 ca->bic_origin_point = ca->last_max_cwnd;
174 }
175 }
176
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900177 /* cubic function - calc*/
178 /* calculate c * time^3 / rtt,
179 * while considering overflow in calculation of time^3
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800180 * (so time^3 is done by using 64 bit)
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800181 * and without the support of division of 64bit numbers
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800182 * (so all divisions are done by using 32 bit)
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900183 * also NOTE the unit of those veriables
184 * time = (t - K) / 2^bictcp_HZ
185 * c = bic_scale >> 10
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800186 * rtt = (srtt >> 3) / HZ
187 * !!! The following code does not have overflow problems,
188 * if the cwnd < 1 million packets !!!
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900189 */
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800190
191 /* change the unit from HZ to bictcp_HZ */
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900192 t = ((tcp_time_stamp + (ca->delay_min>>3) - ca->epoch_start)
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800193 << BICTCP_HZ) / HZ;
194
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900195 if (t < ca->bic_K) /* t - K */
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800196 offs = ca->bic_K - t;
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900197 else
198 offs = t - ca->bic_K;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800199
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800200 /* c/rtt * (t-K)^3 */
201 delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900202 if (t < ca->bic_K) /* below origin*/
203 bic_target = ca->bic_origin_point - delta;
204 else /* above origin*/
205 bic_target = ca->bic_origin_point + delta;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800206
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900207 /* cubic function - calc bictcp_cnt*/
208 if (bic_target > cwnd) {
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800209 ca->cnt = cwnd / (bic_target - cwnd);
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900210 } else {
211 ca->cnt = 100 * cwnd; /* very small increment*/
212 }
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800213
214 if (ca->delay_min > 0) {
215 /* max increment = Smax * rtt / 0.1 */
216 min_cnt = (cwnd * HZ * 8)/(10 * max_increment * ca->delay_min);
Stephen Hemmingere1c3e7a2007-03-24 21:34:38 -0700217
218 /* use concave growth when the target is above the origin */
219 if (ca->cnt < min_cnt && t >= ca->bic_K)
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800220 ca->cnt = min_cnt;
221 }
222
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900223 /* slow start and low utilization */
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800224 if (ca->loss_cwnd == 0) /* could be aggressive in slow start */
225 ca->cnt = 50;
226
227 /* TCP Friendly */
228 if (tcp_friendliness) {
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800229 u32 scale = beta_scale;
230 delta = (cwnd * scale) >> 3;
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900231 while (ca->ack_cnt > delta) { /* update tcp cwnd */
232 ca->ack_cnt -= delta;
233 ca->tcp_cwnd++;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800234 }
235
236 if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800237 delta = ca->tcp_cwnd - cwnd;
238 max_cnt = cwnd / delta;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800239 if (ca->cnt > max_cnt)
240 ca->cnt = max_cnt;
241 }
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900242 }
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800243
244 ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
245 if (ca->cnt == 0) /* cannot be zero */
246 ca->cnt = 1;
247}
248
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800249static void bictcp_cong_avoid(struct sock *sk, u32 ack,
Stephen Hemminger16751342007-07-16 18:35:52 -0700250 u32 in_flight, int data_acked)
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800251{
252 struct tcp_sock *tp = tcp_sk(sk);
253 struct bictcp *ca = inet_csk_ca(sk);
254
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800255 if (!tcp_is_cwnd_limited(sk, in_flight))
256 return;
257
258 if (tp->snd_cwnd <= tp->snd_ssthresh)
259 tcp_slow_start(tp);
260 else {
261 bictcp_update(ca, tp->snd_cwnd);
262
263 /* In dangerous area, increase slowly.
264 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
265 */
266 if (tp->snd_cwnd_cnt >= ca->cnt) {
267 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
268 tp->snd_cwnd++;
269 tp->snd_cwnd_cnt = 0;
270 } else
271 tp->snd_cwnd_cnt++;
272 }
273
274}
275
276static u32 bictcp_recalc_ssthresh(struct sock *sk)
277{
278 const struct tcp_sock *tp = tcp_sk(sk);
279 struct bictcp *ca = inet_csk_ca(sk);
280
281 ca->epoch_start = 0; /* end of epoch */
282
283 /* Wmax and fast convergence */
284 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
285 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
286 / (2 * BICTCP_BETA_SCALE);
287 else
288 ca->last_max_cwnd = tp->snd_cwnd;
289
290 ca->loss_cwnd = tp->snd_cwnd;
291
292 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
293}
294
295static u32 bictcp_undo_cwnd(struct sock *sk)
296{
297 struct bictcp *ca = inet_csk_ca(sk);
298
299 return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd);
300}
301
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800302static void bictcp_state(struct sock *sk, u8 new_state)
303{
304 if (new_state == TCP_CA_Loss)
305 bictcp_reset(inet_csk_ca(sk));
306}
307
308/* Track delayed acknowledgment ratio using sliding window
309 * ratio = (15*ratio + sample) / 16
310 */
Stephen Hemminger30cfd0b2007-07-25 23:49:34 -0700311static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800312{
313 const struct inet_connection_sock *icsk = inet_csk(sk);
Stephen Hemmingere7d0c8852007-07-25 23:50:06 -0700314 struct bictcp *ca = inet_csk_ca(sk);
315 u32 delay;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800316
Ilpo Järvinen35e86942007-05-31 10:16:47 +0300317 if (icsk->icsk_ca_state == TCP_CA_Open) {
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800318 cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT;
319 ca->delayed_ack += cnt;
320 }
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800321
Stephen Hemmingere7d0c8852007-07-25 23:50:06 -0700322 /* Some calls are for duplicates without timetamps */
323 if (rtt_us < 0)
324 return;
325
326 /* Discard delay samples right after fast recovery */
327 if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ)
328 return;
329
330 delay = usecs_to_jiffies(rtt_us) << 3;
331 if (delay == 0)
332 delay = 1;
333
334 /* first time call or link delay decreases */
335 if (ca->delay_min == 0 || ca->delay_min > delay)
336 ca->delay_min = delay;
337}
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800338
339static struct tcp_congestion_ops cubictcp = {
340 .init = bictcp_init,
341 .ssthresh = bictcp_recalc_ssthresh,
342 .cong_avoid = bictcp_cong_avoid,
343 .set_state = bictcp_state,
344 .undo_cwnd = bictcp_undo_cwnd,
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800345 .pkts_acked = bictcp_acked,
346 .owner = THIS_MODULE,
347 .name = "cubic",
348};
349
350static int __init cubictcp_register(void)
351{
Alexey Dobriyan74975d42006-08-25 17:10:33 -0700352 BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800353
354 /* Precompute a bunch of the scaling factors that are used per-packet
355 * based on SRTT of 100ms
356 */
357
358 beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta);
359
Stephen Hemminger22119242006-10-25 23:04:12 -0700360 cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800361
362 /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
363 * so K = cubic_root( (wmax-cwnd)*rtt/c )
364 * the unit of K is bictcp_HZ=2^10, not HZ
365 *
366 * c = bic_scale >> 10
367 * rtt = 100ms
368 *
369 * the following code has been designed and tested for
370 * cwnd < 1 million packets
371 * RTT < 100 seconds
372 * HZ < 1,000,00 (corresponding to 10 nano-second)
373 */
374
375 /* 1/c * 2^2*bictcp_HZ * srtt */
376 cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */
377
378 /* divide by bic_scale and by constant Srtt (100ms) */
379 do_div(cube_factor, bic_scale * 10);
380
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800381 return tcp_register_congestion_control(&cubictcp);
382}
383
384static void __exit cubictcp_unregister(void)
385{
386 tcp_unregister_congestion_control(&cubictcp);
387}
388
389module_init(cubictcp_register);
390module_exit(cubictcp_unregister);
391
392MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
393MODULE_LICENSE("GPL");
394MODULE_DESCRIPTION("CUBIC TCP");
Stephen Hemmingere1c3e7a2007-03-24 21:34:38 -0700395MODULE_VERSION("2.1");