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Commit | Line | Data |
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df3271f3 | 1 | /* |
e1c3e7ab | 2 | * TCP CUBIC: Binary Increase Congestion control for TCP v2.1 |
df3271f3 SH |
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 | ||
df3271f3 SH |
15 | #include <linux/mm.h> |
16 | #include <linux/module.h> | |
17 | #include <net/tcp.h> | |
89b3d9aa | 18 | #include <asm/div64.h> |
df3271f3 SH |
19 | |
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 | ||
59758f44 SH |
29 | static int fast_convergence __read_mostly = 1; |
30 | static int max_increment __read_mostly = 16; | |
31 | static int beta __read_mostly = 819; /* = 819/1024 (BICTCP_BETA_SCALE) */ | |
66e1e3b2 | 32 | static int initial_ssthresh __read_mostly; |
59758f44 SH |
33 | static int bic_scale __read_mostly = 41; |
34 | static int tcp_friendliness __read_mostly = 1; | |
df3271f3 | 35 | |
59758f44 SH |
36 | static u32 cube_rtt_scale __read_mostly; |
37 | static u32 beta_scale __read_mostly; | |
38 | static u64 cube_factor __read_mostly; | |
89b3d9aa SH |
39 | |
40 | /* Note parameters that are used for precomputing scale factors are read-only */ | |
df3271f3 SH |
41 | module_param(fast_convergence, int, 0644); |
42 | MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence"); | |
43 | module_param(max_increment, int, 0644); | |
44 | MODULE_PARM_DESC(max_increment, "Limit on increment allowed during binary search"); | |
89b3d9aa | 45 | module_param(beta, int, 0444); |
df3271f3 SH |
46 | MODULE_PARM_DESC(beta, "beta for multiplicative increase"); |
47 | module_param(initial_ssthresh, int, 0644); | |
48 | MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold"); | |
89b3d9aa | 49 | module_param(bic_scale, int, 0444); |
df3271f3 SH |
50 | MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)"); |
51 | module_param(tcp_friendliness, int, 0644); | |
52 | MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness"); | |
53 | ||
df3271f3 SH |
54 | /* BIC TCP Parameters */ |
55 | struct 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 | ||
71 | static 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 | ||
87 | static 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 | ||
7e58886b SH |
94 | /* calculate the cubic root of x using a table lookup followed by one |
95 | * Newton-Raphson iteration. | |
96 | * Avg err ~= 0.195% | |
df3271f3 | 97 | */ |
9eb2d627 | 98 | static u32 cubic_root(u64 a) |
df3271f3 | 99 | { |
7e58886b SH |
100 | 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 | |
9eb2d627 | 108 | */ |
7e58886b SH |
109 | 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 | }; | |
119 | ||
120 | b = fls64(a); | |
121 | if (b < 7) { | |
122 | /* a in [0..63] */ | |
123 | return ((u32)v[(u32)a] + 35) >> 6; | |
124 | } | |
125 | ||
126 | 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); | |
9eb2d627 | 139 | return x; |
df3271f3 SH |
140 | } |
141 | ||
df3271f3 SH |
142 | /* |
143 | * Compute congestion window to use. | |
144 | */ | |
145 | static inline void bictcp_update(struct bictcp *ca, u32 cwnd) | |
146 | { | |
89b3d9aa SH |
147 | u64 offs; |
148 | u32 delta, t, bic_target, min_cnt, max_cnt; | |
df3271f3 SH |
149 | |
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 | ||
df3271f3 SH |
159 | 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 { | |
89b3d9aa SH |
168 | /* 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)); | |
df3271f3 SH |
173 | ca->bic_origin_point = ca->last_max_cwnd; |
174 | } | |
175 | } | |
176 | ||
e905a9ed YH |
177 | /* cubic function - calc*/ |
178 | /* calculate c * time^3 / rtt, | |
179 | * while considering overflow in calculation of time^3 | |
89b3d9aa | 180 | * (so time^3 is done by using 64 bit) |
df3271f3 | 181 | * and without the support of division of 64bit numbers |
89b3d9aa | 182 | * (so all divisions are done by using 32 bit) |
e905a9ed YH |
183 | * also NOTE the unit of those veriables |
184 | * time = (t - K) / 2^bictcp_HZ | |
185 | * c = bic_scale >> 10 | |
df3271f3 SH |
186 | * rtt = (srtt >> 3) / HZ |
187 | * !!! The following code does not have overflow problems, | |
188 | * if the cwnd < 1 million packets !!! | |
e905a9ed | 189 | */ |
df3271f3 SH |
190 | |
191 | /* change the unit from HZ to bictcp_HZ */ | |
e905a9ed | 192 | t = ((tcp_time_stamp + (ca->delay_min>>3) - ca->epoch_start) |
df3271f3 SH |
193 | << BICTCP_HZ) / HZ; |
194 | ||
e905a9ed | 195 | if (t < ca->bic_K) /* t - K */ |
89b3d9aa | 196 | offs = ca->bic_K - t; |
e905a9ed YH |
197 | else |
198 | offs = t - ca->bic_K; | |
df3271f3 | 199 | |
89b3d9aa SH |
200 | /* c/rtt * (t-K)^3 */ |
201 | delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ); | |
e905a9ed YH |
202 | 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; | |
df3271f3 | 206 | |
e905a9ed YH |
207 | /* cubic function - calc bictcp_cnt*/ |
208 | if (bic_target > cwnd) { | |
df3271f3 | 209 | ca->cnt = cwnd / (bic_target - cwnd); |
e905a9ed YH |
210 | } else { |
211 | ca->cnt = 100 * cwnd; /* very small increment*/ | |
212 | } | |
df3271f3 SH |
213 | |
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); | |
e1c3e7ab SH |
217 | |
218 | /* use concave growth when the target is above the origin */ | |
219 | if (ca->cnt < min_cnt && t >= ca->bic_K) | |
df3271f3 SH |
220 | ca->cnt = min_cnt; |
221 | } | |
222 | ||
e905a9ed | 223 | /* slow start and low utilization */ |
df3271f3 SH |
224 | if (ca->loss_cwnd == 0) /* could be aggressive in slow start */ |
225 | ca->cnt = 50; | |
226 | ||
227 | /* TCP Friendly */ | |
228 | if (tcp_friendliness) { | |
89b3d9aa SH |
229 | u32 scale = beta_scale; |
230 | delta = (cwnd * scale) >> 3; | |
e905a9ed YH |
231 | while (ca->ack_cnt > delta) { /* update tcp cwnd */ |
232 | ca->ack_cnt -= delta; | |
233 | ca->tcp_cwnd++; | |
df3271f3 SH |
234 | } |
235 | ||
236 | if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */ | |
89b3d9aa SH |
237 | delta = ca->tcp_cwnd - cwnd; |
238 | max_cnt = cwnd / delta; | |
df3271f3 SH |
239 | if (ca->cnt > max_cnt) |
240 | ca->cnt = max_cnt; | |
241 | } | |
e905a9ed | 242 | } |
df3271f3 SH |
243 | |
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 | ||
249 | ||
250 | /* Keep track of minimum rtt */ | |
251 | static inline void measure_delay(struct sock *sk) | |
252 | { | |
253 | const struct tcp_sock *tp = tcp_sk(sk); | |
254 | struct bictcp *ca = inet_csk_ca(sk); | |
255 | u32 delay; | |
256 | ||
257 | /* No time stamp */ | |
258 | if (!(tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr) || | |
259 | /* Discard delay samples right after fast recovery */ | |
260 | (s32)(tcp_time_stamp - ca->epoch_start) < HZ) | |
261 | return; | |
262 | ||
22119240 | 263 | delay = (tcp_time_stamp - tp->rx_opt.rcv_tsecr)<<3; |
df3271f3 SH |
264 | if (delay == 0) |
265 | delay = 1; | |
266 | ||
267 | /* first time call or link delay decreases */ | |
268 | if (ca->delay_min == 0 || ca->delay_min > delay) | |
269 | ca->delay_min = delay; | |
270 | } | |
271 | ||
272 | static void bictcp_cong_avoid(struct sock *sk, u32 ack, | |
16751347 | 273 | u32 in_flight, int data_acked) |
df3271f3 SH |
274 | { |
275 | struct tcp_sock *tp = tcp_sk(sk); | |
276 | struct bictcp *ca = inet_csk_ca(sk); | |
277 | ||
278 | if (data_acked) | |
279 | measure_delay(sk); | |
280 | ||
281 | if (!tcp_is_cwnd_limited(sk, in_flight)) | |
282 | return; | |
283 | ||
284 | if (tp->snd_cwnd <= tp->snd_ssthresh) | |
285 | tcp_slow_start(tp); | |
286 | else { | |
287 | bictcp_update(ca, tp->snd_cwnd); | |
288 | ||
289 | /* In dangerous area, increase slowly. | |
290 | * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd | |
291 | */ | |
292 | if (tp->snd_cwnd_cnt >= ca->cnt) { | |
293 | if (tp->snd_cwnd < tp->snd_cwnd_clamp) | |
294 | tp->snd_cwnd++; | |
295 | tp->snd_cwnd_cnt = 0; | |
296 | } else | |
297 | tp->snd_cwnd_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 | ||
df3271f3 SH |
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 | } | |
333 | ||
334 | /* Track delayed acknowledgment ratio using sliding window | |
335 | * ratio = (15*ratio + sample) / 16 | |
336 | */ | |
30cfd0ba | 337 | static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us) |
df3271f3 SH |
338 | { |
339 | const struct inet_connection_sock *icsk = inet_csk(sk); | |
340 | ||
341 | if (cnt > 0 && icsk->icsk_ca_state == TCP_CA_Open) { | |
342 | struct bictcp *ca = inet_csk_ca(sk); | |
343 | cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT; | |
344 | ca->delayed_ack += cnt; | |
345 | } | |
346 | } | |
347 | ||
348 | ||
349 | static struct tcp_congestion_ops cubictcp = { | |
350 | .init = bictcp_init, | |
351 | .ssthresh = bictcp_recalc_ssthresh, | |
352 | .cong_avoid = bictcp_cong_avoid, | |
353 | .set_state = bictcp_state, | |
354 | .undo_cwnd = bictcp_undo_cwnd, | |
df3271f3 SH |
355 | .pkts_acked = bictcp_acked, |
356 | .owner = THIS_MODULE, | |
357 | .name = "cubic", | |
358 | }; | |
359 | ||
360 | static int __init cubictcp_register(void) | |
361 | { | |
74975d40 | 362 | BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); |
89b3d9aa SH |
363 | |
364 | /* Precompute a bunch of the scaling factors that are used per-packet | |
365 | * based on SRTT of 100ms | |
366 | */ | |
367 | ||
368 | beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta); | |
369 | ||
22119240 | 370 | cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */ |
89b3d9aa SH |
371 | |
372 | /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3 | |
373 | * so K = cubic_root( (wmax-cwnd)*rtt/c ) | |
374 | * the unit of K is bictcp_HZ=2^10, not HZ | |
375 | * | |
376 | * c = bic_scale >> 10 | |
377 | * rtt = 100ms | |
378 | * | |
379 | * the following code has been designed and tested for | |
380 | * cwnd < 1 million packets | |
381 | * RTT < 100 seconds | |
382 | * HZ < 1,000,00 (corresponding to 10 nano-second) | |
383 | */ | |
384 | ||
385 | /* 1/c * 2^2*bictcp_HZ * srtt */ | |
386 | cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */ | |
387 | ||
388 | /* divide by bic_scale and by constant Srtt (100ms) */ | |
389 | do_div(cube_factor, bic_scale * 10); | |
390 | ||
df3271f3 SH |
391 | return tcp_register_congestion_control(&cubictcp); |
392 | } | |
393 | ||
394 | static void __exit cubictcp_unregister(void) | |
395 | { | |
396 | tcp_unregister_congestion_control(&cubictcp); | |
397 | } | |
398 | ||
399 | module_init(cubictcp_register); | |
400 | module_exit(cubictcp_unregister); | |
401 | ||
402 | MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger"); | |
403 | MODULE_LICENSE("GPL"); | |
404 | MODULE_DESCRIPTION("CUBIC TCP"); | |
e1c3e7ab | 405 | MODULE_VERSION("2.1"); |