xref: /openbmc/linux/net/ipv4/tcp_cubic.c (revision 400031e0)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * TCP CUBIC: Binary Increase Congestion control for TCP v2.3
4  * Home page:
5  *      http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
6  * This is from the implementation of CUBIC TCP in
7  * Sangtae Ha, Injong Rhee and Lisong Xu,
8  *  "CUBIC: A New TCP-Friendly High-Speed TCP Variant"
9  *  in ACM SIGOPS Operating System Review, July 2008.
10  * Available from:
11  *  http://netsrv.csc.ncsu.edu/export/cubic_a_new_tcp_2008.pdf
12  *
13  * CUBIC integrates a new slow start algorithm, called HyStart.
14  * The details of HyStart are presented in
15  *  Sangtae Ha and Injong Rhee,
16  *  "Taming the Elephants: New TCP Slow Start", NCSU TechReport 2008.
17  * Available from:
18  *  http://netsrv.csc.ncsu.edu/export/hystart_techreport_2008.pdf
19  *
20  * All testing results are available from:
21  * http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_Testing
22  *
23  * Unless CUBIC is enabled and congestion window is large
24  * this behaves the same as the original Reno.
25  */
26 
27 #include <linux/mm.h>
28 #include <linux/btf.h>
29 #include <linux/btf_ids.h>
30 #include <linux/module.h>
31 #include <linux/math64.h>
32 #include <net/tcp.h>
33 
34 #define BICTCP_BETA_SCALE    1024	/* Scale factor beta calculation
35 					 * max_cwnd = snd_cwnd * beta
36 					 */
37 #define	BICTCP_HZ		10	/* BIC HZ 2^10 = 1024 */
38 
39 /* Two methods of hybrid slow start */
40 #define HYSTART_ACK_TRAIN	0x1
41 #define HYSTART_DELAY		0x2
42 
43 /* Number of delay samples for detecting the increase of delay */
44 #define HYSTART_MIN_SAMPLES	8
45 #define HYSTART_DELAY_MIN	(4000U)	/* 4 ms */
46 #define HYSTART_DELAY_MAX	(16000U)	/* 16 ms */
47 #define HYSTART_DELAY_THRESH(x)	clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX)
48 
49 static int fast_convergence __read_mostly = 1;
50 static int beta __read_mostly = 717;	/* = 717/1024 (BICTCP_BETA_SCALE) */
51 static int initial_ssthresh __read_mostly;
52 static int bic_scale __read_mostly = 41;
53 static int tcp_friendliness __read_mostly = 1;
54 
55 static int hystart __read_mostly = 1;
56 static int hystart_detect __read_mostly = HYSTART_ACK_TRAIN | HYSTART_DELAY;
57 static int hystart_low_window __read_mostly = 16;
58 static int hystart_ack_delta_us __read_mostly = 2000;
59 
60 static u32 cube_rtt_scale __read_mostly;
61 static u32 beta_scale __read_mostly;
62 static u64 cube_factor __read_mostly;
63 
64 /* Note parameters that are used for precomputing scale factors are read-only */
65 module_param(fast_convergence, int, 0644);
66 MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
67 module_param(beta, int, 0644);
68 MODULE_PARM_DESC(beta, "beta for multiplicative increase");
69 module_param(initial_ssthresh, int, 0644);
70 MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
71 module_param(bic_scale, int, 0444);
72 MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)");
73 module_param(tcp_friendliness, int, 0644);
74 MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
75 module_param(hystart, int, 0644);
76 MODULE_PARM_DESC(hystart, "turn on/off hybrid slow start algorithm");
77 module_param(hystart_detect, int, 0644);
78 MODULE_PARM_DESC(hystart_detect, "hybrid slow start detection mechanisms"
79 		 " 1: packet-train 2: delay 3: both packet-train and delay");
80 module_param(hystart_low_window, int, 0644);
81 MODULE_PARM_DESC(hystart_low_window, "lower bound cwnd for hybrid slow start");
82 module_param(hystart_ack_delta_us, int, 0644);
83 MODULE_PARM_DESC(hystart_ack_delta_us, "spacing between ack's indicating train (usecs)");
84 
85 /* BIC TCP Parameters */
86 struct bictcp {
87 	u32	cnt;		/* increase cwnd by 1 after ACKs */
88 	u32	last_max_cwnd;	/* last maximum snd_cwnd */
89 	u32	last_cwnd;	/* the last snd_cwnd */
90 	u32	last_time;	/* time when updated last_cwnd */
91 	u32	bic_origin_point;/* origin point of bic function */
92 	u32	bic_K;		/* time to origin point
93 				   from the beginning of the current epoch */
94 	u32	delay_min;	/* min delay (usec) */
95 	u32	epoch_start;	/* beginning of an epoch */
96 	u32	ack_cnt;	/* number of acks */
97 	u32	tcp_cwnd;	/* estimated tcp cwnd */
98 	u16	unused;
99 	u8	sample_cnt;	/* number of samples to decide curr_rtt */
100 	u8	found;		/* the exit point is found? */
101 	u32	round_start;	/* beginning of each round */
102 	u32	end_seq;	/* end_seq of the round */
103 	u32	last_ack;	/* last time when the ACK spacing is close */
104 	u32	curr_rtt;	/* the minimum rtt of current round */
105 };
106 
bictcp_reset(struct bictcp * ca)107 static inline void bictcp_reset(struct bictcp *ca)
108 {
109 	memset(ca, 0, offsetof(struct bictcp, unused));
110 	ca->found = 0;
111 }
112 
bictcp_clock_us(const struct sock * sk)113 static inline u32 bictcp_clock_us(const struct sock *sk)
114 {
115 	return tcp_sk(sk)->tcp_mstamp;
116 }
117 
bictcp_hystart_reset(struct sock * sk)118 static inline void bictcp_hystart_reset(struct sock *sk)
119 {
120 	struct tcp_sock *tp = tcp_sk(sk);
121 	struct bictcp *ca = inet_csk_ca(sk);
122 
123 	ca->round_start = ca->last_ack = bictcp_clock_us(sk);
124 	ca->end_seq = tp->snd_nxt;
125 	ca->curr_rtt = ~0U;
126 	ca->sample_cnt = 0;
127 }
128 
cubictcp_init(struct sock * sk)129 __bpf_kfunc static void cubictcp_init(struct sock *sk)
130 {
131 	struct bictcp *ca = inet_csk_ca(sk);
132 
133 	bictcp_reset(ca);
134 
135 	if (hystart)
136 		bictcp_hystart_reset(sk);
137 
138 	if (!hystart && initial_ssthresh)
139 		tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
140 }
141 
cubictcp_cwnd_event(struct sock * sk,enum tcp_ca_event event)142 __bpf_kfunc static void cubictcp_cwnd_event(struct sock *sk, enum tcp_ca_event event)
143 {
144 	if (event == CA_EVENT_TX_START) {
145 		struct bictcp *ca = inet_csk_ca(sk);
146 		u32 now = tcp_jiffies32;
147 		s32 delta;
148 
149 		delta = now - tcp_sk(sk)->lsndtime;
150 
151 		/* We were application limited (idle) for a while.
152 		 * Shift epoch_start to keep cwnd growth to cubic curve.
153 		 */
154 		if (ca->epoch_start && delta > 0) {
155 			ca->epoch_start += delta;
156 			if (after(ca->epoch_start, now))
157 				ca->epoch_start = now;
158 		}
159 		return;
160 	}
161 }
162 
163 /* calculate the cubic root of x using a table lookup followed by one
164  * Newton-Raphson iteration.
165  * Avg err ~= 0.195%
166  */
cubic_root(u64 a)167 static u32 cubic_root(u64 a)
168 {
169 	u32 x, b, shift;
170 	/*
171 	 * cbrt(x) MSB values for x MSB values in [0..63].
172 	 * Precomputed then refined by hand - Willy Tarreau
173 	 *
174 	 * For x in [0..63],
175 	 *   v = cbrt(x << 18) - 1
176 	 *   cbrt(x) = (v[x] + 10) >> 6
177 	 */
178 	static const u8 v[] = {
179 		/* 0x00 */    0,   54,   54,   54,  118,  118,  118,  118,
180 		/* 0x08 */  123,  129,  134,  138,  143,  147,  151,  156,
181 		/* 0x10 */  157,  161,  164,  168,  170,  173,  176,  179,
182 		/* 0x18 */  181,  185,  187,  190,  192,  194,  197,  199,
183 		/* 0x20 */  200,  202,  204,  206,  209,  211,  213,  215,
184 		/* 0x28 */  217,  219,  221,  222,  224,  225,  227,  229,
185 		/* 0x30 */  231,  232,  234,  236,  237,  239,  240,  242,
186 		/* 0x38 */  244,  245,  246,  248,  250,  251,  252,  254,
187 	};
188 
189 	b = fls64(a);
190 	if (b < 7) {
191 		/* a in [0..63] */
192 		return ((u32)v[(u32)a] + 35) >> 6;
193 	}
194 
195 	b = ((b * 84) >> 8) - 1;
196 	shift = (a >> (b * 3));
197 
198 	x = ((u32)(((u32)v[shift] + 10) << b)) >> 6;
199 
200 	/*
201 	 * Newton-Raphson iteration
202 	 *                         2
203 	 * x    = ( 2 * x  +  a / x  ) / 3
204 	 *  k+1          k         k
205 	 */
206 	x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1)));
207 	x = ((x * 341) >> 10);
208 	return x;
209 }
210 
211 /*
212  * Compute congestion window to use.
213  */
bictcp_update(struct bictcp * ca,u32 cwnd,u32 acked)214 static inline void bictcp_update(struct bictcp *ca, u32 cwnd, u32 acked)
215 {
216 	u32 delta, bic_target, max_cnt;
217 	u64 offs, t;
218 
219 	ca->ack_cnt += acked;	/* count the number of ACKed packets */
220 
221 	if (ca->last_cwnd == cwnd &&
222 	    (s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32)
223 		return;
224 
225 	/* The CUBIC function can update ca->cnt at most once per jiffy.
226 	 * On all cwnd reduction events, ca->epoch_start is set to 0,
227 	 * which will force a recalculation of ca->cnt.
228 	 */
229 	if (ca->epoch_start && tcp_jiffies32 == ca->last_time)
230 		goto tcp_friendliness;
231 
232 	ca->last_cwnd = cwnd;
233 	ca->last_time = tcp_jiffies32;
234 
235 	if (ca->epoch_start == 0) {
236 		ca->epoch_start = tcp_jiffies32;	/* record beginning */
237 		ca->ack_cnt = acked;			/* start counting */
238 		ca->tcp_cwnd = cwnd;			/* syn with cubic */
239 
240 		if (ca->last_max_cwnd <= cwnd) {
241 			ca->bic_K = 0;
242 			ca->bic_origin_point = cwnd;
243 		} else {
244 			/* Compute new K based on
245 			 * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
246 			 */
247 			ca->bic_K = cubic_root(cube_factor
248 					       * (ca->last_max_cwnd - cwnd));
249 			ca->bic_origin_point = ca->last_max_cwnd;
250 		}
251 	}
252 
253 	/* cubic function - calc*/
254 	/* calculate c * time^3 / rtt,
255 	 *  while considering overflow in calculation of time^3
256 	 * (so time^3 is done by using 64 bit)
257 	 * and without the support of division of 64bit numbers
258 	 * (so all divisions are done by using 32 bit)
259 	 *  also NOTE the unit of those veriables
260 	 *	  time  = (t - K) / 2^bictcp_HZ
261 	 *	  c = bic_scale >> 10
262 	 * rtt  = (srtt >> 3) / HZ
263 	 * !!! The following code does not have overflow problems,
264 	 * if the cwnd < 1 million packets !!!
265 	 */
266 
267 	t = (s32)(tcp_jiffies32 - ca->epoch_start);
268 	t += usecs_to_jiffies(ca->delay_min);
269 	/* change the unit from HZ to bictcp_HZ */
270 	t <<= BICTCP_HZ;
271 	do_div(t, HZ);
272 
273 	if (t < ca->bic_K)		/* t - K */
274 		offs = ca->bic_K - t;
275 	else
276 		offs = t - ca->bic_K;
277 
278 	/* c/rtt * (t-K)^3 */
279 	delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
280 	if (t < ca->bic_K)                            /* below origin*/
281 		bic_target = ca->bic_origin_point - delta;
282 	else                                          /* above origin*/
283 		bic_target = ca->bic_origin_point + delta;
284 
285 	/* cubic function - calc bictcp_cnt*/
286 	if (bic_target > cwnd) {
287 		ca->cnt = cwnd / (bic_target - cwnd);
288 	} else {
289 		ca->cnt = 100 * cwnd;              /* very small increment*/
290 	}
291 
292 	/*
293 	 * The initial growth of cubic function may be too conservative
294 	 * when the available bandwidth is still unknown.
295 	 */
296 	if (ca->last_max_cwnd == 0 && ca->cnt > 20)
297 		ca->cnt = 20;	/* increase cwnd 5% per RTT */
298 
299 tcp_friendliness:
300 	/* TCP Friendly */
301 	if (tcp_friendliness) {
302 		u32 scale = beta_scale;
303 
304 		delta = (cwnd * scale) >> 3;
305 		while (ca->ack_cnt > delta) {		/* update tcp cwnd */
306 			ca->ack_cnt -= delta;
307 			ca->tcp_cwnd++;
308 		}
309 
310 		if (ca->tcp_cwnd > cwnd) {	/* if bic is slower than tcp */
311 			delta = ca->tcp_cwnd - cwnd;
312 			max_cnt = cwnd / delta;
313 			if (ca->cnt > max_cnt)
314 				ca->cnt = max_cnt;
315 		}
316 	}
317 
318 	/* The maximum rate of cwnd increase CUBIC allows is 1 packet per
319 	 * 2 packets ACKed, meaning cwnd grows at 1.5x per RTT.
320 	 */
321 	ca->cnt = max(ca->cnt, 2U);
322 }
323 
cubictcp_cong_avoid(struct sock * sk,u32 ack,u32 acked)324 __bpf_kfunc static void cubictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
325 {
326 	struct tcp_sock *tp = tcp_sk(sk);
327 	struct bictcp *ca = inet_csk_ca(sk);
328 
329 	if (!tcp_is_cwnd_limited(sk))
330 		return;
331 
332 	if (tcp_in_slow_start(tp)) {
333 		acked = tcp_slow_start(tp, acked);
334 		if (!acked)
335 			return;
336 	}
337 	bictcp_update(ca, tcp_snd_cwnd(tp), acked);
338 	tcp_cong_avoid_ai(tp, ca->cnt, acked);
339 }
340 
cubictcp_recalc_ssthresh(struct sock * sk)341 __bpf_kfunc static u32 cubictcp_recalc_ssthresh(struct sock *sk)
342 {
343 	const struct tcp_sock *tp = tcp_sk(sk);
344 	struct bictcp *ca = inet_csk_ca(sk);
345 
346 	ca->epoch_start = 0;	/* end of epoch */
347 
348 	/* Wmax and fast convergence */
349 	if (tcp_snd_cwnd(tp) < ca->last_max_cwnd && fast_convergence)
350 		ca->last_max_cwnd = (tcp_snd_cwnd(tp) * (BICTCP_BETA_SCALE + beta))
351 			/ (2 * BICTCP_BETA_SCALE);
352 	else
353 		ca->last_max_cwnd = tcp_snd_cwnd(tp);
354 
355 	return max((tcp_snd_cwnd(tp) * beta) / BICTCP_BETA_SCALE, 2U);
356 }
357 
cubictcp_state(struct sock * sk,u8 new_state)358 __bpf_kfunc static void cubictcp_state(struct sock *sk, u8 new_state)
359 {
360 	if (new_state == TCP_CA_Loss) {
361 		bictcp_reset(inet_csk_ca(sk));
362 		bictcp_hystart_reset(sk);
363 	}
364 }
365 
366 /* Account for TSO/GRO delays.
367  * Otherwise short RTT flows could get too small ssthresh, since during
368  * slow start we begin with small TSO packets and ca->delay_min would
369  * not account for long aggregation delay when TSO packets get bigger.
370  * Ideally even with a very small RTT we would like to have at least one
371  * TSO packet being sent and received by GRO, and another one in qdisc layer.
372  * We apply another 100% factor because @rate is doubled at this point.
373  * We cap the cushion to 1ms.
374  */
hystart_ack_delay(const struct sock * sk)375 static u32 hystart_ack_delay(const struct sock *sk)
376 {
377 	unsigned long rate;
378 
379 	rate = READ_ONCE(sk->sk_pacing_rate);
380 	if (!rate)
381 		return 0;
382 	return min_t(u64, USEC_PER_MSEC,
383 		     div64_ul((u64)sk->sk_gso_max_size * 4 * USEC_PER_SEC, rate));
384 }
385 
hystart_update(struct sock * sk,u32 delay)386 static void hystart_update(struct sock *sk, u32 delay)
387 {
388 	struct tcp_sock *tp = tcp_sk(sk);
389 	struct bictcp *ca = inet_csk_ca(sk);
390 	u32 threshold;
391 
392 	if (after(tp->snd_una, ca->end_seq))
393 		bictcp_hystart_reset(sk);
394 
395 	if (hystart_detect & HYSTART_ACK_TRAIN) {
396 		u32 now = bictcp_clock_us(sk);
397 
398 		/* first detection parameter - ack-train detection */
399 		if ((s32)(now - ca->last_ack) <= hystart_ack_delta_us) {
400 			ca->last_ack = now;
401 
402 			threshold = ca->delay_min + hystart_ack_delay(sk);
403 
404 			/* Hystart ack train triggers if we get ack past
405 			 * ca->delay_min/2.
406 			 * Pacing might have delayed packets up to RTT/2
407 			 * during slow start.
408 			 */
409 			if (sk->sk_pacing_status == SK_PACING_NONE)
410 				threshold >>= 1;
411 
412 			if ((s32)(now - ca->round_start) > threshold) {
413 				ca->found = 1;
414 				pr_debug("hystart_ack_train (%u > %u) delay_min %u (+ ack_delay %u) cwnd %u\n",
415 					 now - ca->round_start, threshold,
416 					 ca->delay_min, hystart_ack_delay(sk), tcp_snd_cwnd(tp));
417 				NET_INC_STATS(sock_net(sk),
418 					      LINUX_MIB_TCPHYSTARTTRAINDETECT);
419 				NET_ADD_STATS(sock_net(sk),
420 					      LINUX_MIB_TCPHYSTARTTRAINCWND,
421 					      tcp_snd_cwnd(tp));
422 				tp->snd_ssthresh = tcp_snd_cwnd(tp);
423 			}
424 		}
425 	}
426 
427 	if (hystart_detect & HYSTART_DELAY) {
428 		/* obtain the minimum delay of more than sampling packets */
429 		if (ca->curr_rtt > delay)
430 			ca->curr_rtt = delay;
431 		if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
432 			ca->sample_cnt++;
433 		} else {
434 			if (ca->curr_rtt > ca->delay_min +
435 			    HYSTART_DELAY_THRESH(ca->delay_min >> 3)) {
436 				ca->found = 1;
437 				NET_INC_STATS(sock_net(sk),
438 					      LINUX_MIB_TCPHYSTARTDELAYDETECT);
439 				NET_ADD_STATS(sock_net(sk),
440 					      LINUX_MIB_TCPHYSTARTDELAYCWND,
441 					      tcp_snd_cwnd(tp));
442 				tp->snd_ssthresh = tcp_snd_cwnd(tp);
443 			}
444 		}
445 	}
446 }
447 
cubictcp_acked(struct sock * sk,const struct ack_sample * sample)448 __bpf_kfunc static void cubictcp_acked(struct sock *sk, const struct ack_sample *sample)
449 {
450 	const struct tcp_sock *tp = tcp_sk(sk);
451 	struct bictcp *ca = inet_csk_ca(sk);
452 	u32 delay;
453 
454 	/* Some calls are for duplicates without timetamps */
455 	if (sample->rtt_us < 0)
456 		return;
457 
458 	/* Discard delay samples right after fast recovery */
459 	if (ca->epoch_start && (s32)(tcp_jiffies32 - ca->epoch_start) < HZ)
460 		return;
461 
462 	delay = sample->rtt_us;
463 	if (delay == 0)
464 		delay = 1;
465 
466 	/* first time call or link delay decreases */
467 	if (ca->delay_min == 0 || ca->delay_min > delay)
468 		ca->delay_min = delay;
469 
470 	/* hystart triggers when cwnd is larger than some threshold */
471 	if (!ca->found && tcp_in_slow_start(tp) && hystart &&
472 	    tcp_snd_cwnd(tp) >= hystart_low_window)
473 		hystart_update(sk, delay);
474 }
475 
476 static struct tcp_congestion_ops cubictcp __read_mostly = {
477 	.init		= cubictcp_init,
478 	.ssthresh	= cubictcp_recalc_ssthresh,
479 	.cong_avoid	= cubictcp_cong_avoid,
480 	.set_state	= cubictcp_state,
481 	.undo_cwnd	= tcp_reno_undo_cwnd,
482 	.cwnd_event	= cubictcp_cwnd_event,
483 	.pkts_acked     = cubictcp_acked,
484 	.owner		= THIS_MODULE,
485 	.name		= "cubic",
486 };
487 
488 BTF_SET8_START(tcp_cubic_check_kfunc_ids)
489 #ifdef CONFIG_X86
490 #ifdef CONFIG_DYNAMIC_FTRACE
491 BTF_ID_FLAGS(func, cubictcp_init)
492 BTF_ID_FLAGS(func, cubictcp_recalc_ssthresh)
493 BTF_ID_FLAGS(func, cubictcp_cong_avoid)
494 BTF_ID_FLAGS(func, cubictcp_state)
495 BTF_ID_FLAGS(func, cubictcp_cwnd_event)
496 BTF_ID_FLAGS(func, cubictcp_acked)
497 #endif
498 #endif
499 BTF_SET8_END(tcp_cubic_check_kfunc_ids)
500 
501 static const struct btf_kfunc_id_set tcp_cubic_kfunc_set = {
502 	.owner = THIS_MODULE,
503 	.set   = &tcp_cubic_check_kfunc_ids,
504 };
505 
cubictcp_register(void)506 static int __init cubictcp_register(void)
507 {
508 	int ret;
509 
510 	BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
511 
512 	/* Precompute a bunch of the scaling factors that are used per-packet
513 	 * based on SRTT of 100ms
514 	 */
515 
516 	beta_scale = 8*(BICTCP_BETA_SCALE+beta) / 3
517 		/ (BICTCP_BETA_SCALE - beta);
518 
519 	cube_rtt_scale = (bic_scale * 10);	/* 1024*c/rtt */
520 
521 	/* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
522 	 *  so K = cubic_root( (wmax-cwnd)*rtt/c )
523 	 * the unit of K is bictcp_HZ=2^10, not HZ
524 	 *
525 	 *  c = bic_scale >> 10
526 	 *  rtt = 100ms
527 	 *
528 	 * the following code has been designed and tested for
529 	 * cwnd < 1 million packets
530 	 * RTT < 100 seconds
531 	 * HZ < 1,000,00  (corresponding to 10 nano-second)
532 	 */
533 
534 	/* 1/c * 2^2*bictcp_HZ * srtt */
535 	cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */
536 
537 	/* divide by bic_scale and by constant Srtt (100ms) */
538 	do_div(cube_factor, bic_scale * 10);
539 
540 	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS, &tcp_cubic_kfunc_set);
541 	if (ret < 0)
542 		return ret;
543 	return tcp_register_congestion_control(&cubictcp);
544 }
545 
cubictcp_unregister(void)546 static void __exit cubictcp_unregister(void)
547 {
548 	tcp_unregister_congestion_control(&cubictcp);
549 }
550 
551 module_init(cubictcp_register);
552 module_exit(cubictcp_unregister);
553 
554 MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger");
555 MODULE_LICENSE("GPL");
556 MODULE_DESCRIPTION("CUBIC TCP");
557 MODULE_VERSION("2.3");
558