blob: 20de0118c98e455447128513610ba04b13f3cd61 [file] [log] [blame]
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -08001/*
Sangtae Haae27e982008-10-29 00:07:18 -04002 * TCP CUBIC: Binary Increase Congestion control for TCP v2.3
Sangtae Ha6b3d6262008-03-04 14:17:41 -08003 * Home page:
4 * http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -08005 * This is from the implementation of CUBIC TCP in
Sangtae Haae27e982008-10-29 00:07:18 -04006 * 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.
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -08009 * Available from:
Sangtae Haae27e982008-10-29 00:07:18 -040010 * 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
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080021 *
22 * Unless CUBIC is enabled and congestion window is large
23 * this behaves the same as the original Reno.
24 */
25
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080026#include <linux/mm.h>
27#include <linux/module.h>
Roman Zippel6f6d6a12008-05-01 04:34:28 -070028#include <linux/math64.h>
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080029#include <net/tcp.h>
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080030
31#define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation
32 * max_cwnd = snd_cwnd * beta
33 */
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080034#define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */
35
Sangtae Haae27e982008-10-29 00:07:18 -040036/* 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
Sangtae Ha2b4636a2011-03-14 07:52:17 +000042#define HYSTART_DELAY_MIN (4U<<3)
Sangtae Haae27e982008-10-29 00:07:18 -040043#define HYSTART_DELAY_MAX (16U<<3)
44#define HYSTART_DELAY_THRESH(x) clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX)
45
Stephen Hemminger59758f42007-02-12 13:15:20 -080046static int fast_convergence __read_mostly = 1;
Sangtae Ha6b3d6262008-03-04 14:17:41 -080047static int beta __read_mostly = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */
David S. Miller66e1e3b2007-06-13 01:03:53 -070048static int initial_ssthresh __read_mostly;
Stephen Hemminger59758f42007-02-12 13:15:20 -080049static int bic_scale __read_mostly = 41;
50static int tcp_friendliness __read_mostly = 1;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080051
Sangtae Haae27e982008-10-29 00:07:18 -040052static int hystart __read_mostly = 1;
53static int hystart_detect __read_mostly = HYSTART_ACK_TRAIN | HYSTART_DELAY;
54static int hystart_low_window __read_mostly = 16;
stephen hemmingeraac46322011-03-14 07:52:14 +000055static int hystart_ack_delta __read_mostly = 2;
Sangtae Haae27e982008-10-29 00:07:18 -040056
Stephen Hemminger59758f42007-02-12 13:15:20 -080057static u32 cube_rtt_scale __read_mostly;
58static u32 beta_scale __read_mostly;
59static u64 cube_factor __read_mostly;
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -080060
61/* Note parameters that are used for precomputing scale factors are read-only */
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080062module_param(fast_convergence, int, 0644);
63MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence");
Sangtae Ha6b3d6262008-03-04 14:17:41 -080064module_param(beta, int, 0644);
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080065MODULE_PARM_DESC(beta, "beta for multiplicative increase");
66module_param(initial_ssthresh, int, 0644);
67MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold");
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -080068module_param(bic_scale, int, 0444);
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080069MODULE_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");
Sangtae Haae27e982008-10-29 00:07:18 -040072module_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");
stephen hemmingeraac46322011-03-14 07:52:14 +000079module_param(hystart_ack_delta, int, 0644);
80MODULE_PARM_DESC(hystart_ack_delta, "spacing between ack's indicating train (msecs)");
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080081
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080082/* BIC TCP Parameters */
83struct bictcp {
84 u32 cnt; /* increase cwnd by 1 after ACKs */
stephen hemminger688d1942014-08-29 23:32:05 -070085 u32 last_max_cwnd; /* last maximum snd_cwnd */
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080086 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 */
stephen hemminger688d1942014-08-29 23:32:05 -070090 u32 bic_K; /* time to origin point
91 from the beginning of the current epoch */
stephen hemminger17a6e9f2011-03-14 07:52:15 +000092 u32 delay_min; /* min delay (msec << 3) */
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -080093 u32 epoch_start; /* beginning of an epoch */
94 u32 ack_cnt; /* number of acks */
95 u32 tcp_cwnd; /* estimated tcp cwnd */
96#define ACK_RATIO_SHIFT 4
stephen hemmingerb9f47a3a2011-05-04 10:04:56 +000097#define ACK_RATIO_LIMIT (32u << ACK_RATIO_SHIFT)
Sangtae Haae27e982008-10-29 00:07:18 -040098 u16 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */
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 */
stephen hemminger17a6e9f2011-03-14 07:52:15 +0000103 u32 last_ack; /* last time when the ACK spacing is close */
Sangtae Haae27e982008-10-29 00:07:18 -0400104 u32 curr_rtt; /* the minimum rtt of current round */
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800105};
106
107static inline void bictcp_reset(struct bictcp *ca)
108{
109 ca->cnt = 0;
110 ca->last_max_cwnd = 0;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800111 ca->last_cwnd = 0;
112 ca->last_time = 0;
113 ca->bic_origin_point = 0;
114 ca->bic_K = 0;
115 ca->delay_min = 0;
116 ca->epoch_start = 0;
117 ca->delayed_ack = 2 << ACK_RATIO_SHIFT;
118 ca->ack_cnt = 0;
119 ca->tcp_cwnd = 0;
Sangtae Haae27e982008-10-29 00:07:18 -0400120 ca->found = 0;
121}
122
stephen hemminger17a6e9f2011-03-14 07:52:15 +0000123static inline u32 bictcp_clock(void)
124{
125#if HZ < 1000
126 return ktime_to_ms(ktime_get_real());
127#else
128 return jiffies_to_msecs(jiffies);
129#endif
130}
131
Sangtae Haae27e982008-10-29 00:07:18 -0400132static inline void bictcp_hystart_reset(struct sock *sk)
133{
134 struct tcp_sock *tp = tcp_sk(sk);
135 struct bictcp *ca = inet_csk_ca(sk);
136
stephen hemminger17a6e9f2011-03-14 07:52:15 +0000137 ca->round_start = ca->last_ack = bictcp_clock();
Sangtae Haae27e982008-10-29 00:07:18 -0400138 ca->end_seq = tp->snd_nxt;
139 ca->curr_rtt = 0;
140 ca->sample_cnt = 0;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800141}
142
143static void bictcp_init(struct sock *sk)
144{
Neal Cardwell5a45f002012-01-18 17:47:59 +0000145 struct bictcp *ca = inet_csk_ca(sk);
146
147 bictcp_reset(ca);
148 ca->loss_cwnd = 0;
Sangtae Haae27e982008-10-29 00:07:18 -0400149
150 if (hystart)
151 bictcp_hystart_reset(sk);
152
153 if (!hystart && initial_ssthresh)
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800154 tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
155}
156
Stephen Hemminger7e588862007-03-22 12:10:58 -0700157/* calculate the cubic root of x using a table lookup followed by one
158 * Newton-Raphson iteration.
159 * Avg err ~= 0.195%
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800160 */
Stephen Hemminger9eb2d622005-12-21 19:32:36 -0800161static u32 cubic_root(u64 a)
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800162{
Stephen Hemminger7e588862007-03-22 12:10:58 -0700163 u32 x, b, shift;
164 /*
165 * cbrt(x) MSB values for x MSB values in [0..63].
166 * Precomputed then refined by hand - Willy Tarreau
167 *
168 * For x in [0..63],
169 * v = cbrt(x << 18) - 1
170 * cbrt(x) = (v[x] + 10) >> 6
Stephen Hemminger9eb2d622005-12-21 19:32:36 -0800171 */
Stephen Hemminger7e588862007-03-22 12:10:58 -0700172 static const u8 v[] = {
173 /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118,
174 /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156,
175 /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179,
176 /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199,
177 /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215,
178 /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229,
179 /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242,
180 /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254,
181 };
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800182
Stephen Hemminger7e588862007-03-22 12:10:58 -0700183 b = fls64(a);
184 if (b < 7) {
185 /* a in [0..63] */
186 return ((u32)v[(u32)a] + 35) >> 6;
187 }
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800188
Stephen Hemminger7e588862007-03-22 12:10:58 -0700189 b = ((b * 84) >> 8) - 1;
190 shift = (a >> (b * 3));
191
192 x = ((u32)(((u32)v[shift] + 10) << b)) >> 6;
193
194 /*
195 * Newton-Raphson iteration
196 * 2
197 * x = ( 2 * x + a / x ) / 3
198 * k+1 k k
199 */
Roman Zippel6f6d6a12008-05-01 04:34:28 -0700200 x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1)));
Stephen Hemminger7e588862007-03-22 12:10:58 -0700201 x = ((x * 341) >> 10);
Stephen Hemminger9eb2d622005-12-21 19:32:36 -0800202 return x;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800203}
204
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800205/*
206 * Compute congestion window to use.
207 */
208static inline void bictcp_update(struct bictcp *ca, u32 cwnd)
209{
Eric Dumazet2ed0edf2013-08-05 17:10:15 -0700210 u32 delta, bic_target, max_cnt;
211 u64 offs, t;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800212
213 ca->ack_cnt++; /* count the number of ACKs */
214
215 if (ca->last_cwnd == cwnd &&
216 (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32)
217 return;
218
219 ca->last_cwnd = cwnd;
220 ca->last_time = tcp_time_stamp;
221
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800222 if (ca->epoch_start == 0) {
stephen hemminger688d1942014-08-29 23:32:05 -0700223 ca->epoch_start = tcp_time_stamp; /* record beginning */
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800224 ca->ack_cnt = 1; /* start counting */
225 ca->tcp_cwnd = cwnd; /* syn with cubic */
226
227 if (ca->last_max_cwnd <= cwnd) {
228 ca->bic_K = 0;
229 ca->bic_origin_point = cwnd;
230 } else {
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800231 /* Compute new K based on
232 * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ)
233 */
234 ca->bic_K = cubic_root(cube_factor
235 * (ca->last_max_cwnd - cwnd));
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800236 ca->bic_origin_point = ca->last_max_cwnd;
237 }
238 }
239
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900240 /* cubic function - calc*/
241 /* calculate c * time^3 / rtt,
242 * while considering overflow in calculation of time^3
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800243 * (so time^3 is done by using 64 bit)
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800244 * and without the support of division of 64bit numbers
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800245 * (so all divisions are done by using 32 bit)
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900246 * also NOTE the unit of those veriables
247 * time = (t - K) / 2^bictcp_HZ
248 * c = bic_scale >> 10
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800249 * rtt = (srtt >> 3) / HZ
250 * !!! The following code does not have overflow problems,
251 * if the cwnd < 1 million packets !!!
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900252 */
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800253
Eric Dumazet2ed0edf2013-08-05 17:10:15 -0700254 t = (s32)(tcp_time_stamp - ca->epoch_start);
255 t += msecs_to_jiffies(ca->delay_min >> 3);
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800256 /* change the unit from HZ to bictcp_HZ */
Eric Dumazet2ed0edf2013-08-05 17:10:15 -0700257 t <<= BICTCP_HZ;
258 do_div(t, HZ);
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800259
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900260 if (t < ca->bic_K) /* t - K */
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800261 offs = ca->bic_K - t;
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900262 else
263 offs = t - ca->bic_K;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800264
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800265 /* c/rtt * (t-K)^3 */
266 delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ);
stephen hemminger688d1942014-08-29 23:32:05 -0700267 if (t < ca->bic_K) /* below origin*/
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900268 bic_target = ca->bic_origin_point - delta;
stephen hemminger688d1942014-08-29 23:32:05 -0700269 else /* above origin*/
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900270 bic_target = ca->bic_origin_point + delta;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800271
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900272 /* cubic function - calc bictcp_cnt*/
273 if (bic_target > cwnd) {
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800274 ca->cnt = cwnd / (bic_target - cwnd);
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900275 } else {
276 ca->cnt = 100 * cwnd; /* very small increment*/
277 }
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800278
Sangtae Hab5ccd072011-03-14 07:52:18 +0000279 /*
280 * The initial growth of cubic function may be too conservative
281 * when the available bandwidth is still unknown.
282 */
Neal Cardwell5a45f002012-01-18 17:47:59 +0000283 if (ca->last_max_cwnd == 0 && ca->cnt > 20)
Sangtae Hab5ccd072011-03-14 07:52:18 +0000284 ca->cnt = 20; /* increase cwnd 5% per RTT */
285
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800286 /* TCP Friendly */
287 if (tcp_friendliness) {
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800288 u32 scale = beta_scale;
stephen hemminger688d1942014-08-29 23:32:05 -0700289
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800290 delta = (cwnd * scale) >> 3;
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900291 while (ca->ack_cnt > delta) { /* update tcp cwnd */
292 ca->ack_cnt -= delta;
293 ca->tcp_cwnd++;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800294 }
295
stephen hemminger688d1942014-08-29 23:32:05 -0700296 if (ca->tcp_cwnd > cwnd) { /* if bic is slower than tcp */
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800297 delta = ca->tcp_cwnd - cwnd;
298 max_cnt = cwnd / delta;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800299 if (ca->cnt > max_cnt)
300 ca->cnt = max_cnt;
301 }
YOSHIFUJI Hideakie905a9e2007-02-09 23:24:47 +0900302 }
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800303
304 ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack;
305 if (ca->cnt == 0) /* cannot be zero */
306 ca->cnt = 1;
307}
308
Eric Dumazet24901552014-05-02 21:18:05 -0700309static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800310{
311 struct tcp_sock *tp = tcp_sk(sk);
312 struct bictcp *ca = inet_csk_ca(sk);
313
Eric Dumazet24901552014-05-02 21:18:05 -0700314 if (!tcp_is_cwnd_limited(sk))
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800315 return;
316
Sangtae Haae27e982008-10-29 00:07:18 -0400317 if (tp->snd_cwnd <= tp->snd_ssthresh) {
318 if (hystart && after(ack, ca->end_seq))
319 bictcp_hystart_reset(sk);
Yuchung Cheng9f9843a72013-10-31 11:07:31 -0700320 tcp_slow_start(tp, acked);
Sangtae Haae27e982008-10-29 00:07:18 -0400321 } else {
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800322 bictcp_update(ca, tp->snd_cwnd);
Ilpo Järvinen758ce5c2009-02-28 04:44:37 +0000323 tcp_cong_avoid_ai(tp, ca->cnt);
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800324 }
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800325}
326
327static u32 bictcp_recalc_ssthresh(struct sock *sk)
328{
329 const struct tcp_sock *tp = tcp_sk(sk);
330 struct bictcp *ca = inet_csk_ca(sk);
331
332 ca->epoch_start = 0; /* end of epoch */
333
334 /* Wmax and fast convergence */
335 if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
336 ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
337 / (2 * BICTCP_BETA_SCALE);
338 else
339 ca->last_max_cwnd = tp->snd_cwnd;
340
341 ca->loss_cwnd = tp->snd_cwnd;
342
343 return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
344}
345
346static u32 bictcp_undo_cwnd(struct sock *sk)
347{
348 struct bictcp *ca = inet_csk_ca(sk);
349
Neal Cardwell5a45f002012-01-18 17:47:59 +0000350 return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800351}
352
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800353static void bictcp_state(struct sock *sk, u8 new_state)
354{
Sangtae Haae27e982008-10-29 00:07:18 -0400355 if (new_state == TCP_CA_Loss) {
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800356 bictcp_reset(inet_csk_ca(sk));
Sangtae Haae27e982008-10-29 00:07:18 -0400357 bictcp_hystart_reset(sk);
358 }
359}
360
361static void hystart_update(struct sock *sk, u32 delay)
362{
363 struct tcp_sock *tp = tcp_sk(sk);
364 struct bictcp *ca = inet_csk_ca(sk);
365
366 if (!(ca->found & hystart_detect)) {
stephen hemminger17a6e9f2011-03-14 07:52:15 +0000367 u32 now = bictcp_clock();
Sangtae Haae27e982008-10-29 00:07:18 -0400368
369 /* first detection parameter - ack-train detection */
stephen hemminger17a6e9f2011-03-14 07:52:15 +0000370 if ((s32)(now - ca->last_ack) <= hystart_ack_delta) {
371 ca->last_ack = now;
372 if ((s32)(now - ca->round_start) > ca->delay_min >> 4)
Sangtae Haae27e982008-10-29 00:07:18 -0400373 ca->found |= HYSTART_ACK_TRAIN;
374 }
375
376 /* obtain the minimum delay of more than sampling packets */
377 if (ca->sample_cnt < HYSTART_MIN_SAMPLES) {
378 if (ca->curr_rtt == 0 || ca->curr_rtt > delay)
379 ca->curr_rtt = delay;
380
381 ca->sample_cnt++;
382 } else {
383 if (ca->curr_rtt > ca->delay_min +
384 HYSTART_DELAY_THRESH(ca->delay_min>>4))
385 ca->found |= HYSTART_DELAY;
386 }
387 /*
388 * Either one of two conditions are met,
389 * we exit from slow start immediately.
390 */
391 if (ca->found & hystart_detect)
392 tp->snd_ssthresh = tp->snd_cwnd;
393 }
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800394}
395
396/* Track delayed acknowledgment ratio using sliding window
397 * ratio = (15*ratio + sample) / 16
398 */
Stephen Hemminger30cfd0b2007-07-25 23:49:34 -0700399static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us)
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800400{
401 const struct inet_connection_sock *icsk = inet_csk(sk);
Sangtae Haae27e982008-10-29 00:07:18 -0400402 const struct tcp_sock *tp = tcp_sk(sk);
Stephen Hemmingere7d0c8852007-07-25 23:50:06 -0700403 struct bictcp *ca = inet_csk_ca(sk);
404 u32 delay;
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800405
Ilpo Järvinen35e86942007-05-31 10:16:47 +0300406 if (icsk->icsk_ca_state == TCP_CA_Open) {
stephen hemmingerb9f47a3a2011-05-04 10:04:56 +0000407 u32 ratio = ca->delayed_ack;
408
409 ratio -= ca->delayed_ack >> ACK_RATIO_SHIFT;
410 ratio += cnt;
411
Liu Yu0cda3452014-04-30 17:34:09 +0800412 ca->delayed_ack = clamp(ratio, 1U, ACK_RATIO_LIMIT);
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800413 }
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800414
Stephen Hemmingere7d0c8852007-07-25 23:50:06 -0700415 /* Some calls are for duplicates without timetamps */
416 if (rtt_us < 0)
417 return;
418
419 /* Discard delay samples right after fast recovery */
Eric Dumazetcd6b4232013-08-05 20:05:12 -0700420 if (ca->epoch_start && (s32)(tcp_time_stamp - ca->epoch_start) < HZ)
Stephen Hemmingere7d0c8852007-07-25 23:50:06 -0700421 return;
422
stephen hemminger17a6e9f2011-03-14 07:52:15 +0000423 delay = (rtt_us << 3) / USEC_PER_MSEC;
Stephen Hemmingere7d0c8852007-07-25 23:50:06 -0700424 if (delay == 0)
425 delay = 1;
426
427 /* first time call or link delay decreases */
428 if (ca->delay_min == 0 || ca->delay_min > delay)
429 ca->delay_min = delay;
Sangtae Haae27e982008-10-29 00:07:18 -0400430
431 /* hystart triggers when cwnd is larger than some threshold */
432 if (hystart && tp->snd_cwnd <= tp->snd_ssthresh &&
433 tp->snd_cwnd >= hystart_low_window)
434 hystart_update(sk, delay);
Stephen Hemmingere7d0c8852007-07-25 23:50:06 -0700435}
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800436
Stephen Hemmingera252beb2011-03-10 00:40:17 -0800437static struct tcp_congestion_ops cubictcp __read_mostly = {
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800438 .init = bictcp_init,
439 .ssthresh = bictcp_recalc_ssthresh,
440 .cong_avoid = bictcp_cong_avoid,
441 .set_state = bictcp_state,
442 .undo_cwnd = bictcp_undo_cwnd,
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800443 .pkts_acked = bictcp_acked,
444 .owner = THIS_MODULE,
445 .name = "cubic",
446};
447
448static int __init cubictcp_register(void)
449{
Alexey Dobriyan74975d42006-08-25 17:10:33 -0700450 BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE);
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800451
452 /* Precompute a bunch of the scaling factors that are used per-packet
453 * based on SRTT of 100ms
454 */
455
stephen hemminger688d1942014-08-29 23:32:05 -0700456 beta_scale = 8*(BICTCP_BETA_SCALE+beta) / 3
457 / (BICTCP_BETA_SCALE - beta);
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800458
Stephen Hemminger22119242006-10-25 23:04:12 -0700459 cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */
Stephen Hemminger89b3d9a2005-12-21 19:32:08 -0800460
461 /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3
462 * so K = cubic_root( (wmax-cwnd)*rtt/c )
463 * the unit of K is bictcp_HZ=2^10, not HZ
464 *
465 * c = bic_scale >> 10
466 * rtt = 100ms
467 *
468 * the following code has been designed and tested for
469 * cwnd < 1 million packets
470 * RTT < 100 seconds
471 * HZ < 1,000,00 (corresponding to 10 nano-second)
472 */
473
474 /* 1/c * 2^2*bictcp_HZ * srtt */
475 cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */
476
477 /* divide by bic_scale and by constant Srtt (100ms) */
478 do_div(cube_factor, bic_scale * 10);
479
Stephen Hemmingerdf3271f2005-12-13 23:13:28 -0800480 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");
Sangtae Haae27e982008-10-29 00:07:18 -0400494MODULE_VERSION("2.3");