1df3271f3SStephen Hemminger /* 2ae27e98aSSangtae Ha * TCP CUBIC: Binary Increase Congestion control for TCP v2.3 36b3d6263SSangtae Ha * Home page: 46b3d6263SSangtae Ha * http://netsrv.csc.ncsu.edu/twiki/bin/view/Main/BIC 5df3271f3SStephen Hemminger * This is from the implementation of CUBIC TCP in 6ae27e98aSSangtae Ha * Sangtae Ha, Injong Rhee and Lisong Xu, 7ae27e98aSSangtae Ha * "CUBIC: A New TCP-Friendly High-Speed TCP Variant" 8ae27e98aSSangtae Ha * in ACM SIGOPS Operating System Review, July 2008. 9df3271f3SStephen Hemminger * Available from: 10ae27e98aSSangtae Ha * http://netsrv.csc.ncsu.edu/export/cubic_a_new_tcp_2008.pdf 11ae27e98aSSangtae Ha * 12ae27e98aSSangtae Ha * CUBIC integrates a new slow start algorithm, called HyStart. 13ae27e98aSSangtae Ha * The details of HyStart are presented in 14ae27e98aSSangtae Ha * Sangtae Ha and Injong Rhee, 15ae27e98aSSangtae Ha * "Taming the Elephants: New TCP Slow Start", NCSU TechReport 2008. 16ae27e98aSSangtae Ha * Available from: 17ae27e98aSSangtae Ha * http://netsrv.csc.ncsu.edu/export/hystart_techreport_2008.pdf 18ae27e98aSSangtae Ha * 19ae27e98aSSangtae Ha * All testing results are available from: 20ae27e98aSSangtae Ha * http://netsrv.csc.ncsu.edu/wiki/index.php/TCP_Testing 21df3271f3SStephen Hemminger * 22df3271f3SStephen Hemminger * Unless CUBIC is enabled and congestion window is large 23df3271f3SStephen Hemminger * this behaves the same as the original Reno. 24df3271f3SStephen Hemminger */ 25df3271f3SStephen Hemminger 26df3271f3SStephen Hemminger #include <linux/mm.h> 27df3271f3SStephen Hemminger #include <linux/module.h> 286f6d6a1aSRoman Zippel #include <linux/math64.h> 29df3271f3SStephen Hemminger #include <net/tcp.h> 30df3271f3SStephen Hemminger 31df3271f3SStephen Hemminger #define BICTCP_BETA_SCALE 1024 /* Scale factor beta calculation 32df3271f3SStephen Hemminger * max_cwnd = snd_cwnd * beta 33df3271f3SStephen Hemminger */ 34df3271f3SStephen Hemminger #define BICTCP_HZ 10 /* BIC HZ 2^10 = 1024 */ 35df3271f3SStephen Hemminger 36ae27e98aSSangtae Ha /* Two methods of hybrid slow start */ 37ae27e98aSSangtae Ha #define HYSTART_ACK_TRAIN 0x1 38ae27e98aSSangtae Ha #define HYSTART_DELAY 0x2 39ae27e98aSSangtae Ha 40ae27e98aSSangtae Ha /* Number of delay samples for detecting the increase of delay */ 41ae27e98aSSangtae Ha #define HYSTART_MIN_SAMPLES 8 42ae27e98aSSangtae Ha #define HYSTART_DELAY_MIN (2U<<3) 43ae27e98aSSangtae Ha #define HYSTART_DELAY_MAX (16U<<3) 44ae27e98aSSangtae Ha #define HYSTART_DELAY_THRESH(x) clamp(x, HYSTART_DELAY_MIN, HYSTART_DELAY_MAX) 45ae27e98aSSangtae Ha 4659758f44SStephen Hemminger static int fast_convergence __read_mostly = 1; 476b3d6263SSangtae Ha static int beta __read_mostly = 717; /* = 717/1024 (BICTCP_BETA_SCALE) */ 4866e1e3b2SDavid S. Miller static int initial_ssthresh __read_mostly; 4959758f44SStephen Hemminger static int bic_scale __read_mostly = 41; 5059758f44SStephen Hemminger static int tcp_friendliness __read_mostly = 1; 51df3271f3SStephen Hemminger 52ae27e98aSSangtae Ha static int hystart __read_mostly = 1; 53ae27e98aSSangtae Ha static int hystart_detect __read_mostly = HYSTART_ACK_TRAIN | HYSTART_DELAY; 54ae27e98aSSangtae Ha static int hystart_low_window __read_mostly = 16; 55aac46324Sstephen hemminger static int hystart_ack_delta __read_mostly = 2; 56ae27e98aSSangtae Ha 5759758f44SStephen Hemminger static u32 cube_rtt_scale __read_mostly; 5859758f44SStephen Hemminger static u32 beta_scale __read_mostly; 5959758f44SStephen Hemminger static u64 cube_factor __read_mostly; 6089b3d9aaSStephen Hemminger 6189b3d9aaSStephen Hemminger /* Note parameters that are used for precomputing scale factors are read-only */ 62df3271f3SStephen Hemminger module_param(fast_convergence, int, 0644); 63df3271f3SStephen Hemminger MODULE_PARM_DESC(fast_convergence, "turn on/off fast convergence"); 646b3d6263SSangtae Ha module_param(beta, int, 0644); 65df3271f3SStephen Hemminger MODULE_PARM_DESC(beta, "beta for multiplicative increase"); 66df3271f3SStephen Hemminger module_param(initial_ssthresh, int, 0644); 67df3271f3SStephen Hemminger MODULE_PARM_DESC(initial_ssthresh, "initial value of slow start threshold"); 6889b3d9aaSStephen Hemminger module_param(bic_scale, int, 0444); 69df3271f3SStephen Hemminger MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_scale/1024)"); 70df3271f3SStephen Hemminger module_param(tcp_friendliness, int, 0644); 71df3271f3SStephen Hemminger MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness"); 72ae27e98aSSangtae Ha module_param(hystart, int, 0644); 73ae27e98aSSangtae Ha MODULE_PARM_DESC(hystart, "turn on/off hybrid slow start algorithm"); 74ae27e98aSSangtae Ha module_param(hystart_detect, int, 0644); 75ae27e98aSSangtae Ha MODULE_PARM_DESC(hystart_detect, "hyrbrid slow start detection mechanisms" 76ae27e98aSSangtae Ha " 1: packet-train 2: delay 3: both packet-train and delay"); 77ae27e98aSSangtae Ha module_param(hystart_low_window, int, 0644); 78ae27e98aSSangtae Ha MODULE_PARM_DESC(hystart_low_window, "lower bound cwnd for hybrid slow start"); 79aac46324Sstephen hemminger module_param(hystart_ack_delta, int, 0644); 80aac46324Sstephen hemminger MODULE_PARM_DESC(hystart_ack_delta, "spacing between ack's indicating train (msecs)"); 81df3271f3SStephen Hemminger 82df3271f3SStephen Hemminger /* BIC TCP Parameters */ 83df3271f3SStephen Hemminger struct bictcp { 84df3271f3SStephen Hemminger u32 cnt; /* increase cwnd by 1 after ACKs */ 85df3271f3SStephen Hemminger u32 last_max_cwnd; /* last maximum snd_cwnd */ 86df3271f3SStephen Hemminger u32 loss_cwnd; /* congestion window at last loss */ 87df3271f3SStephen Hemminger u32 last_cwnd; /* the last snd_cwnd */ 88df3271f3SStephen Hemminger u32 last_time; /* time when updated last_cwnd */ 89df3271f3SStephen Hemminger u32 bic_origin_point;/* origin point of bic function */ 90df3271f3SStephen Hemminger u32 bic_K; /* time to origin point from the beginning of the current epoch */ 91*17a6e9f1Sstephen hemminger u32 delay_min; /* min delay (msec << 3) */ 92df3271f3SStephen Hemminger u32 epoch_start; /* beginning of an epoch */ 93df3271f3SStephen Hemminger u32 ack_cnt; /* number of acks */ 94df3271f3SStephen Hemminger u32 tcp_cwnd; /* estimated tcp cwnd */ 95df3271f3SStephen Hemminger #define ACK_RATIO_SHIFT 4 96ae27e98aSSangtae Ha u16 delayed_ack; /* estimate the ratio of Packets/ACKs << 4 */ 97ae27e98aSSangtae Ha u8 sample_cnt; /* number of samples to decide curr_rtt */ 98ae27e98aSSangtae Ha u8 found; /* the exit point is found? */ 99ae27e98aSSangtae Ha u32 round_start; /* beginning of each round */ 100ae27e98aSSangtae Ha u32 end_seq; /* end_seq of the round */ 101*17a6e9f1Sstephen hemminger u32 last_ack; /* last time when the ACK spacing is close */ 102ae27e98aSSangtae Ha u32 curr_rtt; /* the minimum rtt of current round */ 103df3271f3SStephen Hemminger }; 104df3271f3SStephen Hemminger 105df3271f3SStephen Hemminger static inline void bictcp_reset(struct bictcp *ca) 106df3271f3SStephen Hemminger { 107df3271f3SStephen Hemminger ca->cnt = 0; 108df3271f3SStephen Hemminger ca->last_max_cwnd = 0; 109df3271f3SStephen Hemminger ca->loss_cwnd = 0; 110df3271f3SStephen Hemminger ca->last_cwnd = 0; 111df3271f3SStephen Hemminger ca->last_time = 0; 112df3271f3SStephen Hemminger ca->bic_origin_point = 0; 113df3271f3SStephen Hemminger ca->bic_K = 0; 114df3271f3SStephen Hemminger ca->delay_min = 0; 115df3271f3SStephen Hemminger ca->epoch_start = 0; 116df3271f3SStephen Hemminger ca->delayed_ack = 2 << ACK_RATIO_SHIFT; 117df3271f3SStephen Hemminger ca->ack_cnt = 0; 118df3271f3SStephen Hemminger ca->tcp_cwnd = 0; 119ae27e98aSSangtae Ha ca->found = 0; 120ae27e98aSSangtae Ha } 121ae27e98aSSangtae Ha 122*17a6e9f1Sstephen hemminger static inline u32 bictcp_clock(void) 123*17a6e9f1Sstephen hemminger { 124*17a6e9f1Sstephen hemminger #if HZ < 1000 125*17a6e9f1Sstephen hemminger return ktime_to_ms(ktime_get_real()); 126*17a6e9f1Sstephen hemminger #else 127*17a6e9f1Sstephen hemminger return jiffies_to_msecs(jiffies); 128*17a6e9f1Sstephen hemminger #endif 129*17a6e9f1Sstephen hemminger } 130*17a6e9f1Sstephen hemminger 131ae27e98aSSangtae Ha static inline void bictcp_hystart_reset(struct sock *sk) 132ae27e98aSSangtae Ha { 133ae27e98aSSangtae Ha struct tcp_sock *tp = tcp_sk(sk); 134ae27e98aSSangtae Ha struct bictcp *ca = inet_csk_ca(sk); 135ae27e98aSSangtae Ha 136*17a6e9f1Sstephen hemminger ca->round_start = ca->last_ack = bictcp_clock(); 137ae27e98aSSangtae Ha ca->end_seq = tp->snd_nxt; 138ae27e98aSSangtae Ha ca->curr_rtt = 0; 139ae27e98aSSangtae Ha ca->sample_cnt = 0; 140df3271f3SStephen Hemminger } 141df3271f3SStephen Hemminger 142df3271f3SStephen Hemminger static void bictcp_init(struct sock *sk) 143df3271f3SStephen Hemminger { 144df3271f3SStephen Hemminger bictcp_reset(inet_csk_ca(sk)); 145ae27e98aSSangtae Ha 146ae27e98aSSangtae Ha if (hystart) 147ae27e98aSSangtae Ha bictcp_hystart_reset(sk); 148ae27e98aSSangtae Ha 149ae27e98aSSangtae Ha if (!hystart && initial_ssthresh) 150df3271f3SStephen Hemminger tcp_sk(sk)->snd_ssthresh = initial_ssthresh; 151df3271f3SStephen Hemminger } 152df3271f3SStephen Hemminger 1537e58886bSStephen Hemminger /* calculate the cubic root of x using a table lookup followed by one 1547e58886bSStephen Hemminger * Newton-Raphson iteration. 1557e58886bSStephen Hemminger * Avg err ~= 0.195% 156df3271f3SStephen Hemminger */ 1579eb2d627SStephen Hemminger static u32 cubic_root(u64 a) 158df3271f3SStephen Hemminger { 1597e58886bSStephen Hemminger u32 x, b, shift; 1607e58886bSStephen Hemminger /* 1617e58886bSStephen Hemminger * cbrt(x) MSB values for x MSB values in [0..63]. 1627e58886bSStephen Hemminger * Precomputed then refined by hand - Willy Tarreau 1637e58886bSStephen Hemminger * 1647e58886bSStephen Hemminger * For x in [0..63], 1657e58886bSStephen Hemminger * v = cbrt(x << 18) - 1 1667e58886bSStephen Hemminger * cbrt(x) = (v[x] + 10) >> 6 1679eb2d627SStephen Hemminger */ 1687e58886bSStephen Hemminger static const u8 v[] = { 1697e58886bSStephen Hemminger /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118, 1707e58886bSStephen Hemminger /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156, 1717e58886bSStephen Hemminger /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179, 1727e58886bSStephen Hemminger /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199, 1737e58886bSStephen Hemminger /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215, 1747e58886bSStephen Hemminger /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229, 1757e58886bSStephen Hemminger /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242, 1767e58886bSStephen Hemminger /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254, 1777e58886bSStephen Hemminger }; 178df3271f3SStephen Hemminger 1797e58886bSStephen Hemminger b = fls64(a); 1807e58886bSStephen Hemminger if (b < 7) { 1817e58886bSStephen Hemminger /* a in [0..63] */ 1827e58886bSStephen Hemminger return ((u32)v[(u32)a] + 35) >> 6; 1837e58886bSStephen Hemminger } 184df3271f3SStephen Hemminger 1857e58886bSStephen Hemminger b = ((b * 84) >> 8) - 1; 1867e58886bSStephen Hemminger shift = (a >> (b * 3)); 1877e58886bSStephen Hemminger 1887e58886bSStephen Hemminger x = ((u32)(((u32)v[shift] + 10) << b)) >> 6; 1897e58886bSStephen Hemminger 1907e58886bSStephen Hemminger /* 1917e58886bSStephen Hemminger * Newton-Raphson iteration 1927e58886bSStephen Hemminger * 2 1937e58886bSStephen Hemminger * x = ( 2 * x + a / x ) / 3 1947e58886bSStephen Hemminger * k+1 k k 1957e58886bSStephen Hemminger */ 1966f6d6a1aSRoman Zippel x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1))); 1977e58886bSStephen Hemminger x = ((x * 341) >> 10); 1989eb2d627SStephen Hemminger return x; 199df3271f3SStephen Hemminger } 200df3271f3SStephen Hemminger 201df3271f3SStephen Hemminger /* 202df3271f3SStephen Hemminger * Compute congestion window to use. 203df3271f3SStephen Hemminger */ 204df3271f3SStephen Hemminger static inline void bictcp_update(struct bictcp *ca, u32 cwnd) 205df3271f3SStephen Hemminger { 20689b3d9aaSStephen Hemminger u64 offs; 2076b3d6263SSangtae Ha u32 delta, t, bic_target, max_cnt; 208df3271f3SStephen Hemminger 209df3271f3SStephen Hemminger ca->ack_cnt++; /* count the number of ACKs */ 210df3271f3SStephen Hemminger 211df3271f3SStephen Hemminger if (ca->last_cwnd == cwnd && 212df3271f3SStephen Hemminger (s32)(tcp_time_stamp - ca->last_time) <= HZ / 32) 213df3271f3SStephen Hemminger return; 214df3271f3SStephen Hemminger 215df3271f3SStephen Hemminger ca->last_cwnd = cwnd; 216df3271f3SStephen Hemminger ca->last_time = tcp_time_stamp; 217df3271f3SStephen Hemminger 218df3271f3SStephen Hemminger if (ca->epoch_start == 0) { 219df3271f3SStephen Hemminger ca->epoch_start = tcp_time_stamp; /* record the beginning of an epoch */ 220df3271f3SStephen Hemminger ca->ack_cnt = 1; /* start counting */ 221df3271f3SStephen Hemminger ca->tcp_cwnd = cwnd; /* syn with cubic */ 222df3271f3SStephen Hemminger 223df3271f3SStephen Hemminger if (ca->last_max_cwnd <= cwnd) { 224df3271f3SStephen Hemminger ca->bic_K = 0; 225df3271f3SStephen Hemminger ca->bic_origin_point = cwnd; 226df3271f3SStephen Hemminger } else { 22789b3d9aaSStephen Hemminger /* Compute new K based on 22889b3d9aaSStephen Hemminger * (wmax-cwnd) * (srtt>>3 / HZ) / c * 2^(3*bictcp_HZ) 22989b3d9aaSStephen Hemminger */ 23089b3d9aaSStephen Hemminger ca->bic_K = cubic_root(cube_factor 23189b3d9aaSStephen Hemminger * (ca->last_max_cwnd - cwnd)); 232df3271f3SStephen Hemminger ca->bic_origin_point = ca->last_max_cwnd; 233df3271f3SStephen Hemminger } 234df3271f3SStephen Hemminger } 235df3271f3SStephen Hemminger 236df3271f3SStephen Hemminger /* cubic function - calc*/ 237df3271f3SStephen Hemminger /* calculate c * time^3 / rtt, 238df3271f3SStephen Hemminger * while considering overflow in calculation of time^3 23989b3d9aaSStephen Hemminger * (so time^3 is done by using 64 bit) 240df3271f3SStephen Hemminger * and without the support of division of 64bit numbers 24189b3d9aaSStephen Hemminger * (so all divisions are done by using 32 bit) 242df3271f3SStephen Hemminger * also NOTE the unit of those veriables 243df3271f3SStephen Hemminger * time = (t - K) / 2^bictcp_HZ 244df3271f3SStephen Hemminger * c = bic_scale >> 10 245df3271f3SStephen Hemminger * rtt = (srtt >> 3) / HZ 246df3271f3SStephen Hemminger * !!! The following code does not have overflow problems, 247df3271f3SStephen Hemminger * if the cwnd < 1 million packets !!! 248df3271f3SStephen Hemminger */ 249df3271f3SStephen Hemminger 250df3271f3SStephen Hemminger /* change the unit from HZ to bictcp_HZ */ 251*17a6e9f1Sstephen hemminger t = ((tcp_time_stamp + msecs_to_jiffies(ca->delay_min>>3) 252*17a6e9f1Sstephen hemminger - ca->epoch_start) << BICTCP_HZ) / HZ; 253df3271f3SStephen Hemminger 254df3271f3SStephen Hemminger if (t < ca->bic_K) /* t - K */ 25589b3d9aaSStephen Hemminger offs = ca->bic_K - t; 256df3271f3SStephen Hemminger else 25789b3d9aaSStephen Hemminger offs = t - ca->bic_K; 258df3271f3SStephen Hemminger 25989b3d9aaSStephen Hemminger /* c/rtt * (t-K)^3 */ 26089b3d9aaSStephen Hemminger delta = (cube_rtt_scale * offs * offs * offs) >> (10+3*BICTCP_HZ); 261df3271f3SStephen Hemminger if (t < ca->bic_K) /* below origin*/ 26289b3d9aaSStephen Hemminger bic_target = ca->bic_origin_point - delta; 263df3271f3SStephen Hemminger else /* above origin*/ 26489b3d9aaSStephen Hemminger bic_target = ca->bic_origin_point + delta; 265df3271f3SStephen Hemminger 266df3271f3SStephen Hemminger /* cubic function - calc bictcp_cnt*/ 267df3271f3SStephen Hemminger if (bic_target > cwnd) { 268df3271f3SStephen Hemminger ca->cnt = cwnd / (bic_target - cwnd); 269df3271f3SStephen Hemminger } else { 270df3271f3SStephen Hemminger ca->cnt = 100 * cwnd; /* very small increment*/ 271df3271f3SStephen Hemminger } 272df3271f3SStephen Hemminger 273df3271f3SStephen Hemminger /* TCP Friendly */ 274df3271f3SStephen Hemminger if (tcp_friendliness) { 27589b3d9aaSStephen Hemminger u32 scale = beta_scale; 27689b3d9aaSStephen Hemminger delta = (cwnd * scale) >> 3; 27789b3d9aaSStephen Hemminger while (ca->ack_cnt > delta) { /* update tcp cwnd */ 27889b3d9aaSStephen Hemminger ca->ack_cnt -= delta; 279df3271f3SStephen Hemminger ca->tcp_cwnd++; 280df3271f3SStephen Hemminger } 281df3271f3SStephen Hemminger 282df3271f3SStephen Hemminger if (ca->tcp_cwnd > cwnd){ /* if bic is slower than tcp */ 28389b3d9aaSStephen Hemminger delta = ca->tcp_cwnd - cwnd; 28489b3d9aaSStephen Hemminger max_cnt = cwnd / delta; 285df3271f3SStephen Hemminger if (ca->cnt > max_cnt) 286df3271f3SStephen Hemminger ca->cnt = max_cnt; 287df3271f3SStephen Hemminger } 288df3271f3SStephen Hemminger } 289df3271f3SStephen Hemminger 290df3271f3SStephen Hemminger ca->cnt = (ca->cnt << ACK_RATIO_SHIFT) / ca->delayed_ack; 291df3271f3SStephen Hemminger if (ca->cnt == 0) /* cannot be zero */ 292df3271f3SStephen Hemminger ca->cnt = 1; 293df3271f3SStephen Hemminger } 294df3271f3SStephen Hemminger 295c3a05c60SIlpo Järvinen static void bictcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight) 296df3271f3SStephen Hemminger { 297df3271f3SStephen Hemminger struct tcp_sock *tp = tcp_sk(sk); 298df3271f3SStephen Hemminger struct bictcp *ca = inet_csk_ca(sk); 299df3271f3SStephen Hemminger 300df3271f3SStephen Hemminger if (!tcp_is_cwnd_limited(sk, in_flight)) 301df3271f3SStephen Hemminger return; 302df3271f3SStephen Hemminger 303ae27e98aSSangtae Ha if (tp->snd_cwnd <= tp->snd_ssthresh) { 304ae27e98aSSangtae Ha if (hystart && after(ack, ca->end_seq)) 305ae27e98aSSangtae Ha bictcp_hystart_reset(sk); 306df3271f3SStephen Hemminger tcp_slow_start(tp); 307ae27e98aSSangtae Ha } else { 308df3271f3SStephen Hemminger bictcp_update(ca, tp->snd_cwnd); 309758ce5c8SIlpo Järvinen tcp_cong_avoid_ai(tp, ca->cnt); 310df3271f3SStephen Hemminger } 311df3271f3SStephen Hemminger 312df3271f3SStephen Hemminger } 313df3271f3SStephen Hemminger 314df3271f3SStephen Hemminger static u32 bictcp_recalc_ssthresh(struct sock *sk) 315df3271f3SStephen Hemminger { 316df3271f3SStephen Hemminger const struct tcp_sock *tp = tcp_sk(sk); 317df3271f3SStephen Hemminger struct bictcp *ca = inet_csk_ca(sk); 318df3271f3SStephen Hemminger 319df3271f3SStephen Hemminger ca->epoch_start = 0; /* end of epoch */ 320df3271f3SStephen Hemminger 321df3271f3SStephen Hemminger /* Wmax and fast convergence */ 322df3271f3SStephen Hemminger if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence) 323df3271f3SStephen Hemminger ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta)) 324df3271f3SStephen Hemminger / (2 * BICTCP_BETA_SCALE); 325df3271f3SStephen Hemminger else 326df3271f3SStephen Hemminger ca->last_max_cwnd = tp->snd_cwnd; 327df3271f3SStephen Hemminger 328df3271f3SStephen Hemminger ca->loss_cwnd = tp->snd_cwnd; 329df3271f3SStephen Hemminger 330df3271f3SStephen Hemminger return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U); 331df3271f3SStephen Hemminger } 332df3271f3SStephen Hemminger 333df3271f3SStephen Hemminger static u32 bictcp_undo_cwnd(struct sock *sk) 334df3271f3SStephen Hemminger { 335df3271f3SStephen Hemminger struct bictcp *ca = inet_csk_ca(sk); 336df3271f3SStephen Hemminger 337df3271f3SStephen Hemminger return max(tcp_sk(sk)->snd_cwnd, ca->last_max_cwnd); 338df3271f3SStephen Hemminger } 339df3271f3SStephen Hemminger 340df3271f3SStephen Hemminger static void bictcp_state(struct sock *sk, u8 new_state) 341df3271f3SStephen Hemminger { 342ae27e98aSSangtae Ha if (new_state == TCP_CA_Loss) { 343df3271f3SStephen Hemminger bictcp_reset(inet_csk_ca(sk)); 344ae27e98aSSangtae Ha bictcp_hystart_reset(sk); 345ae27e98aSSangtae Ha } 346ae27e98aSSangtae Ha } 347ae27e98aSSangtae Ha 348ae27e98aSSangtae Ha static void hystart_update(struct sock *sk, u32 delay) 349ae27e98aSSangtae Ha { 350ae27e98aSSangtae Ha struct tcp_sock *tp = tcp_sk(sk); 351ae27e98aSSangtae Ha struct bictcp *ca = inet_csk_ca(sk); 352ae27e98aSSangtae Ha 353ae27e98aSSangtae Ha if (!(ca->found & hystart_detect)) { 354*17a6e9f1Sstephen hemminger u32 now = bictcp_clock(); 355ae27e98aSSangtae Ha 356ae27e98aSSangtae Ha /* first detection parameter - ack-train detection */ 357*17a6e9f1Sstephen hemminger if ((s32)(now - ca->last_ack) <= hystart_ack_delta) { 358*17a6e9f1Sstephen hemminger ca->last_ack = now; 359*17a6e9f1Sstephen hemminger if ((s32)(now - ca->round_start) > ca->delay_min >> 4) 360ae27e98aSSangtae Ha ca->found |= HYSTART_ACK_TRAIN; 361ae27e98aSSangtae Ha } 362ae27e98aSSangtae Ha 363ae27e98aSSangtae Ha /* obtain the minimum delay of more than sampling packets */ 364ae27e98aSSangtae Ha if (ca->sample_cnt < HYSTART_MIN_SAMPLES) { 365ae27e98aSSangtae Ha if (ca->curr_rtt == 0 || ca->curr_rtt > delay) 366ae27e98aSSangtae Ha ca->curr_rtt = delay; 367ae27e98aSSangtae Ha 368ae27e98aSSangtae Ha ca->sample_cnt++; 369ae27e98aSSangtae Ha } else { 370ae27e98aSSangtae Ha if (ca->curr_rtt > ca->delay_min + 371ae27e98aSSangtae Ha HYSTART_DELAY_THRESH(ca->delay_min>>4)) 372ae27e98aSSangtae Ha ca->found |= HYSTART_DELAY; 373ae27e98aSSangtae Ha } 374ae27e98aSSangtae Ha /* 375ae27e98aSSangtae Ha * Either one of two conditions are met, 376ae27e98aSSangtae Ha * we exit from slow start immediately. 377ae27e98aSSangtae Ha */ 378ae27e98aSSangtae Ha if (ca->found & hystart_detect) 379ae27e98aSSangtae Ha tp->snd_ssthresh = tp->snd_cwnd; 380ae27e98aSSangtae Ha } 381df3271f3SStephen Hemminger } 382df3271f3SStephen Hemminger 383df3271f3SStephen Hemminger /* Track delayed acknowledgment ratio using sliding window 384df3271f3SStephen Hemminger * ratio = (15*ratio + sample) / 16 385df3271f3SStephen Hemminger */ 38630cfd0baSStephen Hemminger static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us) 387df3271f3SStephen Hemminger { 388df3271f3SStephen Hemminger const struct inet_connection_sock *icsk = inet_csk(sk); 389ae27e98aSSangtae Ha const struct tcp_sock *tp = tcp_sk(sk); 390e7d0c885SStephen Hemminger struct bictcp *ca = inet_csk_ca(sk); 391e7d0c885SStephen Hemminger u32 delay; 392df3271f3SStephen Hemminger 39335e86941SIlpo Järvinen if (icsk->icsk_ca_state == TCP_CA_Open) { 394df3271f3SStephen Hemminger cnt -= ca->delayed_ack >> ACK_RATIO_SHIFT; 395df3271f3SStephen Hemminger ca->delayed_ack += cnt; 396df3271f3SStephen Hemminger } 397df3271f3SStephen Hemminger 398e7d0c885SStephen Hemminger /* Some calls are for duplicates without timetamps */ 399e7d0c885SStephen Hemminger if (rtt_us < 0) 400e7d0c885SStephen Hemminger return; 401e7d0c885SStephen Hemminger 402e7d0c885SStephen Hemminger /* Discard delay samples right after fast recovery */ 403e7d0c885SStephen Hemminger if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ) 404e7d0c885SStephen Hemminger return; 405e7d0c885SStephen Hemminger 406*17a6e9f1Sstephen hemminger delay = (rtt_us << 3) / USEC_PER_MSEC; 407e7d0c885SStephen Hemminger if (delay == 0) 408e7d0c885SStephen Hemminger delay = 1; 409e7d0c885SStephen Hemminger 410e7d0c885SStephen Hemminger /* first time call or link delay decreases */ 411e7d0c885SStephen Hemminger if (ca->delay_min == 0 || ca->delay_min > delay) 412e7d0c885SStephen Hemminger ca->delay_min = delay; 413ae27e98aSSangtae Ha 414ae27e98aSSangtae Ha /* hystart triggers when cwnd is larger than some threshold */ 415ae27e98aSSangtae Ha if (hystart && tp->snd_cwnd <= tp->snd_ssthresh && 416ae27e98aSSangtae Ha tp->snd_cwnd >= hystart_low_window) 417ae27e98aSSangtae Ha hystart_update(sk, delay); 418e7d0c885SStephen Hemminger } 419df3271f3SStephen Hemminger 420df3271f3SStephen Hemminger static struct tcp_congestion_ops cubictcp = { 421df3271f3SStephen Hemminger .init = bictcp_init, 422df3271f3SStephen Hemminger .ssthresh = bictcp_recalc_ssthresh, 423df3271f3SStephen Hemminger .cong_avoid = bictcp_cong_avoid, 424df3271f3SStephen Hemminger .set_state = bictcp_state, 425df3271f3SStephen Hemminger .undo_cwnd = bictcp_undo_cwnd, 426df3271f3SStephen Hemminger .pkts_acked = bictcp_acked, 427df3271f3SStephen Hemminger .owner = THIS_MODULE, 428df3271f3SStephen Hemminger .name = "cubic", 429df3271f3SStephen Hemminger }; 430df3271f3SStephen Hemminger 431df3271f3SStephen Hemminger static int __init cubictcp_register(void) 432df3271f3SStephen Hemminger { 43374975d40SAlexey Dobriyan BUILD_BUG_ON(sizeof(struct bictcp) > ICSK_CA_PRIV_SIZE); 43489b3d9aaSStephen Hemminger 43589b3d9aaSStephen Hemminger /* Precompute a bunch of the scaling factors that are used per-packet 43689b3d9aaSStephen Hemminger * based on SRTT of 100ms 43789b3d9aaSStephen Hemminger */ 43889b3d9aaSStephen Hemminger 43989b3d9aaSStephen Hemminger beta_scale = 8*(BICTCP_BETA_SCALE+beta)/ 3 / (BICTCP_BETA_SCALE - beta); 44089b3d9aaSStephen Hemminger 44122119240SStephen Hemminger cube_rtt_scale = (bic_scale * 10); /* 1024*c/rtt */ 44289b3d9aaSStephen Hemminger 44389b3d9aaSStephen Hemminger /* calculate the "K" for (wmax-cwnd) = c/rtt * K^3 44489b3d9aaSStephen Hemminger * so K = cubic_root( (wmax-cwnd)*rtt/c ) 44589b3d9aaSStephen Hemminger * the unit of K is bictcp_HZ=2^10, not HZ 44689b3d9aaSStephen Hemminger * 44789b3d9aaSStephen Hemminger * c = bic_scale >> 10 44889b3d9aaSStephen Hemminger * rtt = 100ms 44989b3d9aaSStephen Hemminger * 45089b3d9aaSStephen Hemminger * the following code has been designed and tested for 45189b3d9aaSStephen Hemminger * cwnd < 1 million packets 45289b3d9aaSStephen Hemminger * RTT < 100 seconds 45389b3d9aaSStephen Hemminger * HZ < 1,000,00 (corresponding to 10 nano-second) 45489b3d9aaSStephen Hemminger */ 45589b3d9aaSStephen Hemminger 45689b3d9aaSStephen Hemminger /* 1/c * 2^2*bictcp_HZ * srtt */ 45789b3d9aaSStephen Hemminger cube_factor = 1ull << (10+3*BICTCP_HZ); /* 2^40 */ 45889b3d9aaSStephen Hemminger 45989b3d9aaSStephen Hemminger /* divide by bic_scale and by constant Srtt (100ms) */ 46089b3d9aaSStephen Hemminger do_div(cube_factor, bic_scale * 10); 46189b3d9aaSStephen Hemminger 462df3271f3SStephen Hemminger return tcp_register_congestion_control(&cubictcp); 463df3271f3SStephen Hemminger } 464df3271f3SStephen Hemminger 465df3271f3SStephen Hemminger static void __exit cubictcp_unregister(void) 466df3271f3SStephen Hemminger { 467df3271f3SStephen Hemminger tcp_unregister_congestion_control(&cubictcp); 468df3271f3SStephen Hemminger } 469df3271f3SStephen Hemminger 470df3271f3SStephen Hemminger module_init(cubictcp_register); 471df3271f3SStephen Hemminger module_exit(cubictcp_unregister); 472df3271f3SStephen Hemminger 473df3271f3SStephen Hemminger MODULE_AUTHOR("Sangtae Ha, Stephen Hemminger"); 474df3271f3SStephen Hemminger MODULE_LICENSE("GPL"); 475df3271f3SStephen Hemminger MODULE_DESCRIPTION("CUBIC TCP"); 476ae27e98aSSangtae Ha MODULE_VERSION("2.3"); 477