1 /* 2 * TCP HYBLA 3 * 4 * TCP-HYBLA Congestion control algorithm, based on: 5 * C.Caini, R.Firrincieli, "TCP-Hybla: A TCP Enhancement 6 * for Heterogeneous Networks", 7 * International Journal on satellite Communications, 8 * September 2004 9 * Daniele Lacamera 10 * root at danielinux.net 11 */ 12 13 #include <linux/module.h> 14 #include <net/tcp.h> 15 16 /* Tcp Hybla structure. */ 17 struct hybla { 18 u8 hybla_en; 19 u32 snd_cwnd_cents; /* Keeps increment values when it is <1, <<7 */ 20 u32 rho; /* Rho parameter, integer part */ 21 u32 rho2; /* Rho * Rho, integer part */ 22 u32 rho_3ls; /* Rho parameter, <<3 */ 23 u32 rho2_7ls; /* Rho^2, <<7 */ 24 u32 minrtt; /* Minimum smoothed round trip time value seen */ 25 }; 26 27 /* Hybla reference round trip time (default= 1/40 sec = 25 ms), 28 expressed in jiffies */ 29 static int rtt0 = 25; 30 module_param(rtt0, int, 0644); 31 MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)"); 32 33 34 /* This is called to refresh values for hybla parameters */ 35 static inline void hybla_recalc_param (struct sock *sk) 36 { 37 struct hybla *ca = inet_csk_ca(sk); 38 39 ca->rho_3ls = max_t(u32, tcp_sk(sk)->srtt / msecs_to_jiffies(rtt0), 8); 40 ca->rho = ca->rho_3ls >> 3; 41 ca->rho2_7ls = (ca->rho_3ls * ca->rho_3ls) << 1; 42 ca->rho2 = ca->rho2_7ls >>7; 43 } 44 45 static void hybla_init(struct sock *sk) 46 { 47 struct tcp_sock *tp = tcp_sk(sk); 48 struct hybla *ca = inet_csk_ca(sk); 49 50 ca->rho = 0; 51 ca->rho2 = 0; 52 ca->rho_3ls = 0; 53 ca->rho2_7ls = 0; 54 ca->snd_cwnd_cents = 0; 55 ca->hybla_en = 1; 56 tp->snd_cwnd = 2; 57 tp->snd_cwnd_clamp = 65535; 58 59 /* 1st Rho measurement based on initial srtt */ 60 hybla_recalc_param(sk); 61 62 /* set minimum rtt as this is the 1st ever seen */ 63 ca->minrtt = tp->srtt; 64 tp->snd_cwnd = ca->rho; 65 } 66 67 static void hybla_state(struct sock *sk, u8 ca_state) 68 { 69 struct hybla *ca = inet_csk_ca(sk); 70 ca->hybla_en = (ca_state == TCP_CA_Open); 71 } 72 73 static inline u32 hybla_fraction(u32 odds) 74 { 75 static const u32 fractions[] = { 76 128, 139, 152, 165, 181, 197, 215, 234, 77 }; 78 79 return (odds < ARRAY_SIZE(fractions)) ? fractions[odds] : 128; 80 } 81 82 /* TCP Hybla main routine. 83 * This is the algorithm behavior: 84 * o Recalc Hybla parameters if min_rtt has changed 85 * o Give cwnd a new value based on the model proposed 86 * o remember increments <1 87 */ 88 static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 in_flight) 89 { 90 struct tcp_sock *tp = tcp_sk(sk); 91 struct hybla *ca = inet_csk_ca(sk); 92 u32 increment, odd, rho_fractions; 93 int is_slowstart = 0; 94 95 /* Recalculate rho only if this srtt is the lowest */ 96 if (tp->srtt < ca->minrtt){ 97 hybla_recalc_param(sk); 98 ca->minrtt = tp->srtt; 99 } 100 101 if (!tcp_is_cwnd_limited(sk, in_flight)) 102 return; 103 104 if (!ca->hybla_en) { 105 tcp_reno_cong_avoid(sk, ack, in_flight); 106 return; 107 } 108 109 if (ca->rho == 0) 110 hybla_recalc_param(sk); 111 112 rho_fractions = ca->rho_3ls - (ca->rho << 3); 113 114 if (tp->snd_cwnd < tp->snd_ssthresh) { 115 /* 116 * slow start 117 * INC = 2^RHO - 1 118 * This is done by splitting the rho parameter 119 * into 2 parts: an integer part and a fraction part. 120 * Inrement<<7 is estimated by doing: 121 * [2^(int+fract)]<<7 122 * that is equal to: 123 * (2^int) * [(2^fract) <<7] 124 * 2^int is straightly computed as 1<<int, 125 * while we will use hybla_slowstart_fraction_increment() to 126 * calculate 2^fract in a <<7 value. 127 */ 128 is_slowstart = 1; 129 increment = ((1 << ca->rho) * hybla_fraction(rho_fractions)) 130 - 128; 131 } else { 132 /* 133 * congestion avoidance 134 * INC = RHO^2 / W 135 * as long as increment is estimated as (rho<<7)/window 136 * it already is <<7 and we can easily count its fractions. 137 */ 138 increment = ca->rho2_7ls / tp->snd_cwnd; 139 if (increment < 128) 140 tp->snd_cwnd_cnt++; 141 } 142 143 odd = increment % 128; 144 tp->snd_cwnd += increment >> 7; 145 ca->snd_cwnd_cents += odd; 146 147 /* check when fractions goes >=128 and increase cwnd by 1. */ 148 while (ca->snd_cwnd_cents >= 128) { 149 tp->snd_cwnd++; 150 ca->snd_cwnd_cents -= 128; 151 tp->snd_cwnd_cnt = 0; 152 } 153 154 /* clamp down slowstart cwnd to ssthresh value. */ 155 if (is_slowstart) 156 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh); 157 158 tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp); 159 } 160 161 static struct tcp_congestion_ops tcp_hybla = { 162 .init = hybla_init, 163 .ssthresh = tcp_reno_ssthresh, 164 .min_cwnd = tcp_reno_min_cwnd, 165 .cong_avoid = hybla_cong_avoid, 166 .set_state = hybla_state, 167 168 .owner = THIS_MODULE, 169 .name = "hybla" 170 }; 171 172 static int __init hybla_register(void) 173 { 174 BUILD_BUG_ON(sizeof(struct hybla) > ICSK_CA_PRIV_SIZE); 175 return tcp_register_congestion_control(&tcp_hybla); 176 } 177 178 static void __exit hybla_unregister(void) 179 { 180 tcp_unregister_congestion_control(&tcp_hybla); 181 } 182 183 module_init(hybla_register); 184 module_exit(hybla_unregister); 185 186 MODULE_AUTHOR("Daniele Lacamera"); 187 MODULE_LICENSE("GPL"); 188 MODULE_DESCRIPTION("TCP Hybla"); 189