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 bool 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_us; /* Minimum smoothed round trip time value seen */ 25 }; 26 27 /* Hybla reference round trip time (default= 1/40 sec = 25 ms), in ms */ 28 static int rtt0 = 25; 29 module_param(rtt0, int, 0644); 30 MODULE_PARM_DESC(rtt0, "reference rout trip time (ms)"); 31 32 /* This is called to refresh values for hybla parameters */ 33 static inline void hybla_recalc_param (struct sock *sk) 34 { 35 struct hybla *ca = inet_csk_ca(sk); 36 37 ca->rho_3ls = max_t(u32, 38 tcp_sk(sk)->srtt_us / (rtt0 * USEC_PER_MSEC), 39 8U); 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 = true; 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_us = tp->srtt_us; 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 71 ca->hybla_en = (ca_state == TCP_CA_Open); 72 } 73 74 static inline u32 hybla_fraction(u32 odds) 75 { 76 static const u32 fractions[] = { 77 128, 139, 152, 165, 181, 197, 215, 234, 78 }; 79 80 return (odds < ARRAY_SIZE(fractions)) ? fractions[odds] : 128; 81 } 82 83 /* TCP Hybla main routine. 84 * This is the algorithm behavior: 85 * o Recalc Hybla parameters if min_rtt has changed 86 * o Give cwnd a new value based on the model proposed 87 * o remember increments <1 88 */ 89 static void hybla_cong_avoid(struct sock *sk, u32 ack, u32 acked) 90 { 91 struct tcp_sock *tp = tcp_sk(sk); 92 struct hybla *ca = inet_csk_ca(sk); 93 u32 increment, odd, rho_fractions; 94 int is_slowstart = 0; 95 96 /* Recalculate rho only if this srtt is the lowest */ 97 if (tp->srtt_us < ca->minrtt_us) { 98 hybla_recalc_param(sk); 99 ca->minrtt_us = tp->srtt_us; 100 } 101 102 if (!tcp_is_cwnd_limited(sk)) 103 return; 104 105 if (!ca->hybla_en) { 106 tcp_reno_cong_avoid(sk, ack, acked); 107 return; 108 } 109 110 if (ca->rho == 0) 111 hybla_recalc_param(sk); 112 113 rho_fractions = ca->rho_3ls - (ca->rho << 3); 114 115 if (tp->snd_cwnd < tp->snd_ssthresh) { 116 /* 117 * slow start 118 * INC = 2^RHO - 1 119 * This is done by splitting the rho parameter 120 * into 2 parts: an integer part and a fraction part. 121 * Inrement<<7 is estimated by doing: 122 * [2^(int+fract)]<<7 123 * that is equal to: 124 * (2^int) * [(2^fract) <<7] 125 * 2^int is straightly computed as 1<<int, 126 * while we will use hybla_slowstart_fraction_increment() to 127 * calculate 2^fract in a <<7 value. 128 */ 129 is_slowstart = 1; 130 increment = ((1 << min(ca->rho, 16U)) * 131 hybla_fraction(rho_fractions)) - 128; 132 } else { 133 /* 134 * congestion avoidance 135 * INC = RHO^2 / W 136 * as long as increment is estimated as (rho<<7)/window 137 * it already is <<7 and we can easily count its fractions. 138 */ 139 increment = ca->rho2_7ls / tp->snd_cwnd; 140 if (increment < 128) 141 tp->snd_cwnd_cnt++; 142 } 143 144 odd = increment % 128; 145 tp->snd_cwnd += increment >> 7; 146 ca->snd_cwnd_cents += odd; 147 148 /* check when fractions goes >=128 and increase cwnd by 1. */ 149 while (ca->snd_cwnd_cents >= 128) { 150 tp->snd_cwnd++; 151 ca->snd_cwnd_cents -= 128; 152 tp->snd_cwnd_cnt = 0; 153 } 154 /* check when cwnd has not been incremented for a while */ 155 if (increment == 0 && odd == 0 && tp->snd_cwnd_cnt >= tp->snd_cwnd) { 156 tp->snd_cwnd++; 157 tp->snd_cwnd_cnt = 0; 158 } 159 /* clamp down slowstart cwnd to ssthresh value. */ 160 if (is_slowstart) 161 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh); 162 163 tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp); 164 } 165 166 static struct tcp_congestion_ops tcp_hybla __read_mostly = { 167 .init = hybla_init, 168 .ssthresh = tcp_reno_ssthresh, 169 .cong_avoid = hybla_cong_avoid, 170 .set_state = hybla_state, 171 172 .owner = THIS_MODULE, 173 .name = "hybla" 174 }; 175 176 static int __init hybla_register(void) 177 { 178 BUILD_BUG_ON(sizeof(struct hybla) > ICSK_CA_PRIV_SIZE); 179 return tcp_register_congestion_control(&tcp_hybla); 180 } 181 182 static void __exit hybla_unregister(void) 183 { 184 tcp_unregister_congestion_control(&tcp_hybla); 185 } 186 187 module_init(hybla_register); 188 module_exit(hybla_unregister); 189 190 MODULE_AUTHOR("Daniele Lacamera"); 191 MODULE_LICENSE("GPL"); 192 MODULE_DESCRIPTION("TCP Hybla"); 193