1/* 2 * H-TCP congestion control. The algorithm is detailed in: 3 * R.N.Shorten, D.J.Leith: 4 * "H-TCP: TCP for high-speed and long-distance networks" 5 * Proc. PFLDnet, Argonne, 2004. 6 * http://www.hamilton.ie/net/htcp3.pdf 7 */ 8 9#include <linux/mm.h> 10#include <linux/module.h> 11#include <net/tcp.h> 12 13#define ALPHA_BASE (1<<7) /* 1.0 with shift << 7 */ 14#define BETA_MIN (1<<6) /* 0.5 with shift << 7 */ 15#define BETA_MAX 102 /* 0.8 with shift << 7 */ 16 17static int use_rtt_scaling __read_mostly = 1; 18module_param(use_rtt_scaling, int, 0644); 19MODULE_PARM_DESC(use_rtt_scaling, "turn on/off RTT scaling"); 20 21static int use_bandwidth_switch __read_mostly = 1; 22module_param(use_bandwidth_switch, int, 0644); 23MODULE_PARM_DESC(use_bandwidth_switch, "turn on/off bandwidth switcher"); 24 25struct htcp { 26 u32 alpha; /* Fixed point arith, << 7 */ 27 u8 beta; /* Fixed point arith, << 7 */ 28 u8 modeswitch; /* Delay modeswitch 29 until we had at least one congestion event */ 30 u16 pkts_acked; 31 u32 packetcount; 32 u32 minRTT; 33 u32 maxRTT; 34 u32 last_cong; /* Time since last congestion event end */ 35 u32 undo_last_cong; 36 37 u32 undo_maxRTT; 38 u32 undo_old_maxB; 39 40 /* Bandwidth estimation */ 41 u32 minB; 42 u32 maxB; 43 u32 old_maxB; 44 u32 Bi; 45 u32 lasttime; 46}; 47 48static inline u32 htcp_cong_time(const struct htcp *ca) 49{ 50 return jiffies - ca->last_cong; 51} 52 53static inline u32 htcp_ccount(const struct htcp *ca) 54{ 55 return htcp_cong_time(ca) / ca->minRTT; 56} 57 58static inline void htcp_reset(struct htcp *ca) 59{ 60 ca->undo_last_cong = ca->last_cong; 61 ca->undo_maxRTT = ca->maxRTT; 62 ca->undo_old_maxB = ca->old_maxB; 63 64 ca->last_cong = jiffies; 65} 66 67static u32 htcp_cwnd_undo(struct sock *sk) 68{ 69 const struct tcp_sock *tp = tcp_sk(sk); 70 struct htcp *ca = inet_csk_ca(sk); 71 72 if (ca->undo_last_cong) { 73 ca->last_cong = ca->undo_last_cong; 74 ca->maxRTT = ca->undo_maxRTT; 75 ca->old_maxB = ca->undo_old_maxB; 76 ca->undo_last_cong = 0; 77 } 78 79 return max(tp->snd_cwnd, (tp->snd_ssthresh << 7) / ca->beta); 80} 81 82static inline void measure_rtt(struct sock *sk, u32 srtt) 83{ 84 const struct inet_connection_sock *icsk = inet_csk(sk); 85 struct htcp *ca = inet_csk_ca(sk); 86 87 /* keep track of minimum RTT seen so far, minRTT is zero at first */ 88 if (ca->minRTT > srtt || !ca->minRTT) 89 ca->minRTT = srtt; 90 91 /* max RTT */ 92 if (icsk->icsk_ca_state == TCP_CA_Open) { 93 if (ca->maxRTT < ca->minRTT) 94 ca->maxRTT = ca->minRTT; 95 if (ca->maxRTT < srtt && 96 srtt <= ca->maxRTT + msecs_to_jiffies(20)) 97 ca->maxRTT = srtt; 98 } 99} 100 101static void measure_achieved_throughput(struct sock *sk, u32 pkts_acked, s32 rtt) 102{ 103 const struct inet_connection_sock *icsk = inet_csk(sk); 104 const struct tcp_sock *tp = tcp_sk(sk); 105 struct htcp *ca = inet_csk_ca(sk); 106 u32 now = tcp_time_stamp; 107 108 if (icsk->icsk_ca_state == TCP_CA_Open) 109 ca->pkts_acked = pkts_acked; 110 111 if (rtt > 0) 112 measure_rtt(sk, usecs_to_jiffies(rtt)); 113 114 if (!use_bandwidth_switch) 115 return; 116 117 /* achieved throughput calculations */ 118 if (!((1 << icsk->icsk_ca_state) & (TCPF_CA_Open | TCPF_CA_Disorder))) { 119 ca->packetcount = 0; 120 ca->lasttime = now; 121 return; 122 } 123 124 ca->packetcount += pkts_acked; 125 126 if (ca->packetcount >= tp->snd_cwnd - (ca->alpha >> 7 ? : 1) && 127 now - ca->lasttime >= ca->minRTT && 128 ca->minRTT > 0) { 129 __u32 cur_Bi = ca->packetcount * HZ / (now - ca->lasttime); 130 131 if (htcp_ccount(ca) <= 3) { 132 /* just after backoff */ 133 ca->minB = ca->maxB = ca->Bi = cur_Bi; 134 } else { 135 ca->Bi = (3 * ca->Bi + cur_Bi) / 4; 136 if (ca->Bi > ca->maxB) 137 ca->maxB = ca->Bi; 138 if (ca->minB > ca->maxB) 139 ca->minB = ca->maxB; 140 } 141 ca->packetcount = 0; 142 ca->lasttime = now; 143 } 144} 145 146static inline void htcp_beta_update(struct htcp *ca, u32 minRTT, u32 maxRTT) 147{ 148 if (use_bandwidth_switch) { 149 u32 maxB = ca->maxB; 150 u32 old_maxB = ca->old_maxB; 151 ca->old_maxB = ca->maxB; 152 153 if (!between(5 * maxB, 4 * old_maxB, 6 * old_maxB)) { 154 ca->beta = BETA_MIN; 155 ca->modeswitch = 0; 156 return; 157 } 158 } 159 160 if (ca->modeswitch && minRTT > msecs_to_jiffies(10) && maxRTT) { 161 ca->beta = (minRTT << 7) / maxRTT; 162 if (ca->beta < BETA_MIN) 163 ca->beta = BETA_MIN; 164 else if (ca->beta > BETA_MAX) 165 ca->beta = BETA_MAX; 166 } else { 167 ca->beta = BETA_MIN; 168 ca->modeswitch = 1; 169 } 170} 171 172static inline void htcp_alpha_update(struct htcp *ca) 173{ 174 u32 minRTT = ca->minRTT; 175 u32 factor = 1; 176 u32 diff = htcp_cong_time(ca); 177 178 if (diff > HZ) { 179 diff -= HZ; 180 factor = 1 + (10 * diff + ((diff / 2) * (diff / 2) / HZ)) / HZ; 181 } 182 183 if (use_rtt_scaling && minRTT) { 184 u32 scale = (HZ << 3) / (10 * minRTT); 185 186 /* clamping ratio to interval [0.5,10]<<3 */ 187 scale = min(max(scale, 1U << 2), 10U << 3); 188 factor = (factor << 3) / scale; 189 if (!factor) 190 factor = 1; 191 } 192 193 ca->alpha = 2 * factor * ((1 << 7) - ca->beta); 194 if (!ca->alpha) 195 ca->alpha = ALPHA_BASE; 196} 197 198/* 199 * After we have the rtt data to calculate beta, we'd still prefer to wait one 200 * rtt before we adjust our beta to ensure we are working from a consistent 201 * data. 202 * 203 * This function should be called when we hit a congestion event since only at 204 * that point do we really have a real sense of maxRTT (the queues en route 205 * were getting just too full now). 206 */ 207static void htcp_param_update(struct sock *sk) 208{ 209 struct htcp *ca = inet_csk_ca(sk); 210 u32 minRTT = ca->minRTT; 211 u32 maxRTT = ca->maxRTT; 212 213 htcp_beta_update(ca, minRTT, maxRTT); 214 htcp_alpha_update(ca); 215 216 /* add slowly fading memory for maxRTT to accommodate routing changes */ 217 if (minRTT > 0 && maxRTT > minRTT) 218 ca->maxRTT = minRTT + ((maxRTT - minRTT) * 95) / 100; 219} 220 221static u32 htcp_recalc_ssthresh(struct sock *sk) 222{ 223 const struct tcp_sock *tp = tcp_sk(sk); 224 const struct htcp *ca = inet_csk_ca(sk); 225 226 htcp_param_update(sk); 227 return max((tp->snd_cwnd * ca->beta) >> 7, 2U); 228} 229 230static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight) 231{ 232 struct tcp_sock *tp = tcp_sk(sk); 233 struct htcp *ca = inet_csk_ca(sk); 234 235 if (!tcp_is_cwnd_limited(sk, in_flight)) 236 return; 237 238 if (tp->snd_cwnd <= tp->snd_ssthresh) 239 tcp_slow_start(tp); 240 else { 241 /* In dangerous area, increase slowly. 242 * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd 243 */ 244 if ((tp->snd_cwnd_cnt * ca->alpha)>>7 >= tp->snd_cwnd) { 245 if (tp->snd_cwnd < tp->snd_cwnd_clamp) 246 tp->snd_cwnd++; 247 tp->snd_cwnd_cnt = 0; 248 htcp_alpha_update(ca); 249 } else 250 tp->snd_cwnd_cnt += ca->pkts_acked; 251 252 ca->pkts_acked = 1; 253 } 254} 255 256static void htcp_init(struct sock *sk) 257{ 258 struct htcp *ca = inet_csk_ca(sk); 259 260 memset(ca, 0, sizeof(struct htcp)); 261 ca->alpha = ALPHA_BASE; 262 ca->beta = BETA_MIN; 263 ca->pkts_acked = 1; 264 ca->last_cong = jiffies; 265} 266 267static void htcp_state(struct sock *sk, u8 new_state) 268{ 269 switch (new_state) { 270 case TCP_CA_Open: 271 { 272 struct htcp *ca = inet_csk_ca(sk); 273 if (ca->undo_last_cong) { 274 ca->last_cong = jiffies; 275 ca->undo_last_cong = 0; 276 } 277 } 278 break; 279 case TCP_CA_CWR: 280 case TCP_CA_Recovery: 281 case TCP_CA_Loss: 282 htcp_reset(inet_csk_ca(sk)); 283 break; 284 } 285} 286 287static struct tcp_congestion_ops htcp = { 288 .init = htcp_init, 289 .ssthresh = htcp_recalc_ssthresh, 290 .cong_avoid = htcp_cong_avoid, 291 .set_state = htcp_state, 292 .undo_cwnd = htcp_cwnd_undo, 293 .pkts_acked = measure_achieved_throughput, 294 .owner = THIS_MODULE, 295 .name = "htcp", 296}; 297 298static int __init htcp_register(void) 299{ 300 BUILD_BUG_ON(sizeof(struct htcp) > ICSK_CA_PRIV_SIZE); 301 BUILD_BUG_ON(BETA_MIN >= BETA_MAX); 302 return tcp_register_congestion_control(&htcp); 303} 304 305static void __exit htcp_unregister(void) 306{ 307 tcp_unregister_congestion_control(&htcp); 308} 309 310module_init(htcp_register); 311module_exit(htcp_unregister); 312 313MODULE_AUTHOR("Baruch Even"); 314MODULE_LICENSE("GPL"); 315MODULE_DESCRIPTION("H-TCP"); 316