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