1 /* 2 * TCP Low Priority (TCP-LP) 3 * 4 * TCP Low Priority is a distributed algorithm whose goal is to utilize only 5 * the excess network bandwidth as compared to the ``fair share`` of 6 * bandwidth as targeted by TCP. 7 * 8 * As of 2.6.13, Linux supports pluggable congestion control algorithms. 9 * Due to the limitation of the API, we take the following changes from 10 * the original TCP-LP implementation: 11 * o We use newReno in most core CA handling. Only add some checking 12 * within cong_avoid. 13 * o Error correcting in remote HZ, therefore remote HZ will be keeped 14 * on checking and updating. 15 * o Handling calculation of One-Way-Delay (OWD) within rtt_sample, sicne 16 * OWD have a similar meaning as RTT. Also correct the buggy formular. 17 * o Handle reaction for Early Congestion Indication (ECI) within 18 * pkts_acked, as mentioned within pseudo code. 19 * o OWD is handled in relative format, where local time stamp will in 20 * tcp_time_stamp format. 21 * 22 * Original Author: 23 * Aleksandar Kuzmanovic <akuzma@northwestern.edu> 24 * Available from: 25 * http://www.ece.rice.edu/~akuzma/Doc/akuzma/TCP-LP.pdf 26 * Original implementation for 2.4.19: 27 * http://www-ece.rice.edu/networks/TCP-LP/ 28 * 29 * 2.6.x module Authors: 30 * Wong Hoi Sing, Edison <hswong3i@gmail.com> 31 * Hung Hing Lun, Mike <hlhung3i@gmail.com> 32 * SourceForge project page: 33 * http://tcp-lp-mod.sourceforge.net/ 34 */ 35 36 #include <linux/module.h> 37 #include <net/tcp.h> 38 39 /* resolution of owd */ 40 #define LP_RESOL 1000 41 42 /** 43 * enum tcp_lp_state 44 * @LP_VALID_RHZ: is remote HZ valid? 45 * @LP_VALID_OWD: is OWD valid? 46 * @LP_WITHIN_THR: are we within threshold? 47 * @LP_WITHIN_INF: are we within inference? 48 * 49 * TCP-LP's state flags. 50 * We create this set of state flag mainly for debugging. 51 */ 52 enum tcp_lp_state { 53 LP_VALID_RHZ = (1 << 0), 54 LP_VALID_OWD = (1 << 1), 55 LP_WITHIN_THR = (1 << 3), 56 LP_WITHIN_INF = (1 << 4), 57 }; 58 59 /** 60 * struct lp 61 * @flag: TCP-LP state flag 62 * @sowd: smoothed OWD << 3 63 * @owd_min: min OWD 64 * @owd_max: max OWD 65 * @owd_max_rsv: resrved max owd 66 * @remote_hz: estimated remote HZ 67 * @remote_ref_time: remote reference time 68 * @local_ref_time: local reference time 69 * @last_drop: time for last active drop 70 * @inference: current inference 71 * 72 * TCP-LP's private struct. 73 * We get the idea from original TCP-LP implementation where only left those we 74 * found are really useful. 75 */ 76 struct lp { 77 u32 flag; 78 u32 sowd; 79 u32 owd_min; 80 u32 owd_max; 81 u32 owd_max_rsv; 82 u32 remote_hz; 83 u32 remote_ref_time; 84 u32 local_ref_time; 85 u32 last_drop; 86 u32 inference; 87 }; 88 89 /** 90 * tcp_lp_init 91 * 92 * Init all required variables. 93 * Clone the handling from Vegas module implementation. 94 */ 95 static void tcp_lp_init(struct sock *sk) 96 { 97 struct lp *lp = inet_csk_ca(sk); 98 99 lp->flag = 0; 100 lp->sowd = 0; 101 lp->owd_min = 0xffffffff; 102 lp->owd_max = 0; 103 lp->owd_max_rsv = 0; 104 lp->remote_hz = 0; 105 lp->remote_ref_time = 0; 106 lp->local_ref_time = 0; 107 lp->last_drop = 0; 108 lp->inference = 0; 109 } 110 111 /** 112 * tcp_lp_cong_avoid 113 * 114 * Implementation of cong_avoid. 115 * Will only call newReno CA when away from inference. 116 * From TCP-LP's paper, this will be handled in additive increasement. 117 */ 118 static void tcp_lp_cong_avoid(struct sock *sk, u32 ack, u32 in_flight) 119 { 120 struct lp *lp = inet_csk_ca(sk); 121 122 if (!(lp->flag & LP_WITHIN_INF)) 123 tcp_reno_cong_avoid(sk, ack, in_flight); 124 } 125 126 /** 127 * tcp_lp_remote_hz_estimator 128 * 129 * Estimate remote HZ. 130 * We keep on updating the estimated value, where original TCP-LP 131 * implementation only guest it for once and use forever. 132 */ 133 static u32 tcp_lp_remote_hz_estimator(struct sock *sk) 134 { 135 struct tcp_sock *tp = tcp_sk(sk); 136 struct lp *lp = inet_csk_ca(sk); 137 s64 rhz = lp->remote_hz << 6; /* remote HZ << 6 */ 138 s64 m = 0; 139 140 /* not yet record reference time 141 * go away!! record it before come back!! */ 142 if (lp->remote_ref_time == 0 || lp->local_ref_time == 0) 143 goto out; 144 145 /* we can't calc remote HZ with no different!! */ 146 if (tp->rx_opt.rcv_tsval == lp->remote_ref_time 147 || tp->rx_opt.rcv_tsecr == lp->local_ref_time) 148 goto out; 149 150 m = HZ * (tp->rx_opt.rcv_tsval - 151 lp->remote_ref_time) / (tp->rx_opt.rcv_tsecr - 152 lp->local_ref_time); 153 if (m < 0) 154 m = -m; 155 156 if (rhz > 0) { 157 m -= rhz >> 6; /* m is now error in remote HZ est */ 158 rhz += m; /* 63/64 old + 1/64 new */ 159 } else 160 rhz = m << 6; 161 162 out: 163 /* record time for successful remote HZ calc */ 164 if ((rhz >> 6) > 0) 165 lp->flag |= LP_VALID_RHZ; 166 else 167 lp->flag &= ~LP_VALID_RHZ; 168 169 /* record reference time stamp */ 170 lp->remote_ref_time = tp->rx_opt.rcv_tsval; 171 lp->local_ref_time = tp->rx_opt.rcv_tsecr; 172 173 return rhz >> 6; 174 } 175 176 /** 177 * tcp_lp_owd_calculator 178 * 179 * Calculate one way delay (in relative format). 180 * Original implement OWD as minus of remote time difference to local time 181 * difference directly. As this time difference just simply equal to RTT, when 182 * the network status is stable, remote RTT will equal to local RTT, and result 183 * OWD into zero. 184 * It seems to be a bug and so we fixed it. 185 */ 186 static u32 tcp_lp_owd_calculator(struct sock *sk) 187 { 188 struct tcp_sock *tp = tcp_sk(sk); 189 struct lp *lp = inet_csk_ca(sk); 190 s64 owd = 0; 191 192 lp->remote_hz = tcp_lp_remote_hz_estimator(sk); 193 194 if (lp->flag & LP_VALID_RHZ) { 195 owd = 196 tp->rx_opt.rcv_tsval * (LP_RESOL / lp->remote_hz) - 197 tp->rx_opt.rcv_tsecr * (LP_RESOL / HZ); 198 if (owd < 0) 199 owd = -owd; 200 } 201 202 if (owd > 0) 203 lp->flag |= LP_VALID_OWD; 204 else 205 lp->flag &= ~LP_VALID_OWD; 206 207 return owd; 208 } 209 210 /** 211 * tcp_lp_rtt_sample 212 * 213 * Implementation or rtt_sample. 214 * Will take the following action, 215 * 1. calc OWD, 216 * 2. record the min/max OWD, 217 * 3. calc smoothed OWD (SOWD). 218 * Most ideas come from the original TCP-LP implementation. 219 */ 220 static void tcp_lp_rtt_sample(struct sock *sk, u32 rtt) 221 { 222 struct lp *lp = inet_csk_ca(sk); 223 s64 mowd = tcp_lp_owd_calculator(sk); 224 225 /* sorry that we don't have valid data */ 226 if (!(lp->flag & LP_VALID_RHZ) || !(lp->flag & LP_VALID_OWD)) 227 return; 228 229 /* record the next min owd */ 230 if (mowd < lp->owd_min) 231 lp->owd_min = mowd; 232 233 /* always forget the max of the max 234 * we just set owd_max as one below it */ 235 if (mowd > lp->owd_max) { 236 if (mowd > lp->owd_max_rsv) { 237 if (lp->owd_max_rsv == 0) 238 lp->owd_max = mowd; 239 else 240 lp->owd_max = lp->owd_max_rsv; 241 lp->owd_max_rsv = mowd; 242 } else 243 lp->owd_max = mowd; 244 } 245 246 /* calc for smoothed owd */ 247 if (lp->sowd != 0) { 248 mowd -= lp->sowd >> 3; /* m is now error in owd est */ 249 lp->sowd += mowd; /* owd = 7/8 owd + 1/8 new */ 250 } else 251 lp->sowd = mowd << 3; /* take the measured time be owd */ 252 } 253 254 /** 255 * tcp_lp_pkts_acked 256 * 257 * Implementation of pkts_acked. 258 * Deal with active drop under Early Congestion Indication. 259 * Only drop to half and 1 will be handle, because we hope to use back 260 * newReno in increase case. 261 * We work it out by following the idea from TCP-LP's paper directly 262 */ 263 static void tcp_lp_pkts_acked(struct sock *sk, u32 num_acked, s32 rtt_us) 264 { 265 struct tcp_sock *tp = tcp_sk(sk); 266 struct lp *lp = inet_csk_ca(sk); 267 268 if (rtt_us > 0) 269 tcp_lp_rtt_sample(sk, rtt_us); 270 271 /* calc inference */ 272 if (tcp_time_stamp > tp->rx_opt.rcv_tsecr) 273 lp->inference = 3 * (tcp_time_stamp - tp->rx_opt.rcv_tsecr); 274 275 /* test if within inference */ 276 if (lp->last_drop && (tcp_time_stamp - lp->last_drop < lp->inference)) 277 lp->flag |= LP_WITHIN_INF; 278 else 279 lp->flag &= ~LP_WITHIN_INF; 280 281 /* test if within threshold */ 282 if (lp->sowd >> 3 < 283 lp->owd_min + 15 * (lp->owd_max - lp->owd_min) / 100) 284 lp->flag |= LP_WITHIN_THR; 285 else 286 lp->flag &= ~LP_WITHIN_THR; 287 288 pr_debug("TCP-LP: %05o|%5u|%5u|%15u|%15u|%15u\n", lp->flag, 289 tp->snd_cwnd, lp->remote_hz, lp->owd_min, lp->owd_max, 290 lp->sowd >> 3); 291 292 if (lp->flag & LP_WITHIN_THR) 293 return; 294 295 /* FIXME: try to reset owd_min and owd_max here 296 * so decrease the chance the min/max is no longer suitable 297 * and will usually within threshold when whithin inference */ 298 lp->owd_min = lp->sowd >> 3; 299 lp->owd_max = lp->sowd >> 2; 300 lp->owd_max_rsv = lp->sowd >> 2; 301 302 /* happened within inference 303 * drop snd_cwnd into 1 */ 304 if (lp->flag & LP_WITHIN_INF) 305 tp->snd_cwnd = 1U; 306 307 /* happened after inference 308 * cut snd_cwnd into half */ 309 else 310 tp->snd_cwnd = max(tp->snd_cwnd >> 1U, 1U); 311 312 /* record this drop time */ 313 lp->last_drop = tcp_time_stamp; 314 } 315 316 static struct tcp_congestion_ops tcp_lp = { 317 .flags = TCP_CONG_RTT_STAMP, 318 .init = tcp_lp_init, 319 .ssthresh = tcp_reno_ssthresh, 320 .cong_avoid = tcp_lp_cong_avoid, 321 .min_cwnd = tcp_reno_min_cwnd, 322 .pkts_acked = tcp_lp_pkts_acked, 323 324 .owner = THIS_MODULE, 325 .name = "lp" 326 }; 327 328 static int __init tcp_lp_register(void) 329 { 330 BUILD_BUG_ON(sizeof(struct lp) > ICSK_CA_PRIV_SIZE); 331 return tcp_register_congestion_control(&tcp_lp); 332 } 333 334 static void __exit tcp_lp_unregister(void) 335 { 336 tcp_unregister_congestion_control(&tcp_lp); 337 } 338 339 module_init(tcp_lp_register); 340 module_exit(tcp_lp_unregister); 341 342 MODULE_AUTHOR("Wong Hoi Sing Edison, Hung Hing Lun Mike"); 343 MODULE_LICENSE("GPL"); 344 MODULE_DESCRIPTION("TCP Low Priority"); 345