1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * TCP Low Priority (TCP-LP) 4 * 5 * TCP Low Priority is a distributed algorithm whose goal is to utilize only 6 * the excess network bandwidth as compared to the ``fair share`` of 7 * bandwidth as targeted by TCP. 8 * 9 * As of 2.6.13, Linux supports pluggable congestion control algorithms. 10 * Due to the limitation of the API, we take the following changes from 11 * the original TCP-LP implementation: 12 * o We use newReno in most core CA handling. Only add some checking 13 * within cong_avoid. 14 * o Error correcting in remote HZ, therefore remote HZ will be keeped 15 * on checking and updating. 16 * o Handling calculation of One-Way-Delay (OWD) within rtt_sample, since 17 * OWD have a similar meaning as RTT. Also correct the buggy formular. 18 * o Handle reaction for Early Congestion Indication (ECI) within 19 * pkts_acked, as mentioned within pseudo code. 20 * o OWD is handled in relative format, where local time stamp will in 21 * tcp_time_stamp format. 22 * 23 * Original Author: 24 * Aleksandar Kuzmanovic <akuzma@northwestern.edu> 25 * Available from: 26 * http://www.ece.rice.edu/~akuzma/Doc/akuzma/TCP-LP.pdf 27 * Original implementation for 2.4.19: 28 * http://www-ece.rice.edu/networks/TCP-LP/ 29 * 30 * 2.6.x module Authors: 31 * Wong Hoi Sing, Edison <hswong3i@gmail.com> 32 * Hung Hing Lun, Mike <hlhung3i@gmail.com> 33 * SourceForge project page: 34 * http://tcp-lp-mod.sourceforge.net/ 35 */ 36 37 #include <linux/module.h> 38 #include <net/tcp.h> 39 40 /* resolution of owd */ 41 #define LP_RESOL TCP_TS_HZ 42 43 /** 44 * enum tcp_lp_state 45 * @LP_VALID_RHZ: is remote HZ valid? 46 * @LP_VALID_OWD: is OWD valid? 47 * @LP_WITHIN_THR: are we within threshold? 48 * @LP_WITHIN_INF: are we within inference? 49 * 50 * TCP-LP's state flags. 51 * We create this set of state flag mainly for debugging. 52 */ 53 enum tcp_lp_state { 54 LP_VALID_RHZ = (1 << 0), 55 LP_VALID_OWD = (1 << 1), 56 LP_WITHIN_THR = (1 << 3), 57 LP_WITHIN_INF = (1 << 4), 58 }; 59 60 /** 61 * struct lp 62 * @flag: TCP-LP state flag 63 * @sowd: smoothed OWD << 3 64 * @owd_min: min OWD 65 * @owd_max: max OWD 66 * @owd_max_rsv: resrved max owd 67 * @remote_hz: estimated remote HZ 68 * @remote_ref_time: remote reference time 69 * @local_ref_time: local reference time 70 * @last_drop: time for last active drop 71 * @inference: current inference 72 * 73 * TCP-LP's private struct. 74 * We get the idea from original TCP-LP implementation where only left those we 75 * found are really useful. 76 */ 77 struct lp { 78 u32 flag; 79 u32 sowd; 80 u32 owd_min; 81 u32 owd_max; 82 u32 owd_max_rsv; 83 u32 remote_hz; 84 u32 remote_ref_time; 85 u32 local_ref_time; 86 u32 last_drop; 87 u32 inference; 88 }; 89 90 /** 91 * tcp_lp_init 92 * @sk: socket to initialize congestion control algorithm for 93 * 94 * Init all required variables. 95 * Clone the handling from Vegas module implementation. 96 */ 97 static void tcp_lp_init(struct sock *sk) 98 { 99 struct lp *lp = inet_csk_ca(sk); 100 101 lp->flag = 0; 102 lp->sowd = 0; 103 lp->owd_min = 0xffffffff; 104 lp->owd_max = 0; 105 lp->owd_max_rsv = 0; 106 lp->remote_hz = 0; 107 lp->remote_ref_time = 0; 108 lp->local_ref_time = 0; 109 lp->last_drop = 0; 110 lp->inference = 0; 111 } 112 113 /** 114 * tcp_lp_cong_avoid 115 * @sk: socket to avoid congesting 116 * 117 * Implementation of cong_avoid. 118 * Will only call newReno CA when away from inference. 119 * From TCP-LP's paper, this will be handled in additive increasement. 120 */ 121 static void tcp_lp_cong_avoid(struct sock *sk, u32 ack, u32 acked) 122 { 123 struct lp *lp = inet_csk_ca(sk); 124 125 if (!(lp->flag & LP_WITHIN_INF)) 126 tcp_reno_cong_avoid(sk, ack, acked); 127 } 128 129 /** 130 * tcp_lp_remote_hz_estimator 131 * @sk: socket which needs an estimate for the remote HZs 132 * 133 * Estimate remote HZ. 134 * We keep on updating the estimated value, where original TCP-LP 135 * implementation only guest it for once and use forever. 136 */ 137 static u32 tcp_lp_remote_hz_estimator(struct sock *sk) 138 { 139 struct tcp_sock *tp = tcp_sk(sk); 140 struct lp *lp = inet_csk_ca(sk); 141 s64 rhz = lp->remote_hz << 6; /* remote HZ << 6 */ 142 s64 m = 0; 143 144 /* not yet record reference time 145 * go away!! record it before come back!! */ 146 if (lp->remote_ref_time == 0 || lp->local_ref_time == 0) 147 goto out; 148 149 /* we can't calc remote HZ with no different!! */ 150 if (tp->rx_opt.rcv_tsval == lp->remote_ref_time || 151 tp->rx_opt.rcv_tsecr == lp->local_ref_time) 152 goto out; 153 154 m = TCP_TS_HZ * 155 (tp->rx_opt.rcv_tsval - lp->remote_ref_time) / 156 (tp->rx_opt.rcv_tsecr - lp->local_ref_time); 157 if (m < 0) 158 m = -m; 159 160 if (rhz > 0) { 161 m -= rhz >> 6; /* m is now error in remote HZ est */ 162 rhz += m; /* 63/64 old + 1/64 new */ 163 } else 164 rhz = m << 6; 165 166 out: 167 /* record time for successful remote HZ calc */ 168 if ((rhz >> 6) > 0) 169 lp->flag |= LP_VALID_RHZ; 170 else 171 lp->flag &= ~LP_VALID_RHZ; 172 173 /* record reference time stamp */ 174 lp->remote_ref_time = tp->rx_opt.rcv_tsval; 175 lp->local_ref_time = tp->rx_opt.rcv_tsecr; 176 177 return rhz >> 6; 178 } 179 180 /** 181 * tcp_lp_owd_calculator 182 * @sk: socket to calculate one way delay for 183 * 184 * Calculate one way delay (in relative format). 185 * Original implement OWD as minus of remote time difference to local time 186 * difference directly. As this time difference just simply equal to RTT, when 187 * the network status is stable, remote RTT will equal to local RTT, and result 188 * OWD into zero. 189 * It seems to be a bug and so we fixed it. 190 */ 191 static u32 tcp_lp_owd_calculator(struct sock *sk) 192 { 193 struct tcp_sock *tp = tcp_sk(sk); 194 struct lp *lp = inet_csk_ca(sk); 195 s64 owd = 0; 196 197 lp->remote_hz = tcp_lp_remote_hz_estimator(sk); 198 199 if (lp->flag & LP_VALID_RHZ) { 200 owd = 201 tp->rx_opt.rcv_tsval * (LP_RESOL / lp->remote_hz) - 202 tp->rx_opt.rcv_tsecr * (LP_RESOL / TCP_TS_HZ); 203 if (owd < 0) 204 owd = -owd; 205 } 206 207 if (owd > 0) 208 lp->flag |= LP_VALID_OWD; 209 else 210 lp->flag &= ~LP_VALID_OWD; 211 212 return owd; 213 } 214 215 /** 216 * tcp_lp_rtt_sample 217 * @sk: socket to add a rtt sample to 218 * @rtt: round trip time, which is ignored! 219 * 220 * Implementation or rtt_sample. 221 * Will take the following action, 222 * 1. calc OWD, 223 * 2. record the min/max OWD, 224 * 3. calc smoothed OWD (SOWD). 225 * Most ideas come from the original TCP-LP implementation. 226 */ 227 static void tcp_lp_rtt_sample(struct sock *sk, u32 rtt) 228 { 229 struct lp *lp = inet_csk_ca(sk); 230 s64 mowd = tcp_lp_owd_calculator(sk); 231 232 /* sorry that we don't have valid data */ 233 if (!(lp->flag & LP_VALID_RHZ) || !(lp->flag & LP_VALID_OWD)) 234 return; 235 236 /* record the next min owd */ 237 if (mowd < lp->owd_min) 238 lp->owd_min = mowd; 239 240 /* always forget the max of the max 241 * we just set owd_max as one below it */ 242 if (mowd > lp->owd_max) { 243 if (mowd > lp->owd_max_rsv) { 244 if (lp->owd_max_rsv == 0) 245 lp->owd_max = mowd; 246 else 247 lp->owd_max = lp->owd_max_rsv; 248 lp->owd_max_rsv = mowd; 249 } else 250 lp->owd_max = mowd; 251 } 252 253 /* calc for smoothed owd */ 254 if (lp->sowd != 0) { 255 mowd -= lp->sowd >> 3; /* m is now error in owd est */ 256 lp->sowd += mowd; /* owd = 7/8 owd + 1/8 new */ 257 } else 258 lp->sowd = mowd << 3; /* take the measured time be owd */ 259 } 260 261 /** 262 * tcp_lp_pkts_acked 263 * @sk: socket requiring congestion avoidance calculations 264 * 265 * Implementation of pkts_acked. 266 * Deal with active drop under Early Congestion Indication. 267 * Only drop to half and 1 will be handle, because we hope to use back 268 * newReno in increase case. 269 * We work it out by following the idea from TCP-LP's paper directly 270 */ 271 static void tcp_lp_pkts_acked(struct sock *sk, const struct ack_sample *sample) 272 { 273 struct tcp_sock *tp = tcp_sk(sk); 274 struct lp *lp = inet_csk_ca(sk); 275 u32 now = tcp_time_stamp(tp); 276 u32 delta; 277 278 if (sample->rtt_us > 0) 279 tcp_lp_rtt_sample(sk, sample->rtt_us); 280 281 /* calc inference */ 282 delta = now - tp->rx_opt.rcv_tsecr; 283 if ((s32)delta > 0) 284 lp->inference = 3 * delta; 285 286 /* test if within inference */ 287 if (lp->last_drop && (now - lp->last_drop < lp->inference)) 288 lp->flag |= LP_WITHIN_INF; 289 else 290 lp->flag &= ~LP_WITHIN_INF; 291 292 /* test if within threshold */ 293 if (lp->sowd >> 3 < 294 lp->owd_min + 15 * (lp->owd_max - lp->owd_min) / 100) 295 lp->flag |= LP_WITHIN_THR; 296 else 297 lp->flag &= ~LP_WITHIN_THR; 298 299 pr_debug("TCP-LP: %05o|%5u|%5u|%15u|%15u|%15u\n", lp->flag, 300 tp->snd_cwnd, lp->remote_hz, lp->owd_min, lp->owd_max, 301 lp->sowd >> 3); 302 303 if (lp->flag & LP_WITHIN_THR) 304 return; 305 306 /* FIXME: try to reset owd_min and owd_max here 307 * so decrease the chance the min/max is no longer suitable 308 * and will usually within threshold when whithin inference */ 309 lp->owd_min = lp->sowd >> 3; 310 lp->owd_max = lp->sowd >> 2; 311 lp->owd_max_rsv = lp->sowd >> 2; 312 313 /* happened within inference 314 * drop snd_cwnd into 1 */ 315 if (lp->flag & LP_WITHIN_INF) 316 tp->snd_cwnd = 1U; 317 318 /* happened after inference 319 * cut snd_cwnd into half */ 320 else 321 tp->snd_cwnd = max(tp->snd_cwnd >> 1U, 1U); 322 323 /* record this drop time */ 324 lp->last_drop = now; 325 } 326 327 static struct tcp_congestion_ops tcp_lp __read_mostly = { 328 .init = tcp_lp_init, 329 .ssthresh = tcp_reno_ssthresh, 330 .undo_cwnd = tcp_reno_undo_cwnd, 331 .cong_avoid = tcp_lp_cong_avoid, 332 .pkts_acked = tcp_lp_pkts_acked, 333 334 .owner = THIS_MODULE, 335 .name = "lp" 336 }; 337 338 static int __init tcp_lp_register(void) 339 { 340 BUILD_BUG_ON(sizeof(struct lp) > ICSK_CA_PRIV_SIZE); 341 return tcp_register_congestion_control(&tcp_lp); 342 } 343 344 static void __exit tcp_lp_unregister(void) 345 { 346 tcp_unregister_congestion_control(&tcp_lp); 347 } 348 349 module_init(tcp_lp_register); 350 module_exit(tcp_lp_unregister); 351 352 MODULE_AUTHOR("Wong Hoi Sing Edison, Hung Hing Lun Mike"); 353 MODULE_LICENSE("GPL"); 354 MODULE_DESCRIPTION("TCP Low Priority"); 355