net/ipv4/tcp_lp.c

   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");