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  *
  93  * Init all required variables.
  94  * Clone the handling from Vegas module implementation.
  95  */
  96 static void tcp_lp_init(struct sock *sk)
  97 {
  98         struct lp *lp = inet_csk_ca(sk);
  99
 100         lp->flag = 0;
 101         lp->sowd = 0;
 102         lp->owd_min = 0xffffffff;
 103         lp->owd_max = 0;
 104         lp->owd_max_rsv = 0;
 105         lp->remote_hz = 0;
 106         lp->remote_ref_time = 0;
 107         lp->local_ref_time = 0;
 108         lp->last_drop = 0;
 109         lp->inference = 0;
 110 }
 111
 112 /**
 113  * tcp_lp_cong_avoid
 114  *
 115  * Implementation of cong_avoid.
 116  * Will only call newReno CA when away from inference.
 117  * From TCP-LP's paper, this will be handled in additive increasement.
 118  */
 119 static void tcp_lp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 120 {
 121         struct lp *lp = inet_csk_ca(sk);
 122
 123         if (!(lp->flag & LP_WITHIN_INF))
 124                 tcp_reno_cong_avoid(sk, ack, acked);
 125 }
 126
 127 /**
 128  * tcp_lp_remote_hz_estimator
 129  *
 130  * Estimate remote HZ.
 131  * We keep on updating the estimated value, where original TCP-LP
 132  * implementation only guest it for once and use forever.
 133  */
 134 static u32 tcp_lp_remote_hz_estimator(struct sock *sk)
 135 {
 136         struct tcp_sock *tp = tcp_sk(sk);
 137         struct lp *lp = inet_csk_ca(sk);
 138         s64 rhz = lp->remote_hz << 6;   /* remote HZ << 6 */
 139         s64 m = 0;
 140
 141         /* not yet record reference time
 142          * go away!! record it before come back!! */
 143         if (lp->remote_ref_time == 0 || lp->local_ref_time == 0)
 144                 goto out;
 145
 146         /* we can't calc remote HZ with no different!! */
 147         if (tp->rx_opt.rcv_tsval == lp->remote_ref_time ||
 148             tp->rx_opt.rcv_tsecr == lp->local_ref_time)
 149                 goto out;
 150
 151         m = TCP_TS_HZ *
 152             (tp->rx_opt.rcv_tsval - lp->remote_ref_time) /
 153             (tp->rx_opt.rcv_tsecr - lp->local_ref_time);
 154         if (m < 0)
 155                 m = -m;
 156
 157         if (rhz > 0) {
 158                 m -= rhz >> 6;  /* m is now error in remote HZ est */
 159                 rhz += m;       /* 63/64 old + 1/64 new */
 160         } else
 161                 rhz = m << 6;
 162
 163  out:
 164         /* record time for successful remote HZ calc */
 165         if ((rhz >> 6) > 0)
 166                 lp->flag |= LP_VALID_RHZ;
 167         else
 168                 lp->flag &= ~LP_VALID_RHZ;
 169
 170         /* record reference time stamp */
 171         lp->remote_ref_time = tp->rx_opt.rcv_tsval;
 172         lp->local_ref_time = tp->rx_opt.rcv_tsecr;
 173
 174         return rhz >> 6;
 175 }
 176
 177 /**
 178  * tcp_lp_owd_calculator
 179  *
 180  * Calculate one way delay (in relative format).
 181  * Original implement OWD as minus of remote time difference to local time
 182  * difference directly. As this time difference just simply equal to RTT, when
 183  * the network status is stable, remote RTT will equal to local RTT, and result
 184  * OWD into zero.
 185  * It seems to be a bug and so we fixed it.
 186  */
 187 static u32 tcp_lp_owd_calculator(struct sock *sk)
 188 {
 189         struct tcp_sock *tp = tcp_sk(sk);
 190         struct lp *lp = inet_csk_ca(sk);
 191         s64 owd = 0;
 192
 193         lp->remote_hz = tcp_lp_remote_hz_estimator(sk);
 194
 195         if (lp->flag & LP_VALID_RHZ) {
 196                 owd =
 197                     tp->rx_opt.rcv_tsval * (LP_RESOL / lp->remote_hz) -
 198                     tp->rx_opt.rcv_tsecr * (LP_RESOL / TCP_TS_HZ);
 199                 if (owd < 0)
 200                         owd = -owd;
 201         }
 202
 203         if (owd > 0)
 204                 lp->flag |= LP_VALID_OWD;
 205         else
 206                 lp->flag &= ~LP_VALID_OWD;
 207
 208         return owd;
 209 }
 210
 211 /**
 212  * tcp_lp_rtt_sample
 213  *
 214  * Implementation or rtt_sample.
 215  * Will take the following action,
 216  *   1. calc OWD,
 217  *   2. record the min/max OWD,
 218  *   3. calc smoothed OWD (SOWD).
 219  * Most ideas come from the original TCP-LP implementation.
 220  */
 221 static void tcp_lp_rtt_sample(struct sock *sk, u32 rtt)
 222 {
 223         struct lp *lp = inet_csk_ca(sk);
 224         s64 mowd = tcp_lp_owd_calculator(sk);
 225
 226         /* sorry that we don't have valid data */
 227         if (!(lp->flag & LP_VALID_RHZ) || !(lp->flag & LP_VALID_OWD))
 228                 return;
 229
 230         /* record the next min owd */
 231         if (mowd < lp->owd_min)
 232                 lp->owd_min = mowd;
 233
 234         /* always forget the max of the max
 235          * we just set owd_max as one below it */
 236         if (mowd > lp->owd_max) {
 237                 if (mowd > lp->owd_max_rsv) {
 238                         if (lp->owd_max_rsv == 0)
 239                                 lp->owd_max = mowd;
 240                         else
 241                                 lp->owd_max = lp->owd_max_rsv;
 242                         lp->owd_max_rsv = mowd;
 243                 } else
 244                         lp->owd_max = mowd;
 245         }
 246
 247         /* calc for smoothed owd */
 248         if (lp->sowd != 0) {
 249                 mowd -= lp->sowd >> 3;  /* m is now error in owd est */
 250                 lp->sowd += mowd;       /* owd = 7/8 owd + 1/8 new */
 251         } else
 252                 lp->sowd = mowd << 3;   /* take the measured time be owd */
 253 }
 254
 255 /**
 256  * tcp_lp_pkts_acked
 257  *
 258  * Implementation of pkts_acked.
 259  * Deal with active drop under Early Congestion Indication.
 260  * Only drop to half and 1 will be handle, because we hope to use back
 261  * newReno in increase case.
 262  * We work it out by following the idea from TCP-LP's paper directly
 263  */
 264 static void tcp_lp_pkts_acked(struct sock *sk, const struct ack_sample *sample)
 265 {
 266         struct tcp_sock *tp = tcp_sk(sk);
 267         struct lp *lp = inet_csk_ca(sk);
 268         u32 now = tcp_time_stamp(tp);
 269         u32 delta;
 270
 271         if (sample->rtt_us > 0)
 272                 tcp_lp_rtt_sample(sk, sample->rtt_us);
 273
 274         /* calc inference */
 275         delta = now - tp->rx_opt.rcv_tsecr;
 276         if ((s32)delta > 0)
 277                 lp->inference = 3 * delta;
 278
 279         /* test if within inference */
 280         if (lp->last_drop && (now - lp->last_drop < lp->inference))
 281                 lp->flag |= LP_WITHIN_INF;
 282         else
 283                 lp->flag &= ~LP_WITHIN_INF;
 284
 285         /* test if within threshold */
 286         if (lp->sowd >> 3 <
 287             lp->owd_min + 15 * (lp->owd_max - lp->owd_min) / 100)
 288                 lp->flag |= LP_WITHIN_THR;
 289         else
 290                 lp->flag &= ~LP_WITHIN_THR;
 291
 292         pr_debug("TCP-LP: %05o|%5u|%5u|%15u|%15u|%15u\n", lp->flag,
 293                  tp->snd_cwnd, lp->remote_hz, lp->owd_min, lp->owd_max,
 294                  lp->sowd >> 3);
 295
 296         if (lp->flag & LP_WITHIN_THR)
 297                 return;
 298
 299         /* FIXME: try to reset owd_min and owd_max here
 300          * so decrease the chance the min/max is no longer suitable
 301          * and will usually within threshold when whithin inference */
 302         lp->owd_min = lp->sowd >> 3;
 303         lp->owd_max = lp->sowd >> 2;
 304         lp->owd_max_rsv = lp->sowd >> 2;
 305
 306         /* happened within inference
 307          * drop snd_cwnd into 1 */
 308         if (lp->flag & LP_WITHIN_INF)
 309                 tp->snd_cwnd = 1U;
 310
 311         /* happened after inference
 312          * cut snd_cwnd into half */
 313         else
 314                 tp->snd_cwnd = max(tp->snd_cwnd >> 1U, 1U);
 315
 316         /* record this drop time */
 317         lp->last_drop = now;
 318 }
 319
 320 static struct tcp_congestion_ops tcp_lp __read_mostly = {
 321         .init = tcp_lp_init,
 322         .ssthresh = tcp_reno_ssthresh,
 323         .undo_cwnd = tcp_reno_undo_cwnd,
 324         .cong_avoid = tcp_lp_cong_avoid,
 325         .pkts_acked = tcp_lp_pkts_acked,
 326
 327         .owner = THIS_MODULE,
 328         .name = "lp"
 329 };
 330
 331 static int __init tcp_lp_register(void)
 332 {
 333         BUILD_BUG_ON(sizeof(struct lp) > ICSK_CA_PRIV_SIZE);
 334         return tcp_register_congestion_control(&tcp_lp);
 335 }
 336
 337 static void __exit tcp_lp_unregister(void)
 338 {
 339         tcp_unregister_congestion_control(&tcp_lp);
 340 }
 341
 342 module_init(tcp_lp_register);
 343 module_exit(tcp_lp_unregister);
 344
 345 MODULE_AUTHOR("Wong Hoi Sing Edison, Hung Hing Lun Mike");
 346 MODULE_LICENSE("GPL");
 347 MODULE_DESCRIPTION("TCP Low Priority");