LXR linux/net/ipv4/tcp

   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 */
  53enum 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 */
  77struct 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 */
  96static 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 */
 119static 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 */
 134static 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 */
 187static 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 */
 221static 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 */
 264static 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
 320static 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
 331static 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
 337static void __exit tcp_lp_unregister(void)
 338{
 339        tcp_unregister_congestion_control(&tcp_lp);
 340}
 341
 342module_init(tcp_lp_register);
 343module_exit(tcp_lp_unregister);
 344
 345MODULE_AUTHOR("Wong Hoi Sing Edison, Hung Hing Lun Mike");
 346MODULE_LICENSE("GPL");
 347MODULE_DESCRIPTION("TCP Low Priority");
 348