linux/net/ipv4/tcp_lp.c
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   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, since
  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 */
  52enum 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 */
  76struct 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 */
  95static 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 */
 118static 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 */
 133static 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 */
 186static 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 */
 220static 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 */
 263static 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
 316static struct tcp_congestion_ops tcp_lp __read_mostly = {
 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
 328static 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
 334static void __exit tcp_lp_unregister(void)
 335{
 336        tcp_unregister_congestion_control(&tcp_lp);
 337}
 338
 339module_init(tcp_lp_register);
 340module_exit(tcp_lp_unregister);
 341
 342MODULE_AUTHOR("Wong Hoi Sing Edison, Hung Hing Lun Mike");
 343MODULE_LICENSE("GPL");
 344MODULE_DESCRIPTION("TCP Low Priority");
 345
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