net/ipv4/tcp_lp.c

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