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  * Version: $Id: tcp_lp.c,v 1.24 2006/09/05 20:22:53 hswong3i Exp $
  36  */
  37
  38 #include <linux/module.h>
  39 #include <net/tcp.h>
  40
  41 /* resolution of owd */
  42 #define LP_RESOL       1000
  43
  44 /**
  45  * enum tcp_lp_state
  46  * @LP_VALID_RHZ: is remote HZ valid?
  47  * @LP_VALID_OWD: is OWD valid?
  48  * @LP_WITHIN_THR: are we within threshold?
  49  * @LP_WITHIN_INF: are we within inference?
  50  *
  51  * TCP-LP's state flags.
  52  * We create this set of state flag mainly for debugging.
  53  */
  54 enum tcp_lp_state {
  55         LP_VALID_RHZ = (1 << 0),
  56         LP_VALID_OWD = (1 << 1),
  57         LP_WITHIN_THR = (1 << 3),
  58         LP_WITHIN_INF = (1 << 4),
  59 };
  60
  61 /**
  62  * struct lp
  63  * @flag: TCP-LP state flag
  64  * @sowd: smoothed OWD << 3
  65  * @owd_min: min OWD
  66  * @owd_max: max OWD
  67  * @owd_max_rsv: resrved max owd
  68  * @remote_hz: estimated remote HZ
  69  * @remote_ref_time: remote reference time
  70  * @local_ref_time: local reference time
  71  * @last_drop: time for last active drop
  72  * @inference: current inference
  73  *
  74  * TCP-LP's private struct.
  75  * We get the idea from original TCP-LP implementation where only left those we
  76  * found are really useful.
  77  */
  78 struct lp {
  79         u32 flag;
  80         u32 sowd;
  81         u32 owd_min;
  82         u32 owd_max;
  83         u32 owd_max_rsv;
  84         u32 remote_hz;
  85         u32 remote_ref_time;
  86         u32 local_ref_time;
  87         u32 last_drop;
  88         u32 inference;
  89 };
  90
  91 /**
  92  * tcp_lp_init
  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  *
 116  * Implementation of cong_avoid.
 117  * Will only call newReno CA when away from inference.
 118  * From TCP-LP's paper, this will be handled in additive increasement.
 119  */
 120 static void tcp_lp_cong_avoid(struct sock *sk, u32 ack, u32 rtt, u32 in_flight,
 121                               int flag)
 122 {
 123         struct lp *lp = inet_csk_ca(sk);
 124
 125         if (!(lp->flag & LP_WITHIN_INF))
 126                 tcp_reno_cong_avoid(sk, ack, rtt, in_flight, flag);
 127 }
 128
 129 /**
 130  * tcp_lp_remote_hz_estimator
 131  *
 132  * Estimate remote HZ.
 133  * We keep on updating the estimated value, where original TCP-LP
 134  * implementation only guest it for once and use forever.
 135  */
 136 static u32 tcp_lp_remote_hz_estimator(struct sock *sk)
 137 {
 138         struct tcp_sock *tp = tcp_sk(sk);
 139         struct lp *lp = inet_csk_ca(sk);
 140         s64 rhz = lp->remote_hz << 6;   /* remote HZ << 6 */
 141         s64 m = 0;
 142
 143         /* not yet record reference time
 144          * go away!! record it before come back!! */
 145         if (lp->remote_ref_time == 0 || lp->local_ref_time == 0)
 146                 goto out;
 147
 148         /* we can't calc remote HZ with no different!! */
 149         if (tp->rx_opt.rcv_tsval == lp->remote_ref_time
 150             || tp->rx_opt.rcv_tsecr == lp->local_ref_time)
 151                 goto out;
 152
 153         m = HZ * (tp->rx_opt.rcv_tsval -
 154                   lp->remote_ref_time) / (tp->rx_opt.rcv_tsecr -
 155                                           lp->local_ref_time);
 156         if (m < 0)
 157                 m = -m;
 158
 159         if (rhz > 0) {
 160                 m -= rhz >> 6;  /* m is now error in remote HZ est */
 161                 rhz += m;       /* 63/64 old + 1/64 new */
 162         } else
 163                 rhz = m << 6;
 164
 165  out:
 166         /* record time for successful remote HZ calc */
 167         if (rhz > 0)
 168                 lp->flag |= LP_VALID_RHZ;
 169         else
 170                 lp->flag &= ~LP_VALID_RHZ;
 171
 172         /* record reference time stamp */
 173         lp->remote_ref_time = tp->rx_opt.rcv_tsval;
 174         lp->local_ref_time = tp->rx_opt.rcv_tsecr;
 175
 176         return rhz >> 6;
 177 }
 178
 179 /**
 180  * tcp_lp_owd_calculator
 181  *
 182  * Calculate one way delay (in relative format).
 183  * Original implement OWD as minus of remote time difference to local time
 184  * difference directly. As this time difference just simply equal to RTT, when
 185  * the network status is stable, remote RTT will equal to local RTT, and result
 186  * OWD into zero.
 187  * It seems to be a bug and so we fixed it.
 188  */
 189 static u32 tcp_lp_owd_calculator(struct sock *sk)
 190 {
 191         struct tcp_sock *tp = tcp_sk(sk);
 192         struct lp *lp = inet_csk_ca(sk);
 193         s64 owd = 0;
 194
 195         lp->remote_hz = tcp_lp_remote_hz_estimator(sk);
 196
 197         if (lp->flag & LP_VALID_RHZ) {
 198                 owd =
 199                     tp->rx_opt.rcv_tsval * (LP_RESOL / lp->remote_hz) -
 200                     tp->rx_opt.rcv_tsecr * (LP_RESOL / HZ);
 201                 if (owd < 0)
 202                         owd = -owd;
 203         }
 204
 205         if (owd > 0)
 206                 lp->flag |= LP_VALID_OWD;
 207         else
 208                 lp->flag &= ~LP_VALID_OWD;
 209
 210         return owd;
 211 }
 212
 213 /**
 214  * tcp_lp_rtt_sample
 215  *
 216  * Implementation or rtt_sample.
 217  * Will take the following action,
 218  *   1. calc OWD,
 219  *   2. record the min/max OWD,
 220  *   3. calc smoothed OWD (SOWD).
 221  * Most ideas come from the original TCP-LP implementation.
 222  */
 223 static void tcp_lp_rtt_sample(struct sock *sk, u32 usrtt)
 224 {
 225         struct lp *lp = inet_csk_ca(sk);
 226         s64 mowd = tcp_lp_owd_calculator(sk);
 227
 228         /* sorry that we don't have valid data */
 229         if (!(lp->flag & LP_VALID_RHZ) || !(lp->flag & LP_VALID_OWD))
 230                 return;
 231
 232         /* record the next min owd */
 233         if (mowd < lp->owd_min)
 234                 lp->owd_min = mowd;
 235
 236         /* always forget the max of the max
 237          * we just set owd_max as one below it */
 238         if (mowd > lp->owd_max) {
 239                 if (mowd > lp->owd_max_rsv) {
 240                         if (lp->owd_max_rsv == 0)
 241                                 lp->owd_max = mowd;
 242                         else
 243                                 lp->owd_max = lp->owd_max_rsv;
 244                         lp->owd_max_rsv = mowd;
 245                 } else
 246                         lp->owd_max = mowd;
 247         }
 248
 249         /* calc for smoothed owd */
 250         if (lp->sowd != 0) {
 251                 mowd -= lp->sowd >> 3;  /* m is now error in owd est */
 252                 lp->sowd += mowd;       /* owd = 7/8 owd + 1/8 new */
 253         } else
 254                 lp->sowd = mowd << 3;   /* take the measured time be owd */
 255 }
 256
 257 /**
 258  * tcp_lp_pkts_acked
 259  *
 260  * Implementation of pkts_acked.
 261  * Deal with active drop under Early Congestion Indication.
 262  * Only drop to half and 1 will be handle, because we hope to use back
 263  * newReno in increase case.
 264  * We work it out by following the idea from TCP-LP's paper directly
 265  */
 266 static void tcp_lp_pkts_acked(struct sock *sk, u32 num_acked)
 267 {
 268         struct tcp_sock *tp = tcp_sk(sk);
 269         struct lp *lp = inet_csk_ca(sk);
 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         .init = tcp_lp_init,
 318         .ssthresh = tcp_reno_ssthresh,
 319         .cong_avoid = tcp_lp_cong_avoid,
 320         .min_cwnd = tcp_reno_min_cwnd,
 321         .rtt_sample = tcp_lp_rtt_sample,
 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");