package/mac80211/src/net/mac80211/rc80211_pid_algo.c

   1 /*
   2  * Copyright 2002-2005, Instant802 Networks, Inc.
   3  * Copyright 2005, Devicescape Software, Inc.
   4  * Copyright 2007, Mattias Nissler <mattias.nissler@gmx.de>
   5  * Copyright 2007-2008, Stefano Brivio <stefano.brivio@polimi.it>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11
  12 #include <linux/netdevice.h>
  13 #include <linux/types.h>
  14 #include <linux/skbuff.h>
  15 #include <linux/debugfs.h>
  16 #include <net/mac80211.h>
  17 #include "ieee80211_rate.h"
  18
  19 #include "rc80211_pid.h"
  20
  21
  22 /* This is an implementation of a TX rate control algorithm that uses a PID
  23  * controller. Given a target failed frames rate, the controller decides about
  24  * TX rate changes to meet the target failed frames rate.
  25  *
  26  * The controller basically computes the following:
  27  *
  28  * adj = CP * err + CI * err_avg + CD * (err - last_err) * (1 + sharpening)
  29  *
  30  * where
  31  *      adj     adjustment value that is used to switch TX rate (see below)
  32  *      err     current error: target vs. current failed frames percentage
  33  *      last_err        last error
  34  *      err_avg average (i.e. poor man's integral) of recent errors
  35  *      sharpening      non-zero when fast response is needed (i.e. right after
  36  *                      association or no frames sent for a long time), heading
  37  *                      to zero over time
  38  *      CP      Proportional coefficient
  39  *      CI      Integral coefficient
  40  *      CD      Derivative coefficient
  41  *
  42  * CP, CI, CD are subject to careful tuning.
  43  *
  44  * The integral component uses a exponential moving average approach instead of
  45  * an actual sliding window. The advantage is that we don't need to keep an
  46  * array of the last N error values and computation is easier.
  47  *
  48  * Once we have the adj value, we map it to a rate by means of a learning
  49  * algorithm. This algorithm keeps the state of the percentual failed frames
  50  * difference between rates. The behaviour of the lowest available rate is kept
  51  * as a reference value, and every time we switch between two rates, we compute
  52  * the difference between the failed frames each rate exhibited. By doing so,
  53  * we compare behaviours which different rates exhibited in adjacent timeslices,
  54  * thus the comparison is minimally affected by external conditions. This
  55  * difference gets propagated to the whole set of measurements, so that the
  56  * reference is always the same. Periodically, we normalize this set so that
  57  * recent events weigh the most. By comparing the adj value with this set, we
  58  * avoid pejorative switches to lower rates and allow for switches to higher
  59  * rates if they behaved well.
  60  *
  61  * Note that for the computations we use a fixed-point representation to avoid
  62  * floating point arithmetic. Hence, all values are shifted left by
  63  * RC_PID_ARITH_SHIFT.
  64  */
  65
  66
  67 /* Adjust the rate while ensuring that we won't switch to a lower rate if it
  68  * exhibited a worse failed frames behaviour and we'll choose the highest rate
  69  * whose failed frames behaviour is not worse than the one of the original rate
  70  * target. While at it, check that the new rate is valid. */
  71 static void rate_control_pid_adjust_rate(struct ieee80211_local *local,
  72                                          struct sta_info *sta, int adj,
  73                                          struct rc_pid_rateinfo *rinfo)
  74 {
  75         struct ieee80211_sub_if_data *sdata;
  76         struct ieee80211_supported_band *sband;
  77         int cur_sorted, new_sorted, probe, tmp, n_bitrates, band;
  78         int cur = sta->txrate_idx;
  79
  80         sdata = IEEE80211_DEV_TO_SUB_IF(sta->dev);
  81         sband = local->hw.wiphy->bands[local->hw.conf.channel->band];
  82         band = sband->band;
  83         n_bitrates = sband->n_bitrates;
  84
  85         /* Map passed arguments to sorted values. */
  86         cur_sorted = rinfo[cur].rev_index;
  87         new_sorted = cur_sorted + adj;
  88
  89         /* Check limits. */
  90         if (new_sorted < 0)
  91                 new_sorted = rinfo[0].rev_index;
  92         else if (new_sorted >= n_bitrates)
  93                 new_sorted = rinfo[n_bitrates - 1].rev_index;
  94
  95         tmp = new_sorted;
  96
  97         if (adj < 0) {
  98                 /* Ensure that the rate decrease isn't disadvantageous. */
  99                 for (probe = cur_sorted; probe >= new_sorted; probe--)
 100                         if (rinfo[probe].diff <= rinfo[cur_sorted].diff &&
 101                             rate_supported(sta, band, rinfo[probe].index))
 102                                 tmp = probe;
 103         } else {
 104                 /* Look for rate increase with zero (or below) cost. */
 105                 for (probe = new_sorted + 1; probe < n_bitrates; probe++)
 106                         if (rinfo[probe].diff <= rinfo[new_sorted].diff &&
 107                             rate_supported(sta, band, rinfo[probe].index))
 108                                 tmp = probe;
 109         }
 110
 111         /* Fit the rate found to the nearest supported rate. */
 112         do {
 113                 if (rate_supported(sta, band, rinfo[tmp].index)) {
 114                         sta->txrate_idx = rinfo[tmp].index;
 115                         break;
 116                 }
 117                 if (adj < 0)
 118                         tmp--;
 119                 else
 120                         tmp++;
 121         } while (tmp < n_bitrates && tmp >= 0);
 122
 123 #ifdef CONFIG_MAC80211_DEBUGFS
 124         rate_control_pid_event_rate_change(
 125                 &((struct rc_pid_sta_info *)sta->rate_ctrl_priv)->events,
 126                 sta->txrate_idx, sband->bitrates[sta->txrate_idx].bitrate);
 127 #endif
 128 }
 129
 130 /* Normalize the failed frames per-rate differences. */
 131 static void rate_control_pid_normalize(struct rc_pid_info *pinfo, int l)
 132 {
 133         int i, norm_offset = pinfo->norm_offset;
 134         struct rc_pid_rateinfo *r = pinfo->rinfo;
 135
 136         if (r[0].diff > norm_offset)
 137                 r[0].diff -= norm_offset;
 138         else if (r[0].diff < -norm_offset)
 139                 r[0].diff += norm_offset;
 140         for (i = 0; i < l - 1; i++)
 141                 if (r[i + 1].diff > r[i].diff + norm_offset)
 142                         r[i + 1].diff -= norm_offset;
 143                 else if (r[i + 1].diff <= r[i].diff)
 144                         r[i + 1].diff += norm_offset;
 145 }
 146
 147 static void rate_control_pid_sample(struct rc_pid_info *pinfo,
 148                                     struct ieee80211_local *local,
 149                                     struct sta_info *sta)
 150 {
 151         struct rc_pid_sta_info *spinfo = sta->rate_ctrl_priv;
 152         struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
 153         struct ieee80211_supported_band *sband;
 154         u32 pf;
 155         s32 err_avg;
 156         u32 err_prop;
 157         u32 err_int;
 158         u32 err_der;
 159         int adj, i, j, tmp;
 160         unsigned long period;
 161
 162         sband = local->hw.wiphy->bands[local->hw.conf.channel->band];
 163         spinfo = sta->rate_ctrl_priv;
 164
 165         /* In case nothing happened during the previous control interval, turn
 166          * the sharpening factor on. */
 167         period = (HZ * pinfo->sampling_period + 500) / 1000;
 168         if (!period)
 169                 period = 1;
 170         if (jiffies - spinfo->last_sample > 2 * period)
 171                 spinfo->sharp_cnt = pinfo->sharpen_duration;
 172
 173         spinfo->last_sample = jiffies;
 174
 175         /* This should never happen, but in case, we assume the old sample is
 176          * still a good measurement and copy it. */
 177         if (unlikely(spinfo->tx_num_xmit == 0))
 178                 pf = spinfo->last_pf;
 179         else {
 180                 pf = spinfo->tx_num_failed * 100 / spinfo->tx_num_xmit;
 181                 pf <<= RC_PID_ARITH_SHIFT;
 182         }
 183
 184         spinfo->tx_num_xmit = 0;
 185         spinfo->tx_num_failed = 0;
 186
 187         /* If we just switched rate, update the rate behaviour info. */
 188         if (pinfo->oldrate != sta->txrate_idx) {
 189
 190                 i = rinfo[pinfo->oldrate].rev_index;
 191                 j = rinfo[sta->txrate_idx].rev_index;
 192
 193                 tmp = (pf - spinfo->last_pf);
 194                 tmp = RC_PID_DO_ARITH_RIGHT_SHIFT(tmp, RC_PID_ARITH_SHIFT);
 195
 196                 rinfo[j].diff = rinfo[i].diff + tmp;
 197                 pinfo->oldrate = sta->txrate_idx;
 198         }
 199         rate_control_pid_normalize(pinfo, sband->n_bitrates);
 200
 201         /* Compute the proportional, integral and derivative errors. */
 202         err_prop = (pinfo->target << RC_PID_ARITH_SHIFT) - pf;
 203
 204         err_avg = spinfo->err_avg_sc >> pinfo->smoothing_shift;
 205         spinfo->err_avg_sc = spinfo->err_avg_sc - err_avg + err_prop;
 206         err_int = spinfo->err_avg_sc >> pinfo->smoothing_shift;
 207
 208         err_der = (pf - spinfo->last_pf) *
 209                   (1 + pinfo->sharpen_factor * spinfo->sharp_cnt);
 210         spinfo->last_pf = pf;
 211         if (spinfo->sharp_cnt)
 212                         spinfo->sharp_cnt--;
 213
 214 #ifdef CONFIG_MAC80211_DEBUGFS
 215         rate_control_pid_event_pf_sample(&spinfo->events, pf, err_prop, err_int,
 216                                          err_der);
 217 #endif
 218
 219         /* Compute the controller output. */
 220         adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i
 221               + err_der * pinfo->coeff_d);
 222         adj = RC_PID_DO_ARITH_RIGHT_SHIFT(adj, 2 * RC_PID_ARITH_SHIFT);
 223
 224         /* Change rate. */
 225         if (adj)
 226                 rate_control_pid_adjust_rate(local, sta, adj, rinfo);
 227 }
 228
 229 static void rate_control_pid_tx_status(void *priv, struct net_device *dev,
 230                                        struct sk_buff *skb,
 231                                        struct ieee80211_tx_status *status)
 232 {
 233         struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
 234         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 235         struct ieee80211_sub_if_data *sdata;
 236         struct rc_pid_info *pinfo = priv;
 237         struct sta_info *sta;
 238         struct rc_pid_sta_info *spinfo;
 239         unsigned long period;
 240         struct ieee80211_supported_band *sband;
 241
 242         sta = sta_info_get(local, hdr->addr1);
 243         sband = local->hw.wiphy->bands[local->hw.conf.channel->band];
 244
 245         if (!sta)
 246                 return;
 247
 248         /* Don't update the state if we're not controlling the rate. */
 249         sdata = IEEE80211_DEV_TO_SUB_IF(sta->dev);
 250         if (sdata->bss && sdata->bss->force_unicast_rateidx > -1) {
 251                 sta->txrate_idx = sdata->bss->max_ratectrl_rateidx;
 252                 return;
 253         }
 254
 255         /* Ignore all frames that were sent with a different rate than the rate
 256          * we currently advise mac80211 to use. */
 257         if (status->control.tx_rate != &sband->bitrates[sta->txrate_idx])
 258                 goto ignore;
 259
 260         spinfo = sta->rate_ctrl_priv;
 261         spinfo->tx_num_xmit++;
 262
 263 #ifdef CONFIG_MAC80211_DEBUGFS
 264         rate_control_pid_event_tx_status(&spinfo->events, status);
 265 #endif
 266
 267         /* We count frames that totally failed to be transmitted as two bad
 268          * frames, those that made it out but had some retries as one good and
 269          * one bad frame. */
 270         if (status->excessive_retries) {
 271                 spinfo->tx_num_failed += 2;
 272                 spinfo->tx_num_xmit++;
 273         } else if (status->retry_count) {
 274                 spinfo->tx_num_failed++;
 275                 spinfo->tx_num_xmit++;
 276         }
 277
 278         if (status->excessive_retries) {
 279                 sta->tx_retry_failed++;
 280                 sta->tx_num_consecutive_failures++;
 281                 sta->tx_num_mpdu_fail++;
 282         } else {
 283                 sta->last_ack_rssi[0] = sta->last_ack_rssi[1];
 284                 sta->last_ack_rssi[1] = sta->last_ack_rssi[2];
 285                 sta->last_ack_rssi[2] = status->ack_signal;
 286                 sta->tx_num_consecutive_failures = 0;
 287                 sta->tx_num_mpdu_ok++;
 288         }
 289         sta->tx_retry_count += status->retry_count;
 290         sta->tx_num_mpdu_fail += status->retry_count;
 291
 292         /* Update PID controller state. */
 293         period = (HZ * pinfo->sampling_period + 500) / 1000;
 294         if (!period)
 295                 period = 1;
 296         if (time_after(jiffies, spinfo->last_sample + period))
 297                 rate_control_pid_sample(pinfo, local, sta);
 298
 299 ignore:
 300         sta_info_put(sta);
 301 }
 302
 303 static void rate_control_pid_get_rate(void *priv, struct net_device *dev,
 304                                       struct ieee80211_supported_band *sband,
 305                                       struct sk_buff *skb,
 306                                       struct rate_selection *sel)
 307 {
 308         struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
 309         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 310         struct ieee80211_sub_if_data *sdata;
 311         struct sta_info *sta;
 312         int rateidx;
 313         u16 fc;
 314
 315         sta = sta_info_get(local, hdr->addr1);
 316
 317         /* Send management frames and broadcast/multicast data using lowest
 318          * rate. */
 319         fc = le16_to_cpu(hdr->frame_control);
 320         if ((fc & IEEE80211_FCTL_FTYPE) != IEEE80211_FTYPE_DATA ||
 321             is_multicast_ether_addr(hdr->addr1) || !sta) {
 322                 sel->rate = rate_lowest(local, sband, sta);
 323                 if (sta)
 324                         sta_info_put(sta);
 325                 return;
 326         }
 327
 328         /* If a forced rate is in effect, select it. */
 329         sdata = IEEE80211_DEV_TO_SUB_IF(dev);
 330         if (sdata->bss && sdata->bss->force_unicast_rateidx > -1)
 331                 sta->txrate_idx = sdata->bss->force_unicast_rateidx;
 332
 333         rateidx = sta->txrate_idx;
 334
 335         if (rateidx >= sband->n_bitrates)
 336                 rateidx = sband->n_bitrates - 1;
 337
 338         sta->last_txrate_idx = rateidx;
 339
 340         sta_info_put(sta);
 341
 342         sel->rate = &sband->bitrates[rateidx];
 343
 344 #ifdef CONFIG_MAC80211_DEBUGFS
 345         rate_control_pid_event_tx_rate(
 346                 &((struct rc_pid_sta_info *) sta->rate_ctrl_priv)->events,
 347                 rateidx, sband->bitrates[rateidx].bitrate);
 348 #endif
 349 }
 350
 351 static void rate_control_pid_rate_init(void *priv, void *priv_sta,
 352                                           struct ieee80211_local *local,
 353                                           struct sta_info *sta)
 354 {
 355         /* TODO: This routine should consider using RSSI from previous packets
 356          * as we need to have IEEE 802.1X auth succeed immediately after assoc..
 357          * Until that method is implemented, we will use the lowest supported
 358          * rate as a workaround. */
 359         struct ieee80211_supported_band *sband;
 360
 361         sband = local->hw.wiphy->bands[local->hw.conf.channel->band];
 362         sta->txrate_idx = rate_lowest_index(local, sband, sta);
 363 }
 364
 365 static void *rate_control_pid_alloc(struct ieee80211_local *local)
 366 {
 367         struct rc_pid_info *pinfo;
 368         struct rc_pid_rateinfo *rinfo;
 369         struct ieee80211_supported_band *sband;
 370         int i, j, tmp;
 371         bool s;
 372 #ifdef CONFIG_MAC80211_DEBUGFS
 373         struct rc_pid_debugfs_entries *de;
 374 #endif
 375
 376         sband = local->hw.wiphy->bands[local->hw.conf.channel->band];
 377
 378         pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
 379         if (!pinfo)
 380                 return NULL;
 381
 382         /* We can safely assume that sband won't change unless we get
 383          * reinitialized. */
 384         rinfo = kmalloc(sizeof(*rinfo) * sband->n_bitrates, GFP_ATOMIC);
 385         if (!rinfo) {
 386                 kfree(pinfo);
 387                 return NULL;
 388         }
 389
 390         /* Sort the rates. This is optimized for the most common case (i.e.
 391          * almost-sorted CCK+OFDM rates). Kind of bubble-sort with reversed
 392          * mapping too. */
 393         for (i = 0; i < sband->n_bitrates; i++) {
 394                 rinfo[i].index = i;
 395                 rinfo[i].rev_index = i;
 396                 if (pinfo->fast_start)
 397                         rinfo[i].diff = 0;
 398                 else
 399                         rinfo[i].diff = i * pinfo->norm_offset;
 400         }
 401         for (i = 1; i < sband->n_bitrates; i++) {
 402                 s = 0;
 403                 for (j = 0; j < sband->n_bitrates - i; j++)
 404                         if (unlikely(sband->bitrates[rinfo[j].index].bitrate >
 405                                      sband->bitrates[rinfo[j + 1].index].bitrate)) {
 406                                 tmp = rinfo[j].index;
 407                                 rinfo[j].index = rinfo[j + 1].index;
 408                                 rinfo[j + 1].index = tmp;
 409                                 rinfo[rinfo[j].index].rev_index = j;
 410                                 rinfo[rinfo[j + 1].index].rev_index = j + 1;
 411                                 s = 1;
 412                         }
 413                 if (!s)
 414                         break;
 415         }
 416
 417         pinfo->target = RC_PID_TARGET_PF;
 418         pinfo->sampling_period = RC_PID_INTERVAL;
 419         pinfo->coeff_p = RC_PID_COEFF_P;
 420         pinfo->coeff_i = RC_PID_COEFF_I;
 421         pinfo->coeff_d = RC_PID_COEFF_D;
 422         pinfo->smoothing_shift = RC_PID_SMOOTHING_SHIFT;
 423         pinfo->sharpen_factor = RC_PID_SHARPENING_FACTOR;
 424         pinfo->sharpen_duration = RC_PID_SHARPENING_DURATION;
 425         pinfo->norm_offset = RC_PID_NORM_OFFSET;
 426         pinfo->fast_start = RC_PID_FAST_START;
 427         pinfo->rinfo = rinfo;
 428         pinfo->oldrate = 0;
 429
 430 #ifdef CONFIG_MAC80211_DEBUGFS
 431         de = &pinfo->dentries;
 432         de->dir = debugfs_create_dir("rc80211_pid",
 433                                      local->hw.wiphy->debugfsdir);
 434         de->target = debugfs_create_u32("target_pf", S_IRUSR | S_IWUSR,
 435                                         de->dir, &pinfo->target);
 436         de->sampling_period = debugfs_create_u32("sampling_period",
 437                                                  S_IRUSR | S_IWUSR, de->dir,
 438                                                  &pinfo->sampling_period);
 439         de->coeff_p = debugfs_create_u32("coeff_p", S_IRUSR | S_IWUSR,
 440                                          de->dir, &pinfo->coeff_p);
 441         de->coeff_i = debugfs_create_u32("coeff_i", S_IRUSR | S_IWUSR,
 442                                          de->dir, &pinfo->coeff_i);
 443         de->coeff_d = debugfs_create_u32("coeff_d", S_IRUSR | S_IWUSR,
 444                                          de->dir, &pinfo->coeff_d);
 445         de->smoothing_shift = debugfs_create_u32("smoothing_shift",
 446                                                  S_IRUSR | S_IWUSR, de->dir,
 447                                                  &pinfo->smoothing_shift);
 448         de->sharpen_factor = debugfs_create_u32("sharpen_factor",
 449                                                S_IRUSR | S_IWUSR, de->dir,
 450                                                &pinfo->sharpen_factor);
 451         de->sharpen_duration = debugfs_create_u32("sharpen_duration",
 452                                                   S_IRUSR | S_IWUSR, de->dir,
 453                                                   &pinfo->sharpen_duration);
 454         de->norm_offset = debugfs_create_u32("norm_offset",
 455                                              S_IRUSR | S_IWUSR, de->dir,
 456                                              &pinfo->norm_offset);
 457         de->fast_start = debugfs_create_bool("fast_start",
 458                                              S_IRUSR | S_IWUSR, de->dir,
 459                                              &pinfo->fast_start);
 460 #endif
 461
 462         return pinfo;
 463 }
 464
 465 static void rate_control_pid_free(void *priv)
 466 {
 467         struct rc_pid_info *pinfo = priv;
 468 #ifdef CONFIG_MAC80211_DEBUGFS
 469         struct rc_pid_debugfs_entries *de = &pinfo->dentries;
 470
 471         debugfs_remove(de->fast_start);
 472         debugfs_remove(de->norm_offset);
 473         debugfs_remove(de->sharpen_duration);
 474         debugfs_remove(de->sharpen_factor);
 475         debugfs_remove(de->smoothing_shift);
 476         debugfs_remove(de->coeff_d);
 477         debugfs_remove(de->coeff_i);
 478         debugfs_remove(de->coeff_p);
 479         debugfs_remove(de->sampling_period);
 480         debugfs_remove(de->target);
 481         debugfs_remove(de->dir);
 482 #endif
 483
 484         kfree(pinfo->rinfo);
 485         kfree(pinfo);
 486 }
 487
 488 static void rate_control_pid_clear(void *priv)
 489 {
 490 }
 491
 492 static void *rate_control_pid_alloc_sta(void *priv, gfp_t gfp)
 493 {
 494         struct rc_pid_sta_info *spinfo;
 495
 496         spinfo = kzalloc(sizeof(*spinfo), gfp);
 497         if (spinfo == NULL)
 498                 return NULL;
 499
 500         spinfo->last_sample = jiffies;
 501
 502 #ifdef CONFIG_MAC80211_DEBUGFS
 503         spin_lock_init(&spinfo->events.lock);
 504         init_waitqueue_head(&spinfo->events.waitqueue);
 505 #endif
 506
 507         return spinfo;
 508 }
 509
 510 static void rate_control_pid_free_sta(void *priv, void *priv_sta)
 511 {
 512         struct rc_pid_sta_info *spinfo = priv_sta;
 513         kfree(spinfo);
 514 }
 515
 516 static struct rate_control_ops mac80211_rcpid = {
 517         .name = "pid",
 518         .tx_status = rate_control_pid_tx_status,
 519         .get_rate = rate_control_pid_get_rate,
 520         .rate_init = rate_control_pid_rate_init,
 521         .clear = rate_control_pid_clear,
 522         .alloc = rate_control_pid_alloc,
 523         .free = rate_control_pid_free,
 524         .alloc_sta = rate_control_pid_alloc_sta,
 525         .free_sta = rate_control_pid_free_sta,
 526 #ifdef CONFIG_MAC80211_DEBUGFS
 527         .add_sta_debugfs = rate_control_pid_add_sta_debugfs,
 528         .remove_sta_debugfs = rate_control_pid_remove_sta_debugfs,
 529 #endif
 530 };
 531
 532 MODULE_DESCRIPTION("PID controller based rate control algorithm");
 533 MODULE_AUTHOR("Stefano Brivio");
 534 MODULE_AUTHOR("Mattias Nissler");
 535 MODULE_LICENSE("GPL");
 536
 537 int __init rc80211_pid_init(void)
 538 {
 539         return ieee80211_rate_control_register(&mac80211_rcpid);
 540 }
 541
 542 void rc80211_pid_exit(void)
 543 {
 544         ieee80211_rate_control_unregister(&mac80211_rcpid);
 545 }
 546
 547 #ifdef CONFIG_MAC80211_RC_PID_MODULE
 548 module_init(rc80211_pid_init);
 549 module_exit(rc80211_pid_exit);
 550 #endif