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 /* Adjust the rate while ensuring that we won't switch to a lower rate if it
  67  * exhibited a worse failed frames behaviour and we'll choose the highest rate
  68  * whose failed frames behaviour is not worse than the one of the original rate
  69  * target. While at it, check that the new rate is valid. */
  70 static void rate_control_pid_adjust_rate(struct ieee80211_local *local,
  71                                          struct sta_info *sta, int adj,
  72                                          struct rc_pid_rateinfo *rinfo)
  73 {
  74         struct ieee80211_sub_if_data *sdata;
  75         struct ieee80211_hw_mode *mode;
  76         int cur_sorted, new_sorted, probe, tmp, n_bitrates;
  77         int cur = sta->txrate;
  78
  79         sdata = IEEE80211_DEV_TO_SUB_IF(sta->dev);
  80
  81         mode = local->oper_hw_mode;
  82         n_bitrates = mode->num_rates;
  83
  84         /* Map passed arguments to sorted values. */
  85         cur_sorted = rinfo[cur].rev_index;
  86         new_sorted = cur_sorted + adj;
  87
  88         /* Check limits. */
  89         if (new_sorted < 0)
  90                 new_sorted = rinfo[0].rev_index;
  91         else if (new_sorted >= n_bitrates)
  92                 new_sorted = rinfo[n_bitrates - 1].rev_index;
  93
  94         tmp = new_sorted;
  95
  96         if (adj < 0) {
  97                 /* Ensure that the rate decrease isn't disadvantageous. */
  98                 for (probe = cur_sorted; probe >= new_sorted; probe--)
  99                         if (rinfo[probe].diff <= rinfo[cur_sorted].diff &&
 100                             rate_supported(sta, mode, rinfo[probe].index))
 101                                 tmp = probe;
 102         } else {
 103                 /* Look for rate increase with zero (or below) cost. */
 104                 for (probe = new_sorted + 1; probe < n_bitrates; probe++)
 105                         if (rinfo[probe].diff <= rinfo[new_sorted].diff &&
 106                             rate_supported(sta, mode, rinfo[probe].index))
 107                                 tmp = probe;
 108         }
 109
 110         /* Fit the rate found to the nearest supported rate. */
 111         do {
 112                 if (rate_supported(sta, mode, rinfo[tmp].index)) {
 113                         sta->txrate = rinfo[tmp].index;
 114                         break;
 115                 }
 116                 if (adj < 0)
 117                         tmp--;
 118                 else
 119                         tmp++;
 120         } while (tmp < n_bitrates && tmp >= 0);
 121
 122 #ifdef CONFIG_MAC80211_DEBUGFS
 123         rate_control_pid_event_rate_change(
 124                 &((struct rc_pid_sta_info *)sta->rate_ctrl_priv)->events,
 125                 cur, mode->rates[cur].rate);
 126 #endif
 127 }
 128
 129 /* Normalize the failed frames per-rate differences. */
 130 static void rate_control_pid_normalize(struct rc_pid_info *pinfo, int l)
 131 {
 132         int i, norm_offset = pinfo->norm_offset;
 133         struct rc_pid_rateinfo *r = pinfo->rinfo;
 134
 135         if (r[0].diff > norm_offset)
 136                 r[0].diff -= norm_offset;
 137         else if (r[0].diff < -norm_offset)
 138                 r[0].diff += norm_offset;
 139         for (i = 0; i < l - 1; i++)
 140                 if (r[i + 1].diff > r[i].diff + norm_offset)
 141                         r[i + 1].diff -= norm_offset;
 142                 else if (r[i + 1].diff <= r[i].diff)
 143                         r[i + 1].diff += norm_offset;
 144 }
 145
 146 static void rate_control_pid_sample(struct rc_pid_info *pinfo,
 147                                     struct ieee80211_local *local,
 148                                     struct sta_info *sta)
 149 {
 150         struct rc_pid_sta_info *spinfo = sta->rate_ctrl_priv;
 151         struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
 152         struct ieee80211_hw_mode *mode;
 153         u32 pf;
 154         s32 err_avg;
 155         u32 err_prop;
 156         u32 err_int;
 157         u32 err_der;
 158         int adj, i, j, tmp;
 159         unsigned long period;
 160
 161         mode = local->oper_hw_mode;
 162         spinfo = sta->rate_ctrl_priv;
 163
 164         /* In case nothing happened during the previous control interval, turn
 165          * the sharpening factor on. */
 166         period = (HZ * pinfo->sampling_period + 500) / 1000;
 167         if (!period)
 168                 period = 1;
 169         if (jiffies - spinfo->last_sample > 2 * period)
 170                 spinfo->sharp_cnt = pinfo->sharpen_duration;
 171
 172         spinfo->last_sample = jiffies;
 173
 174         /* This should never happen, but in case, we assume the old sample is
 175          * still a good measurement and copy it. */
 176         if (unlikely(spinfo->tx_num_xmit == 0))
 177                 pf = spinfo->last_pf;
 178         else {
 179                 pf = spinfo->tx_num_failed * 100 / spinfo->tx_num_xmit;
 180                 pf <<= RC_PID_ARITH_SHIFT;
 181         }
 182
 183         spinfo->tx_num_xmit = 0;
 184         spinfo->tx_num_failed = 0;
 185
 186         /* If we just switched rate, update the rate behaviour info. */
 187         if (pinfo->oldrate != sta->txrate) {
 188
 189                 i = rinfo[pinfo->oldrate].rev_index;
 190                 j = rinfo[sta->txrate].rev_index;
 191
 192                 tmp = (pf - spinfo->last_pf);
 193                 tmp = RC_PID_DO_ARITH_RIGHT_SHIFT(tmp, RC_PID_ARITH_SHIFT);
 194
 195                 rinfo[j].diff = rinfo[i].diff + tmp;
 196                 pinfo->oldrate = sta->txrate;
 197         }
 198         rate_control_pid_normalize(pinfo, mode->num_rates);
 199
 200         /* Compute the proportional, integral and derivative errors. */
 201         err_prop = (pinfo->target << RC_PID_ARITH_SHIFT) - pf;
 202
 203         err_avg = spinfo->err_avg_sc >> pinfo->smoothing_shift;
 204         spinfo->err_avg_sc = spinfo->err_avg_sc - err_avg + err_prop;
 205         err_int = spinfo->err_avg_sc >> pinfo->smoothing_shift;
 206
 207         err_der = (pf - spinfo->last_pf) *
 208                   (1 + pinfo->sharpen_factor * spinfo->sharp_cnt);
 209         spinfo->last_pf = pf;
 210         if (spinfo->sharp_cnt)
 211                         spinfo->sharp_cnt--;
 212
 213 #ifdef CONFIG_MAC80211_DEBUGFS
 214         rate_control_pid_event_pf_sample(&spinfo->events, pf, err_prop, err_int,
 215                                          err_der);
 216 #endif
 217
 218         /* Compute the controller output. */
 219         adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i
 220               + err_der * pinfo->coeff_d);
 221         adj = RC_PID_DO_ARITH_RIGHT_SHIFT(adj, 2 * RC_PID_ARITH_SHIFT);
 222
 223         /* Change rate. */
 224         if (adj)
 225                 rate_control_pid_adjust_rate(local, sta, adj, rinfo);
 226 }
 227
 228 static void rate_control_pid_tx_status(void *priv, struct net_device *dev,
 229                                        struct sk_buff *skb,
 230                                        struct ieee80211_tx_status *status)
 231 {
 232         struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
 233         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 234         struct ieee80211_sub_if_data *sdata;
 235         struct rc_pid_info *pinfo = priv;
 236         struct sta_info *sta;
 237         struct rc_pid_sta_info *spinfo;
 238         unsigned long period;
 239
 240         sta = sta_info_get(local, hdr->addr1);
 241
 242         if (!sta)
 243                 return;
 244
 245         /* Don't update the state if we're not controlling the rate. */
 246         sdata = IEEE80211_DEV_TO_SUB_IF(sta->dev);
 247         if (sdata->bss && sdata->bss->force_unicast_rateidx > -1) {
 248                 sta->txrate = sdata->bss->max_ratectrl_rateidx;
 249                 return;
 250         }
 251
 252         /* Ignore all frames that were sent with a different rate than the rate
 253          * we currently advise mac80211 to use. */
 254         if (status->control.rate != &local->oper_hw_mode->rates[sta->txrate])
 255                 goto ignore;
 256
 257         spinfo = sta->rate_ctrl_priv;
 258         spinfo->tx_num_xmit++;
 259
 260 #ifdef CONFIG_MAC80211_DEBUGFS
 261         rate_control_pid_event_tx_status(&spinfo->events, status);
 262 #endif
 263
 264         /* We count frames that totally failed to be transmitted as two bad
 265          * frames, those that made it out but had some retries as one good and
 266          * one bad frame. */
 267         if (status->excessive_retries) {
 268                 spinfo->tx_num_failed += 2;
 269                 spinfo->tx_num_xmit++;
 270         } else if (status->retry_count) {
 271                 spinfo->tx_num_failed++;
 272                 spinfo->tx_num_xmit++;
 273         }
 274
 275         if (status->excessive_retries) {
 276                 sta->tx_retry_failed++;
 277                 sta->tx_num_consecutive_failures++;
 278                 sta->tx_num_mpdu_fail++;
 279         } else {
 280                 sta->last_ack_rssi[0] = sta->last_ack_rssi[1];
 281                 sta->last_ack_rssi[1] = sta->last_ack_rssi[2];
 282                 sta->last_ack_rssi[2] = status->ack_signal;
 283                 sta->tx_num_consecutive_failures = 0;
 284                 sta->tx_num_mpdu_ok++;
 285         }
 286         sta->tx_retry_count += status->retry_count;
 287         sta->tx_num_mpdu_fail += status->retry_count;
 288
 289         /* Update PID controller state. */
 290         period = (HZ * pinfo->sampling_period + 500) / 1000;
 291         if (!period)
 292                 period = 1;
 293         if (time_after(jiffies, spinfo->last_sample + period))
 294                 rate_control_pid_sample(pinfo, local, sta);
 295
 296 ignore:
 297         sta_info_put(sta);
 298 }
 299
 300 static void rate_control_pid_get_rate(void *priv, struct net_device *dev,
 301                                       struct ieee80211_hw_mode *mode,
 302                                       struct sk_buff *skb,
 303                                       struct rate_selection *sel)
 304 {
 305         struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
 306         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 307         struct ieee80211_sub_if_data *sdata;
 308         struct sta_info *sta;
 309         int rateidx;
 310         u16 fc;
 311
 312         sta = sta_info_get(local, hdr->addr1);
 313
 314         /* Send management frames and broadcast/multicast data using lowest
 315          * rate. */
 316         fc = le16_to_cpu(hdr->frame_control);
 317         if ((fc & IEEE80211_FCTL_FTYPE) != IEEE80211_FTYPE_DATA ||
 318             is_multicast_ether_addr(hdr->addr1) || !sta) {
 319                 sel->rate = rate_lowest(local, mode, sta);
 320                 if (sta)
 321                         sta_info_put(sta);
 322                 return;
 323         }
 324
 325         /* If a forced rate is in effect, select it. */
 326         sdata = IEEE80211_DEV_TO_SUB_IF(dev);
 327         if (sdata->bss && sdata->bss->force_unicast_rateidx > -1)
 328                 sta->txrate = sdata->bss->force_unicast_rateidx;
 329
 330         rateidx = sta->txrate;
 331
 332         if (rateidx >= mode->num_rates)
 333                 rateidx = mode->num_rates - 1;
 334
 335         sta->last_txrate = rateidx;
 336
 337         sta_info_put(sta);
 338
 339         sel->rate = &mode->rates[rateidx];
 340
 341 #ifdef CONFIG_MAC80211_DEBUGFS
 342         rate_control_pid_event_tx_rate(
 343                 &((struct rc_pid_sta_info *) sta->rate_ctrl_priv)->events,
 344                 rateidx, mode->rates[rateidx].rate);
 345 #endif
 346 }
 347
 348 static void rate_control_pid_rate_init(void *priv, void *priv_sta,
 349                                           struct ieee80211_local *local,
 350                                           struct sta_info *sta)
 351 {
 352         /* TODO: This routine should consider using RSSI from previous packets
 353          * as we need to have IEEE 802.1X auth succeed immediately after assoc..
 354          * Until that method is implemented, we will use the lowest supported
 355          * rate as a workaround. */
 356         sta->txrate = rate_lowest_index(local, local->oper_hw_mode, sta);
 357 }
 358
 359 static void *rate_control_pid_alloc(struct ieee80211_local *local)
 360 {
 361         struct rc_pid_info *pinfo;
 362         struct rc_pid_rateinfo *rinfo;
 363         struct ieee80211_hw_mode *mode;
 364         int i, j, tmp;
 365         bool s;
 366 #ifdef CONFIG_MAC80211_DEBUGFS
 367         struct rc_pid_debugfs_entries *de;
 368 #endif
 369
 370         pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
 371         if (!pinfo)
 372                 return NULL;
 373
 374         /* We can safely assume that oper_hw_mode won't change unless we get
 375          * reinitialized. */
 376         mode = local->oper_hw_mode;
 377         rinfo = kmalloc(sizeof(*rinfo) * mode->num_rates, GFP_ATOMIC);
 378         if (!rinfo) {
 379                 kfree(pinfo);
 380                 return NULL;
 381         }
 382
 383         /* Sort the rates. This is optimized for the most common case (i.e.
 384          * almost-sorted CCK+OFDM rates). Kind of bubble-sort with reversed
 385          * mapping too. */
 386         for (i = 0; i < mode->num_rates; i++) {
 387                 rinfo[i].index = i;
 388                 rinfo[i].rev_index = i;
 389                 if (pinfo->fast_start)
 390                         rinfo[i].diff = 0;
 391                 else
 392                         rinfo[i].diff = i * pinfo->norm_offset;
 393         }
 394         for (i = 1; i < mode->num_rates; i++) {
 395                 s = 0;
 396                 for (j = 0; j < mode->num_rates - i; j++)
 397                         if (unlikely(mode->rates[rinfo[j].index].rate >
 398                                      mode->rates[rinfo[j + 1].index].rate)) {
 399                                 tmp = rinfo[j].index;
 400                                 rinfo[j].index = rinfo[j + 1].index;
 401                                 rinfo[j + 1].index = tmp;
 402                                 rinfo[rinfo[j].index].rev_index = j;
 403                                 rinfo[rinfo[j + 1].index].rev_index = j + 1;
 404                                 s = 1;
 405                         }
 406                 if (!s)
 407                         break;
 408         }
 409
 410         pinfo->target = RC_PID_TARGET_PF;
 411         pinfo->sampling_period = RC_PID_INTERVAL;
 412         pinfo->coeff_p = RC_PID_COEFF_P;
 413         pinfo->coeff_i = RC_PID_COEFF_I;
 414         pinfo->coeff_d = RC_PID_COEFF_D;
 415         pinfo->smoothing_shift = RC_PID_SMOOTHING_SHIFT;
 416         pinfo->sharpen_factor = RC_PID_SHARPENING_FACTOR;
 417         pinfo->sharpen_duration = RC_PID_SHARPENING_DURATION;
 418         pinfo->norm_offset = RC_PID_NORM_OFFSET;
 419         pinfo->fast_start = RC_PID_FAST_START;
 420         pinfo->rinfo = rinfo;
 421         pinfo->oldrate = 0;
 422
 423 #ifdef CONFIG_MAC80211_DEBUGFS
 424         de = &pinfo->dentries;
 425         de->dir = debugfs_create_dir("rc80211_pid",
 426                                      local->hw.wiphy->debugfsdir);
 427         de->target = debugfs_create_u32("target_pf", S_IRUSR | S_IWUSR,
 428                                         de->dir, &pinfo->target);
 429         de->sampling_period = debugfs_create_u32("sampling_period",
 430                                                  S_IRUSR | S_IWUSR, de->dir,
 431                                                  &pinfo->sampling_period);
 432         de->coeff_p = debugfs_create_u32("coeff_p", S_IRUSR | S_IWUSR,
 433                                          de->dir, &pinfo->coeff_p);
 434         de->coeff_i = debugfs_create_u32("coeff_i", S_IRUSR | S_IWUSR,
 435                                          de->dir, &pinfo->coeff_i);
 436         de->coeff_d = debugfs_create_u32("coeff_d", S_IRUSR | S_IWUSR,
 437                                          de->dir, &pinfo->coeff_d);
 438         de->smoothing_shift = debugfs_create_u32("smoothing_shift",
 439                                                  S_IRUSR | S_IWUSR, de->dir,
 440                                                  &pinfo->smoothing_shift);
 441         de->sharpen_factor = debugfs_create_u32("sharpen_factor",
 442                                                S_IRUSR | S_IWUSR, de->dir,
 443                                                &pinfo->sharpen_factor);
 444         de->sharpen_duration = debugfs_create_u32("sharpen_duration",
 445                                                   S_IRUSR | S_IWUSR, de->dir,
 446                                                   &pinfo->sharpen_duration);
 447         de->norm_offset = debugfs_create_u32("norm_offset",
 448                                              S_IRUSR | S_IWUSR, de->dir,
 449                                              &pinfo->norm_offset);
 450         de->fast_start = debugfs_create_bool("fast_start",
 451                                              S_IRUSR | S_IWUSR, de->dir,
 452                                              &pinfo->fast_start);
 453 #endif
 454
 455         return pinfo;
 456 }
 457
 458 static void rate_control_pid_free(void *priv)
 459 {
 460         struct rc_pid_info *pinfo = priv;
 461 #ifdef CONFIG_MAC80211_DEBUGFS
 462         struct rc_pid_debugfs_entries *de = &pinfo->dentries;
 463
 464         debugfs_remove(de->fast_start);
 465         debugfs_remove(de->norm_offset);
 466         debugfs_remove(de->sharpen_duration);
 467         debugfs_remove(de->sharpen_factor);
 468         debugfs_remove(de->smoothing_shift);
 469         debugfs_remove(de->coeff_d);
 470         debugfs_remove(de->coeff_i);
 471         debugfs_remove(de->coeff_p);
 472         debugfs_remove(de->sampling_period);
 473         debugfs_remove(de->target);
 474         debugfs_remove(de->dir);
 475 #endif
 476
 477         kfree(pinfo->rinfo);
 478         kfree(pinfo);
 479 }
 480
 481 static void rate_control_pid_clear(void *priv)
 482 {
 483 }
 484
 485 static void *rate_control_pid_alloc_sta(void *priv, gfp_t gfp)
 486 {
 487         struct rc_pid_sta_info *spinfo;
 488
 489         spinfo = kzalloc(sizeof(*spinfo), gfp);
 490         if (spinfo == NULL)
 491                 return NULL;
 492
 493         spinfo->last_sample = jiffies;
 494
 495 #ifdef CONFIG_MAC80211_DEBUGFS
 496         spin_lock_init(&spinfo->events.lock);
 497         init_waitqueue_head(&spinfo->events.waitqueue);
 498 #endif
 499
 500         return spinfo;
 501 }
 502
 503 static void rate_control_pid_free_sta(void *priv, void *priv_sta)
 504 {
 505         struct rc_pid_sta_info *spinfo = priv_sta;
 506         kfree(spinfo);
 507 }
 508
 509 static struct rate_control_ops mac80211_rcpid = {
 510         .name = "pid",
 511         .tx_status = rate_control_pid_tx_status,
 512         .get_rate = rate_control_pid_get_rate,
 513         .rate_init = rate_control_pid_rate_init,
 514         .clear = rate_control_pid_clear,
 515         .alloc = rate_control_pid_alloc,
 516         .free = rate_control_pid_free,
 517         .alloc_sta = rate_control_pid_alloc_sta,
 518         .free_sta = rate_control_pid_free_sta,
 519 #ifdef CONFIG_MAC80211_DEBUGFS
 520         .add_sta_debugfs = rate_control_pid_add_sta_debugfs,
 521         .remove_sta_debugfs = rate_control_pid_remove_sta_debugfs,
 522 #endif
 523 };
 524
 525 MODULE_DESCRIPTION("PID controller based rate control algorithm");
 526 MODULE_AUTHOR("Stefano Brivio");
 527 MODULE_AUTHOR("Mattias Nissler");
 528 MODULE_LICENSE("GPL");
 529
 530 int __init rc80211_pid_init(void)
 531 {
 532         return ieee80211_rate_control_register(&mac80211_rcpid);
 533 }
 534
 535 void rc80211_pid_exit(void)
 536 {
 537         ieee80211_rate_control_unregister(&mac80211_rcpid);
 538 }
 539
 540 #ifdef CONFIG_MAC80211_RC_PID_MODULE
 541 module_init(rc80211_pid_init);
 542 module_exit(rc80211_pid_exit);
 543 #endif