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 "rate.h"
  18 #include "mesh.h"
  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 = sta->sdata;
  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 ieee80211_sub_if_data *sdata = sta->sdata;
 152         struct rc_pid_sta_info *spinfo = sta->rate_ctrl_priv;
 153         struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
 154         struct ieee80211_supported_band *sband;
 155         u32 pf;
 156         s32 err_avg;
 157         u32 err_prop;
 158         u32 err_int;
 159         u32 err_der;
 160         int adj, i, j, tmp;
 161         unsigned long period;
 162
 163         sband = local->hw.wiphy->bands[local->hw.conf.channel->band];
 164         spinfo = sta->rate_ctrl_priv;
 165
 166         /* In case nothing happened during the previous control interval, turn
 167          * the sharpening factor on. */
 168         period = (HZ * pinfo->sampling_period + 500) / 1000;
 169         if (!period)
 170                 period = 1;
 171         if (jiffies - spinfo->last_sample > 2 * period)
 172                 spinfo->sharp_cnt = pinfo->sharpen_duration;
 173
 174         spinfo->last_sample = jiffies;
 175
 176         /* This should never happen, but in case, we assume the old sample is
 177          * still a good measurement and copy it. */
 178         if (unlikely(spinfo->tx_num_xmit == 0))
 179                 pf = spinfo->last_pf;
 180         else {
 181                 pf = spinfo->tx_num_failed * 100 / spinfo->tx_num_xmit;
 182                 if (ieee80211_vif_is_mesh(&sdata->vif) && pf == 100)
 183                         mesh_plink_broken(sta);
 184                 pf <<= RC_PID_ARITH_SHIFT;
 185                 sta->fail_avg = ((pf + (spinfo->last_pf << 3)) / 9)
 186                                         >> RC_PID_ARITH_SHIFT;
 187         }
 188
 189         spinfo->tx_num_xmit = 0;
 190         spinfo->tx_num_failed = 0;
 191
 192         /* If we just switched rate, update the rate behaviour info. */
 193         if (pinfo->oldrate != sta->txrate_idx) {
 194
 195                 i = rinfo[pinfo->oldrate].rev_index;
 196                 j = rinfo[sta->txrate_idx].rev_index;
 197
 198                 tmp = (pf - spinfo->last_pf);
 199                 tmp = RC_PID_DO_ARITH_RIGHT_SHIFT(tmp, RC_PID_ARITH_SHIFT);
 200
 201                 rinfo[j].diff = rinfo[i].diff + tmp;
 202                 pinfo->oldrate = sta->txrate_idx;
 203         }
 204         rate_control_pid_normalize(pinfo, sband->n_bitrates);
 205
 206         /* Compute the proportional, integral and derivative errors. */
 207         err_prop = (pinfo->target << RC_PID_ARITH_SHIFT) - pf;
 208
 209         err_avg = spinfo->err_avg_sc >> pinfo->smoothing_shift;
 210         spinfo->err_avg_sc = spinfo->err_avg_sc - err_avg + err_prop;
 211         err_int = spinfo->err_avg_sc >> pinfo->smoothing_shift;
 212
 213         err_der = (pf - spinfo->last_pf) *
 214                   (1 + pinfo->sharpen_factor * spinfo->sharp_cnt);
 215         spinfo->last_pf = pf;
 216         if (spinfo->sharp_cnt)
 217                         spinfo->sharp_cnt--;
 218
 219 #ifdef CONFIG_MAC80211_DEBUGFS
 220         rate_control_pid_event_pf_sample(&spinfo->events, pf, err_prop, err_int,
 221                                          err_der);
 222 #endif
 223
 224         /* Compute the controller output. */
 225         adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i
 226               + err_der * pinfo->coeff_d);
 227         adj = RC_PID_DO_ARITH_RIGHT_SHIFT(adj, 2 * RC_PID_ARITH_SHIFT);
 228
 229         /* Change rate. */
 230         if (adj)
 231                 rate_control_pid_adjust_rate(local, sta, adj, rinfo);
 232 }
 233
 234 static void rate_control_pid_tx_status(void *priv, struct net_device *dev,
 235                                        struct sk_buff *skb)
 236 {
 237         struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
 238         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 239         struct ieee80211_sub_if_data *sdata;
 240         struct rc_pid_info *pinfo = priv;
 241         struct sta_info *sta;
 242         struct rc_pid_sta_info *spinfo;
 243         unsigned long period;
 244         struct ieee80211_supported_band *sband;
 245         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 246
 247         rcu_read_lock();
 248
 249         sta = sta_info_get(local, hdr->addr1);
 250         sband = local->hw.wiphy->bands[local->hw.conf.channel->band];
 251
 252         if (!sta)
 253                 goto unlock;
 254
 255         /* Don't update the state if we're not controlling the rate. */
 256         sdata = sta->sdata;
 257         if (sdata->force_unicast_rateidx > -1) {
 258                 sta->txrate_idx = sdata->max_ratectrl_rateidx;
 259                 goto unlock;
 260         }
 261
 262         /* Ignore all frames that were sent with a different rate than the rate
 263          * we currently advise mac80211 to use. */
 264         if (info->tx_rate_idx != sta->txrate_idx)
 265                 goto unlock;
 266
 267         spinfo = sta->rate_ctrl_priv;
 268         spinfo->tx_num_xmit++;
 269
 270 #ifdef CONFIG_MAC80211_DEBUGFS
 271         rate_control_pid_event_tx_status(&spinfo->events, info);
 272 #endif
 273
 274         /* We count frames that totally failed to be transmitted as two bad
 275          * frames, those that made it out but had some retries as one good and
 276          * one bad frame. */
 277         if (info->status.excessive_retries) {
 278                 spinfo->tx_num_failed += 2;
 279                 spinfo->tx_num_xmit++;
 280         } else if (info->status.retry_count) {
 281                 spinfo->tx_num_failed++;
 282                 spinfo->tx_num_xmit++;
 283         }
 284
 285         /* Update PID controller state. */
 286         period = (HZ * pinfo->sampling_period + 500) / 1000;
 287         if (!period)
 288                 period = 1;
 289         if (time_after(jiffies, spinfo->last_sample + period))
 290                 rate_control_pid_sample(pinfo, local, sta);
 291
 292  unlock:
 293         rcu_read_unlock();
 294 }
 295
 296 static void rate_control_pid_get_rate(void *priv, struct net_device *dev,
 297                                       struct ieee80211_supported_band *sband,
 298                                       struct sk_buff *skb,
 299                                       struct rate_selection *sel)
 300 {
 301         struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
 302         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 303         struct ieee80211_sub_if_data *sdata;
 304         struct sta_info *sta;
 305         int rateidx;
 306         u16 fc;
 307
 308         rcu_read_lock();
 309
 310         sta = sta_info_get(local, hdr->addr1);
 311
 312         /* Send management frames and broadcast/multicast data using lowest
 313          * rate. */
 314         fc = le16_to_cpu(hdr->frame_control);
 315         if ((fc & IEEE80211_FCTL_FTYPE) != IEEE80211_FTYPE_DATA ||
 316             is_multicast_ether_addr(hdr->addr1) || !sta) {
 317                 sel->rate_idx = rate_lowest_index(local, sband, sta);
 318                 rcu_read_unlock();
 319                 return;
 320         }
 321
 322         /* If a forced rate is in effect, select it. */
 323         sdata = IEEE80211_DEV_TO_SUB_IF(dev);
 324         if (sdata->force_unicast_rateidx > -1)
 325                 sta->txrate_idx = sdata->force_unicast_rateidx;
 326
 327         rateidx = sta->txrate_idx;
 328
 329         if (rateidx >= sband->n_bitrates)
 330                 rateidx = sband->n_bitrates - 1;
 331
 332         sta->last_txrate_idx = rateidx;
 333
 334         rcu_read_unlock();
 335
 336         sel->rate_idx = rateidx;
 337
 338 #ifdef CONFIG_MAC80211_DEBUGFS
 339         rate_control_pid_event_tx_rate(
 340                 &((struct rc_pid_sta_info *) sta->rate_ctrl_priv)->events,
 341                 rateidx, sband->bitrates[rateidx].bitrate);
 342 #endif
 343 }
 344
 345 static void rate_control_pid_rate_init(void *priv, void *priv_sta,
 346                                           struct ieee80211_local *local,
 347                                           struct sta_info *sta)
 348 {
 349         /* TODO: This routine should consider using RSSI from previous packets
 350          * as we need to have IEEE 802.1X auth succeed immediately after assoc..
 351          * Until that method is implemented, we will use the lowest supported
 352          * rate as a workaround. */
 353         struct ieee80211_supported_band *sband;
 354
 355         sband = local->hw.wiphy->bands[local->hw.conf.channel->band];
 356         sta->txrate_idx = rate_lowest_index(local, sband, sta);
 357         sta->fail_avg = 0;
 358 }
 359
 360 static void *rate_control_pid_alloc(struct ieee80211_local *local)
 361 {
 362         struct rc_pid_info *pinfo;
 363         struct rc_pid_rateinfo *rinfo;
 364         struct ieee80211_supported_band *sband;
 365         int i, j, tmp;
 366         bool s;
 367 #ifdef CONFIG_MAC80211_DEBUGFS
 368         struct rc_pid_debugfs_entries *de;
 369 #endif
 370
 371         sband = local->hw.wiphy->bands[local->hw.conf.channel->band];
 372
 373         pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
 374         if (!pinfo)
 375                 return NULL;
 376
 377         /* We can safely assume that sband won't change unless we get
 378          * reinitialized. */
 379         rinfo = kmalloc(sizeof(*rinfo) * sband->n_bitrates, GFP_ATOMIC);
 380         if (!rinfo) {
 381                 kfree(pinfo);
 382                 return NULL;
 383         }
 384
 385         pinfo->target = RC_PID_TARGET_PF;
 386         pinfo->sampling_period = RC_PID_INTERVAL;
 387         pinfo->coeff_p = RC_PID_COEFF_P;
 388         pinfo->coeff_i = RC_PID_COEFF_I;
 389         pinfo->coeff_d = RC_PID_COEFF_D;
 390         pinfo->smoothing_shift = RC_PID_SMOOTHING_SHIFT;
 391         pinfo->sharpen_factor = RC_PID_SHARPENING_FACTOR;
 392         pinfo->sharpen_duration = RC_PID_SHARPENING_DURATION;
 393         pinfo->norm_offset = RC_PID_NORM_OFFSET;
 394         pinfo->rinfo = rinfo;
 395         pinfo->oldrate = 0;
 396
 397         /* Sort the rates. This is optimized for the most common case (i.e.
 398          * almost-sorted CCK+OFDM rates). Kind of bubble-sort with reversed
 399          * mapping too. */
 400         for (i = 0; i < sband->n_bitrates; i++) {
 401                 rinfo[i].index = i;
 402                 rinfo[i].rev_index = i;
 403                 if (RC_PID_FAST_START)
 404                         rinfo[i].diff = 0;
 405                 else
 406                         rinfo[i].diff = i * pinfo->norm_offset;
 407         }
 408         for (i = 1; i < sband->n_bitrates; i++) {
 409                 s = 0;
 410                 for (j = 0; j < sband->n_bitrates - i; j++)
 411                         if (unlikely(sband->bitrates[rinfo[j].index].bitrate >
 412                                      sband->bitrates[rinfo[j + 1].index].bitrate)) {
 413                                 tmp = rinfo[j].index;
 414                                 rinfo[j].index = rinfo[j + 1].index;
 415                                 rinfo[j + 1].index = tmp;
 416                                 rinfo[rinfo[j].index].rev_index = j;
 417                                 rinfo[rinfo[j + 1].index].rev_index = j + 1;
 418                                 s = 1;
 419                         }
 420                 if (!s)
 421                         break;
 422         }
 423
 424 #ifdef CONFIG_MAC80211_DEBUGFS
 425         de = &pinfo->dentries;
 426         de->dir = debugfs_create_dir("rc80211_pid",
 427                                      local->hw.wiphy->debugfsdir);
 428         de->target = debugfs_create_u32("target_pf", S_IRUSR | S_IWUSR,
 429                                         de->dir, &pinfo->target);
 430         de->sampling_period = debugfs_create_u32("sampling_period",
 431                                                  S_IRUSR | S_IWUSR, de->dir,
 432                                                  &pinfo->sampling_period);
 433         de->coeff_p = debugfs_create_u32("coeff_p", S_IRUSR | S_IWUSR,
 434                                          de->dir, &pinfo->coeff_p);
 435         de->coeff_i = debugfs_create_u32("coeff_i", S_IRUSR | S_IWUSR,
 436                                          de->dir, &pinfo->coeff_i);
 437         de->coeff_d = debugfs_create_u32("coeff_d", S_IRUSR | S_IWUSR,
 438                                          de->dir, &pinfo->coeff_d);
 439         de->smoothing_shift = debugfs_create_u32("smoothing_shift",
 440                                                  S_IRUSR | S_IWUSR, de->dir,
 441                                                  &pinfo->smoothing_shift);
 442         de->sharpen_factor = debugfs_create_u32("sharpen_factor",
 443                                                S_IRUSR | S_IWUSR, de->dir,
 444                                                &pinfo->sharpen_factor);
 445         de->sharpen_duration = debugfs_create_u32("sharpen_duration",
 446                                                   S_IRUSR | S_IWUSR, de->dir,
 447                                                   &pinfo->sharpen_duration);
 448         de->norm_offset = debugfs_create_u32("norm_offset",
 449                                              S_IRUSR | S_IWUSR, de->dir,
 450                                              &pinfo->norm_offset);
 451 #endif
 452
 453         return pinfo;
 454 }
 455
 456 static void rate_control_pid_free(void *priv)
 457 {
 458         struct rc_pid_info *pinfo = priv;
 459 #ifdef CONFIG_MAC80211_DEBUGFS
 460         struct rc_pid_debugfs_entries *de = &pinfo->dentries;
 461
 462         debugfs_remove(de->norm_offset);
 463         debugfs_remove(de->sharpen_duration);
 464         debugfs_remove(de->sharpen_factor);
 465         debugfs_remove(de->smoothing_shift);
 466         debugfs_remove(de->coeff_d);
 467         debugfs_remove(de->coeff_i);
 468         debugfs_remove(de->coeff_p);
 469         debugfs_remove(de->sampling_period);
 470         debugfs_remove(de->target);
 471         debugfs_remove(de->dir);
 472 #endif
 473
 474         kfree(pinfo->rinfo);
 475         kfree(pinfo);
 476 }
 477
 478 static void rate_control_pid_clear(void *priv)
 479 {
 480 }
 481
 482 static void *rate_control_pid_alloc_sta(void *priv, gfp_t gfp)
 483 {
 484         struct rc_pid_sta_info *spinfo;
 485
 486         spinfo = kzalloc(sizeof(*spinfo), gfp);
 487         if (spinfo == NULL)
 488                 return NULL;
 489
 490         spinfo->last_sample = jiffies;
 491
 492 #ifdef CONFIG_MAC80211_DEBUGFS
 493         spin_lock_init(&spinfo->events.lock);
 494         init_waitqueue_head(&spinfo->events.waitqueue);
 495 #endif
 496
 497         return spinfo;
 498 }
 499
 500 static void rate_control_pid_free_sta(void *priv, void *priv_sta)
 501 {
 502         struct rc_pid_sta_info *spinfo = priv_sta;
 503         kfree(spinfo);
 504 }
 505
 506 static struct rate_control_ops mac80211_rcpid = {
 507         .name = "pid",
 508         .tx_status = rate_control_pid_tx_status,
 509         .get_rate = rate_control_pid_get_rate,
 510         .rate_init = rate_control_pid_rate_init,
 511         .clear = rate_control_pid_clear,
 512         .alloc = rate_control_pid_alloc,
 513         .free = rate_control_pid_free,
 514         .alloc_sta = rate_control_pid_alloc_sta,
 515         .free_sta = rate_control_pid_free_sta,
 516 #ifdef CONFIG_MAC80211_DEBUGFS
 517         .add_sta_debugfs = rate_control_pid_add_sta_debugfs,
 518         .remove_sta_debugfs = rate_control_pid_remove_sta_debugfs,
 519 #endif
 520 };
 521
 522 int __init rc80211_pid_init(void)
 523 {
 524         return ieee80211_rate_control_register(&mac80211_rcpid);
 525 }
 526
 527 void rc80211_pid_exit(void)
 528 {
 529         ieee80211_rate_control_unregister(&mac80211_rcpid);
 530 }