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 #ifdef CONFIG_MAC80211_MESH
 152         struct ieee80211_sub_if_data *sdata = sta->sdata;
 153 #endif
 154         struct rc_pid_sta_info *spinfo = sta->rate_ctrl_priv;
 155         struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
 156         struct ieee80211_supported_band *sband;
 157         u32 pf;
 158         s32 err_avg;
 159         u32 err_prop;
 160         u32 err_int;
 161         u32 err_der;
 162         int adj, i, j, tmp;
 163         unsigned long period;
 164
 165         sband = local->hw.wiphy->bands[local->hw.conf.channel->band];
 166         spinfo = sta->rate_ctrl_priv;
 167
 168         /* In case nothing happened during the previous control interval, turn
 169          * the sharpening factor on. */
 170         period = (HZ * pinfo->sampling_period + 500) / 1000;
 171         if (!period)
 172                 period = 1;
 173         if (jiffies - spinfo->last_sample > 2 * period)
 174                 spinfo->sharp_cnt = pinfo->sharpen_duration;
 175
 176         spinfo->last_sample = jiffies;
 177
 178         /* This should never happen, but in case, we assume the old sample is
 179          * still a good measurement and copy it. */
 180         if (unlikely(spinfo->tx_num_xmit == 0))
 181                 pf = spinfo->last_pf;
 182         else {
 183                 pf = spinfo->tx_num_failed * 100 / spinfo->tx_num_xmit;
 184 #ifdef CONFIG_MAC80211_MESH
 185                 if (pf == 100 &&
 186                     sdata->vif.type == IEEE80211_IF_TYPE_MESH_POINT)
 187                         mesh_plink_broken(sta);
 188 #endif
 189                 pf <<= RC_PID_ARITH_SHIFT;
 190                 sta->fail_avg = ((pf + (spinfo->last_pf << 3)) / 9)
 191                                         >> RC_PID_ARITH_SHIFT;
 192         }
 193
 194         spinfo->tx_num_xmit = 0;
 195         spinfo->tx_num_failed = 0;
 196
 197         /* If we just switched rate, update the rate behaviour info. */
 198         if (pinfo->oldrate != sta->txrate_idx) {
 199
 200                 i = rinfo[pinfo->oldrate].rev_index;
 201                 j = rinfo[sta->txrate_idx].rev_index;
 202
 203                 tmp = (pf - spinfo->last_pf);
 204                 tmp = RC_PID_DO_ARITH_RIGHT_SHIFT(tmp, RC_PID_ARITH_SHIFT);
 205
 206                 rinfo[j].diff = rinfo[i].diff + tmp;
 207                 pinfo->oldrate = sta->txrate_idx;
 208         }
 209         rate_control_pid_normalize(pinfo, sband->n_bitrates);
 210
 211         /* Compute the proportional, integral and derivative errors. */
 212         err_prop = (pinfo->target << RC_PID_ARITH_SHIFT) - pf;
 213
 214         err_avg = spinfo->err_avg_sc >> pinfo->smoothing_shift;
 215         spinfo->err_avg_sc = spinfo->err_avg_sc - err_avg + err_prop;
 216         err_int = spinfo->err_avg_sc >> pinfo->smoothing_shift;
 217
 218         err_der = (pf - spinfo->last_pf) *
 219                   (1 + pinfo->sharpen_factor * spinfo->sharp_cnt);
 220         spinfo->last_pf = pf;
 221         if (spinfo->sharp_cnt)
 222                         spinfo->sharp_cnt--;
 223
 224 #ifdef CONFIG_MAC80211_DEBUGFS
 225         rate_control_pid_event_pf_sample(&spinfo->events, pf, err_prop, err_int,
 226                                          err_der);
 227 #endif
 228
 229         /* Compute the controller output. */
 230         adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i
 231               + err_der * pinfo->coeff_d);
 232         adj = RC_PID_DO_ARITH_RIGHT_SHIFT(adj, 2 * RC_PID_ARITH_SHIFT);
 233
 234         /* Change rate. */
 235         if (adj)
 236                 rate_control_pid_adjust_rate(local, sta, adj, rinfo);
 237 }
 238
 239 static void rate_control_pid_tx_status(void *priv, struct net_device *dev,
 240                                        struct sk_buff *skb)
 241 {
 242         struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
 243         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 244         struct ieee80211_sub_if_data *sdata;
 245         struct rc_pid_info *pinfo = priv;
 246         struct sta_info *sta;
 247         struct rc_pid_sta_info *spinfo;
 248         unsigned long period;
 249         struct ieee80211_supported_band *sband;
 250         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 251
 252         rcu_read_lock();
 253
 254         sta = sta_info_get(local, hdr->addr1);
 255         sband = local->hw.wiphy->bands[local->hw.conf.channel->band];
 256
 257         if (!sta)
 258                 goto unlock;
 259
 260         /* Don't update the state if we're not controlling the rate. */
 261         sdata = sta->sdata;
 262         if (sdata->force_unicast_rateidx > -1) {
 263                 sta->txrate_idx = sdata->max_ratectrl_rateidx;
 264                 goto unlock;
 265         }
 266
 267         /* Ignore all frames that were sent with a different rate than the rate
 268          * we currently advise mac80211 to use. */
 269         if (info->tx_rate_idx != sta->txrate_idx)
 270                 goto unlock;
 271
 272         spinfo = sta->rate_ctrl_priv;
 273         spinfo->tx_num_xmit++;
 274
 275 #ifdef CONFIG_MAC80211_DEBUGFS
 276         rate_control_pid_event_tx_status(&spinfo->events, info);
 277 #endif
 278
 279         /* We count frames that totally failed to be transmitted as two bad
 280          * frames, those that made it out but had some retries as one good and
 281          * one bad frame. */
 282         if (info->status.excessive_retries) {
 283                 spinfo->tx_num_failed += 2;
 284                 spinfo->tx_num_xmit++;
 285         } else if (info->status.retry_count) {
 286                 spinfo->tx_num_failed++;
 287                 spinfo->tx_num_xmit++;
 288         }
 289
 290         if (info->status.excessive_retries) {
 291                 sta->tx_retry_failed++;
 292                 sta->tx_num_consecutive_failures++;
 293                 sta->tx_num_mpdu_fail++;
 294         } else {
 295                 sta->tx_num_consecutive_failures = 0;
 296                 sta->tx_num_mpdu_ok++;
 297         }
 298         sta->tx_retry_count += info->status.retry_count;
 299         sta->tx_num_mpdu_fail += info->status.retry_count;
 300
 301         /* Update PID controller state. */
 302         period = (HZ * pinfo->sampling_period + 500) / 1000;
 303         if (!period)
 304                 period = 1;
 305         if (time_after(jiffies, spinfo->last_sample + period))
 306                 rate_control_pid_sample(pinfo, local, sta);
 307
 308  unlock:
 309         rcu_read_unlock();
 310 }
 311
 312 static void rate_control_pid_get_rate(void *priv, struct net_device *dev,
 313                                       struct ieee80211_supported_band *sband,
 314                                       struct sk_buff *skb,
 315                                       struct rate_selection *sel)
 316 {
 317         struct ieee80211_local *local = wdev_priv(dev->ieee80211_ptr);
 318         struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 319         struct ieee80211_sub_if_data *sdata;
 320         struct sta_info *sta;
 321         int rateidx;
 322         u16 fc;
 323
 324         rcu_read_lock();
 325
 326         sta = sta_info_get(local, hdr->addr1);
 327
 328         /* Send management frames and broadcast/multicast data using lowest
 329          * rate. */
 330         fc = le16_to_cpu(hdr->frame_control);
 331         if ((fc & IEEE80211_FCTL_FTYPE) != IEEE80211_FTYPE_DATA ||
 332             is_multicast_ether_addr(hdr->addr1) || !sta) {
 333                 sel->rate_idx = rate_lowest_index(local, sband, sta);
 334                 rcu_read_unlock();
 335                 return;
 336         }
 337
 338         /* If a forced rate is in effect, select it. */
 339         sdata = IEEE80211_DEV_TO_SUB_IF(dev);
 340         if (sdata->force_unicast_rateidx > -1)
 341                 sta->txrate_idx = sdata->force_unicast_rateidx;
 342
 343         rateidx = sta->txrate_idx;
 344
 345         if (rateidx >= sband->n_bitrates)
 346                 rateidx = sband->n_bitrates - 1;
 347
 348         sta->last_txrate_idx = rateidx;
 349
 350         rcu_read_unlock();
 351
 352         sel->rate_idx = rateidx;
 353
 354 #ifdef CONFIG_MAC80211_DEBUGFS
 355         rate_control_pid_event_tx_rate(
 356                 &((struct rc_pid_sta_info *) sta->rate_ctrl_priv)->events,
 357                 rateidx, sband->bitrates[rateidx].bitrate);
 358 #endif
 359 }
 360
 361 static void rate_control_pid_rate_init(void *priv, void *priv_sta,
 362                                           struct ieee80211_local *local,
 363                                           struct sta_info *sta)
 364 {
 365         /* TODO: This routine should consider using RSSI from previous packets
 366          * as we need to have IEEE 802.1X auth succeed immediately after assoc..
 367          * Until that method is implemented, we will use the lowest supported
 368          * rate as a workaround. */
 369         struct ieee80211_supported_band *sband;
 370
 371         sband = local->hw.wiphy->bands[local->hw.conf.channel->band];
 372         sta->txrate_idx = rate_lowest_index(local, sband, sta);
 373         sta->fail_avg = 0;
 374 }
 375
 376 static void *rate_control_pid_alloc(struct ieee80211_local *local)
 377 {
 378         struct rc_pid_info *pinfo;
 379         struct rc_pid_rateinfo *rinfo;
 380         struct ieee80211_supported_band *sband;
 381         int i, j, tmp;
 382         bool s;
 383 #ifdef CONFIG_MAC80211_DEBUGFS
 384         struct rc_pid_debugfs_entries *de;
 385 #endif
 386
 387         sband = local->hw.wiphy->bands[local->hw.conf.channel->band];
 388
 389         pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
 390         if (!pinfo)
 391                 return NULL;
 392
 393         /* We can safely assume that sband won't change unless we get
 394          * reinitialized. */
 395         rinfo = kmalloc(sizeof(*rinfo) * sband->n_bitrates, GFP_ATOMIC);
 396         if (!rinfo) {
 397                 kfree(pinfo);
 398                 return NULL;
 399         }
 400
 401         pinfo->target = RC_PID_TARGET_PF;
 402         pinfo->sampling_period = RC_PID_INTERVAL;
 403         pinfo->coeff_p = RC_PID_COEFF_P;
 404         pinfo->coeff_i = RC_PID_COEFF_I;
 405         pinfo->coeff_d = RC_PID_COEFF_D;
 406         pinfo->smoothing_shift = RC_PID_SMOOTHING_SHIFT;
 407         pinfo->sharpen_factor = RC_PID_SHARPENING_FACTOR;
 408         pinfo->sharpen_duration = RC_PID_SHARPENING_DURATION;
 409         pinfo->norm_offset = RC_PID_NORM_OFFSET;
 410         pinfo->rinfo = rinfo;
 411         pinfo->oldrate = 0;
 412
 413         /* Sort the rates. This is optimized for the most common case (i.e.
 414          * almost-sorted CCK+OFDM rates). Kind of bubble-sort with reversed
 415          * mapping too. */
 416         for (i = 0; i < sband->n_bitrates; i++) {
 417                 rinfo[i].index = i;
 418                 rinfo[i].rev_index = i;
 419                 if (RC_PID_FAST_START)
 420                         rinfo[i].diff = 0;
 421                 else
 422                         rinfo[i].diff = i * pinfo->norm_offset;
 423         }
 424         for (i = 1; i < sband->n_bitrates; i++) {
 425                 s = 0;
 426                 for (j = 0; j < sband->n_bitrates - i; j++)
 427                         if (unlikely(sband->bitrates[rinfo[j].index].bitrate >
 428                                      sband->bitrates[rinfo[j + 1].index].bitrate)) {
 429                                 tmp = rinfo[j].index;
 430                                 rinfo[j].index = rinfo[j + 1].index;
 431                                 rinfo[j + 1].index = tmp;
 432                                 rinfo[rinfo[j].index].rev_index = j;
 433                                 rinfo[rinfo[j + 1].index].rev_index = j + 1;
 434                                 s = 1;
 435                         }
 436                 if (!s)
 437                         break;
 438         }
 439
 440 #ifdef CONFIG_MAC80211_DEBUGFS
 441         de = &pinfo->dentries;
 442         de->dir = debugfs_create_dir("rc80211_pid",
 443                                      local->hw.wiphy->debugfsdir);
 444         de->target = debugfs_create_u32("target_pf", S_IRUSR | S_IWUSR,
 445                                         de->dir, &pinfo->target);
 446         de->sampling_period = debugfs_create_u32("sampling_period",
 447                                                  S_IRUSR | S_IWUSR, de->dir,
 448                                                  &pinfo->sampling_period);
 449         de->coeff_p = debugfs_create_u32("coeff_p", S_IRUSR | S_IWUSR,
 450                                          de->dir, &pinfo->coeff_p);
 451         de->coeff_i = debugfs_create_u32("coeff_i", S_IRUSR | S_IWUSR,
 452                                          de->dir, &pinfo->coeff_i);
 453         de->coeff_d = debugfs_create_u32("coeff_d", S_IRUSR | S_IWUSR,
 454                                          de->dir, &pinfo->coeff_d);
 455         de->smoothing_shift = debugfs_create_u32("smoothing_shift",
 456                                                  S_IRUSR | S_IWUSR, de->dir,
 457                                                  &pinfo->smoothing_shift);
 458         de->sharpen_factor = debugfs_create_u32("sharpen_factor",
 459                                                S_IRUSR | S_IWUSR, de->dir,
 460                                                &pinfo->sharpen_factor);
 461         de->sharpen_duration = debugfs_create_u32("sharpen_duration",
 462                                                   S_IRUSR | S_IWUSR, de->dir,
 463                                                   &pinfo->sharpen_duration);
 464         de->norm_offset = debugfs_create_u32("norm_offset",
 465                                              S_IRUSR | S_IWUSR, de->dir,
 466                                              &pinfo->norm_offset);
 467 #endif
 468
 469         return pinfo;
 470 }
 471
 472 static void rate_control_pid_free(void *priv)
 473 {
 474         struct rc_pid_info *pinfo = priv;
 475 #ifdef CONFIG_MAC80211_DEBUGFS
 476         struct rc_pid_debugfs_entries *de = &pinfo->dentries;
 477
 478         debugfs_remove(de->norm_offset);
 479         debugfs_remove(de->sharpen_duration);
 480         debugfs_remove(de->sharpen_factor);
 481         debugfs_remove(de->smoothing_shift);
 482         debugfs_remove(de->coeff_d);
 483         debugfs_remove(de->coeff_i);
 484         debugfs_remove(de->coeff_p);
 485         debugfs_remove(de->sampling_period);
 486         debugfs_remove(de->target);
 487         debugfs_remove(de->dir);
 488 #endif
 489
 490         kfree(pinfo->rinfo);
 491         kfree(pinfo);
 492 }
 493
 494 static void rate_control_pid_clear(void *priv)
 495 {
 496 }
 497
 498 static void *rate_control_pid_alloc_sta(void *priv, gfp_t gfp)
 499 {
 500         struct rc_pid_sta_info *spinfo;
 501
 502         spinfo = kzalloc(sizeof(*spinfo), gfp);
 503         if (spinfo == NULL)
 504                 return NULL;
 505
 506         spinfo->last_sample = jiffies;
 507
 508 #ifdef CONFIG_MAC80211_DEBUGFS
 509         spin_lock_init(&spinfo->events.lock);
 510         init_waitqueue_head(&spinfo->events.waitqueue);
 511 #endif
 512
 513         return spinfo;
 514 }
 515
 516 static void rate_control_pid_free_sta(void *priv, void *priv_sta)
 517 {
 518         struct rc_pid_sta_info *spinfo = priv_sta;
 519         kfree(spinfo);
 520 }
 521
 522 static struct rate_control_ops mac80211_rcpid = {
 523         .name = "pid",
 524         .tx_status = rate_control_pid_tx_status,
 525         .get_rate = rate_control_pid_get_rate,
 526         .rate_init = rate_control_pid_rate_init,
 527         .clear = rate_control_pid_clear,
 528         .alloc = rate_control_pid_alloc,
 529         .free = rate_control_pid_free,
 530         .alloc_sta = rate_control_pid_alloc_sta,
 531         .free_sta = rate_control_pid_free_sta,
 532 #ifdef CONFIG_MAC80211_DEBUGFS
 533         .add_sta_debugfs = rate_control_pid_add_sta_debugfs,
 534         .remove_sta_debugfs = rate_control_pid_remove_sta_debugfs,
 535 #endif
 536 };
 537
 538 int __init rc80211_pid_init(void)
 539 {
 540         return ieee80211_rate_control_register(&mac80211_rcpid);
 541 }
 542
 543 void rc80211_pid_exit(void)
 544 {
 545         ieee80211_rate_control_unregister(&mac80211_rcpid);
 546 }