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 <linux/slab.h>
  17 #include <net/mac80211.h>
  18 #include "rate.h"
  19 #include "mesh.h"
  20 #include "rc80211_pid.h"
  21
  22
  23 /* This is an implementation of a TX rate control algorithm that uses a PID
  24  * controller. Given a target failed frames rate, the controller decides about
  25  * TX rate changes to meet the target failed frames rate.
  26  *
  27  * The controller basically computes the following:
  28  *
  29  * adj = CP * err + CI * err_avg + CD * (err - last_err) * (1 + sharpening)
  30  *
  31  * where
  32  *      adj     adjustment value that is used to switch TX rate (see below)
  33  *      err     current error: target vs. current failed frames percentage
  34  *      last_err        last error
  35  *      err_avg average (i.e. poor man's integral) of recent errors
  36  *      sharpening      non-zero when fast response is needed (i.e. right after
  37  *                      association or no frames sent for a long time), heading
  38  *                      to zero over time
  39  *      CP      Proportional coefficient
  40  *      CI      Integral coefficient
  41  *      CD      Derivative coefficient
  42  *
  43  * CP, CI, CD are subject to careful tuning.
  44  *
  45  * The integral component uses a exponential moving average approach instead of
  46  * an actual sliding window. The advantage is that we don't need to keep an
  47  * array of the last N error values and computation is easier.
  48  *
  49  * Once we have the adj value, we map it to a rate by means of a learning
  50  * algorithm. This algorithm keeps the state of the percentual failed frames
  51  * difference between rates. The behaviour of the lowest available rate is kept
  52  * as a reference value, and every time we switch between two rates, we compute
  53  * the difference between the failed frames each rate exhibited. By doing so,
  54  * we compare behaviours which different rates exhibited in adjacent timeslices,
  55  * thus the comparison is minimally affected by external conditions. This
  56  * difference gets propagated to the whole set of measurements, so that the
  57  * reference is always the same. Periodically, we normalize this set so that
  58  * recent events weigh the most. By comparing the adj value with this set, we
  59  * avoid pejorative switches to lower rates and allow for switches to higher
  60  * rates if they behaved well.
  61  *
  62  * Note that for the computations we use a fixed-point representation to avoid
  63  * floating point arithmetic. Hence, all values are shifted left by
  64  * RC_PID_ARITH_SHIFT.
  65  */
  66
  67
  68 /* Adjust the rate while ensuring that we won't switch to a lower rate if it
  69  * exhibited a worse failed frames behaviour and we'll choose the highest rate
  70  * whose failed frames behaviour is not worse than the one of the original rate
  71  * target. While at it, check that the new rate is valid. */
  72 static void rate_control_pid_adjust_rate(struct ieee80211_supported_band *sband,
  73                                          struct ieee80211_sta *sta,
  74                                          struct rc_pid_sta_info *spinfo, int adj,
  75                                          struct rc_pid_rateinfo *rinfo)
  76 {
  77         int cur_sorted, new_sorted, probe, tmp, n_bitrates, band;
  78         int cur = spinfo->txrate_idx;
  79
  80         band = sband->band;
  81         n_bitrates = sband->n_bitrates;
  82
  83         /* Map passed arguments to sorted values. */
  84         cur_sorted = rinfo[cur].rev_index;
  85         new_sorted = cur_sorted + adj;
  86
  87         /* Check limits. */
  88         if (new_sorted < 0)
  89                 new_sorted = rinfo[0].rev_index;
  90         else if (new_sorted >= n_bitrates)
  91                 new_sorted = rinfo[n_bitrates - 1].rev_index;
  92
  93         tmp = new_sorted;
  94
  95         if (adj < 0) {
  96                 /* Ensure that the rate decrease isn't disadvantageous. */
  97                 for (probe = cur_sorted; probe >= new_sorted; probe--)
  98                         if (rinfo[probe].diff <= rinfo[cur_sorted].diff &&
  99                             rate_supported(sta, band, rinfo[probe].index))
 100                                 tmp = probe;
 101         } else {
 102                 /* Look for rate increase with zero (or below) cost. */
 103                 for (probe = new_sorted + 1; probe < n_bitrates; probe++)
 104                         if (rinfo[probe].diff <= rinfo[new_sorted].diff &&
 105                             rate_supported(sta, band, rinfo[probe].index))
 106                                 tmp = probe;
 107         }
 108
 109         /* Fit the rate found to the nearest supported rate. */
 110         do {
 111                 if (rate_supported(sta, band, rinfo[tmp].index)) {
 112                         spinfo->txrate_idx = rinfo[tmp].index;
 113                         break;
 114                 }
 115                 if (adj < 0)
 116                         tmp--;
 117                 else
 118                         tmp++;
 119         } while (tmp < n_bitrates && tmp >= 0);
 120
 121 #ifdef CONFIG_MAC80211_DEBUGFS
 122         rate_control_pid_event_rate_change(&spinfo->events,
 123                 spinfo->txrate_idx,
 124                 sband->bitrates[spinfo->txrate_idx].bitrate);
 125 #endif
 126 }
 127
 128 /* Normalize the failed frames per-rate differences. */
 129 static void rate_control_pid_normalize(struct rc_pid_info *pinfo, int l)
 130 {
 131         int i, norm_offset = pinfo->norm_offset;
 132         struct rc_pid_rateinfo *r = pinfo->rinfo;
 133
 134         if (r[0].diff > norm_offset)
 135                 r[0].diff -= norm_offset;
 136         else if (r[0].diff < -norm_offset)
 137                 r[0].diff += norm_offset;
 138         for (i = 0; i < l - 1; i++)
 139                 if (r[i + 1].diff > r[i].diff + norm_offset)
 140                         r[i + 1].diff -= norm_offset;
 141                 else if (r[i + 1].diff <= r[i].diff)
 142                         r[i + 1].diff += norm_offset;
 143 }
 144
 145 static void rate_control_pid_sample(struct rc_pid_info *pinfo,
 146                                     struct ieee80211_supported_band *sband,
 147                                     struct ieee80211_sta *sta,
 148                                     struct rc_pid_sta_info *spinfo)
 149 {
 150         struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
 151         u32 pf;
 152         s32 err_avg;
 153         u32 err_prop;
 154         u32 err_int;
 155         u32 err_der;
 156         int adj, i, j, tmp;
 157         unsigned long period;
 158
 159         /* In case nothing happened during the previous control interval, turn
 160          * the sharpening factor on. */
 161         period = msecs_to_jiffies(pinfo->sampling_period);
 162         if (jiffies - spinfo->last_sample > 2 * period)
 163                 spinfo->sharp_cnt = pinfo->sharpen_duration;
 164
 165         spinfo->last_sample = jiffies;
 166
 167         /* This should never happen, but in case, we assume the old sample is
 168          * still a good measurement and copy it. */
 169         if (unlikely(spinfo->tx_num_xmit == 0))
 170                 pf = spinfo->last_pf;
 171         else
 172                 pf = spinfo->tx_num_failed * 100 / spinfo->tx_num_xmit;
 173
 174         spinfo->tx_num_xmit = 0;
 175         spinfo->tx_num_failed = 0;
 176
 177         /* If we just switched rate, update the rate behaviour info. */
 178         if (pinfo->oldrate != spinfo->txrate_idx) {
 179
 180                 i = rinfo[pinfo->oldrate].rev_index;
 181                 j = rinfo[spinfo->txrate_idx].rev_index;
 182
 183                 tmp = (pf - spinfo->last_pf);
 184                 tmp = RC_PID_DO_ARITH_RIGHT_SHIFT(tmp, RC_PID_ARITH_SHIFT);
 185
 186                 rinfo[j].diff = rinfo[i].diff + tmp;
 187                 pinfo->oldrate = spinfo->txrate_idx;
 188         }
 189         rate_control_pid_normalize(pinfo, sband->n_bitrates);
 190
 191         /* Compute the proportional, integral and derivative errors. */
 192         err_prop = (pinfo->target - pf) << RC_PID_ARITH_SHIFT;
 193
 194         err_avg = spinfo->err_avg_sc >> pinfo->smoothing_shift;
 195         spinfo->err_avg_sc = spinfo->err_avg_sc - err_avg + err_prop;
 196         err_int = spinfo->err_avg_sc >> pinfo->smoothing_shift;
 197
 198         err_der = (pf - spinfo->last_pf) *
 199                   (1 + pinfo->sharpen_factor * spinfo->sharp_cnt);
 200         spinfo->last_pf = pf;
 201         if (spinfo->sharp_cnt)
 202                         spinfo->sharp_cnt--;
 203
 204 #ifdef CONFIG_MAC80211_DEBUGFS
 205         rate_control_pid_event_pf_sample(&spinfo->events, pf, err_prop, err_int,
 206                                          err_der);
 207 #endif
 208
 209         /* Compute the controller output. */
 210         adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i
 211               + err_der * pinfo->coeff_d);
 212         adj = RC_PID_DO_ARITH_RIGHT_SHIFT(adj, 2 * RC_PID_ARITH_SHIFT);
 213
 214         /* Change rate. */
 215         if (adj)
 216                 rate_control_pid_adjust_rate(sband, sta, spinfo, adj, rinfo);
 217 }
 218
 219 static void rate_control_pid_tx_status(void *priv, struct ieee80211_supported_band *sband,
 220                                        struct ieee80211_sta *sta, void *priv_sta,
 221                                        struct sk_buff *skb)
 222 {
 223         struct rc_pid_info *pinfo = priv;
 224         struct rc_pid_sta_info *spinfo = priv_sta;
 225         unsigned long period;
 226         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 227
 228         if (!spinfo)
 229                 return;
 230
 231         /* Ignore all frames that were sent with a different rate than the rate
 232          * we currently advise mac80211 to use. */
 233         if (info->status.rates[0].idx != spinfo->txrate_idx)
 234                 return;
 235
 236         spinfo->tx_num_xmit++;
 237
 238 #ifdef CONFIG_MAC80211_DEBUGFS
 239         rate_control_pid_event_tx_status(&spinfo->events, info);
 240 #endif
 241
 242         /* We count frames that totally failed to be transmitted as two bad
 243          * frames, those that made it out but had some retries as one good and
 244          * one bad frame. */
 245         if (!(info->flags & IEEE80211_TX_STAT_ACK)) {
 246                 spinfo->tx_num_failed += 2;
 247                 spinfo->tx_num_xmit++;
 248         } else if (info->status.rates[0].count > 1) {
 249                 spinfo->tx_num_failed++;
 250                 spinfo->tx_num_xmit++;
 251         }
 252
 253         /* Update PID controller state. */
 254         period = msecs_to_jiffies(pinfo->sampling_period);
 255         if (time_after(jiffies, spinfo->last_sample + period))
 256                 rate_control_pid_sample(pinfo, sband, sta, spinfo);
 257 }
 258
 259 static void
 260 rate_control_pid_get_rate(void *priv, struct ieee80211_sta *sta,
 261                           void *priv_sta,
 262                           struct ieee80211_tx_rate_control *txrc)
 263 {
 264         struct sk_buff *skb = txrc->skb;
 265         struct ieee80211_supported_band *sband = txrc->sband;
 266         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 267         struct rc_pid_sta_info *spinfo = priv_sta;
 268         int rateidx;
 269
 270         if (txrc->rts)
 271                 info->control.rates[0].count =
 272                         txrc->hw->conf.long_frame_max_tx_count;
 273         else
 274                 info->control.rates[0].count =
 275                         txrc->hw->conf.short_frame_max_tx_count;
 276
 277         /* Send management frames and NO_ACK data using lowest rate. */
 278         if (rate_control_send_low(sta, priv_sta, txrc))
 279                 return;
 280
 281         rateidx = spinfo->txrate_idx;
 282
 283         if (rateidx >= sband->n_bitrates)
 284                 rateidx = sband->n_bitrates - 1;
 285
 286         info->control.rates[0].idx = rateidx;
 287
 288 #ifdef CONFIG_MAC80211_DEBUGFS
 289         rate_control_pid_event_tx_rate(&spinfo->events,
 290                 rateidx, sband->bitrates[rateidx].bitrate);
 291 #endif
 292 }
 293
 294 static void
 295 rate_control_pid_rate_init(void *priv, struct ieee80211_supported_band *sband,
 296                            struct ieee80211_sta *sta, void *priv_sta)
 297 {
 298         struct rc_pid_sta_info *spinfo = priv_sta;
 299         struct rc_pid_info *pinfo = priv;
 300         struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
 301         int i, j, tmp;
 302         bool s;
 303
 304         /* TODO: This routine should consider using RSSI from previous packets
 305          * as we need to have IEEE 802.1X auth succeed immediately after assoc..
 306          * Until that method is implemented, we will use the lowest supported
 307          * rate as a workaround. */
 308
 309         /* Sort the rates. This is optimized for the most common case (i.e.
 310          * almost-sorted CCK+OFDM rates). Kind of bubble-sort with reversed
 311          * mapping too. */
 312         for (i = 0; i < sband->n_bitrates; i++) {
 313                 rinfo[i].index = i;
 314                 rinfo[i].rev_index = i;
 315                 if (RC_PID_FAST_START)
 316                         rinfo[i].diff = 0;
 317                 else
 318                         rinfo[i].diff = i * pinfo->norm_offset;
 319         }
 320         for (i = 1; i < sband->n_bitrates; i++) {
 321                 s = false;
 322                 for (j = 0; j < sband->n_bitrates - i; j++)
 323                         if (unlikely(sband->bitrates[rinfo[j].index].bitrate >
 324                                      sband->bitrates[rinfo[j + 1].index].bitrate)) {
 325                                 tmp = rinfo[j].index;
 326                                 rinfo[j].index = rinfo[j + 1].index;
 327                                 rinfo[j + 1].index = tmp;
 328                                 rinfo[rinfo[j].index].rev_index = j;
 329                                 rinfo[rinfo[j + 1].index].rev_index = j + 1;
 330                                 s = true;
 331                         }
 332                 if (!s)
 333                         break;
 334         }
 335
 336         spinfo->txrate_idx = rate_lowest_index(sband, sta);
 337 }
 338
 339 static void *rate_control_pid_alloc(struct ieee80211_hw *hw,
 340                                     struct dentry *debugfsdir)
 341 {
 342         struct rc_pid_info *pinfo;
 343         struct rc_pid_rateinfo *rinfo;
 344         struct ieee80211_supported_band *sband;
 345         int i, max_rates = 0;
 346 #ifdef CONFIG_MAC80211_DEBUGFS
 347         struct rc_pid_debugfs_entries *de;
 348 #endif
 349
 350         pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
 351         if (!pinfo)
 352                 return NULL;
 353
 354         for (i = 0; i < IEEE80211_NUM_BANDS; i++) {
 355                 sband = hw->wiphy->bands[i];
 356                 if (sband && sband->n_bitrates > max_rates)
 357                         max_rates = sband->n_bitrates;
 358         }
 359
 360         rinfo = kmalloc(sizeof(*rinfo) * max_rates, GFP_ATOMIC);
 361         if (!rinfo) {
 362                 kfree(pinfo);
 363                 return NULL;
 364         }
 365
 366         pinfo->target = RC_PID_TARGET_PF;
 367         pinfo->sampling_period = RC_PID_INTERVAL;
 368         pinfo->coeff_p = RC_PID_COEFF_P;
 369         pinfo->coeff_i = RC_PID_COEFF_I;
 370         pinfo->coeff_d = RC_PID_COEFF_D;
 371         pinfo->smoothing_shift = RC_PID_SMOOTHING_SHIFT;
 372         pinfo->sharpen_factor = RC_PID_SHARPENING_FACTOR;
 373         pinfo->sharpen_duration = RC_PID_SHARPENING_DURATION;
 374         pinfo->norm_offset = RC_PID_NORM_OFFSET;
 375         pinfo->rinfo = rinfo;
 376         pinfo->oldrate = 0;
 377
 378 #ifdef CONFIG_MAC80211_DEBUGFS
 379         de = &pinfo->dentries;
 380         de->target = debugfs_create_u32("target_pf", S_IRUSR | S_IWUSR,
 381                                         debugfsdir, &pinfo->target);
 382         de->sampling_period = debugfs_create_u32("sampling_period",
 383                                                  S_IRUSR | S_IWUSR, debugfsdir,
 384                                                  &pinfo->sampling_period);
 385         de->coeff_p = debugfs_create_u32("coeff_p", S_IRUSR | S_IWUSR,
 386                                          debugfsdir, (u32 *)&pinfo->coeff_p);
 387         de->coeff_i = debugfs_create_u32("coeff_i", S_IRUSR | S_IWUSR,
 388                                          debugfsdir, (u32 *)&pinfo->coeff_i);
 389         de->coeff_d = debugfs_create_u32("coeff_d", S_IRUSR | S_IWUSR,
 390                                          debugfsdir, (u32 *)&pinfo->coeff_d);
 391         de->smoothing_shift = debugfs_create_u32("smoothing_shift",
 392                                                  S_IRUSR | S_IWUSR, debugfsdir,
 393                                                  &pinfo->smoothing_shift);
 394         de->sharpen_factor = debugfs_create_u32("sharpen_factor",
 395                                                S_IRUSR | S_IWUSR, debugfsdir,
 396                                                &pinfo->sharpen_factor);
 397         de->sharpen_duration = debugfs_create_u32("sharpen_duration",
 398                                                   S_IRUSR | S_IWUSR, debugfsdir,
 399                                                   &pinfo->sharpen_duration);
 400         de->norm_offset = debugfs_create_u32("norm_offset",
 401                                              S_IRUSR | S_IWUSR, debugfsdir,
 402                                              &pinfo->norm_offset);
 403 #endif
 404
 405         return pinfo;
 406 }
 407
 408 static void rate_control_pid_free(void *priv)
 409 {
 410         struct rc_pid_info *pinfo = priv;
 411 #ifdef CONFIG_MAC80211_DEBUGFS
 412         struct rc_pid_debugfs_entries *de = &pinfo->dentries;
 413
 414         debugfs_remove(de->norm_offset);
 415         debugfs_remove(de->sharpen_duration);
 416         debugfs_remove(de->sharpen_factor);
 417         debugfs_remove(de->smoothing_shift);
 418         debugfs_remove(de->coeff_d);
 419         debugfs_remove(de->coeff_i);
 420         debugfs_remove(de->coeff_p);
 421         debugfs_remove(de->sampling_period);
 422         debugfs_remove(de->target);
 423 #endif
 424
 425         kfree(pinfo->rinfo);
 426         kfree(pinfo);
 427 }
 428
 429 static void *rate_control_pid_alloc_sta(void *priv, struct ieee80211_sta *sta,
 430                                         gfp_t gfp)
 431 {
 432         struct rc_pid_sta_info *spinfo;
 433
 434         spinfo = kzalloc(sizeof(*spinfo), gfp);
 435         if (spinfo == NULL)
 436                 return NULL;
 437
 438         spinfo->last_sample = jiffies;
 439
 440 #ifdef CONFIG_MAC80211_DEBUGFS
 441         spin_lock_init(&spinfo->events.lock);
 442         init_waitqueue_head(&spinfo->events.waitqueue);
 443 #endif
 444
 445         return spinfo;
 446 }
 447
 448 static void rate_control_pid_free_sta(void *priv, struct ieee80211_sta *sta,
 449                                       void *priv_sta)
 450 {
 451         kfree(priv_sta);
 452 }
 453
 454 static struct rate_control_ops mac80211_rcpid = {
 455         .name = "pid",
 456         .tx_status = rate_control_pid_tx_status,
 457         .get_rate = rate_control_pid_get_rate,
 458         .rate_init = rate_control_pid_rate_init,
 459         .alloc = rate_control_pid_alloc,
 460         .free = rate_control_pid_free,
 461         .alloc_sta = rate_control_pid_alloc_sta,
 462         .free_sta = rate_control_pid_free_sta,
 463 #ifdef CONFIG_MAC80211_DEBUGFS
 464         .add_sta_debugfs = rate_control_pid_add_sta_debugfs,
 465         .remove_sta_debugfs = rate_control_pid_remove_sta_debugfs,
 466 #endif
 467 };
 468
 469 int __init rc80211_pid_init(void)
 470 {
 471         return ieee80211_rate_control_register(&mac80211_rcpid);
 472 }
 473
 474 void rc80211_pid_exit(void)
 475 {
 476         ieee80211_rate_control_unregister(&mac80211_rcpid);
 477 }