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_supported_band *sband,
  72                                          struct ieee80211_sta *sta,
  73                                          struct rc_pid_sta_info *spinfo, int adj,
  74                                          struct rc_pid_rateinfo *rinfo)
  75 {
  76         int cur_sorted, new_sorted, probe, tmp, n_bitrates, band;
  77         int cur = spinfo->txrate_idx;
  78
  79         band = sband->band;
  80         n_bitrates = sband->n_bitrates;
  81
  82         /* Map passed arguments to sorted values. */
  83         cur_sorted = rinfo[cur].rev_index;
  84         new_sorted = cur_sorted + adj;
  85
  86         /* Check limits. */
  87         if (new_sorted < 0)
  88                 new_sorted = rinfo[0].rev_index;
  89         else if (new_sorted >= n_bitrates)
  90                 new_sorted = rinfo[n_bitrates - 1].rev_index;
  91
  92         tmp = new_sorted;
  93
  94         if (adj < 0) {
  95                 /* Ensure that the rate decrease isn't disadvantageous. */
  96                 for (probe = cur_sorted; probe >= new_sorted; probe--)
  97                         if (rinfo[probe].diff <= rinfo[cur_sorted].diff &&
  98                             rate_supported(sta, band, rinfo[probe].index))
  99                                 tmp = probe;
 100         } else {
 101                 /* Look for rate increase with zero (or below) cost. */
 102                 for (probe = new_sorted + 1; probe < n_bitrates; probe++)
 103                         if (rinfo[probe].diff <= rinfo[new_sorted].diff &&
 104                             rate_supported(sta, band, rinfo[probe].index))
 105                                 tmp = probe;
 106         }
 107
 108         /* Fit the rate found to the nearest supported rate. */
 109         do {
 110                 if (rate_supported(sta, band, rinfo[tmp].index)) {
 111                         spinfo->txrate_idx = rinfo[tmp].index;
 112                         break;
 113                 }
 114                 if (adj < 0)
 115                         tmp--;
 116                 else
 117                         tmp++;
 118         } while (tmp < n_bitrates && tmp >= 0);
 119
 120 #ifdef CONFIG_MAC80211_DEBUGFS
 121         rate_control_pid_event_rate_change(&spinfo->events,
 122                 spinfo->txrate_idx,
 123                 sband->bitrates[spinfo->txrate_idx].bitrate);
 124 #endif
 125 }
 126
 127 /* Normalize the failed frames per-rate differences. */
 128 static void rate_control_pid_normalize(struct rc_pid_info *pinfo, int l)
 129 {
 130         int i, norm_offset = pinfo->norm_offset;
 131         struct rc_pid_rateinfo *r = pinfo->rinfo;
 132
 133         if (r[0].diff > norm_offset)
 134                 r[0].diff -= norm_offset;
 135         else if (r[0].diff < -norm_offset)
 136                 r[0].diff += norm_offset;
 137         for (i = 0; i < l - 1; i++)
 138                 if (r[i + 1].diff > r[i].diff + norm_offset)
 139                         r[i + 1].diff -= norm_offset;
 140                 else if (r[i + 1].diff <= r[i].diff)
 141                         r[i + 1].diff += norm_offset;
 142 }
 143
 144 static void rate_control_pid_sample(struct rc_pid_info *pinfo,
 145                                     struct ieee80211_supported_band *sband,
 146                                     struct ieee80211_sta *sta,
 147                                     struct rc_pid_sta_info *spinfo)
 148 {
 149         struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
 150         u32 pf;
 151         s32 err_avg;
 152         u32 err_prop;
 153         u32 err_int;
 154         u32 err_der;
 155         int adj, i, j, tmp;
 156         unsigned long period;
 157
 158         /* In case nothing happened during the previous control interval, turn
 159          * the sharpening factor on. */
 160         period = (HZ * pinfo->sampling_period + 500) / 1000;
 161         if (!period)
 162                 period = 1;
 163         if (jiffies - spinfo->last_sample > 2 * period)
 164                 spinfo->sharp_cnt = pinfo->sharpen_duration;
 165
 166         spinfo->last_sample = jiffies;
 167
 168         /* This should never happen, but in case, we assume the old sample is
 169          * still a good measurement and copy it. */
 170         if (unlikely(spinfo->tx_num_xmit == 0))
 171                 pf = spinfo->last_pf;
 172         else
 173                 pf = spinfo->tx_num_failed * 100 / spinfo->tx_num_xmit;
 174
 175         spinfo->tx_num_xmit = 0;
 176         spinfo->tx_num_failed = 0;
 177
 178         /* If we just switched rate, update the rate behaviour info. */
 179         if (pinfo->oldrate != spinfo->txrate_idx) {
 180
 181                 i = rinfo[pinfo->oldrate].rev_index;
 182                 j = rinfo[spinfo->txrate_idx].rev_index;
 183
 184                 tmp = (pf - spinfo->last_pf);
 185                 tmp = RC_PID_DO_ARITH_RIGHT_SHIFT(tmp, RC_PID_ARITH_SHIFT);
 186
 187                 rinfo[j].diff = rinfo[i].diff + tmp;
 188                 pinfo->oldrate = spinfo->txrate_idx;
 189         }
 190         rate_control_pid_normalize(pinfo, sband->n_bitrates);
 191
 192         /* Compute the proportional, integral and derivative errors. */
 193         err_prop = (pinfo->target << RC_PID_ARITH_SHIFT) - pf;
 194
 195         err_avg = spinfo->err_avg_sc >> pinfo->smoothing_shift;
 196         spinfo->err_avg_sc = spinfo->err_avg_sc - err_avg + err_prop;
 197         err_int = spinfo->err_avg_sc >> pinfo->smoothing_shift;
 198
 199         err_der = (pf - spinfo->last_pf) *
 200                   (1 + pinfo->sharpen_factor * spinfo->sharp_cnt);
 201         spinfo->last_pf = pf;
 202         if (spinfo->sharp_cnt)
 203                         spinfo->sharp_cnt--;
 204
 205 #ifdef CONFIG_MAC80211_DEBUGFS
 206         rate_control_pid_event_pf_sample(&spinfo->events, pf, err_prop, err_int,
 207                                          err_der);
 208 #endif
 209
 210         /* Compute the controller output. */
 211         adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i
 212               + err_der * pinfo->coeff_d);
 213         adj = RC_PID_DO_ARITH_RIGHT_SHIFT(adj, 2 * RC_PID_ARITH_SHIFT);
 214
 215         /* Change rate. */
 216         if (adj)
 217                 rate_control_pid_adjust_rate(sband, sta, spinfo, adj, rinfo);
 218 }
 219
 220 static void rate_control_pid_tx_status(void *priv, struct ieee80211_supported_band *sband,
 221                                        struct ieee80211_sta *sta, void *priv_sta,
 222                                        struct sk_buff *skb)
 223 {
 224         struct rc_pid_info *pinfo = priv;
 225         struct rc_pid_sta_info *spinfo = priv_sta;
 226         unsigned long period;
 227         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 228
 229         if (!spinfo)
 230                 return;
 231
 232         /* Ignore all frames that were sent with a different rate than the rate
 233          * we currently advise mac80211 to use. */
 234         if (info->status.rates[0].idx != spinfo->txrate_idx)
 235                 return;
 236
 237         spinfo->tx_num_xmit++;
 238
 239 #ifdef CONFIG_MAC80211_DEBUGFS
 240         rate_control_pid_event_tx_status(&spinfo->events, info);
 241 #endif
 242
 243         /* We count frames that totally failed to be transmitted as two bad
 244          * frames, those that made it out but had some retries as one good and
 245          * one bad frame. */
 246         if (!(info->flags & IEEE80211_TX_STAT_ACK)) {
 247                 spinfo->tx_num_failed += 2;
 248                 spinfo->tx_num_xmit++;
 249         } else if (info->status.rates[0].count > 1) {
 250                 spinfo->tx_num_failed++;
 251                 spinfo->tx_num_xmit++;
 252         }
 253
 254         /* Update PID controller state. */
 255         period = (HZ * pinfo->sampling_period + 500) / 1000;
 256         if (!period)
 257                 period = 1;
 258         if (time_after(jiffies, spinfo->last_sample + period))
 259                 rate_control_pid_sample(pinfo, sband, sta, spinfo);
 260 }
 261
 262 static void
 263 rate_control_pid_get_rate(void *priv, struct ieee80211_sta *sta,
 264                           void *priv_sta,
 265                           struct ieee80211_tx_rate_control *txrc)
 266 {
 267         struct sk_buff *skb = txrc->skb;
 268         struct ieee80211_supported_band *sband = txrc->sband;
 269         struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 270         struct rc_pid_sta_info *spinfo = priv_sta;
 271         int rateidx;
 272
 273         if (txrc->rts)
 274                 info->control.rates[0].count =
 275                         txrc->hw->conf.long_frame_max_tx_count;
 276         else
 277                 info->control.rates[0].count =
 278                         txrc->hw->conf.short_frame_max_tx_count;
 279
 280         /* Send management frames and NO_ACK data using lowest rate. */
 281         if (rate_control_send_low(sta, priv_sta, txrc))
 282                 return;
 283
 284         rateidx = spinfo->txrate_idx;
 285
 286         if (rateidx >= sband->n_bitrates)
 287                 rateidx = sband->n_bitrates - 1;
 288
 289         info->control.rates[0].idx = rateidx;
 290
 291 #ifdef CONFIG_MAC80211_DEBUGFS
 292         rate_control_pid_event_tx_rate(&spinfo->events,
 293                 rateidx, sband->bitrates[rateidx].bitrate);
 294 #endif
 295 }
 296
 297 static void
 298 rate_control_pid_rate_init(void *priv, struct ieee80211_supported_band *sband,
 299                            struct ieee80211_sta *sta, void *priv_sta)
 300 {
 301         struct rc_pid_sta_info *spinfo = priv_sta;
 302         struct rc_pid_info *pinfo = priv;
 303         struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
 304         int i, j, tmp;
 305         bool s;
 306
 307         /* TODO: This routine should consider using RSSI from previous packets
 308          * as we need to have IEEE 802.1X auth succeed immediately after assoc..
 309          * Until that method is implemented, we will use the lowest supported
 310          * rate as a workaround. */
 311
 312         /* Sort the rates. This is optimized for the most common case (i.e.
 313          * almost-sorted CCK+OFDM rates). Kind of bubble-sort with reversed
 314          * mapping too. */
 315         for (i = 0; i < sband->n_bitrates; i++) {
 316                 rinfo[i].index = i;
 317                 rinfo[i].rev_index = i;
 318                 if (RC_PID_FAST_START)
 319                         rinfo[i].diff = 0;
 320                 else
 321                         rinfo[i].diff = i * pinfo->norm_offset;
 322         }
 323         for (i = 1; i < sband->n_bitrates; i++) {
 324                 s = 0;
 325                 for (j = 0; j < sband->n_bitrates - i; j++)
 326                         if (unlikely(sband->bitrates[rinfo[j].index].bitrate >
 327                                      sband->bitrates[rinfo[j + 1].index].bitrate)) {
 328                                 tmp = rinfo[j].index;
 329                                 rinfo[j].index = rinfo[j + 1].index;
 330                                 rinfo[j + 1].index = tmp;
 331                                 rinfo[rinfo[j].index].rev_index = j;
 332                                 rinfo[rinfo[j + 1].index].rev_index = j + 1;
 333                                 s = 1;
 334                         }
 335                 if (!s)
 336                         break;
 337         }
 338
 339         spinfo->txrate_idx = rate_lowest_index(sband, sta);
 340 }
 341
 342 static void *rate_control_pid_alloc(struct ieee80211_hw *hw,
 343                                     struct dentry *debugfsdir)
 344 {
 345         struct rc_pid_info *pinfo;
 346         struct rc_pid_rateinfo *rinfo;
 347         struct ieee80211_supported_band *sband;
 348         int i, max_rates = 0;
 349 #ifdef CONFIG_MAC80211_DEBUGFS
 350         struct rc_pid_debugfs_entries *de;
 351 #endif
 352
 353         pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
 354         if (!pinfo)
 355                 return NULL;
 356
 357         for (i = 0; i < IEEE80211_NUM_BANDS; i++) {
 358                 sband = hw->wiphy->bands[i];
 359                 if (sband && sband->n_bitrates > max_rates)
 360                         max_rates = sband->n_bitrates;
 361         }
 362
 363         rinfo = kmalloc(sizeof(*rinfo) * max_rates, GFP_ATOMIC);
 364         if (!rinfo) {
 365                 kfree(pinfo);
 366                 return NULL;
 367         }
 368
 369         pinfo->target = RC_PID_TARGET_PF;
 370         pinfo->sampling_period = RC_PID_INTERVAL;
 371         pinfo->coeff_p = RC_PID_COEFF_P;
 372         pinfo->coeff_i = RC_PID_COEFF_I;
 373         pinfo->coeff_d = RC_PID_COEFF_D;
 374         pinfo->smoothing_shift = RC_PID_SMOOTHING_SHIFT;
 375         pinfo->sharpen_factor = RC_PID_SHARPENING_FACTOR;
 376         pinfo->sharpen_duration = RC_PID_SHARPENING_DURATION;
 377         pinfo->norm_offset = RC_PID_NORM_OFFSET;
 378         pinfo->rinfo = rinfo;
 379         pinfo->oldrate = 0;
 380
 381 #ifdef CONFIG_MAC80211_DEBUGFS
 382         de = &pinfo->dentries;
 383         de->target = debugfs_create_u32("target_pf", S_IRUSR | S_IWUSR,
 384                                         debugfsdir, &pinfo->target);
 385         de->sampling_period = debugfs_create_u32("sampling_period",
 386                                                  S_IRUSR | S_IWUSR, debugfsdir,
 387                                                  &pinfo->sampling_period);
 388         de->coeff_p = debugfs_create_u32("coeff_p", S_IRUSR | S_IWUSR,
 389                                          debugfsdir, (u32 *)&pinfo->coeff_p);
 390         de->coeff_i = debugfs_create_u32("coeff_i", S_IRUSR | S_IWUSR,
 391                                          debugfsdir, (u32 *)&pinfo->coeff_i);
 392         de->coeff_d = debugfs_create_u32("coeff_d", S_IRUSR | S_IWUSR,
 393                                          debugfsdir, (u32 *)&pinfo->coeff_d);
 394         de->smoothing_shift = debugfs_create_u32("smoothing_shift",
 395                                                  S_IRUSR | S_IWUSR, debugfsdir,
 396                                                  &pinfo->smoothing_shift);
 397         de->sharpen_factor = debugfs_create_u32("sharpen_factor",
 398                                                S_IRUSR | S_IWUSR, debugfsdir,
 399                                                &pinfo->sharpen_factor);
 400         de->sharpen_duration = debugfs_create_u32("sharpen_duration",
 401                                                   S_IRUSR | S_IWUSR, debugfsdir,
 402                                                   &pinfo->sharpen_duration);
 403         de->norm_offset = debugfs_create_u32("norm_offset",
 404                                              S_IRUSR | S_IWUSR, debugfsdir,
 405                                              &pinfo->norm_offset);
 406 #endif
 407
 408         return pinfo;
 409 }
 410
 411 static void rate_control_pid_free(void *priv)
 412 {
 413         struct rc_pid_info *pinfo = priv;
 414 #ifdef CONFIG_MAC80211_DEBUGFS
 415         struct rc_pid_debugfs_entries *de = &pinfo->dentries;
 416
 417         debugfs_remove(de->norm_offset);
 418         debugfs_remove(de->sharpen_duration);
 419         debugfs_remove(de->sharpen_factor);
 420         debugfs_remove(de->smoothing_shift);
 421         debugfs_remove(de->coeff_d);
 422         debugfs_remove(de->coeff_i);
 423         debugfs_remove(de->coeff_p);
 424         debugfs_remove(de->sampling_period);
 425         debugfs_remove(de->target);
 426 #endif
 427
 428         kfree(pinfo->rinfo);
 429         kfree(pinfo);
 430 }
 431
 432 static void *rate_control_pid_alloc_sta(void *priv, struct ieee80211_sta *sta,
 433                                         gfp_t gfp)
 434 {
 435         struct rc_pid_sta_info *spinfo;
 436
 437         spinfo = kzalloc(sizeof(*spinfo), gfp);
 438         if (spinfo == NULL)
 439                 return NULL;
 440
 441         spinfo->last_sample = jiffies;
 442
 443 #ifdef CONFIG_MAC80211_DEBUGFS
 444         spin_lock_init(&spinfo->events.lock);
 445         init_waitqueue_head(&spinfo->events.waitqueue);
 446 #endif
 447
 448         return spinfo;
 449 }
 450
 451 static void rate_control_pid_free_sta(void *priv, struct ieee80211_sta *sta,
 452                                       void *priv_sta)
 453 {
 454         kfree(priv_sta);
 455 }
 456
 457 static struct rate_control_ops mac80211_rcpid = {
 458         .name = "pid",
 459         .tx_status = rate_control_pid_tx_status,
 460         .get_rate = rate_control_pid_get_rate,
 461         .rate_init = rate_control_pid_rate_init,
 462         .alloc = rate_control_pid_alloc,
 463         .free = rate_control_pid_free,
 464         .alloc_sta = rate_control_pid_alloc_sta,
 465         .free_sta = rate_control_pid_free_sta,
 466 #ifdef CONFIG_MAC80211_DEBUGFS
 467         .add_sta_debugfs = rate_control_pid_add_sta_debugfs,
 468         .remove_sta_debugfs = rate_control_pid_remove_sta_debugfs,
 469 #endif
 470 };
 471
 472 int __init rc80211_pid_init(void)
 473 {
 474         return ieee80211_rate_control_register(&mac80211_rcpid);
 475 }
 476
 477 void rc80211_pid_exit(void)
 478 {
 479         ieee80211_rate_control_unregister(&mac80211_rcpid);
 480 }