linux/net/mac80211/rc80211_pid_algo.c
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   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. */
  71static 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. */
 128static 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
 144static 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                /* XXX: BAD HACK!!! */
 174                struct sta_info *si = container_of(sta, struct sta_info, sta);
 175
 176                pf = spinfo->tx_num_failed * 100 / spinfo->tx_num_xmit;
 177
 178                if (ieee80211_vif_is_mesh(&si->sdata->vif) && pf == 100)
 179                        mesh_plink_broken(si);
 180                pf <<= RC_PID_ARITH_SHIFT;
 181                si->fail_avg = ((pf + (spinfo->last_pf << 3)) / 9)
 182                                        >> RC_PID_ARITH_SHIFT;
 183        }
 184
 185        spinfo->tx_num_xmit = 0;
 186        spinfo->tx_num_failed = 0;
 187
 188        /* If we just switched rate, update the rate behaviour info. */
 189        if (pinfo->oldrate != spinfo->txrate_idx) {
 190
 191                i = rinfo[pinfo->oldrate].rev_index;
 192                j = rinfo[spinfo->txrate_idx].rev_index;
 193
 194                tmp = (pf - spinfo->last_pf);
 195                tmp = RC_PID_DO_ARITH_RIGHT_SHIFT(tmp, RC_PID_ARITH_SHIFT);
 196
 197                rinfo[j].diff = rinfo[i].diff + tmp;
 198                pinfo->oldrate = spinfo->txrate_idx;
 199        }
 200        rate_control_pid_normalize(pinfo, sband->n_bitrates);
 201
 202        /* Compute the proportional, integral and derivative errors. */
 203        err_prop = (pinfo->target << RC_PID_ARITH_SHIFT) - pf;
 204
 205        err_avg = spinfo->err_avg_sc >> pinfo->smoothing_shift;
 206        spinfo->err_avg_sc = spinfo->err_avg_sc - err_avg + err_prop;
 207        err_int = spinfo->err_avg_sc >> pinfo->smoothing_shift;
 208
 209        err_der = (pf - spinfo->last_pf) *
 210                  (1 + pinfo->sharpen_factor * spinfo->sharp_cnt);
 211        spinfo->last_pf = pf;
 212        if (spinfo->sharp_cnt)
 213                        spinfo->sharp_cnt--;
 214
 215#ifdef CONFIG_MAC80211_DEBUGFS
 216        rate_control_pid_event_pf_sample(&spinfo->events, pf, err_prop, err_int,
 217                                         err_der);
 218#endif
 219
 220        /* Compute the controller output. */
 221        adj = (err_prop * pinfo->coeff_p + err_int * pinfo->coeff_i
 222              + err_der * pinfo->coeff_d);
 223        adj = RC_PID_DO_ARITH_RIGHT_SHIFT(adj, 2 * RC_PID_ARITH_SHIFT);
 224
 225        /* Change rate. */
 226        if (adj)
 227                rate_control_pid_adjust_rate(sband, sta, spinfo, adj, rinfo);
 228}
 229
 230static void rate_control_pid_tx_status(void *priv, struct ieee80211_supported_band *sband,
 231                                       struct ieee80211_sta *sta, void *priv_sta,
 232                                       struct sk_buff *skb)
 233{
 234        struct rc_pid_info *pinfo = priv;
 235        struct rc_pid_sta_info *spinfo = priv_sta;
 236        unsigned long period;
 237        struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 238
 239        if (!spinfo)
 240                return;
 241
 242        /* Ignore all frames that were sent with a different rate than the rate
 243         * we currently advise mac80211 to use. */
 244        if (info->status.rates[0].idx != spinfo->txrate_idx)
 245                return;
 246
 247        spinfo->tx_num_xmit++;
 248
 249#ifdef CONFIG_MAC80211_DEBUGFS
 250        rate_control_pid_event_tx_status(&spinfo->events, info);
 251#endif
 252
 253        /* We count frames that totally failed to be transmitted as two bad
 254         * frames, those that made it out but had some retries as one good and
 255         * one bad frame. */
 256        if (!(info->flags & IEEE80211_TX_STAT_ACK)) {
 257                spinfo->tx_num_failed += 2;
 258                spinfo->tx_num_xmit++;
 259        } else if (info->status.rates[0].count > 1) {
 260                spinfo->tx_num_failed++;
 261                spinfo->tx_num_xmit++;
 262        }
 263
 264        /* Update PID controller state. */
 265        period = (HZ * pinfo->sampling_period + 500) / 1000;
 266        if (!period)
 267                period = 1;
 268        if (time_after(jiffies, spinfo->last_sample + period))
 269                rate_control_pid_sample(pinfo, sband, sta, spinfo);
 270}
 271
 272static void
 273rate_control_pid_get_rate(void *priv, struct ieee80211_sta *sta,
 274                          void *priv_sta,
 275                          struct ieee80211_tx_rate_control *txrc)
 276{
 277        struct sk_buff *skb = txrc->skb;
 278        struct ieee80211_supported_band *sband = txrc->sband;
 279        struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
 280        struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
 281        struct rc_pid_sta_info *spinfo = priv_sta;
 282        int rateidx;
 283        u16 fc;
 284
 285        if (txrc->rts)
 286                info->control.rates[0].count =
 287                        txrc->hw->conf.long_frame_max_tx_count;
 288        else
 289                info->control.rates[0].count =
 290                        txrc->hw->conf.short_frame_max_tx_count;
 291
 292        /* Send management frames and broadcast/multicast data using lowest
 293         * rate. */
 294        fc = le16_to_cpu(hdr->frame_control);
 295        if (!sta || !spinfo ||
 296            (fc & IEEE80211_FCTL_FTYPE) != IEEE80211_FTYPE_DATA ||
 297            is_multicast_ether_addr(hdr->addr1)) {
 298                info->control.rates[0].idx = rate_lowest_index(sband, sta);
 299                return;
 300        }
 301
 302        rateidx = spinfo->txrate_idx;
 303
 304        if (rateidx >= sband->n_bitrates)
 305                rateidx = sband->n_bitrates - 1;
 306
 307        info->control.rates[0].idx = rateidx;
 308
 309#ifdef CONFIG_MAC80211_DEBUGFS
 310        rate_control_pid_event_tx_rate(&spinfo->events,
 311                rateidx, sband->bitrates[rateidx].bitrate);
 312#endif
 313}
 314
 315static void
 316rate_control_pid_rate_init(void *priv, struct ieee80211_supported_band *sband,
 317                           struct ieee80211_sta *sta, void *priv_sta)
 318{
 319        struct rc_pid_sta_info *spinfo = priv_sta;
 320        struct rc_pid_info *pinfo = priv;
 321        struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
 322        struct sta_info *si;
 323        int i, j, tmp;
 324        bool s;
 325
 326        /* TODO: This routine should consider using RSSI from previous packets
 327         * as we need to have IEEE 802.1X auth succeed immediately after assoc..
 328         * Until that method is implemented, we will use the lowest supported
 329         * rate as a workaround. */
 330
 331        /* Sort the rates. This is optimized for the most common case (i.e.
 332         * almost-sorted CCK+OFDM rates). Kind of bubble-sort with reversed
 333         * mapping too. */
 334        for (i = 0; i < sband->n_bitrates; i++) {
 335                rinfo[i].index = i;
 336                rinfo[i].rev_index = i;
 337                if (RC_PID_FAST_START)
 338                        rinfo[i].diff = 0;
 339                else
 340                        rinfo[i].diff = i * pinfo->norm_offset;
 341        }
 342        for (i = 1; i < sband->n_bitrates; i++) {
 343                s = 0;
 344                for (j = 0; j < sband->n_bitrates - i; j++)
 345                        if (unlikely(sband->bitrates[rinfo[j].index].bitrate >
 346                                     sband->bitrates[rinfo[j + 1].index].bitrate)) {
 347                                tmp = rinfo[j].index;
 348                                rinfo[j].index = rinfo[j + 1].index;
 349                                rinfo[j + 1].index = tmp;
 350                                rinfo[rinfo[j].index].rev_index = j;
 351                                rinfo[rinfo[j + 1].index].rev_index = j + 1;
 352                                s = 1;
 353                        }
 354                if (!s)
 355                        break;
 356        }
 357
 358        spinfo->txrate_idx = rate_lowest_index(sband, sta);
 359        /* HACK */
 360        si = container_of(sta, struct sta_info, sta);
 361        si->fail_avg = 0;
 362}
 363
 364static void *rate_control_pid_alloc(struct ieee80211_hw *hw,
 365                                    struct dentry *debugfsdir)
 366{
 367        struct rc_pid_info *pinfo;
 368        struct rc_pid_rateinfo *rinfo;
 369        struct ieee80211_supported_band *sband;
 370        int i, max_rates = 0;
 371#ifdef CONFIG_MAC80211_DEBUGFS
 372        struct rc_pid_debugfs_entries *de;
 373#endif
 374
 375        pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
 376        if (!pinfo)
 377                return NULL;
 378
 379        for (i = 0; i < IEEE80211_NUM_BANDS; i++) {
 380                sband = hw->wiphy->bands[i];
 381                if (sband && sband->n_bitrates > max_rates)
 382                        max_rates = sband->n_bitrates;
 383        }
 384
 385        rinfo = kmalloc(sizeof(*rinfo) * max_rates, GFP_ATOMIC);
 386        if (!rinfo) {
 387                kfree(pinfo);
 388                return NULL;
 389        }
 390
 391        pinfo->target = RC_PID_TARGET_PF;
 392        pinfo->sampling_period = RC_PID_INTERVAL;
 393        pinfo->coeff_p = RC_PID_COEFF_P;
 394        pinfo->coeff_i = RC_PID_COEFF_I;
 395        pinfo->coeff_d = RC_PID_COEFF_D;
 396        pinfo->smoothing_shift = RC_PID_SMOOTHING_SHIFT;
 397        pinfo->sharpen_factor = RC_PID_SHARPENING_FACTOR;
 398        pinfo->sharpen_duration = RC_PID_SHARPENING_DURATION;
 399        pinfo->norm_offset = RC_PID_NORM_OFFSET;
 400        pinfo->rinfo = rinfo;
 401        pinfo->oldrate = 0;
 402
 403#ifdef CONFIG_MAC80211_DEBUGFS
 404        de = &pinfo->dentries;
 405        de->target = debugfs_create_u32("target_pf", S_IRUSR | S_IWUSR,
 406                                        debugfsdir, &pinfo->target);
 407        de->sampling_period = debugfs_create_u32("sampling_period",
 408                                                 S_IRUSR | S_IWUSR, debugfsdir,
 409                                                 &pinfo->sampling_period);
 410        de->coeff_p = debugfs_create_u32("coeff_p", S_IRUSR | S_IWUSR,
 411                                         debugfsdir, (u32 *)&pinfo->coeff_p);
 412        de->coeff_i = debugfs_create_u32("coeff_i", S_IRUSR | S_IWUSR,
 413                                         debugfsdir, (u32 *)&pinfo->coeff_i);
 414        de->coeff_d = debugfs_create_u32("coeff_d", S_IRUSR | S_IWUSR,
 415                                         debugfsdir, (u32 *)&pinfo->coeff_d);
 416        de->smoothing_shift = debugfs_create_u32("smoothing_shift",
 417                                                 S_IRUSR | S_IWUSR, debugfsdir,
 418                                                 &pinfo->smoothing_shift);
 419        de->sharpen_factor = debugfs_create_u32("sharpen_factor",
 420                                               S_IRUSR | S_IWUSR, debugfsdir,
 421                                               &pinfo->sharpen_factor);
 422        de->sharpen_duration = debugfs_create_u32("sharpen_duration",
 423                                                  S_IRUSR | S_IWUSR, debugfsdir,
 424                                                  &pinfo->sharpen_duration);
 425        de->norm_offset = debugfs_create_u32("norm_offset",
 426                                             S_IRUSR | S_IWUSR, debugfsdir,
 427                                             &pinfo->norm_offset);
 428#endif
 429
 430        return pinfo;
 431}
 432
 433static void rate_control_pid_free(void *priv)
 434{
 435        struct rc_pid_info *pinfo = priv;
 436#ifdef CONFIG_MAC80211_DEBUGFS
 437        struct rc_pid_debugfs_entries *de = &pinfo->dentries;
 438
 439        debugfs_remove(de->norm_offset);
 440        debugfs_remove(de->sharpen_duration);
 441        debugfs_remove(de->sharpen_factor);
 442        debugfs_remove(de->smoothing_shift);
 443        debugfs_remove(de->coeff_d);
 444        debugfs_remove(de->coeff_i);
 445        debugfs_remove(de->coeff_p);
 446        debugfs_remove(de->sampling_period);
 447        debugfs_remove(de->target);
 448#endif
 449
 450        kfree(pinfo->rinfo);
 451        kfree(pinfo);
 452}
 453
 454static void *rate_control_pid_alloc_sta(void *priv, struct ieee80211_sta *sta,
 455                                        gfp_t gfp)
 456{
 457        struct rc_pid_sta_info *spinfo;
 458
 459        spinfo = kzalloc(sizeof(*spinfo), gfp);
 460        if (spinfo == NULL)
 461                return NULL;
 462
 463        spinfo->last_sample = jiffies;
 464
 465#ifdef CONFIG_MAC80211_DEBUGFS
 466        spin_lock_init(&spinfo->events.lock);
 467        init_waitqueue_head(&spinfo->events.waitqueue);
 468#endif
 469
 470        return spinfo;
 471}
 472
 473static void rate_control_pid_free_sta(void *priv, struct ieee80211_sta *sta,
 474                                      void *priv_sta)
 475{
 476        kfree(priv_sta);
 477}
 478
 479static struct rate_control_ops mac80211_rcpid = {
 480        .name = "pid",
 481        .tx_status = rate_control_pid_tx_status,
 482        .get_rate = rate_control_pid_get_rate,
 483        .rate_init = rate_control_pid_rate_init,
 484        .alloc = rate_control_pid_alloc,
 485        .free = rate_control_pid_free,
 486        .alloc_sta = rate_control_pid_alloc_sta,
 487        .free_sta = rate_control_pid_free_sta,
 488#ifdef CONFIG_MAC80211_DEBUGFS
 489        .add_sta_debugfs = rate_control_pid_add_sta_debugfs,
 490        .remove_sta_debugfs = rate_control_pid_remove_sta_debugfs,
 491#endif
 492};
 493
 494int __init rc80211_pid_init(void)
 495{
 496        return ieee80211_rate_control_register(&mac80211_rcpid);
 497}
 498
 499void rc80211_pid_exit(void)
 500{
 501        ieee80211_rate_control_unregister(&mac80211_rcpid);
 502}
 503