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 <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. */
  72static 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. */
 129static 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
 145static 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
 219static 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
 259static void
 260rate_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
 294static void
 295rate_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
 339static 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
 408static 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
 429static 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
 448static void rate_control_pid_free_sta(void *priv, struct ieee80211_sta *sta,
 449                                      void *priv_sta)
 450{
 451        kfree(priv_sta);
 452}
 453
 454static 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
 469int __init rc80211_pid_init(void)
 470{
 471        return ieee80211_rate_control_register(&mac80211_rcpid);
 472}
 473
 474void rc80211_pid_exit(void)
 475{
 476        ieee80211_rate_control_unregister(&mac80211_rcpid);
 477}
 478
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