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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. */
 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 }
478 

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