aboutsummaryrefslogtreecommitdiff
path: root/net/mac80211/rc80211_minstrel.c
blob: 247552a7f6c2f23a1e4bc89b647d8d37680bf2c3 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
/*
 * Copyright (C) 2008 Felix Fietkau <nbd@openwrt.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Based on minstrel.c:
 *   Copyright (C) 2005-2007 Derek Smithies <derek@indranet.co.nz>
 *   Sponsored by Indranet Technologies Ltd
 *
 * Based on sample.c:
 *   Copyright (c) 2005 John Bicket
 *   All rights reserved.
 *
 *   Redistribution and use in source and binary forms, with or without
 *   modification, are permitted provided that the following conditions
 *   are met:
 *   1. Redistributions of source code must retain the above copyright
 *      notice, this list of conditions and the following disclaimer,
 *      without modification.
 *   2. Redistributions in binary form must reproduce at minimum a disclaimer
 *      similar to the "NO WARRANTY" disclaimer below ("Disclaimer") and any
 *      redistribution must be conditioned upon including a substantially
 *      similar Disclaimer requirement for further binary redistribution.
 *   3. Neither the names of the above-listed copyright holders nor the names
 *      of any contributors may be used to endorse or promote products derived
 *      from this software without specific prior written permission.
 *
 *   Alternatively, this software may be distributed under the terms of the
 *   GNU General Public License ("GPL") version 2 as published by the Free
 *   Software Foundation.
 *
 *   NO WARRANTY
 *   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 *   ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 *   LIMITED TO, THE IMPLIED WARRANTIES OF NONINFRINGEMENT, MERCHANTIBILITY
 *   AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
 *   THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR SPECIAL, EXEMPLARY,
 *   OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 *   SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 *   INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
 *   IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 *   ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 *   THE POSSIBILITY OF SUCH DAMAGES.
 */
#include <linux/netdevice.h>
#include <linux/types.h>
#include <linux/skbuff.h>
#include <linux/debugfs.h>
#include <linux/random.h>
#include <linux/ieee80211.h>
#include <linux/slab.h>
#include <net/mac80211.h>
#include "rate.h"
#include "rc80211_minstrel.h"

#define SAMPLE_TBL(_mi, _idx, _col) \
		_mi->sample_table[(_idx * SAMPLE_COLUMNS) + _col]

/* convert mac80211 rate index to local array index */
static inline int
rix_to_ndx(struct minstrel_sta_info *mi, int rix)
{
	int i = rix;
	for (i = rix; i >= 0; i--)
		if (mi->r[i].rix == rix)
			break;
	return i;
}

/* return current EMWA throughput */
int minstrel_get_tp_avg(struct minstrel_rate *mr, int prob_ewma)
{
	int usecs;

	usecs = mr->perfect_tx_time;
	if (!usecs)
		usecs = 1000000;

	/* reset thr. below 10% success */
	if (mr->stats.prob_ewma < MINSTREL_FRAC(10, 100))
		return 0;

	if (prob_ewma > MINSTREL_FRAC(90, 100))
		return MINSTREL_TRUNC(100000 * (MINSTREL_FRAC(90, 100) / usecs));
	else
		return MINSTREL_TRUNC(100000 * (prob_ewma / usecs));
}

/* find & sort topmost throughput rates */
static inline void
minstrel_sort_best_tp_rates(struct minstrel_sta_info *mi, int i, u8 *tp_list)
{
	int j = MAX_THR_RATES;
	struct minstrel_rate_stats *tmp_mrs = &mi->r[j - 1].stats;
	struct minstrel_rate_stats *cur_mrs = &mi->r[i].stats;

	while (j > 0 && (minstrel_get_tp_avg(&mi->r[i], cur_mrs->prob_ewma) >
	       minstrel_get_tp_avg(&mi->r[tp_list[j - 1]], tmp_mrs->prob_ewma))) {
		j--;
		tmp_mrs = &mi->r[tp_list[j - 1]].stats;
	}

	if (j < MAX_THR_RATES - 1)
		memmove(&tp_list[j + 1], &tp_list[j], MAX_THR_RATES - (j + 1));
	if (j < MAX_THR_RATES)
		tp_list[j] = i;
}

static void
minstrel_set_rate(struct minstrel_sta_info *mi, struct ieee80211_sta_rates *ratetbl,
		  int offset, int idx)
{
	struct minstrel_rate *r = &mi->r[idx];

	ratetbl->rate[offset].idx = r->rix;
	ratetbl->rate[offset].count = r->adjusted_retry_count;
	ratetbl->rate[offset].count_cts = r->retry_count_cts;
	ratetbl->rate[offset].count_rts = r->stats.retry_count_rtscts;
}

static void
minstrel_update_rates(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
{
	struct ieee80211_sta_rates *ratetbl;
	int i = 0;

	ratetbl = kzalloc(sizeof(*ratetbl), GFP_ATOMIC);
	if (!ratetbl)
		return;

	/* Start with max_tp_rate */
	minstrel_set_rate(mi, ratetbl, i++, mi->max_tp_rate[0]);

	if (mp->hw->max_rates >= 3) {
		/* At least 3 tx rates supported, use max_tp_rate2 next */
		minstrel_set_rate(mi, ratetbl, i++, mi->max_tp_rate[1]);
	}

	if (mp->hw->max_rates >= 2) {
		/* At least 2 tx rates supported, use max_prob_rate next */
		minstrel_set_rate(mi, ratetbl, i++, mi->max_prob_rate);
	}

	/* Use lowest rate last */
	ratetbl->rate[i].idx = mi->lowest_rix;
	ratetbl->rate[i].count = mp->max_retry;
	ratetbl->rate[i].count_cts = mp->max_retry;
	ratetbl->rate[i].count_rts = mp->max_retry;

	rate_control_set_rates(mp->hw, mi->sta, ratetbl);
}

/*
* Recalculate statistics and counters of a given rate
*/
void
minstrel_calc_rate_stats(struct minstrel_rate_stats *mrs)
{
	if (unlikely(mrs->attempts > 0)) {
		mrs->sample_skipped = 0;
		mrs->cur_prob = MINSTREL_FRAC(mrs->success, mrs->attempts);
		if (unlikely(!mrs->att_hist)) {
			mrs->prob_ewma = mrs->cur_prob;
		} else {
			/* update exponential weighted moving variance */
			mrs->prob_ewmsd = minstrel_ewmsd(mrs->prob_ewmsd,
							 mrs->cur_prob,
							 mrs->prob_ewma,
							 EWMA_LEVEL);

			/*update exponential weighted moving avarage */
			mrs->prob_ewma = minstrel_ewma(mrs->prob_ewma,
						       mrs->cur_prob,
						       EWMA_LEVEL);
		}
		mrs->att_hist += mrs->attempts;
		mrs->succ_hist += mrs->success;
	} else {
		mrs->sample_skipped++;
	}

	mrs->last_success = mrs->success;
	mrs->last_attempts = mrs->attempts;
	mrs->success = 0;
	mrs->attempts = 0;
}

static void
minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
{
	u8 tmp_tp_rate[MAX_THR_RATES];
	u8 tmp_prob_rate = 0;
	int i, tmp_cur_tp, tmp_prob_tp;

	for (i = 0; i < MAX_THR_RATES; i++)
	    tmp_tp_rate[i] = 0;

	for (i = 0; i < mi->n_rates; i++) {
		struct minstrel_rate *mr = &mi->r[i];
		struct minstrel_rate_stats *mrs = &mi->r[i].stats;
		struct minstrel_rate_stats *tmp_mrs = &mi->r[tmp_prob_rate].stats;

		/* Update statistics of success probability per rate */
		minstrel_calc_rate_stats(mrs);

		/* Sample less often below the 10% chance of success.
		 * Sample less often above the 95% chance of success. */
		if (mrs->prob_ewma > MINSTREL_FRAC(95, 100) ||
		    mrs->prob_ewma < MINSTREL_FRAC(10, 100)) {
			mr->adjusted_retry_count = mrs->retry_count >> 1;
			if (mr->adjusted_retry_count > 2)
				mr->adjusted_retry_count = 2;
			mr->sample_limit = 4;
		} else {
			mr->sample_limit = -1;
			mr->adjusted_retry_count = mrs->retry_count;
		}
		if (!mr->adjusted_retry_count)
			mr->adjusted_retry_count = 2;

		minstrel_sort_best_tp_rates(mi, i, tmp_tp_rate);

		/* To determine the most robust rate (max_prob_rate) used at
		 * 3rd mmr stage we distinct between two cases:
		 * (1) if any success probabilitiy >= 95%, out of those rates
		 * choose the maximum throughput rate as max_prob_rate
		 * (2) if all success probabilities < 95%, the rate with
		 * highest success probability is chosen as max_prob_rate */
		if (mrs->prob_ewma >= MINSTREL_FRAC(95, 100)) {
			tmp_cur_tp = minstrel_get_tp_avg(mr, mrs->prob_ewma);
			tmp_prob_tp = minstrel_get_tp_avg(&mi->r[tmp_prob_rate],
							  tmp_mrs->prob_ewma);
			if (tmp_cur_tp >= tmp_prob_tp)
				tmp_prob_rate = i;
		} else {
			if (mrs->prob_ewma >= tmp_mrs->prob_ewma)
				tmp_prob_rate = i;
		}
	}

	/* Assign the new rate set */
	memcpy(mi->max_tp_rate, tmp_tp_rate, sizeof(mi->max_tp_rate));
	mi->max_prob_rate = tmp_prob_rate;

#ifdef CONFIG_MAC80211_DEBUGFS
	/* use fixed index if set */
	if (mp->fixed_rate_idx != -1) {
		mi->max_tp_rate[0] = mp->fixed_rate_idx;
		mi->max_tp_rate[1] = mp->fixed_rate_idx;
		mi->max_prob_rate = mp->fixed_rate_idx;
	}
#endif

	/* Reset update timer */
	mi->last_stats_update = jiffies;

	minstrel_update_rates(mp, mi);
}

static void
minstrel_tx_status(void *priv, struct ieee80211_supported_band *sband,
		   struct ieee80211_sta *sta, void *priv_sta,
		   struct ieee80211_tx_info *info)
{
	struct minstrel_priv *mp = priv;
	struct minstrel_sta_info *mi = priv_sta;
	struct ieee80211_tx_rate *ar = info->status.rates;
	int i, ndx;
	int success;

	success = !!(info->flags & IEEE80211_TX_STAT_ACK);

	for (i = 0; i < IEEE80211_TX_MAX_RATES; i++) {
		if (ar[i].idx < 0)
			break;

		ndx = rix_to_ndx(mi, ar[i].idx);
		if (ndx < 0)
			continue;

		mi->r[ndx].stats.attempts += ar[i].count;

		if ((i != IEEE80211_TX_MAX_RATES - 1) && (ar[i + 1].idx < 0))
			mi->r[ndx].stats.success += success;
	}

	if ((info->flags & IEEE80211_TX_CTL_RATE_CTRL_PROBE) && (i >= 0))
		mi->sample_packets++;

	if (mi->sample_deferred > 0)
		mi->sample_deferred--;

	if (time_after(jiffies, mi->last_stats_update +
				(mp->update_interval * HZ) / 1000))
		minstrel_update_stats(mp, mi);
}


static inline unsigned int
minstrel_get_retry_count(struct minstrel_rate *mr,
			 struct ieee80211_tx_info *info)
{
	u8 retry = mr->adjusted_retry_count;

	if (info->control.use_rts)
		retry = max_t(u8, 2, min(mr->stats.retry_count_rtscts, retry));
	else if (info->control.use_cts_prot)
		retry = max_t(u8, 2, min(mr->retry_count_cts, retry));
	return retry;
}


static int
minstrel_get_next_sample(struct minstrel_sta_info *mi)
{
	unsigned int sample_ndx;
	sample_ndx = SAMPLE_TBL(mi, mi->sample_row, mi->sample_column);
	mi->sample_row++;
	if ((int) mi->sample_row >= mi->n_rates) {
		mi->sample_row = 0;
		mi->sample_column++;
		if (mi->sample_column >= SAMPLE_COLUMNS)
			mi->sample_column = 0;
	}
	return sample_ndx;
}

static void
minstrel_get_rate(void *priv, struct ieee80211_sta *sta,
		  void *priv_sta, struct ieee80211_tx_rate_control *txrc)
{
	struct sk_buff *skb = txrc->skb;
	struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
	struct minstrel_sta_info *mi = priv_sta;
	struct minstrel_priv *mp = priv;
	struct ieee80211_tx_rate *rate = &info->control.rates[0];
	struct minstrel_rate *msr, *mr;
	unsigned int ndx;
	bool mrr_capable;
	bool prev_sample;
	int delta;
	int sampling_ratio;

	/* management/no-ack frames do not use rate control */
	if (rate_control_send_low(sta, priv_sta, txrc))
		return;

	/* check multi-rate-retry capabilities & adjust lookaround_rate */
	mrr_capable = mp->has_mrr &&
		      !txrc->rts &&
		      !txrc->bss_conf->use_cts_prot;
	if (mrr_capable)
		sampling_ratio = mp->lookaround_rate_mrr;
	else
		sampling_ratio = mp->lookaround_rate;

	/* increase sum packet counter */
	mi->total_packets++;

#ifdef CONFIG_MAC80211_DEBUGFS
	if (mp->fixed_rate_idx != -1)
		return;
#endif

	delta = (mi->total_packets * sampling_ratio / 100) -
			(mi->sample_packets + mi->sample_deferred / 2);

	/* delta < 0: no sampling required */
	prev_sample = mi->prev_sample;
	mi->prev_sample = false;
	if (delta < 0 || (!mrr_capable && prev_sample))
		return;

	if (mi->total_packets >= 10000) {
		mi->sample_deferred = 0;
		mi->sample_packets = 0;
		mi->total_packets = 0;
	} else if (delta > mi->n_rates * 2) {
		/* With multi-rate retry, not every planned sample
		 * attempt actually gets used, due to the way the retry
		 * chain is set up - [max_tp,sample,prob,lowest] for
		 * sample_rate < max_tp.
		 *
		 * If there's too much sampling backlog and the link
		 * starts getting worse, minstrel would start bursting
		 * out lots of sampling frames, which would result
		 * in a large throughput loss. */
		mi->sample_packets += (delta - mi->n_rates * 2);
	}

	/* get next random rate sample */
	ndx = minstrel_get_next_sample(mi);
	msr = &mi->r[ndx];
	mr = &mi->r[mi->max_tp_rate[0]];

	/* Decide if direct ( 1st mrr stage) or indirect (2nd mrr stage)
	 * rate sampling method should be used.
	 * Respect such rates that are not sampled for 20 interations.
	 */
	if (mrr_capable &&
	    msr->perfect_tx_time > mr->perfect_tx_time &&
	    msr->stats.sample_skipped < 20) {
		/* Only use IEEE80211_TX_CTL_RATE_CTRL_PROBE to mark
		 * packets that have the sampling rate deferred to the
		 * second MRR stage. Increase the sample counter only
		 * if the deferred sample rate was actually used.
		 * Use the sample_deferred counter to make sure that
		 * the sampling is not done in large bursts */
		info->flags |= IEEE80211_TX_CTL_RATE_CTRL_PROBE;
		rate++;
		mi->sample_deferred++;
	} else {
		if (!msr->sample_limit)
			return;

		mi->sample_packets++;
		if (msr->sample_limit > 0)
			msr->sample_limit--;
	}

	/* If we're not using MRR and the sampling rate already
	 * has a probability of >95%, we shouldn't be attempting
	 * to use it, as this only wastes precious airtime */
	if (!mrr_capable &&
	   (mi->r[ndx].stats.prob_ewma > MINSTREL_FRAC(95, 100)))
		return;

	mi->prev_sample = true;

	rate->idx = mi->r[ndx].rix;
	rate->count = minstrel_get_retry_count(&mi->r[ndx], info);
}


static void
calc_rate_durations(enum ieee80211_band band,
		    struct minstrel_rate *d,
		    struct ieee80211_rate *rate,
		    struct cfg80211_chan_def *chandef)
{
	int erp = !!(rate->flags & IEEE80211_RATE_ERP_G);
	int shift = ieee80211_chandef_get_shift(chandef);

	d->perfect_tx_time = ieee80211_frame_duration(band, 1200,
			DIV_ROUND_UP(rate->bitrate, 1 << shift), erp, 1,
			shift);
	d->ack_time = ieee80211_frame_duration(band, 10,
			DIV_ROUND_UP(rate->bitrate, 1 << shift), erp, 1,
			shift);
}

static void
init_sample_table(struct minstrel_sta_info *mi)
{
	unsigned int i, col, new_idx;
	u8 rnd[8];

	mi->sample_column = 0;
	mi->sample_row = 0;
	memset(mi->sample_table, 0xff, SAMPLE_COLUMNS * mi->n_rates);

	for (col = 0; col < SAMPLE_COLUMNS; col++) {
		prandom_bytes(rnd, sizeof(rnd));
		for (i = 0; i < mi->n_rates; i++) {
			new_idx = (i + rnd[i & 7]) % mi->n_rates;
			while (SAMPLE_TBL(mi, new_idx, col) != 0xff)
				new_idx = (new_idx + 1) % mi->n_rates;

			SAMPLE_TBL(mi, new_idx, col) = i;
		}
	}
}

static void
minstrel_rate_init(void *priv, struct ieee80211_supported_band *sband,
		   struct cfg80211_chan_def *chandef,
		   struct ieee80211_sta *sta, void *priv_sta)
{
	struct minstrel_sta_info *mi = priv_sta;
	struct minstrel_priv *mp = priv;
	struct ieee80211_rate *ctl_rate;
	unsigned int i, n = 0;
	unsigned int t_slot = 9; /* FIXME: get real slot time */
	u32 rate_flags;

	mi->sta = sta;
	mi->lowest_rix = rate_lowest_index(sband, sta);
	ctl_rate = &sband->bitrates[mi->lowest_rix];
	mi->sp_ack_dur = ieee80211_frame_duration(sband->band, 10,
				ctl_rate->bitrate,
				!!(ctl_rate->flags & IEEE80211_RATE_ERP_G), 1,
				ieee80211_chandef_get_shift(chandef));

	rate_flags = ieee80211_chandef_rate_flags(&mp->hw->conf.chandef);
	memset(mi->max_tp_rate, 0, sizeof(mi->max_tp_rate));
	mi->max_prob_rate = 0;

	for (i = 0; i < sband->n_bitrates; i++) {
		struct minstrel_rate *mr = &mi->r[n];
		struct minstrel_rate_stats *mrs = &mi->r[n].stats;
		unsigned int tx_time = 0, tx_time_cts = 0, tx_time_rtscts = 0;
		unsigned int tx_time_single;
		unsigned int cw = mp->cw_min;
		int shift;

		if (!rate_supported(sta, sband->band, i))
			continue;
		if ((rate_flags & sband->bitrates[i].flags) != rate_flags)
			continue;

		n++;
		memset(mr, 0, sizeof(*mr));
		memset(mrs, 0, sizeof(*mrs));

		mr->rix = i;
		shift = ieee80211_chandef_get_shift(chandef);
		mr->bitrate = DIV_ROUND_UP(sband->bitrates[i].bitrate,
					   (1 << shift) * 5);
		calc_rate_durations(sband->band, mr, &sband->bitrates[i],
				    chandef);

		/* calculate maximum number of retransmissions before
		 * fallback (based on maximum segment size) */
		mr->sample_limit = -1;
		mrs->retry_count = 1;
		mr->retry_count_cts = 1;
		mrs->retry_count_rtscts = 1;
		tx_time = mr->perfect_tx_time + mi->sp_ack_dur;
		do {
			/* add one retransmission */
			tx_time_single = mr->ack_time + mr->perfect_tx_time;

			/* contention window */
			tx_time_single += (t_slot * cw) >> 1;
			cw = min((cw << 1) | 1, mp->cw_max);

			tx_time += tx_time_single;
			tx_time_cts += tx_time_single + mi->sp_ack_dur;
			tx_time_rtscts += tx_time_single + 2 * mi->sp_ack_dur;
			if ((tx_time_cts < mp->segment_size) &&
				(mr->retry_count_cts < mp->max_retry))
				mr->retry_count_cts++;
			if ((tx_time_rtscts < mp->segment_size) &&
				(mrs->retry_count_rtscts < mp->max_retry))
				mrs->retry_count_rtscts++;
		} while ((tx_time < mp->segment_size) &&
				(++mr->stats.retry_count < mp->max_retry));
		mr->adjusted_retry_count = mrs->retry_count;
		if (!(sband->bitrates[i].flags & IEEE80211_RATE_ERP_G))
			mr->retry_count_cts = mrs->retry_count;
	}

	for (i = n; i < sband->n_bitrates; i++) {
		struct minstrel_rate *mr = &mi->r[i];
		mr->rix = -1;
	}

	mi->n_rates = n;
	mi->last_stats_update = jiffies;

	init_sample_table(mi);
	minstrel_update_rates(mp, mi);
}

static void *
minstrel_alloc_sta(void *priv, struct ieee80211_sta *sta, gfp_t gfp)
{
	struct ieee80211_supported_band *sband;
	struct minstrel_sta_info *mi;
	struct minstrel_priv *mp = priv;
	struct ieee80211_hw *hw = mp->hw;
	int max_rates = 0;
	int i;

	mi = kzalloc(sizeof(struct minstrel_sta_info), gfp);
	if (!mi)
		return NULL;

	for (i = 0; i < IEEE80211_NUM_BANDS; i++) {
		sband = hw->wiphy->bands[i];
		if (sband && sband->n_bitrates > max_rates)
			max_rates = sband->n_bitrates;
	}

	mi->r = kzalloc(sizeof(struct minstrel_rate) * max_rates, gfp);
	if (!mi->r)
		goto error;

	mi->sample_table = kmalloc(SAMPLE_COLUMNS * max_rates, gfp);
	if (!mi->sample_table)
		goto error1;

	mi->last_stats_update = jiffies;
	return mi;

error1:
	kfree(mi->r);
error:
	kfree(mi);
	return NULL;
}

static void
minstrel_free_sta(void *priv, struct ieee80211_sta *sta, void *priv_sta)
{
	struct minstrel_sta_info *mi = priv_sta;

	kfree(mi->sample_table);
	kfree(mi->r);
	kfree(mi);
}

static void
minstrel_init_cck_rates(struct minstrel_priv *mp)
{
	static const int bitrates[4] = { 10, 20, 55, 110 };
	struct ieee80211_supported_band *sband;
	u32 rate_flags = ieee80211_chandef_rate_flags(&mp->hw->conf.chandef);
	int i, j;

	sband = mp->hw->wiphy->bands[IEEE80211_BAND_2GHZ];
	if (!sband)
		return;

	for (i = 0, j = 0; i < sband->n_bitrates; i++) {
		struct ieee80211_rate *rate = &sband->bitrates[i];

		if (rate->flags & IEEE80211_RATE_ERP_G)
			continue;

		if ((rate_flags & sband->bitrates[i].flags) != rate_flags)
			continue;

		for (j = 0; j < ARRAY_SIZE(bitrates); j++) {
			if (rate->bitrate != bitrates[j])
				continue;

			mp->cck_rates[j] = i;
			break;
		}
	}
}

static void *
minstrel_alloc(struct ieee80211_hw *hw, struct dentry *debugfsdir)
{
	struct minstrel_priv *mp;

	mp = kzalloc(sizeof(struct minstrel_priv), GFP_ATOMIC);
	if (!mp)
		return NULL;

	/* contention window settings
	 * Just an approximation. Using the per-queue values would complicate
	 * the calculations and is probably unnecessary */
	mp->cw_min = 15;
	mp->cw_max = 1023;

	/* number of packets (in %) to use for sampling other rates
	 * sample less often for non-mrr packets, because the overhead
	 * is much higher than with mrr */
	mp->lookaround_rate = 5;
	mp->lookaround_rate_mrr = 10;

	/* maximum time that the hw is allowed to stay in one MRR segment */
	mp->segment_size = 6000;

	if (hw->max_rate_tries > 0)
		mp->max_retry = hw->max_rate_tries;
	else
		/* safe default, does not necessarily have to match hw properties */
		mp->max_retry = 7;

	if (hw->max_rates >= 4)
		mp->has_mrr = true;

	mp->hw = hw;
	mp->update_interval = 100;

#ifdef CONFIG_MAC80211_DEBUGFS
	mp->fixed_rate_idx = (u32) -1;
	mp->dbg_fixed_rate = debugfs_create_u32("fixed_rate_idx",
			S_IRUGO | S_IWUGO, debugfsdir, &mp->fixed_rate_idx);
#endif

	minstrel_init_cck_rates(mp);

	return mp;
}

static void
minstrel_free(void *priv)
{
#ifdef CONFIG_MAC80211_DEBUGFS
	debugfs_remove(((struct minstrel_priv *)priv)->dbg_fixed_rate);
#endif
	kfree(priv);
}

static u32 minstrel_get_expected_throughput(void *priv_sta)
{
	struct minstrel_sta_info *mi = priv_sta;
	struct minstrel_rate_stats *tmp_mrs;
	int idx = mi->max_tp_rate[0];
	int tmp_cur_tp;

	/* convert pkt per sec in kbps (1200 is the average pkt size used for
	 * computing cur_tp
	 */
	tmp_mrs = &mi->r[idx].stats;
	tmp_cur_tp = minstrel_get_tp_avg(&mi->r[idx], tmp_mrs->prob_ewma);
	tmp_cur_tp = tmp_cur_tp * 1200 * 8 / 1024;

	return tmp_cur_tp;
}

const struct rate_control_ops mac80211_minstrel = {
	.name = "minstrel",
	.tx_status_noskb = minstrel_tx_status,
	.get_rate = minstrel_get_rate,
	.rate_init = minstrel_rate_init,
	.alloc = minstrel_alloc,
	.free = minstrel_free,
	.alloc_sta = minstrel_alloc_sta,
	.free_sta = minstrel_free_sta,
#ifdef CONFIG_MAC80211_DEBUGFS
	.add_sta_debugfs = minstrel_add_sta_debugfs,
	.remove_sta_debugfs = minstrel_remove_sta_debugfs,
#endif
	.get_expected_throughput = minstrel_get_expected_throughput,
};

int __init
rc80211_minstrel_init(void)
{
	return ieee80211_rate_control_register(&mac80211_minstrel);
}

void
rc80211_minstrel_exit(void)
{
	ieee80211_rate_control_unregister(&mac80211_minstrel);
}