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/net/mac80211/rc80211_pid_algo.c

http://github.com/mirrors/linux
C | 478 lines | 327 code | 66 blank | 85 comment | 50 complexity | 910c4e05396e8a66eb08336735d085c9 MD5 | raw file
  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 cfg80211_chan_def *chandef,
297			   struct ieee80211_sta *sta, void *priv_sta)
298{
299	struct rc_pid_sta_info *spinfo = priv_sta;
300	struct rc_pid_info *pinfo = priv;
301	struct rc_pid_rateinfo *rinfo = pinfo->rinfo;
302	int i, j, tmp;
303	bool s;
304
305	/* TODO: This routine should consider using RSSI from previous packets
306	 * as we need to have IEEE 802.1X auth succeed immediately after assoc..
307	 * Until that method is implemented, we will use the lowest supported
308	 * rate as a workaround. */
309
310	/* Sort the rates. This is optimized for the most common case (i.e.
311	 * almost-sorted CCK+OFDM rates). Kind of bubble-sort with reversed
312	 * mapping too. */
313	for (i = 0; i < sband->n_bitrates; i++) {
314		rinfo[i].index = i;
315		rinfo[i].rev_index = i;
316		if (RC_PID_FAST_START)
317			rinfo[i].diff = 0;
318		else
319			rinfo[i].diff = i * pinfo->norm_offset;
320	}
321	for (i = 1; i < sband->n_bitrates; i++) {
322		s = false;
323		for (j = 0; j < sband->n_bitrates - i; j++)
324			if (unlikely(sband->bitrates[rinfo[j].index].bitrate >
325				     sband->bitrates[rinfo[j + 1].index].bitrate)) {
326				tmp = rinfo[j].index;
327				rinfo[j].index = rinfo[j + 1].index;
328				rinfo[j + 1].index = tmp;
329				rinfo[rinfo[j].index].rev_index = j;
330				rinfo[rinfo[j + 1].index].rev_index = j + 1;
331				s = true;
332			}
333		if (!s)
334			break;
335	}
336
337	spinfo->txrate_idx = rate_lowest_index(sband, sta);
338}
339
340static void *rate_control_pid_alloc(struct ieee80211_hw *hw,
341				    struct dentry *debugfsdir)
342{
343	struct rc_pid_info *pinfo;
344	struct rc_pid_rateinfo *rinfo;
345	struct ieee80211_supported_band *sband;
346	int i, max_rates = 0;
347#ifdef CONFIG_MAC80211_DEBUGFS
348	struct rc_pid_debugfs_entries *de;
349#endif
350
351	pinfo = kmalloc(sizeof(*pinfo), GFP_ATOMIC);
352	if (!pinfo)
353		return NULL;
354
355	for (i = 0; i < IEEE80211_NUM_BANDS; i++) {
356		sband = hw->wiphy->bands[i];
357		if (sband && sband->n_bitrates > max_rates)
358			max_rates = sband->n_bitrates;
359	}
360
361	rinfo = kmalloc(sizeof(*rinfo) * max_rates, GFP_ATOMIC);
362	if (!rinfo) {
363		kfree(pinfo);
364		return NULL;
365	}
366
367	pinfo->target = RC_PID_TARGET_PF;
368	pinfo->sampling_period = RC_PID_INTERVAL;
369	pinfo->coeff_p = RC_PID_COEFF_P;
370	pinfo->coeff_i = RC_PID_COEFF_I;
371	pinfo->coeff_d = RC_PID_COEFF_D;
372	pinfo->smoothing_shift = RC_PID_SMOOTHING_SHIFT;
373	pinfo->sharpen_factor = RC_PID_SHARPENING_FACTOR;
374	pinfo->sharpen_duration = RC_PID_SHARPENING_DURATION;
375	pinfo->norm_offset = RC_PID_NORM_OFFSET;
376	pinfo->rinfo = rinfo;
377	pinfo->oldrate = 0;
378
379#ifdef CONFIG_MAC80211_DEBUGFS
380	de = &pinfo->dentries;
381	de->target = debugfs_create_u32("target_pf", S_IRUSR | S_IWUSR,
382					debugfsdir, &pinfo->target);
383	de->sampling_period = debugfs_create_u32("sampling_period",
384						 S_IRUSR | S_IWUSR, debugfsdir,
385						 &pinfo->sampling_period);
386	de->coeff_p = debugfs_create_u32("coeff_p", S_IRUSR | S_IWUSR,
387					 debugfsdir, (u32 *)&pinfo->coeff_p);
388	de->coeff_i = debugfs_create_u32("coeff_i", S_IRUSR | S_IWUSR,
389					 debugfsdir, (u32 *)&pinfo->coeff_i);
390	de->coeff_d = debugfs_create_u32("coeff_d", S_IRUSR | S_IWUSR,
391					 debugfsdir, (u32 *)&pinfo->coeff_d);
392	de->smoothing_shift = debugfs_create_u32("smoothing_shift",
393						 S_IRUSR | S_IWUSR, debugfsdir,
394						 &pinfo->smoothing_shift);
395	de->sharpen_factor = debugfs_create_u32("sharpen_factor",
396					       S_IRUSR | S_IWUSR, debugfsdir,
397					       &pinfo->sharpen_factor);
398	de->sharpen_duration = debugfs_create_u32("sharpen_duration",
399						  S_IRUSR | S_IWUSR, debugfsdir,
400						  &pinfo->sharpen_duration);
401	de->norm_offset = debugfs_create_u32("norm_offset",
402					     S_IRUSR | S_IWUSR, debugfsdir,
403					     &pinfo->norm_offset);
404#endif
405
406	return pinfo;
407}
408
409static void rate_control_pid_free(void *priv)
410{
411	struct rc_pid_info *pinfo = priv;
412#ifdef CONFIG_MAC80211_DEBUGFS
413	struct rc_pid_debugfs_entries *de = &pinfo->dentries;
414
415	debugfs_remove(de->norm_offset);
416	debugfs_remove(de->sharpen_duration);
417	debugfs_remove(de->sharpen_factor);
418	debugfs_remove(de->smoothing_shift);
419	debugfs_remove(de->coeff_d);
420	debugfs_remove(de->coeff_i);
421	debugfs_remove(de->coeff_p);
422	debugfs_remove(de->sampling_period);
423	debugfs_remove(de->target);
424#endif
425
426	kfree(pinfo->rinfo);
427	kfree(pinfo);
428}
429
430static void *rate_control_pid_alloc_sta(void *priv, struct ieee80211_sta *sta,
431					gfp_t gfp)
432{
433	struct rc_pid_sta_info *spinfo;
434
435	spinfo = kzalloc(sizeof(*spinfo), gfp);
436	if (spinfo == NULL)
437		return NULL;
438
439	spinfo->last_sample = jiffies;
440
441#ifdef CONFIG_MAC80211_DEBUGFS
442	spin_lock_init(&spinfo->events.lock);
443	init_waitqueue_head(&spinfo->events.waitqueue);
444#endif
445
446	return spinfo;
447}
448
449static void rate_control_pid_free_sta(void *priv, struct ieee80211_sta *sta,
450				      void *priv_sta)
451{
452	kfree(priv_sta);
453}
454
455static struct rate_control_ops mac80211_rcpid = {
456	.name = "pid",
457	.tx_status = rate_control_pid_tx_status,
458	.get_rate = rate_control_pid_get_rate,
459	.rate_init = rate_control_pid_rate_init,
460	.alloc = rate_control_pid_alloc,
461	.free = rate_control_pid_free,
462	.alloc_sta = rate_control_pid_alloc_sta,
463	.free_sta = rate_control_pid_free_sta,
464#ifdef CONFIG_MAC80211_DEBUGFS
465	.add_sta_debugfs = rate_control_pid_add_sta_debugfs,
466	.remove_sta_debugfs = rate_control_pid_remove_sta_debugfs,
467#endif
468};
469
470int __init rc80211_pid_init(void)
471{
472	return ieee80211_rate_control_register(&mac80211_rcpid);
473}
474
475void rc80211_pid_exit(void)
476{
477	ieee80211_rate_control_unregister(&mac80211_rcpid);
478}