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
|
From: Felix Fietkau <nbd@nbd.name>
Date: Sat, 28 Sep 2019 15:46:06 +0200
Subject: [PATCH] mac80211: minstrel_ht: replace rate stats ewma with a
better moving average
Rate success probability usually fluctuates a lot under normal conditions.
With a simple EWMA, noise and fluctuation can be reduced by increasing the
window length, but that comes at the cost of introducing lag on sudden
changes.
This change replaces the EWMA implementation with a moving average that's
designed to significantly reduce lag while keeping a bigger window size
by being better at filtering out noise.
It is only slightly more expensive than the simple EWMA and still avoids
divisions in its calculation.
The algorithm is adapted from an implementation intended for a completely
different field (stock market trading), where the tradeoff of lag vs
noise filtering is equally important.
The algorithm works in the same way as the "smoothing filter" from
http://www.stockspotter.com/files/PredictiveIndicators.pdf adapted for
fixed-point math with some constants, using only addition, bit shifts
and multiplication
To better make use of the filtering and bigger window size, the update
interval is cut in half.
For testing, the algorithm can be reverted to the older one via debugfs
Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -157,14 +157,18 @@ minstrel_update_rates(struct minstrel_pr
* Recalculate statistics and counters of a given rate
*/
void
-minstrel_calc_rate_stats(struct minstrel_rate_stats *mrs)
+minstrel_calc_rate_stats(struct minstrel_priv *mp,
+ struct minstrel_rate_stats *mrs)
{
unsigned int cur_prob;
if (unlikely(mrs->attempts > 0)) {
mrs->sample_skipped = 0;
cur_prob = MINSTREL_FRAC(mrs->success, mrs->attempts);
- if (unlikely(!mrs->att_hist)) {
+ if (mp->new_avg) {
+ mrs->prob_ewma = minstrel_filter_avg_add(&mrs->avg,
+ cur_prob);
+ } else if (unlikely(!mrs->att_hist)) {
mrs->prob_ewma = cur_prob;
} else {
/*update exponential weighted moving avarage */
@@ -200,7 +204,7 @@ minstrel_update_stats(struct minstrel_pr
struct minstrel_rate_stats *tmp_mrs = &mi->r[tmp_prob_rate].stats;
/* Update statistics of success probability per rate */
- minstrel_calc_rate_stats(mrs);
+ minstrel_calc_rate_stats(mp, mrs);
/* Sample less often below the 10% chance of success.
* Sample less often above the 95% chance of success. */
@@ -289,7 +293,8 @@ minstrel_tx_status(void *priv, struct ie
if (mi->sample_deferred > 0)
mi->sample_deferred--;
- if (time_after(jiffies, mi->last_stats_update + mp->update_interval))
+ if (time_after(jiffies, mi->last_stats_update +
+ mp->update_interval / (mp->new_avg ? 2 : 1)))
minstrel_update_stats(mp, mi);
}
--- a/net/mac80211/rc80211_minstrel.h
+++ b/net/mac80211/rc80211_minstrel.h
@@ -19,6 +19,21 @@
#define MAX_THR_RATES 4
/*
+ * Coefficients for moving average with noise filter (period=16),
+ * scaled by 10 bits
+ *
+ * a1 = exp(-pi * sqrt(2) / period)
+ * coeff2 = 2 * a1 * cos(sqrt(2) * 2 * pi / period)
+ * coeff3 = -sqr(a1)
+ * coeff1 = 1 - coeff2 - coeff3
+ */
+#define MINSTREL_AVG_COEFF1 (MINSTREL_FRAC(1, 1) - \
+ MINSTREL_AVG_COEFF2 - \
+ MINSTREL_AVG_COEFF3)
+#define MINSTREL_AVG_COEFF2 0x00001499
+#define MINSTREL_AVG_COEFF3 -0x0000092e
+
+/*
* Perform EWMA (Exponentially Weighted Moving Average) calculation
*/
static inline int
@@ -32,6 +47,41 @@ minstrel_ewma(int old, int new, int weig
return old + incr;
}
+struct minstrel_avg_ctx {
+ s32 prev[2];
+};
+
+static inline int minstrel_filter_avg_add(struct minstrel_avg_ctx *ctx, s32 in)
+{
+ s32 out_1 = ctx->prev[0];
+ s32 out_2 = ctx->prev[1];
+ s32 val;
+
+ if (!in)
+ in += 1;
+
+ if (!out_1) {
+ val = out_1 = in;
+ goto out;
+ }
+
+ val = MINSTREL_AVG_COEFF1 * in;
+ val += MINSTREL_AVG_COEFF2 * out_1;
+ val += MINSTREL_AVG_COEFF3 * out_2;
+ val >>= MINSTREL_SCALE;
+
+ if (val > 1 << MINSTREL_SCALE)
+ val = 1 << MINSTREL_SCALE;
+ if (val < 0)
+ val = 1;
+
+out:
+ ctx->prev[1] = out_1;
+ ctx->prev[0] = val;
+
+ return val;
+}
+
struct minstrel_rate_stats {
/* current / last sampling period attempts/success counters */
u16 attempts, last_attempts;
@@ -40,6 +90,8 @@ struct minstrel_rate_stats {
/* total attempts/success counters */
u32 att_hist, succ_hist;
+ struct minstrel_avg_ctx avg;
+
/* prob_ewma - exponential weighted moving average of prob */
u16 prob_ewma;
@@ -95,6 +147,7 @@ struct minstrel_sta_info {
struct minstrel_priv {
struct ieee80211_hw *hw;
bool has_mrr;
+ bool new_avg;
u32 sample_switch;
unsigned int cw_min;
unsigned int cw_max;
@@ -126,7 +179,8 @@ extern const struct rate_control_ops mac
void minstrel_add_sta_debugfs(void *priv, void *priv_sta, struct dentry *dir);
/* Recalculate success probabilities and counters for a given rate using EWMA */
-void minstrel_calc_rate_stats(struct minstrel_rate_stats *mrs);
+void minstrel_calc_rate_stats(struct minstrel_priv *mp,
+ struct minstrel_rate_stats *mrs);
int minstrel_get_tp_avg(struct minstrel_rate *mr, int prob_ewma);
/* debugfs */
--- a/net/mac80211/rc80211_minstrel_ht.c
+++ b/net/mac80211/rc80211_minstrel_ht.c
@@ -737,7 +737,7 @@ minstrel_ht_update_stats(struct minstrel
mrs = &mg->rates[i];
mrs->retry_updated = false;
- minstrel_calc_rate_stats(mrs);
+ minstrel_calc_rate_stats(mp, mrs);
cur_prob = mrs->prob_ewma;
if (minstrel_ht_get_tp_avg(mi, group, i, cur_prob) == 0)
@@ -773,6 +773,8 @@ minstrel_ht_update_stats(struct minstrel
/* try to sample all available rates during each interval */
mi->sample_count *= 8;
+ if (mp->new_avg)
+ mi->sample_count /= 2;
if (sample)
minstrel_ht_rate_sample_switch(mp, mi);
@@ -889,6 +891,7 @@ minstrel_ht_tx_status(void *priv, struct
struct ieee80211_tx_rate *ar = info->status.rates;
struct minstrel_rate_stats *rate, *rate2, *rate_sample = NULL;
struct minstrel_priv *mp = priv;
+ u32 update_interval = mp->update_interval / 2;
bool last, update = false;
bool sample_status = false;
int i;
@@ -943,6 +946,10 @@ minstrel_ht_tx_status(void *priv, struct
switch (mi->sample_mode) {
case MINSTREL_SAMPLE_IDLE:
+ if (mp->new_avg &&
+ (mp->hw->max_rates > 1 ||
+ mi->total_packets_cur < SAMPLE_SWITCH_THR))
+ update_interval /= 2;
break;
case MINSTREL_SAMPLE_ACTIVE:
@@ -983,8 +990,7 @@ minstrel_ht_tx_status(void *priv, struct
}
}
- if (time_after(jiffies, mi->last_stats_update +
- mp->update_interval / 2)) {
+ if (time_after(jiffies, mi->last_stats_update + update_interval)) {
update = true;
minstrel_ht_update_stats(mp, mi, true);
}
@@ -1665,6 +1671,7 @@ minstrel_ht_alloc(struct ieee80211_hw *h
mp->hw = hw;
mp->update_interval = HZ / 10;
+ mp->new_avg = true;
#ifdef CPTCFG_MAC80211_DEBUGFS
mp->fixed_rate_idx = (u32) -1;
@@ -1672,6 +1679,8 @@ minstrel_ht_alloc(struct ieee80211_hw *h
&mp->fixed_rate_idx);
debugfs_create_u32("sample_switch", S_IRUGO | S_IWUSR, debugfsdir,
&mp->sample_switch);
+ debugfs_create_bool("new_avg", S_IRUGO | S_IWUSR, debugfsdir,
+ &mp->new_avg);
#endif
minstrel_ht_init_cck_rates(mp);
|
