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mac80211: rc80211_minstrel: remove variance / stddev calculation
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When there are few packets (e.g. for sampling attempts), the exponentially
weighted variance is usually vastly overestimated, making the resulting data
essentially useless. As far as I know, there has not been any practical use
for this, so let's not waste any cycles on it.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
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Felix Fietkau authored and Johannes Berg committed Oct 11, 2018
1 parent f4ec7cb commit 506dbf9
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Showing 4 changed files with 9 additions and 51 deletions.
6 changes: 0 additions & 6 deletions net/mac80211/rc80211_minstrel.c
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Original file line number Diff line number Diff line change
Expand Up @@ -167,12 +167,6 @@ minstrel_calc_rate_stats(struct minstrel_rate_stats *mrs)
if (unlikely(!mrs->att_hist)) {
mrs->prob_ewma = cur_prob;
} else {
/* update exponential weighted moving variance */
mrs->prob_ewmv = minstrel_ewmv(mrs->prob_ewmv,
cur_prob,
mrs->prob_ewma,
EWMA_LEVEL);

/*update exponential weighted moving avarage */
mrs->prob_ewma = minstrel_ewma(mrs->prob_ewma,
cur_prob,
Expand Down
26 changes: 1 addition & 25 deletions net/mac80211/rc80211_minstrel.h
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Original file line number Diff line number Diff line change
Expand Up @@ -35,19 +35,6 @@ minstrel_ewma(int old, int new, int weight)
return old + incr;
}

/*
* Perform EWMV (Exponentially Weighted Moving Variance) calculation
*/
static inline int
minstrel_ewmv(int old_ewmv, int cur_prob, int prob_ewma, int weight)
{
int diff, incr;

diff = cur_prob - prob_ewma;
incr = (EWMA_DIV - weight) * diff / EWMA_DIV;
return weight * (old_ewmv + MINSTREL_TRUNC(diff * incr)) / EWMA_DIV;
}

struct minstrel_rate_stats {
/* current / last sampling period attempts/success counters */
u16 attempts, last_attempts;
Expand All @@ -56,11 +43,8 @@ struct minstrel_rate_stats {
/* total attempts/success counters */
u32 att_hist, succ_hist;

/* statistis of packet delivery probability
* prob_ewma - exponential weighted moving average of prob
* prob_ewmsd - exp. weighted moving standard deviation of prob */
/* prob_ewma - exponential weighted moving average of prob */
u16 prob_ewma;
u16 prob_ewmv;

/* maximum retry counts */
u8 retry_count;
Expand Down Expand Up @@ -140,14 +124,6 @@ struct minstrel_debugfs_info {
char buf[];
};

/* Get EWMSD (Exponentially Weighted Moving Standard Deviation) * 10 */
static inline int
minstrel_get_ewmsd10(struct minstrel_rate_stats *mrs)
{
unsigned int ewmv = mrs->prob_ewmv;
return int_sqrt(MINSTREL_TRUNC(ewmv * 1000 * 1000));
}

extern const struct rate_control_ops mac80211_minstrel;
void minstrel_add_sta_debugfs(void *priv, void *priv_sta, struct dentry *dir);

Expand Down
14 changes: 4 additions & 10 deletions net/mac80211/rc80211_minstrel_debugfs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -70,14 +70,13 @@ minstrel_stats_open(struct inode *inode, struct file *file)
p = ms->buf;
p += sprintf(p, "\n");
p += sprintf(p,
"best __________rate_________ ________statistics________ ____last_____ ______sum-of________\n");
"best __________rate_________ ____statistics___ ____last_____ ______sum-of________\n");
p += sprintf(p,
"rate [name idx airtime max_tp] [avg(tp) avg(prob) sd(prob)] [retry|suc|att] [#success | #attempts]\n");
"rate [name idx airtime max_tp] [avg(tp) avg(prob)] [retry|suc|att] [#success | #attempts]\n");

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

*(p++) = (i == mi->max_tp_rate[0]) ? 'A' : ' ';
*(p++) = (i == mi->max_tp_rate[1]) ? 'B' : ' ';
Expand All @@ -93,15 +92,13 @@ minstrel_stats_open(struct inode *inode, struct file *file)
tp_max = minstrel_get_tp_avg(mr, MINSTREL_FRAC(100,100));
tp_avg = minstrel_get_tp_avg(mr, mrs->prob_ewma);
eprob = MINSTREL_TRUNC(mrs->prob_ewma * 1000);
prob_ewmsd = minstrel_get_ewmsd10(mrs);

p += sprintf(p, "%4u.%1u %4u.%1u %3u.%1u %3u.%1u"
p += sprintf(p, "%4u.%1u %4u.%1u %3u.%1u"
" %3u %3u %-3u "
"%9llu %-9llu\n",
tp_max / 10, tp_max % 10,
tp_avg / 10, tp_avg % 10,
eprob / 10, eprob % 10,
prob_ewmsd / 10, prob_ewmsd % 10,
mrs->retry_count,
mrs->last_success,
mrs->last_attempts,
Expand Down Expand Up @@ -137,7 +134,6 @@ minstrel_stats_csv_open(struct inode *inode, struct file *file)
for (i = 0; i < mi->n_rates; i++) {
struct minstrel_rate *mr = &mi->r[i];
struct minstrel_rate_stats *mrs = &mi->r[i].stats;
unsigned int prob_ewmsd;

p += sprintf(p, "%s" ,((i == mi->max_tp_rate[0]) ? "A" : ""));
p += sprintf(p, "%s" ,((i == mi->max_tp_rate[1]) ? "B" : ""));
Expand All @@ -153,14 +149,12 @@ minstrel_stats_csv_open(struct inode *inode, struct file *file)
tp_max = minstrel_get_tp_avg(mr, MINSTREL_FRAC(100,100));
tp_avg = minstrel_get_tp_avg(mr, mrs->prob_ewma);
eprob = MINSTREL_TRUNC(mrs->prob_ewma * 1000);
prob_ewmsd = minstrel_get_ewmsd10(mrs);

p += sprintf(p, "%u.%u,%u.%u,%u.%u,%u.%u,%u,%u,%u,"
p += sprintf(p, "%u.%u,%u.%u,%u.%u,%u,%u,%u,"
"%llu,%llu,%d,%d\n",
tp_max / 10, tp_max % 10,
tp_avg / 10, tp_avg % 10,
eprob / 10, eprob % 10,
prob_ewmsd / 10, prob_ewmsd % 10,
mrs->retry_count,
mrs->last_success,
mrs->last_attempts,
Expand Down
14 changes: 4 additions & 10 deletions net/mac80211/rc80211_minstrel_ht_debugfs.c
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Original file line number Diff line number Diff line change
Expand Up @@ -57,7 +57,6 @@ minstrel_ht_stats_dump(struct minstrel_ht_sta *mi, int i, char *p)
struct minstrel_rate_stats *mrs = &mi->groups[i].rates[j];
static const int bitrates[4] = { 10, 20, 55, 110 };
int idx = i * MCS_GROUP_RATES + j;
unsigned int prob_ewmsd;
unsigned int duration;

if (!(mi->supported[i] & BIT(j)))
Expand Down Expand Up @@ -104,15 +103,13 @@ minstrel_ht_stats_dump(struct minstrel_ht_sta *mi, int i, char *p)
tp_max = minstrel_ht_get_tp_avg(mi, i, j, MINSTREL_FRAC(100, 100));
tp_avg = minstrel_ht_get_tp_avg(mi, i, j, mrs->prob_ewma);
eprob = MINSTREL_TRUNC(mrs->prob_ewma * 1000);
prob_ewmsd = minstrel_get_ewmsd10(mrs);

p += sprintf(p, "%4u.%1u %4u.%1u %3u.%1u %3u.%1u"
p += sprintf(p, "%4u.%1u %4u.%1u %3u.%1u"
" %3u %3u %-3u "
"%9llu %-9llu\n",
tp_max / 10, tp_max % 10,
tp_avg / 10, tp_avg % 10,
eprob / 10, eprob % 10,
prob_ewmsd / 10, prob_ewmsd % 10,
mrs->retry_count,
mrs->last_success,
mrs->last_attempts,
Expand Down Expand Up @@ -149,9 +146,9 @@ minstrel_ht_stats_open(struct inode *inode, struct file *file)

p += sprintf(p, "\n");
p += sprintf(p,
" best ____________rate__________ ________statistics________ _____last____ ______sum-of________\n");
" best ____________rate__________ ____statistics___ _____last____ ______sum-of________\n");
p += sprintf(p,
"mode guard # rate [name idx airtime max_tp] [avg(tp) avg(prob) sd(prob)] [retry|suc|att] [#success | #attempts]\n");
"mode guard # rate [name idx airtime max_tp] [avg(tp) avg(prob)] [retry|suc|att] [#success | #attempts]\n");

p = minstrel_ht_stats_dump(mi, MINSTREL_CCK_GROUP, p);
for (i = 0; i < MINSTREL_CCK_GROUP; i++)
Expand Down Expand Up @@ -206,7 +203,6 @@ minstrel_ht_stats_csv_dump(struct minstrel_ht_sta *mi, int i, char *p)
struct minstrel_rate_stats *mrs = &mi->groups[i].rates[j];
static const int bitrates[4] = { 10, 20, 55, 110 };
int idx = i * MCS_GROUP_RATES + j;
unsigned int prob_ewmsd;
unsigned int duration;

if (!(mi->supported[i] & BIT(j)))
Expand Down Expand Up @@ -251,14 +247,12 @@ minstrel_ht_stats_csv_dump(struct minstrel_ht_sta *mi, int i, char *p)
tp_max = minstrel_ht_get_tp_avg(mi, i, j, MINSTREL_FRAC(100, 100));
tp_avg = minstrel_ht_get_tp_avg(mi, i, j, mrs->prob_ewma);
eprob = MINSTREL_TRUNC(mrs->prob_ewma * 1000);
prob_ewmsd = minstrel_get_ewmsd10(mrs);

p += sprintf(p, "%u.%u,%u.%u,%u.%u,%u.%u,%u,%u,"
p += sprintf(p, "%u.%u,%u.%u,%u.%u,%u,%u,"
"%u,%llu,%llu,",
tp_max / 10, tp_max % 10,
tp_avg / 10, tp_avg % 10,
eprob / 10, eprob % 10,
prob_ewmsd / 10, prob_ewmsd % 10,
mrs->retry_count,
mrs->last_success,
mrs->last_attempts,
Expand Down

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