mac80211: add standard deviation to Minstrel stats

This patch adds the statistical descriptor "standard deviation"
to better describe the current properties of Minstrel and
Minstrel-HTs success probability distribution. The standard
deviation (SD) is calculated as exponential weighted moving
standard deviation (EWMSD) and its current value is added as
new column in all rc_stats (in debugfs).

Signed-off-by: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
Acked-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index c4a3477..247552a 100644 (file)
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -153,7 +153,7 @@ minstrel_update_rates(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
 }
 
 /*
-* Recalculate success probabilities and counters for a given rate using EWMA
+* Recalculate statistics and counters of a given rate
 */
 void
 minstrel_calc_rate_stats(struct minstrel_rate_stats *mrs)
@@ -161,11 +161,20 @@ 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))
+               if (unlikely(!mrs->att_hist)) {
                        mrs->prob_ewma = mrs->cur_prob;
-               else
+               } 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->cur_prob,
+                                                      EWMA_LEVEL);
+               }
                mrs->att_hist += mrs->attempts;
                mrs->succ_hist += mrs->success;
        } else {
@@ -193,7 +202,7 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
                struct minstrel_rate_stats *mrs = &mi->r[i].stats;
                struct minstrel_rate_stats *tmp_mrs = &mi->r[tmp_prob_rate].stats;
 
-               /* Update success probabilities per rate */
+               /* Update statistics of success probability per rate */
                minstrel_calc_rate_stats(mrs);
 
                /* Sample less often below the 10% chance of success.

diff --git a/net/mac80211/rc80211_minstrel.h b/net/mac80211/rc80211_minstrel.h
index 9c85a61..c230bbe 100644 (file)
--- a/net/mac80211/rc80211_minstrel.h
+++ b/net/mac80211/rc80211_minstrel.h
@@ -35,6 +35,24 @@ minstrel_ewma(int old, int new, int weight)
        return old + incr;
 }
 
+/*
+ * Perform EWMSD (Exponentially Weighted Moving Standard Deviation) calculation
+ */
+static inline int
+minstrel_ewmsd(int old_ewmsd, int cur_prob, int prob_ewma, int weight)
+{
+       int diff, incr, tmp_var;
+
+       /* calculate exponential weighted moving variance */
+       diff = MINSTREL_TRUNC((cur_prob - prob_ewma) * 1000000);
+       incr = (EWMA_DIV - weight) * diff / EWMA_DIV;
+       tmp_var = old_ewmsd * old_ewmsd;
+       tmp_var = weight * (tmp_var + diff * incr / 1000000) / EWMA_DIV;
+
+       /* return standard deviation */
+       return (u16) int_sqrt(tmp_var);
+}
+
 struct minstrel_rate_stats {
        /* current / last sampling period attempts/success counters */
        u16 attempts, last_attempts;
@@ -45,9 +63,11 @@ struct minstrel_rate_stats {
 
        /* statistis of packet delivery probability
         *  cur_prob  - current prob within last update intervall
-        *  prob_ewma - exponential weighted moving average of prob */
+        *  prob_ewma - exponential weighted moving average of prob
+        *  prob_ewmsd - exp. weighted moving standard deviation of prob */
        unsigned int cur_prob;
        unsigned int prob_ewma;
+       u16 prob_ewmsd;
 
        /* maximum retry counts */
        u8 retry_count;

diff --git a/net/mac80211/rc80211_minstrel_debugfs.c b/net/mac80211/rc80211_minstrel_debugfs.c
index 617b81f..1db5f7c 100644 (file)
--- a/net/mac80211/rc80211_minstrel_debugfs.c
+++ b/net/mac80211/rc80211_minstrel_debugfs.c
@@ -85,10 +85,12 @@ minstrel_stats_open(struct inode *inode, struct file *file)
        file->private_data = ms;
        p = ms->buf;
        p += sprintf(p, "\n");
-       p += sprintf(p, "best   __________rate_________    __statistics__    "
-                       "________last_______    ______sum-of________\n");
-       p += sprintf(p, "rate  [name idx airtime max_tp]  [ ø(tp) ø(prob)]  "
-                       "[prob.|retry|suc|att]  [#success | #attempts]\n");
+       p += sprintf(p, "best   __________rate_________    ______"
+                       "statistics______    ________last_______    "
+                       "______sum-of________\n");
+       p += sprintf(p, "rate  [name idx airtime max_tp]  [ ø(tp) ø(prob) "
+                       "sd(prob)]  [prob.|retry|suc|att]  "
+                       "[#success | #attempts]\n");
 
        for (i = 0; i < mi->n_rates; i++) {
                struct minstrel_rate *mr = &mi->r[i];
@@ -110,11 +112,13 @@ minstrel_stats_open(struct inode *inode, struct file *file)
                prob = MINSTREL_TRUNC(mrs->cur_prob * 1000);
                eprob = MINSTREL_TRUNC(mrs->prob_ewma * 1000);
 
-               p += sprintf(p, "%4u.%1u   %4u.%1u   %3u.%1u     %3u.%1u %3u"
-                               "   %3u %-3u   %9llu   %-9llu\n",
+               p += sprintf(p, "%4u.%1u   %4u.%1u   %3u.%1u    %3u.%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,
+                               mrs->prob_ewmsd / 10, mrs->prob_ewmsd % 10,
                                prob / 10, prob % 10,
                                mrs->retry_count,
                                mrs->last_success,
@@ -176,11 +180,12 @@ minstrel_stats_csv_open(struct inode *inode, struct file *file)
                prob = MINSTREL_TRUNC(mrs->cur_prob * 1000);
                eprob = MINSTREL_TRUNC(mrs->prob_ewma * 1000);
 
-               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.%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,
+                               mrs->prob_ewmsd / 10, mrs->prob_ewmsd % 10,
                                prob / 10, prob % 10,
                                mrs->retry_count,
                                mrs->last_success,

diff --git a/net/mac80211/rc80211_minstrel_ht_debugfs.c b/net/mac80211/rc80211_minstrel_ht_debugfs.c
index 135ed39..6822ce0 100644 (file)
--- a/net/mac80211/rc80211_minstrel_ht_debugfs.c
+++ b/net/mac80211/rc80211_minstrel_ht_debugfs.c
@@ -86,11 +86,13 @@ minstrel_ht_stats_dump(struct minstrel_ht_sta *mi, int i, char *p)
                prob = MINSTREL_TRUNC(mrs->cur_prob * 1000);
                eprob = MINSTREL_TRUNC(mrs->prob_ewma * 1000);
 
-               p += sprintf(p, "%4u.%1u    %4u.%1u   %3u.%1u    %3u.%1u "
-                               "%3u   %3u %-3u   %9llu   %-9llu\n",
+               p += sprintf(p, "%4u.%1u   %4u.%1u   %3u.%1u    %3u.%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,
+                               mrs->prob_ewmsd / 10, mrs->prob_ewmsd % 10,
                                prob / 10, prob % 10,
                                mrs->retry_count,
                                mrs->last_success,
@@ -128,10 +130,10 @@ minstrel_ht_stats_open(struct inode *inode, struct file *file)
 
        p += sprintf(p, "\n");
        p += sprintf(p, "              best   ____________rate__________    "
-                       "__statistics__    ________last_______    "
+                       "______statistics______    ________last_______    "
                        "______sum-of________\n");
        p += sprintf(p, "mode guard #  rate  [name   idx airtime  max_tp]  "
-                       "[ ø(tp) ø(prob)]  [prob.|retry|suc|att]  [#success | "
+                       "[ ø(tp) ø(prob) sd(prob)]  [prob.|retry|suc|att]  [#success | "
                        "#attempts]\n");
 
        p = minstrel_ht_stats_dump(mi, MINSTREL_CCK_GROUP, p);
@@ -229,10 +231,12 @@ minstrel_ht_stats_csv_dump(struct minstrel_ht_sta *mi, int i, char *p)
                prob = MINSTREL_TRUNC(mrs->cur_prob * 1000);
                eprob = MINSTREL_TRUNC(mrs->prob_ewma * 1000);
 
-               p += sprintf(p, "%u.%u,%u.%u,%u.%u,%u.%u,%u,%u,%u,%llu,%llu,",
+               p += sprintf(p, "%u.%u,%u.%u,%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,
+                               mrs->prob_ewmsd / 10, mrs->prob_ewmsd % 10,
                                prob / 10, prob % 10,
                                mrs->retry_count,
                                mrs->last_success,