minstrel: improve performance for non-MRR drivers

This patch enhances minstrel's performance for non-MRR setups,
by preventing it from sampling slower rates with >95% success
probability and by putting at least 1 non-sample frame between
several sample frames.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

2 files changed, 27 insertions, 4 deletions

diff --git a/net/mac80211/rc80211_minstrel.c b/net/mac80211/rc80211_minstrel.c
index 759ddd8bf0f4..c10debc29ad6 100644
--- a/net/mac80211/rc80211_minstrel.c
+++ b/net/mac80211/rc80211_minstrel.c
@@ -126,7 +126,9 @@ minstrel_update_stats(struct minstrel_priv *mp, struct minstrel_sta_info *mi)
                         mr->adjusted_retry_count = mr->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 = mr->retry_count;
                 }
                 if (!mr->adjusted_retry_count)
@@ -265,7 +267,8 @@ minstrel_get_rate(void *priv, struct ieee80211_sta *sta,
                         (mi->sample_count + mi->sample_deferred / 2);
 
         /* delta > 0: sampling required */
-        if (delta > 0) {
+        if ((delta > 0) && (mrr || !mi->prev_sample)) {
+                struct minstrel_rate *msr;
                 if (mi->packet_count >= 10000) {
                         mi->sample_deferred = 0;
                         mi->sample_count = 0;
@@ -284,13 +287,20 @@ minstrel_get_rate(void *priv, struct ieee80211_sta *sta,
                 }
 
                 sample_ndx = minstrel_get_next_sample(mi);
+                msr = &mi->r[sample_ndx];
                 sample = true;
-                sample_slower = mrr && (mi->r[sample_ndx].perfect_tx_time >
+                sample_slower = mrr && (msr->perfect_tx_time >
                         mi->r[ndx].perfect_tx_time);
 
                 if (!sample_slower) {
-                        ndx = sample_ndx;
-                        mi->sample_count++;
+                        if (msr->sample_limit != 0) {
+                                ndx = sample_ndx;
+                                mi->sample_count++;
+                                if (msr->sample_limit > 0)
+                                        msr->sample_limit--;
+                        } else {
+                                sample = false;
+                        }
                 } else {
                         /* Only use IEEE80211_TX_CTL_RATE_CTRL_PROBE to mark
                          * packets that have the sampling rate deferred to the
@@ -302,10 +312,20 @@ minstrel_get_rate(void *priv, struct ieee80211_sta *sta,
                         mi->sample_deferred++;
                 }
         }
+        mi->prev_sample = sample;
+
+        /* 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 && sample && (mi->r[ndx].probability > 17100))
+                ndx = mi->max_tp_rate;
+
         ar[0].idx = mi->r[ndx].rix;
         ar[0].count = minstrel_get_retry_count(&mi->r[ndx], info);
 
         if (!mrr) {
+                if (!sample)
+                        ar[0].count = mp->max_retry;
                 ar[1].idx = mi->lowest_rix;
                 ar[1].count = mp->max_retry;
                 return;
@@ -401,6 +421,7 @@ minstrel_rate_init(void *priv, struct ieee80211_supported_band *sband,
 
                 /* calculate maximum number of retransmissions before
                  * fallback (based on maximum segment size) */
+                mr->sample_limit = -1;
                 mr->retry_count = 1;
                 mr->retry_count_cts = 1;
                 mr->retry_count_rtscts = 1;
diff --git a/net/mac80211/rc80211_minstrel.h b/net/mac80211/rc80211_minstrel.h
index 9a90a6aee043..869fe0ef951d 100644
--- a/net/mac80211/rc80211_minstrel.h
+++ b/net/mac80211/rc80211_minstrel.h
@@ -16,6 +16,7 @@ struct minstrel_rate {
         unsigned int perfect_tx_time;
         unsigned int ack_time;
 
+        int sample_limit;
         unsigned int retry_count;
         unsigned int retry_count_cts;
         unsigned int retry_count_rtscts;
@@ -57,6 +58,7 @@ struct minstrel_sta_info {
 
         int n_rates;
         struct minstrel_rate *r;
+        bool prev_sample;
 
         /* sampling table */
         u8 *sample_table;