[PATCH v2 3/6] mac80211: minstrel_ht: reduce the need to sample slower rates

[Felix Fietkau <nbd@nbd.name>]

In order to more gracefully be able to fall back to lower rates without too
much throughput fluctuations, initialize all untested rates below tested ones
to the maximum probabilty of higher rates.
Usually this leads to untested lower rates getting initialized with a
probability value of 100%, making them better candidates for fallback without
having to rely on random probing

Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
 net/mac80211/rc80211_minstrel_ht.c | 18 ++++++++----------
 net/mac80211/rc80211_minstrel_ht.h |  2 --
 2 files changed, 8 insertions(+), 12 deletions(-)

diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c
index 7846782840a9..4d4eb4aa46bd 100644
--- a/net/mac80211/rc80211_minstrel_ht.c
+++ b/net/mac80211/rc80211_minstrel_ht.c
@@ -791,14 +791,11 @@ minstrel_ht_calc_rate_stats(struct minstrel_priv *mp,
 	unsigned int cur_prob;
 
 	if (unlikely(mrs->attempts > 0)) {
-		mrs->sample_skipped = 0;
 		cur_prob = MINSTREL_FRAC(mrs->success, mrs->attempts);
 		minstrel_filter_avg_add(&mrs->prob_avg,
 					&mrs->prob_avg_1, cur_prob);
 		mrs->att_hist += mrs->attempts;
 		mrs->succ_hist += mrs->success;
-	} else {
-		mrs->sample_skipped++;
 	}
 
 	mrs->last_success = mrs->success;
@@ -851,7 +848,6 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
 		mi->ampdu_packets = 0;
 	}
 
-	mi->sample_slow = 0;
 	mi->sample_count = 0;
 
 	if (mi->supported[MINSTREL_CCK_GROUP])
@@ -882,6 +878,7 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
 	/* Find best rate sets within all MCS groups*/
 	for (group = 0; group < ARRAY_SIZE(minstrel_mcs_groups); group++) {
 		u16 *tp_rate = tmp_mcs_tp_rate;
+		u16 last_prob = 0;
 
 		mg = &mi->groups[group];
 		if (!mi->supported[group])
@@ -896,7 +893,7 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
 		if (group == MINSTREL_CCK_GROUP && ht_supported)
 			tp_rate = tmp_legacy_tp_rate;
 
-		for (i = 0; i < MCS_GROUP_RATES; i++) {
+		for (i = MCS_GROUP_RATES - 1; i >= 0; i--) {
 			if (!(mi->supported[group] & BIT(i)))
 				continue;
 
@@ -905,6 +902,11 @@ minstrel_ht_update_stats(struct minstrel_priv *mp, struct minstrel_ht_sta *mi,
 			mrs = &mg->rates[i];
 			mrs->retry_updated = false;
 			minstrel_ht_calc_rate_stats(mp, mrs);
+
+			if (mrs->att_hist)
+				last_prob = max(last_prob, mrs->prob_avg);
+			else
+				mrs->prob_avg = max(last_prob, mrs->prob_avg);
 			cur_prob = mrs->prob_avg;
 
 			if (minstrel_ht_get_tp_avg(mi, group, i, cur_prob) == 0)
@@ -1469,13 +1471,9 @@ minstrel_get_sample_rate(struct minstrel_priv *mp, struct minstrel_ht_sta *mi)
 	if (sample_dur >= minstrel_get_duration(tp_rate2) &&
 	    (cur_max_tp_streams - 1 <
 	     minstrel_mcs_groups[sample_group].streams ||
-	     sample_dur >= minstrel_get_duration(mi->max_prob_rate))) {
-		if (mrs->sample_skipped < 20)
+	     sample_dur >= minstrel_get_duration(mi->max_prob_rate)))
 			return -1;
 
-		if (mi->sample_slow++ > 2)
-			return -1;
-	}
 	mi->sample_tries--;
 
 	return sample_idx;
diff --git a/net/mac80211/rc80211_minstrel_ht.h b/net/mac80211/rc80211_minstrel_ht.h
index 5912f7dc5267..ebb2b88f44d9 100644
--- a/net/mac80211/rc80211_minstrel_ht.h
+++ b/net/mac80211/rc80211_minstrel_ht.h
@@ -123,7 +123,6 @@ struct minstrel_rate_stats {
 	u8 retry_count;
 	u8 retry_count_rtscts;
 
-	u8 sample_skipped;
 	bool retry_updated;
 };
 
@@ -179,7 +178,6 @@ struct minstrel_ht_sta {
 	u8 sample_wait;
 	u8 sample_tries;
 	u8 sample_count;
-	u8 sample_slow;
 
 	enum minstrel_sample_mode sample_mode;
 	u16 sample_rate;
-- 
2.28.0