mac80211: add minstrel performance improvements

Reduce fluctuations in rate selection / statistics

Signed-off-by: Felix Fietkau <nbd@nbd.name>

2 files changed, 181 insertions, 0 deletions

diff --git a/package/kernel/mac80211/patches/subsys/354-mac80211-minstrel_ht-reduce-fluctuations-in-rate-pro.patch b/package/kernel/mac80211/patches/subsys/354-mac80211-minstrel_ht-reduce-fluctuations-in-rate-pro.patch
new file mode 100644
index 0000000000..16bcbc2ef9
--- /dev/null
+++ b/package/kernel/mac80211/patches/subsys/354-mac80211-minstrel_ht-reduce-fluctuations-in-rate-pro.patch
@@ -0,0 +1,30 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Sat, 6 Feb 2021 16:08:01 +0100
+Subject: [PATCH] mac80211: minstrel_ht: reduce fluctuations in rate
+ probability stats
+
+In some scenarios when there is a lot of fluctuation in packet error rates,
+rate switching can be amplified when the statistics get skewed by time slots
+with very few tries.
+Make the input data to the moving average more smooth by adding the
+success/attempts count from the last stats window as well. This has the
+advantage of smoothing the data without introducing any extra lag to sampling
+rates.
+This significantly improves rate stability on a strong test link subjected to
+periodic noise bursts generated with a SDR
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/net/mac80211/rc80211_minstrel_ht.c
++++ b/net/mac80211/rc80211_minstrel_ht.c
+@@ -700,7 +700,8 @@ minstrel_ht_calc_rate_stats(struct minst
+ 	unsigned int cur_prob;
+ 
+ 	if (unlikely(mrs->attempts > 0)) {
+-		cur_prob = MINSTREL_FRAC(mrs->success, mrs->attempts);
++		cur_prob = MINSTREL_FRAC(mrs->success + mrs->last_success,
++					 mrs->attempts + mrs->last_attempts);
+ 		minstrel_filter_avg_add(&mrs->prob_avg,
+ 					&mrs->prob_avg_1, cur_prob);
+ 		mrs->att_hist += mrs->attempts;
diff --git a/package/kernel/mac80211/patches/subsys/355-mac80211-minstrel_ht-rework-rate-downgrade-code-and-.patch b/package/kernel/mac80211/patches/subsys/355-mac80211-minstrel_ht-rework-rate-downgrade-code-and-.patch
new file mode 100644
index 0000000000..aec2e07781
--- /dev/null
+++ b/package/kernel/mac80211/patches/subsys/355-mac80211-minstrel_ht-rework-rate-downgrade-code-and-.patch
@@ -0,0 +1,151 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Sat, 6 Feb 2021 16:33:14 +0100
+Subject: [PATCH] mac80211: minstrel_ht: rework rate downgrade code and
+ max_prob rate selection
+
+The current fallback code for fast rate switching on potentially failing rates
+is triggering too often if there is some strong noise on the channel. This can
+lead to wild fluctuations in the rate selection.
+Additionally, switching down to max_prob_rate can create a significant gap down
+in throughput, especially when using only 2 spatial streams, because max_prob_rate
+is limited to using fewer streams than the max_tp rates.
+In order to improve throughput without reducing reliability too much, use the
+rate downgrade code for the max_prob_rate only, and allow the non-downgraded
+max_prob_rate to use as many spatial streams as the max_tp rates
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/net/mac80211/rc80211_minstrel_ht.c
++++ b/net/mac80211/rc80211_minstrel_ht.c
+@@ -511,6 +511,14 @@ minstrel_ht_set_best_prob_rate(struct mi
+ 	int cur_tp_avg, cur_group, cur_idx;
+ 	int max_gpr_group, max_gpr_idx;
+ 	int max_gpr_tp_avg, max_gpr_prob;
++	int min_dur;
++
++	min_dur = max(minstrel_get_duration(mi->max_tp_rate[0]),
++		      minstrel_get_duration(mi->max_tp_rate[1]));
++
++	/* make the rate at least 18% slower than max tp rates */
++	if (minstrel_get_duration(index) <= min_dur * 19 / 16)
++		return;
+ 
+ 	cur_group = MI_RATE_GROUP(index);
+ 	cur_idx = MI_RATE_IDX(index);
+@@ -532,11 +540,6 @@ minstrel_ht_set_best_prob_rate(struct mi
+ 	    !minstrel_ht_is_legacy_group(max_tp_group))
+ 		return;
+ 
+-	/* skip rates faster than max tp rate with lower prob */
+-	if (minstrel_get_duration(mi->max_tp_rate[0]) > minstrel_get_duration(index) &&
+-	    mrs->prob_avg < max_tp_prob)
+-		return;
+-
+ 	max_gpr_group = MI_RATE_GROUP(mg->max_group_prob_rate);
+ 	max_gpr_idx = MI_RATE_IDX(mg->max_group_prob_rate);
+ 	max_gpr_prob = mi->groups[max_gpr_group].rates[max_gpr_idx].prob_avg;
+@@ -594,40 +597,6 @@ minstrel_ht_assign_best_tp_rates(struct
+ 
+ }
+ 
+-/*
+- * Try to increase robustness of max_prob rate by decrease number of
+- * streams if possible.
+- */
+-static inline void
+-minstrel_ht_prob_rate_reduce_streams(struct minstrel_ht_sta *mi)
+-{
+-	struct minstrel_mcs_group_data *mg;
+-	int tmp_max_streams, group, tmp_idx, tmp_prob;
+-	int tmp_tp = 0;
+-
+-	if (!mi->sta->ht_cap.ht_supported)
+-		return;
+-
+-	group = MI_RATE_GROUP(mi->max_tp_rate[0]);
+-	tmp_max_streams = minstrel_mcs_groups[group].streams;
+-	for (group = 0; group < ARRAY_SIZE(minstrel_mcs_groups); group++) {
+-		mg = &mi->groups[group];
+-		if (!mi->supported[group] || group == MINSTREL_CCK_GROUP)
+-			continue;
+-
+-		tmp_idx = MI_RATE_IDX(mg->max_group_prob_rate);
+-		tmp_prob = mi->groups[group].rates[tmp_idx].prob_avg;
+-
+-		if (tmp_tp < minstrel_ht_get_tp_avg(mi, group, tmp_idx, tmp_prob) &&
+-		   (minstrel_mcs_groups[group].streams < tmp_max_streams)) {
+-				mi->max_prob_rate = mg->max_group_prob_rate;
+-				tmp_tp = minstrel_ht_get_tp_avg(mi, group,
+-								tmp_idx,
+-								tmp_prob);
+-		}
+-	}
+-}
+-
+ static u16
+ __minstrel_ht_get_sample_rate(struct minstrel_ht_sta *mi,
+ 			      enum minstrel_sample_type type)
+@@ -1111,8 +1080,6 @@ minstrel_ht_update_stats(struct minstrel
+ 
+ 	mi->max_prob_rate = tmp_max_prob_rate;
+ 
+-	/* Try to increase robustness of max_prob_rate*/
+-	minstrel_ht_prob_rate_reduce_streams(mi);
+ 	minstrel_ht_refill_sample_rates(mi);
+ 
+ #ifdef CPTCFG_MAC80211_DEBUGFS
+@@ -1157,7 +1124,7 @@ minstrel_ht_txstat_valid(struct minstrel
+ }
+ 
+ static void
+-minstrel_downgrade_rate(struct minstrel_ht_sta *mi, u16 *idx, bool primary)
++minstrel_downgrade_prob_rate(struct minstrel_ht_sta *mi, u16 *idx)
+ {
+ 	int group, orig_group;
+ 
+@@ -1172,11 +1139,7 @@ minstrel_downgrade_rate(struct minstrel_
+ 		    minstrel_mcs_groups[orig_group].streams)
+ 			continue;
+ 
+-		if (primary)
+-			*idx = mi->groups[group].max_group_tp_rate[0];
+-		else
+-			*idx = mi->groups[group].max_group_tp_rate[1];
+-		break;
++		*idx = mi->groups[group].max_group_prob_rate;
+ 	}
+ }
+ 
+@@ -1210,7 +1173,7 @@ minstrel_ht_tx_status(void *priv, struct
+ 	struct ieee80211_tx_info *info = st->info;
+ 	struct minstrel_ht_sta *mi = priv_sta;
+ 	struct ieee80211_tx_rate *ar = info->status.rates;
+-	struct minstrel_rate_stats *rate, *rate2;
++	struct minstrel_rate_stats *rate;
+ 	struct minstrel_priv *mp = priv;
+ 	u32 update_interval = mp->update_interval;
+ 	bool last, update = false;
+@@ -1256,18 +1219,13 @@ minstrel_ht_tx_status(void *priv, struct
+ 		/*
+ 		 * check for sudden death of spatial multiplexing,
+ 		 * downgrade to a lower number of streams if necessary.
++		 * only do this for the max_prob_rate to prevent spurious
++		 * rate fluctuations when the link changes suddenly
+ 		 */
+-		rate = minstrel_get_ratestats(mi, mi->max_tp_rate[0]);
++		rate = minstrel_get_ratestats(mi, mi->max_prob_rate);
+ 		if (rate->attempts > 30 &&
+ 		    rate->success < rate->attempts / 4) {
+-			minstrel_downgrade_rate(mi, &mi->max_tp_rate[0], true);
+-			update = true;
+-		}
+-
+-		rate2 = minstrel_get_ratestats(mi, mi->max_tp_rate[1]);
+-		if (rate2->attempts > 30 &&
+-		    rate2->success < rate2->attempts / 4) {
+-			minstrel_downgrade_rate(mi, &mi->max_tp_rate[1], false);
++			minstrel_downgrade_prob_rate(mi, &mi->max_prob_rate);
+ 			update = true;
+ 		}
+ 	}