mac80211: improve rate control performance

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

SVN-Revision: 48897

package/kernel/mac80211/patches/343-mac80211-minstrel_ht-improve-sample-rate-skip-logic.patch

+From: Felix Fietkau <nbd@openwrt.org>
+Date: Thu, 3 Mar 2016 23:20:06 +0100
+Subject: [PATCH] mac80211: minstrel_ht: improve sample rate skip logic
+
+There were a few issues that were slowing down the process of finding
+the optimal rate, especially on devices with multi-rate retry
+limitations:
+
+When max_tp_rate[0] was slower than max_tp_rate[1], the code did not
+sample max_tp_rate[1], which would often allow it to switch places with
+max_tp_rate[0] (e.g. if only the first sampling attempts were bad, but the
+rate is otherwise good).
+
+Also, sample attempts of rates between max_tp_rate[0] and [1] were being
+ignored in this case, because the code only checked if the rate was
+slower than [1].
+
+Fix this by checking against the fastest / second fastest max_tp_rate
+instead of assuming a specific order between the two.
+
+In my tests this patch significantly reduces the time until minstrel_ht
+finds the optimal rate right after assoc
+
+Signed-off-by: Felix Fietkau <nbd@openwrt.org>
+---
+
+--- a/net/mac80211/rc80211_minstrel_ht.c
++++ b/net/mac80211/rc80211_minstrel_ht.c
+@@ -958,6 +958,7 @@ minstrel_get_sample_rate(struct minstrel
+ 	struct minstrel_rate_stats *mrs;
+ 	struct minstrel_mcs_group_data *mg;
+ 	unsigned int sample_dur, sample_group, cur_max_tp_streams;
++	int tp_rate1, tp_rate2;
+ 	int sample_idx = 0;
+ 
+ 	if (mi->sample_wait > 0) {
+@@ -979,14 +980,22 @@ minstrel_get_sample_rate(struct minstrel
+ 	mrs = &mg->rates[sample_idx];
+ 	sample_idx += sample_group * MCS_GROUP_RATES;
+ 
++	/* Set tp_rate1, tp_rate2 to the highest / second highest max_tp_rate */
++	if (minstrel_get_duration(mi->max_tp_rate[0]) >
++	    minstrel_get_duration(mi->max_tp_rate[1])) {
++		tp_rate1 = mi->max_tp_rate[1];
++		tp_rate2 = mi->max_tp_rate[0];
++	} else {
++		tp_rate1 = mi->max_tp_rate[0];
++		tp_rate2 = mi->max_tp_rate[1];
++	}
++
+ 	/*
+ 	 * Sampling might add some overhead (RTS, no aggregation)
+-	 * to the frame. Hence, don't use sampling for the currently
+-	 * used rates.
++	 * to the frame. Hence, don't use sampling for the highest currently
++	 * used highest throughput or probability rate.
+ 	 */
+-	if (sample_idx == mi->max_tp_rate[0] ||
+-	    sample_idx == mi->max_tp_rate[1] ||
+-	    sample_idx == mi->max_prob_rate)
++	if (sample_idx == mi->max_tp_rate[0] || sample_idx == mi->max_prob_rate)
+ 		return -1;
+ 
+ 	/*
+@@ -1001,10 +1010,10 @@ minstrel_get_sample_rate(struct minstrel
+ 	 * if the link is working perfectly.
+ 	 */
+ 
+-	cur_max_tp_streams = minstrel_mcs_groups[mi->max_tp_rate[0] /
++	cur_max_tp_streams = minstrel_mcs_groups[tp_rate1 /
+ 		MCS_GROUP_RATES].streams;
+ 	sample_dur = minstrel_get_duration(sample_idx);
+-	if (sample_dur >= minstrel_get_duration(mi->max_tp_rate[1]) &&
++	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))) {