mac80211: improve rate control performance

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Backport of r48897

git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@48899 3c298f89-4303-0410-b956-a3cf2f4a3e73

diff --git a/package/kernel/mac80211/patches/343-mac80211-minstrel_ht-improve-sample-rate-skip-logic.patch b/package/kernel/mac80211/patches/343-mac80211-minstrel_ht-improve-sample-rate-skip-logic.patch
new file mode 100644 (file)
index 0000000..55ff817
--- /dev/null
+++ b/package/kernel/mac80211/patches/343-mac80211-minstrel_ht-improve-sample-rate-skip-logic.patch
@@ -0,0 +1,77 @@
+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))) {