mac80211: avoid sampling rates that are too slow, improves throughput

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

diff --git a/package/kernel/mac80211/patches/377-mac80211-minstrel-do-not-sample-rates-3-times-slower.patch b/package/kernel/mac80211/patches/377-mac80211-minstrel-do-not-sample-rates-3-times-slower.patch
new file mode 100644 (file)
index 0000000..414cb13
--- /dev/null
+++ b/package/kernel/mac80211/patches/377-mac80211-minstrel-do-not-sample-rates-3-times-slower.patch
@@ -0,0 +1,40 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Sat, 3 Mar 2018 18:48:58 +0100
+Subject: [PATCH] mac80211: minstrel: do not sample rates 3 times slower than
+ max_prob_rate
+
+These rates are highly unlikely to be used quickly, even if the link
+deteriorates rapidly. This improves throughput in cases where CCK rates
+are not reliable enough to be skipped entirely during sampling.
+Sampling these rates regularly can cost a lot of airtime.
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/net/mac80211/rc80211_minstrel_ht.c
++++ b/net/mac80211/rc80211_minstrel_ht.c
+@@ -1004,10 +1004,13 @@ minstrel_get_sample_rate(struct minstrel
+               return -1;
+ 
+       /*
+-       * Do not sample if the probability is already higher than 95%
+-       * to avoid wasting airtime.
++       * Do not sample if the probability is already higher than 95%,
++       * or if the rate is 3 times slower than the current max probability
++       * rate, to avoid wasting airtime.
+        */
+-      if (mrs->prob_ewma > MINSTREL_FRAC(95, 100))
++      sample_dur = minstrel_get_duration(sample_idx);
++      if (mrs->prob_ewma > MINSTREL_FRAC(95, 100) ||
++          minstrel_get_duration(mi->max_prob_rate) * 3 < sample_dur)
+               return -1;
+ 
+       /*
+@@ -1017,7 +1020,6 @@ minstrel_get_sample_rate(struct minstrel
+ 
+       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(tp_rate2) &&
+           (cur_max_tp_streams - 1 <
+            minstrel_mcs_groups[sample_group].streams ||