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authorFelix Fietkau <nbd@nbd.name>2021-01-15 13:05:25 +0100
committerFelix Fietkau <nbd@nbd.name>2021-01-15 13:05:40 +0100
commitb0ad07e9a0fcdf59430547773e4ccc2416a2185a (patch)
tree5ec6d17664272125ff8d65690ff3481bf702b492
parent4dad3244297d8315b25ef029286681be4e7123a0 (diff)
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mac80211: fix rounding error in minstrel_ht throughput calculation
Fixes rate selection with lower data rates Signed-off-by: Felix Fietkau <nbd@nbd.name>
-rw-r--r--package/kernel/mac80211/patches/subsys/345-mac80211-minstrel_ht-fix-rounding-error-in-throughpu.patch34
1 files changed, 34 insertions, 0 deletions
diff --git a/package/kernel/mac80211/patches/subsys/345-mac80211-minstrel_ht-fix-rounding-error-in-throughpu.patch b/package/kernel/mac80211/patches/subsys/345-mac80211-minstrel_ht-fix-rounding-error-in-throughpu.patch
new file mode 100644
index 0000000000..1df5dec039
--- /dev/null
+++ b/package/kernel/mac80211/patches/subsys/345-mac80211-minstrel_ht-fix-rounding-error-in-throughpu.patch
@@ -0,0 +1,34 @@
+From: Felix Fietkau <nbd@nbd.name>
+Date: Fri, 15 Jan 2021 12:15:06 +0100
+Subject: [PATCH] mac80211: minstrel_ht: fix rounding error in throughput
+ calculation
+
+On lower data rates, the throughput calculation has a significant rounding
+error, causing rates like 48M and 54M OFDM to share the same throughput
+value with >= 90% success probablity.
+
+This is because the result of the division (prob_avg * 1000) / nsecs
+is really small (8 in this example).
+
+Improve accuracy by moving over some zeroes, making better use of the full
+range of u32 before the division.
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+
+--- a/net/mac80211/rc80211_minstrel_ht.c
++++ b/net/mac80211/rc80211_minstrel_ht.c
+@@ -445,10 +445,9 @@ minstrel_ht_get_tp_avg(struct minstrel_h
+ * (prob is scaled - see MINSTREL_FRAC above)
+ */
+ if (prob_avg > MINSTREL_FRAC(90, 100))
+- return MINSTREL_TRUNC(100000 * ((MINSTREL_FRAC(90, 100) * 1000)
+- / nsecs));
+- else
+- return MINSTREL_TRUNC(100000 * ((prob_avg * 1000) / nsecs));
++ prob_avg = MINSTREL_FRAC(90, 100);
++
++ return MINSTREL_TRUNC(100 * ((prob_avg * 1000000) / nsecs));
+ }
+
+ /*