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authorFelix Fietkau <nbd@openwrt.org>2015-03-14 02:00:44 +0000
committerFelix Fietkau <nbd@openwrt.org>2015-03-14 02:00:44 +0000
commit90b3984e6026b28f90a820c461e11812d5d4e930 (patch)
tree30dfabcb788552f9bf449b3e990c7ef0d862d014
parent25d13b89eeaa9a2df5458ed3d7e5ebe97c3f6560 (diff)
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mac80211: fix a rounding issue in minstrel MCS rate duration calculation
Signed-off-by: Felix Fietkau <nbd@openwrt.org> SVN-Revision: 44749
-rw-r--r--package/kernel/mac80211/patches/308-mac80211-minstrel_ht-fix-rounding-issue-in-MCS-durat.patch43
1 files changed, 43 insertions, 0 deletions
diff --git a/package/kernel/mac80211/patches/308-mac80211-minstrel_ht-fix-rounding-issue-in-MCS-durat.patch b/package/kernel/mac80211/patches/308-mac80211-minstrel_ht-fix-rounding-issue-in-MCS-durat.patch
new file mode 100644
index 0000000000..d13263655e
--- /dev/null
+++ b/package/kernel/mac80211/patches/308-mac80211-minstrel_ht-fix-rounding-issue-in-MCS-durat.patch
@@ -0,0 +1,43 @@
+From: Felix Fietkau <nbd@openwrt.org>
+Date: Fri, 13 Mar 2015 10:49:40 +0100
+Subject: [PATCH] mac80211: minstrel_ht: fix rounding issue in MCS duration
+ calculation
+
+On very high MCS bitrates, the calculated duration of rates that are
+next to each other can be very imprecise, due to the small packet size
+used as reference (1200 bytes).
+This is most visible in VHT80 nss=2 MCS8/9, for which minstrel shows the
+same throughput when the probability is also the same. This leads to a
+bad rate selection for such rates.
+
+Fix this issue by introducing an average A-MPDU size factor into the
+calculation.
+
+Signed-off-by: Felix Fietkau <nbd@openwrt.org>
+---
+
+--- a/net/mac80211/rc80211_minstrel_ht.c
++++ b/net/mac80211/rc80211_minstrel_ht.c
+@@ -17,10 +17,11 @@
+ #include "rc80211_minstrel.h"
+ #include "rc80211_minstrel_ht.h"
+
++#define AVG_AMPDU_SIZE 16
+ #define AVG_PKT_SIZE 1200
+
+ /* Number of bits for an average sized packet */
+-#define MCS_NBITS (AVG_PKT_SIZE << 3)
++#define MCS_NBITS ((AVG_PKT_SIZE * AVG_AMPDU_SIZE) << 3)
+
+ /* Number of symbols for a packet with (bps) bits per symbol */
+ #define MCS_NSYMS(bps) DIV_ROUND_UP(MCS_NBITS, (bps))
+@@ -33,7 +34,8 @@
+ )
+
+ /* Transmit duration for the raw data part of an average sized packet */
+-#define MCS_DURATION(streams, sgi, bps) MCS_SYMBOL_TIME(sgi, MCS_NSYMS((streams) * (bps)))
++#define MCS_DURATION(streams, sgi, bps) \
++ (MCS_SYMBOL_TIME(sgi, MCS_NSYMS((streams) * (bps))) / AVG_AMPDU_SIZE)
+
+ #define BW_20 0
+ #define BW_40 1