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@@ -0,0 +1,43 @@
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+From: Felix Fietkau <[email protected]>
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+Date: Fri, 13 Mar 2015 10:49:40 +0100
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+Subject: [PATCH] mac80211: minstrel_ht: fix rounding issue in MCS duration
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+ calculation
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+
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+On very high MCS bitrates, the calculated duration of rates that are
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+next to each other can be very imprecise, due to the small packet size
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+used as reference (1200 bytes).
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+This is most visible in VHT80 nss=2 MCS8/9, for which minstrel shows the
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+same throughput when the probability is also the same. This leads to a
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+bad rate selection for such rates.
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+
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+Fix this issue by introducing an average A-MPDU size factor into the
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+calculation.
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+
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+Signed-off-by: Felix Fietkau <[email protected]>
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+---
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+
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+--- a/net/mac80211/rc80211_minstrel_ht.c
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++++ b/net/mac80211/rc80211_minstrel_ht.c
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+@@ -17,10 +17,11 @@
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+ #include "rc80211_minstrel.h"
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+ #include "rc80211_minstrel_ht.h"
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+
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++#define AVG_AMPDU_SIZE 16
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+ #define AVG_PKT_SIZE 1200
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+
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+ /* Number of bits for an average sized packet */
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+-#define MCS_NBITS (AVG_PKT_SIZE << 3)
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++#define MCS_NBITS ((AVG_PKT_SIZE * AVG_AMPDU_SIZE) << 3)
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+
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+ /* Number of symbols for a packet with (bps) bits per symbol */
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+ #define MCS_NSYMS(bps) DIV_ROUND_UP(MCS_NBITS, (bps))
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+@@ -33,7 +34,8 @@
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+ )
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+
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+ /* Transmit duration for the raw data part of an average sized packet */
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+-#define MCS_DURATION(streams, sgi, bps) MCS_SYMBOL_TIME(sgi, MCS_NSYMS((streams) * (bps)))
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++#define MCS_DURATION(streams, sgi, bps) \
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++ (MCS_SYMBOL_TIME(sgi, MCS_NSYMS((streams) * (bps))) / AVG_AMPDU_SIZE)
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+
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+ #define BW_20 0
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+ #define BW_40 1
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Felix Fietkau