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- From: Felix Fietkau <[email protected]>
- 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 <[email protected]>
- ---
- --- 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
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