package/kernel/mac80211/patches/308-mac80211-minstrel_ht-fix-rounding-issue-in-MCS-durat.patch

   1 From: Felix Fietkau <nbd@openwrt.org>
   2 Date: Fri, 13 Mar 2015 10:49:40 +0100
   3 Subject: [PATCH] mac80211: minstrel_ht: fix rounding issue in MCS duration
   4  calculation
   5
   6 On very high MCS bitrates, the calculated duration of rates that are
   7 next to each other can be very imprecise, due to the small packet size
   8 used as reference (1200 bytes).
   9 This is most visible in VHT80 nss=2 MCS8/9, for which minstrel shows the
  10 same throughput when the probability is also the same. This leads to a
  11 bad rate selection for such rates.
  12
  13 Fix this issue by introducing an average A-MPDU size factor into the
  14 calculation.
  15
  16 Signed-off-by: Felix Fietkau <nbd@openwrt.org>
  17 ---
  18
  19 --- a/net/mac80211/rc80211_minstrel_ht.c
  20 +++ b/net/mac80211/rc80211_minstrel_ht.c
  21 @@ -17,10 +17,11 @@
  22  #include "rc80211_minstrel.h"
  23  #include "rc80211_minstrel_ht.h"
  24
  25 +#define AVG_AMPDU_SIZE 16
  26  #define AVG_PKT_SIZE   1200
  27
  28  /* Number of bits for an average sized packet */
  29 -#define MCS_NBITS (AVG_PKT_SIZE << 3)
  30 +#define MCS_NBITS ((AVG_PKT_SIZE * AVG_AMPDU_SIZE) << 3)
  31
  32  /* Number of symbols for a packet with (bps) bits per symbol */
  33  #define MCS_NSYMS(bps) DIV_ROUND_UP(MCS_NBITS, (bps))
  34 @@ -33,7 +34,8 @@
  35         )
  36
  37  /* Transmit duration for the raw data part of an average sized packet */
  38 -#define MCS_DURATION(streams, sgi, bps) MCS_SYMBOL_TIME(sgi, MCS_NSYMS((streams) * (bps)))
  39 +#define MCS_DURATION(streams, sgi, bps) \
  40 +       (MCS_SYMBOL_TIME(sgi, MCS_NSYMS((streams) * (bps))) / AVG_AMPDU_SIZE)
  41
  42  #define BW_20                  0
  43  #define BW_40                  1