From ed97a13c540eb8fdbb6250eaa6471a4263204af8 Mon Sep 17 00:00:00 2001 From: Felix Fietkau Date: Sat, 2 Mar 2013 21:20:12 +0100 Subject: [PATCH] mac80211/minstrel_ht: improve accuracy of throughput metric at high data rates At high data rates the average frame transmission durations are small enough for rounding errors to matter, sometimes causing minstrel to use slightly lower transmit rates than necessary. To fix this, change the unit of the duration value to nanoseconds instead of microseconds, and reorder the multiplications/divisions when calculating the throughput metric so that they don't overflow or truncate prematurely. At 2-stream HT40 this makes TCP throughput a bit more stable. Signed-off-by: Felix Fietkau Signed-off-by: Johannes Berg --- net/mac80211/rc80211_minstrel_ht.c | 23 +++++++++++++---------- 1 file changed, 13 insertions(+), 10 deletions(-) diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c index 3af141c69712..0b5cdd94d4f0 100644 --- a/net/mac80211/rc80211_minstrel_ht.c +++ b/net/mac80211/rc80211_minstrel_ht.c @@ -26,11 +26,11 @@ /* Number of symbols for a packet with (bps) bits per symbol */ #define MCS_NSYMS(bps) ((MCS_NBITS + (bps) - 1) / (bps)) -/* Transmission time for a packet containing (syms) symbols */ +/* Transmission time (nanoseconds) for a packet containing (syms) symbols */ #define MCS_SYMBOL_TIME(sgi, syms) \ (sgi ? \ - ((syms) * 18 + 4) / 5 : /* syms * 3.6 us */ \ - (syms) << 2 /* syms * 4 us */ \ + ((syms) * 18000 + 4000) / 5 : /* syms * 3.6 us */ \ + ((syms) * 1000) << 2 /* syms * 4 us */ \ ) /* Transmit duration for the raw data part of an average sized packet */ @@ -64,9 +64,9 @@ } #define CCK_DURATION(_bitrate, _short, _len) \ - (10 /* SIFS */ + \ + (1000 * (10 /* SIFS */ + \ (_short ? 72 + 24 : 144 + 48 ) + \ - (8 * (_len + 4) * 10) / (_bitrate)) + (8 * (_len + 4) * 10) / (_bitrate))) #define CCK_ACK_DURATION(_bitrate, _short) \ (CCK_DURATION((_bitrate > 10 ? 20 : 10), false, 60) + \ @@ -211,7 +211,8 @@ static void minstrel_ht_calc_tp(struct minstrel_ht_sta *mi, int group, int rate) { struct minstrel_rate_stats *mr; - unsigned int usecs = 0; + unsigned int nsecs = 0; + unsigned int tp; mr = &mi->groups[group].rates[rate]; @@ -221,10 +222,12 @@ minstrel_ht_calc_tp(struct minstrel_ht_sta *mi, int group, int rate) } if (group != MINSTREL_CCK_GROUP) - usecs = mi->overhead / MINSTREL_TRUNC(mi->avg_ampdu_len); + nsecs = 1000 * mi->overhead / MINSTREL_TRUNC(mi->avg_ampdu_len); - usecs += minstrel_mcs_groups[group].duration[rate]; - mr->cur_tp = MINSTREL_TRUNC((1000000 / usecs) * mr->probability); + nsecs += minstrel_mcs_groups[group].duration[rate]; + tp = 1000000 * ((mr->probability * 1000) / nsecs); + + mr->cur_tp = MINSTREL_TRUNC(tp); } /* @@ -536,7 +539,7 @@ minstrel_calc_retransmit(struct minstrel_priv *mp, struct minstrel_ht_sta *mi, mr->retry_updated = true; group = &minstrel_mcs_groups[index / MCS_GROUP_RATES]; - tx_time_data = group->duration[index % MCS_GROUP_RATES] * ampdu_len; + tx_time_data = group->duration[index % MCS_GROUP_RATES] * ampdu_len / 1000; /* Contention time for first 2 tries */ ctime = (t_slot * cw) >> 1; -- 2.30.2