From: Felix Fietkau Date: Fri, 15 Jan 2021 12:15:06 +0100 Subject: [PATCH] mac80211: minstrel_ht: fix rounding error in throughput calculation On lower data rates, the throughput calculation has a significant rounding error, causing rates like 48M and 54M OFDM to share the same throughput value with >= 90% success probablity. This is because the result of the division (prob_avg * 1000) / nsecs is really small (8 in this example). Improve accuracy by moving over some zeroes, making better use of the full range of u32 before the division. Signed-off-by: Felix Fietkau --- --- a/net/mac80211/rc80211_minstrel_ht.c +++ b/net/mac80211/rc80211_minstrel_ht.c @@ -445,10 +445,9 @@ minstrel_ht_get_tp_avg(struct minstrel_h * (prob is scaled - see MINSTREL_FRAC above) */ if (prob_avg > MINSTREL_FRAC(90, 100)) - return MINSTREL_TRUNC(100000 * ((MINSTREL_FRAC(90, 100) * 1000) - / nsecs)); - else - return MINSTREL_TRUNC(100000 * ((prob_avg * 1000) / nsecs)); + prob_avg = MINSTREL_FRAC(90, 100); + + return MINSTREL_TRUNC(100 * ((prob_avg * 1000000) / nsecs)); } /*