From 347c2989a8ba8a231f2ffc0635f2f36fedd30bde Mon Sep 17 00:00:00 2001 From: Felix Fietkau Date: Fri, 15 Jan 2021 13:02:42 +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 Link: https://lore.kernel.org/r/20210115120242.89616-10-nbd@nbd.name Signed-off-by: Johannes Berg --- net/mac80211/rc80211_minstrel_ht.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/net/mac80211/rc80211_minstrel_ht.c b/net/mac80211/rc80211_minstrel_ht.c index 782b4668a3da..e35948f4e1bf 100644 --- 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_ht_sta *mi, int group, int rate, * (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)); } /*