Commit 347c2989 authored by Felix Fietkau's avatar Felix Fietkau Committed by Johannes Berg
Browse files

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: default avatarFelix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20210115120242.89616-10-nbd@nbd.name


Signed-off-by: default avatarJohannes Berg <johannes.berg@intel.com>
parent 7e2123ab

net/mac80211/rc80211_minstrel_ht.c

+3 −4
Original line number Diff line number Diff line
@@ -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));

}



/*