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From: Felix Fietkau <nbd@nbd.name>
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 <nbd@nbd.name>
---
--- 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));
}
/*
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