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- From: Felix Fietkau <[email protected]>
- 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 <[email protected]>
- ---
- --- 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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