mac80211: reduce calculation costs of EWMA

This patch reduces the calculation costs of the EWMA macro from
"2x multiplication and 1 addition" down to "1x multiplication and
2x additions". This slightly improves performance depending on the
CPU architecture.

Signed-off-by: Thomas Huehn <thomas@net.t-labs.tu-berlin.de>
Acked-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/net/mac80211/rc80211_minstrel.h b/net/mac80211/rc80211_minstrel.h
index 0083036161af..9c85a610b57b 100644
--- a/net/mac80211/rc80211_minstrel.h
+++ b/net/mac80211/rc80211_minstrel.h
@@ -27,7 +27,12 @@
 static inline int
 minstrel_ewma(int old, int new, int weight)
 {
-        return (new * (EWMA_DIV - weight) + old * weight) / EWMA_DIV;
+        int diff, incr;
+
+        diff = new - old;
+        incr = (EWMA_DIV - weight) * diff / EWMA_DIV;
+
+        return old + incr;
 }
 
 struct minstrel_rate_stats {