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[v2,09/10] mac80211: reduce calculation costs of EWMA

Message ID 1423839472-15625-10-git-send-email-thomas@net.t-labs.tu-berlin.de (mailing list archive)
State Changes Requested
Delegated to: Johannes Berg
Headers show

Commit Message

Thomas Huehn Feb. 13, 2015, 2:57 p.m. UTC 
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>
---
 net/mac80211/rc80211_minstrel.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
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Patch

diff --git a/net/mac80211/rc80211_minstrel.h b/net/mac80211/rc80211_minstrel.h
index 6693d8d..38158b0 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 {