backports: average: backport efficiency improvements

This is what we get for not copying it directly :-)
For now, backport af556884359 manually.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/backport/compat/average.c b/backport/compat/average.c
index 37cbfd6bdc7ec370c9c11c72002f09ab5561e114..b7a51a1fcccd0aac359a9f0d4f26b3511f120ea0 100644 (file)
--- a/backport/compat/average.c
+++ b/backport/compat/average.c
@@ -11,23 +11,27 @@
 #include <linux/average.h>
 #include <linux/module.h>
 #include <linux/bug.h>
+#include <linux/log2.h>
 
 /**
  * ewma_init() - Initialize EWMA parameters
  * @avg: Average structure
  * @factor: Factor to use for the scaled up internal value. The maximum value
- *     of averages can be ULONG_MAX/(factor*weight).
+ *     of averages can be ULONG_MAX/(factor*weight). For performance reasons
+ *     factor has to be a power of 2.
  * @weight: Exponential weight, or decay rate. This defines how fast the
- *     influence of older values decreases. Has to be bigger than 1.
+ *     influence of older values decreases. For performance reasons weight has
+ *     to be a power of 2.
  *
  * Initialize the EWMA parameters for a given struct ewma @avg.
  */
 void ewma_init(struct ewma *avg, unsigned long factor, unsigned long weight)
 {
-       WARN_ON(weight <= 1 || factor == 0);
+       WARN_ON(!is_power_of_2(weight) || !is_power_of_2(factor));
+
+       avg->weight = ilog2(weight);
+       avg->factor = ilog2(factor);
        avg->internal = 0;
-       avg->weight = weight;
-       avg->factor = factor;
 }
 EXPORT_SYMBOL_GPL(ewma_init);
 
@@ -41,9 +45,9 @@ EXPORT_SYMBOL_GPL(ewma_init);
 struct ewma *ewma_add(struct ewma *avg, unsigned long val)
 {
        avg->internal = avg->internal  ?
-               (((avg->internal * (avg->weight - 1)) +
-                       (val * avg->factor)) / avg->weight) :
-               (val * avg->factor);
+               (((avg->internal << avg->weight) - avg->internal) +
+                       (val << avg->factor)) >> avg->weight :
+               (val << avg->factor);
        return avg;
 }
 EXPORT_SYMBOL_GPL(ewma_add);

diff --git a/backport/include/linux/average.h b/backport/include/linux/average.h
index 16eff0da3b7fd0bd90991e8715bd53ca33e63351..2d6210e53105467a4559ff7d1216f0923d2b5dff 100644 (file)
--- a/backport/include/linux/average.h
+++ b/backport/include/linux/average.h
@@ -29,6 +29,6 @@ extern struct ewma *ewma_add(struct ewma *avg, unsigned long val);
  */
 static inline unsigned long ewma_read(const struct ewma *avg)
 {
-       return DIV_ROUND_CLOSEST(avg->internal, avg->factor);
+       return avg->internal >> avg->factor;
 }
 #endif /* (LINUX_VERSION_CODE > KERNEL_VERSION(2,6,37)) */