1 files changed, 64 insertions, 0 deletions
diff --git a/lib/average.c b/lib/average.c
new file mode 100644
index 000000000..114d1beae
--- /dev/null
+++ b/lib/average.c
@@ -0,0 +1,64 @@
+/*
+ * lib/average.c
+ *
+ * This source code is licensed under the GNU General Public License,
+ * Version 2.  See the file COPYING for more details.
+ */
+
+#include <linux/export.h>
+#include <linux/average.h>
+#include <linux/kernel.h>
+#include <linux/bug.h>
+#include <linux/log2.h>
+
+/**
+ * DOC: Exponentially Weighted Moving Average (EWMA)
+ *
+ * These are generic functions for calculating Exponentially Weighted Moving
+ * Averages (EWMA). We keep a structure with the EWMA parameters and a scaled
+ * up internal representation of the average value to prevent rounding errors.
+ * The factor for scaling up and the exponential weight (or decay rate) have to
+ * be specified thru the init fuction. The structure should not be accessed
+ * directly but only thru the helper functions.
+ */
+
+/**
+ * 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). 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. 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(!is_power_of_2(weight) || !is_power_of_2(factor));
+
+	avg->weight = ilog2(weight);
+	avg->factor = ilog2(factor);
+	avg->internal = 0;
+}
+EXPORT_SYMBOL(ewma_init);
+
+/**
+ * ewma_add() - Exponentially weighted moving average (EWMA)
+ * @avg: Average structure
+ * @val: Current value
+ *
+ * Add a sample to the average.
+ */
+struct ewma *ewma_add(struct ewma *avg, unsigned long val)
+{
+	unsigned long internal = ACCESS_ONCE(avg->internal);
+
+	ACCESS_ONCE(avg->internal) = internal ?
+		(((internal << avg->weight) - internal) +
+			(val << avg->factor)) >> avg->weight :
+		(val << avg->factor);
+	return avg;
+}
+EXPORT_SYMBOL(ewma_add);