Line data    Source code

       1             : /*
       2             :  * lib/average.c
       3             :  *
       4             :  * This source code is licensed under the GNU General Public License,
       5             :  * Version 2.  See the file COPYING for more details.
       6             :  */
       7             : 
       8             : #include <linux/export.h>
       9             : #include <linux/average.h>
      10             : #include <linux/kernel.h>
      11             : #include <linux/bug.h>
      12             : #include <linux/log2.h>
      13             : 
      14             : /**
      15             :  * DOC: Exponentially Weighted Moving Average (EWMA)
      16             :  *
      17             :  * These are generic functions for calculating Exponentially Weighted Moving
      18             :  * Averages (EWMA). We keep a structure with the EWMA parameters and a scaled
      19             :  * up internal representation of the average value to prevent rounding errors.
      20             :  * The factor for scaling up and the exponential weight (or decay rate) have to
      21             :  * be specified thru the init fuction. The structure should not be accessed
      22             :  * directly but only thru the helper functions.
      23             :  */
      24             : 
      25             : /**
      26             :  * ewma_init() - Initialize EWMA parameters
      27             :  * @avg: Average structure
      28             :  * @factor: Factor to use for the scaled up internal value. The maximum value
      29             :  *      of averages can be ULONG_MAX/(factor*weight). For performance reasons
      30             :  *      factor has to be a power of 2.
      31             :  * @weight: Exponential weight, or decay rate. This defines how fast the
      32             :  *      influence of older values decreases. For performance reasons weight has
      33             :  *      to be a power of 2.
      34             :  *
      35             :  * Initialize the EWMA parameters for a given struct ewma @avg.
      36             :  */
      37           0 : void ewma_init(struct ewma *avg, unsigned long factor, unsigned long weight)
      38             : {
      39             :         WARN_ON(!is_power_of_2(weight) || !is_power_of_2(factor));
      40             : 
      41           0 :         avg->weight = ilog2(weight);
      42           0 :         avg->factor = ilog2(factor);
      43           0 :         avg->internal = 0;
      44           0 : }
      45             : EXPORT_SYMBOL(ewma_init);
      46             : 
      47             : /**
      48             :  * ewma_add() - Exponentially weighted moving average (EWMA)
      49             :  * @avg: Average structure
      50             :  * @val: Current value
      51             :  *
      52             :  * Add a sample to the average.
      53             :  */
      54           0 : struct ewma *ewma_add(struct ewma *avg, unsigned long val)
      55             : {
      56           0 :         unsigned long internal = ACCESS_ONCE(avg->internal);
      57             : 
      58           0 :         ACCESS_ONCE(avg->internal) = internal ?
      59           0 :                 (((internal << avg->weight) - internal) +
      60           0 :                         (val << avg->factor)) >> avg->weight :
      61           0 :                 (val << avg->factor);
      62           0 :         return avg;
      63             : }
      64             : EXPORT_SYMBOL(ewma_add);