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