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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 | 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 | avg->weight = ilog2(weight); |
42 | avg->factor = ilog2(factor); |
43 | avg->internal = 0; |
44 | } |
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 | struct ewma *ewma_add(struct ewma *avg, unsigned long val) |
55 | { |
56 | unsigned long internal = ACCESS_ONCE(avg->internal); |
57 | |
58 | ACCESS_ONCE(avg->internal) = internal ? |
59 | (((internal << avg->weight) - internal) + |
60 | (val << avg->factor)) >> avg->weight : |
61 | (val << avg->factor); |
62 | return avg; |
63 | } |
64 | EXPORT_SYMBOL(ewma_add); |
65 |
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