kernel / pub / scm / linux / kernel / git / djbw / ahci / eee0815dabbdd7d584bea8275f5758d25c97cb9b / . / lib / average.c

/* | |

* 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); |