linux/lib/flex_proportions.c

// SPDX-License-Identifier: GPL-2.0
/*
 *  Floating proportions with flexible aging period
 *
 *   Copyright (C) 2011, SUSE, Jan Kara <[email protected]>
 *
 * The goal of this code is: Given different types of event, measure proportion
 * of each type of event over time. The proportions are measured with
 * exponentially decaying history to give smooth transitions. A formula
 * expressing proportion of event of type 'j' is:
 *
 *   p_{j} = (\Sum_{i>=0} x_{i,j}/2^{i+1})/(\Sum_{i>=0} x_i/2^{i+1})
 *
 * Where x_{i,j} is j's number of events in i-th last time period and x_i is
 * total number of events in i-th last time period.
 *
 * Note that p_{j}'s are normalised, i.e.
 *
 *   \Sum_{j} p_{j} = 1,
 *
 * This formula can be straightforwardly computed by maintaining denominator
 * (let's call it 'd') and for each event type its numerator (let's call it
 * 'n_j'). When an event of type 'j' happens, we simply need to do:
 *   n_j++; d++;
 *
 * When a new period is declared, we could do:
 *   d /= 2
 *   for each j
 *     n_j /= 2
 *
 * To avoid iteration over all event types, we instead shift numerator of event
 * j lazily when someone asks for a proportion of event j or when event j
 * occurs. This can bit trivially implemented by remembering last period in
 * which something happened with proportion of type j.
 */
#include <linux/flex_proportions.h>

int fprop_global_init(struct fprop_global *p, gfp_t gfp)
{ … }

void fprop_global_destroy(struct fprop_global *p)
{ … }

/*
 * Declare @periods new periods. It is upto the caller to make sure period
 * transitions cannot happen in parallel.
 *
 * The function returns true if the proportions are still defined and false
 * if aging zeroed out all events. This can be used to detect whether declaring
 * further periods has any effect.
 */
bool fprop_new_period(struct fprop_global *p, int periods)
{ … }

/*
 * ---- PERCPU ----
 */
#define PROP_BATCH …

int fprop_local_init_percpu(struct fprop_local_percpu *pl, gfp_t gfp)
{ … }

void fprop_local_destroy_percpu(struct fprop_local_percpu *pl)
{ … }

static void fprop_reflect_period_percpu(struct fprop_global *p,
					struct fprop_local_percpu *pl)
{ … }

/* Event of type pl happened */
void __fprop_add_percpu(struct fprop_global *p, struct fprop_local_percpu *pl,
		long nr)
{ … }

void fprop_fraction_percpu(struct fprop_global *p,
			   struct fprop_local_percpu *pl,
			   unsigned long *numerator, unsigned long *denominator)
{ … }

/*
 * Like __fprop_add_percpu() except that event is counted only if the given
 * type has fraction smaller than @max_frac/FPROP_FRAC_BASE
 */
void __fprop_add_percpu_max(struct fprop_global *p,
		struct fprop_local_percpu *pl, int max_frac, long nr)
{ … }