[linux-block.git] / lib / flex_proportions.c

// SPDX-License-Identifier: GPL-2.0
/*
 *  Floating proportions with flexible aging period
 *
 *   Copyright (C) 2011, SUSE, Jan Kara <jack@suse.cz>
 *
 * 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)
{
	int err;

	p->period = 0;
	/* Use 1 to avoid dealing with periods with 0 events... */
	err = percpu_counter_init(&p->events, 1, gfp);
	if (err)
		return err;
	seqcount_init(&p->sequence);
	return 0;
}

void fprop_global_destroy(struct fprop_global *p)
{
	percpu_counter_destroy(&p->events);
}

/*
 * 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)
{
	s64 events = percpu_counter_sum(&p->events);

	/*
	 * Don't do anything if there are no events.
	 */
	if (events <= 1)
		return false;
	write_seqcount_begin(&p->sequence);
	if (periods < 64)
		events -= events >> periods;
	/* Use addition to avoid losing events happening between sum and set */
	percpu_counter_add(&p->events, -events);
	p->period += periods;
	write_seqcount_end(&p->sequence);

	return true;
}

/*
 * ---- SINGLE ----
 */

int fprop_local_init_single(struct fprop_local_single *pl)
{
	pl->events = 0;
	pl->period = 0;
	raw_spin_lock_init(&pl->lock);
	return 0;
}

void fprop_local_destroy_single(struct fprop_local_single *pl)
{
}

static void fprop_reflect_period_single(struct fprop_global *p,
					struct fprop_local_single *pl)
{
	unsigned int period = p->period;
	unsigned long flags;

	/* Fast path - period didn't change */
	if (pl->period == period)
		return;
	raw_spin_lock_irqsave(&pl->lock, flags);
	/* Someone updated pl->period while we were spinning? */
	if (pl->period >= period) {
		raw_spin_unlock_irqrestore(&pl->lock, flags);
		return;
	}
	/* Aging zeroed our fraction? */
	if (period - pl->period < BITS_PER_LONG)
		pl->events >>= period - pl->period;
	else
		pl->events = 0;
	pl->period = period;
	raw_spin_unlock_irqrestore(&pl->lock, flags);
}

/* Event of type pl happened */
void __fprop_inc_single(struct fprop_global *p, struct fprop_local_single *pl)
{
	fprop_reflect_period_single(p, pl);
	pl->events++;
	percpu_counter_add(&p->events, 1);
}

/* Return fraction of events of type pl */
void fprop_fraction_single(struct fprop_global *p,
			   struct fprop_local_single *pl,
			   unsigned long *numerator, unsigned long *denominator)
{
	unsigned int seq;
	s64 num, den;

	do {
		seq = read_seqcount_begin(&p->sequence);
		fprop_reflect_period_single(p, pl);
		num = pl->events;
		den = percpu_counter_read_positive(&p->events);
	} while (read_seqcount_retry(&p->sequence, seq));

	/*
	 * Make fraction <= 1 and denominator > 0 even in presence of percpu
	 * counter errors
	 */
	if (den <= num) {
		if (num)
			den = num;
		else
			den = 1;
	}
	*denominator = den;
	*numerator = num;
}

/*
 * ---- PERCPU ----
 */
#define PROP_BATCH (8*(1+ilog2(nr_cpu_ids)))

int fprop_local_init_percpu(struct fprop_local_percpu *pl, gfp_t gfp)
{
	int err;

	err = percpu_counter_init(&pl->events, 0, gfp);
	if (err)
		return err;
	pl->period = 0;
	raw_spin_lock_init(&pl->lock);
	return 0;
}

void fprop_local_destroy_percpu(struct fprop_local_percpu *pl)
{
	percpu_counter_destroy(&pl->events);
}

static void fprop_reflect_period_percpu(struct fprop_global *p,
					struct fprop_local_percpu *pl)
{
	unsigned int period = p->period;
	unsigned long flags;

	/* Fast path - period didn't change */
	if (pl->period == period)
		return;
	raw_spin_lock_irqsave(&pl->lock, flags);
	/* Someone updated pl->period while we were spinning? */
	if (pl->period >= period) {
		raw_spin_unlock_irqrestore(&pl->lock, flags);
		return;
	}
	/* Aging zeroed our fraction? */
	if (period - pl->period < BITS_PER_LONG) {
		s64 val = percpu_counter_read(&pl->events);

		if (val < (nr_cpu_ids * PROP_BATCH))
			val = percpu_counter_sum(&pl->events);

		percpu_counter_add_batch(&pl->events,
			-val + (val >> (period-pl->period)), PROP_BATCH);
	} else
		percpu_counter_set(&pl->events, 0);
	pl->period = period;
	raw_spin_unlock_irqrestore(&pl->lock, flags);
}

/* Event of type pl happened */
void __fprop_add_percpu(struct fprop_global *p, struct fprop_local_percpu *pl,
		long nr)
{
	fprop_reflect_period_percpu(p, pl);
	percpu_counter_add_batch(&pl->events, nr, PROP_BATCH);
	percpu_counter_add(&p->events, nr);
}

void fprop_fraction_percpu(struct fprop_global *p,
			   struct fprop_local_percpu *pl,
			   unsigned long *numerator, unsigned long *denominator)
{
	unsigned int seq;
	s64 num, den;

	do {
		seq = read_seqcount_begin(&p->sequence);
		fprop_reflect_period_percpu(p, pl);
		num = percpu_counter_read_positive(&pl->events);
		den = percpu_counter_read_positive(&p->events);
	} while (read_seqcount_retry(&p->sequence, seq));

	/*
	 * Make fraction <= 1 and denominator > 0 even in presence of percpu
	 * counter errors
	 */
	if (den <= num) {
		if (num)
			den = num;
		else
			den = 1;
	}
	*denominator = den;
	*numerator = num;
}

/*
 * 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)
{
	if (unlikely(max_frac < FPROP_FRAC_BASE)) {
		unsigned long numerator, denominator;
		s64 tmp;

		fprop_fraction_percpu(p, pl, &numerator, &denominator);
		/* Adding 'nr' to fraction exceeds max_frac/FPROP_FRAC_BASE? */
		tmp = (u64)denominator * max_frac -
					((u64)numerator << FPROP_FRAC_SHIFT);
		if (tmp < 0) {
			/* Maximum fraction already exceeded? */
			return;
		} else if (tmp < nr * (FPROP_FRAC_BASE - max_frac)) {
			/* Add just enough for the fraction to saturate */
			nr = div_u64(tmp + FPROP_FRAC_BASE - max_frac - 1,
					FPROP_FRAC_BASE - max_frac);
		}
	}

	__fprop_add_percpu(p, pl, nr);
}
Commit	Line	Data
b2441318	1	// SPDX-License-Identifier: GPL-2.0
f3109a51 JK	2	/*
	3	* Floating proportions with flexible aging period
	4	*
	5	* Copyright (C) 2011, SUSE, Jan Kara <jack@suse.cz>
	6	*
	7	* The goal of this code is: Given different types of event, measure proportion
	8	* of each type of event over time. The proportions are measured with
	9	* exponentially decaying history to give smooth transitions. A formula
	10	* expressing proportion of event of type 'j' is:
	11	*
	12	* p_{j} = (\Sum_{i>=0} x_{i,j}/2^{i+1})/(\Sum_{i>=0} x_i/2^{i+1})
	13	*
	14	* Where x_{i,j} is j's number of events in i-th last time period and x_i is
	15	* total number of events in i-th last time period.
	16	*
	17	* Note that p_{j}'s are normalised, i.e.
	18	*
	19	* \Sum_{j} p_{j} = 1,
	20	*
bdb428c8	21	* This formula can be straightforwardly computed by maintaining denominator
f3109a51 JK	22	* (let's call it 'd') and for each event type its numerator (let's call it
	23	* 'n_j'). When an event of type 'j' happens, we simply need to do:
	24	* n_j++; d++;
	25	*
	26	* When a new period is declared, we could do:
	27	* d /= 2
	28	* for each j
	29	* n_j /= 2
	30	*
	31	* To avoid iteration over all event types, we instead shift numerator of event
	32	* j lazily when someone asks for a proportion of event j or when event j
	33	* occurs. This can bit trivially implemented by remembering last period in
	34	* which something happened with proportion of type j.
	35	*/
	36	#include <linux/flex_proportions.h>
	37
20ae0079	38	int fprop_global_init(struct fprop_global *p, gfp_t gfp)
f3109a51 JK	39	{
	40	int err;
	41
	42	p->period = 0;
	43	/* Use 1 to avoid dealing with periods with 0 events... */
20ae0079	44	err = percpu_counter_init(&p->events, 1, gfp);
f3109a51 JK	45	if (err)
	46	return err;
	47	seqcount_init(&p->sequence);
	48	return 0;
	49	}
	50
	51	void fprop_global_destroy(struct fprop_global *p)
	52	{
	53	percpu_counter_destroy(&p->events);
	54	}
	55
	56	/*
	57	* Declare @periods new periods. It is upto the caller to make sure period
	58	* transitions cannot happen in parallel.
	59	*
	60	* The function returns true if the proportions are still defined and false
	61	* if aging zeroed out all events. This can be used to detect whether declaring
	62	* further periods has any effect.
	63	*/
	64	bool fprop_new_period(struct fprop_global *p, int periods)
	65	{
a91befde	66	s64 events = percpu_counter_sum(&p->events);
f3109a51 JK	67
	68	/*
	69	* Don't do anything if there are no events.
	70	*/
a91befde	71	if (events <= 1)
f3109a51 JK	72	return false;
	73	write_seqcount_begin(&p->sequence);
	74	if (periods < 64)
	75	events -= events >> periods;
	76	/* Use addition to avoid losing events happening between sum and set */
	77	percpu_counter_add(&p->events, -events);
	78	p->period += periods;
	79	write_seqcount_end(&p->sequence);
	80
	81	return true;
	82	}
	83
	84	/*
	85	* ---- SINGLE ----
	86	*/
	87
	88	int fprop_local_init_single(struct fprop_local_single *pl)
	89	{
	90	pl->events = 0;
	91	pl->period = 0;
	92	raw_spin_lock_init(&pl->lock);
	93	return 0;
	94	}
	95
	96	void fprop_local_destroy_single(struct fprop_local_single *pl)
	97	{
	98	}
	99
	100	static void fprop_reflect_period_single(struct fprop_global *p,
	101	struct fprop_local_single *pl)
	102	{
	103	unsigned int period = p->period;
	104	unsigned long flags;
	105
	106	/* Fast path - period didn't change */
	107	if (pl->period == period)
	108	return;
	109	raw_spin_lock_irqsave(&pl->lock, flags);
	110	/* Someone updated pl->period while we were spinning? */
	111	if (pl->period >= period) {
	112	raw_spin_unlock_irqrestore(&pl->lock, flags);
	113	return;
	114	}
	115	/* Aging zeroed our fraction? */
	116	if (period - pl->period < BITS_PER_LONG)
	117	pl->events >>= period - pl->period;
	118	else
	119	pl->events = 0;
	120	pl->period = period;
	121	raw_spin_unlock_irqrestore(&pl->lock, flags);
	122	}
	123
	124	/* Event of type pl happened */
	125	void __fprop_inc_single(struct fprop_global p, struct fprop_local_single pl)
	126	{
	127	fprop_reflect_period_single(p, pl);
	128	pl->events++;
	129	percpu_counter_add(&p->events, 1);
	130	}
	131
	132	/* Return fraction of events of type pl */
	133	void fprop_fraction_single(struct fprop_global *p,
	134	struct fprop_local_single *pl,
	135	unsigned long numerator, unsigned long denominator)
136	{
137	unsigned int seq;
138	s64 num, den;
139
140	do {
141	seq = read_seqcount_begin(&p->sequence);
142	fprop_reflect_period_single(p, pl);
143	num = pl->events;
144	den = percpu_counter_read_positive(&p->events);
145	} while (read_seqcount_retry(&p->sequence, seq));
146
147	/*
148	* Make fraction <= 1 and denominator > 0 even in presence of percpu
149	* counter errors
150	*/
151	if (den <= num) {
152	if (num)
153	den = num;
154	else
155	den = 1;
156	}
157	*denominator = den;
158	*numerator = num;
159	}
160
161	/*
162	* ---- PERCPU ----
163	*/
164	#define PROP_BATCH (8*(1+ilog2(nr_cpu_ids)))
165
20ae0079	166	int fprop_local_init_percpu(struct fprop_local_percpu *pl, gfp_t gfp)
f3109a51 JK	167	{
	168	int err;
	169
20ae0079	170	err = percpu_counter_init(&pl->events, 0, gfp);
f3109a51 JK	171	if (err)
	172	return err;
	173	pl->period = 0;
	174	raw_spin_lock_init(&pl->lock);
	175	return 0;
	176	}
	177
	178	void fprop_local_destroy_percpu(struct fprop_local_percpu *pl)
	179	{
	180	percpu_counter_destroy(&pl->events);
	181	}
	182
	183	static void fprop_reflect_period_percpu(struct fprop_global *p,
	184	struct fprop_local_percpu *pl)
	185	{
	186	unsigned int period = p->period;
	187	unsigned long flags;
	188
	189	/* Fast path - period didn't change */
	190	if (pl->period == period)
	191	return;
	192	raw_spin_lock_irqsave(&pl->lock, flags);
	193	/* Someone updated pl->period while we were spinning? */
	194	if (pl->period >= period) {
	195	raw_spin_unlock_irqrestore(&pl->lock, flags);
	196	return;
	197	}
	198	/* Aging zeroed our fraction? */
	199	if (period - pl->period < BITS_PER_LONG) {
	200	s64 val = percpu_counter_read(&pl->events);
	201
	202	if (val < (nr_cpu_ids * PROP_BATCH))
	203	val = percpu_counter_sum(&pl->events);
	204
104b4e51	205	percpu_counter_add_batch(&pl->events,
f3109a51 JK	206	-val + (val >> (period-pl->period)), PROP_BATCH);
	207	} else
	208	percpu_counter_set(&pl->events, 0);
	209	pl->period = period;
	210	raw_spin_unlock_irqrestore(&pl->lock, flags);
	211	}
	212
	213	/* Event of type pl happened */
be5f1797 MWO	214	void __fprop_add_percpu(struct fprop_global p, struct fprop_local_percpu pl,
be5f1797 MWO	215	long nr)
f3109a51 JK	216	{
f3109a51 JK	217	fprop_reflect_period_percpu(p, pl);
be5f1797 MWO	218	percpu_counter_add_batch(&pl->events, nr, PROP_BATCH);
be5f1797 MWO	219	percpu_counter_add(&p->events, nr);
f3109a51 JK	220	}
	221
	222	void fprop_fraction_percpu(struct fprop_global *p,
	223	struct fprop_local_percpu *pl,
	224	unsigned long numerator, unsigned long denominator)
	225	{
	226	unsigned int seq;
	227	s64 num, den;
	228
	229	do {
	230	seq = read_seqcount_begin(&p->sequence);
	231	fprop_reflect_period_percpu(p, pl);
	232	num = percpu_counter_read_positive(&pl->events);
	233	den = percpu_counter_read_positive(&p->events);
	234	} while (read_seqcount_retry(&p->sequence, seq));
	235
	236	/*
	237	* Make fraction <= 1 and denominator > 0 even in presence of percpu
	238	* counter errors
	239	*/
	240	if (den <= num) {
	241	if (num)
	242	den = num;
	243	else
	244	den = 1;
	245	}
	246	*denominator = den;
	247	*numerator = num;
	248	}
	249
	250	/*
be5f1797	251	* Like __fprop_add_percpu() except that event is counted only if the given
f3109a51 JK	252	* type has fraction smaller than @max_frac/FPROP_FRAC_BASE
f3109a51 JK	253	*/
be5f1797 MWO	254	void __fprop_add_percpu_max(struct fprop_global *p,
be5f1797 MWO	255	struct fprop_local_percpu *pl, int max_frac, long nr)
f3109a51 JK	256	{
	257	if (unlikely(max_frac < FPROP_FRAC_BASE)) {
	258	unsigned long numerator, denominator;
be5f1797	259	s64 tmp;
f3109a51 JK	260
f3109a51 JK	261	fprop_fraction_percpu(p, pl, &numerator, &denominator);
be5f1797 MWO	262	/* Adding 'nr' to fraction exceeds max_frac/FPROP_FRAC_BASE? */
	263	tmp = (u64)denominator * max_frac -
	264	((u64)numerator << FPROP_FRAC_SHIFT);
	265	if (tmp < 0) {
	266	/* Maximum fraction already exceeded? */
f3109a51	267	return;
be5f1797 MWO	268	} else if (tmp < nr * (FPROP_FRAC_BASE - max_frac)) {
	269	/* Add just enough for the fraction to saturate */
	270	nr = div_u64(tmp + FPROP_FRAC_BASE - max_frac - 1,
	271	FPROP_FRAC_BASE - max_frac);
	272	}
63d7f816 TH	273	}
63d7f816 TH	274
be5f1797	275	__fprop_add_percpu(p, pl, nr);
f3109a51	276	}