# Release 4.8 lib/flex_proportions.c

Directory: lib
```/*
*  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;
}

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

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/*
* 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;
unsigned long flags;

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

return true;
}

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/*
* ---- 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;
}

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void fprop_local_destroy_single(struct fprop_local_single *pl)
{
}

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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);
}

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/* 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++;
}

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/* 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 {
fprop_reflect_period_single(p, pl);
num = pl->events;

/*
* 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;
}

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/*
* ---- 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;
}

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

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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) {

if (val < (nr_cpu_ids * PROP_BATCH))
val = percpu_counter_sum(&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);
}

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/* Event of type pl happened */

void __fprop_inc_percpu(struct fprop_global *p, struct fprop_local_percpu *pl)
{
fprop_reflect_period_percpu(p, pl);
}

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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 {
fprop_reflect_period_percpu(p, pl);

/*
* 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;
}

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/*
* Like __fprop_inc_percpu() except that event is counted only if the given
* type has fraction smaller than @max_frac/FPROP_FRAC_BASE
*/

void __fprop_inc_percpu_max(struct fprop_global *p,
struct fprop_local_percpu *pl, int max_frac)
{
if (unlikely(max_frac < FPROP_FRAC_BASE)) {
unsigned long numerator, denominator;

fprop_fraction_percpu(p, pl, &numerator, &denominator);
if (numerator >
(((u64)denominator) * max_frac) >> FPROP_FRAC_SHIFT)
return;
} else
fprop_reflect_period_percpu(p, pl);