273 lines
6.9 KiB
C
273 lines
6.9 KiB
C
/*
|
|
* 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 maintaing 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;
|
|
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 */
|
|
percpu_counter_add(&p->events, -events);
|
|
p->period += periods;
|
|
write_seqcount_end(&p->sequence);
|
|
local_irq_restore(flags);
|
|
|
|
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(&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_inc_percpu(struct fprop_global *p, struct fprop_local_percpu *pl)
|
|
{
|
|
fprop_reflect_period_percpu(p, pl);
|
|
__percpu_counter_add(&pl->events, 1, PROP_BATCH);
|
|
percpu_counter_add(&p->events, 1);
|
|
}
|
|
|
|
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_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);
|
|
__percpu_counter_add(&pl->events, 1, PROP_BATCH);
|
|
percpu_counter_add(&p->events, 1);
|
|
}
|