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/*
* menu.c - the menu idle governor
*
* Copyright (C) 2006-2007 Adam Belay <abelay@novell.com>
*
* This code is licenced under the GPL.
*/
#include <linux/kernel.h>
#include <linux/cpuidle.h>
#include <linux/latency.h>
#include <linux/time.h>
#include <linux/ktime.h>
#include <linux/hrtimer.h>
#include <linux/tick.h>
#define BREAK_FUZZ 4 /* 4 us */
struct menu_device {
int last_state_idx;
unsigned int expected_us;
unsigned int predicted_us;
unsigned int last_measured_us;
unsigned int elapsed_us;
};
static DEFINE_PER_CPU(struct menu_device, menu_devices);
/**
* menu_select - selects the next idle state to enter
* @dev: the CPU
*/
static int menu_select(struct cpuidle_device *dev)
{
struct menu_device *data = &__get_cpu_var(menu_devices);
int i;
/* determine the expected residency time */
data->expected_us =
(u32) ktime_to_ns(tick_nohz_get_sleep_length()) / 1000;
/* find the deepest idle state that satisfies our constraints */
for (i = 1; i < dev->state_count; i++) {
struct cpuidle_state *s = &dev->states[i];
if (s->target_residency > data->expected_us)
break;
if (s->target_residency > data->predicted_us)
break;
if (s->exit_latency > system_latency_constraint())
break;
}
data->last_state_idx = i - 1;
return i - 1;
}
/**
* menu_reflect - attempts to guess what happened after entry
* @dev: the CPU
*
* NOTE: it's important to be fast here because this operation will add to
* the overall exit latency.
*/
static void menu_reflect(struct cpuidle_device *dev)
{
struct menu_device *data = &__get_cpu_var(menu_devices);
int last_idx = data->last_state_idx;
unsigned int measured_us =
cpuidle_get_last_residency(dev) + data->elapsed_us;
struct cpuidle_state *target = &dev->states[last_idx];
/*
* Ugh, this idle state doesn't support residency measurements, so we
* are basically lost in the dark. As a compromise, assume we slept
* for one full standard timer tick. However, be aware that this
* could potentially result in a suboptimal state transition.
*/
if (!(target->flags & CPUIDLE_FLAG_TIME_VALID))
measured_us = USEC_PER_SEC / HZ;
/* Predict time remaining until next break event */
if (measured_us + BREAK_FUZZ < data->expected_us - target->exit_latency) {
data->predicted_us = max(measured_us, data->last_measured_us);
data->last_measured_us = measured_us;
data->elapsed_us = 0;
} else {
if (data->elapsed_us < data->elapsed_us + measured_us)
data->elapsed_us = measured_us;
else
data->elapsed_us = -1;
data->predicted_us = max(measured_us, data->last_measured_us);
}
}
/**
* menu_enable_device - scans a CPU's states and does setup
* @dev: the CPU
*/
static int menu_enable_device(struct cpuidle_device *dev)
{
struct menu_device *data = &per_cpu(menu_devices, dev->cpu);
memset(data, 0, sizeof(struct menu_device));
return 0;
}
static struct cpuidle_governor menu_governor = {
.name = "menu",
.rating = 20,
.enable = menu_enable_device,
.select = menu_select,
.reflect = menu_reflect,
.owner = THIS_MODULE,
};
/**
* init_menu - initializes the governor
*/
static int __init init_menu(void)
{
return cpuidle_register_governor(&menu_governor);
}
/**
* exit_menu - exits the governor
*/
static void __exit exit_menu(void)
{
cpuidle_unregister_governor(&menu_governor);
}
MODULE_LICENSE("GPL");
module_init(init_menu);
module_exit(exit_menu);
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