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