Len Brown | 4f86d3a | 2007-10-03 18:58:00 -0400 | [diff] [blame] | 1 | /* |
| 2 | * menu.c - the menu idle governor |
| 3 | * |
| 4 | * Copyright (C) 2006-2007 Adam Belay <abelay@novell.com> |
| 5 | * |
| 6 | * This code is licenced under the GPL. |
| 7 | */ |
| 8 | |
| 9 | #include <linux/kernel.h> |
| 10 | #include <linux/cpuidle.h> |
| 11 | #include <linux/latency.h> |
| 12 | #include <linux/time.h> |
| 13 | #include <linux/ktime.h> |
| 14 | #include <linux/hrtimer.h> |
| 15 | #include <linux/tick.h> |
| 16 | |
| 17 | #define BREAK_FUZZ 4 /* 4 us */ |
| 18 | |
| 19 | struct menu_device { |
| 20 | int last_state_idx; |
| 21 | |
| 22 | unsigned int expected_us; |
| 23 | unsigned int predicted_us; |
| 24 | unsigned int last_measured_us; |
| 25 | unsigned int elapsed_us; |
| 26 | }; |
| 27 | |
| 28 | static DEFINE_PER_CPU(struct menu_device, menu_devices); |
| 29 | |
| 30 | /** |
| 31 | * menu_select - selects the next idle state to enter |
| 32 | * @dev: the CPU |
| 33 | */ |
| 34 | static int menu_select(struct cpuidle_device *dev) |
| 35 | { |
| 36 | struct menu_device *data = &__get_cpu_var(menu_devices); |
| 37 | int i; |
| 38 | |
| 39 | /* determine the expected residency time */ |
| 40 | data->expected_us = |
| 41 | (u32) ktime_to_ns(tick_nohz_get_sleep_length()) / 1000; |
| 42 | |
| 43 | /* find the deepest idle state that satisfies our constraints */ |
| 44 | for (i = 1; i < dev->state_count; i++) { |
| 45 | struct cpuidle_state *s = &dev->states[i]; |
| 46 | |
| 47 | if (s->target_residency > data->expected_us) |
| 48 | break; |
| 49 | if (s->target_residency > data->predicted_us) |
| 50 | break; |
| 51 | if (s->exit_latency > system_latency_constraint()) |
| 52 | break; |
| 53 | } |
| 54 | |
| 55 | data->last_state_idx = i - 1; |
| 56 | return i - 1; |
| 57 | } |
| 58 | |
| 59 | /** |
| 60 | * menu_reflect - attempts to guess what happened after entry |
| 61 | * @dev: the CPU |
| 62 | * |
| 63 | * NOTE: it's important to be fast here because this operation will add to |
| 64 | * the overall exit latency. |
| 65 | */ |
| 66 | static void menu_reflect(struct cpuidle_device *dev) |
| 67 | { |
| 68 | struct menu_device *data = &__get_cpu_var(menu_devices); |
| 69 | int last_idx = data->last_state_idx; |
| 70 | unsigned int measured_us = |
| 71 | cpuidle_get_last_residency(dev) + data->elapsed_us; |
| 72 | struct cpuidle_state *target = &dev->states[last_idx]; |
| 73 | |
| 74 | /* |
| 75 | * Ugh, this idle state doesn't support residency measurements, so we |
| 76 | * are basically lost in the dark. As a compromise, assume we slept |
| 77 | * for one full standard timer tick. However, be aware that this |
| 78 | * could potentially result in a suboptimal state transition. |
| 79 | */ |
| 80 | if (!(target->flags & CPUIDLE_FLAG_TIME_VALID)) |
| 81 | measured_us = USEC_PER_SEC / HZ; |
| 82 | |
| 83 | /* Predict time remaining until next break event */ |
| 84 | if (measured_us + BREAK_FUZZ < data->expected_us - target->exit_latency) { |
| 85 | data->predicted_us = max(measured_us, data->last_measured_us); |
| 86 | data->last_measured_us = measured_us; |
| 87 | data->elapsed_us = 0; |
| 88 | } else { |
| 89 | if (data->elapsed_us < data->elapsed_us + measured_us) |
| 90 | data->elapsed_us = measured_us; |
| 91 | else |
| 92 | data->elapsed_us = -1; |
| 93 | data->predicted_us = max(measured_us, data->last_measured_us); |
| 94 | } |
| 95 | } |
| 96 | |
| 97 | /** |
| 98 | * menu_enable_device - scans a CPU's states and does setup |
| 99 | * @dev: the CPU |
| 100 | */ |
| 101 | static int menu_enable_device(struct cpuidle_device *dev) |
| 102 | { |
| 103 | struct menu_device *data = &per_cpu(menu_devices, dev->cpu); |
| 104 | |
| 105 | memset(data, 0, sizeof(struct menu_device)); |
| 106 | |
| 107 | return 0; |
| 108 | } |
| 109 | |
| 110 | static struct cpuidle_governor menu_governor = { |
| 111 | .name = "menu", |
| 112 | .rating = 20, |
| 113 | .enable = menu_enable_device, |
| 114 | .select = menu_select, |
| 115 | .reflect = menu_reflect, |
| 116 | .owner = THIS_MODULE, |
| 117 | }; |
| 118 | |
| 119 | /** |
| 120 | * init_menu - initializes the governor |
| 121 | */ |
| 122 | static int __init init_menu(void) |
| 123 | { |
| 124 | return cpuidle_register_governor(&menu_governor); |
| 125 | } |
| 126 | |
| 127 | /** |
| 128 | * exit_menu - exits the governor |
| 129 | */ |
| 130 | static void __exit exit_menu(void) |
| 131 | { |
| 132 | cpuidle_unregister_governor(&menu_governor); |
| 133 | } |
| 134 | |
| 135 | MODULE_LICENSE("GPL"); |
| 136 | module_init(init_menu); |
| 137 | module_exit(exit_menu); |