1/* 2 * ladder.c - the residency ladder algorithm 3 * 4 * Copyright (C) 2001, 2002 Andy Grover <andrew.grover@intel.com> 5 * Copyright (C) 2001, 2002 Paul Diefenbaugh <paul.s.diefenbaugh@intel.com> 6 * Copyright (C) 2004, 2005 Dominik Brodowski <linux@brodo.de> 7 * 8 * (C) 2006-2007 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> 9 * Shaohua Li <shaohua.li@intel.com> 10 * Adam Belay <abelay@novell.com> 11 * 12 * This code is licenced under the GPL. 13 */ 14 15#include <linux/kernel.h> 16#include <linux/cpuidle.h> 17#include <linux/pm_qos_params.h> 18#include <linux/moduleparam.h> 19#include <linux/jiffies.h> 20 21#include <asm/io.h> 22#include <asm/uaccess.h> 23 24#define PROMOTION_COUNT 4 25#define DEMOTION_COUNT 1 26 27struct ladder_device_state { 28 struct { 29 u32 promotion_count; 30 u32 demotion_count; 31 u32 promotion_time; 32 u32 demotion_time; 33 } threshold; 34 struct { 35 int promotion_count; 36 int demotion_count; 37 } stats; 38}; 39 40struct ladder_device { 41 struct ladder_device_state states[CPUIDLE_STATE_MAX]; 42 int last_state_idx; 43}; 44 45static DEFINE_PER_CPU(struct ladder_device, ladder_devices); 46 47/** 48 * ladder_do_selection - prepares private data for a state change 49 * @ldev: the ladder device 50 * @old_idx: the current state index 51 * @new_idx: the new target state index 52 */ 53static inline void ladder_do_selection(struct ladder_device *ldev, 54 int old_idx, int new_idx) 55{ 56 ldev->states[old_idx].stats.promotion_count = 0; 57 ldev->states[old_idx].stats.demotion_count = 0; 58 ldev->last_state_idx = new_idx; 59} 60 61/** 62 * ladder_select_state - selects the next state to enter 63 * @dev: the CPU 64 */ 65static int ladder_select_state(struct cpuidle_device *dev) 66{ 67 struct ladder_device *ldev = &__get_cpu_var(ladder_devices); 68 struct ladder_device_state *last_state; 69 int last_residency, last_idx = ldev->last_state_idx; 70 int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY); 71 72 /* Special case when user has set very strict latency requirement */ 73 if (unlikely(latency_req == 0)) { 74 ladder_do_selection(ldev, last_idx, 0); 75 return 0; 76 } 77 78 last_state = &ldev->states[last_idx]; 79 80 if (dev->states[last_idx].flags & CPUIDLE_FLAG_TIME_VALID) 81 last_residency = cpuidle_get_last_residency(dev) - dev->states[last_idx].exit_latency; 82 else 83 last_residency = last_state->threshold.promotion_time + 1; 84 85 /* consider promotion */ 86 if (last_idx < dev->state_count - 1 && 87 last_residency > last_state->threshold.promotion_time && 88 dev->states[last_idx + 1].exit_latency <= latency_req) { 89 last_state->stats.promotion_count++; 90 last_state->stats.demotion_count = 0; 91 if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) { 92 ladder_do_selection(ldev, last_idx, last_idx + 1); 93 return last_idx + 1; 94 } 95 } 96 97 /* consider demotion */ 98 if (last_idx > CPUIDLE_DRIVER_STATE_START && 99 dev->states[last_idx].exit_latency > latency_req) { 100 int i; 101 102 for (i = last_idx - 1; i > CPUIDLE_DRIVER_STATE_START; i--) { 103 if (dev->states[i].exit_latency <= latency_req) 104 break; 105 } 106 ladder_do_selection(ldev, last_idx, i); 107 return i; 108 } 109 110 if (last_idx > CPUIDLE_DRIVER_STATE_START && 111 last_residency < last_state->threshold.demotion_time) { 112 last_state->stats.demotion_count++; 113 last_state->stats.promotion_count = 0; 114 if (last_state->stats.demotion_count >= last_state->threshold.demotion_count) { 115 ladder_do_selection(ldev, last_idx, last_idx - 1); 116 return last_idx - 1; 117 } 118 } 119 120 /* otherwise remain at the current state */ 121 return last_idx; 122} 123 124/** 125 * ladder_enable_device - setup for the governor 126 * @dev: the CPU 127 */ 128static int ladder_enable_device(struct cpuidle_device *dev) 129{ 130 int i; 131 struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu); 132 struct ladder_device_state *lstate; 133 struct cpuidle_state *state; 134 135 ldev->last_state_idx = CPUIDLE_DRIVER_STATE_START; 136 137 for (i = 0; i < dev->state_count; i++) { 138 state = &dev->states[i]; 139 lstate = &ldev->states[i]; 140 141 lstate->stats.promotion_count = 0; 142 lstate->stats.demotion_count = 0; 143 144 lstate->threshold.promotion_count = PROMOTION_COUNT; 145 lstate->threshold.demotion_count = DEMOTION_COUNT; 146 147 if (i < dev->state_count - 1) 148 lstate->threshold.promotion_time = state->exit_latency; 149 if (i > 0) 150 lstate->threshold.demotion_time = state->exit_latency; 151 } 152 153 return 0; 154} 155 156static struct cpuidle_governor ladder_governor = { 157 .name = "ladder", 158 .rating = 10, 159 .enable = ladder_enable_device, 160 .select = ladder_select_state, 161 .owner = THIS_MODULE, 162}; 163 164/** 165 * init_ladder - initializes the governor 166 */ 167static int __init init_ladder(void) 168{ 169 return cpuidle_register_governor(&ladder_governor); 170} 171 172/** 173 * exit_ladder - exits the governor 174 */ 175static void __exit exit_ladder(void) 176{ 177 cpuidle_unregister_governor(&ladder_governor); 178} 179 180MODULE_LICENSE("GPL"); 181module_init(init_ladder); 182module_exit(exit_ladder); 183