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 27 struct 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 40 struct ladder_device { 41 struct ladder_device_state states[CPUIDLE_STATE_MAX]; 42 int last_state_idx; 43 }; 44 45 static 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 */ 53 static 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 */ 65 static 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_requirement(PM_QOS_CPU_DMA_LATENCY); 71 72 if (unlikely(!ldev)) 73 return 0; 74 75 /* Special case when user has set very strict latency requirement */ 76 if (unlikely(latency_req == 0)) { 77 ladder_do_selection(ldev, last_idx, 0); 78 return 0; 79 } 80 81 last_state = &ldev->states[last_idx]; 82 83 if (dev->states[last_idx].flags & CPUIDLE_FLAG_TIME_VALID) 84 last_residency = cpuidle_get_last_residency(dev) - dev->states[last_idx].exit_latency; 85 else 86 last_residency = last_state->threshold.promotion_time + 1; 87 88 /* consider promotion */ 89 if (last_idx < dev->state_count - 1 && 90 last_residency > last_state->threshold.promotion_time && 91 dev->states[last_idx + 1].exit_latency <= latency_req) { 92 last_state->stats.promotion_count++; 93 last_state->stats.demotion_count = 0; 94 if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) { 95 ladder_do_selection(ldev, last_idx, last_idx + 1); 96 return last_idx + 1; 97 } 98 } 99 100 /* consider demotion */ 101 if (last_idx > CPUIDLE_DRIVER_STATE_START && 102 dev->states[last_idx].exit_latency > latency_req) { 103 int i; 104 105 for (i = last_idx - 1; i > CPUIDLE_DRIVER_STATE_START; i--) { 106 if (dev->states[i].exit_latency <= latency_req) 107 break; 108 } 109 ladder_do_selection(ldev, last_idx, i); 110 return i; 111 } 112 113 if (last_idx > CPUIDLE_DRIVER_STATE_START && 114 last_residency < last_state->threshold.demotion_time) { 115 last_state->stats.demotion_count++; 116 last_state->stats.promotion_count = 0; 117 if (last_state->stats.demotion_count >= last_state->threshold.demotion_count) { 118 ladder_do_selection(ldev, last_idx, last_idx - 1); 119 return last_idx - 1; 120 } 121 } 122 123 /* otherwise remain at the current state */ 124 return last_idx; 125 } 126 127 /** 128 * ladder_enable_device - setup for the governor 129 * @dev: the CPU 130 */ 131 static int ladder_enable_device(struct cpuidle_device *dev) 132 { 133 int i; 134 struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu); 135 struct ladder_device_state *lstate; 136 struct cpuidle_state *state; 137 138 ldev->last_state_idx = CPUIDLE_DRIVER_STATE_START; 139 140 for (i = 0; i < dev->state_count; i++) { 141 state = &dev->states[i]; 142 lstate = &ldev->states[i]; 143 144 lstate->stats.promotion_count = 0; 145 lstate->stats.demotion_count = 0; 146 147 lstate->threshold.promotion_count = PROMOTION_COUNT; 148 lstate->threshold.demotion_count = DEMOTION_COUNT; 149 150 if (i < dev->state_count - 1) 151 lstate->threshold.promotion_time = state->exit_latency; 152 if (i > 0) 153 lstate->threshold.demotion_time = state->exit_latency; 154 } 155 156 return 0; 157 } 158 159 static struct cpuidle_governor ladder_governor = { 160 .name = "ladder", 161 .rating = 10, 162 .enable = ladder_enable_device, 163 .select = ladder_select_state, 164 .owner = THIS_MODULE, 165 }; 166 167 /** 168 * init_ladder - initializes the governor 169 */ 170 static int __init init_ladder(void) 171 { 172 return cpuidle_register_governor(&ladder_governor); 173 } 174 175 /** 176 * exit_ladder - exits the governor 177 */ 178 static void __exit exit_ladder(void) 179 { 180 cpuidle_unregister_governor(&ladder_governor); 181 } 182 183 MODULE_LICENSE("GPL"); 184 module_init(init_ladder); 185 module_exit(exit_ladder); 186