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/jiffies.h> 18 #include <linux/tick.h> 19 20 #include <asm/io.h> 21 #include <linux/uaccess.h> 22 23 #define PROMOTION_COUNT 4 24 #define DEMOTION_COUNT 1 25 26 struct ladder_device_state { 27 struct { 28 u32 promotion_count; 29 u32 demotion_count; 30 u64 promotion_time_ns; 31 u64 demotion_time_ns; 32 } threshold; 33 struct { 34 int promotion_count; 35 int demotion_count; 36 } stats; 37 }; 38 39 struct ladder_device { 40 struct ladder_device_state states[CPUIDLE_STATE_MAX]; 41 }; 42 43 static DEFINE_PER_CPU(struct ladder_device, ladder_devices); 44 45 /** 46 * ladder_do_selection - prepares private data for a state change 47 * @dev: the CPU 48 * @ldev: the ladder device 49 * @old_idx: the current state index 50 * @new_idx: the new target state index 51 */ 52 static inline void ladder_do_selection(struct cpuidle_device *dev, 53 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 dev->last_state_idx = new_idx; 59 } 60 61 /** 62 * ladder_select_state - selects the next state to enter 63 * @drv: cpuidle driver 64 * @dev: the CPU 65 * @dummy: not used 66 */ 67 static int ladder_select_state(struct cpuidle_driver *drv, 68 struct cpuidle_device *dev, bool *dummy) 69 { 70 struct ladder_device *ldev = this_cpu_ptr(&ladder_devices); 71 struct ladder_device_state *last_state; 72 int last_idx = dev->last_state_idx; 73 int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0; 74 s64 latency_req = cpuidle_governor_latency_req(dev->cpu); 75 s64 last_residency; 76 77 /* Special case when user has set very strict latency requirement */ 78 if (unlikely(latency_req == 0)) { 79 ladder_do_selection(dev, ldev, last_idx, 0); 80 return 0; 81 } 82 83 last_state = &ldev->states[last_idx]; 84 85 last_residency = dev->last_residency_ns - drv->states[last_idx].exit_latency_ns; 86 87 /* consider promotion */ 88 if (last_idx < drv->state_count - 1 && 89 !dev->states_usage[last_idx + 1].disable && 90 last_residency > last_state->threshold.promotion_time_ns && 91 drv->states[last_idx + 1].exit_latency_ns <= 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(dev, ldev, last_idx, last_idx + 1); 96 return last_idx + 1; 97 } 98 } 99 100 /* consider demotion */ 101 if (last_idx > first_idx && 102 (dev->states_usage[last_idx].disable || 103 drv->states[last_idx].exit_latency_ns > latency_req)) { 104 int i; 105 106 for (i = last_idx - 1; i > first_idx; i--) { 107 if (drv->states[i].exit_latency_ns <= latency_req) 108 break; 109 } 110 ladder_do_selection(dev, ldev, last_idx, i); 111 return i; 112 } 113 114 if (last_idx > first_idx && 115 last_residency < last_state->threshold.demotion_time_ns) { 116 last_state->stats.demotion_count++; 117 last_state->stats.promotion_count = 0; 118 if (last_state->stats.demotion_count >= last_state->threshold.demotion_count) { 119 ladder_do_selection(dev, ldev, last_idx, last_idx - 1); 120 return last_idx - 1; 121 } 122 } 123 124 /* otherwise remain at the current state */ 125 return last_idx; 126 } 127 128 /** 129 * ladder_enable_device - setup for the governor 130 * @drv: cpuidle driver 131 * @dev: the CPU 132 */ 133 static int ladder_enable_device(struct cpuidle_driver *drv, 134 struct cpuidle_device *dev) 135 { 136 int i; 137 int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0; 138 struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu); 139 struct ladder_device_state *lstate; 140 struct cpuidle_state *state; 141 142 dev->last_state_idx = first_idx; 143 144 for (i = first_idx; i < drv->state_count; i++) { 145 state = &drv->states[i]; 146 lstate = &ldev->states[i]; 147 148 lstate->stats.promotion_count = 0; 149 lstate->stats.demotion_count = 0; 150 151 lstate->threshold.promotion_count = PROMOTION_COUNT; 152 lstate->threshold.demotion_count = DEMOTION_COUNT; 153 154 if (i < drv->state_count - 1) 155 lstate->threshold.promotion_time_ns = state->exit_latency_ns; 156 if (i > first_idx) 157 lstate->threshold.demotion_time_ns = state->exit_latency_ns; 158 } 159 160 return 0; 161 } 162 163 /** 164 * ladder_reflect - update the correct last_state_idx 165 * @dev: the CPU 166 * @index: the index of actual state entered 167 */ 168 static void ladder_reflect(struct cpuidle_device *dev, int index) 169 { 170 if (index > 0) 171 dev->last_state_idx = index; 172 } 173 174 static struct cpuidle_governor ladder_governor = { 175 .name = "ladder", 176 .rating = 10, 177 .enable = ladder_enable_device, 178 .select = ladder_select_state, 179 .reflect = ladder_reflect, 180 }; 181 182 /** 183 * init_ladder - initializes the governor 184 */ 185 static int __init init_ladder(void) 186 { 187 /* 188 * When NO_HZ is disabled, or when booting with nohz=off, the ladder 189 * governor is better so give it a higher rating than the menu 190 * governor. 191 */ 192 if (!tick_nohz_enabled) 193 ladder_governor.rating = 25; 194 195 return cpuidle_register_governor(&ladder_governor); 196 } 197 198 postcore_initcall(init_ladder); 199