ladder.c (5323B)
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 26struct 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 39struct ladder_device { 40 struct ladder_device_state states[CPUIDLE_STATE_MAX]; 41}; 42 43static DEFINE_PER_CPU(struct ladder_device, ladder_devices); 44 45/** 46 * ladder_do_selection - prepares private data for a state change 47 * @ldev: the ladder device 48 * @old_idx: the current state index 49 * @new_idx: the new target state index 50 */ 51static inline void ladder_do_selection(struct cpuidle_device *dev, 52 struct ladder_device *ldev, 53 int old_idx, int new_idx) 54{ 55 ldev->states[old_idx].stats.promotion_count = 0; 56 ldev->states[old_idx].stats.demotion_count = 0; 57 dev->last_state_idx = new_idx; 58} 59 60/** 61 * ladder_select_state - selects the next state to enter 62 * @drv: cpuidle driver 63 * @dev: the CPU 64 * @dummy: not used 65 */ 66static int ladder_select_state(struct cpuidle_driver *drv, 67 struct cpuidle_device *dev, bool *dummy) 68{ 69 struct ladder_device *ldev = this_cpu_ptr(&ladder_devices); 70 struct ladder_device_state *last_state; 71 int last_idx = dev->last_state_idx; 72 int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0; 73 s64 latency_req = cpuidle_governor_latency_req(dev->cpu); 74 s64 last_residency; 75 76 /* Special case when user has set very strict latency requirement */ 77 if (unlikely(latency_req == 0)) { 78 ladder_do_selection(dev, ldev, last_idx, 0); 79 return 0; 80 } 81 82 last_state = &ldev->states[last_idx]; 83 84 last_residency = dev->last_residency_ns - drv->states[last_idx].exit_latency_ns; 85 86 /* consider promotion */ 87 if (last_idx < drv->state_count - 1 && 88 !dev->states_usage[last_idx + 1].disable && 89 last_residency > last_state->threshold.promotion_time_ns && 90 drv->states[last_idx + 1].exit_latency_ns <= latency_req) { 91 last_state->stats.promotion_count++; 92 last_state->stats.demotion_count = 0; 93 if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) { 94 ladder_do_selection(dev, ldev, last_idx, last_idx + 1); 95 return last_idx + 1; 96 } 97 } 98 99 /* consider demotion */ 100 if (last_idx > first_idx && 101 (dev->states_usage[last_idx].disable || 102 drv->states[last_idx].exit_latency_ns > latency_req)) { 103 int i; 104 105 for (i = last_idx - 1; i > first_idx; i--) { 106 if (drv->states[i].exit_latency_ns <= latency_req) 107 break; 108 } 109 ladder_do_selection(dev, ldev, last_idx, i); 110 return i; 111 } 112 113 if (last_idx > first_idx && 114 last_residency < last_state->threshold.demotion_time_ns) { 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(dev, 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 * @drv: cpuidle driver 130 * @dev: the CPU 131 */ 132static int ladder_enable_device(struct cpuidle_driver *drv, 133 struct cpuidle_device *dev) 134{ 135 int i; 136 int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0; 137 struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu); 138 struct ladder_device_state *lstate; 139 struct cpuidle_state *state; 140 141 dev->last_state_idx = first_idx; 142 143 for (i = first_idx; i < drv->state_count; i++) { 144 state = &drv->states[i]; 145 lstate = &ldev->states[i]; 146 147 lstate->stats.promotion_count = 0; 148 lstate->stats.demotion_count = 0; 149 150 lstate->threshold.promotion_count = PROMOTION_COUNT; 151 lstate->threshold.demotion_count = DEMOTION_COUNT; 152 153 if (i < drv->state_count - 1) 154 lstate->threshold.promotion_time_ns = state->exit_latency_ns; 155 if (i > first_idx) 156 lstate->threshold.demotion_time_ns = state->exit_latency_ns; 157 } 158 159 return 0; 160} 161 162/** 163 * ladder_reflect - update the correct last_state_idx 164 * @dev: the CPU 165 * @index: the index of actual state entered 166 */ 167static void ladder_reflect(struct cpuidle_device *dev, int index) 168{ 169 if (index > 0) 170 dev->last_state_idx = index; 171} 172 173static struct cpuidle_governor ladder_governor = { 174 .name = "ladder", 175 .rating = 10, 176 .enable = ladder_enable_device, 177 .select = ladder_select_state, 178 .reflect = ladder_reflect, 179}; 180 181/** 182 * init_ladder - initializes the governor 183 */ 184static int __init init_ladder(void) 185{ 186 /* 187 * When NO_HZ is disabled, or when booting with nohz=off, the ladder 188 * governor is better so give it a higher rating than the menu 189 * governor. 190 */ 191 if (!tick_nohz_enabled) 192 ladder_governor.rating = 25; 193 194 return cpuidle_register_governor(&ladder_governor); 195} 196 197postcore_initcall(init_ladder);