drivers/cpuidle/governors/ladder.c

   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);