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.h>
  18 #include <linux/module.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  * @drv: cpuidle driver
  64  * @dev: the CPU
  65  */
  66 static int ladder_select_state(struct cpuidle_driver *drv,
  67                                 struct cpuidle_device *dev)
  68 {
  69         struct ladder_device *ldev = &__get_cpu_var(ladder_devices);
  70         struct ladder_device_state *last_state;
  71         int last_residency, last_idx = ldev->last_state_idx;
  72         int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
  73
  74         /* Special case when user has set very strict latency requirement */
  75         if (unlikely(latency_req == 0)) {
  76                 ladder_do_selection(ldev, last_idx, 0);
  77                 return 0;
  78         }
  79
  80         last_state = &ldev->states[last_idx];
  81
  82         if (drv->states[last_idx].flags & CPUIDLE_FLAG_TIME_VALID) {
  83                 last_residency = cpuidle_get_last_residency(dev) - \
  84                                          drv->states[last_idx].exit_latency;
  85         }
  86         else
  87                 last_residency = last_state->threshold.promotion_time + 1;
  88
  89         /* consider promotion */
  90         if (last_idx < drv->state_count - 1 &&
  91             last_residency > last_state->threshold.promotion_time &&
  92             drv->states[last_idx + 1].exit_latency <= latency_req) {
  93                 last_state->stats.promotion_count++;
  94                 last_state->stats.demotion_count = 0;
  95                 if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) {
  96                         ladder_do_selection(ldev, last_idx, last_idx + 1);
  97                         return last_idx + 1;
  98                 }
  99         }
 100
 101         /* consider demotion */
 102         if (last_idx > CPUIDLE_DRIVER_STATE_START &&
 103             drv->states[last_idx].exit_latency > latency_req) {
 104                 int i;
 105
 106                 for (i = last_idx - 1; i > CPUIDLE_DRIVER_STATE_START; i--) {
 107                         if (drv->states[i].exit_latency <= latency_req)
 108                                 break;
 109                 }
 110                 ladder_do_selection(ldev, last_idx, i);
 111                 return i;
 112         }
 113
 114         if (last_idx > CPUIDLE_DRIVER_STATE_START &&
 115             last_residency < last_state->threshold.demotion_time) {
 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(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         struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
 138         struct ladder_device_state *lstate;
 139         struct cpuidle_state *state;
 140
 141         ldev->last_state_idx = CPUIDLE_DRIVER_STATE_START;
 142
 143         for (i = 0; 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 = state->exit_latency;
 155                 if (i > 0)
 156                         lstate->threshold.demotion_time = state->exit_latency;
 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  */
 167 static void ladder_reflect(struct cpuidle_device *dev, int index)
 168 {
 169         struct ladder_device *ldev = &__get_cpu_var(ladder_devices);
 170         if (index > 0)
 171                 ldev->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         .owner =        THIS_MODULE,
 181 };
 182
 183 /**
 184  * init_ladder - initializes the governor
 185  */
 186 static int __init init_ladder(void)
 187 {
 188         return cpuidle_register_governor(&ladder_governor);
 189 }
 190
 191 /**
 192  * exit_ladder - exits the governor
 193  */
 194 static void __exit exit_ladder(void)
 195 {
 196         cpuidle_unregister_governor(&ladder_governor);
 197 }
 198
 199 MODULE_LICENSE("GPL");
 200 module_init(init_ladder);
 201 module_exit(exit_ladder);