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