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 #include <linux/tick.h>
  21
  22 #include <asm/io.h>
  23 #include <asm/uaccess.h>
  24
  25 #define PROMOTION_COUNT 4
  26 #define DEMOTION_COUNT 1
  27
  28 struct ladder_device_state {
  29         struct {
  30                 u32 promotion_count;
  31                 u32 demotion_count;
  32                 u32 promotion_time;
  33                 u32 demotion_time;
  34         } threshold;
  35         struct {
  36                 int promotion_count;
  37                 int demotion_count;
  38         } stats;
  39 };
  40
  41 struct ladder_device {
  42         struct ladder_device_state states[CPUIDLE_STATE_MAX];
  43         int last_state_idx;
  44 };
  45
  46 static DEFINE_PER_CPU(struct ladder_device, ladder_devices);
  47
  48 /**
  49  * ladder_do_selection - prepares private data for a state change
  50  * @ldev: the ladder device
  51  * @old_idx: the current state index
  52  * @new_idx: the new target state index
  53  */
  54 static inline void ladder_do_selection(struct ladder_device *ldev,
  55                                        int old_idx, int new_idx)
  56 {
  57         ldev->states[old_idx].stats.promotion_count = 0;
  58         ldev->states[old_idx].stats.demotion_count = 0;
  59         ldev->last_state_idx = new_idx;
  60 }
  61
  62 /**
  63  * ladder_select_state - selects the next state to enter
  64  * @drv: cpuidle driver
  65  * @dev: the CPU
  66  */
  67 static int ladder_select_state(struct cpuidle_driver *drv,
  68                                 struct cpuidle_device *dev)
  69 {
  70         struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
  71         struct ladder_device_state *last_state;
  72         int last_residency, last_idx = ldev->last_state_idx;
  73         int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
  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         last_residency = cpuidle_get_last_residency(dev) - drv->states[last_idx].exit_latency;
  84
  85         /* consider promotion */
  86         if (last_idx < drv->state_count - 1 &&
  87             !drv->states[last_idx + 1].disabled &&
  88             !dev->states_usage[last_idx + 1].disable &&
  89             last_residency > last_state->threshold.promotion_time &&
  90             drv->states[last_idx + 1].exit_latency <= 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(ldev, last_idx, last_idx + 1);
  95                         return last_idx + 1;
  96                 }
  97         }
  98
  99         /* consider demotion */
 100         if (last_idx > CPUIDLE_DRIVER_STATE_START &&
 101             (drv->states[last_idx].disabled ||
 102             dev->states_usage[last_idx].disable ||
 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 = CPUIDLE_DRIVER_STATE_START; 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 > CPUIDLE_DRIVER_STATE_START)
 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 = this_cpu_ptr(&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         /*
 189          * When NO_HZ is disabled, or when booting with nohz=off, the ladder
 190          * governor is better so give it a higher rating than the menu
 191          * governor.
 192          */
 193         if (!tick_nohz_enabled)
 194                 ladder_governor.rating = 25;
 195
 196         return cpuidle_register_governor(&ladder_governor);
 197 }
 198
 199 postcore_initcall(init_ladder);