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/jiffies.h>
  19 #include <linux/tick.h>
  20 #include <linux/cpu.h>
  21
  22 #include <asm/io.h>
  23 #include <linux/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 device *device = get_cpu_device(dev->cpu);
  72         struct ladder_device_state *last_state;
  73         int last_residency, last_idx = ldev->last_state_idx;
  74         int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
  75         int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
  76         int resume_latency = dev_pm_qos_raw_read_value(device);
  77
  78         if (resume_latency < latency_req &&
  79             resume_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT)
  80                 latency_req = resume_latency;
  81
  82         /* Special case when user has set very strict latency requirement */
  83         if (unlikely(latency_req == 0)) {
  84                 ladder_do_selection(ldev, last_idx, 0);
  85                 return 0;
  86         }
  87
  88         last_state = &ldev->states[last_idx];
  89
  90         last_residency = cpuidle_get_last_residency(dev) - drv->states[last_idx].exit_latency;
  91
  92         /* consider promotion */
  93         if (last_idx < drv->state_count - 1 &&
  94             !drv->states[last_idx + 1].disabled &&
  95             !dev->states_usage[last_idx + 1].disable &&
  96             last_residency > last_state->threshold.promotion_time &&
  97             drv->states[last_idx + 1].exit_latency <= latency_req) {
  98                 last_state->stats.promotion_count++;
  99                 last_state->stats.demotion_count = 0;
 100                 if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) {
 101                         ladder_do_selection(ldev, last_idx, last_idx + 1);
 102                         return last_idx + 1;
 103                 }
 104         }
 105
 106         /* consider demotion */
 107         if (last_idx > first_idx &&
 108             (drv->states[last_idx].disabled ||
 109             dev->states_usage[last_idx].disable ||
 110             drv->states[last_idx].exit_latency > latency_req)) {
 111                 int i;
 112
 113                 for (i = last_idx - 1; i > first_idx; i--) {
 114                         if (drv->states[i].exit_latency <= latency_req)
 115                                 break;
 116                 }
 117                 ladder_do_selection(ldev, last_idx, i);
 118                 return i;
 119         }
 120
 121         if (last_idx > first_idx &&
 122             last_residency < last_state->threshold.demotion_time) {
 123                 last_state->stats.demotion_count++;
 124                 last_state->stats.promotion_count = 0;
 125                 if (last_state->stats.demotion_count >= last_state->threshold.demotion_count) {
 126                         ladder_do_selection(ldev, last_idx, last_idx - 1);
 127                         return last_idx - 1;
 128                 }
 129         }
 130
 131         /* otherwise remain at the current state */
 132         return last_idx;
 133 }
 134
 135 /**
 136  * ladder_enable_device - setup for the governor
 137  * @drv: cpuidle driver
 138  * @dev: the CPU
 139  */
 140 static int ladder_enable_device(struct cpuidle_driver *drv,
 141                                 struct cpuidle_device *dev)
 142 {
 143         int i;
 144         int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
 145         struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
 146         struct ladder_device_state *lstate;
 147         struct cpuidle_state *state;
 148
 149         ldev->last_state_idx = first_idx;
 150
 151         for (i = first_idx; i < drv->state_count; i++) {
 152                 state = &drv->states[i];
 153                 lstate = &ldev->states[i];
 154
 155                 lstate->stats.promotion_count = 0;
 156                 lstate->stats.demotion_count = 0;
 157
 158                 lstate->threshold.promotion_count = PROMOTION_COUNT;
 159                 lstate->threshold.demotion_count = DEMOTION_COUNT;
 160
 161                 if (i < drv->state_count - 1)
 162                         lstate->threshold.promotion_time = state->exit_latency;
 163                 if (i > first_idx)
 164                         lstate->threshold.demotion_time = state->exit_latency;
 165         }
 166
 167         return 0;
 168 }
 169
 170 /**
 171  * ladder_reflect - update the correct last_state_idx
 172  * @dev: the CPU
 173  * @index: the index of actual state entered
 174  */
 175 static void ladder_reflect(struct cpuidle_device *dev, int index)
 176 {
 177         struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
 178         if (index > 0)
 179                 ldev->last_state_idx = index;
 180 }
 181
 182 static struct cpuidle_governor ladder_governor = {
 183         .name =         "ladder",
 184         .rating =       10,
 185         .enable =       ladder_enable_device,
 186         .select =       ladder_select_state,
 187         .reflect =      ladder_reflect,
 188 };
 189
 190 /**
 191  * init_ladder - initializes the governor
 192  */
 193 static int __init init_ladder(void)
 194 {
 195         /*
 196          * When NO_HZ is disabled, or when booting with nohz=off, the ladder
 197          * governor is better so give it a higher rating than the menu
 198          * governor.
 199          */
 200         if (!tick_nohz_enabled)
 201                 ladder_governor.rating = 25;
 202
 203         return cpuidle_register_governor(&ladder_governor);
 204 }
 205
 206 postcore_initcall(init_ladder);