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
  21 #include <asm/io.h>
  22 #include <linux/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 = this_cpu_ptr(&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         last_residency = cpuidle_get_last_residency(dev) - drv->states[last_idx].exit_latency;
  83
  84         /* consider promotion */
  85         if (last_idx < drv->state_count - 1 &&
  86             !drv->states[last_idx + 1].disabled &&
  87             !dev->states_usage[last_idx + 1].disable &&
  88             last_residency > last_state->threshold.promotion_time &&
  89             drv->states[last_idx + 1].exit_latency <= latency_req) {
  90                 last_state->stats.promotion_count++;
  91                 last_state->stats.demotion_count = 0;
  92                 if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) {
  93                         ladder_do_selection(ldev, last_idx, last_idx + 1);
  94                         return last_idx + 1;
  95                 }
  96         }
  97
  98         /* consider demotion */
  99         if (last_idx > CPUIDLE_DRIVER_STATE_START &&
 100             (drv->states[last_idx].disabled ||
 101             dev->states_usage[last_idx].disable ||
 102             drv->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 (drv->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  * @drv: cpuidle driver
 130  * @dev: the CPU
 131  */
 132 static int ladder_enable_device(struct cpuidle_driver *drv,
 133                                 struct cpuidle_device *dev)
 134 {
 135         int i;
 136         struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
 137         struct ladder_device_state *lstate;
 138         struct cpuidle_state *state;
 139
 140         ldev->last_state_idx = CPUIDLE_DRIVER_STATE_START;
 141
 142         for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
 143                 state = &drv->states[i];
 144                 lstate = &ldev->states[i];
 145
 146                 lstate->stats.promotion_count = 0;
 147                 lstate->stats.demotion_count = 0;
 148
 149                 lstate->threshold.promotion_count = PROMOTION_COUNT;
 150                 lstate->threshold.demotion_count = DEMOTION_COUNT;
 151
 152                 if (i < drv->state_count - 1)
 153                         lstate->threshold.promotion_time = state->exit_latency;
 154                 if (i > CPUIDLE_DRIVER_STATE_START)
 155                         lstate->threshold.demotion_time = state->exit_latency;
 156         }
 157
 158         return 0;
 159 }
 160
 161 /**
 162  * ladder_reflect - update the correct last_state_idx
 163  * @dev: the CPU
 164  * @index: the index of actual state entered
 165  */
 166 static void ladder_reflect(struct cpuidle_device *dev, int index)
 167 {
 168         struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
 169         if (index > 0)
 170                 ldev->last_state_idx = index;
 171 }
 172
 173 static struct cpuidle_governor ladder_governor = {
 174         .name =         "ladder",
 175         .rating =       10,
 176         .enable =       ladder_enable_device,
 177         .select =       ladder_select_state,
 178         .reflect =      ladder_reflect,
 179 };
 180
 181 /**
 182  * init_ladder - initializes the governor
 183  */
 184 static int __init init_ladder(void)
 185 {
 186         /*
 187          * When NO_HZ is disabled, or when booting with nohz=off, the ladder
 188          * governor is better so give it a higher rating than the menu
 189          * governor.
 190          */
 191         if (!tick_nohz_enabled)
 192                 ladder_governor.rating = 25;
 193
 194         return cpuidle_register_governor(&ladder_governor);
 195 }
 196
 197 postcore_initcall(init_ladder);