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/jiffies.h>
  18 #include <linux/tick.h>
  19
  20 #include <asm/io.h>
  21 #include <linux/uaccess.h>
  22
  23 #define PROMOTION_COUNT 4
  24 #define DEMOTION_COUNT 1
  25
  26 struct ladder_device_state {
  27         struct {
  28                 u32 promotion_count;
  29                 u32 demotion_count;
  30                 u64 promotion_time_ns;
  31                 u64 demotion_time_ns;
  32         } threshold;
  33         struct {
  34                 int promotion_count;
  35                 int demotion_count;
  36         } stats;
  37 };
  38
  39 struct ladder_device {
  40         struct ladder_device_state states[CPUIDLE_STATE_MAX];
  41 };
  42
  43 static DEFINE_PER_CPU(struct ladder_device, ladder_devices);
  44
  45 /**
  46  * ladder_do_selection - prepares private data for a state change
  47  * @ldev: the ladder device
  48  * @old_idx: the current state index
  49  * @new_idx: the new target state index
  50  */
  51 static inline void ladder_do_selection(struct cpuidle_device *dev,
  52                                        struct ladder_device *ldev,
  53                                        int old_idx, int new_idx)
  54 {
  55         ldev->states[old_idx].stats.promotion_count = 0;
  56         ldev->states[old_idx].stats.demotion_count = 0;
  57         dev->last_state_idx = new_idx;
  58 }
  59
  60 /**
  61  * ladder_select_state - selects the next state to enter
  62  * @drv: cpuidle driver
  63  * @dev: the CPU
  64  * @dummy: not used
  65  */
  66 static int ladder_select_state(struct cpuidle_driver *drv,
  67                                struct cpuidle_device *dev, bool *dummy)
  68 {
  69         struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
  70         struct ladder_device_state *last_state;
  71         int last_idx = dev->last_state_idx;
  72         int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
  73         s64 latency_req = cpuidle_governor_latency_req(dev->cpu);
  74         s64 last_residency;
  75
  76         /* Special case when user has set very strict latency requirement */
  77         if (unlikely(latency_req == 0)) {
  78                 ladder_do_selection(dev, ldev, last_idx, 0);
  79                 return 0;
  80         }
  81
  82         last_state = &ldev->states[last_idx];
  83
  84         last_residency = dev->last_residency_ns - drv->states[last_idx].exit_latency_ns;
  85
  86         /* consider promotion */
  87         if (last_idx < drv->state_count - 1 &&
  88             !dev->states_usage[last_idx + 1].disable &&
  89             last_residency > last_state->threshold.promotion_time_ns &&
  90             drv->states[last_idx + 1].exit_latency_ns <= 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(dev, ldev, last_idx, last_idx + 1);
  95                         return last_idx + 1;
  96                 }
  97         }
  98
  99         /* consider demotion */
 100         if (last_idx > first_idx &&
 101             (dev->states_usage[last_idx].disable ||
 102             drv->states[last_idx].exit_latency_ns > latency_req)) {
 103                 int i;
 104
 105                 for (i = last_idx - 1; i > first_idx; i--) {
 106                         if (drv->states[i].exit_latency_ns <= latency_req)
 107                                 break;
 108                 }
 109                 ladder_do_selection(dev, ldev, last_idx, i);
 110                 return i;
 111         }
 112
 113         if (last_idx > first_idx &&
 114             last_residency < last_state->threshold.demotion_time_ns) {
 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(dev, 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         int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
 137         struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
 138         struct ladder_device_state *lstate;
 139         struct cpuidle_state *state;
 140
 141         dev->last_state_idx = first_idx;
 142
 143         for (i = first_idx; 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_ns = state->exit_latency_ns;
 155                 if (i > first_idx)
 156                         lstate->threshold.demotion_time_ns = state->exit_latency_ns;
 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         if (index > 0)
 170                 dev->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);