linux/drivers/cpuidle/governors/ladder.c
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   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
  27struct 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
  40struct ladder_device {
  41        struct ladder_device_state states[CPUIDLE_STATE_MAX];
  42        int last_state_idx;
  43};
  44
  45static 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 */
  53static 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 */
  65static 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_requirement(PM_QOS_CPU_DMA_LATENCY);
  71
  72        if (unlikely(!ldev))
  73                return 0;
  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        if (dev->states[last_idx].flags & CPUIDLE_FLAG_TIME_VALID)
  84                last_residency = cpuidle_get_last_residency(dev) - dev->states[last_idx].exit_latency;
  85        else
  86                last_residency = last_state->threshold.promotion_time + 1;
  87
  88        /* consider promotion */
  89        if (last_idx < dev->state_count - 1 &&
  90            last_residency > last_state->threshold.promotion_time &&
  91            dev->states[last_idx + 1].exit_latency <= latency_req) {
  92                last_state->stats.promotion_count++;
  93                last_state->stats.demotion_count = 0;
  94                if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) {
  95                        ladder_do_selection(ldev, last_idx, last_idx + 1);
  96                        return last_idx + 1;
  97                }
  98        }
  99
 100        /* consider demotion */
 101        if (last_idx > CPUIDLE_DRIVER_STATE_START &&
 102            dev->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 (dev->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 * @dev: the CPU
 130 */
 131static int ladder_enable_device(struct cpuidle_device *dev)
 132{
 133        int i;
 134        struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
 135        struct ladder_device_state *lstate;
 136        struct cpuidle_state *state;
 137
 138        ldev->last_state_idx = CPUIDLE_DRIVER_STATE_START;
 139
 140        for (i = 0; i < dev->state_count; i++) {
 141                state = &dev->states[i];
 142                lstate = &ldev->states[i];
 143
 144                lstate->stats.promotion_count = 0;
 145                lstate->stats.demotion_count = 0;
 146
 147                lstate->threshold.promotion_count = PROMOTION_COUNT;
 148                lstate->threshold.demotion_count = DEMOTION_COUNT;
 149
 150                if (i < dev->state_count - 1)
 151                        lstate->threshold.promotion_time = state->exit_latency;
 152                if (i > 0)
 153                        lstate->threshold.demotion_time = state->exit_latency;
 154        }
 155
 156        return 0;
 157}
 158
 159static struct cpuidle_governor ladder_governor = {
 160        .name =         "ladder",
 161        .rating =       10,
 162        .enable =       ladder_enable_device,
 163        .select =       ladder_select_state,
 164        .owner =        THIS_MODULE,
 165};
 166
 167/**
 168 * init_ladder - initializes the governor
 169 */
 170static int __init init_ladder(void)
 171{
 172        return cpuidle_register_governor(&ladder_governor);
 173}
 174
 175/**
 176 * exit_ladder - exits the governor
 177 */
 178static void __exit exit_ladder(void)
 179{
 180        cpuidle_unregister_governor(&ladder_governor);
 181}
 182
 183MODULE_LICENSE("GPL");
 184module_init(init_ladder);
 185module_exit(exit_ladder);
 186