LXR linux/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
  26struct ladder_device_state {
  27        struct {
  28                u32 promotion_count;
  29                u32 demotion_count;
  30                u32 promotion_time;
  31                u32 demotion_time;
  32        } threshold;
  33        struct {
  34                int promotion_count;
  35                int demotion_count;
  36        } stats;
  37};
  38
  39struct ladder_device {
  40        struct ladder_device_state states[CPUIDLE_STATE_MAX];
  41        int last_state_idx;
  42};
  43
  44static DEFINE_PER_CPU(struct ladder_device, ladder_devices);
  45
  46/**
  47 * ladder_do_selection - prepares private data for a state change
  48 * @ldev: the ladder device
  49 * @old_idx: the current state index
  50 * @new_idx: the new target state index
  51 */
  52static inline void ladder_do_selection(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        ldev->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 */
  66static 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_residency, last_idx = ldev->last_state_idx;
  72        int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
  73        int latency_req = cpuidle_governor_latency_req(dev->cpu);
  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 = dev->last_residency - 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 > first_idx &&
 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 > first_idx; 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 > first_idx &&
 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 */
 133static int ladder_enable_device(struct cpuidle_driver *drv,
 134                                struct cpuidle_device *dev)
 135{
 136        int i;
 137        int first_idx = drv->states[0].flags & CPUIDLE_FLAG_POLLING ? 1 : 0;
 138        struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
 139        struct ladder_device_state *lstate;
 140        struct cpuidle_state *state;
 141
 142        ldev->last_state_idx = first_idx;
 143
 144        for (i = first_idx; i < drv->state_count; i++) {
 145                state = &drv->states[i];
 146                lstate = &ldev->states[i];
 147
 148                lstate->stats.promotion_count = 0;
 149                lstate->stats.demotion_count = 0;
 150
 151                lstate->threshold.promotion_count = PROMOTION_COUNT;
 152                lstate->threshold.demotion_count = DEMOTION_COUNT;
 153
 154                if (i < drv->state_count - 1)
 155                        lstate->threshold.promotion_time = state->exit_latency;
 156                if (i > first_idx)
 157                        lstate->threshold.demotion_time = state->exit_latency;
 158        }
 159
 160        return 0;
 161}
 162
 163/**
 164 * ladder_reflect - update the correct last_state_idx
 165 * @dev: the CPU
 166 * @index: the index of actual state entered
 167 */
 168static void ladder_reflect(struct cpuidle_device *dev, int index)
 169{
 170        struct ladder_device *ldev = this_cpu_ptr(&ladder_devices);
 171        if (index > 0)
 172                ldev->last_state_idx = index;
 173}
 174
 175static struct cpuidle_governor ladder_governor = {
 176        .name =         "ladder",
 177        .rating =       10,
 178        .enable =       ladder_enable_device,
 179        .select =       ladder_select_state,
 180        .reflect =      ladder_reflect,
 181};
 182
 183/**
 184 * init_ladder - initializes the governor
 185 */
 186static 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
 199postcore_initcall(init_ladder);
 200