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ladder.c

/*
 * ladder.c - the residency ladder algorithm
 *
 *  Copyright (C) 2001, 2002 Andy Grover <andrew.grover@intel.com>
 *  Copyright (C) 2001, 2002 Paul Diefenbaugh <paul.s.diefenbaugh@intel.com>
 *  Copyright (C) 2004, 2005 Dominik Brodowski <linux@brodo.de>
 *
 * (C) 2006-2007 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
 *               Shaohua Li <shaohua.li@intel.com>
 *               Adam Belay <abelay@novell.com>
 *
 * This code is licenced under the GPL.
 */

#include <linux/kernel.h>
#include <linux/cpuidle.h>
#include <linux/latency.h>
#include <linux/moduleparam.h>
#include <linux/jiffies.h>

#include <asm/io.h>
#include <asm/uaccess.h>

#define PROMOTION_COUNT 4
#define DEMOTION_COUNT 1

struct ladder_device_state {
      struct {
            u32 promotion_count;
            u32 demotion_count;
            u32 promotion_time;
            u32 demotion_time;
      } threshold;
      struct {
            int promotion_count;
            int demotion_count;
      } stats;
};

struct ladder_device {
      struct ladder_device_state states[CPUIDLE_STATE_MAX];
      int last_state_idx;
};

static DEFINE_PER_CPU(struct ladder_device, ladder_devices);

/**
 * ladder_do_selection - prepares private data for a state change
 * @ldev: the ladder device
 * @old_idx: the current state index
 * @new_idx: the new target state index
 */
static inline void ladder_do_selection(struct ladder_device *ldev,
                               int old_idx, int new_idx)
{
      ldev->states[old_idx].stats.promotion_count = 0;
      ldev->states[old_idx].stats.demotion_count = 0;
      ldev->last_state_idx = new_idx;
}

/**
 * ladder_select_state - selects the next state to enter
 * @dev: the CPU
 */
static int ladder_select_state(struct cpuidle_device *dev)
{
      struct ladder_device *ldev = &__get_cpu_var(ladder_devices);
      struct ladder_device_state *last_state;
      int last_residency, last_idx = ldev->last_state_idx;

      if (unlikely(!ldev))
            return 0;

      last_state = &ldev->states[last_idx];

      if (dev->states[last_idx].flags & CPUIDLE_FLAG_TIME_VALID)
            last_residency = cpuidle_get_last_residency(dev) - dev->states[last_idx].exit_latency;
      else
            last_residency = last_state->threshold.promotion_time + 1;

      /* consider promotion */
      if (last_idx < dev->state_count - 1 &&
          last_residency > last_state->threshold.promotion_time &&
          dev->states[last_idx + 1].exit_latency <= system_latency_constraint()) {
            last_state->stats.promotion_count++;
            last_state->stats.demotion_count = 0;
            if (last_state->stats.promotion_count >= last_state->threshold.promotion_count) {
                  ladder_do_selection(ldev, last_idx, last_idx + 1);
                  return last_idx + 1;
            }
      }

      /* consider demotion */
      if (last_idx > 0 &&
          last_residency < last_state->threshold.demotion_time) {
            last_state->stats.demotion_count++;
            last_state->stats.promotion_count = 0;
            if (last_state->stats.demotion_count >= last_state->threshold.demotion_count) {
                  ladder_do_selection(ldev, last_idx, last_idx - 1);
                  return last_idx - 1;
            }
      }

      /* otherwise remain at the current state */
      return last_idx;
}

/**
 * ladder_enable_device - setup for the governor
 * @dev: the CPU
 */
static int ladder_enable_device(struct cpuidle_device *dev)
{
      int i;
      struct ladder_device *ldev = &per_cpu(ladder_devices, dev->cpu);
      struct ladder_device_state *lstate;
      struct cpuidle_state *state;

      ldev->last_state_idx = 0;

      for (i = 0; i < dev->state_count; i++) {
            state = &dev->states[i];
            lstate = &ldev->states[i];

            lstate->stats.promotion_count = 0;
            lstate->stats.demotion_count = 0;

            lstate->threshold.promotion_count = PROMOTION_COUNT;
            lstate->threshold.demotion_count = DEMOTION_COUNT;

            if (i < dev->state_count - 1)
                  lstate->threshold.promotion_time = state->exit_latency;
            if (i > 0)
                  lstate->threshold.demotion_time = state->exit_latency;
      }

      return 0;
}

static struct cpuidle_governor ladder_governor = {
      .name =           "ladder",
      .rating =   10,
      .enable =   ladder_enable_device,
      .select =   ladder_select_state,
      .owner =    THIS_MODULE,
};

/**
 * init_ladder - initializes the governor
 */
static int __init init_ladder(void)
{
      return cpuidle_register_governor(&ladder_governor);
}

/**
 * exit_ladder - exits the governor
 */
static void __exit exit_ladder(void)
{
      cpuidle_unregister_governor(&ladder_governor);
}

MODULE_LICENSE("GPL");
module_init(init_ladder);
module_exit(exit_ladder);

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