SAFE public projects git trees. - safe/jmp/linux-2.6/blob - drivers/cpuidle/governors/menu.c

   1 /*
   2  * menu.c - the menu idle governor
   3  *
   4  * Copyright (C) 2006-2007 Adam Belay <abelay@novell.com>
   5  *
   6  * This code is licenced under the GPL.
   7  */
   8
   9 #include <linux/kernel.h>
  10 #include <linux/cpuidle.h>
  11 #include <linux/pm_qos_params.h>
  12 #include <linux/time.h>
  13 #include <linux/ktime.h>
  14 #include <linux/hrtimer.h>
  15 #include <linux/tick.h>
  16
  17 #define BREAK_FUZZ      4       /* 4 us */
  18
  19 struct menu_device {
  20         int             last_state_idx;
  21
  22         unsigned int    expected_us;
  23         unsigned int    predicted_us;
  24         unsigned int    last_measured_us;
  25         unsigned int    elapsed_us;
  26 };
  27
  28 static DEFINE_PER_CPU(struct menu_device, menu_devices);
  29
  30 /**
  31  * menu_select - selects the next idle state to enter
  32  * @dev: the CPU
  33  */
  34 static int menu_select(struct cpuidle_device *dev)
  35 {
  36         struct menu_device *data = &__get_cpu_var(menu_devices);
  37         int latency_req = pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY);
  38         int i;
  39
  40         /* Special case when user has set very strict latency requirement */
  41         if (unlikely(latency_req == 0)) {
  42                 data->last_state_idx = 0;
  43                 return 0;
  44         }
  45
  46         /* determine the expected residency time */
  47         data->expected_us =
  48                 (u32) ktime_to_ns(tick_nohz_get_sleep_length()) / 1000;
  49
  50         /* find the deepest idle state that satisfies our constraints */
  51         for (i = CPUIDLE_DRIVER_STATE_START + 1; i < dev->state_count; i++) {
  52                 struct cpuidle_state *s = &dev->states[i];
  53
  54                 if (s->target_residency > data->expected_us)
  55                         break;
  56                 if (s->target_residency > data->predicted_us)
  57                         break;
  58                 if (s->exit_latency > latency_req)
  59                         break;
  60         }
  61
  62         data->last_state_idx = i - 1;
  63         return i - 1;
  64 }
  65
  66 /**
  67  * menu_reflect - attempts to guess what happened after entry
  68  * @dev: the CPU
  69  *
  70  * NOTE: it's important to be fast here because this operation will add to
  71  *       the overall exit latency.
  72  */
  73 static void menu_reflect(struct cpuidle_device *dev)
  74 {
  75         struct menu_device *data = &__get_cpu_var(menu_devices);
  76         int last_idx = data->last_state_idx;
  77         unsigned int measured_us =
  78                 cpuidle_get_last_residency(dev) + data->elapsed_us;
  79         struct cpuidle_state *target = &dev->states[last_idx];
  80
  81         /*
  82          * Ugh, this idle state doesn't support residency measurements, so we
  83          * are basically lost in the dark.  As a compromise, assume we slept
  84          * for one full standard timer tick.  However, be aware that this
  85          * could potentially result in a suboptimal state transition.
  86          */
  87         if (!(target->flags & CPUIDLE_FLAG_TIME_VALID))
  88                 measured_us = USEC_PER_SEC / HZ;
  89
  90         /* Predict time remaining until next break event */
  91         if (measured_us + BREAK_FUZZ < data->expected_us - target->exit_latency) {
  92                 data->predicted_us = max(measured_us, data->last_measured_us);
  93                 data->last_measured_us = measured_us;
  94                 data->elapsed_us = 0;
  95         } else {
  96                 if (data->elapsed_us < data->elapsed_us + measured_us)
  97                         data->elapsed_us = measured_us;
  98                 else
  99                         data->elapsed_us = -1;
 100                 data->predicted_us = max(measured_us, data->last_measured_us);
 101         }
 102 }
 103
 104 /**
 105  * menu_enable_device - scans a CPU's states and does setup
 106  * @dev: the CPU
 107  */
 108 static int menu_enable_device(struct cpuidle_device *dev)
 109 {
 110         struct menu_device *data = &per_cpu(menu_devices, dev->cpu);
 111
 112         memset(data, 0, sizeof(struct menu_device));
 113
 114         return 0;
 115 }
 116
 117 static struct cpuidle_governor menu_governor = {
 118         .name =         "menu",
 119         .rating =       20,
 120         .enable =       menu_enable_device,
 121         .select =       menu_select,
 122         .reflect =      menu_reflect,
 123         .owner =        THIS_MODULE,
 124 };
 125
 126 /**
 127  * init_menu - initializes the governor
 128  */
 129 static int __init init_menu(void)
 130 {
 131         return cpuidle_register_governor(&menu_governor);
 132 }
 133
 134 /**
 135  * exit_menu - exits the governor
 136  */
 137 static void __exit exit_menu(void)
 138 {
 139         cpuidle_unregister_governor(&menu_governor);
 140 }
 141
 142 MODULE_LICENSE("GPL");
 143 module_init(init_menu);
 144 module_exit(exit_menu);