kernel/time/tick-oneshot.c

   1 /*
   2  * linux/kernel/time/tick-oneshot.c
   3  *
   4  * This file contains functions which manage high resolution tick
   5  * related events.
   6  *
   7  * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
   8  * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
   9  * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
  10  *
  11  * This code is licenced under the GPL version 2. For details see
  12  * kernel-base/COPYING.
  13  */
  14 #include <linux/cpu.h>
  15 #include <linux/err.h>
  16 #include <linux/hrtimer.h>
  17 #include <linux/interrupt.h>
  18 #include <linux/percpu.h>
  19 #include <linux/profile.h>
  20 #include <linux/sched.h>
  21 #include <linux/tick.h>
  22
  23 #include "tick-internal.h"
  24
  25 /**
  26  * tick_program_event internal worker function
  27  */
  28 int tick_dev_program_event(struct clock_event_device *dev, ktime_t expires,
  29                            int force)
  30 {
  31         ktime_t now = ktime_get();
  32         int i;
  33
  34         for (i = 0;;) {
  35                 int ret = clockevents_program_event(dev, expires, now);
  36
  37                 if (!ret || !force)
  38                         return ret;
  39
  40                 /*
  41                  * We tried 2 times to program the device with the given
  42                  * min_delta_ns. If that's not working then we double it
  43                  * and emit a warning.
  44                  */
  45                 if (++i > 2) {
  46                         /* Increase the min. delta and try again */
  47                         if (!dev->min_delta_ns)
  48                                 dev->min_delta_ns = 5000;
  49                         else
  50                                 dev->min_delta_ns += dev->min_delta_ns >> 1;
  51
  52                         printk(KERN_WARNING
  53                                "CE: %s increasing min_delta_ns to %lu nsec\n",
  54                                dev->name ? dev->name : "?",
  55                                dev->min_delta_ns << 1);
  56
  57                         i = 0;
  58                 }
  59
  60                 now = ktime_get();
  61                 expires = ktime_add_ns(now, dev->min_delta_ns);
  62         }
  63 }
  64
  65 /**
  66  * tick_program_event
  67  */
  68 int tick_program_event(ktime_t expires, int force)
  69 {
  70         struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
  71
  72         return tick_dev_program_event(dev, expires, force);
  73 }
  74
  75 /**
  76  * tick_resume_onshot - resume oneshot mode
  77  */
  78 void tick_resume_oneshot(void)
  79 {
  80         struct tick_device *td = &__get_cpu_var(tick_cpu_device);
  81         struct clock_event_device *dev = td->evtdev;
  82
  83         clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
  84         tick_program_event(ktime_get(), 1);
  85 }
  86
  87 /**
  88  * tick_setup_oneshot - setup the event device for oneshot mode (hres or nohz)
  89  */
  90 void tick_setup_oneshot(struct clock_event_device *newdev,
  91                         void (*handler)(struct clock_event_device *),
  92                         ktime_t next_event)
  93 {
  94         newdev->event_handler = handler;
  95         clockevents_set_mode(newdev, CLOCK_EVT_MODE_ONESHOT);
  96         tick_dev_program_event(newdev, next_event, 1);
  97 }
  98
  99 /**
 100  * tick_switch_to_oneshot - switch to oneshot mode
 101  */
 102 int tick_switch_to_oneshot(void (*handler)(struct clock_event_device *))
 103 {
 104         struct tick_device *td = &__get_cpu_var(tick_cpu_device);
 105         struct clock_event_device *dev = td->evtdev;
 106
 107         if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT) ||
 108                     !tick_device_is_functional(dev)) {
 109
 110                 printk(KERN_INFO "Clockevents: "
 111                        "could not switch to one-shot mode:");
 112                 if (!dev) {
 113                         printk(" no tick device\n");
 114                 } else {
 115                         if (!tick_device_is_functional(dev))
 116                                 printk(" %s is not functional.\n", dev->name);
 117                         else
 118                                 printk(" %s does not support one-shot mode.\n",
 119                                        dev->name);
 120                 }
 121                 return -EINVAL;
 122         }
 123
 124         td->mode = TICKDEV_MODE_ONESHOT;
 125         dev->event_handler = handler;
 126         clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
 127         tick_broadcast_switch_to_oneshot();
 128         return 0;
 129 }
 130
 131 /**
 132  * tick_check_oneshot_mode - check whether the system is in oneshot mode
 133  *
 134  * returns 1 when either nohz or highres are enabled. otherwise 0.
 135  */
 136 int tick_oneshot_mode_active(void)
 137 {
 138         unsigned long flags;
 139         int ret;
 140
 141         local_irq_save(flags);
 142         ret = __get_cpu_var(tick_cpu_device).mode == TICKDEV_MODE_ONESHOT;
 143         local_irq_restore(flags);
 144
 145         return ret;
 146 }
 147
 148 #ifdef CONFIG_HIGH_RES_TIMERS
 149 /**
 150  * tick_init_highres - switch to high resolution mode
 151  *
 152  * Called with interrupts disabled.
 153  */
 154 int tick_init_highres(void)
 155 {
 156         return tick_switch_to_oneshot(hrtimer_interrupt);
 157 }
 158 #endif