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
  22 #include "tick-internal.h"
  23
  24 /* Limit min_delta to a jiffie */
  25 #define MIN_DELTA_LIMIT         (NSEC_PER_SEC / HZ)
  26
  27 static int tick_increase_min_delta(struct clock_event_device *dev)
  28 {
  29         /* Nothing to do if we already reached the limit */
  30         if (dev->min_delta_ns >= MIN_DELTA_LIMIT)
  31                 return -ETIME;
  32
  33         if (dev->min_delta_ns < 5000)
  34                 dev->min_delta_ns = 5000;
  35         else
  36                 dev->min_delta_ns += dev->min_delta_ns >> 1;
  37
  38         if (dev->min_delta_ns > MIN_DELTA_LIMIT)
  39                 dev->min_delta_ns = MIN_DELTA_LIMIT;
  40
  41         printk(KERN_WARNING "CE: %s increased min_delta_ns to %llu nsec\n",
  42                dev->name ? dev->name : "?",
  43                (unsigned long long) dev->min_delta_ns);
  44         return 0;
  45 }
  46
  47 /**
  48  * tick_program_event internal worker function
  49  */
  50 int tick_dev_program_event(struct clock_event_device *dev, ktime_t expires,
  51                            int force)
  52 {
  53         ktime_t now = ktime_get();
  54         int i;
  55
  56         for (i = 0;;) {
  57                 int ret = clockevents_program_event(dev, expires, now);
  58
  59                 if (!ret || !force)
  60                         return ret;
  61
  62                 dev->retries++;
  63                 /*
  64                  * We tried 3 times to program the device with the given
  65                  * min_delta_ns. If that's not working then we increase it
  66                  * and emit a warning.
  67                  */
  68                 if (++i > 2) {
  69                         /* Increase the min. delta and try again */
  70                         if (tick_increase_min_delta(dev)) {
  71                                 /*
  72                                  * Get out of the loop if min_delta_ns
  73                                  * hit the limit already. That's
  74                                  * better than staying here forever.
  75                                  *
  76                                  * We clear next_event so we have a
  77                                  * chance that the box survives.
  78                                  */
  79                                 printk(KERN_WARNING
  80                                        "CE: Reprogramming failure. Giving up\n");
  81                                 dev->next_event.tv64 = KTIME_MAX;
  82                                 return -ETIME;
  83                         }
  84                         i = 0;
  85                 }
  86
  87                 now = ktime_get();
  88                 expires = ktime_add_ns(now, dev->min_delta_ns);
  89         }
  90 }
  91
  92 /**
  93  * tick_program_event
  94  */
  95 int tick_program_event(ktime_t expires, int force)
  96 {
  97         struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
  98
  99         return tick_dev_program_event(dev, expires, force);
 100 }
 101
 102 /**
 103  * tick_resume_onshot - resume oneshot mode
 104  */
 105 void tick_resume_oneshot(void)
 106 {
 107         struct tick_device *td = &__get_cpu_var(tick_cpu_device);
 108         struct clock_event_device *dev = td->evtdev;
 109
 110         clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
 111         tick_program_event(ktime_get(), 1);
 112 }
 113
 114 /**
 115  * tick_setup_oneshot - setup the event device for oneshot mode (hres or nohz)
 116  */
 117 void tick_setup_oneshot(struct clock_event_device *newdev,
 118                         void (*handler)(struct clock_event_device *),
 119                         ktime_t next_event)
 120 {
 121         newdev->event_handler = handler;
 122         clockevents_set_mode(newdev, CLOCK_EVT_MODE_ONESHOT);
 123         tick_dev_program_event(newdev, next_event, 1);
 124 }
 125
 126 /**
 127  * tick_switch_to_oneshot - switch to oneshot mode
 128  */
 129 int tick_switch_to_oneshot(void (*handler)(struct clock_event_device *))
 130 {
 131         struct tick_device *td = &__get_cpu_var(tick_cpu_device);
 132         struct clock_event_device *dev = td->evtdev;
 133
 134         if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT) ||
 135                     !tick_device_is_functional(dev)) {
 136
 137                 printk(KERN_INFO "Clockevents: "
 138                        "could not switch to one-shot mode:");
 139                 if (!dev) {
 140                         printk(" no tick device\n");
 141                 } else {
 142                         if (!tick_device_is_functional(dev))
 143                                 printk(" %s is not functional.\n", dev->name);
 144                         else
 145                                 printk(" %s does not support one-shot mode.\n",
 146                                        dev->name);
 147                 }
 148                 return -EINVAL;
 149         }
 150
 151         td->mode = TICKDEV_MODE_ONESHOT;
 152         dev->event_handler = handler;
 153         clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
 154         tick_broadcast_switch_to_oneshot();
 155         return 0;
 156 }
 157
 158 /**
 159  * tick_check_oneshot_mode - check whether the system is in oneshot mode
 160  *
 161  * returns 1 when either nohz or highres are enabled. otherwise 0.
 162  */
 163 int tick_oneshot_mode_active(void)
 164 {
 165         unsigned long flags;
 166         int ret;
 167
 168         local_irq_save(flags);
 169         ret = __this_cpu_read(tick_cpu_device.mode) == TICKDEV_MODE_ONESHOT;
 170         local_irq_restore(flags);
 171
 172         return ret;
 173 }
 174
 175 #ifdef CONFIG_HIGH_RES_TIMERS
 176 /**
 177  * tick_init_highres - switch to high resolution mode
 178  *
 179  * Called with interrupts disabled.
 180  */
 181 int tick_init_highres(void)
 182 {
 183         return tick_switch_to_oneshot(hrtimer_interrupt);
 184 }
 185 #endif