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/* Limit min_delta to a jiffie */ 26#define MIN_DELTA_LIMIT (NSEC_PER_SEC / HZ) 27 28static int tick_increase_min_delta(struct clock_event_device *dev) 29{ 30 /* Nothing to do if we already reached the limit */ 31 if (dev->min_delta_ns >= MIN_DELTA_LIMIT) 32 return -ETIME; 33 34 if (dev->min_delta_ns < 5000) 35 dev->min_delta_ns = 5000; 36 else 37 dev->min_delta_ns += dev->min_delta_ns >> 1; 38 39 if (dev->min_delta_ns > MIN_DELTA_LIMIT) 40 dev->min_delta_ns = MIN_DELTA_LIMIT; 41 42 printk(KERN_WARNING "CE: %s increased min_delta_ns to %llu nsec\n", 43 dev->name ? dev->name : "?", 44 (unsigned long long) dev->min_delta_ns); 45 return 0; 46} 47 48/** 49 * tick_program_event internal worker function 50 */ 51int tick_dev_program_event(struct clock_event_device *dev, ktime_t expires, 52 int force) 53{ 54 ktime_t now = ktime_get(); 55 int i; 56 57 for (i = 0;;) { 58 int ret = clockevents_program_event(dev, expires, now); 59 60 if (!ret || !force) 61 return ret; 62 63 dev->retries++; 64 /* 65 * We tried 3 times to program the device with the given 66 * min_delta_ns. If that's not working then we increase it 67 * and emit a warning. 68 */ 69 if (++i > 2) { 70 /* Increase the min. delta and try again */ 71 if (tick_increase_min_delta(dev)) { 72 /* 73 * Get out of the loop if min_delta_ns 74 * hit the limit already. That's 75 * better than staying here forever. 76 * 77 * We clear next_event so we have a 78 * chance that the box survives. 79 */ 80 printk(KERN_WARNING 81 "CE: Reprogramming failure. Giving up\n"); 82 dev->next_event.tv64 = KTIME_MAX; 83 return -ETIME; 84 } 85 i = 0; 86 } 87 88 now = ktime_get(); 89 expires = ktime_add_ns(now, dev->min_delta_ns); 90 } 91} 92 93/** 94 * tick_program_event 95 */ 96int tick_program_event(ktime_t expires, int force) 97{ 98 struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev; 99 100 return tick_dev_program_event(dev, expires, force); 101} 102 103/** 104 * tick_resume_onshot - resume oneshot mode 105 */ 106void tick_resume_oneshot(void) 107{ 108 struct tick_device *td = &__get_cpu_var(tick_cpu_device); 109 struct clock_event_device *dev = td->evtdev; 110 111 clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT); 112 tick_program_event(ktime_get(), 1); 113} 114 115/** 116 * tick_setup_oneshot - setup the event device for oneshot mode (hres or nohz) 117 */ 118void tick_setup_oneshot(struct clock_event_device *newdev, 119 void (*handler)(struct clock_event_device *), 120 ktime_t next_event) 121{ 122 newdev->event_handler = handler; 123 clockevents_set_mode(newdev, CLOCK_EVT_MODE_ONESHOT); 124 tick_dev_program_event(newdev, next_event, 1); 125} 126 127/** 128 * tick_switch_to_oneshot - switch to oneshot mode 129 */ 130int tick_switch_to_oneshot(void (*handler)(struct clock_event_device *)) 131{ 132 struct tick_device *td = &__get_cpu_var(tick_cpu_device); 133 struct clock_event_device *dev = td->evtdev; 134 135 if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT) || 136 !tick_device_is_functional(dev)) { 137 138 printk(KERN_INFO "Clockevents: " 139 "could not switch to one-shot mode:"); 140 if (!dev) { 141 printk(" no tick device\n"); 142 } else { 143 if (!tick_device_is_functional(dev)) 144 printk(" %s is not functional.\n", dev->name); 145 else 146 printk(" %s does not support one-shot mode.\n", 147 dev->name); 148 } 149 return -EINVAL; 150 } 151 152 td->mode = TICKDEV_MODE_ONESHOT; 153 dev->event_handler = handler; 154 clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT); 155 tick_broadcast_switch_to_oneshot(); 156 return 0; 157} 158 159/** 160 * tick_check_oneshot_mode - check whether the system is in oneshot mode 161 * 162 * returns 1 when either nohz or highres are enabled. otherwise 0. 163 */ 164int tick_oneshot_mode_active(void) 165{ 166 unsigned long flags; 167 int ret; 168 169 local_irq_save(flags); 170 ret = __get_cpu_var(tick_cpu_device).mode == TICKDEV_MODE_ONESHOT; 171 local_irq_restore(flags); 172 173 return ret; 174} 175 176#ifdef CONFIG_HIGH_RES_TIMERS 177/** 178 * tick_init_highres - switch to high resolution mode 179 * 180 * Called with interrupts disabled. 181 */ 182int tick_init_highres(void) 183{ 184 return tick_switch_to_oneshot(hrtimer_interrupt); 185} 186#endif 187