/* * linux/kernel/time/tick-common.c * * This file contains the base functions to manage periodic tick * related events. * * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de> * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner * * This code is licenced under the GPL version 2. For details see * kernel-base/COPYING. */#include <linux/cpu.h>#include <linux/err.h>#include <linux/hrtimer.h>#include <linux/interrupt.h>#include <linux/percpu.h>#include <linux/profile.h>#include <linux/sched.h>#include <linux/module.h> #include <asm/irq_regs.h> #include "tick-internal.h" /* * Tick devices */DEFINE_PER_CPU(struct tick_device, tick_cpu_device);/* * Tick next event: keeps track of the tick time */ktime_t tick_next_period;ktime_t tick_period; /* * tick_do_timer_cpu is a timer core internal variable which holds the CPU NR * which is responsible for calling do_timer(), i.e. the timekeeping stuff. This * variable has two functions: * * 1) Prevent a thundering herd issue of a gazillion of CPUs trying to grab the *    timekeeping lock all at once. Only the CPU which is assigned to do the *    update is handling it. * * 2) Hand off the duty in the NOHZ idle case by setting the value to *    TICK_DO_TIMER_NONE, i.e. a non existing CPU. So the next cpu which looks *    at it will take over and keep the time keeping alive.  The handover *    procedure also covers cpu hotplug. */int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT; /* * Debugging: see timer_list.c */struct tick_device *tick_get_device(int cpu){	return &per_cpu(tick_cpu_device, cpu);} /** * tick_is_oneshot_available - check for a oneshot capable event device */int tick_is_oneshot_available(void){	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); 	if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT))		return 0;	if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))		return 1;	return tick_broadcast_oneshot_available();} /* * Periodic tick */static void tick_periodic(int cpu){	if (tick_do_timer_cpu == cpu) {		write_seqlock(&jiffies_lock); 		/* Keep track of the next tick event */		tick_next_period = ktime_add(tick_next_period, tick_period); 		do_timer(1);		write_sequnlock(&jiffies_lock);	} 	update_process_times(user_mode(get_irq_regs()));	profile_tick(CPU_PROFILING);} /* * Event handler for periodic ticks */void tick_handle_periodic(struct clock_event_device *dev){	int cpu = smp_processor_id();	ktime_t next; 	tick_periodic(cpu); 	if (dev->mode != CLOCK_EVT_MODE_ONESHOT)		return;	/*	 * Setup the next period for devices, which do not have	 * periodic mode:	 */	next = ktime_add(dev->next_event, tick_period);	for (;;) {		if (!clockevents_program_event(dev, next, false))			return;		/*		 * Have to be careful here. If we're in oneshot mode,		 * before we call tick_periodic() in a loop, we need		 * to be sure we're using a real hardware clocksource.		 * Otherwise we could get trapped in an infinite		 * loop, as the tick_periodic() increments jiffies,		 * when then will increment time, posibly causing		 * the loop to trigger again and again.		 */		if (timekeeping_valid_for_hres())			tick_periodic(cpu);		next = ktime_add(next, tick_period);	}} /* * Setup the device for a periodic tick */void tick_setup_periodic(struct clock_event_device *dev, int broadcast){	tick_set_periodic_handler(dev, broadcast); 	/* Broadcast setup ? */	if (!tick_device_is_functional(dev))		return; 	if ((dev->features & CLOCK_EVT_FEAT_PERIODIC) &&	    !tick_broadcast_oneshot_active()) {		clockevents_set_mode(dev, CLOCK_EVT_MODE_PERIODIC);	} else {		unsigned long seq;		ktime_t next; 		do {			seq = read_seqbegin(&jiffies_lock);			next = tick_next_period;		} while (read_seqretry(&jiffies_lock, seq)); 		clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT); 		for (;;) {			if (!clockevents_program_event(dev, next, false))				return;			next = ktime_add(next, tick_period);		}	}} /* * Setup the tick device */static void tick_setup_device(struct tick_device *td,			      struct clock_event_device *newdev, int cpu,			      const struct cpumask *cpumask){	ktime_t next_event;	void (*handler)(struct clock_event_device *) = NULL; 	/*	 * First device setup ?	 */	if (!td->evtdev) {		/*		 * If no cpu took the do_timer update, assign it to		 * this cpu:		 */		if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {			if (!tick_nohz_full_cpu(cpu))				tick_do_timer_cpu = cpu;			else				tick_do_timer_cpu = TICK_DO_TIMER_NONE;			tick_next_period = ktime_get();			tick_period = ktime_set(0, NSEC_PER_SEC / HZ);		} 		/*		 * Startup in periodic mode first.		 */		td->mode = TICKDEV_MODE_PERIODIC;	} else {		handler = td->evtdev->event_handler;		next_event = td->evtdev->next_event;		td->evtdev->event_handler = clockevents_handle_noop;	} 	td->evtdev = newdev; 	/*	 * When the device is not per cpu, pin the interrupt to the	 * current cpu:	 */	if (!cpumask_equal(newdev->cpumask, cpumask))		irq_set_affinity(newdev->irq, cpumask); 	/*	 * When global broadcasting is active, check if the current	 * device is registered as a placeholder for broadcast mode.	 * This allows us to handle this x86 misfeature in a generic	 * way. This function also returns !=0 when we keep the	 * current active broadcast state for this CPU.	 */	if (tick_device_uses_broadcast(newdev, cpu))		return; 	if (td->mode == TICKDEV_MODE_PERIODIC)		tick_setup_periodic(newdev, 0);	else		tick_setup_oneshot(newdev, handler, next_event);} void tick_install_replacement(struct clock_event_device *newdev){	struct tick_device *td = &__get_cpu_var(tick_cpu_device);	int cpu = smp_processor_id(); 	clockevents_exchange_device(td->evtdev, newdev);	tick_setup_device(td, newdev, cpu, cpumask_of(cpu));	if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)		tick_oneshot_notify();} static bool tick_check_percpu(struct clock_event_device *curdev,			      struct clock_event_device *newdev, int cpu){	if (!cpumask_test_cpu(cpu, newdev->cpumask))		return false;	if (cpumask_equal(newdev->cpumask, cpumask_of(cpu)))		return true;	/* Check if irq affinity can be set */	if (newdev->irq >= 0 && !irq_can_set_affinity(newdev->irq))		return false;	/* Prefer an existing cpu local device */	if (curdev && cpumask_equal(curdev->cpumask, cpumask_of(cpu)))		return false;	return true;} static bool tick_check_preferred(struct clock_event_device *curdev,				 struct clock_event_device *newdev){	/* Prefer oneshot capable device */	if (!(newdev->features & CLOCK_EVT_FEAT_ONESHOT)) {		if (curdev && (curdev->features & CLOCK_EVT_FEAT_ONESHOT))			return false;		if (tick_oneshot_mode_active())			return false;	} 	/*	 * Use the higher rated one, but prefer a CPU local device with a lower	 * rating than a non-CPU local device	 */	return !curdev ||		newdev->rating > curdev->rating ||	       !cpumask_equal(curdev->cpumask, newdev->cpumask);} /* * Check whether the new device is a better fit than curdev. curdev * can be NULL ! */bool tick_check_replacement(struct clock_event_device *curdev,			    struct clock_event_device *newdev){	if (tick_check_percpu(curdev, newdev, smp_processor_id()))		return false; 	return tick_check_preferred(curdev, newdev);} /* * Check, if the new registered device should be used. Called with * clockevents_lock held and interrupts disabled. */void tick_check_new_device(struct clock_event_device *newdev){	struct clock_event_device *curdev;	struct tick_device *td;	int cpu; 	cpu = smp_processor_id();	if (!cpumask_test_cpu(cpu, newdev->cpumask))		goto out_bc; 	td = &per_cpu(tick_cpu_device, cpu);	curdev = td->evtdev; 	/* cpu local device ? */	if (!tick_check_percpu(curdev, newdev, cpu))		goto out_bc; 	/* Preference decision */	if (!tick_check_preferred(curdev, newdev))		goto out_bc; 	if (!try_module_get(newdev->owner))		return; 	/*	 * Replace the eventually existing device by the new	 * device. If the current device is the broadcast device, do	 * not give it back to the clockevents layer !	 */	if (tick_is_broadcast_device(curdev)) {		clockevents_shutdown(curdev);		curdev = NULL;	}	clockevents_exchange_device(curdev, newdev);	tick_setup_device(td, newdev, cpu, cpumask_of(cpu));	if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)		tick_oneshot_notify();	return; out_bc:	/*	 * Can the new device be used as a broadcast device ?	 */	tick_install_broadcast_device(newdev);} /* * Transfer the do_timer job away from a dying cpu. * * Called with interrupts disabled. */void tick_handover_do_timer(int *cpup){	if (*cpup == tick_do_timer_cpu) {		int cpu = cpumask_first(cpu_online_mask); 		tick_do_timer_cpu = (cpu < nr_cpu_ids) ? cpu :			TICK_DO_TIMER_NONE;	}} /* * Shutdown an event device on a given cpu: * * This is called on a life CPU, when a CPU is dead. So we cannot * access the hardware device itself. * We just set the mode and remove it from the lists. */void tick_shutdown(unsigned int *cpup){	struct tick_device *td = &per_cpu(tick_cpu_device, *cpup);	struct clock_event_device *dev = td->evtdev; 	td->mode = TICKDEV_MODE_PERIODIC;	if (dev) {		/*		 * Prevent that the clock events layer tries to call		 * the set mode function!		 */		dev->mode = CLOCK_EVT_MODE_UNUSED;		clockevents_exchange_device(dev, NULL);		dev->event_handler = clockevents_handle_noop;		td->evtdev = NULL;	}} void tick_suspend(void){	struct tick_device *td = &__get_cpu_var(tick_cpu_device); 	clockevents_shutdown(td->evtdev);} void tick_resume(void){	struct tick_device *td = &__get_cpu_var(tick_cpu_device);	int broadcast = tick_resume_broadcast(); 	clockevents_set_mode(td->evtdev, CLOCK_EVT_MODE_RESUME); 	if (!broadcast) {		if (td->mode == TICKDEV_MODE_PERIODIC)			tick_setup_periodic(td->evtdev, 0);		else			tick_resume_oneshot();	}} /** * tick_init - initialize the tick control */void __init tick_init(void){	tick_broadcast_init();}