kernel/time/tick-common.c - linux - Git at Google

 /*
  * 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();
 }
	/*
	* 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();
	}