alistair23-linux/kernel/sched/idle.c

/*
 * Generic entry point for the idle threads
 */
#include <linux/sched.h>
#include <linux/cpu.h>
#include <linux/cpuidle.h>
#include <linux/tick.h>
#include <linux/mm.h>
#include <linux/stackprotector.h>

#include <asm/tlb.h>

#include <trace/events/power.h>

static int __read_mostly cpu_idle_force_poll;

void cpu_idle_poll_ctrl(bool enable)
{
	if (enable) {
		cpu_idle_force_poll++;
	} else {
		cpu_idle_force_poll--;
		WARN_ON_ONCE(cpu_idle_force_poll < 0);
	}
}

#ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
static int __init cpu_idle_poll_setup(char *__unused)
{
	cpu_idle_force_poll = 1;
	return 1;
}
__setup("nohlt", cpu_idle_poll_setup);

static int __init cpu_idle_nopoll_setup(char *__unused)
{
	cpu_idle_force_poll = 0;
	return 1;
}
__setup("hlt", cpu_idle_nopoll_setup);
#endif

static inline int cpu_idle_poll(void)
{
	rcu_idle_enter();
	trace_cpu_idle_rcuidle(0, smp_processor_id());
	local_irq_enable();
	while (!tif_need_resched())
		cpu_relax();
	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
	rcu_idle_exit();
	return 1;
}

/* Weak implementations for optional arch specific functions */
void __weak arch_cpu_idle_prepare(void) { }
void __weak arch_cpu_idle_enter(void) { }
void __weak arch_cpu_idle_exit(void) { }
void __weak arch_cpu_idle_dead(void) { }
void __weak arch_cpu_idle(void)
{
	cpu_idle_force_poll = 1;
	local_irq_enable();
}

/**
 * cpuidle_idle_call - the main idle function
 *
 * NOTE: no locks or semaphores should be used here
 * return non-zero on failure
 */
static int cpuidle_idle_call(void)
{
	struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
	int next_state, entered_state, ret;
	bool broadcast;

	/*
	 * Check if the idle task must be rescheduled. If it is the
	 * case, exit the function after re-enabling the local irq.
	 */
	if (need_resched()) {
		local_irq_enable();
		return 0;
	}

	/*
	 * During the idle period, stop measuring the disabled irqs
	 * critical sections latencies
	 */
	stop_critical_timings();

	/*
	 * Tell the RCU framework we are entering an idle section,
	 * so no more rcu read side critical sections and one more
	 * step to the grace period
	 */
	rcu_idle_enter();

	/*
	 * Check if the cpuidle framework is ready, otherwise fallback
	 * to the default arch specific idle method
	 */
	ret = cpuidle_enabled(drv, dev);

	if (!ret) {
		/*
		 * Ask the governor to choose an idle state it thinks
		 * it is convenient to go to. There is *always* a
		 * convenient idle state
		 */
		next_state = cpuidle_select(drv, dev);

		/*
		 * The idle task must be scheduled, it is pointless to
		 * go to idle, just update no idle residency and get
		 * out of this function
		 */
		if (current_clr_polling_and_test()) {
			dev->last_residency = 0;
			entered_state = next_state;
			local_irq_enable();
		} else {
			broadcast = !!(drv->states[next_state].flags &
				       CPUIDLE_FLAG_TIMER_STOP);

			if (broadcast) {
				/*
				 * Tell the time framework to switch
				 * to a broadcast timer because our
				 * local timer will be shutdown. If a
				 * local timer is used from another
				 * cpu as a broadcast timer, this call
				 * may fail if it is not available
				 */
				ret = clockevents_notify(
					CLOCK_EVT_NOTIFY_BROADCAST_ENTER,
					&dev->cpu);
			}

			if (!ret) {
				trace_cpu_idle_rcuidle(next_state, dev->cpu);

				/*
				 * Enter the idle state previously
				 * returned by the governor
				 * decision. This function will block
				 * until an interrupt occurs and will
				 * take care of re-enabling the local
				 * interrupts
				 */
				entered_state = cpuidle_enter(drv, dev,
							      next_state);

				trace_cpu_idle_rcuidle(PWR_EVENT_EXIT,
						       dev->cpu);

				if (broadcast)
					clockevents_notify(
						CLOCK_EVT_NOTIFY_BROADCAST_EXIT,
						&dev->cpu);

				/*
				 * Give the governor an opportunity to reflect on the
				 * outcome
				 */
				cpuidle_reflect(dev, entered_state);
			}
		}
	}

	/*
	 * We can't use the cpuidle framework, let's use the default
	 * idle routine
	 */
	if (ret) {
		if (!current_clr_polling_and_test())
			arch_cpu_idle();
		else
			local_irq_enable();
	}

	__current_set_polling();

	/*
	 * It is up to the idle functions to enable back the local
	 * interrupt
	 */
	if (WARN_ON_ONCE(irqs_disabled()))
		local_irq_enable();

	rcu_idle_exit();
	start_critical_timings();

	return 0;
}

/*
 * Generic idle loop implementation
 */
static void cpu_idle_loop(void)
{
	while (1) {
		tick_nohz_idle_enter();

		while (!need_resched()) {
			check_pgt_cache();
			rmb();

			if (cpu_is_offline(smp_processor_id()))
				arch_cpu_idle_dead();

			local_irq_disable();
			arch_cpu_idle_enter();

			/*
			 * In poll mode we reenable interrupts and spin.
			 *
			 * Also if we detected in the wakeup from idle
			 * path that the tick broadcast device expired
			 * for us, we don't want to go deep idle as we
			 * know that the IPI is going to arrive right
			 * away
			 */
			if (cpu_idle_force_poll || tick_check_broadcast_expired())
				cpu_idle_poll();
			else
				cpuidle_idle_call();

			arch_cpu_idle_exit();
		}

		/*
		 * Since we fell out of the loop above, we know
		 * TIF_NEED_RESCHED must be set, propagate it into
		 * PREEMPT_NEED_RESCHED.
		 *
		 * This is required because for polling idle loops we will
		 * not have had an IPI to fold the state for us.
		 */
		preempt_set_need_resched();
		tick_nohz_idle_exit();
		schedule_preempt_disabled();
	}
}

void cpu_startup_entry(enum cpuhp_state state)
{
	/*
	 * This #ifdef needs to die, but it's too late in the cycle to
	 * make this generic (arm and sh have never invoked the canary
	 * init for the non boot cpus!). Will be fixed in 3.11
	 */
#ifdef CONFIG_X86
	/*
	 * If we're the non-boot CPU, nothing set the stack canary up
	 * for us. The boot CPU already has it initialized but no harm
	 * in doing it again. This is a good place for updating it, as
	 * we wont ever return from this function (so the invalid
	 * canaries already on the stack wont ever trigger).
	 */
	boot_init_stack_canary();
#endif
	__current_set_polling();
	arch_cpu_idle_prepare();
	cpu_idle_loop();
}