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/cpuhotplug.h>
#include <linux/tick.h>
#include <linux/mm.h>
#include <linux/stackprotector.h>
#include <linux/suspend.h>

#include <asm/tlb.h>

#include <trace/events/power.h>

#include "sched.h"

/* Linker adds these: start and end of __cpuidle functions */
extern char __cpuidle_text_start[], __cpuidle_text_end[];

/**
 * sched_idle_set_state - Record idle state for the current CPU.
 * @idle_state: State to record.
 */
void sched_idle_set_state(struct cpuidle_state *idle_state)
{
	idle_set_state(this_rq(), idle_state);
}

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 noinline int __cpuidle cpu_idle_poll(void)
{
	rcu_idle_enter();
	trace_cpu_idle_rcuidle(0, smp_processor_id());
	local_irq_enable();
	stop_critical_timings();
	while (!tif_need_resched() &&
		(cpu_idle_force_poll || tick_check_broadcast_expired()))
		cpu_relax();
	start_critical_timings();
	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();
}

/**
 * default_idle_call - Default CPU idle routine.
 *
 * To use when the cpuidle framework cannot be used.
 */
void __cpuidle default_idle_call(void)
{
	if (current_clr_polling_and_test()) {
		local_irq_enable();
	} else {
		stop_critical_timings();
		arch_cpu_idle();
		start_critical_timings();
	}
}

static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
		      int next_state)
{
	/*
	 * The idle task must be scheduled, it is pointless to go to idle, just
	 * update no idle residency and return.
	 */
	if (current_clr_polling_and_test()) {
		dev->last_residency = 0;
		local_irq_enable();
		return -EBUSY;
	}

	/*
	 * 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
	 */
	return cpuidle_enter(drv, dev, next_state);
}

/**
 * cpuidle_idle_call - the main idle function
 *
 * NOTE: no locks or semaphores should be used here
 *
 * On archs that support TIF_POLLING_NRFLAG, is called with polling
 * set, and it returns with polling set.  If it ever stops polling, it
 * must clear the polling bit.
 */
static void cpuidle_idle_call(void)
{
	struct cpuidle_device *dev = cpuidle_get_device();
	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
	int next_state, entered_state;

	/*
	 * 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;
	}

	/*
	 * 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();

	if (cpuidle_not_available(drv, dev)) {
		default_idle_call();
		goto exit_idle;
	}

	/*
	 * Suspend-to-idle ("freeze") is a system state in which all user space
	 * has been frozen, all I/O devices have been suspended and the only
	 * activity happens here and in iterrupts (if any).  In that case bypass
	 * the cpuidle governor and go stratight for the deepest idle state
	 * available.  Possibly also suspend the local tick and the entire
	 * timekeeping to prevent timer interrupts from kicking us out of idle
	 * until a proper wakeup interrupt happens.
	 */

	if (idle_should_freeze() || dev->use_deepest_state) {
		if (idle_should_freeze()) {
			entered_state = cpuidle_enter_freeze(drv, dev);
			if (entered_state > 0) {
				local_irq_enable();
				goto exit_idle;
			}
		}

		next_state = cpuidle_find_deepest_state(drv, dev);
		call_cpuidle(drv, dev, next_state);
	} else {
		/*
		 * Ask the cpuidle framework to choose a convenient idle state.
		 */
		next_state = cpuidle_select(drv, dev);
		entered_state = call_cpuidle(drv, dev, next_state);
		/*
		 * Give the governor an opportunity to reflect on the outcome
		 */
		cpuidle_reflect(dev, entered_state);
	}

exit_idle:
	__current_set_polling();

	/*
	 * It is up to the idle functions to reenable local interrupts
	 */
	if (WARN_ON_ONCE(irqs_disabled()))
		local_irq_enable();

	rcu_idle_exit();
}

/*
 * Generic idle loop implementation
 *
 * Called with polling cleared.
 */
static void do_idle(void)
{
	/*
	 * If the arch has a polling bit, we maintain an invariant:
	 *
	 * Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=
	 * rq->idle). This means that, if rq->idle has the polling bit set,
	 * then setting need_resched is guaranteed to cause the CPU to
	 * reschedule.
	 */

	__current_set_polling();
	tick_nohz_idle_enter();

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

		if (cpu_is_offline(smp_processor_id())) {
			cpuhp_report_idle_dead();
			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();
	__current_clr_polling();

	/*
	 * We promise to call sched_ttwu_pending() and reschedule if
	 * need_resched() is set while polling is set. That means that clearing
	 * polling needs to be visible before doing these things.
	 */
	smp_mb__after_atomic();

	sched_ttwu_pending();
	schedule_preempt_disabled();
}

bool cpu_in_idle(unsigned long pc)
{
	return pc >= (unsigned long)__cpuidle_text_start &&
		pc < (unsigned long)__cpuidle_text_end;
}

struct idle_timer {
	struct hrtimer timer;
	int done;
};

static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
{
	struct idle_timer *it = container_of(timer, struct idle_timer, timer);

	WRITE_ONCE(it->done, 1);
	set_tsk_need_resched(current);

	return HRTIMER_NORESTART;
}

void play_idle(unsigned long duration_ms)
{
	struct idle_timer it;

	/*
	 * Only FIFO tasks can disable the tick since they don't need the forced
	 * preemption.
	 */
	WARN_ON_ONCE(current->policy != SCHED_FIFO);
	WARN_ON_ONCE(current->nr_cpus_allowed != 1);
	WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
	WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
	WARN_ON_ONCE(!duration_ms);

	rcu_sleep_check();
	preempt_disable();
	current->flags |= PF_IDLE;
	cpuidle_use_deepest_state(true);

	it.done = 0;
	hrtimer_init_on_stack(&it.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
	it.timer.function = idle_inject_timer_fn;
	hrtimer_start(&it.timer, ms_to_ktime(duration_ms), HRTIMER_MODE_REL_PINNED);

	while (!READ_ONCE(it.done))
		do_idle();

	cpuidle_use_deepest_state(false);
	current->flags &= ~PF_IDLE;

	preempt_fold_need_resched();
	preempt_enable();
}
EXPORT_SYMBOL_GPL(play_idle);

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
	arch_cpu_idle_prepare();
	cpuhp_online_idle(state);
	while (1)
		do_idle();
}