Example #1
0
/*
 * The idle thread.  We try to conserve power, while trying to keep
 * overall latency low.  The architecture specific idle is passed
 * a value to indicate the level of "idleness" of the system.
 */
void cpu_idle(void)
{
	/* endless idle loop with no priority at all */
	while (1) {
		void (*idle)(void) = pm_idle;

#ifdef CONFIG_HOTPLUG_CPU
		if (cpu_is_offline(smp_processor_id()))
			cpu_die();
#endif
		if (!idle)
			idle = default_idle;
		tick_nohz_stop_sched_tick(1);
		while (!need_resched())
			idle();
		tick_nohz_restart_sched_tick();
		preempt_enable_no_resched();
		schedule();
		preempt_disable();
	}
}
Example #2
0
/*
 * The idle thread. There's no useful work to be
 * done, so just try to conserve power and have a
 * low exit latency (ie sit in a loop waiting for
 * somebody to say that they'd like to reschedule)
 */
void cpu_idle(void)
{
	int cpu = smp_processor_id();

	/*
	 * If we're the non-boot CPU, nothing set the stack canary up
	 * for us.  CPU0 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();

	current_thread_info()->status |= TS_POLLING;

	/* endless idle loop with no priority at all */
	while (1) {
		tick_nohz_stop_sched_tick(1);
		while (!need_resched()) {

			check_pgt_cache();
			rmb();

			if (cpu_is_offline(cpu))
				play_dead();

			local_touch_nmi();
			local_irq_disable();
			/* Don't trace irqs off for idle */
			stop_critical_timings();
			if (cpuidle_idle_call())
				pm_idle();
			start_critical_timings();
		}
		tick_nohz_restart_sched_tick();
		preempt_enable_no_resched();
		schedule();
		preempt_disable();
	}
}
Example #3
0
void cpu_idle(void)
{
	set_thread_flag(TIF_POLLING_NRFLAG);

	/* endless idle loop with no priority at all */
	while (1) {
		void (*idle)(void) = pm_idle;

		if (!idle)
			idle = default_idle;

		tick_nohz_stop_sched_tick(1);
		while (!need_resched())
			idle();
		tick_nohz_restart_sched_tick();

		preempt_enable_no_resched();
		schedule();
		preempt_disable();
		check_pgt_cache();
	}
}
Example #4
0
/*
 * The idle thread. There's no useful work to be done, so just try to conserve
 * power and have a low exit latency (ie sit in a loop waiting for somebody to
 * say that they'd like to reschedule)
 */
void __noreturn cpu_idle(void)
{
	int cpu;

	/* CPU is going idle. */
	cpu = smp_processor_id();

	/* endless idle loop with no priority at all */
	while (1) {
		tick_nohz_stop_sched_tick(1);
		while (!need_resched() && cpu_online(cpu)) {
#ifdef CONFIG_MIPS_MT_SMTC
			extern void smtc_idle_loop_hook(void);

			smtc_idle_loop_hook();
#endif

			if (cpu_wait) {
				/* Don't trace irqs off for idle */
				stop_critical_timings();
				(*cpu_wait)();
				start_critical_timings();
			}
		}
#ifdef CONFIG_HOTPLUG_CPU
		if (!cpu_online(cpu) && !cpu_isset(cpu, cpu_callin_map) &&
		    (system_state == SYSTEM_RUNNING ||
		     system_state == SYSTEM_BOOTING))
			play_dead();
#endif
		tick_nohz_restart_sched_tick();
		preempt_enable_no_resched();
		schedule();
		preempt_disable();
	}
}
Example #5
0
static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
					 ktime_t now, int cpu)
{
	unsigned long seq, last_jiffies, next_jiffies, delta_jiffies;
	ktime_t last_update, expires, ret = { .tv64 = 0 };
	struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
	u64 time_delta;


	/* Read jiffies and the time when jiffies were updated last */
	do {
		seq = read_seqbegin(&xtime_lock);
		last_update = last_jiffies_update;
		last_jiffies = jiffies;
		time_delta = timekeeping_max_deferment();
	} while (read_seqretry(&xtime_lock, seq));

	if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) ||
	    arch_needs_cpu(cpu)) {
		next_jiffies = last_jiffies + 1;
		delta_jiffies = 1;
	} else {
		/* Get the next timer wheel timer */
		next_jiffies = get_next_timer_interrupt(last_jiffies);
		delta_jiffies = next_jiffies - last_jiffies;
	}
	/*
	 * Do not stop the tick, if we are only one off
	 * or if the cpu is required for rcu
	 */
	if (!ts->tick_stopped && delta_jiffies == 1)
		goto out;

	/* Schedule the tick, if we are at least one jiffie off */
	if ((long)delta_jiffies >= 1) {

		/*
		 * If this cpu is the one which updates jiffies, then
		 * give up the assignment and let it be taken by the
		 * cpu which runs the tick timer next, which might be
		 * this cpu as well. If we don't drop this here the
		 * jiffies might be stale and do_timer() never
		 * invoked. Keep track of the fact that it was the one
		 * which had the do_timer() duty last. If this cpu is
		 * the one which had the do_timer() duty last, we
		 * limit the sleep time to the timekeeping
		 * max_deferement value which we retrieved
		 * above. Otherwise we can sleep as long as we want.
		 */
		if (cpu == tick_do_timer_cpu) {
			tick_do_timer_cpu = TICK_DO_TIMER_NONE;
			ts->do_timer_last = 1;
		} else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
			time_delta = KTIME_MAX;
			ts->do_timer_last = 0;
		} else if (!ts->do_timer_last) {
			time_delta = KTIME_MAX;
		}

		/*
		 * calculate the expiry time for the next timer wheel
		 * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
		 * that there is no timer pending or at least extremely
		 * far into the future (12 days for HZ=1000). In this
		 * case we set the expiry to the end of time.
		 */
		if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
			/*
			 * Calculate the time delta for the next timer event.
			 * If the time delta exceeds the maximum time delta
			 * permitted by the current clocksource then adjust
			 * the time delta accordingly to ensure the
			 * clocksource does not wrap.
			 */
			time_delta = min_t(u64, time_delta,
					   tick_period.tv64 * delta_jiffies);
		}

		if (time_delta < KTIME_MAX)
			expires = ktime_add_ns(last_update, time_delta);
		else
			expires.tv64 = KTIME_MAX;

		/* Skip reprogram of event if its not changed */
		if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
			goto out;

		ret = expires;

		/*
		 * nohz_stop_sched_tick can be called several times before
		 * the nohz_restart_sched_tick is called. This happens when
		 * interrupts arrive which do not cause a reschedule. In the
		 * first call we save the current tick time, so we can restart
		 * the scheduler tick in nohz_restart_sched_tick.
		 */
		if (!ts->tick_stopped) {
			nohz_balance_enter_idle(cpu);
			calc_load_enter_idle();

			ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
			ts->tick_stopped = 1;
		}

		/*
		 * If the expiration time == KTIME_MAX, then
		 * in this case we simply stop the tick timer.
		 */
		 if (unlikely(expires.tv64 == KTIME_MAX)) {
			if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
				hrtimer_cancel(&ts->sched_timer);
			goto out;
		}

		if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
			hrtimer_start(&ts->sched_timer, expires,
				      HRTIMER_MODE_ABS_PINNED);
			/* Check, if the timer was already in the past */
			if (hrtimer_active(&ts->sched_timer))
				goto out;
		} else if (!tick_program_event(expires, 0))
				goto out;
		/*
		 * We are past the event already. So we crossed a
		 * jiffie boundary. Update jiffies and raise the
		 * softirq.
		 */
		tick_do_update_jiffies64(ktime_get());
	}
	raise_softirq_irqoff(TIMER_SOFTIRQ);
out:
	ts->next_jiffies = next_jiffies;
	ts->last_jiffies = last_jiffies;

	return ret;
}

static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
{
	/*
	 * If this cpu is offline and it is the one which updates
	 * jiffies, then give up the assignment and let it be taken by
	 * the cpu which runs the tick timer next. If we don't drop
	 * this here the jiffies might be stale and do_timer() never
	 * invoked.
	 */
	if (unlikely(!cpu_online(cpu))) {
		if (cpu == tick_do_timer_cpu)
			tick_do_timer_cpu = TICK_DO_TIMER_NONE;
	}

	if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
		return false;

	if (need_resched())
		return false;

	if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
		static int ratelimit;

		if (ratelimit < 10) {
			printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
			       (unsigned int) local_softirq_pending());
			ratelimit++;
		}
		return false;
	}

	return true;
}

static void __tick_nohz_idle_enter(struct tick_sched *ts)
{
	ktime_t now, expires;
	int cpu = smp_processor_id();

	now = tick_nohz_start_idle(cpu, ts);

	if (can_stop_idle_tick(cpu, ts)) {
		int was_stopped = ts->tick_stopped;

		ts->idle_calls++;

		expires = tick_nohz_stop_sched_tick(ts, now, cpu);
		if (expires.tv64 > 0LL) {
			ts->idle_sleeps++;
			ts->idle_expires = expires;
		}

		if (!was_stopped && ts->tick_stopped)
			ts->idle_jiffies = ts->last_jiffies;
	}
}