int cpuidle_enter_state()

in cpuidle.c [200:304]

• 69 lines of code
• 18 McCabe index (conditional complexity)

int cpuidle_enter_state(struct cpuidle_device *dev, struct cpuidle_driver *drv,
			int index)
{
	int entered_state;

	struct cpuidle_state *target_state = &drv->states[index];
	bool broadcast = !!(target_state->flags & CPUIDLE_FLAG_TIMER_STOP);
	ktime_t time_start, time_end;

	/*
	 * Tell the time framework to switch to a broadcast timer because our
	 * local timer will be shut down.  If a local timer is used from another
	 * CPU as a broadcast timer, this call may fail if it is not available.
	 */
	if (broadcast && tick_broadcast_enter()) {
		index = find_deepest_state(drv, dev, target_state->exit_latency_ns,
					   CPUIDLE_FLAG_TIMER_STOP, false);
		if (index < 0) {
			default_idle_call();
			return -EBUSY;
		}
		target_state = &drv->states[index];
		broadcast = false;
	}

	if (target_state->flags & CPUIDLE_FLAG_TLB_FLUSHED)
		leave_mm(dev->cpu);

	/* Take note of the planned idle state. */
	sched_idle_set_state(target_state);

	trace_cpu_idle(index, dev->cpu);
	time_start = ns_to_ktime(local_clock());

	stop_critical_timings();
	if (!(target_state->flags & CPUIDLE_FLAG_RCU_IDLE))
		rcu_idle_enter();
	entered_state = target_state->enter(dev, drv, index);
	if (!(target_state->flags & CPUIDLE_FLAG_RCU_IDLE))
		rcu_idle_exit();
	start_critical_timings();

	sched_clock_idle_wakeup_event();
	time_end = ns_to_ktime(local_clock());
	trace_cpu_idle(PWR_EVENT_EXIT, dev->cpu);

	/* The cpu is no longer idle or about to enter idle. */
	sched_idle_set_state(NULL);

	if (broadcast) {
		if (WARN_ON_ONCE(!irqs_disabled()))
			local_irq_disable();

		tick_broadcast_exit();
	}

	if (!cpuidle_state_is_coupled(drv, index))
		local_irq_enable();

	if (entered_state >= 0) {
		s64 diff, delay = drv->states[entered_state].exit_latency_ns;
		int i;

		/*
		 * Update cpuidle counters
		 * This can be moved to within driver enter routine,
		 * but that results in multiple copies of same code.
		 */
		diff = ktime_sub(time_end, time_start);

		dev->last_residency_ns = diff;
		dev->states_usage[entered_state].time_ns += diff;
		dev->states_usage[entered_state].usage++;

		if (diff < drv->states[entered_state].target_residency_ns) {
			for (i = entered_state - 1; i >= 0; i--) {
				if (dev->states_usage[i].disable)
					continue;

				/* Shallower states are enabled, so update. */
				dev->states_usage[entered_state].above++;
				break;
			}
		} else if (diff > delay) {
			for (i = entered_state + 1; i < drv->state_count; i++) {
				if (dev->states_usage[i].disable)
					continue;

				/*
				 * Update if a deeper state would have been a
				 * better match for the observed idle duration.
				 */
				if (diff - delay >= drv->states[i].target_residency_ns)
					dev->states_usage[entered_state].below++;

				break;
			}
		}
	} else {
		dev->last_residency_ns = 0;
		dev->states_usage[index].rejected++;
	}

	return entered_state;
}