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Commit a1d028bd authored by Daniel Lezcano's avatar Daniel Lezcano Committed by Ingo Molnar
Browse files

sched/idle: Add more comments to the code 



The idle main function is a complex and a critical function. Added more
comments to the code.

Signed-off-by: default avatarDaniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: default avatarNicolas Pitre <nico@linaro.org>
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: tglx@linutronix.de
Cc: rjw@rjwysocki.net
Cc: preeti@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1393832934-11625-5-git-send-email-daniel.lezcano@linaro.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 8ca3c642

kernel/sched/idle.c

+57 −2
Original line number Diff line number Diff line
@@ -76,21 +76,49 @@ static int cpuidle_idle_call(void) 
	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 and

	 * set again the polling flag

	 */

	if (current_clr_polling_and_test()) {

		local_irq_enable();

		__current_set_polling();

		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 for the next state */

		/*

		 * 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;
@@ -100,6 +128,14 @@ static int cpuidle_idle_call(void) 
				       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);
@@ -107,6 +143,14 @@ static int cpuidle_idle_call(void) 
			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);
@@ -118,17 +162,28 @@ static int cpuidle_idle_call(void) 
						CLOCK_EVT_NOTIFY_BROADCAST_EXIT,

						&dev->cpu);



				/* give the governor an opportunity to reflect on the outcome */

				/*

				 * 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)

		arch_cpu_idle();



	__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();