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sched/idle: Add more comments to the code

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

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Peter 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Daniel Lezcano 2014-03-03 08:48:54 +01:00 committed by Ingo Molnar
parent 8ca3c6424f
commit a1d028bd6d
1 changed files with 57 additions and 2 deletions
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59
kernel/sched/idle.c
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@ -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();