The idle main function is a complex and a critical function. Added more
comments to the code.
Signed-off-by: Daniel Lezcano <daniel.lezc...@linaro.org>
Acked-by: Nicolas Pitre <n...@linaro.org>
---
Changelog:
V4:
* updated comments with new code
V3:
* no changes
V2:
* fixed typo in comment
---
kernel/sched/idle.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 57 insertions(+), 2 deletions(-)
Index: cpuidle-next/kernel/sched/idle.c
===================================================================
--- cpuidle-next.orig/kernel/sched/idle.c
+++ cpuidle-next/kernel/sched/idle.c
@@ -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();
--
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