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:
V2:
* fixed typo in comment
---
kernel/sched/idle.c | 43 +++++++++++++++++++++++++++++++++++++++++--
1 file changed, 41 insertions(+), 2 deletions(-)
Index: cpuidle-next/kernel/sched/idle.c
===================================================================
--- cpuidle-next.orig/kernel/sched/idle.c
+++ cpuidle-next/kernel/sched/idle.c
@@ -76,20 +76,48 @@ static int cpuidle_idle_call(void)
int next_state, entered_state;
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
+ */
if (cpuidle_enabled(drv, dev) == 0) {
- /* 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;
@@ -104,7 +132,13 @@ static int cpuidle_idle_call(void)
clockevents_notify(
CLOCK_EVT_NOTIFY_BROADCAST_ENTER,
&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);
if (broadcast)
@@ -164,6 +198,11 @@ static void cpu_idle_loop(void)
if (cpu_idle_force_poll ||
tick_check_broadcast_expired())
cpu_idle_poll();
else
+ /*
+ * It is up to the underlying
+ * functions to enable the local
+ * interrupts again
+ */
cpuidle_idle_call();
arch_cpu_idle_exit();
--
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