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 --- 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();