The idle main function is a complex and a critical function. Added more comments to the code.
Signed-off-by: Daniel Lezcano <[email protected]> --- kernel/sched/idle.c | 37 +++++++++++++++++++++++++++++++++---- 1 file changed, 33 insertions(+), 4 deletions(-) diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 72b5926..36ff1a7 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -86,19 +86,34 @@ static int cpuidle_idle_call(void) if (cpu_idle_force_poll || tick_check_broadcast_expired()) return cpu_idle_poll(); + /* + * Check if the idle task must 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(); - /* Ask the governor for the next state, this call can fail for - * different reasons: cpuidle is not enabled or an idle state - * fulfilling the constraints was not found. In this case, we fall - * back to the default idle function + /* + * Ask the governor to choose an idle state it thinks it is + * convenient to go to. There is *always* a convenient idle + * state but the call could fail if cpuidle is not enabled */ next_state = cpuidle_select(drv, dev); if (next_state < 0) { @@ -106,6 +121,10 @@ static int cpuidle_idle_call(void) goto out; } + /* + * 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 (need_resched()) { dev->last_residency = 0; /* give the governor an opportunity to reflect on the outcome */ @@ -116,6 +135,12 @@ static int cpuidle_idle_call(void) 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); trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu); @@ -152,6 +177,10 @@ static void cpu_idle_loop(void) local_irq_disable(); arch_cpu_idle_enter(); + /* + * It is up to the underlying functions to + * enable the local interrupts again + */ cpuidle_idle_call(); arch_cpu_idle_exit(); -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
