Messages in this thread Patch in this message |  | | From | Daniel Lezcano <> | Subject | [PATCH V2 5/5] idle: Add more comments to the code | Date | Mon, 24 Feb 2014 14:55:51 +0100 |
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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> --- Changelog:
V2: * fixed typo in comment --- kernel/sched/idle.c | 40 ++++++++++++++++++++++++++++++++++++---- 1 file changed, 36 insertions(+), 4 deletions(-)
Index: cpuidle-next/kernel/sched/idle.c =================================================================== --- cpuidle-next.orig/kernel/sched/idle.c +++ cpuidle-next/kernel/sched/idle.c @@ -86,15 +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 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 + */ next_state = cpuidle_enabled(drv, dev); if (next_state < 0) { arch_cpu_idle(); @@ -102,13 +121,16 @@ static int cpuidle_idle_call(void) } /* - * 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 */ 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 (need_resched()) { dev->last_residency = 0; /* give the governor an opportunity to reflect on the outcome */ @@ -119,6 +141,12 @@ 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); @@ -155,6 +183,10 @@ 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();
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