From a1d028bd6d2b7789d15eddfd07c5bea2aaf36040 Mon Sep 17 00:00:00 2001 From: Daniel Lezcano Date: Mon, 3 Mar 2014 08:48:54 +0100 Subject: [PATCH] sched/idle: Add more comments to the code The idle main function is a complex and a critical function. Added more comments to the code. Signed-off-by: Daniel Lezcano Acked-by: Nicolas Pitre Signed-off-by: Peter Zijlstra Cc: tglx@linutronix.de Cc: rjw@rjwysocki.net Cc: preeti@linux.vnet.ibm.com Link: http://lkml.kernel.org/r/1393832934-11625-5-git-send-email-daniel.lezcano@linaro.org Signed-off-by: Ingo Molnar --- kernel/sched/idle.c | 59 +++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 57 insertions(+), 2 deletions(-) diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index cc7a6f3801ff..8f4390a079c7 100644 --- a/kernel/sched/idle.c +++ b/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(); -- 2.20.1