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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 <daniel.lezcano@linaro.org> Acked-by: Nicolas Pitre <nico@linaro.org> Signed-off-by: Peter Zijlstra <peterz@infradead.org> 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 <mingo@kernel.org>
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1 changed files with 57 additions and 2 deletions
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@ -76,21 +76,49 @@ static int cpuidle_idle_call(void)
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int next_state, entered_state, ret;
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bool broadcast;
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/*
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* Check if the idle task must be rescheduled. If it is the
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* case, exit the function after re-enabling the local irq and
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* set again the polling flag
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*/
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if (current_clr_polling_and_test()) {
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local_irq_enable();
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__current_set_polling();
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return 0;
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}
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/*
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* During the idle period, stop measuring the disabled irqs
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* critical sections latencies
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*/
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stop_critical_timings();
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/*
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* Tell the RCU framework we are entering an idle section,
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* so no more rcu read side critical sections and one more
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* step to the grace period
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*/
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rcu_idle_enter();
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/*
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* Check if the cpuidle framework is ready, otherwise fallback
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* to the default arch specific idle method
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*/
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ret = cpuidle_enabled(drv, dev);
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if (!ret) {
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/* ask the governor for the next state */
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/*
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* Ask the governor to choose an idle state it thinks
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* it is convenient to go to. There is *always* a
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* convenient idle state
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*/
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next_state = cpuidle_select(drv, dev);
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/*
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* The idle task must be scheduled, it is pointless to
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* go to idle, just update no idle residency and get
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* out of this function
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*/
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if (current_clr_polling_and_test()) {
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dev->last_residency = 0;
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entered_state = next_state;
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@ -100,6 +128,14 @@ static int cpuidle_idle_call(void)
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CPUIDLE_FLAG_TIMER_STOP);
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if (broadcast)
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/*
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* Tell the time framework to switch
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* to a broadcast timer because our
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* local timer will be shutdown. If a
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* local timer is used from another
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* cpu as a broadcast timer, this call
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* may fail if it is not available
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*/
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ret = clockevents_notify(
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CLOCK_EVT_NOTIFY_BROADCAST_ENTER,
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&dev->cpu);
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@ -107,6 +143,14 @@ static int cpuidle_idle_call(void)
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if (!ret) {
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trace_cpu_idle_rcuidle(next_state, dev->cpu);
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/*
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* Enter the idle state previously
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* returned by the governor
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* decision. This function will block
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* until an interrupt occurs and will
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* take care of re-enabling the local
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* interrupts
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*/
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entered_state = cpuidle_enter(drv, dev,
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next_state);
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@ -118,17 +162,28 @@ static int cpuidle_idle_call(void)
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CLOCK_EVT_NOTIFY_BROADCAST_EXIT,
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&dev->cpu);
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/* give the governor an opportunity to reflect on the outcome */
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/*
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* Give the governor an opportunity to reflect on the
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* outcome
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*/
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cpuidle_reflect(dev, entered_state);
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}
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}
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}
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/*
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* We can't use the cpuidle framework, let's use the default
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* idle routine
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*/
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if (ret)
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arch_cpu_idle();
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__current_set_polling();
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/*
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* It is up to the idle functions to enable back the local
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* interrupt
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*/
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if (WARN_ON_ONCE(irqs_disabled()))
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local_irq_enable();
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