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a1d028bd6d
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>
266 lines
6.0 KiB
C
266 lines
6.0 KiB
C
/*
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* Generic entry point for the idle threads
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*/
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#include <linux/sched.h>
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#include <linux/cpu.h>
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#include <linux/cpuidle.h>
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#include <linux/tick.h>
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#include <linux/mm.h>
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#include <linux/stackprotector.h>
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#include <asm/tlb.h>
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#include <trace/events/power.h>
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static int __read_mostly cpu_idle_force_poll;
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void cpu_idle_poll_ctrl(bool enable)
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{
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if (enable) {
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cpu_idle_force_poll++;
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} else {
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cpu_idle_force_poll--;
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WARN_ON_ONCE(cpu_idle_force_poll < 0);
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}
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}
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#ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
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static int __init cpu_idle_poll_setup(char *__unused)
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{
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cpu_idle_force_poll = 1;
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return 1;
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}
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__setup("nohlt", cpu_idle_poll_setup);
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static int __init cpu_idle_nopoll_setup(char *__unused)
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{
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cpu_idle_force_poll = 0;
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return 1;
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}
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__setup("hlt", cpu_idle_nopoll_setup);
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#endif
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static inline int cpu_idle_poll(void)
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{
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rcu_idle_enter();
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trace_cpu_idle_rcuidle(0, smp_processor_id());
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local_irq_enable();
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while (!tif_need_resched())
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cpu_relax();
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trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
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rcu_idle_exit();
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return 1;
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}
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/* Weak implementations for optional arch specific functions */
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void __weak arch_cpu_idle_prepare(void) { }
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void __weak arch_cpu_idle_enter(void) { }
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void __weak arch_cpu_idle_exit(void) { }
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void __weak arch_cpu_idle_dead(void) { }
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void __weak arch_cpu_idle(void)
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{
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cpu_idle_force_poll = 1;
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local_irq_enable();
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}
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/**
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* cpuidle_idle_call - the main idle function
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*
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* NOTE: no locks or semaphores should be used here
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* return non-zero on failure
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*/
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static int cpuidle_idle_call(void)
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{
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struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
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struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
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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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/*
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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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local_irq_enable();
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} else {
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broadcast = !!(drv->states[next_state].flags &
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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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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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trace_cpu_idle_rcuidle(PWR_EVENT_EXIT,
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dev->cpu);
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if (broadcast)
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clockevents_notify(
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CLOCK_EVT_NOTIFY_BROADCAST_EXIT,
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&dev->cpu);
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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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rcu_idle_exit();
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start_critical_timings();
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return 0;
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}
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/*
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* Generic idle loop implementation
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*/
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static void cpu_idle_loop(void)
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{
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while (1) {
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tick_nohz_idle_enter();
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while (!need_resched()) {
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check_pgt_cache();
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rmb();
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if (cpu_is_offline(smp_processor_id()))
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arch_cpu_idle_dead();
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local_irq_disable();
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arch_cpu_idle_enter();
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/*
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* In poll mode we reenable interrupts and spin.
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*
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* Also if we detected in the wakeup from idle
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* path that the tick broadcast device expired
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* for us, we don't want to go deep idle as we
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* know that the IPI is going to arrive right
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* away
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*/
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if (cpu_idle_force_poll || tick_check_broadcast_expired())
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cpu_idle_poll();
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else
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cpuidle_idle_call();
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arch_cpu_idle_exit();
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}
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/*
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* Since we fell out of the loop above, we know
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* TIF_NEED_RESCHED must be set, propagate it into
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* PREEMPT_NEED_RESCHED.
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*
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* This is required because for polling idle loops we will
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* not have had an IPI to fold the state for us.
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*/
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preempt_set_need_resched();
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tick_nohz_idle_exit();
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schedule_preempt_disabled();
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}
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}
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void cpu_startup_entry(enum cpuhp_state state)
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{
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/*
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* This #ifdef needs to die, but it's too late in the cycle to
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* make this generic (arm and sh have never invoked the canary
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* init for the non boot cpus!). Will be fixed in 3.11
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*/
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#ifdef CONFIG_X86
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/*
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* If we're the non-boot CPU, nothing set the stack canary up
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* for us. The boot CPU already has it initialized but no harm
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* in doing it again. This is a good place for updating it, as
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* we wont ever return from this function (so the invalid
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* canaries already on the stack wont ever trigger).
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*/
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boot_init_stack_canary();
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#endif
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__current_set_polling();
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arch_cpu_idle_prepare();
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cpu_idle_loop();
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}
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