kernel/sched/idle.c

   1 /*
   2  * Generic entry point for the idle threads
   3  */
   4 #include <linux/sched.h>
   5 #include <linux/cpu.h>
   6 #include <linux/cpuidle.h>
   7 #include <linux/tick.h>
   8 #include <linux/mm.h>
   9 #include <linux/stackprotector.h>
  10
  11 #include <asm/tlb.h>
  12
  13 #include <trace/events/power.h>
  14
  15 static int __read_mostly cpu_idle_force_poll;
  16
  17 void cpu_idle_poll_ctrl(bool enable)
  18 {
  19         if (enable) {
  20                 cpu_idle_force_poll++;
  21         } else {
  22                 cpu_idle_force_poll--;
  23                 WARN_ON_ONCE(cpu_idle_force_poll < 0);
  24         }
  25 }
  26
  27 #ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
  28 static int __init cpu_idle_poll_setup(char *__unused)
  29 {
  30         cpu_idle_force_poll = 1;
  31         return 1;
  32 }
  33 __setup("nohlt", cpu_idle_poll_setup);
  34
  35 static int __init cpu_idle_nopoll_setup(char *__unused)
  36 {
  37         cpu_idle_force_poll = 0;
  38         return 1;
  39 }
  40 __setup("hlt", cpu_idle_nopoll_setup);
  41 #endif
  42
  43 static inline int cpu_idle_poll(void)
  44 {
  45         rcu_idle_enter();
  46         trace_cpu_idle_rcuidle(0, smp_processor_id());
  47         local_irq_enable();
  48         while (!tif_need_resched())
  49                 cpu_relax();
  50         trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
  51         rcu_idle_exit();
  52         return 1;
  53 }
  54
  55 /* Weak implementations for optional arch specific functions */
  56 void __weak arch_cpu_idle_prepare(void) { }
  57 void __weak arch_cpu_idle_enter(void) { }
  58 void __weak arch_cpu_idle_exit(void) { }
  59 void __weak arch_cpu_idle_dead(void) { }
  60 void __weak arch_cpu_idle(void)
  61 {
  62         cpu_idle_force_poll = 1;
  63         local_irq_enable();
  64 }
  65
  66 /*
  67  * Generic idle loop implementation
  68  */
  69 static void cpu_idle_loop(void)
  70 {
  71         while (1) {
  72                 tick_nohz_idle_enter();
  73
  74                 while (!need_resched()) {
  75                         check_pgt_cache();
  76                         rmb();
  77
  78                         if (cpu_is_offline(smp_processor_id()))
  79                                 arch_cpu_idle_dead();
  80
  81                         local_irq_disable();
  82                         arch_cpu_idle_enter();
  83
  84                         /*
  85                          * In poll mode we reenable interrupts and spin.
  86                          *
  87                          * Also if we detected in the wakeup from idle
  88                          * path that the tick broadcast device expired
  89                          * for us, we don't want to go deep idle as we
  90                          * know that the IPI is going to arrive right
  91                          * away
  92                          */
  93                         if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
  94                                 cpu_idle_poll();
  95                         } else {
  96                                 if (!current_clr_polling_and_test()) {
  97                                         stop_critical_timings();
  98                                         rcu_idle_enter();
  99                                         if (cpuidle_idle_call())
 100                                                 arch_cpu_idle();
 101                                         if (WARN_ON_ONCE(irqs_disabled()))
 102                                                 local_irq_enable();
 103                                         rcu_idle_exit();
 104                                         start_critical_timings();
 105                                 } else {
 106                                         local_irq_enable();
 107                                 }
 108                                 __current_set_polling();
 109                         }
 110                         arch_cpu_idle_exit();
 111                 }
 112
 113                 /*
 114                  * Since we fell out of the loop above, we know
 115                  * TIF_NEED_RESCHED must be set, propagate it into
 116                  * PREEMPT_NEED_RESCHED.
 117                  *
 118                  * This is required because for polling idle loops we will
 119                  * not have had an IPI to fold the state for us.
 120                  */
 121                 preempt_set_need_resched();
 122                 tick_nohz_idle_exit();
 123                 schedule_preempt_disabled();
 124         }
 125 }
 126
 127 void cpu_startup_entry(enum cpuhp_state state)
 128 {
 129         /*
 130          * This #ifdef needs to die, but it's too late in the cycle to
 131          * make this generic (arm and sh have never invoked the canary
 132          * init for the non boot cpus!). Will be fixed in 3.11
 133          */
 134 #ifdef CONFIG_X86
 135         /*
 136          * If we're the non-boot CPU, nothing set the stack canary up
 137          * for us. The boot CPU already has it initialized but no harm
 138          * in doing it again. This is a good place for updating it, as
 139          * we wont ever return from this function (so the invalid
 140          * canaries already on the stack wont ever trigger).
 141          */
 142         boot_init_stack_canary();
 143 #endif
 144         __current_set_polling();
 145         arch_cpu_idle_prepare();
 146         cpu_idle_loop();
 147 }