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