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
   9 #include <asm/tlb.h>
  10
  11 #include <trace/events/power.h>
  12
  13 static int __read_mostly cpu_idle_force_poll;
  14
  15 void cpu_idle_poll_ctrl(bool enable)
  16 {
  17         if (enable) {
  18                 cpu_idle_force_poll++;
  19         } else {
  20                 cpu_idle_force_poll--;
  21                 WARN_ON_ONCE(cpu_idle_force_poll < 0);
  22         }
  23 }
  24
  25 #ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
  26 static int __init cpu_idle_poll_setup(char *__unused)
  27 {
  28         cpu_idle_force_poll = 1;
  29         return 1;
  30 }
  31 __setup("nohlt", cpu_idle_poll_setup);
  32
  33 static int __init cpu_idle_nopoll_setup(char *__unused)
  34 {
  35         cpu_idle_force_poll = 0;
  36         return 1;
  37 }
  38 __setup("hlt", cpu_idle_nopoll_setup);
  39 #endif
  40
  41 static inline int cpu_idle_poll(void)
  42 {
  43         rcu_idle_enter();
  44         trace_cpu_idle_rcuidle(0, smp_processor_id());
  45         local_irq_enable();
  46         while (!need_resched())
  47                 cpu_relax();
  48         trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
  49         rcu_idle_exit();
  50         return 1;
  51 }
  52
  53 /* Weak implementations for optional arch specific functions */
  54 void __weak arch_cpu_idle_prepare(void) { }
  55 void __weak arch_cpu_idle_enter(void) { }
  56 void __weak arch_cpu_idle_exit(void) { }
  57 void __weak arch_cpu_idle_dead(void) { }
  58 void __weak arch_cpu_idle(void)
  59 {
  60         cpu_idle_force_poll = 1;
  61 }
  62
  63 /*
  64  * Generic idle loop implementation
  65  */
  66 static void cpu_idle_loop(void)
  67 {
  68         while (1) {
  69                 tick_nohz_idle_enter();
  70
  71                 while (!need_resched()) {
  72                         check_pgt_cache();
  73                         rmb();
  74
  75                         if (cpu_is_offline(smp_processor_id()))
  76                                 arch_cpu_idle_dead();
  77
  78                         local_irq_disable();
  79                         arch_cpu_idle_enter();
  80
  81                         /*
  82                          * In poll mode we reenable interrupts and spin.
  83                          *
  84                          * Also if we detected in the wakeup from idle
  85                          * path that the tick broadcast device expired
  86                          * for us, we don't want to go deep idle as we
  87                          * know that the IPI is going to arrive right
  88                          * away
  89                          */
  90                         if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
  91                                 cpu_idle_poll();
  92                         } else {
  93                                 current_clr_polling();
  94                                 if (!need_resched()) {
  95                                         stop_critical_timings();
  96                                         rcu_idle_enter();
  97                                         arch_cpu_idle();
  98                                         WARN_ON_ONCE(irqs_disabled());
  99                                         rcu_idle_exit();
 100                                         start_critical_timings();
 101                                 } else {
 102                                         local_irq_enable();
 103                                 }
 104                                 current_set_polling();
 105                         }
 106                         arch_cpu_idle_exit();
 107                 }
 108                 tick_nohz_idle_exit();
 109                 schedule_preempt_disabled();
 110         }
 111 }
 112
 113 void cpu_startup_entry(enum cpuhp_state state)
 114 {
 115         current_set_polling();
 116         arch_cpu_idle_prepare();
 117         cpu_idle_loop();
 118 }