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 #include <linux/suspend.h>
  11
  12 #include <asm/tlb.h>
  13
  14 #include <trace/events/power.h>
  15
  16 #include "sched.h"
  17
  18 /**
  19  * sched_idle_set_state - Record idle state for the current CPU.
  20  * @idle_state: State to record.
  21  */
  22 void sched_idle_set_state(struct cpuidle_state *idle_state)
  23 {
  24         idle_set_state(this_rq(), idle_state);
  25 }
  26
  27 static int __read_mostly cpu_idle_force_poll;
  28
  29 void cpu_idle_poll_ctrl(bool enable)
  30 {
  31         if (enable) {
  32                 cpu_idle_force_poll++;
  33         } else {
  34                 cpu_idle_force_poll--;
  35                 WARN_ON_ONCE(cpu_idle_force_poll < 0);
  36         }
  37 }
  38
  39 #ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
  40 static int __init cpu_idle_poll_setup(char *__unused)
  41 {
  42         cpu_idle_force_poll = 1;
  43         return 1;
  44 }
  45 __setup("nohlt", cpu_idle_poll_setup);
  46
  47 static int __init cpu_idle_nopoll_setup(char *__unused)
  48 {
  49         cpu_idle_force_poll = 0;
  50         return 1;
  51 }
  52 __setup("hlt", cpu_idle_nopoll_setup);
  53 #endif
  54
  55 static inline int cpu_idle_poll(void)
  56 {
  57         rcu_idle_enter();
  58         trace_cpu_idle_rcuidle(0, smp_processor_id());
  59         local_irq_enable();
  60         stop_critical_timings();
  61         while (!tif_need_resched() &&
  62                 (cpu_idle_force_poll || tick_check_broadcast_expired()))
  63                 cpu_relax();
  64         start_critical_timings();
  65         trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
  66         rcu_idle_exit();
  67         return 1;
  68 }
  69
  70 /* Weak implementations for optional arch specific functions */
  71 void __weak arch_cpu_idle_prepare(void) { }
  72 void __weak arch_cpu_idle_enter(void) { }
  73 void __weak arch_cpu_idle_exit(void) { }
  74 void __weak arch_cpu_idle_dead(void) { }
  75 void __weak arch_cpu_idle(void)
  76 {
  77         cpu_idle_force_poll = 1;
  78         local_irq_enable();
  79 }
  80
  81 /**
  82  * default_idle_call - Default CPU idle routine.
  83  *
  84  * To use when the cpuidle framework cannot be used.
  85  */
  86 void default_idle_call(void)
  87 {
  88         if (current_clr_polling_and_test()) {
  89                 local_irq_enable();
  90         } else {
  91                 stop_critical_timings();
  92                 arch_cpu_idle();
  93                 start_critical_timings();
  94         }
  95 }
  96
  97 static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
  98                       int next_state)
  99 {
 100         /* Fall back to the default arch idle method on errors. */
 101         if (next_state < 0) {
 102                 default_idle_call();
 103                 return next_state;
 104         }
 105
 106         /*
 107          * The idle task must be scheduled, it is pointless to go to idle, just
 108          * update no idle residency and return.
 109          */
 110         if (current_clr_polling_and_test()) {
 111                 dev->last_residency = 0;
 112                 local_irq_enable();
 113                 return -EBUSY;
 114         }
 115
 116         /*
 117          * Enter the idle state previously returned by the governor decision.
 118          * This function will block until an interrupt occurs and will take
 119          * care of re-enabling the local interrupts
 120          */
 121         return cpuidle_enter(drv, dev, next_state);
 122 }
 123
 124 /**
 125  * cpuidle_idle_call - the main idle function
 126  *
 127  * NOTE: no locks or semaphores should be used here
 128  *
 129  * On archs that support TIF_POLLING_NRFLAG, is called with polling
 130  * set, and it returns with polling set.  If it ever stops polling, it
 131  * must clear the polling bit.
 132  */
 133 static void cpuidle_idle_call(void)
 134 {
 135         struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
 136         struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
 137         int next_state, entered_state;
 138
 139         /*
 140          * Check if the idle task must be rescheduled. If it is the
 141          * case, exit the function after re-enabling the local irq.
 142          */
 143         if (need_resched()) {
 144                 local_irq_enable();
 145                 return;
 146         }
 147
 148         /*
 149          * Tell the RCU framework we are entering an idle section,
 150          * so no more rcu read side critical sections and one more
 151          * step to the grace period
 152          */
 153         rcu_idle_enter();
 154
 155         if (cpuidle_not_available(drv, dev)) {
 156                 default_idle_call();
 157                 goto exit_idle;
 158         }
 159
 160         /*
 161          * Suspend-to-idle ("freeze") is a system state in which all user space
 162          * has been frozen, all I/O devices have been suspended and the only
 163          * activity happens here and in iterrupts (if any).  In that case bypass
 164          * the cpuidle governor and go stratight for the deepest idle state
 165          * available.  Possibly also suspend the local tick and the entire
 166          * timekeeping to prevent timer interrupts from kicking us out of idle
 167          * until a proper wakeup interrupt happens.
 168          */
 169         if (idle_should_freeze()) {
 170                 entered_state = cpuidle_enter_freeze(drv, dev);
 171                 if (entered_state >= 0) {
 172                         local_irq_enable();
 173                         goto exit_idle;
 174                 }
 175
 176                 next_state = cpuidle_find_deepest_state(drv, dev);
 177                 call_cpuidle(drv, dev, next_state);
 178         } else {
 179                 /*
 180                  * Ask the cpuidle framework to choose a convenient idle state.
 181                  */
 182                 next_state = cpuidle_select(drv, dev);
 183                 entered_state = call_cpuidle(drv, dev, next_state);
 184                 /*
 185                  * Give the governor an opportunity to reflect on the outcome
 186                  */
 187                 cpuidle_reflect(dev, entered_state);
 188         }
 189
 190 exit_idle:
 191         __current_set_polling();
 192
 193         /*
 194          * It is up to the idle functions to reenable local interrupts
 195          */
 196         if (WARN_ON_ONCE(irqs_disabled()))
 197                 local_irq_enable();
 198
 199         rcu_idle_exit();
 200 }
 201
 202 DEFINE_PER_CPU(bool, cpu_dead_idle);
 203
 204 /*
 205  * Generic idle loop implementation
 206  *
 207  * Called with polling cleared.
 208  */
 209 static void cpu_idle_loop(void)
 210 {
 211         while (1) {
 212                 /*
 213                  * If the arch has a polling bit, we maintain an invariant:
 214                  *
 215                  * Our polling bit is clear if we're not scheduled (i.e. if
 216                  * rq->curr != rq->idle).  This means that, if rq->idle has
 217                  * the polling bit set, then setting need_resched is
 218                  * guaranteed to cause the cpu to reschedule.
 219                  */
 220
 221                 __current_set_polling();
 222                 tick_nohz_idle_enter();
 223
 224                 while (!need_resched()) {
 225                         check_pgt_cache();
 226                         rmb();
 227
 228                         if (cpu_is_offline(smp_processor_id())) {
 229                                 rcu_cpu_notify(NULL, CPU_DYING_IDLE,
 230                                                (void *)(long)smp_processor_id());
 231                                 smp_mb(); /* all activity before dead. */
 232                                 this_cpu_write(cpu_dead_idle, true);
 233                                 arch_cpu_idle_dead();
 234                         }
 235
 236                         local_irq_disable();
 237                         arch_cpu_idle_enter();
 238
 239                         /*
 240                          * In poll mode we reenable interrupts and spin.
 241                          *
 242                          * Also if we detected in the wakeup from idle
 243                          * path that the tick broadcast device expired
 244                          * for us, we don't want to go deep idle as we
 245                          * know that the IPI is going to arrive right
 246                          * away
 247                          */
 248                         if (cpu_idle_force_poll || tick_check_broadcast_expired())
 249                                 cpu_idle_poll();
 250                         else
 251                                 cpuidle_idle_call();
 252
 253                         arch_cpu_idle_exit();
 254                 }
 255
 256                 /*
 257                  * Since we fell out of the loop above, we know
 258                  * TIF_NEED_RESCHED must be set, propagate it into
 259                  * PREEMPT_NEED_RESCHED.
 260                  *
 261                  * This is required because for polling idle loops we will
 262                  * not have had an IPI to fold the state for us.
 263                  */
 264                 preempt_set_need_resched();
 265                 tick_nohz_idle_exit();
 266                 __current_clr_polling();
 267
 268                 /*
 269                  * We promise to call sched_ttwu_pending and reschedule
 270                  * if need_resched is set while polling is set.  That
 271                  * means that clearing polling needs to be visible
 272                  * before doing these things.
 273                  */
 274                 smp_mb__after_atomic();
 275
 276                 sched_ttwu_pending();
 277                 schedule_preempt_disabled();
 278         }
 279 }
 280
 281 void cpu_startup_entry(enum cpuhp_state state)
 282 {
 283         /*
 284          * This #ifdef needs to die, but it's too late in the cycle to
 285          * make this generic (arm and sh have never invoked the canary
 286          * init for the non boot cpus!). Will be fixed in 3.11
 287          */
 288 #ifdef CONFIG_X86
 289         /*
 290          * If we're the non-boot CPU, nothing set the stack canary up
 291          * for us. The boot CPU already has it initialized but no harm
 292          * in doing it again. This is a good place for updating it, as
 293          * we wont ever return from this function (so the invalid
 294          * canaries already on the stack wont ever trigger).
 295          */
 296         boot_init_stack_canary();
 297 #endif
 298         arch_cpu_idle_prepare();
 299         cpu_idle_loop();
 300 }