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/cpuhotplug.h>
   8 #include <linux/tick.h>
   9 #include <linux/mm.h>
  10 #include <linux/stackprotector.h>
  11 #include <linux/suspend.h>
  12
  13 #include <asm/tlb.h>
  14
  15 #include <trace/events/power.h>
  16
  17 #include "sched.h"
  18
  19 /* Linker adds these: start and end of __cpuidle functions */
  20 extern char __cpuidle_text_start[], __cpuidle_text_end[];
  21
  22 /**
  23  * sched_idle_set_state - Record idle state for the current CPU.
  24  * @idle_state: State to record.
  25  */
  26 void sched_idle_set_state(struct cpuidle_state *idle_state)
  27 {
  28         idle_set_state(this_rq(), idle_state);
  29 }
  30
  31 static int __read_mostly cpu_idle_force_poll;
  32
  33 void cpu_idle_poll_ctrl(bool enable)
  34 {
  35         if (enable) {
  36                 cpu_idle_force_poll++;
  37         } else {
  38                 cpu_idle_force_poll--;
  39                 WARN_ON_ONCE(cpu_idle_force_poll < 0);
  40         }
  41 }
  42
  43 #ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
  44 static int __init cpu_idle_poll_setup(char *__unused)
  45 {
  46         cpu_idle_force_poll = 1;
  47         return 1;
  48 }
  49 __setup("nohlt", cpu_idle_poll_setup);
  50
  51 static int __init cpu_idle_nopoll_setup(char *__unused)
  52 {
  53         cpu_idle_force_poll = 0;
  54         return 1;
  55 }
  56 __setup("hlt", cpu_idle_nopoll_setup);
  57 #endif
  58
  59 static noinline int __cpuidle cpu_idle_poll(void)
  60 {
  61         rcu_idle_enter();
  62         trace_cpu_idle_rcuidle(0, smp_processor_id());
  63         local_irq_enable();
  64         stop_critical_timings();
  65         while (!tif_need_resched() &&
  66                 (cpu_idle_force_poll || tick_check_broadcast_expired()))
  67                 cpu_relax();
  68         start_critical_timings();
  69         trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
  70         rcu_idle_exit();
  71         return 1;
  72 }
  73
  74 /* Weak implementations for optional arch specific functions */
  75 void __weak arch_cpu_idle_prepare(void) { }
  76 void __weak arch_cpu_idle_enter(void) { }
  77 void __weak arch_cpu_idle_exit(void) { }
  78 void __weak arch_cpu_idle_dead(void) { }
  79 void __weak arch_cpu_idle(void)
  80 {
  81         cpu_idle_force_poll = 1;
  82         local_irq_enable();
  83 }
  84
  85 /**
  86  * default_idle_call - Default CPU idle routine.
  87  *
  88  * To use when the cpuidle framework cannot be used.
  89  */
  90 void __cpuidle default_idle_call(void)
  91 {
  92         if (current_clr_polling_and_test()) {
  93                 local_irq_enable();
  94         } else {
  95                 stop_critical_timings();
  96                 arch_cpu_idle();
  97                 start_critical_timings();
  98         }
  99 }
 100
 101 static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 102                       int next_state)
 103 {
 104         /*
 105          * The idle task must be scheduled, it is pointless to go to idle, just
 106          * update no idle residency and return.
 107          */
 108         if (current_clr_polling_and_test()) {
 109                 dev->last_residency = 0;
 110                 local_irq_enable();
 111                 return -EBUSY;
 112         }
 113
 114         /*
 115          * Enter the idle state previously returned by the governor decision.
 116          * This function will block until an interrupt occurs and will take
 117          * care of re-enabling the local interrupts
 118          */
 119         return cpuidle_enter(drv, dev, next_state);
 120 }
 121
 122 /**
 123  * cpuidle_idle_call - the main idle function
 124  *
 125  * NOTE: no locks or semaphores should be used here
 126  *
 127  * On archs that support TIF_POLLING_NRFLAG, is called with polling
 128  * set, and it returns with polling set.  If it ever stops polling, it
 129  * must clear the polling bit.
 130  */
 131 static void cpuidle_idle_call(void)
 132 {
 133         struct cpuidle_device *dev = cpuidle_get_device();
 134         struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
 135         int next_state, entered_state;
 136
 137         /*
 138          * Check if the idle task must be rescheduled. If it is the
 139          * case, exit the function after re-enabling the local irq.
 140          */
 141         if (need_resched()) {
 142                 local_irq_enable();
 143                 return;
 144         }
 145
 146         /*
 147          * Tell the RCU framework we are entering an idle section,
 148          * so no more rcu read side critical sections and one more
 149          * step to the grace period
 150          */
 151         rcu_idle_enter();
 152
 153         if (cpuidle_not_available(drv, dev)) {
 154                 default_idle_call();
 155                 goto exit_idle;
 156         }
 157
 158         /*
 159          * Suspend-to-idle ("freeze") is a system state in which all user space
 160          * has been frozen, all I/O devices have been suspended and the only
 161          * activity happens here and in iterrupts (if any).  In that case bypass
 162          * the cpuidle governor and go stratight for the deepest idle state
 163          * available.  Possibly also suspend the local tick and the entire
 164          * timekeeping to prevent timer interrupts from kicking us out of idle
 165          * until a proper wakeup interrupt happens.
 166          */
 167         if (idle_should_freeze()) {
 168                 entered_state = cpuidle_enter_freeze(drv, dev);
 169                 if (entered_state > 0) {
 170                         local_irq_enable();
 171                         goto exit_idle;
 172                 }
 173
 174                 next_state = cpuidle_find_deepest_state(drv, dev);
 175                 call_cpuidle(drv, dev, next_state);
 176         } else {
 177                 /*
 178                  * Ask the cpuidle framework to choose a convenient idle state.
 179                  */
 180                 next_state = cpuidle_select(drv, dev);
 181                 entered_state = call_cpuidle(drv, dev, next_state);
 182                 /*
 183                  * Give the governor an opportunity to reflect on the outcome
 184                  */
 185                 cpuidle_reflect(dev, entered_state);
 186         }
 187
 188 exit_idle:
 189         __current_set_polling();
 190
 191         /*
 192          * It is up to the idle functions to reenable local interrupts
 193          */
 194         if (WARN_ON_ONCE(irqs_disabled()))
 195                 local_irq_enable();
 196
 197         rcu_idle_exit();
 198 }
 199
 200 /*
 201  * Generic idle loop implementation
 202  *
 203  * Called with polling cleared.
 204  */
 205 static void cpu_idle_loop(void)
 206 {
 207         int cpu = smp_processor_id();
 208
 209         while (1) {
 210                 /*
 211                  * If the arch has a polling bit, we maintain an invariant:
 212                  *
 213                  * Our polling bit is clear if we're not scheduled (i.e. if
 214                  * rq->curr != rq->idle).  This means that, if rq->idle has
 215                  * the polling bit set, then setting need_resched is
 216                  * guaranteed to cause the cpu to reschedule.
 217                  */
 218
 219                 __current_set_polling();
 220                 quiet_vmstat();
 221                 tick_nohz_idle_enter();
 222
 223                 while (!need_resched()) {
 224                         check_pgt_cache();
 225                         rmb();
 226
 227                         if (cpu_is_offline(cpu)) {
 228                                 cpuhp_report_idle_dead();
 229                                 arch_cpu_idle_dead();
 230                         }
 231
 232                         local_irq_disable();
 233                         arch_cpu_idle_enter();
 234
 235                         /*
 236                          * In poll mode we reenable interrupts and spin.
 237                          *
 238                          * Also if we detected in the wakeup from idle
 239                          * path that the tick broadcast device expired
 240                          * for us, we don't want to go deep idle as we
 241                          * know that the IPI is going to arrive right
 242                          * away
 243                          */
 244                         if (cpu_idle_force_poll || tick_check_broadcast_expired())
 245                                 cpu_idle_poll();
 246                         else
 247                                 cpuidle_idle_call();
 248
 249                         arch_cpu_idle_exit();
 250                 }
 251
 252                 /*
 253                  * Since we fell out of the loop above, we know
 254                  * TIF_NEED_RESCHED must be set, propagate it into
 255                  * PREEMPT_NEED_RESCHED.
 256                  *
 257                  * This is required because for polling idle loops we will
 258                  * not have had an IPI to fold the state for us.
 259                  */
 260                 preempt_set_need_resched();
 261                 tick_nohz_idle_exit();
 262                 __current_clr_polling();
 263
 264                 /*
 265                  * We promise to call sched_ttwu_pending and reschedule
 266                  * if need_resched is set while polling is set.  That
 267                  * means that clearing polling needs to be visible
 268                  * before doing these things.
 269                  */
 270                 smp_mb__after_atomic();
 271
 272                 sched_ttwu_pending();
 273                 schedule_preempt_disabled();
 274         }
 275 }
 276
 277 bool cpu_in_idle(unsigned long pc)
 278 {
 279         return pc >= (unsigned long)__cpuidle_text_start &&
 280                 pc < (unsigned long)__cpuidle_text_end;
 281 }
 282
 283 void cpu_startup_entry(enum cpuhp_state state)
 284 {
 285         /*
 286          * This #ifdef needs to die, but it's too late in the cycle to
 287          * make this generic (arm and sh have never invoked the canary
 288          * init for the non boot cpus!). Will be fixed in 3.11
 289          */
 290 #ifdef CONFIG_X86
 291         /*
 292          * If we're the non-boot CPU, nothing set the stack canary up
 293          * for us. The boot CPU already has it initialized but no harm
 294          * in doing it again. This is a good place for updating it, as
 295          * we wont ever return from this function (so the invalid
 296          * canaries already on the stack wont ever trigger).
 297          */
 298         boot_init_stack_canary();
 299 #endif
 300         arch_cpu_idle_prepare();
 301         cpuhp_online_idle(state);
 302         cpu_idle_loop();
 303 }