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