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         /*
 151          * Enter the idle state previously returned by the governor decision.
 152          * This function will block until an interrupt occurs and will take
 153          * care of re-enabling the local interrupts
 154          */
 155         entered_state = cpuidle_enter(drv, dev, next_state);
 156
 157         if (broadcast)
 158                 clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);
 159
 160         /*
 161          * Give the governor an opportunity to reflect on the outcome
 162          */
 163         cpuidle_reflect(dev, entered_state);
 164
 165 exit_idle:
 166         __current_set_polling();
 167
 168         /*
 169          * It is up to the idle functions to reenable local interrupts
 170          */
 171         if (WARN_ON_ONCE(irqs_disabled()))
 172                 local_irq_enable();
 173
 174         rcu_idle_exit();
 175         start_critical_timings();
 176 }
 177
 178 /*
 179  * Generic idle loop implementation
 180  *
 181  * Called with polling cleared.
 182  */
 183 static void cpu_idle_loop(void)
 184 {
 185         while (1) {
 186                 /*
 187                  * If the arch has a polling bit, we maintain an invariant:
 188                  *
 189                  * Our polling bit is clear if we're not scheduled (i.e. if
 190                  * rq->curr != rq->idle).  This means that, if rq->idle has
 191                  * the polling bit set, then setting need_resched is
 192                  * guaranteed to cause the cpu to reschedule.
 193                  */
 194
 195                 __current_set_polling();
 196                 tick_nohz_idle_enter();
 197
 198                 while (!need_resched()) {
 199                         check_pgt_cache();
 200                         rmb();
 201
 202                         if (cpu_is_offline(smp_processor_id()))
 203                                 arch_cpu_idle_dead();
 204
 205                         local_irq_disable();
 206                         arch_cpu_idle_enter();
 207
 208                         /*
 209                          * In poll mode we reenable interrupts and spin.
 210                          *
 211                          * Also if we detected in the wakeup from idle
 212                          * path that the tick broadcast device expired
 213                          * for us, we don't want to go deep idle as we
 214                          * know that the IPI is going to arrive right
 215                          * away
 216                          */
 217                         if (cpu_idle_force_poll || tick_check_broadcast_expired())
 218                                 cpu_idle_poll();
 219                         else
 220                                 cpuidle_idle_call();
 221
 222                         arch_cpu_idle_exit();
 223                 }
 224
 225                 /*
 226                  * Since we fell out of the loop above, we know
 227                  * TIF_NEED_RESCHED must be set, propagate it into
 228                  * PREEMPT_NEED_RESCHED.
 229                  *
 230                  * This is required because for polling idle loops we will
 231                  * not have had an IPI to fold the state for us.
 232                  */
 233                 preempt_set_need_resched();
 234                 tick_nohz_idle_exit();
 235                 __current_clr_polling();
 236
 237                 /*
 238                  * We promise to call sched_ttwu_pending and reschedule
 239                  * if need_resched is set while polling is set.  That
 240                  * means that clearing polling needs to be visible
 241                  * before doing these things.
 242                  */
 243                 smp_mb__after_atomic();
 244
 245                 sched_ttwu_pending();
 246                 schedule_preempt_disabled();
 247         }
 248 }
 249
 250 void cpu_startup_entry(enum cpuhp_state state)
 251 {
 252         /*
 253          * This #ifdef needs to die, but it's too late in the cycle to
 254          * make this generic (arm and sh have never invoked the canary
 255          * init for the non boot cpus!). Will be fixed in 3.11
 256          */
 257 #ifdef CONFIG_X86
 258         /*
 259          * If we're the non-boot CPU, nothing set the stack canary up
 260          * for us. The boot CPU already has it initialized but no harm
 261          * in doing it again. This is a good place for updating it, as
 262          * we wont ever return from this function (so the invalid
 263          * canaries already on the stack wont ever trigger).
 264          */
 265         boot_init_stack_canary();
 266 #endif
 267         arch_cpu_idle_prepare();
 268         cpu_idle_loop();
 269 }