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Linux/kernel/sched/idle.c

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

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