kernel/sched/idle.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Generic entry points for the idle threads and
   4  * implementation of the idle task scheduling class.
   5  *
   6  * (NOTE: these are not related to SCHED_IDLE batch scheduled
   7  *        tasks which are handled in sched/fair.c )
   8  */
   9 #include "sched.h"
  10
  11 #include <trace/events/power.h>
  12
  13 /* Linker adds these: start and end of __cpuidle functions */
  14 extern char __cpuidle_text_start[], __cpuidle_text_end[];
  15
  16 /**
  17  * sched_idle_set_state - Record idle state for the current CPU.
  18  * @idle_state: State to record.
  19  */
  20 void sched_idle_set_state(struct cpuidle_state *idle_state)
  21 {
  22         idle_set_state(this_rq(), idle_state);
  23 }
  24
  25 static int __read_mostly cpu_idle_force_poll;
  26
  27 void cpu_idle_poll_ctrl(bool enable)
  28 {
  29         if (enable) {
  30                 cpu_idle_force_poll++;
  31         } else {
  32                 cpu_idle_force_poll--;
  33                 WARN_ON_ONCE(cpu_idle_force_poll < 0);
  34         }
  35 }
  36
  37 #ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
  38 static int __init cpu_idle_poll_setup(char *__unused)
  39 {
  40         cpu_idle_force_poll = 1;
  41
  42         return 1;
  43 }
  44 __setup("nohlt", cpu_idle_poll_setup);
  45
  46 static int __init cpu_idle_nopoll_setup(char *__unused)
  47 {
  48         cpu_idle_force_poll = 0;
  49
  50         return 1;
  51 }
  52 __setup("hlt", cpu_idle_nopoll_setup);
  53 #endif
  54
  55 static noinline int __cpuidle 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
  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
  69         return 1;
  70 }
  71
  72 /* Weak implementations for optional arch specific functions */
  73 void __weak arch_cpu_idle_prepare(void) { }
  74 void __weak arch_cpu_idle_enter(void) { }
  75 void __weak arch_cpu_idle_exit(void) { }
  76 void __weak arch_cpu_idle_dead(void) { }
  77 void __weak arch_cpu_idle(void)
  78 {
  79         cpu_idle_force_poll = 1;
  80         local_irq_enable();
  81 }
  82
  83 /**
  84  * default_idle_call - Default CPU idle routine.
  85  *
  86  * To use when the cpuidle framework cannot be used.
  87  */
  88 void __cpuidle default_idle_call(void)
  89 {
  90         if (current_clr_polling_and_test()) {
  91                 local_irq_enable();
  92         } else {
  93                 stop_critical_timings();
  94                 arch_cpu_idle();
  95                 start_critical_timings();
  96         }
  97 }
  98
  99 static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 100                       int next_state)
 101 {
 102         /*
 103          * The idle task must be scheduled, it is pointless to go to idle, just
 104          * update no idle residency and return.
 105          */
 106         if (current_clr_polling_and_test()) {
 107                 dev->last_residency = 0;
 108                 local_irq_enable();
 109                 return -EBUSY;
 110         }
 111
 112         /*
 113          * Enter the idle state previously returned by the governor decision.
 114          * This function will block until an interrupt occurs and will take
 115          * care of re-enabling the local interrupts
 116          */
 117         return cpuidle_enter(drv, dev, next_state);
 118 }
 119
 120 /**
 121  * cpuidle_idle_call - the main idle function
 122  *
 123  * NOTE: no locks or semaphores should be used here
 124  *
 125  * On archs that support TIF_POLLING_NRFLAG, is called with polling
 126  * set, and it returns with polling set.  If it ever stops polling, it
 127  * must clear the polling bit.
 128  */
 129 static void cpuidle_idle_call(void)
 130 {
 131         struct cpuidle_device *dev = cpuidle_get_device();
 132         struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
 133         int next_state, entered_state;
 134
 135         /*
 136          * Check if the idle task must be rescheduled. If it is the
 137          * case, exit the function after re-enabling the local irq.
 138          */
 139         if (need_resched()) {
 140                 local_irq_enable();
 141                 return;
 142         }
 143
 144         /*
 145          * The RCU framework needs to be told that we are entering an idle
 146          * section, so no more rcu read side critical sections and one more
 147          * step to the grace period
 148          */
 149
 150         if (cpuidle_not_available(drv, dev)) {
 151                 tick_nohz_idle_stop_tick();
 152                 rcu_idle_enter();
 153
 154                 default_idle_call();
 155                 goto exit_idle;
 156         }
 157
 158         /*
 159          * Suspend-to-idle ("s2idle") 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
 168         if (idle_should_enter_s2idle() || dev->use_deepest_state) {
 169                 if (idle_should_enter_s2idle()) {
 170                         rcu_idle_enter();
 171
 172                         entered_state = cpuidle_enter_s2idle(drv, dev);
 173                         if (entered_state > 0) {
 174                                 local_irq_enable();
 175                                 goto exit_idle;
 176                         }
 177
 178                         rcu_idle_exit();
 179                 }
 180
 181                 tick_nohz_idle_stop_tick();
 182                 rcu_idle_enter();
 183
 184                 next_state = cpuidle_find_deepest_state(drv, dev);
 185                 call_cpuidle(drv, dev, next_state);
 186         } else {
 187                 bool stop_tick = true;
 188
 189                 /*
 190                  * Ask the cpuidle framework to choose a convenient idle state.
 191                  */
 192                 next_state = cpuidle_select(drv, dev, &stop_tick);
 193
 194                 if (stop_tick || tick_nohz_tick_stopped())
 195                         tick_nohz_idle_stop_tick();
 196                 else
 197                         tick_nohz_idle_retain_tick();
 198
 199                 rcu_idle_enter();
 200
 201                 entered_state = call_cpuidle(drv, dev, next_state);
 202                 /*
 203                  * Give the governor an opportunity to reflect on the outcome
 204                  */
 205                 cpuidle_reflect(dev, entered_state);
 206         }
 207
 208 exit_idle:
 209         __current_set_polling();
 210
 211         /*
 212          * It is up to the idle functions to reenable local interrupts
 213          */
 214         if (WARN_ON_ONCE(irqs_disabled()))
 215                 local_irq_enable();
 216
 217         rcu_idle_exit();
 218 }
 219
 220 /*
 221  * Generic idle loop implementation
 222  *
 223  * Called with polling cleared.
 224  */
 225 static void do_idle(void)
 226 {
 227         int cpu = smp_processor_id();
 228         /*
 229          * If the arch has a polling bit, we maintain an invariant:
 230          *
 231          * Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=
 232          * rq->idle). This means that, if rq->idle has the polling bit set,
 233          * then setting need_resched is guaranteed to cause the CPU to
 234          * reschedule.
 235          */
 236
 237         __current_set_polling();
 238         tick_nohz_idle_enter();
 239
 240         while (!need_resched()) {
 241                 check_pgt_cache();
 242                 rmb();
 243
 244                 if (cpu_is_offline(cpu)) {
 245                         tick_nohz_idle_stop_tick_protected();
 246                         cpuhp_report_idle_dead();
 247                         arch_cpu_idle_dead();
 248                 }
 249
 250                 local_irq_disable();
 251                 arch_cpu_idle_enter();
 252
 253                 /*
 254                  * In poll mode we reenable interrupts and spin. Also if we
 255                  * detected in the wakeup from idle path that the tick
 256                  * broadcast device expired for us, we don't want to go deep
 257                  * idle as we know that the IPI is going to arrive right away.
 258                  */
 259                 if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
 260                         tick_nohz_idle_restart_tick();
 261                         cpu_idle_poll();
 262                 } else {
 263                         cpuidle_idle_call();
 264                 }
 265                 arch_cpu_idle_exit();
 266         }
 267
 268         /*
 269          * Since we fell out of the loop above, we know TIF_NEED_RESCHED must
 270          * be set, propagate it into PREEMPT_NEED_RESCHED.
 271          *
 272          * This is required because for polling idle loops we will not have had
 273          * an IPI to fold the state for us.
 274          */
 275         preempt_set_need_resched();
 276         tick_nohz_idle_exit();
 277         __current_clr_polling();
 278
 279         /*
 280          * We promise to call sched_ttwu_pending() and reschedule if
 281          * need_resched() is set while polling is set. That means that clearing
 282          * polling needs to be visible before doing these things.
 283          */
 284         smp_mb__after_atomic();
 285
 286         sched_ttwu_pending();
 287         schedule_idle();
 288
 289         if (unlikely(klp_patch_pending(current)))
 290                 klp_update_patch_state(current);
 291 }
 292
 293 bool cpu_in_idle(unsigned long pc)
 294 {
 295         return pc >= (unsigned long)__cpuidle_text_start &&
 296                 pc < (unsigned long)__cpuidle_text_end;
 297 }
 298
 299 struct idle_timer {
 300         struct hrtimer timer;
 301         int done;
 302 };
 303
 304 static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
 305 {
 306         struct idle_timer *it = container_of(timer, struct idle_timer, timer);
 307
 308         WRITE_ONCE(it->done, 1);
 309         set_tsk_need_resched(current);
 310
 311         return HRTIMER_NORESTART;
 312 }
 313
 314 void play_idle(unsigned long duration_ms)
 315 {
 316         struct idle_timer it;
 317
 318         /*
 319          * Only FIFO tasks can disable the tick since they don't need the forced
 320          * preemption.
 321          */
 322         WARN_ON_ONCE(current->policy != SCHED_FIFO);
 323         WARN_ON_ONCE(current->nr_cpus_allowed != 1);
 324         WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
 325         WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
 326         WARN_ON_ONCE(!duration_ms);
 327
 328         rcu_sleep_check();
 329         preempt_disable();
 330         current->flags |= PF_IDLE;
 331         cpuidle_use_deepest_state(true);
 332
 333         it.done = 0;
 334         hrtimer_init_on_stack(&it.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 335         it.timer.function = idle_inject_timer_fn;
 336         hrtimer_start(&it.timer, ms_to_ktime(duration_ms), HRTIMER_MODE_REL_PINNED);
 337
 338         while (!READ_ONCE(it.done))
 339                 do_idle();
 340
 341         cpuidle_use_deepest_state(false);
 342         current->flags &= ~PF_IDLE;
 343
 344         preempt_fold_need_resched();
 345         preempt_enable();
 346 }
 347 EXPORT_SYMBOL_GPL(play_idle);
 348
 349 void cpu_startup_entry(enum cpuhp_state state)
 350 {
 351         arch_cpu_idle_prepare();
 352         cpuhp_online_idle(state);
 353         while (1)
 354                 do_idle();
 355 }
 356
 357 /*
 358  * idle-task scheduling class.
 359  */
 360
 361 #ifdef CONFIG_SMP
 362 static int
 363 select_task_rq_idle(struct task_struct *p, int cpu, int sd_flag, int flags)
 364 {
 365         return task_cpu(p); /* IDLE tasks as never migrated */
 366 }
 367 #endif
 368
 369 /*
 370  * Idle tasks are unconditionally rescheduled:
 371  */
 372 static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
 373 {
 374         resched_curr(rq);
 375 }
 376
 377 static struct task_struct *
 378 pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 379 {
 380         put_prev_task(rq, prev);
 381         update_idle_core(rq);
 382         schedstat_inc(rq->sched_goidle);
 383
 384         return rq->idle;
 385 }
 386
 387 /*
 388  * It is not legal to sleep in the idle task - print a warning
 389  * message if some code attempts to do it:
 390  */
 391 static void
 392 dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
 393 {
 394         raw_spin_unlock_irq(&rq->lock);
 395         printk(KERN_ERR "bad: scheduling from the idle thread!\n");
 396         dump_stack();
 397         raw_spin_lock_irq(&rq->lock);
 398 }
 399
 400 static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
 401 {
 402 }
 403
 404 /*
 405  * scheduler tick hitting a task of our scheduling class.
 406  *
 407  * NOTE: This function can be called remotely by the tick offload that
 408  * goes along full dynticks. Therefore no local assumption can be made
 409  * and everything must be accessed through the @rq and @curr passed in
 410  * parameters.
 411  */
 412 static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
 413 {
 414 }
 415
 416 static void set_curr_task_idle(struct rq *rq)
 417 {
 418 }
 419
 420 static void switched_to_idle(struct rq *rq, struct task_struct *p)
 421 {
 422         BUG();
 423 }
 424
 425 static void
 426 prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
 427 {
 428         BUG();
 429 }
 430
 431 static unsigned int get_rr_interval_idle(struct rq *rq, struct task_struct *task)
 432 {
 433         return 0;
 434 }
 435
 436 static void update_curr_idle(struct rq *rq)
 437 {
 438 }
 439
 440 /*
 441  * Simple, special scheduling class for the per-CPU idle tasks:
 442  */
 443 const struct sched_class idle_sched_class = {
 444         /* .next is NULL */
 445         /* no enqueue/yield_task for idle tasks */
 446
 447         /* dequeue is not valid, we print a debug message there: */
 448         .dequeue_task           = dequeue_task_idle,
 449
 450         .check_preempt_curr     = check_preempt_curr_idle,
 451
 452         .pick_next_task         = pick_next_task_idle,
 453         .put_prev_task          = put_prev_task_idle,
 454
 455 #ifdef CONFIG_SMP
 456         .select_task_rq         = select_task_rq_idle,
 457         .set_cpus_allowed       = set_cpus_allowed_common,
 458 #endif
 459
 460         .set_curr_task          = set_curr_task_idle,
 461         .task_tick              = task_tick_idle,
 462
 463         .get_rr_interval        = get_rr_interval_idle,
 464
 465         .prio_changed           = prio_changed_idle,
 466         .switched_to            = switched_to_idle,
 467         .update_curr            = update_curr_idle,
 468 };