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 | |
10 | /* Linker adds these: start and end of __cpuidle functions */ |
11 | extern char __cpuidle_text_start[], __cpuidle_text_end[]; |
12 | |
13 | /** |
14 | * sched_idle_set_state - Record idle state for the current CPU. |
15 | * @idle_state: State to record. |
16 | */ |
17 | void sched_idle_set_state(struct cpuidle_state *idle_state) |
18 | { |
19 | idle_set_state(this_rq(), idle_state); |
20 | } |
21 | |
22 | static int __read_mostly cpu_idle_force_poll; |
23 | |
24 | void cpu_idle_poll_ctrl(bool enable) |
25 | { |
26 | if (enable) { |
27 | cpu_idle_force_poll++; |
28 | } else { |
29 | cpu_idle_force_poll--; |
30 | WARN_ON_ONCE(cpu_idle_force_poll < 0); |
31 | } |
32 | } |
33 | |
34 | #ifdef CONFIG_GENERIC_IDLE_POLL_SETUP |
35 | static int __init cpu_idle_poll_setup(char *__unused) |
36 | { |
37 | cpu_idle_force_poll = 1; |
38 | |
39 | return 1; |
40 | } |
41 | __setup("nohlt" , cpu_idle_poll_setup); |
42 | |
43 | static int __init cpu_idle_nopoll_setup(char *__unused) |
44 | { |
45 | cpu_idle_force_poll = 0; |
46 | |
47 | return 1; |
48 | } |
49 | __setup("hlt" , cpu_idle_nopoll_setup); |
50 | #endif |
51 | |
52 | static noinline int __cpuidle cpu_idle_poll(void) |
53 | { |
54 | instrumentation_begin(); |
55 | trace_cpu_idle(state: 0, smp_processor_id()); |
56 | stop_critical_timings(); |
57 | ct_cpuidle_enter(); |
58 | |
59 | raw_local_irq_enable(); |
60 | while (!tif_need_resched() && |
61 | (cpu_idle_force_poll || tick_check_broadcast_expired())) |
62 | cpu_relax(); |
63 | raw_local_irq_disable(); |
64 | |
65 | ct_cpuidle_exit(); |
66 | start_critical_timings(); |
67 | trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id()); |
68 | local_irq_enable(); |
69 | instrumentation_end(); |
70 | |
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 __noreturn arch_cpu_idle_dead(void) { while (1); } |
79 | void __weak arch_cpu_idle(void) |
80 | { |
81 | cpu_idle_force_poll = 1; |
82 | } |
83 | |
84 | /** |
85 | * default_idle_call - Default CPU idle routine. |
86 | * |
87 | * To use when the cpuidle framework cannot be used. |
88 | */ |
89 | void __cpuidle default_idle_call(void) |
90 | { |
91 | instrumentation_begin(); |
92 | if (!current_clr_polling_and_test()) { |
93 | trace_cpu_idle(state: 1, smp_processor_id()); |
94 | stop_critical_timings(); |
95 | |
96 | ct_cpuidle_enter(); |
97 | arch_cpu_idle(); |
98 | ct_cpuidle_exit(); |
99 | |
100 | start_critical_timings(); |
101 | trace_cpu_idle(PWR_EVENT_EXIT, smp_processor_id()); |
102 | } |
103 | local_irq_enable(); |
104 | instrumentation_end(); |
105 | } |
106 | |
107 | static int call_cpuidle_s2idle(struct cpuidle_driver *drv, |
108 | struct cpuidle_device *dev) |
109 | { |
110 | if (current_clr_polling_and_test()) |
111 | return -EBUSY; |
112 | |
113 | return cpuidle_enter_s2idle(drv, dev); |
114 | } |
115 | |
116 | static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev, |
117 | int next_state) |
118 | { |
119 | /* |
120 | * The idle task must be scheduled, it is pointless to go to idle, just |
121 | * update no idle residency and return. |
122 | */ |
123 | if (current_clr_polling_and_test()) { |
124 | dev->last_residency_ns = 0; |
125 | local_irq_enable(); |
126 | return -EBUSY; |
127 | } |
128 | |
129 | /* |
130 | * Enter the idle state previously returned by the governor decision. |
131 | * This function will block until an interrupt occurs and will take |
132 | * care of re-enabling the local interrupts |
133 | */ |
134 | return cpuidle_enter(drv, dev, index: next_state); |
135 | } |
136 | |
137 | /** |
138 | * cpuidle_idle_call - the main idle function |
139 | * |
140 | * NOTE: no locks or semaphores should be used here |
141 | * |
142 | * On architectures that support TIF_POLLING_NRFLAG, is called with polling |
143 | * set, and it returns with polling set. If it ever stops polling, it |
144 | * must clear the polling bit. |
145 | */ |
146 | static void cpuidle_idle_call(void) |
147 | { |
148 | struct cpuidle_device *dev = cpuidle_get_device(); |
149 | struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev); |
150 | int next_state, entered_state; |
151 | |
152 | /* |
153 | * Check if the idle task must be rescheduled. If it is the |
154 | * case, exit the function after re-enabling the local irq. |
155 | */ |
156 | if (need_resched()) { |
157 | local_irq_enable(); |
158 | return; |
159 | } |
160 | |
161 | /* |
162 | * The RCU framework needs to be told that we are entering an idle |
163 | * section, so no more rcu read side critical sections and one more |
164 | * step to the grace period |
165 | */ |
166 | |
167 | if (cpuidle_not_available(drv, dev)) { |
168 | tick_nohz_idle_stop_tick(); |
169 | |
170 | default_idle_call(); |
171 | goto exit_idle; |
172 | } |
173 | |
174 | /* |
175 | * Suspend-to-idle ("s2idle") is a system state in which all user space |
176 | * has been frozen, all I/O devices have been suspended and the only |
177 | * activity happens here and in interrupts (if any). In that case bypass |
178 | * the cpuidle governor and go straight for the deepest idle state |
179 | * available. Possibly also suspend the local tick and the entire |
180 | * timekeeping to prevent timer interrupts from kicking us out of idle |
181 | * until a proper wakeup interrupt happens. |
182 | */ |
183 | |
184 | if (idle_should_enter_s2idle() || dev->forced_idle_latency_limit_ns) { |
185 | u64 max_latency_ns; |
186 | |
187 | if (idle_should_enter_s2idle()) { |
188 | |
189 | entered_state = call_cpuidle_s2idle(drv, dev); |
190 | if (entered_state > 0) |
191 | goto exit_idle; |
192 | |
193 | max_latency_ns = U64_MAX; |
194 | } else { |
195 | max_latency_ns = dev->forced_idle_latency_limit_ns; |
196 | } |
197 | |
198 | tick_nohz_idle_stop_tick(); |
199 | |
200 | next_state = cpuidle_find_deepest_state(drv, dev, latency_limit_ns: max_latency_ns); |
201 | call_cpuidle(drv, dev, next_state); |
202 | } else { |
203 | bool stop_tick = true; |
204 | |
205 | /* |
206 | * Ask the cpuidle framework to choose a convenient idle state. |
207 | */ |
208 | next_state = cpuidle_select(drv, dev, stop_tick: &stop_tick); |
209 | |
210 | if (stop_tick || tick_nohz_tick_stopped()) |
211 | tick_nohz_idle_stop_tick(); |
212 | else |
213 | tick_nohz_idle_retain_tick(); |
214 | |
215 | entered_state = call_cpuidle(drv, dev, next_state); |
216 | /* |
217 | * Give the governor an opportunity to reflect on the outcome |
218 | */ |
219 | cpuidle_reflect(dev, index: entered_state); |
220 | } |
221 | |
222 | exit_idle: |
223 | __current_set_polling(); |
224 | |
225 | /* |
226 | * It is up to the idle functions to reenable local interrupts |
227 | */ |
228 | if (WARN_ON_ONCE(irqs_disabled())) |
229 | local_irq_enable(); |
230 | } |
231 | |
232 | /* |
233 | * Generic idle loop implementation |
234 | * |
235 | * Called with polling cleared. |
236 | */ |
237 | static void do_idle(void) |
238 | { |
239 | int cpu = smp_processor_id(); |
240 | |
241 | /* |
242 | * Check if we need to update blocked load |
243 | */ |
244 | nohz_run_idle_balance(cpu); |
245 | |
246 | /* |
247 | * If the arch has a polling bit, we maintain an invariant: |
248 | * |
249 | * Our polling bit is clear if we're not scheduled (i.e. if rq->curr != |
250 | * rq->idle). This means that, if rq->idle has the polling bit set, |
251 | * then setting need_resched is guaranteed to cause the CPU to |
252 | * reschedule. |
253 | */ |
254 | |
255 | __current_set_polling(); |
256 | tick_nohz_idle_enter(); |
257 | |
258 | while (!need_resched()) { |
259 | rmb(); |
260 | |
261 | local_irq_disable(); |
262 | |
263 | if (cpu_is_offline(cpu)) { |
264 | tick_nohz_idle_stop_tick(); |
265 | cpuhp_report_idle_dead(); |
266 | arch_cpu_idle_dead(); |
267 | } |
268 | |
269 | arch_cpu_idle_enter(); |
270 | rcu_nocb_flush_deferred_wakeup(); |
271 | |
272 | /* |
273 | * In poll mode we reenable interrupts and spin. Also if we |
274 | * detected in the wakeup from idle path that the tick |
275 | * broadcast device expired for us, we don't want to go deep |
276 | * idle as we know that the IPI is going to arrive right away. |
277 | */ |
278 | if (cpu_idle_force_poll || tick_check_broadcast_expired()) { |
279 | tick_nohz_idle_restart_tick(); |
280 | cpu_idle_poll(); |
281 | } else { |
282 | cpuidle_idle_call(); |
283 | } |
284 | arch_cpu_idle_exit(); |
285 | } |
286 | |
287 | /* |
288 | * Since we fell out of the loop above, we know TIF_NEED_RESCHED must |
289 | * be set, propagate it into PREEMPT_NEED_RESCHED. |
290 | * |
291 | * This is required because for polling idle loops we will not have had |
292 | * an IPI to fold the state for us. |
293 | */ |
294 | preempt_set_need_resched(); |
295 | tick_nohz_idle_exit(); |
296 | __current_clr_polling(); |
297 | |
298 | /* |
299 | * We promise to call sched_ttwu_pending() and reschedule if |
300 | * need_resched() is set while polling is set. That means that clearing |
301 | * polling needs to be visible before doing these things. |
302 | */ |
303 | smp_mb__after_atomic(); |
304 | |
305 | /* |
306 | * RCU relies on this call to be done outside of an RCU read-side |
307 | * critical section. |
308 | */ |
309 | flush_smp_call_function_queue(); |
310 | schedule_idle(); |
311 | |
312 | if (unlikely(klp_patch_pending(current))) |
313 | klp_update_patch_state(current); |
314 | } |
315 | |
316 | bool cpu_in_idle(unsigned long pc) |
317 | { |
318 | return pc >= (unsigned long)__cpuidle_text_start && |
319 | pc < (unsigned long)__cpuidle_text_end; |
320 | } |
321 | |
322 | struct idle_timer { |
323 | struct hrtimer timer; |
324 | int done; |
325 | }; |
326 | |
327 | static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer) |
328 | { |
329 | struct idle_timer *it = container_of(timer, struct idle_timer, timer); |
330 | |
331 | WRITE_ONCE(it->done, 1); |
332 | set_tsk_need_resched(current); |
333 | |
334 | return HRTIMER_NORESTART; |
335 | } |
336 | |
337 | void play_idle_precise(u64 duration_ns, u64 latency_ns) |
338 | { |
339 | struct idle_timer it; |
340 | |
341 | /* |
342 | * Only FIFO tasks can disable the tick since they don't need the forced |
343 | * preemption. |
344 | */ |
345 | WARN_ON_ONCE(current->policy != SCHED_FIFO); |
346 | WARN_ON_ONCE(current->nr_cpus_allowed != 1); |
347 | WARN_ON_ONCE(!(current->flags & PF_KTHREAD)); |
348 | WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY)); |
349 | WARN_ON_ONCE(!duration_ns); |
350 | WARN_ON_ONCE(current->mm); |
351 | |
352 | rcu_sleep_check(); |
353 | preempt_disable(); |
354 | current->flags |= PF_IDLE; |
355 | cpuidle_use_deepest_state(latency_limit_ns: latency_ns); |
356 | |
357 | it.done = 0; |
358 | hrtimer_init_on_stack(timer: &it.timer, CLOCK_MONOTONIC, mode: HRTIMER_MODE_REL_HARD); |
359 | it.timer.function = idle_inject_timer_fn; |
360 | hrtimer_start(timer: &it.timer, tim: ns_to_ktime(ns: duration_ns), |
361 | mode: HRTIMER_MODE_REL_PINNED_HARD); |
362 | |
363 | while (!READ_ONCE(it.done)) |
364 | do_idle(); |
365 | |
366 | cpuidle_use_deepest_state(latency_limit_ns: 0); |
367 | current->flags &= ~PF_IDLE; |
368 | |
369 | preempt_fold_need_resched(); |
370 | preempt_enable(); |
371 | } |
372 | EXPORT_SYMBOL_GPL(play_idle_precise); |
373 | |
374 | void cpu_startup_entry(enum cpuhp_state state) |
375 | { |
376 | current->flags |= PF_IDLE; |
377 | arch_cpu_idle_prepare(); |
378 | cpuhp_online_idle(state); |
379 | while (1) |
380 | do_idle(); |
381 | } |
382 | |
383 | /* |
384 | * idle-task scheduling class. |
385 | */ |
386 | |
387 | #ifdef CONFIG_SMP |
388 | static int |
389 | select_task_rq_idle(struct task_struct *p, int cpu, int flags) |
390 | { |
391 | return task_cpu(p); /* IDLE tasks as never migrated */ |
392 | } |
393 | |
394 | static int |
395 | balance_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) |
396 | { |
397 | return WARN_ON_ONCE(1); |
398 | } |
399 | #endif |
400 | |
401 | /* |
402 | * Idle tasks are unconditionally rescheduled: |
403 | */ |
404 | static void wakeup_preempt_idle(struct rq *rq, struct task_struct *p, int flags) |
405 | { |
406 | resched_curr(rq); |
407 | } |
408 | |
409 | static void put_prev_task_idle(struct rq *rq, struct task_struct *prev) |
410 | { |
411 | } |
412 | |
413 | static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first) |
414 | { |
415 | update_idle_core(rq); |
416 | schedstat_inc(rq->sched_goidle); |
417 | } |
418 | |
419 | #ifdef CONFIG_SMP |
420 | static struct task_struct *pick_task_idle(struct rq *rq) |
421 | { |
422 | return rq->idle; |
423 | } |
424 | #endif |
425 | |
426 | struct task_struct *pick_next_task_idle(struct rq *rq) |
427 | { |
428 | struct task_struct *next = rq->idle; |
429 | |
430 | set_next_task_idle(rq, next, first: true); |
431 | |
432 | return next; |
433 | } |
434 | |
435 | /* |
436 | * It is not legal to sleep in the idle task - print a warning |
437 | * message if some code attempts to do it: |
438 | */ |
439 | static void |
440 | dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags) |
441 | { |
442 | raw_spin_rq_unlock_irq(rq); |
443 | printk(KERN_ERR "bad: scheduling from the idle thread!\n" ); |
444 | dump_stack(); |
445 | raw_spin_rq_lock_irq(rq); |
446 | } |
447 | |
448 | /* |
449 | * scheduler tick hitting a task of our scheduling class. |
450 | * |
451 | * NOTE: This function can be called remotely by the tick offload that |
452 | * goes along full dynticks. Therefore no local assumption can be made |
453 | * and everything must be accessed through the @rq and @curr passed in |
454 | * parameters. |
455 | */ |
456 | static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued) |
457 | { |
458 | } |
459 | |
460 | static void switched_to_idle(struct rq *rq, struct task_struct *p) |
461 | { |
462 | BUG(); |
463 | } |
464 | |
465 | static void |
466 | prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio) |
467 | { |
468 | BUG(); |
469 | } |
470 | |
471 | static void update_curr_idle(struct rq *rq) |
472 | { |
473 | } |
474 | |
475 | /* |
476 | * Simple, special scheduling class for the per-CPU idle tasks: |
477 | */ |
478 | DEFINE_SCHED_CLASS(idle) = { |
479 | |
480 | /* no enqueue/yield_task for idle tasks */ |
481 | |
482 | /* dequeue is not valid, we print a debug message there: */ |
483 | .dequeue_task = dequeue_task_idle, |
484 | |
485 | .wakeup_preempt = wakeup_preempt_idle, |
486 | |
487 | .pick_next_task = pick_next_task_idle, |
488 | .put_prev_task = put_prev_task_idle, |
489 | .set_next_task = set_next_task_idle, |
490 | |
491 | #ifdef CONFIG_SMP |
492 | .balance = balance_idle, |
493 | .pick_task = pick_task_idle, |
494 | .select_task_rq = select_task_rq_idle, |
495 | .set_cpus_allowed = set_cpus_allowed_common, |
496 | #endif |
497 | |
498 | .task_tick = task_tick_idle, |
499 | |
500 | .prio_changed = prio_changed_idle, |
501 | .switched_to = switched_to_idle, |
502 | .update_curr = update_curr_idle, |
503 | }; |
504 | |