summaryrefslogtreecommitdiff
path: root/kernel/sched/idle.c
blob: b743bf38f08fbd4c56aa4b82f138278b29794f3c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Generic entry points for the idle threads and
 * implementation of the idle task scheduling class.
 *
 * (NOTE: these are not related to SCHED_IDLE batch scheduled
 *        tasks which are handled in sched/fair.c )
 */
#include "sched.h"

#include <trace/events/power.h>

/* Linker adds these: start and end of __cpuidle functions */
extern char __cpuidle_text_start[], __cpuidle_text_end[];

/**
 * sched_idle_set_state - Record idle state for the current CPU.
 * @idle_state: State to record.
 */
void sched_idle_set_state(struct cpuidle_state *idle_state)
{
	idle_set_state(this_rq(), idle_state);
}

static int __read_mostly cpu_idle_force_poll;

void cpu_idle_poll_ctrl(bool enable)
{
	if (enable) {
		cpu_idle_force_poll++;
	} else {
		cpu_idle_force_poll--;
		WARN_ON_ONCE(cpu_idle_force_poll < 0);
	}
}

#ifdef CONFIG_GENERIC_IDLE_POLL_SETUP
static int __init cpu_idle_poll_setup(char *__unused)
{
	cpu_idle_force_poll = 1;

	return 1;
}
__setup("nohlt", cpu_idle_poll_setup);

static int __init cpu_idle_nopoll_setup(char *__unused)
{
	cpu_idle_force_poll = 0;

	return 1;
}
__setup("hlt", cpu_idle_nopoll_setup);
#endif

static noinline int __cpuidle cpu_idle_poll(void)
{
	rcu_idle_enter();
	trace_cpu_idle_rcuidle(0, smp_processor_id());
	local_irq_enable();
	stop_critical_timings();

	while (!tif_need_resched() &&
		(cpu_idle_force_poll || tick_check_broadcast_expired()))
		cpu_relax();
	start_critical_timings();
	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
	rcu_idle_exit();

	return 1;
}

/* Weak implementations for optional arch specific functions */
void __weak arch_cpu_idle_prepare(void) { }
void __weak arch_cpu_idle_enter(void) { }
void __weak arch_cpu_idle_exit(void) { }
void __weak arch_cpu_idle_dead(void) { }
void __weak arch_cpu_idle(void)
{
	cpu_idle_force_poll = 1;
	local_irq_enable();
}

/**
 * default_idle_call - Default CPU idle routine.
 *
 * To use when the cpuidle framework cannot be used.
 */
void __cpuidle default_idle_call(void)
{
	if (current_clr_polling_and_test()) {
		local_irq_enable();
	} else {
		stop_critical_timings();
		arch_cpu_idle();
		start_critical_timings();
	}
}

static int call_cpuidle(struct cpuidle_driver *drv, struct cpuidle_device *dev,
		      int next_state)
{
	/*
	 * The idle task must be scheduled, it is pointless to go to idle, just
	 * update no idle residency and return.
	 */
	if (current_clr_polling_and_test()) {
		dev->last_residency_ns = 0;
		local_irq_enable();
		return -EBUSY;
	}

	/*
	 * Enter the idle state previously returned by the governor decision.
	 * This function will block until an interrupt occurs and will take
	 * care of re-enabling the local interrupts
	 */
	return cpuidle_enter(drv, dev, next_state);
}

/**
 * cpuidle_idle_call - the main idle function
 *
 * NOTE: no locks or semaphores should be used here
 *
 * On archs that support TIF_POLLING_NRFLAG, is called with polling
 * set, and it returns with polling set.  If it ever stops polling, it
 * must clear the polling bit.
 */
static void cpuidle_idle_call(void)
{
	struct cpuidle_device *dev = cpuidle_get_device();
	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
	int next_state, entered_state;

	/*
	 * Check if the idle task must be rescheduled. If it is the
	 * case, exit the function after re-enabling the local irq.
	 */
	if (need_resched()) {
		local_irq_enable();
		return;
	}

	/*
	 * The RCU framework needs to be told that we are entering an idle
	 * section, so no more rcu read side critical sections and one more
	 * step to the grace period
	 */

	if (cpuidle_not_available(drv, dev)) {
		tick_nohz_idle_stop_tick();
		rcu_idle_enter();

		default_idle_call();
		goto exit_idle;
	}

	/*
	 * Suspend-to-idle ("s2idle") is a system state in which all user space
	 * has been frozen, all I/O devices have been suspended and the only
	 * activity happens here and in interrupts (if any). In that case bypass
	 * the cpuidle governor and go stratight for the deepest idle state
	 * available.  Possibly also suspend the local tick and the entire
	 * timekeeping to prevent timer interrupts from kicking us out of idle
	 * until a proper wakeup interrupt happens.
	 */

	if (idle_should_enter_s2idle() || dev->forced_idle_latency_limit_ns) {
		u64 max_latency_ns;

		if (idle_should_enter_s2idle()) {
			rcu_idle_enter();

			entered_state = cpuidle_enter_s2idle(drv, dev);
			if (entered_state > 0) {
				local_irq_enable();
				goto exit_idle;
			}

			rcu_idle_exit();

			max_latency_ns = U64_MAX;
		} else {
			max_latency_ns = dev->forced_idle_latency_limit_ns;
		}

		tick_nohz_idle_stop_tick();
		rcu_idle_enter();

		next_state = cpuidle_find_deepest_state(drv, dev, max_latency_ns);
		call_cpuidle(drv, dev, next_state);
	} else {
		bool stop_tick = true;

		/*
		 * Ask the cpuidle framework to choose a convenient idle state.
		 */
		next_state = cpuidle_select(drv, dev, &stop_tick);

		if (stop_tick || tick_nohz_tick_stopped())
			tick_nohz_idle_stop_tick();
		else
			tick_nohz_idle_retain_tick();

		rcu_idle_enter();

		entered_state = call_cpuidle(drv, dev, next_state);
		/*
		 * Give the governor an opportunity to reflect on the outcome
		 */
		cpuidle_reflect(dev, entered_state);
	}

exit_idle:
	__current_set_polling();

	/*
	 * It is up to the idle functions to reenable local interrupts
	 */
	if (WARN_ON_ONCE(irqs_disabled()))
		local_irq_enable();

	rcu_idle_exit();
}

/*
 * Generic idle loop implementation
 *
 * Called with polling cleared.
 */
static void do_idle(void)
{
	int cpu = smp_processor_id();
	/*
	 * If the arch has a polling bit, we maintain an invariant:
	 *
	 * Our polling bit is clear if we're not scheduled (i.e. if rq->curr !=
	 * rq->idle). This means that, if rq->idle has the polling bit set,
	 * then setting need_resched is guaranteed to cause the CPU to
	 * reschedule.
	 */

	__current_set_polling();
	tick_nohz_idle_enter();

	while (!need_resched()) {
		rmb();

		local_irq_disable();

		if (cpu_is_offline(cpu)) {
			tick_nohz_idle_stop_tick();
			cpuhp_report_idle_dead();
			arch_cpu_idle_dead();
		}

		arch_cpu_idle_enter();

		/*
		 * In poll mode we reenable interrupts and spin. Also if we
		 * detected in the wakeup from idle path that the tick
		 * broadcast device expired for us, we don't want to go deep
		 * idle as we know that the IPI is going to arrive right away.
		 */
		if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
			tick_nohz_idle_restart_tick();
			cpu_idle_poll();
		} else {
			cpuidle_idle_call();
		}
		arch_cpu_idle_exit();
	}

	/*
	 * Since we fell out of the loop above, we know TIF_NEED_RESCHED must
	 * be set, propagate it into PREEMPT_NEED_RESCHED.
	 *
	 * This is required because for polling idle loops we will not have had
	 * an IPI to fold the state for us.
	 */
	preempt_set_need_resched();
	tick_nohz_idle_exit();
	__current_clr_polling();

	/*
	 * We promise to call sched_ttwu_pending() and reschedule if
	 * need_resched() is set while polling is set. That means that clearing
	 * polling needs to be visible before doing these things.
	 */
	smp_mb__after_atomic();

	sched_ttwu_pending();
	schedule_idle();

	if (unlikely(klp_patch_pending(current)))
		klp_update_patch_state(current);
}

bool cpu_in_idle(unsigned long pc)
{
	return pc >= (unsigned long)__cpuidle_text_start &&
		pc < (unsigned long)__cpuidle_text_end;
}

struct idle_timer {
	struct hrtimer timer;
	int done;
};

static enum hrtimer_restart idle_inject_timer_fn(struct hrtimer *timer)
{
	struct idle_timer *it = container_of(timer, struct idle_timer, timer);

	WRITE_ONCE(it->done, 1);
	set_tsk_need_resched(current);

	return HRTIMER_NORESTART;
}

void play_idle_precise(u64 duration_ns, u64 latency_ns)
{
	struct idle_timer it;

	/*
	 * Only FIFO tasks can disable the tick since they don't need the forced
	 * preemption.
	 */
	WARN_ON_ONCE(current->policy != SCHED_FIFO);
	WARN_ON_ONCE(current->nr_cpus_allowed != 1);
	WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
	WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
	WARN_ON_ONCE(!duration_ns);

	rcu_sleep_check();
	preempt_disable();
	current->flags |= PF_IDLE;
	cpuidle_use_deepest_state(latency_ns);

	it.done = 0;
	hrtimer_init_on_stack(&it.timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
	it.timer.function = idle_inject_timer_fn;
	hrtimer_start(&it.timer, ns_to_ktime(duration_ns),
		      HRTIMER_MODE_REL_PINNED);

	while (!READ_ONCE(it.done))
		do_idle();

	cpuidle_use_deepest_state(0);
	current->flags &= ~PF_IDLE;

	preempt_fold_need_resched();
	preempt_enable();
}
EXPORT_SYMBOL_GPL(play_idle_precise);

void cpu_startup_entry(enum cpuhp_state state)
{
	arch_cpu_idle_prepare();
	cpuhp_online_idle(state);
	while (1)
		do_idle();
}

/*
 * idle-task scheduling class.
 */

#ifdef CONFIG_SMP
static int
select_task_rq_idle(struct task_struct *p, int cpu, int sd_flag, int flags)
{
	return task_cpu(p); /* IDLE tasks as never migrated */
}

static int
balance_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
	return WARN_ON_ONCE(1);
}
#endif

/*
 * Idle tasks are unconditionally rescheduled:
 */
static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
{
	resched_curr(rq);
}

static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
{
}

static void set_next_task_idle(struct rq *rq, struct task_struct *next, bool first)
{
	update_idle_core(rq);
	schedstat_inc(rq->sched_goidle);
}

struct task_struct *pick_next_task_idle(struct rq *rq)
{
	struct task_struct *next = rq->idle;

	set_next_task_idle(rq, next, true);

	return next;
}

/*
 * It is not legal to sleep in the idle task - print a warning
 * message if some code attempts to do it:
 */
static void
dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
{
	raw_spin_unlock_irq(&rq->lock);
	printk(KERN_ERR "bad: scheduling from the idle thread!\n");
	dump_stack();
	raw_spin_lock_irq(&rq->lock);
}

/*
 * scheduler tick hitting a task of our scheduling class.
 *
 * NOTE: This function can be called remotely by the tick offload that
 * goes along full dynticks. Therefore no local assumption can be made
 * and everything must be accessed through the @rq and @curr passed in
 * parameters.
 */
static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
{
}

static void switched_to_idle(struct rq *rq, struct task_struct *p)
{
	BUG();
}

static void
prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
{
	BUG();
}

static unsigned int get_rr_interval_idle(struct rq *rq, struct task_struct *task)
{
	return 0;
}

static void update_curr_idle(struct rq *rq)
{
}

/*
 * Simple, special scheduling class for the per-CPU idle tasks:
 */
const struct sched_class idle_sched_class = {
	/* .next is NULL */
	/* no enqueue/yield_task for idle tasks */

	/* dequeue is not valid, we print a debug message there: */
	.dequeue_task		= dequeue_task_idle,

	.check_preempt_curr	= check_preempt_curr_idle,

	.pick_next_task		= pick_next_task_idle,
	.put_prev_task		= put_prev_task_idle,
	.set_next_task          = set_next_task_idle,

#ifdef CONFIG_SMP
	.balance		= balance_idle,
	.select_task_rq		= select_task_rq_idle,
	.set_cpus_allowed	= set_cpus_allowed_common,
#endif

	.task_tick		= task_tick_idle,

	.get_rr_interval	= get_rr_interval_idle,

	.prio_changed		= prio_changed_idle,
	.switched_to		= switched_to_idle,
	.update_curr		= update_curr_idle,
};