summaryrefslogtreecommitdiffstats
path: root/kernel/sched/idle.c
blob: c47fce75e66648b25e71da3d3ecdca8ec4448227 (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
/*
 * Generic entry point for the idle threads
 */
#include <linux/sched.h>
#include <linux/cpu.h>
#include <linux/cpuidle.h>
#include <linux/tick.h>
#include <linux/mm.h>
#include <linux/stackprotector.h>

#include <asm/tlb.h>

#include <trace/events/power.h>

#include "sched.h"

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 inline int cpu_idle_poll(void)
{
	rcu_idle_enter();
	trace_cpu_idle_rcuidle(0, smp_processor_id());
	local_irq_enable();
	while (!tif_need_resched())
		cpu_relax();
	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();
}

/**
 * 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 = __this_cpu_read(cpuidle_devices);
	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
	int next_state, entered_state;
	unsigned int broadcast;

	/*
	 * 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;
	}

	/*
	 * During the idle period, stop measuring the disabled irqs
	 * critical sections latencies
	 */
	stop_critical_timings();

	/*
	 * Tell the RCU framework we are entering an idle section,
	 * so no more rcu read side critical sections and one more
	 * step to the grace period
	 */
	rcu_idle_enter();

	/*
	 * Ask the cpuidle framework to choose a convenient idle state.
	 * Fall back to the default arch idle method on errors.
	 */
	next_state = cpuidle_select(drv, dev);
	if (next_state < 0) {
use_default:
		/*
		 * We can't use the cpuidle framework, let's use the default
		 * idle routine.
		 */
		if (current_clr_polling_and_test())
			local_irq_enable();
		else
			arch_cpu_idle();

		goto exit_idle;
	}


	/*
	 * The idle task must be scheduled, it is pointless to
	 * go to idle, just update no idle residency and get
	 * out of this function
	 */
	if (current_clr_polling_and_test()) {
		dev->last_residency = 0;
		entered_state = next_state;
		local_irq_enable();
		goto exit_idle;
	}

	broadcast = drv->states[next_state].flags & CPUIDLE_FLAG_TIMER_STOP;

	/*
	 * Tell the time framework to switch to a broadcast timer
	 * because our local timer will be shutdown. If a local timer
	 * is used from another cpu as a broadcast timer, this call may
	 * fail if it is not available
	 */
	if (broadcast &&
	    clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &dev->cpu))
		goto use_default;

	/* Take note of the planned idle state. */
	idle_set_state(this_rq(), &drv->states[next_state]);

	/*
	 * 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
	 */
	entered_state = cpuidle_enter(drv, dev, next_state);

	/* The cpu is no longer idle or about to enter idle. */
	idle_set_state(this_rq(), NULL);

	if (broadcast)
		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &dev->cpu);

	/*
	 * 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();
	start_critical_timings();
}

/*
 * Generic idle loop implementation
 *
 * Called with polling cleared.
 */
static void cpu_idle_loop(void)
{
	while (1) {
		/*
		 * 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()) {
			check_pgt_cache();
			rmb();

			if (cpu_is_offline(smp_processor_id()))
				arch_cpu_idle_dead();

			local_irq_disable();
			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())
				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_preempt_disabled();
	}
}

void cpu_startup_entry(enum cpuhp_state state)
{
	/*
	 * This #ifdef needs to die, but it's too late in the cycle to
	 * make this generic (arm and sh have never invoked the canary
	 * init for the non boot cpus!). Will be fixed in 3.11
	 */
#ifdef CONFIG_X86
	/*
	 * If we're the non-boot CPU, nothing set the stack canary up
	 * for us. The boot CPU already has it initialized but no harm
	 * in doing it again. This is a good place for updating it, as
	 * we wont ever return from this function (so the invalid
	 * canaries already on the stack wont ever trigger).
	 */
	boot_init_stack_canary();
#endif
	arch_cpu_idle_prepare();
	cpu_idle_loop();
}