xref: /openbmc/linux/kernel/time/tick-common.c (revision b34e08d5)
1 /*
2  * linux/kernel/time/tick-common.c
3  *
4  * This file contains the base functions to manage periodic tick
5  * related events.
6  *
7  * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
8  * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
9  * Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
10  *
11  * This code is licenced under the GPL version 2. For details see
12  * kernel-base/COPYING.
13  */
14 #include <linux/cpu.h>
15 #include <linux/err.h>
16 #include <linux/hrtimer.h>
17 #include <linux/interrupt.h>
18 #include <linux/percpu.h>
19 #include <linux/profile.h>
20 #include <linux/sched.h>
21 #include <linux/module.h>
22 
23 #include <asm/irq_regs.h>
24 
25 #include "tick-internal.h"
26 
27 /*
28  * Tick devices
29  */
30 DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
31 /*
32  * Tick next event: keeps track of the tick time
33  */
34 ktime_t tick_next_period;
35 ktime_t tick_period;
36 
37 /*
38  * tick_do_timer_cpu is a timer core internal variable which holds the CPU NR
39  * which is responsible for calling do_timer(), i.e. the timekeeping stuff. This
40  * variable has two functions:
41  *
42  * 1) Prevent a thundering herd issue of a gazillion of CPUs trying to grab the
43  *    timekeeping lock all at once. Only the CPU which is assigned to do the
44  *    update is handling it.
45  *
46  * 2) Hand off the duty in the NOHZ idle case by setting the value to
47  *    TICK_DO_TIMER_NONE, i.e. a non existing CPU. So the next cpu which looks
48  *    at it will take over and keep the time keeping alive.  The handover
49  *    procedure also covers cpu hotplug.
50  */
51 int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;
52 
53 /*
54  * Debugging: see timer_list.c
55  */
56 struct tick_device *tick_get_device(int cpu)
57 {
58 	return &per_cpu(tick_cpu_device, cpu);
59 }
60 
61 /**
62  * tick_is_oneshot_available - check for a oneshot capable event device
63  */
64 int tick_is_oneshot_available(void)
65 {
66 	struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
67 
68 	if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT))
69 		return 0;
70 	if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
71 		return 1;
72 	return tick_broadcast_oneshot_available();
73 }
74 
75 /*
76  * Periodic tick
77  */
78 static void tick_periodic(int cpu)
79 {
80 	if (tick_do_timer_cpu == cpu) {
81 		write_seqlock(&jiffies_lock);
82 
83 		/* Keep track of the next tick event */
84 		tick_next_period = ktime_add(tick_next_period, tick_period);
85 
86 		do_timer(1);
87 		write_sequnlock(&jiffies_lock);
88 		update_wall_time();
89 	}
90 
91 	update_process_times(user_mode(get_irq_regs()));
92 	profile_tick(CPU_PROFILING);
93 }
94 
95 /*
96  * Event handler for periodic ticks
97  */
98 void tick_handle_periodic(struct clock_event_device *dev)
99 {
100 	int cpu = smp_processor_id();
101 	ktime_t next = dev->next_event;
102 
103 	tick_periodic(cpu);
104 
105 	if (dev->mode != CLOCK_EVT_MODE_ONESHOT)
106 		return;
107 	for (;;) {
108 		/*
109 		 * Setup the next period for devices, which do not have
110 		 * periodic mode:
111 		 */
112 		next = ktime_add(next, tick_period);
113 
114 		if (!clockevents_program_event(dev, next, false))
115 			return;
116 		/*
117 		 * Have to be careful here. If we're in oneshot mode,
118 		 * before we call tick_periodic() in a loop, we need
119 		 * to be sure we're using a real hardware clocksource.
120 		 * Otherwise we could get trapped in an infinite
121 		 * loop, as the tick_periodic() increments jiffies,
122 		 * which then will increment time, possibly causing
123 		 * the loop to trigger again and again.
124 		 */
125 		if (timekeeping_valid_for_hres())
126 			tick_periodic(cpu);
127 	}
128 }
129 
130 /*
131  * Setup the device for a periodic tick
132  */
133 void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
134 {
135 	tick_set_periodic_handler(dev, broadcast);
136 
137 	/* Broadcast setup ? */
138 	if (!tick_device_is_functional(dev))
139 		return;
140 
141 	if ((dev->features & CLOCK_EVT_FEAT_PERIODIC) &&
142 	    !tick_broadcast_oneshot_active()) {
143 		clockevents_set_mode(dev, CLOCK_EVT_MODE_PERIODIC);
144 	} else {
145 		unsigned long seq;
146 		ktime_t next;
147 
148 		do {
149 			seq = read_seqbegin(&jiffies_lock);
150 			next = tick_next_period;
151 		} while (read_seqretry(&jiffies_lock, seq));
152 
153 		clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
154 
155 		for (;;) {
156 			if (!clockevents_program_event(dev, next, false))
157 				return;
158 			next = ktime_add(next, tick_period);
159 		}
160 	}
161 }
162 
163 /*
164  * Setup the tick device
165  */
166 static void tick_setup_device(struct tick_device *td,
167 			      struct clock_event_device *newdev, int cpu,
168 			      const struct cpumask *cpumask)
169 {
170 	ktime_t next_event;
171 	void (*handler)(struct clock_event_device *) = NULL;
172 
173 	/*
174 	 * First device setup ?
175 	 */
176 	if (!td->evtdev) {
177 		/*
178 		 * If no cpu took the do_timer update, assign it to
179 		 * this cpu:
180 		 */
181 		if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {
182 			if (!tick_nohz_full_cpu(cpu))
183 				tick_do_timer_cpu = cpu;
184 			else
185 				tick_do_timer_cpu = TICK_DO_TIMER_NONE;
186 			tick_next_period = ktime_get();
187 			tick_period = ktime_set(0, NSEC_PER_SEC / HZ);
188 		}
189 
190 		/*
191 		 * Startup in periodic mode first.
192 		 */
193 		td->mode = TICKDEV_MODE_PERIODIC;
194 	} else {
195 		handler = td->evtdev->event_handler;
196 		next_event = td->evtdev->next_event;
197 		td->evtdev->event_handler = clockevents_handle_noop;
198 	}
199 
200 	td->evtdev = newdev;
201 
202 	/*
203 	 * When the device is not per cpu, pin the interrupt to the
204 	 * current cpu:
205 	 */
206 	if (!cpumask_equal(newdev->cpumask, cpumask))
207 		irq_set_affinity(newdev->irq, cpumask);
208 
209 	/*
210 	 * When global broadcasting is active, check if the current
211 	 * device is registered as a placeholder for broadcast mode.
212 	 * This allows us to handle this x86 misfeature in a generic
213 	 * way. This function also returns !=0 when we keep the
214 	 * current active broadcast state for this CPU.
215 	 */
216 	if (tick_device_uses_broadcast(newdev, cpu))
217 		return;
218 
219 	if (td->mode == TICKDEV_MODE_PERIODIC)
220 		tick_setup_periodic(newdev, 0);
221 	else
222 		tick_setup_oneshot(newdev, handler, next_event);
223 }
224 
225 void tick_install_replacement(struct clock_event_device *newdev)
226 {
227 	struct tick_device *td = &__get_cpu_var(tick_cpu_device);
228 	int cpu = smp_processor_id();
229 
230 	clockevents_exchange_device(td->evtdev, newdev);
231 	tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
232 	if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
233 		tick_oneshot_notify();
234 }
235 
236 static bool tick_check_percpu(struct clock_event_device *curdev,
237 			      struct clock_event_device *newdev, int cpu)
238 {
239 	if (!cpumask_test_cpu(cpu, newdev->cpumask))
240 		return false;
241 	if (cpumask_equal(newdev->cpumask, cpumask_of(cpu)))
242 		return true;
243 	/* Check if irq affinity can be set */
244 	if (newdev->irq >= 0 && !irq_can_set_affinity(newdev->irq))
245 		return false;
246 	/* Prefer an existing cpu local device */
247 	if (curdev && cpumask_equal(curdev->cpumask, cpumask_of(cpu)))
248 		return false;
249 	return true;
250 }
251 
252 static bool tick_check_preferred(struct clock_event_device *curdev,
253 				 struct clock_event_device *newdev)
254 {
255 	/* Prefer oneshot capable device */
256 	if (!(newdev->features & CLOCK_EVT_FEAT_ONESHOT)) {
257 		if (curdev && (curdev->features & CLOCK_EVT_FEAT_ONESHOT))
258 			return false;
259 		if (tick_oneshot_mode_active())
260 			return false;
261 	}
262 
263 	/*
264 	 * Use the higher rated one, but prefer a CPU local device with a lower
265 	 * rating than a non-CPU local device
266 	 */
267 	return !curdev ||
268 		newdev->rating > curdev->rating ||
269 	       !cpumask_equal(curdev->cpumask, newdev->cpumask);
270 }
271 
272 /*
273  * Check whether the new device is a better fit than curdev. curdev
274  * can be NULL !
275  */
276 bool tick_check_replacement(struct clock_event_device *curdev,
277 			    struct clock_event_device *newdev)
278 {
279 	if (tick_check_percpu(curdev, newdev, smp_processor_id()))
280 		return false;
281 
282 	return tick_check_preferred(curdev, newdev);
283 }
284 
285 /*
286  * Check, if the new registered device should be used. Called with
287  * clockevents_lock held and interrupts disabled.
288  */
289 void tick_check_new_device(struct clock_event_device *newdev)
290 {
291 	struct clock_event_device *curdev;
292 	struct tick_device *td;
293 	int cpu;
294 
295 	cpu = smp_processor_id();
296 	if (!cpumask_test_cpu(cpu, newdev->cpumask))
297 		goto out_bc;
298 
299 	td = &per_cpu(tick_cpu_device, cpu);
300 	curdev = td->evtdev;
301 
302 	/* cpu local device ? */
303 	if (!tick_check_percpu(curdev, newdev, cpu))
304 		goto out_bc;
305 
306 	/* Preference decision */
307 	if (!tick_check_preferred(curdev, newdev))
308 		goto out_bc;
309 
310 	if (!try_module_get(newdev->owner))
311 		return;
312 
313 	/*
314 	 * Replace the eventually existing device by the new
315 	 * device. If the current device is the broadcast device, do
316 	 * not give it back to the clockevents layer !
317 	 */
318 	if (tick_is_broadcast_device(curdev)) {
319 		clockevents_shutdown(curdev);
320 		curdev = NULL;
321 	}
322 	clockevents_exchange_device(curdev, newdev);
323 	tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
324 	if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
325 		tick_oneshot_notify();
326 	return;
327 
328 out_bc:
329 	/*
330 	 * Can the new device be used as a broadcast device ?
331 	 */
332 	tick_install_broadcast_device(newdev);
333 }
334 
335 /*
336  * Transfer the do_timer job away from a dying cpu.
337  *
338  * Called with interrupts disabled.
339  */
340 void tick_handover_do_timer(int *cpup)
341 {
342 	if (*cpup == tick_do_timer_cpu) {
343 		int cpu = cpumask_first(cpu_online_mask);
344 
345 		tick_do_timer_cpu = (cpu < nr_cpu_ids) ? cpu :
346 			TICK_DO_TIMER_NONE;
347 	}
348 }
349 
350 /*
351  * Shutdown an event device on a given cpu:
352  *
353  * This is called on a life CPU, when a CPU is dead. So we cannot
354  * access the hardware device itself.
355  * We just set the mode and remove it from the lists.
356  */
357 void tick_shutdown(unsigned int *cpup)
358 {
359 	struct tick_device *td = &per_cpu(tick_cpu_device, *cpup);
360 	struct clock_event_device *dev = td->evtdev;
361 
362 	td->mode = TICKDEV_MODE_PERIODIC;
363 	if (dev) {
364 		/*
365 		 * Prevent that the clock events layer tries to call
366 		 * the set mode function!
367 		 */
368 		dev->mode = CLOCK_EVT_MODE_UNUSED;
369 		clockevents_exchange_device(dev, NULL);
370 		dev->event_handler = clockevents_handle_noop;
371 		td->evtdev = NULL;
372 	}
373 }
374 
375 void tick_suspend(void)
376 {
377 	struct tick_device *td = &__get_cpu_var(tick_cpu_device);
378 
379 	clockevents_shutdown(td->evtdev);
380 }
381 
382 void tick_resume(void)
383 {
384 	struct tick_device *td = &__get_cpu_var(tick_cpu_device);
385 	int broadcast = tick_resume_broadcast();
386 
387 	clockevents_set_mode(td->evtdev, CLOCK_EVT_MODE_RESUME);
388 
389 	if (!broadcast) {
390 		if (td->mode == TICKDEV_MODE_PERIODIC)
391 			tick_setup_periodic(td->evtdev, 0);
392 		else
393 			tick_resume_oneshot();
394 	}
395 }
396 
397 /**
398  * tick_init - initialize the tick control
399  */
400 void __init tick_init(void)
401 {
402 	tick_broadcast_init();
403 }
404