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Thomas Gleixner79bf2bb2007-02-16 01:28:03 -08001/*
2 * linux/kernel/time/tick-sched.c
3 *
4 * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de>
5 * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
6 * Copyright(C) 2006-2007 Timesys Corp., Thomas Gleixner
7 *
8 * No idle tick implementation for low and high resolution timers
9 *
10 * Started by: Thomas Gleixner and Ingo Molnar
11 *
12 * For licencing details see 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/kernel_stat.h>
19#include <linux/percpu.h>
20#include <linux/profile.h>
21#include <linux/sched.h>
22#include <linux/tick.h>
23
David S. Miller9e203bc2007-02-24 22:10:13 -080024#include <asm/irq_regs.h>
25
Thomas Gleixner79bf2bb2007-02-16 01:28:03 -080026#include "tick-internal.h"
27
28/*
29 * Per cpu nohz control structure
30 */
31static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
32
33/*
34 * The time, when the last jiffy update happened. Protected by xtime_lock.
35 */
36static ktime_t last_jiffies_update;
37
Ingo Molnar289f4802007-02-16 01:28:15 -080038struct tick_sched *tick_get_tick_sched(int cpu)
39{
40 return &per_cpu(tick_cpu_sched, cpu);
41}
42
Thomas Gleixner79bf2bb2007-02-16 01:28:03 -080043/*
44 * Must be called with interrupts disabled !
45 */
46static void tick_do_update_jiffies64(ktime_t now)
47{
48 unsigned long ticks = 0;
49 ktime_t delta;
50
51 /* Reevalute with xtime_lock held */
52 write_seqlock(&xtime_lock);
53
54 delta = ktime_sub(now, last_jiffies_update);
55 if (delta.tv64 >= tick_period.tv64) {
56
57 delta = ktime_sub(delta, tick_period);
58 last_jiffies_update = ktime_add(last_jiffies_update,
59 tick_period);
60
61 /* Slow path for long timeouts */
62 if (unlikely(delta.tv64 >= tick_period.tv64)) {
63 s64 incr = ktime_to_ns(tick_period);
64
65 ticks = ktime_divns(delta, incr);
66
67 last_jiffies_update = ktime_add_ns(last_jiffies_update,
68 incr * ticks);
69 }
70 do_timer(++ticks);
71 }
72 write_sequnlock(&xtime_lock);
73}
74
75/*
76 * Initialize and return retrieve the jiffies update.
77 */
78static ktime_t tick_init_jiffy_update(void)
79{
80 ktime_t period;
81
82 write_seqlock(&xtime_lock);
83 /* Did we start the jiffies update yet ? */
84 if (last_jiffies_update.tv64 == 0)
85 last_jiffies_update = tick_next_period;
86 period = last_jiffies_update;
87 write_sequnlock(&xtime_lock);
88 return period;
89}
90
91/*
92 * NOHZ - aka dynamic tick functionality
93 */
94#ifdef CONFIG_NO_HZ
95/*
96 * NO HZ enabled ?
97 */
98static int tick_nohz_enabled __read_mostly = 1;
99
100/*
101 * Enable / Disable tickless mode
102 */
103static int __init setup_tick_nohz(char *str)
104{
105 if (!strcmp(str, "off"))
106 tick_nohz_enabled = 0;
107 else if (!strcmp(str, "on"))
108 tick_nohz_enabled = 1;
109 else
110 return 0;
111 return 1;
112}
113
114__setup("nohz=", setup_tick_nohz);
115
116/**
117 * tick_nohz_update_jiffies - update jiffies when idle was interrupted
118 *
119 * Called from interrupt entry when the CPU was idle
120 *
121 * In case the sched_tick was stopped on this CPU, we have to check if jiffies
122 * must be updated. Otherwise an interrupt handler could use a stale jiffy
123 * value. We do this unconditionally on any cpu, as we don't know whether the
124 * cpu, which has the update task assigned is in a long sleep.
125 */
126void tick_nohz_update_jiffies(void)
127{
128 int cpu = smp_processor_id();
129 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
130 unsigned long flags;
131 ktime_t now;
132
133 if (!ts->tick_stopped)
134 return;
135
136 cpu_clear(cpu, nohz_cpu_mask);
137 now = ktime_get();
138
139 local_irq_save(flags);
140 tick_do_update_jiffies64(now);
141 local_irq_restore(flags);
142}
143
144/**
145 * tick_nohz_stop_sched_tick - stop the idle tick from the idle task
146 *
147 * When the next event is more than a tick into the future, stop the idle tick
148 * Called either from the idle loop or from irq_exit() when an idle period was
149 * just interrupted by an interrupt which did not cause a reschedule.
150 */
151void tick_nohz_stop_sched_tick(void)
152{
153 unsigned long seq, last_jiffies, next_jiffies, delta_jiffies, flags;
154 struct tick_sched *ts;
155 ktime_t last_update, expires, now, delta;
156 int cpu;
157
158 local_irq_save(flags);
159
160 cpu = smp_processor_id();
161 ts = &per_cpu(tick_cpu_sched, cpu);
162
163 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
164 goto end;
165
166 if (need_resched())
167 goto end;
168
169 cpu = smp_processor_id();
Thomas Gleixnerbc5393a2007-02-19 18:12:05 +0000170 if (unlikely(local_softirq_pending()))
171 printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
172 local_softirq_pending());
Thomas Gleixner79bf2bb2007-02-16 01:28:03 -0800173
174 now = ktime_get();
175 /*
176 * When called from irq_exit we need to account the idle sleep time
177 * correctly.
178 */
179 if (ts->tick_stopped) {
180 delta = ktime_sub(now, ts->idle_entrytime);
181 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
182 }
183
184 ts->idle_entrytime = now;
185 ts->idle_calls++;
186
187 /* Read jiffies and the time when jiffies were updated last */
188 do {
189 seq = read_seqbegin(&xtime_lock);
190 last_update = last_jiffies_update;
191 last_jiffies = jiffies;
192 } while (read_seqretry(&xtime_lock, seq));
193
194 /* Get the next timer wheel timer */
195 next_jiffies = get_next_timer_interrupt(last_jiffies);
196 delta_jiffies = next_jiffies - last_jiffies;
197
Ingo Molnar6ba9b342007-02-19 18:11:56 +0000198 if (rcu_needs_cpu(cpu))
199 delta_jiffies = 1;
Thomas Gleixner79bf2bb2007-02-16 01:28:03 -0800200 /*
201 * Do not stop the tick, if we are only one off
202 * or if the cpu is required for rcu
203 */
Ingo Molnar6ba9b342007-02-19 18:11:56 +0000204 if (!ts->tick_stopped && delta_jiffies == 1)
Thomas Gleixner79bf2bb2007-02-16 01:28:03 -0800205 goto out;
206
207 /* Schedule the tick, if we are at least one jiffie off */
208 if ((long)delta_jiffies >= 1) {
209
Ingo Molnar6ba9b342007-02-19 18:11:56 +0000210 if (delta_jiffies > 1)
Thomas Gleixner79bf2bb2007-02-16 01:28:03 -0800211 cpu_set(cpu, nohz_cpu_mask);
212 /*
213 * nohz_stop_sched_tick can be called several times before
214 * the nohz_restart_sched_tick is called. This happens when
215 * interrupts arrive which do not cause a reschedule. In the
216 * first call we save the current tick time, so we can restart
217 * the scheduler tick in nohz_restart_sched_tick.
218 */
219 if (!ts->tick_stopped) {
220 ts->idle_tick = ts->sched_timer.expires;
221 ts->tick_stopped = 1;
222 ts->idle_jiffies = last_jiffies;
223 }
224 /*
225 * calculate the expiry time for the next timer wheel
226 * timer
227 */
228 expires = ktime_add_ns(last_update, tick_period.tv64 *
229 delta_jiffies);
230 ts->idle_expires = expires;
231 ts->idle_sleeps++;
232
233 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
234 hrtimer_start(&ts->sched_timer, expires,
235 HRTIMER_MODE_ABS);
236 /* Check, if the timer was already in the past */
237 if (hrtimer_active(&ts->sched_timer))
238 goto out;
239 } else if(!tick_program_event(expires, 0))
240 goto out;
241 /*
242 * We are past the event already. So we crossed a
243 * jiffie boundary. Update jiffies and raise the
244 * softirq.
245 */
246 tick_do_update_jiffies64(ktime_get());
247 cpu_clear(cpu, nohz_cpu_mask);
248 }
249 raise_softirq_irqoff(TIMER_SOFTIRQ);
250out:
251 ts->next_jiffies = next_jiffies;
252 ts->last_jiffies = last_jiffies;
253end:
254 local_irq_restore(flags);
255}
256
257/**
258 * nohz_restart_sched_tick - restart the idle tick from the idle task
259 *
260 * Restart the idle tick when the CPU is woken up from idle
261 */
262void tick_nohz_restart_sched_tick(void)
263{
264 int cpu = smp_processor_id();
265 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
266 unsigned long ticks;
267 ktime_t now, delta;
268
269 if (!ts->tick_stopped)
270 return;
271
272 /* Update jiffies first */
273 now = ktime_get();
274
275 local_irq_disable();
276 tick_do_update_jiffies64(now);
277 cpu_clear(cpu, nohz_cpu_mask);
278
279 /* Account the idle time */
280 delta = ktime_sub(now, ts->idle_entrytime);
281 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
282
283 /*
284 * We stopped the tick in idle. Update process times would miss the
285 * time we slept as update_process_times does only a 1 tick
286 * accounting. Enforce that this is accounted to idle !
287 */
288 ticks = jiffies - ts->idle_jiffies;
289 /*
290 * We might be one off. Do not randomly account a huge number of ticks!
291 */
292 if (ticks && ticks < LONG_MAX) {
293 add_preempt_count(HARDIRQ_OFFSET);
294 account_system_time(current, HARDIRQ_OFFSET,
295 jiffies_to_cputime(ticks));
296 sub_preempt_count(HARDIRQ_OFFSET);
297 }
298
299 /*
300 * Cancel the scheduled timer and restore the tick
301 */
302 ts->tick_stopped = 0;
303 hrtimer_cancel(&ts->sched_timer);
304 ts->sched_timer.expires = ts->idle_tick;
305
306 while (1) {
307 /* Forward the time to expire in the future */
308 hrtimer_forward(&ts->sched_timer, now, tick_period);
309
310 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
311 hrtimer_start(&ts->sched_timer,
312 ts->sched_timer.expires,
313 HRTIMER_MODE_ABS);
314 /* Check, if the timer was already in the past */
315 if (hrtimer_active(&ts->sched_timer))
316 break;
317 } else {
318 if (!tick_program_event(ts->sched_timer.expires, 0))
319 break;
320 }
321 /* Update jiffies and reread time */
322 tick_do_update_jiffies64(now);
323 now = ktime_get();
324 }
325 local_irq_enable();
326}
327
328static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
329{
330 hrtimer_forward(&ts->sched_timer, now, tick_period);
331 return tick_program_event(ts->sched_timer.expires, 0);
332}
333
334/*
335 * The nohz low res interrupt handler
336 */
337static void tick_nohz_handler(struct clock_event_device *dev)
338{
339 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
340 struct pt_regs *regs = get_irq_regs();
341 ktime_t now = ktime_get();
342
343 dev->next_event.tv64 = KTIME_MAX;
344
345 /* Check, if the jiffies need an update */
346 tick_do_update_jiffies64(now);
347
348 /*
349 * When we are idle and the tick is stopped, we have to touch
350 * the watchdog as we might not schedule for a really long
351 * time. This happens on complete idle SMP systems while
352 * waiting on the login prompt. We also increment the "start
353 * of idle" jiffy stamp so the idle accounting adjustment we
354 * do when we go busy again does not account too much ticks.
355 */
356 if (ts->tick_stopped) {
357 touch_softlockup_watchdog();
358 ts->idle_jiffies++;
359 }
360
361 update_process_times(user_mode(regs));
362 profile_tick(CPU_PROFILING);
363
364 /* Do not restart, when we are in the idle loop */
365 if (ts->tick_stopped)
366 return;
367
368 while (tick_nohz_reprogram(ts, now)) {
369 now = ktime_get();
370 tick_do_update_jiffies64(now);
371 }
372}
373
374/**
375 * tick_nohz_switch_to_nohz - switch to nohz mode
376 */
377static void tick_nohz_switch_to_nohz(void)
378{
379 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
380 ktime_t next;
381
382 if (!tick_nohz_enabled)
383 return;
384
385 local_irq_disable();
386 if (tick_switch_to_oneshot(tick_nohz_handler)) {
387 local_irq_enable();
388 return;
389 }
390
391 ts->nohz_mode = NOHZ_MODE_LOWRES;
392
393 /*
394 * Recycle the hrtimer in ts, so we can share the
395 * hrtimer_forward with the highres code.
396 */
397 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
398 /* Get the next period */
399 next = tick_init_jiffy_update();
400
401 for (;;) {
402 ts->sched_timer.expires = next;
403 if (!tick_program_event(next, 0))
404 break;
405 next = ktime_add(next, tick_period);
406 }
407 local_irq_enable();
408
409 printk(KERN_INFO "Switched to NOHz mode on CPU #%d\n",
410 smp_processor_id());
411}
412
413#else
414
415static inline void tick_nohz_switch_to_nohz(void) { }
416
417#endif /* NO_HZ */
418
419/*
420 * High resolution timer specific code
421 */
422#ifdef CONFIG_HIGH_RES_TIMERS
423/*
424 * We rearm the timer until we get disabled by the idle code
425 * Called with interrupts disabled and timer->base->cpu_base->lock held.
426 */
427static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
428{
429 struct tick_sched *ts =
430 container_of(timer, struct tick_sched, sched_timer);
431 struct hrtimer_cpu_base *base = timer->base->cpu_base;
432 struct pt_regs *regs = get_irq_regs();
433 ktime_t now = ktime_get();
434
435 /* Check, if the jiffies need an update */
436 tick_do_update_jiffies64(now);
437
438 /*
439 * Do not call, when we are not in irq context and have
440 * no valid regs pointer
441 */
442 if (regs) {
443 /*
444 * When we are idle and the tick is stopped, we have to touch
445 * the watchdog as we might not schedule for a really long
446 * time. This happens on complete idle SMP systems while
447 * waiting on the login prompt. We also increment the "start of
448 * idle" jiffy stamp so the idle accounting adjustment we do
449 * when we go busy again does not account too much ticks.
450 */
451 if (ts->tick_stopped) {
452 touch_softlockup_watchdog();
453 ts->idle_jiffies++;
454 }
455 /*
456 * update_process_times() might take tasklist_lock, hence
457 * drop the base lock. sched-tick hrtimers are per-CPU and
458 * never accessible by userspace APIs, so this is safe to do.
459 */
460 spin_unlock(&base->lock);
461 update_process_times(user_mode(regs));
462 profile_tick(CPU_PROFILING);
463 spin_lock(&base->lock);
464 }
465
466 /* Do not restart, when we are in the idle loop */
467 if (ts->tick_stopped)
468 return HRTIMER_NORESTART;
469
470 hrtimer_forward(timer, now, tick_period);
471
472 return HRTIMER_RESTART;
473}
474
475/**
476 * tick_setup_sched_timer - setup the tick emulation timer
477 */
478void tick_setup_sched_timer(void)
479{
480 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
481 ktime_t now = ktime_get();
482
483 /*
484 * Emulate tick processing via per-CPU hrtimers:
485 */
486 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
487 ts->sched_timer.function = tick_sched_timer;
488 ts->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
489
490 /* Get the next period */
491 ts->sched_timer.expires = tick_init_jiffy_update();
492
493 for (;;) {
494 hrtimer_forward(&ts->sched_timer, now, tick_period);
495 hrtimer_start(&ts->sched_timer, ts->sched_timer.expires,
496 HRTIMER_MODE_ABS);
497 /* Check, if the timer was already in the past */
498 if (hrtimer_active(&ts->sched_timer))
499 break;
500 now = ktime_get();
501 }
502
503#ifdef CONFIG_NO_HZ
504 if (tick_nohz_enabled)
505 ts->nohz_mode = NOHZ_MODE_HIGHRES;
506#endif
507}
508
509void tick_cancel_sched_timer(int cpu)
510{
511 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
512
513 if (ts->sched_timer.base)
514 hrtimer_cancel(&ts->sched_timer);
515 ts->tick_stopped = 0;
516 ts->nohz_mode = NOHZ_MODE_INACTIVE;
517}
518#endif /* HIGH_RES_TIMERS */
519
520/**
521 * Async notification about clocksource changes
522 */
523void tick_clock_notify(void)
524{
525 int cpu;
526
527 for_each_possible_cpu(cpu)
528 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
529}
530
531/*
532 * Async notification about clock event changes
533 */
534void tick_oneshot_notify(void)
535{
536 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
537
538 set_bit(0, &ts->check_clocks);
539}
540
541/**
542 * Check, if a change happened, which makes oneshot possible.
543 *
544 * Called cyclic from the hrtimer softirq (driven by the timer
545 * softirq) allow_nohz signals, that we can switch into low-res nohz
546 * mode, because high resolution timers are disabled (either compile
547 * or runtime).
548 */
549int tick_check_oneshot_change(int allow_nohz)
550{
551 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
552
553 if (!test_and_clear_bit(0, &ts->check_clocks))
554 return 0;
555
556 if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
557 return 0;
558
559 if (!timekeeping_is_continuous() || !tick_is_oneshot_available())
560 return 0;
561
562 if (!allow_nohz)
563 return 1;
564
565 tick_nohz_switch_to_nohz();
566 return 0;
567}