Commit | Line | Data |
---|---|---|
79bf2bb3 TG |
1 | /* |
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 | ||
24 | #include "tick-internal.h" | |
25 | ||
26 | /* | |
27 | * Per cpu nohz control structure | |
28 | */ | |
29 | static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched); | |
30 | ||
31 | /* | |
32 | * The time, when the last jiffy update happened. Protected by xtime_lock. | |
33 | */ | |
34 | static ktime_t last_jiffies_update; | |
35 | ||
36 | /* | |
37 | * Must be called with interrupts disabled ! | |
38 | */ | |
39 | static void tick_do_update_jiffies64(ktime_t now) | |
40 | { | |
41 | unsigned long ticks = 0; | |
42 | ktime_t delta; | |
43 | ||
44 | /* Reevalute with xtime_lock held */ | |
45 | write_seqlock(&xtime_lock); | |
46 | ||
47 | delta = ktime_sub(now, last_jiffies_update); | |
48 | if (delta.tv64 >= tick_period.tv64) { | |
49 | ||
50 | delta = ktime_sub(delta, tick_period); | |
51 | last_jiffies_update = ktime_add(last_jiffies_update, | |
52 | tick_period); | |
53 | ||
54 | /* Slow path for long timeouts */ | |
55 | if (unlikely(delta.tv64 >= tick_period.tv64)) { | |
56 | s64 incr = ktime_to_ns(tick_period); | |
57 | ||
58 | ticks = ktime_divns(delta, incr); | |
59 | ||
60 | last_jiffies_update = ktime_add_ns(last_jiffies_update, | |
61 | incr * ticks); | |
62 | } | |
63 | do_timer(++ticks); | |
64 | } | |
65 | write_sequnlock(&xtime_lock); | |
66 | } | |
67 | ||
68 | /* | |
69 | * Initialize and return retrieve the jiffies update. | |
70 | */ | |
71 | static ktime_t tick_init_jiffy_update(void) | |
72 | { | |
73 | ktime_t period; | |
74 | ||
75 | write_seqlock(&xtime_lock); | |
76 | /* Did we start the jiffies update yet ? */ | |
77 | if (last_jiffies_update.tv64 == 0) | |
78 | last_jiffies_update = tick_next_period; | |
79 | period = last_jiffies_update; | |
80 | write_sequnlock(&xtime_lock); | |
81 | return period; | |
82 | } | |
83 | ||
84 | /* | |
85 | * NOHZ - aka dynamic tick functionality | |
86 | */ | |
87 | #ifdef CONFIG_NO_HZ | |
88 | /* | |
89 | * NO HZ enabled ? | |
90 | */ | |
91 | static int tick_nohz_enabled __read_mostly = 1; | |
92 | ||
93 | /* | |
94 | * Enable / Disable tickless mode | |
95 | */ | |
96 | static int __init setup_tick_nohz(char *str) | |
97 | { | |
98 | if (!strcmp(str, "off")) | |
99 | tick_nohz_enabled = 0; | |
100 | else if (!strcmp(str, "on")) | |
101 | tick_nohz_enabled = 1; | |
102 | else | |
103 | return 0; | |
104 | return 1; | |
105 | } | |
106 | ||
107 | __setup("nohz=", setup_tick_nohz); | |
108 | ||
109 | /** | |
110 | * tick_nohz_update_jiffies - update jiffies when idle was interrupted | |
111 | * | |
112 | * Called from interrupt entry when the CPU was idle | |
113 | * | |
114 | * In case the sched_tick was stopped on this CPU, we have to check if jiffies | |
115 | * must be updated. Otherwise an interrupt handler could use a stale jiffy | |
116 | * value. We do this unconditionally on any cpu, as we don't know whether the | |
117 | * cpu, which has the update task assigned is in a long sleep. | |
118 | */ | |
119 | void tick_nohz_update_jiffies(void) | |
120 | { | |
121 | int cpu = smp_processor_id(); | |
122 | struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); | |
123 | unsigned long flags; | |
124 | ktime_t now; | |
125 | ||
126 | if (!ts->tick_stopped) | |
127 | return; | |
128 | ||
129 | cpu_clear(cpu, nohz_cpu_mask); | |
130 | now = ktime_get(); | |
131 | ||
132 | local_irq_save(flags); | |
133 | tick_do_update_jiffies64(now); | |
134 | local_irq_restore(flags); | |
135 | } | |
136 | ||
137 | /** | |
138 | * tick_nohz_stop_sched_tick - stop the idle tick from the idle task | |
139 | * | |
140 | * When the next event is more than a tick into the future, stop the idle tick | |
141 | * Called either from the idle loop or from irq_exit() when an idle period was | |
142 | * just interrupted by an interrupt which did not cause a reschedule. | |
143 | */ | |
144 | void tick_nohz_stop_sched_tick(void) | |
145 | { | |
146 | unsigned long seq, last_jiffies, next_jiffies, delta_jiffies, flags; | |
147 | struct tick_sched *ts; | |
148 | ktime_t last_update, expires, now, delta; | |
149 | int cpu; | |
150 | ||
151 | local_irq_save(flags); | |
152 | ||
153 | cpu = smp_processor_id(); | |
154 | ts = &per_cpu(tick_cpu_sched, cpu); | |
155 | ||
156 | if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) | |
157 | goto end; | |
158 | ||
159 | if (need_resched()) | |
160 | goto end; | |
161 | ||
162 | cpu = smp_processor_id(); | |
163 | BUG_ON(local_softirq_pending()); | |
164 | ||
165 | now = ktime_get(); | |
166 | /* | |
167 | * When called from irq_exit we need to account the idle sleep time | |
168 | * correctly. | |
169 | */ | |
170 | if (ts->tick_stopped) { | |
171 | delta = ktime_sub(now, ts->idle_entrytime); | |
172 | ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); | |
173 | } | |
174 | ||
175 | ts->idle_entrytime = now; | |
176 | ts->idle_calls++; | |
177 | ||
178 | /* Read jiffies and the time when jiffies were updated last */ | |
179 | do { | |
180 | seq = read_seqbegin(&xtime_lock); | |
181 | last_update = last_jiffies_update; | |
182 | last_jiffies = jiffies; | |
183 | } while (read_seqretry(&xtime_lock, seq)); | |
184 | ||
185 | /* Get the next timer wheel timer */ | |
186 | next_jiffies = get_next_timer_interrupt(last_jiffies); | |
187 | delta_jiffies = next_jiffies - last_jiffies; | |
188 | ||
189 | /* | |
190 | * Do not stop the tick, if we are only one off | |
191 | * or if the cpu is required for rcu | |
192 | */ | |
193 | if (!ts->tick_stopped && (delta_jiffies == 1 || rcu_needs_cpu(cpu))) | |
194 | goto out; | |
195 | ||
196 | /* Schedule the tick, if we are at least one jiffie off */ | |
197 | if ((long)delta_jiffies >= 1) { | |
198 | ||
199 | if (rcu_needs_cpu(cpu)) | |
200 | delta_jiffies = 1; | |
201 | else | |
202 | cpu_set(cpu, nohz_cpu_mask); | |
203 | /* | |
204 | * nohz_stop_sched_tick can be called several times before | |
205 | * the nohz_restart_sched_tick is called. This happens when | |
206 | * interrupts arrive which do not cause a reschedule. In the | |
207 | * first call we save the current tick time, so we can restart | |
208 | * the scheduler tick in nohz_restart_sched_tick. | |
209 | */ | |
210 | if (!ts->tick_stopped) { | |
211 | ts->idle_tick = ts->sched_timer.expires; | |
212 | ts->tick_stopped = 1; | |
213 | ts->idle_jiffies = last_jiffies; | |
214 | } | |
215 | /* | |
216 | * calculate the expiry time for the next timer wheel | |
217 | * timer | |
218 | */ | |
219 | expires = ktime_add_ns(last_update, tick_period.tv64 * | |
220 | delta_jiffies); | |
221 | ts->idle_expires = expires; | |
222 | ts->idle_sleeps++; | |
223 | ||
224 | if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { | |
225 | hrtimer_start(&ts->sched_timer, expires, | |
226 | HRTIMER_MODE_ABS); | |
227 | /* Check, if the timer was already in the past */ | |
228 | if (hrtimer_active(&ts->sched_timer)) | |
229 | goto out; | |
230 | } else if(!tick_program_event(expires, 0)) | |
231 | goto out; | |
232 | /* | |
233 | * We are past the event already. So we crossed a | |
234 | * jiffie boundary. Update jiffies and raise the | |
235 | * softirq. | |
236 | */ | |
237 | tick_do_update_jiffies64(ktime_get()); | |
238 | cpu_clear(cpu, nohz_cpu_mask); | |
239 | } | |
240 | raise_softirq_irqoff(TIMER_SOFTIRQ); | |
241 | out: | |
242 | ts->next_jiffies = next_jiffies; | |
243 | ts->last_jiffies = last_jiffies; | |
244 | end: | |
245 | local_irq_restore(flags); | |
246 | } | |
247 | ||
248 | /** | |
249 | * nohz_restart_sched_tick - restart the idle tick from the idle task | |
250 | * | |
251 | * Restart the idle tick when the CPU is woken up from idle | |
252 | */ | |
253 | void tick_nohz_restart_sched_tick(void) | |
254 | { | |
255 | int cpu = smp_processor_id(); | |
256 | struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); | |
257 | unsigned long ticks; | |
258 | ktime_t now, delta; | |
259 | ||
260 | if (!ts->tick_stopped) | |
261 | return; | |
262 | ||
263 | /* Update jiffies first */ | |
264 | now = ktime_get(); | |
265 | ||
266 | local_irq_disable(); | |
267 | tick_do_update_jiffies64(now); | |
268 | cpu_clear(cpu, nohz_cpu_mask); | |
269 | ||
270 | /* Account the idle time */ | |
271 | delta = ktime_sub(now, ts->idle_entrytime); | |
272 | ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); | |
273 | ||
274 | /* | |
275 | * We stopped the tick in idle. Update process times would miss the | |
276 | * time we slept as update_process_times does only a 1 tick | |
277 | * accounting. Enforce that this is accounted to idle ! | |
278 | */ | |
279 | ticks = jiffies - ts->idle_jiffies; | |
280 | /* | |
281 | * We might be one off. Do not randomly account a huge number of ticks! | |
282 | */ | |
283 | if (ticks && ticks < LONG_MAX) { | |
284 | add_preempt_count(HARDIRQ_OFFSET); | |
285 | account_system_time(current, HARDIRQ_OFFSET, | |
286 | jiffies_to_cputime(ticks)); | |
287 | sub_preempt_count(HARDIRQ_OFFSET); | |
288 | } | |
289 | ||
290 | /* | |
291 | * Cancel the scheduled timer and restore the tick | |
292 | */ | |
293 | ts->tick_stopped = 0; | |
294 | hrtimer_cancel(&ts->sched_timer); | |
295 | ts->sched_timer.expires = ts->idle_tick; | |
296 | ||
297 | while (1) { | |
298 | /* Forward the time to expire in the future */ | |
299 | hrtimer_forward(&ts->sched_timer, now, tick_period); | |
300 | ||
301 | if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { | |
302 | hrtimer_start(&ts->sched_timer, | |
303 | ts->sched_timer.expires, | |
304 | HRTIMER_MODE_ABS); | |
305 | /* Check, if the timer was already in the past */ | |
306 | if (hrtimer_active(&ts->sched_timer)) | |
307 | break; | |
308 | } else { | |
309 | if (!tick_program_event(ts->sched_timer.expires, 0)) | |
310 | break; | |
311 | } | |
312 | /* Update jiffies and reread time */ | |
313 | tick_do_update_jiffies64(now); | |
314 | now = ktime_get(); | |
315 | } | |
316 | local_irq_enable(); | |
317 | } | |
318 | ||
319 | static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now) | |
320 | { | |
321 | hrtimer_forward(&ts->sched_timer, now, tick_period); | |
322 | return tick_program_event(ts->sched_timer.expires, 0); | |
323 | } | |
324 | ||
325 | /* | |
326 | * The nohz low res interrupt handler | |
327 | */ | |
328 | static void tick_nohz_handler(struct clock_event_device *dev) | |
329 | { | |
330 | struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); | |
331 | struct pt_regs *regs = get_irq_regs(); | |
332 | ktime_t now = ktime_get(); | |
333 | ||
334 | dev->next_event.tv64 = KTIME_MAX; | |
335 | ||
336 | /* Check, if the jiffies need an update */ | |
337 | tick_do_update_jiffies64(now); | |
338 | ||
339 | /* | |
340 | * When we are idle and the tick is stopped, we have to touch | |
341 | * the watchdog as we might not schedule for a really long | |
342 | * time. This happens on complete idle SMP systems while | |
343 | * waiting on the login prompt. We also increment the "start | |
344 | * of idle" jiffy stamp so the idle accounting adjustment we | |
345 | * do when we go busy again does not account too much ticks. | |
346 | */ | |
347 | if (ts->tick_stopped) { | |
348 | touch_softlockup_watchdog(); | |
349 | ts->idle_jiffies++; | |
350 | } | |
351 | ||
352 | update_process_times(user_mode(regs)); | |
353 | profile_tick(CPU_PROFILING); | |
354 | ||
355 | /* Do not restart, when we are in the idle loop */ | |
356 | if (ts->tick_stopped) | |
357 | return; | |
358 | ||
359 | while (tick_nohz_reprogram(ts, now)) { | |
360 | now = ktime_get(); | |
361 | tick_do_update_jiffies64(now); | |
362 | } | |
363 | } | |
364 | ||
365 | /** | |
366 | * tick_nohz_switch_to_nohz - switch to nohz mode | |
367 | */ | |
368 | static void tick_nohz_switch_to_nohz(void) | |
369 | { | |
370 | struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); | |
371 | ktime_t next; | |
372 | ||
373 | if (!tick_nohz_enabled) | |
374 | return; | |
375 | ||
376 | local_irq_disable(); | |
377 | if (tick_switch_to_oneshot(tick_nohz_handler)) { | |
378 | local_irq_enable(); | |
379 | return; | |
380 | } | |
381 | ||
382 | ts->nohz_mode = NOHZ_MODE_LOWRES; | |
383 | ||
384 | /* | |
385 | * Recycle the hrtimer in ts, so we can share the | |
386 | * hrtimer_forward with the highres code. | |
387 | */ | |
388 | hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); | |
389 | /* Get the next period */ | |
390 | next = tick_init_jiffy_update(); | |
391 | ||
392 | for (;;) { | |
393 | ts->sched_timer.expires = next; | |
394 | if (!tick_program_event(next, 0)) | |
395 | break; | |
396 | next = ktime_add(next, tick_period); | |
397 | } | |
398 | local_irq_enable(); | |
399 | ||
400 | printk(KERN_INFO "Switched to NOHz mode on CPU #%d\n", | |
401 | smp_processor_id()); | |
402 | } | |
403 | ||
404 | #else | |
405 | ||
406 | static inline void tick_nohz_switch_to_nohz(void) { } | |
407 | ||
408 | #endif /* NO_HZ */ | |
409 | ||
410 | /* | |
411 | * High resolution timer specific code | |
412 | */ | |
413 | #ifdef CONFIG_HIGH_RES_TIMERS | |
414 | /* | |
415 | * We rearm the timer until we get disabled by the idle code | |
416 | * Called with interrupts disabled and timer->base->cpu_base->lock held. | |
417 | */ | |
418 | static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) | |
419 | { | |
420 | struct tick_sched *ts = | |
421 | container_of(timer, struct tick_sched, sched_timer); | |
422 | struct hrtimer_cpu_base *base = timer->base->cpu_base; | |
423 | struct pt_regs *regs = get_irq_regs(); | |
424 | ktime_t now = ktime_get(); | |
425 | ||
426 | /* Check, if the jiffies need an update */ | |
427 | tick_do_update_jiffies64(now); | |
428 | ||
429 | /* | |
430 | * Do not call, when we are not in irq context and have | |
431 | * no valid regs pointer | |
432 | */ | |
433 | if (regs) { | |
434 | /* | |
435 | * When we are idle and the tick is stopped, we have to touch | |
436 | * the watchdog as we might not schedule for a really long | |
437 | * time. This happens on complete idle SMP systems while | |
438 | * waiting on the login prompt. We also increment the "start of | |
439 | * idle" jiffy stamp so the idle accounting adjustment we do | |
440 | * when we go busy again does not account too much ticks. | |
441 | */ | |
442 | if (ts->tick_stopped) { | |
443 | touch_softlockup_watchdog(); | |
444 | ts->idle_jiffies++; | |
445 | } | |
446 | /* | |
447 | * update_process_times() might take tasklist_lock, hence | |
448 | * drop the base lock. sched-tick hrtimers are per-CPU and | |
449 | * never accessible by userspace APIs, so this is safe to do. | |
450 | */ | |
451 | spin_unlock(&base->lock); | |
452 | update_process_times(user_mode(regs)); | |
453 | profile_tick(CPU_PROFILING); | |
454 | spin_lock(&base->lock); | |
455 | } | |
456 | ||
457 | /* Do not restart, when we are in the idle loop */ | |
458 | if (ts->tick_stopped) | |
459 | return HRTIMER_NORESTART; | |
460 | ||
461 | hrtimer_forward(timer, now, tick_period); | |
462 | ||
463 | return HRTIMER_RESTART; | |
464 | } | |
465 | ||
466 | /** | |
467 | * tick_setup_sched_timer - setup the tick emulation timer | |
468 | */ | |
469 | void tick_setup_sched_timer(void) | |
470 | { | |
471 | struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); | |
472 | ktime_t now = ktime_get(); | |
473 | ||
474 | /* | |
475 | * Emulate tick processing via per-CPU hrtimers: | |
476 | */ | |
477 | hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); | |
478 | ts->sched_timer.function = tick_sched_timer; | |
479 | ts->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ; | |
480 | ||
481 | /* Get the next period */ | |
482 | ts->sched_timer.expires = tick_init_jiffy_update(); | |
483 | ||
484 | for (;;) { | |
485 | hrtimer_forward(&ts->sched_timer, now, tick_period); | |
486 | hrtimer_start(&ts->sched_timer, ts->sched_timer.expires, | |
487 | HRTIMER_MODE_ABS); | |
488 | /* Check, if the timer was already in the past */ | |
489 | if (hrtimer_active(&ts->sched_timer)) | |
490 | break; | |
491 | now = ktime_get(); | |
492 | } | |
493 | ||
494 | #ifdef CONFIG_NO_HZ | |
495 | if (tick_nohz_enabled) | |
496 | ts->nohz_mode = NOHZ_MODE_HIGHRES; | |
497 | #endif | |
498 | } | |
499 | ||
500 | void tick_cancel_sched_timer(int cpu) | |
501 | { | |
502 | struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); | |
503 | ||
504 | if (ts->sched_timer.base) | |
505 | hrtimer_cancel(&ts->sched_timer); | |
506 | ts->tick_stopped = 0; | |
507 | ts->nohz_mode = NOHZ_MODE_INACTIVE; | |
508 | } | |
509 | #endif /* HIGH_RES_TIMERS */ | |
510 | ||
511 | /** | |
512 | * Async notification about clocksource changes | |
513 | */ | |
514 | void tick_clock_notify(void) | |
515 | { | |
516 | int cpu; | |
517 | ||
518 | for_each_possible_cpu(cpu) | |
519 | set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks); | |
520 | } | |
521 | ||
522 | /* | |
523 | * Async notification about clock event changes | |
524 | */ | |
525 | void tick_oneshot_notify(void) | |
526 | { | |
527 | struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); | |
528 | ||
529 | set_bit(0, &ts->check_clocks); | |
530 | } | |
531 | ||
532 | /** | |
533 | * Check, if a change happened, which makes oneshot possible. | |
534 | * | |
535 | * Called cyclic from the hrtimer softirq (driven by the timer | |
536 | * softirq) allow_nohz signals, that we can switch into low-res nohz | |
537 | * mode, because high resolution timers are disabled (either compile | |
538 | * or runtime). | |
539 | */ | |
540 | int tick_check_oneshot_change(int allow_nohz) | |
541 | { | |
542 | struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); | |
543 | ||
544 | if (!test_and_clear_bit(0, &ts->check_clocks)) | |
545 | return 0; | |
546 | ||
547 | if (ts->nohz_mode != NOHZ_MODE_INACTIVE) | |
548 | return 0; | |
549 | ||
550 | if (!timekeeping_is_continuous() || !tick_is_oneshot_available()) | |
551 | return 0; | |
552 | ||
553 | if (!allow_nohz) | |
554 | return 1; | |
555 | ||
556 | tick_nohz_switch_to_nohz(); | |
557 | return 0; | |
558 | } |