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Linux/kernel/time/tick-sched.c

  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  *  Distribute under GPLv2.
 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/module.h>
 23 #include <linux/irq_work.h>
 24 #include <linux/posix-timers.h>
 25 #include <linux/perf_event.h>
 26 #include <linux/context_tracking.h>
 27 
 28 #include <asm/irq_regs.h>
 29 
 30 #include "tick-internal.h"
 31 
 32 #include <trace/events/timer.h>
 33 
 34 /*
 35  * Per cpu nohz control structure
 36  */
 37 DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
 38 
 39 /*
 40  * The time, when the last jiffy update happened. Protected by jiffies_lock.
 41  */
 42 static ktime_t last_jiffies_update;
 43 
 44 struct tick_sched *tick_get_tick_sched(int cpu)
 45 {
 46         return &per_cpu(tick_cpu_sched, cpu);
 47 }
 48 
 49 /*
 50  * Must be called with interrupts disabled !
 51  */
 52 static void tick_do_update_jiffies64(ktime_t now)
 53 {
 54         unsigned long ticks = 0;
 55         ktime_t delta;
 56 
 57         /*
 58          * Do a quick check without holding jiffies_lock:
 59          */
 60         delta = ktime_sub(now, last_jiffies_update);
 61         if (delta.tv64 < tick_period.tv64)
 62                 return;
 63 
 64         /* Reevalute with jiffies_lock held */
 65         write_seqlock(&jiffies_lock);
 66 
 67         delta = ktime_sub(now, last_jiffies_update);
 68         if (delta.tv64 >= tick_period.tv64) {
 69 
 70                 delta = ktime_sub(delta, tick_period);
 71                 last_jiffies_update = ktime_add(last_jiffies_update,
 72                                                 tick_period);
 73 
 74                 /* Slow path for long timeouts */
 75                 if (unlikely(delta.tv64 >= tick_period.tv64)) {
 76                         s64 incr = ktime_to_ns(tick_period);
 77 
 78                         ticks = ktime_divns(delta, incr);
 79 
 80                         last_jiffies_update = ktime_add_ns(last_jiffies_update,
 81                                                            incr * ticks);
 82                 }
 83                 do_timer(++ticks);
 84 
 85                 /* Keep the tick_next_period variable up to date */
 86                 tick_next_period = ktime_add(last_jiffies_update, tick_period);
 87         } else {
 88                 write_sequnlock(&jiffies_lock);
 89                 return;
 90         }
 91         write_sequnlock(&jiffies_lock);
 92         update_wall_time();
 93 }
 94 
 95 /*
 96  * Initialize and return retrieve the jiffies update.
 97  */
 98 static ktime_t tick_init_jiffy_update(void)
 99 {
100         ktime_t period;
101 
102         write_seqlock(&jiffies_lock);
103         /* Did we start the jiffies update yet ? */
104         if (last_jiffies_update.tv64 == 0)
105                 last_jiffies_update = tick_next_period;
106         period = last_jiffies_update;
107         write_sequnlock(&jiffies_lock);
108         return period;
109 }
110 
111 
112 static void tick_sched_do_timer(ktime_t now)
113 {
114         int cpu = smp_processor_id();
115 
116 #ifdef CONFIG_NO_HZ_COMMON
117         /*
118          * Check if the do_timer duty was dropped. We don't care about
119          * concurrency: This happens only when the cpu in charge went
120          * into a long sleep. If two cpus happen to assign themself to
121          * this duty, then the jiffies update is still serialized by
122          * jiffies_lock.
123          */
124         if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)
125             && !tick_nohz_full_cpu(cpu))
126                 tick_do_timer_cpu = cpu;
127 #endif
128 
129         /* Check, if the jiffies need an update */
130         if (tick_do_timer_cpu == cpu)
131                 tick_do_update_jiffies64(now);
132 }
133 
134 static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
135 {
136 #ifdef CONFIG_NO_HZ_COMMON
137         /*
138          * When we are idle and the tick is stopped, we have to touch
139          * the watchdog as we might not schedule for a really long
140          * time. This happens on complete idle SMP systems while
141          * waiting on the login prompt. We also increment the "start of
142          * idle" jiffy stamp so the idle accounting adjustment we do
143          * when we go busy again does not account too much ticks.
144          */
145         if (ts->tick_stopped) {
146                 touch_softlockup_watchdog();
147                 if (is_idle_task(current))
148                         ts->idle_jiffies++;
149         }
150 #endif
151         update_process_times(user_mode(regs));
152         profile_tick(CPU_PROFILING);
153 }
154 
155 #ifdef CONFIG_NO_HZ_FULL
156 cpumask_var_t tick_nohz_full_mask;
157 cpumask_var_t housekeeping_mask;
158 bool tick_nohz_full_running;
159 
160 static bool can_stop_full_tick(void)
161 {
162         WARN_ON_ONCE(!irqs_disabled());
163 
164         if (!sched_can_stop_tick()) {
165                 trace_tick_stop(0, "more than 1 task in runqueue\n");
166                 return false;
167         }
168 
169         if (!posix_cpu_timers_can_stop_tick(current)) {
170                 trace_tick_stop(0, "posix timers running\n");
171                 return false;
172         }
173 
174         if (!perf_event_can_stop_tick()) {
175                 trace_tick_stop(0, "perf events running\n");
176                 return false;
177         }
178 
179         /* sched_clock_tick() needs us? */
180 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
181         /*
182          * TODO: kick full dynticks CPUs when
183          * sched_clock_stable is set.
184          */
185         if (!sched_clock_stable()) {
186                 trace_tick_stop(0, "unstable sched clock\n");
187                 /*
188                  * Don't allow the user to think they can get
189                  * full NO_HZ with this machine.
190                  */
191                 WARN_ONCE(tick_nohz_full_running,
192                           "NO_HZ FULL will not work with unstable sched clock");
193                 return false;
194         }
195 #endif
196 
197         return true;
198 }
199 
200 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now);
201 
202 /*
203  * Re-evaluate the need for the tick on the current CPU
204  * and restart it if necessary.
205  */
206 void __tick_nohz_full_check(void)
207 {
208         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
209 
210         if (tick_nohz_full_cpu(smp_processor_id())) {
211                 if (ts->tick_stopped && !is_idle_task(current)) {
212                         if (!can_stop_full_tick())
213                                 tick_nohz_restart_sched_tick(ts, ktime_get());
214                 }
215         }
216 }
217 
218 static void nohz_full_kick_work_func(struct irq_work *work)
219 {
220         __tick_nohz_full_check();
221 }
222 
223 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
224         .func = nohz_full_kick_work_func,
225 };
226 
227 /*
228  * Kick this CPU if it's full dynticks in order to force it to
229  * re-evaluate its dependency on the tick and restart it if necessary.
230  * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
231  * is NMI safe.
232  */
233 void tick_nohz_full_kick(void)
234 {
235         if (!tick_nohz_full_cpu(smp_processor_id()))
236                 return;
237 
238         irq_work_queue(&__get_cpu_var(nohz_full_kick_work));
239 }
240 
241 /*
242  * Kick the CPU if it's full dynticks in order to force it to
243  * re-evaluate its dependency on the tick and restart it if necessary.
244  */
245 void tick_nohz_full_kick_cpu(int cpu)
246 {
247         if (!tick_nohz_full_cpu(cpu))
248                 return;
249 
250         irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
251 }
252 
253 static void nohz_full_kick_ipi(void *info)
254 {
255         __tick_nohz_full_check();
256 }
257 
258 /*
259  * Kick all full dynticks CPUs in order to force these to re-evaluate
260  * their dependency on the tick and restart it if necessary.
261  */
262 void tick_nohz_full_kick_all(void)
263 {
264         if (!tick_nohz_full_running)
265                 return;
266 
267         preempt_disable();
268         smp_call_function_many(tick_nohz_full_mask,
269                                nohz_full_kick_ipi, NULL, false);
270         tick_nohz_full_kick();
271         preempt_enable();
272 }
273 
274 /*
275  * Re-evaluate the need for the tick as we switch the current task.
276  * It might need the tick due to per task/process properties:
277  * perf events, posix cpu timers, ...
278  */
279 void __tick_nohz_task_switch(struct task_struct *tsk)
280 {
281         unsigned long flags;
282 
283         local_irq_save(flags);
284 
285         if (!tick_nohz_full_cpu(smp_processor_id()))
286                 goto out;
287 
288         if (tick_nohz_tick_stopped() && !can_stop_full_tick())
289                 tick_nohz_full_kick();
290 
291 out:
292         local_irq_restore(flags);
293 }
294 
295 /* Parse the boot-time nohz CPU list from the kernel parameters. */
296 static int __init tick_nohz_full_setup(char *str)
297 {
298         int cpu;
299 
300         alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
301         alloc_bootmem_cpumask_var(&housekeeping_mask);
302         if (cpulist_parse(str, tick_nohz_full_mask) < 0) {
303                 pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
304                 return 1;
305         }
306 
307         cpu = smp_processor_id();
308         if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
309                 pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu);
310                 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
311         }
312         cpumask_andnot(housekeeping_mask,
313                        cpu_possible_mask, tick_nohz_full_mask);
314         tick_nohz_full_running = true;
315 
316         return 1;
317 }
318 __setup("nohz_full=", tick_nohz_full_setup);
319 
320 static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,
321                                                  unsigned long action,
322                                                  void *hcpu)
323 {
324         unsigned int cpu = (unsigned long)hcpu;
325 
326         switch (action & ~CPU_TASKS_FROZEN) {
327         case CPU_DOWN_PREPARE:
328                 /*
329                  * If we handle the timekeeping duty for full dynticks CPUs,
330                  * we can't safely shutdown that CPU.
331                  */
332                 if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
333                         return NOTIFY_BAD;
334                 break;
335         }
336         return NOTIFY_OK;
337 }
338 
339 /*
340  * Worst case string length in chunks of CPU range seems 2 steps
341  * separations: 0,2,4,6,...
342  * This is NR_CPUS + sizeof('\0')
343  */
344 static char __initdata nohz_full_buf[NR_CPUS + 1];
345 
346 static int tick_nohz_init_all(void)
347 {
348         int err = -1;
349 
350 #ifdef CONFIG_NO_HZ_FULL_ALL
351         if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
352                 pr_err("NO_HZ: Can't allocate full dynticks cpumask\n");
353                 return err;
354         }
355         if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) {
356                 pr_err("NO_HZ: Can't allocate not-full dynticks cpumask\n");
357                 return err;
358         }
359         err = 0;
360         cpumask_setall(tick_nohz_full_mask);
361         cpumask_clear_cpu(smp_processor_id(), tick_nohz_full_mask);
362         cpumask_clear(housekeeping_mask);
363         cpumask_set_cpu(smp_processor_id(), housekeeping_mask);
364         tick_nohz_full_running = true;
365 #endif
366         return err;
367 }
368 
369 void __init tick_nohz_init(void)
370 {
371         int cpu;
372 
373         if (!tick_nohz_full_running) {
374                 if (tick_nohz_init_all() < 0)
375                         return;
376         }
377 
378         for_each_cpu(cpu, tick_nohz_full_mask)
379                 context_tracking_cpu_set(cpu);
380 
381         cpu_notifier(tick_nohz_cpu_down_callback, 0);
382         cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), tick_nohz_full_mask);
383         pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf);
384 }
385 #endif
386 
387 /*
388  * NOHZ - aka dynamic tick functionality
389  */
390 #ifdef CONFIG_NO_HZ_COMMON
391 /*
392  * NO HZ enabled ?
393  */
394 static int tick_nohz_enabled __read_mostly  = 1;
395 int tick_nohz_active  __read_mostly;
396 /*
397  * Enable / Disable tickless mode
398  */
399 static int __init setup_tick_nohz(char *str)
400 {
401         if (!strcmp(str, "off"))
402                 tick_nohz_enabled = 0;
403         else if (!strcmp(str, "on"))
404                 tick_nohz_enabled = 1;
405         else
406                 return 0;
407         return 1;
408 }
409 
410 __setup("nohz=", setup_tick_nohz);
411 
412 /**
413  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
414  *
415  * Called from interrupt entry when the CPU was idle
416  *
417  * In case the sched_tick was stopped on this CPU, we have to check if jiffies
418  * must be updated. Otherwise an interrupt handler could use a stale jiffy
419  * value. We do this unconditionally on any cpu, as we don't know whether the
420  * cpu, which has the update task assigned is in a long sleep.
421  */
422 static void tick_nohz_update_jiffies(ktime_t now)
423 {
424         unsigned long flags;
425 
426         __this_cpu_write(tick_cpu_sched.idle_waketime, now);
427 
428         local_irq_save(flags);
429         tick_do_update_jiffies64(now);
430         local_irq_restore(flags);
431 
432         touch_softlockup_watchdog();
433 }
434 
435 /*
436  * Updates the per cpu time idle statistics counters
437  */
438 static void
439 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
440 {
441         ktime_t delta;
442 
443         if (ts->idle_active) {
444                 delta = ktime_sub(now, ts->idle_entrytime);
445                 if (nr_iowait_cpu(cpu) > 0)
446                         ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
447                 else
448                         ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
449                 ts->idle_entrytime = now;
450         }
451 
452         if (last_update_time)
453                 *last_update_time = ktime_to_us(now);
454 
455 }
456 
457 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
458 {
459         update_ts_time_stats(smp_processor_id(), ts, now, NULL);
460         ts->idle_active = 0;
461 
462         sched_clock_idle_wakeup_event(0);
463 }
464 
465 static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
466 {
467         ktime_t now = ktime_get();
468 
469         ts->idle_entrytime = now;
470         ts->idle_active = 1;
471         sched_clock_idle_sleep_event();
472         return now;
473 }
474 
475 /**
476  * get_cpu_idle_time_us - get the total idle time of a cpu
477  * @cpu: CPU number to query
478  * @last_update_time: variable to store update time in. Do not update
479  * counters if NULL.
480  *
481  * Return the cummulative idle time (since boot) for a given
482  * CPU, in microseconds.
483  *
484  * This time is measured via accounting rather than sampling,
485  * and is as accurate as ktime_get() is.
486  *
487  * This function returns -1 if NOHZ is not enabled.
488  */
489 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
490 {
491         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
492         ktime_t now, idle;
493 
494         if (!tick_nohz_active)
495                 return -1;
496 
497         now = ktime_get();
498         if (last_update_time) {
499                 update_ts_time_stats(cpu, ts, now, last_update_time);
500                 idle = ts->idle_sleeptime;
501         } else {
502                 if (ts->idle_active && !nr_iowait_cpu(cpu)) {
503                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
504 
505                         idle = ktime_add(ts->idle_sleeptime, delta);
506                 } else {
507                         idle = ts->idle_sleeptime;
508                 }
509         }
510 
511         return ktime_to_us(idle);
512 
513 }
514 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
515 
516 /**
517  * get_cpu_iowait_time_us - get the total iowait time of a cpu
518  * @cpu: CPU number to query
519  * @last_update_time: variable to store update time in. Do not update
520  * counters if NULL.
521  *
522  * Return the cummulative iowait time (since boot) for a given
523  * CPU, in microseconds.
524  *
525  * This time is measured via accounting rather than sampling,
526  * and is as accurate as ktime_get() is.
527  *
528  * This function returns -1 if NOHZ is not enabled.
529  */
530 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
531 {
532         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
533         ktime_t now, iowait;
534 
535         if (!tick_nohz_active)
536                 return -1;
537 
538         now = ktime_get();
539         if (last_update_time) {
540                 update_ts_time_stats(cpu, ts, now, last_update_time);
541                 iowait = ts->iowait_sleeptime;
542         } else {
543                 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
544                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
545 
546                         iowait = ktime_add(ts->iowait_sleeptime, delta);
547                 } else {
548                         iowait = ts->iowait_sleeptime;
549                 }
550         }
551 
552         return ktime_to_us(iowait);
553 }
554 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
555 
556 static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
557                                          ktime_t now, int cpu)
558 {
559         unsigned long seq, last_jiffies, next_jiffies, delta_jiffies;
560         ktime_t last_update, expires, ret = { .tv64 = 0 };
561         unsigned long rcu_delta_jiffies;
562         struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
563         u64 time_delta;
564 
565         time_delta = timekeeping_max_deferment();
566 
567         /* Read jiffies and the time when jiffies were updated last */
568         do {
569                 seq = read_seqbegin(&jiffies_lock);
570                 last_update = last_jiffies_update;
571                 last_jiffies = jiffies;
572         } while (read_seqretry(&jiffies_lock, seq));
573 
574         if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) ||
575             arch_needs_cpu(cpu) || irq_work_needs_cpu()) {
576                 next_jiffies = last_jiffies + 1;
577                 delta_jiffies = 1;
578         } else {
579                 /* Get the next timer wheel timer */
580                 next_jiffies = get_next_timer_interrupt(last_jiffies);
581                 delta_jiffies = next_jiffies - last_jiffies;
582                 if (rcu_delta_jiffies < delta_jiffies) {
583                         next_jiffies = last_jiffies + rcu_delta_jiffies;
584                         delta_jiffies = rcu_delta_jiffies;
585                 }
586         }
587 
588         /*
589          * Do not stop the tick, if we are only one off (or less)
590          * or if the cpu is required for RCU:
591          */
592         if (!ts->tick_stopped && delta_jiffies <= 1)
593                 goto out;
594 
595         /* Schedule the tick, if we are at least one jiffie off */
596         if ((long)delta_jiffies >= 1) {
597 
598                 /*
599                  * If this cpu is the one which updates jiffies, then
600                  * give up the assignment and let it be taken by the
601                  * cpu which runs the tick timer next, which might be
602                  * this cpu as well. If we don't drop this here the
603                  * jiffies might be stale and do_timer() never
604                  * invoked. Keep track of the fact that it was the one
605                  * which had the do_timer() duty last. If this cpu is
606                  * the one which had the do_timer() duty last, we
607                  * limit the sleep time to the timekeeping
608                  * max_deferement value which we retrieved
609                  * above. Otherwise we can sleep as long as we want.
610                  */
611                 if (cpu == tick_do_timer_cpu) {
612                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
613                         ts->do_timer_last = 1;
614                 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
615                         time_delta = KTIME_MAX;
616                         ts->do_timer_last = 0;
617                 } else if (!ts->do_timer_last) {
618                         time_delta = KTIME_MAX;
619                 }
620 
621 #ifdef CONFIG_NO_HZ_FULL
622                 if (!ts->inidle) {
623                         time_delta = min(time_delta,
624                                          scheduler_tick_max_deferment());
625                 }
626 #endif
627 
628                 /*
629                  * calculate the expiry time for the next timer wheel
630                  * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
631                  * that there is no timer pending or at least extremely
632                  * far into the future (12 days for HZ=1000). In this
633                  * case we set the expiry to the end of time.
634                  */
635                 if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
636                         /*
637                          * Calculate the time delta for the next timer event.
638                          * If the time delta exceeds the maximum time delta
639                          * permitted by the current clocksource then adjust
640                          * the time delta accordingly to ensure the
641                          * clocksource does not wrap.
642                          */
643                         time_delta = min_t(u64, time_delta,
644                                            tick_period.tv64 * delta_jiffies);
645                 }
646 
647                 if (time_delta < KTIME_MAX)
648                         expires = ktime_add_ns(last_update, time_delta);
649                 else
650                         expires.tv64 = KTIME_MAX;
651 
652                 /* Skip reprogram of event if its not changed */
653                 if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
654                         goto out;
655 
656                 ret = expires;
657 
658                 /*
659                  * nohz_stop_sched_tick can be called several times before
660                  * the nohz_restart_sched_tick is called. This happens when
661                  * interrupts arrive which do not cause a reschedule. In the
662                  * first call we save the current tick time, so we can restart
663                  * the scheduler tick in nohz_restart_sched_tick.
664                  */
665                 if (!ts->tick_stopped) {
666                         nohz_balance_enter_idle(cpu);
667                         calc_load_enter_idle();
668 
669                         ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
670                         ts->tick_stopped = 1;
671                         trace_tick_stop(1, " ");
672                 }
673 
674                 /*
675                  * If the expiration time == KTIME_MAX, then
676                  * in this case we simply stop the tick timer.
677                  */
678                  if (unlikely(expires.tv64 == KTIME_MAX)) {
679                         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
680                                 hrtimer_cancel(&ts->sched_timer);
681                         goto out;
682                 }
683 
684                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
685                         hrtimer_start(&ts->sched_timer, expires,
686                                       HRTIMER_MODE_ABS_PINNED);
687                         /* Check, if the timer was already in the past */
688                         if (hrtimer_active(&ts->sched_timer))
689                                 goto out;
690                 } else if (!tick_program_event(expires, 0))
691                                 goto out;
692                 /*
693                  * We are past the event already. So we crossed a
694                  * jiffie boundary. Update jiffies and raise the
695                  * softirq.
696                  */
697                 tick_do_update_jiffies64(ktime_get());
698         }
699         raise_softirq_irqoff(TIMER_SOFTIRQ);
700 out:
701         ts->next_jiffies = next_jiffies;
702         ts->last_jiffies = last_jiffies;
703         ts->sleep_length = ktime_sub(dev->next_event, now);
704 
705         return ret;
706 }
707 
708 static void tick_nohz_full_stop_tick(struct tick_sched *ts)
709 {
710 #ifdef CONFIG_NO_HZ_FULL
711         int cpu = smp_processor_id();
712 
713         if (!tick_nohz_full_cpu(cpu) || is_idle_task(current))
714                 return;
715 
716         if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
717                 return;
718 
719         if (!can_stop_full_tick())
720                 return;
721 
722         tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
723 #endif
724 }
725 
726 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
727 {
728         /*
729          * If this cpu is offline and it is the one which updates
730          * jiffies, then give up the assignment and let it be taken by
731          * the cpu which runs the tick timer next. If we don't drop
732          * this here the jiffies might be stale and do_timer() never
733          * invoked.
734          */
735         if (unlikely(!cpu_online(cpu))) {
736                 if (cpu == tick_do_timer_cpu)
737                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
738                 return false;
739         }
740 
741         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
742                 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
743                 return false;
744         }
745 
746         if (need_resched())
747                 return false;
748 
749         if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
750                 static int ratelimit;
751 
752                 if (ratelimit < 10 &&
753                     (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
754                         pr_warn("NOHZ: local_softirq_pending %02x\n",
755                                 (unsigned int) local_softirq_pending());
756                         ratelimit++;
757                 }
758                 return false;
759         }
760 
761         if (tick_nohz_full_enabled()) {
762                 /*
763                  * Keep the tick alive to guarantee timekeeping progression
764                  * if there are full dynticks CPUs around
765                  */
766                 if (tick_do_timer_cpu == cpu)
767                         return false;
768                 /*
769                  * Boot safety: make sure the timekeeping duty has been
770                  * assigned before entering dyntick-idle mode,
771                  */
772                 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
773                         return false;
774         }
775 
776         return true;
777 }
778 
779 static void __tick_nohz_idle_enter(struct tick_sched *ts)
780 {
781         ktime_t now, expires;
782         int cpu = smp_processor_id();
783 
784         now = tick_nohz_start_idle(ts);
785 
786         if (can_stop_idle_tick(cpu, ts)) {
787                 int was_stopped = ts->tick_stopped;
788 
789                 ts->idle_calls++;
790 
791                 expires = tick_nohz_stop_sched_tick(ts, now, cpu);
792                 if (expires.tv64 > 0LL) {
793                         ts->idle_sleeps++;
794                         ts->idle_expires = expires;
795                 }
796 
797                 if (!was_stopped && ts->tick_stopped)
798                         ts->idle_jiffies = ts->last_jiffies;
799         }
800 }
801 
802 /**
803  * tick_nohz_idle_enter - stop the idle tick from the idle task
804  *
805  * When the next event is more than a tick into the future, stop the idle tick
806  * Called when we start the idle loop.
807  *
808  * The arch is responsible of calling:
809  *
810  * - rcu_idle_enter() after its last use of RCU before the CPU is put
811  *  to sleep.
812  * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
813  */
814 void tick_nohz_idle_enter(void)
815 {
816         struct tick_sched *ts;
817 
818         WARN_ON_ONCE(irqs_disabled());
819 
820         /*
821          * Update the idle state in the scheduler domain hierarchy
822          * when tick_nohz_stop_sched_tick() is called from the idle loop.
823          * State will be updated to busy during the first busy tick after
824          * exiting idle.
825          */
826         set_cpu_sd_state_idle();
827 
828         local_irq_disable();
829 
830         ts = &__get_cpu_var(tick_cpu_sched);
831         ts->inidle = 1;
832         __tick_nohz_idle_enter(ts);
833 
834         local_irq_enable();
835 }
836 EXPORT_SYMBOL_GPL(tick_nohz_idle_enter);
837 
838 /**
839  * tick_nohz_irq_exit - update next tick event from interrupt exit
840  *
841  * When an interrupt fires while we are idle and it doesn't cause
842  * a reschedule, it may still add, modify or delete a timer, enqueue
843  * an RCU callback, etc...
844  * So we need to re-calculate and reprogram the next tick event.
845  */
846 void tick_nohz_irq_exit(void)
847 {
848         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
849 
850         if (ts->inidle)
851                 __tick_nohz_idle_enter(ts);
852         else
853                 tick_nohz_full_stop_tick(ts);
854 }
855 
856 /**
857  * tick_nohz_get_sleep_length - return the length of the current sleep
858  *
859  * Called from power state control code with interrupts disabled
860  */
861 ktime_t tick_nohz_get_sleep_length(void)
862 {
863         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
864 
865         return ts->sleep_length;
866 }
867 
868 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
869 {
870         hrtimer_cancel(&ts->sched_timer);
871         hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
872 
873         while (1) {
874                 /* Forward the time to expire in the future */
875                 hrtimer_forward(&ts->sched_timer, now, tick_period);
876 
877                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
878                         hrtimer_start_expires(&ts->sched_timer,
879                                               HRTIMER_MODE_ABS_PINNED);
880                         /* Check, if the timer was already in the past */
881                         if (hrtimer_active(&ts->sched_timer))
882                                 break;
883                 } else {
884                         if (!tick_program_event(
885                                 hrtimer_get_expires(&ts->sched_timer), 0))
886                                 break;
887                 }
888                 /* Reread time and update jiffies */
889                 now = ktime_get();
890                 tick_do_update_jiffies64(now);
891         }
892 }
893 
894 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
895 {
896         /* Update jiffies first */
897         tick_do_update_jiffies64(now);
898         update_cpu_load_nohz();
899 
900         calc_load_exit_idle();
901         touch_softlockup_watchdog();
902         /*
903          * Cancel the scheduled timer and restore the tick
904          */
905         ts->tick_stopped  = 0;
906         ts->idle_exittime = now;
907 
908         tick_nohz_restart(ts, now);
909 }
910 
911 static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
912 {
913 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
914         unsigned long ticks;
915 
916         if (vtime_accounting_enabled())
917                 return;
918         /*
919          * We stopped the tick in idle. Update process times would miss the
920          * time we slept as update_process_times does only a 1 tick
921          * accounting. Enforce that this is accounted to idle !
922          */
923         ticks = jiffies - ts->idle_jiffies;
924         /*
925          * We might be one off. Do not randomly account a huge number of ticks!
926          */
927         if (ticks && ticks < LONG_MAX)
928                 account_idle_ticks(ticks);
929 #endif
930 }
931 
932 /**
933  * tick_nohz_idle_exit - restart the idle tick from the idle task
934  *
935  * Restart the idle tick when the CPU is woken up from idle
936  * This also exit the RCU extended quiescent state. The CPU
937  * can use RCU again after this function is called.
938  */
939 void tick_nohz_idle_exit(void)
940 {
941         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
942         ktime_t now;
943 
944         local_irq_disable();
945 
946         WARN_ON_ONCE(!ts->inidle);
947 
948         ts->inidle = 0;
949 
950         if (ts->idle_active || ts->tick_stopped)
951                 now = ktime_get();
952 
953         if (ts->idle_active)
954                 tick_nohz_stop_idle(ts, now);
955 
956         if (ts->tick_stopped) {
957                 tick_nohz_restart_sched_tick(ts, now);
958                 tick_nohz_account_idle_ticks(ts);
959         }
960 
961         local_irq_enable();
962 }
963 EXPORT_SYMBOL_GPL(tick_nohz_idle_exit);
964 
965 static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
966 {
967         hrtimer_forward(&ts->sched_timer, now, tick_period);
968         return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0);
969 }
970 
971 /*
972  * The nohz low res interrupt handler
973  */
974 static void tick_nohz_handler(struct clock_event_device *dev)
975 {
976         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
977         struct pt_regs *regs = get_irq_regs();
978         ktime_t now = ktime_get();
979 
980         dev->next_event.tv64 = KTIME_MAX;
981 
982         tick_sched_do_timer(now);
983         tick_sched_handle(ts, regs);
984 
985         while (tick_nohz_reprogram(ts, now)) {
986                 now = ktime_get();
987                 tick_do_update_jiffies64(now);
988         }
989 }
990 
991 /**
992  * tick_nohz_switch_to_nohz - switch to nohz mode
993  */
994 static void tick_nohz_switch_to_nohz(void)
995 {
996         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
997         ktime_t next;
998 
999         if (!tick_nohz_enabled)
1000                 return;
1001 
1002         local_irq_disable();
1003         if (tick_switch_to_oneshot(tick_nohz_handler)) {
1004                 local_irq_enable();
1005                 return;
1006         }
1007         tick_nohz_active = 1;
1008         ts->nohz_mode = NOHZ_MODE_LOWRES;
1009 
1010         /*
1011          * Recycle the hrtimer in ts, so we can share the
1012          * hrtimer_forward with the highres code.
1013          */
1014         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1015         /* Get the next period */
1016         next = tick_init_jiffy_update();
1017 
1018         for (;;) {
1019                 hrtimer_set_expires(&ts->sched_timer, next);
1020                 if (!tick_program_event(next, 0))
1021                         break;
1022                 next = ktime_add(next, tick_period);
1023         }
1024         local_irq_enable();
1025 }
1026 
1027 /*
1028  * When NOHZ is enabled and the tick is stopped, we need to kick the
1029  * tick timer from irq_enter() so that the jiffies update is kept
1030  * alive during long running softirqs. That's ugly as hell, but
1031  * correctness is key even if we need to fix the offending softirq in
1032  * the first place.
1033  *
1034  * Note, this is different to tick_nohz_restart. We just kick the
1035  * timer and do not touch the other magic bits which need to be done
1036  * when idle is left.
1037  */
1038 static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now)
1039 {
1040 #if 0
1041         /* Switch back to 2.6.27 behaviour */
1042         ktime_t delta;
1043 
1044         /*
1045          * Do not touch the tick device, when the next expiry is either
1046          * already reached or less/equal than the tick period.
1047          */
1048         delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
1049         if (delta.tv64 <= tick_period.tv64)
1050                 return;
1051 
1052         tick_nohz_restart(ts, now);
1053 #endif
1054 }
1055 
1056 static inline void tick_nohz_irq_enter(void)
1057 {
1058         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1059         ktime_t now;
1060 
1061         if (!ts->idle_active && !ts->tick_stopped)
1062                 return;
1063         now = ktime_get();
1064         if (ts->idle_active)
1065                 tick_nohz_stop_idle(ts, now);
1066         if (ts->tick_stopped) {
1067                 tick_nohz_update_jiffies(now);
1068                 tick_nohz_kick_tick(ts, now);
1069         }
1070 }
1071 
1072 #else
1073 
1074 static inline void tick_nohz_switch_to_nohz(void) { }
1075 static inline void tick_nohz_irq_enter(void) { }
1076 
1077 #endif /* CONFIG_NO_HZ_COMMON */
1078 
1079 /*
1080  * Called from irq_enter to notify about the possible interruption of idle()
1081  */
1082 void tick_irq_enter(void)
1083 {
1084         tick_check_oneshot_broadcast_this_cpu();
1085         tick_nohz_irq_enter();
1086 }
1087 
1088 /*
1089  * High resolution timer specific code
1090  */
1091 #ifdef CONFIG_HIGH_RES_TIMERS
1092 /*
1093  * We rearm the timer until we get disabled by the idle code.
1094  * Called with interrupts disabled.
1095  */
1096 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1097 {
1098         struct tick_sched *ts =
1099                 container_of(timer, struct tick_sched, sched_timer);
1100         struct pt_regs *regs = get_irq_regs();
1101         ktime_t now = ktime_get();
1102 
1103         tick_sched_do_timer(now);
1104 
1105         /*
1106          * Do not call, when we are not in irq context and have
1107          * no valid regs pointer
1108          */
1109         if (regs)
1110                 tick_sched_handle(ts, regs);
1111 
1112         hrtimer_forward(timer, now, tick_period);
1113 
1114         return HRTIMER_RESTART;
1115 }
1116 
1117 static int sched_skew_tick;
1118 
1119 static int __init skew_tick(char *str)
1120 {
1121         get_option(&str, &sched_skew_tick);
1122 
1123         return 0;
1124 }
1125 early_param("skew_tick", skew_tick);
1126 
1127 /**
1128  * tick_setup_sched_timer - setup the tick emulation timer
1129  */
1130 void tick_setup_sched_timer(void)
1131 {
1132         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1133         ktime_t now = ktime_get();
1134 
1135         /*
1136          * Emulate tick processing via per-CPU hrtimers:
1137          */
1138         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1139         ts->sched_timer.function = tick_sched_timer;
1140 
1141         /* Get the next period (per cpu) */
1142         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1143 
1144         /* Offset the tick to avert jiffies_lock contention. */
1145         if (sched_skew_tick) {
1146                 u64 offset = ktime_to_ns(tick_period) >> 1;
1147                 do_div(offset, num_possible_cpus());
1148                 offset *= smp_processor_id();
1149                 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1150         }
1151 
1152         for (;;) {
1153                 hrtimer_forward(&ts->sched_timer, now, tick_period);
1154                 hrtimer_start_expires(&ts->sched_timer,
1155                                       HRTIMER_MODE_ABS_PINNED);
1156                 /* Check, if the timer was already in the past */
1157                 if (hrtimer_active(&ts->sched_timer))
1158                         break;
1159                 now = ktime_get();
1160         }
1161 
1162 #ifdef CONFIG_NO_HZ_COMMON
1163         if (tick_nohz_enabled) {
1164                 ts->nohz_mode = NOHZ_MODE_HIGHRES;
1165                 tick_nohz_active = 1;
1166         }
1167 #endif
1168 }
1169 #endif /* HIGH_RES_TIMERS */
1170 
1171 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1172 void tick_cancel_sched_timer(int cpu)
1173 {
1174         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1175 
1176 # ifdef CONFIG_HIGH_RES_TIMERS
1177         if (ts->sched_timer.base)
1178                 hrtimer_cancel(&ts->sched_timer);
1179 # endif
1180 
1181         memset(ts, 0, sizeof(*ts));
1182 }
1183 #endif
1184 
1185 /**
1186  * Async notification about clocksource changes
1187  */
1188 void tick_clock_notify(void)
1189 {
1190         int cpu;
1191 
1192         for_each_possible_cpu(cpu)
1193                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1194 }
1195 
1196 /*
1197  * Async notification about clock event changes
1198  */
1199 void tick_oneshot_notify(void)
1200 {
1201         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1202 
1203         set_bit(0, &ts->check_clocks);
1204 }
1205 
1206 /**
1207  * Check, if a change happened, which makes oneshot possible.
1208  *
1209  * Called cyclic from the hrtimer softirq (driven by the timer
1210  * softirq) allow_nohz signals, that we can switch into low-res nohz
1211  * mode, because high resolution timers are disabled (either compile
1212  * or runtime).
1213  */
1214 int tick_check_oneshot_change(int allow_nohz)
1215 {
1216         struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
1217 
1218         if (!test_and_clear_bit(0, &ts->check_clocks))
1219                 return 0;
1220 
1221         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1222                 return 0;
1223 
1224         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1225                 return 0;
1226 
1227         if (!allow_nohz)
1228                 return 1;
1229 
1230         tick_nohz_switch_to_nohz();
1231         return 0;
1232 }
1233 

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