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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 = this_cpu_ptr(&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         alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
299         if (cpulist_parse(str, tick_nohz_full_mask) < 0) {
300                 pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
301                 free_bootmem_cpumask_var(tick_nohz_full_mask);
302                 return 1;
303         }
304         tick_nohz_full_running = true;
305 
306         return 1;
307 }
308 __setup("nohz_full=", tick_nohz_full_setup);
309 
310 static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,
311                                                  unsigned long action,
312                                                  void *hcpu)
313 {
314         unsigned int cpu = (unsigned long)hcpu;
315 
316         switch (action & ~CPU_TASKS_FROZEN) {
317         case CPU_DOWN_PREPARE:
318                 /*
319                  * If we handle the timekeeping duty for full dynticks CPUs,
320                  * we can't safely shutdown that CPU.
321                  */
322                 if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
323                         return NOTIFY_BAD;
324                 break;
325         }
326         return NOTIFY_OK;
327 }
328 
329 /*
330  * Worst case string length in chunks of CPU range seems 2 steps
331  * separations: 0,2,4,6,...
332  * This is NR_CPUS + sizeof('\0')
333  */
334 static char __initdata nohz_full_buf[NR_CPUS + 1];
335 
336 static int tick_nohz_init_all(void)
337 {
338         int err = -1;
339 
340 #ifdef CONFIG_NO_HZ_FULL_ALL
341         if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
342                 WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n");
343                 return err;
344         }
345         err = 0;
346         cpumask_setall(tick_nohz_full_mask);
347         tick_nohz_full_running = true;
348 #endif
349         return err;
350 }
351 
352 void __init tick_nohz_init(void)
353 {
354         int cpu;
355 
356         if (!tick_nohz_full_running) {
357                 if (tick_nohz_init_all() < 0)
358                         return;
359         }
360 
361         if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) {
362                 WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n");
363                 cpumask_clear(tick_nohz_full_mask);
364                 tick_nohz_full_running = false;
365                 return;
366         }
367 
368         /*
369          * Full dynticks uses irq work to drive the tick rescheduling on safe
370          * locking contexts. But then we need irq work to raise its own
371          * interrupts to avoid circular dependency on the tick
372          */
373         if (!arch_irq_work_has_interrupt()) {
374                 pr_warning("NO_HZ: Can't run full dynticks because arch doesn't "
375                            "support irq work self-IPIs\n");
376                 cpumask_clear(tick_nohz_full_mask);
377                 cpumask_copy(housekeeping_mask, cpu_possible_mask);
378                 tick_nohz_full_running = false;
379                 return;
380         }
381 
382         cpu = smp_processor_id();
383 
384         if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
385                 pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu);
386                 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
387         }
388 
389         cpumask_andnot(housekeeping_mask,
390                        cpu_possible_mask, tick_nohz_full_mask);
391 
392         for_each_cpu(cpu, tick_nohz_full_mask)
393                 context_tracking_cpu_set(cpu);
394 
395         cpu_notifier(tick_nohz_cpu_down_callback, 0);
396         cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), tick_nohz_full_mask);
397         pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf);
398 }
399 #endif
400 
401 /*
402  * NOHZ - aka dynamic tick functionality
403  */
404 #ifdef CONFIG_NO_HZ_COMMON
405 /*
406  * NO HZ enabled ?
407  */
408 static int tick_nohz_enabled __read_mostly  = 1;
409 int tick_nohz_active  __read_mostly;
410 /*
411  * Enable / Disable tickless mode
412  */
413 static int __init setup_tick_nohz(char *str)
414 {
415         if (!strcmp(str, "off"))
416                 tick_nohz_enabled = 0;
417         else if (!strcmp(str, "on"))
418                 tick_nohz_enabled = 1;
419         else
420                 return 0;
421         return 1;
422 }
423 
424 __setup("nohz=", setup_tick_nohz);
425 
426 /**
427  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
428  *
429  * Called from interrupt entry when the CPU was idle
430  *
431  * In case the sched_tick was stopped on this CPU, we have to check if jiffies
432  * must be updated. Otherwise an interrupt handler could use a stale jiffy
433  * value. We do this unconditionally on any cpu, as we don't know whether the
434  * cpu, which has the update task assigned is in a long sleep.
435  */
436 static void tick_nohz_update_jiffies(ktime_t now)
437 {
438         unsigned long flags;
439 
440         __this_cpu_write(tick_cpu_sched.idle_waketime, now);
441 
442         local_irq_save(flags);
443         tick_do_update_jiffies64(now);
444         local_irq_restore(flags);
445 
446         touch_softlockup_watchdog();
447 }
448 
449 /*
450  * Updates the per cpu time idle statistics counters
451  */
452 static void
453 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
454 {
455         ktime_t delta;
456 
457         if (ts->idle_active) {
458                 delta = ktime_sub(now, ts->idle_entrytime);
459                 if (nr_iowait_cpu(cpu) > 0)
460                         ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
461                 else
462                         ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
463                 ts->idle_entrytime = now;
464         }
465 
466         if (last_update_time)
467                 *last_update_time = ktime_to_us(now);
468 
469 }
470 
471 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
472 {
473         update_ts_time_stats(smp_processor_id(), ts, now, NULL);
474         ts->idle_active = 0;
475 
476         sched_clock_idle_wakeup_event(0);
477 }
478 
479 static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
480 {
481         ktime_t now = ktime_get();
482 
483         ts->idle_entrytime = now;
484         ts->idle_active = 1;
485         sched_clock_idle_sleep_event();
486         return now;
487 }
488 
489 /**
490  * get_cpu_idle_time_us - get the total idle time of a cpu
491  * @cpu: CPU number to query
492  * @last_update_time: variable to store update time in. Do not update
493  * counters if NULL.
494  *
495  * Return the cummulative idle time (since boot) for a given
496  * CPU, in microseconds.
497  *
498  * This time is measured via accounting rather than sampling,
499  * and is as accurate as ktime_get() is.
500  *
501  * This function returns -1 if NOHZ is not enabled.
502  */
503 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
504 {
505         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
506         ktime_t now, idle;
507 
508         if (!tick_nohz_active)
509                 return -1;
510 
511         now = ktime_get();
512         if (last_update_time) {
513                 update_ts_time_stats(cpu, ts, now, last_update_time);
514                 idle = ts->idle_sleeptime;
515         } else {
516                 if (ts->idle_active && !nr_iowait_cpu(cpu)) {
517                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
518 
519                         idle = ktime_add(ts->idle_sleeptime, delta);
520                 } else {
521                         idle = ts->idle_sleeptime;
522                 }
523         }
524 
525         return ktime_to_us(idle);
526 
527 }
528 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
529 
530 /**
531  * get_cpu_iowait_time_us - get the total iowait time of a cpu
532  * @cpu: CPU number to query
533  * @last_update_time: variable to store update time in. Do not update
534  * counters if NULL.
535  *
536  * Return the cummulative iowait time (since boot) for a given
537  * CPU, in microseconds.
538  *
539  * This time is measured via accounting rather than sampling,
540  * and is as accurate as ktime_get() is.
541  *
542  * This function returns -1 if NOHZ is not enabled.
543  */
544 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
545 {
546         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
547         ktime_t now, iowait;
548 
549         if (!tick_nohz_active)
550                 return -1;
551 
552         now = ktime_get();
553         if (last_update_time) {
554                 update_ts_time_stats(cpu, ts, now, last_update_time);
555                 iowait = ts->iowait_sleeptime;
556         } else {
557                 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
558                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
559 
560                         iowait = ktime_add(ts->iowait_sleeptime, delta);
561                 } else {
562                         iowait = ts->iowait_sleeptime;
563                 }
564         }
565 
566         return ktime_to_us(iowait);
567 }
568 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
569 
570 static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
571                                          ktime_t now, int cpu)
572 {
573         unsigned long seq, last_jiffies, next_jiffies, delta_jiffies;
574         ktime_t last_update, expires, ret = { .tv64 = 0 };
575         unsigned long rcu_delta_jiffies;
576         struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
577         u64 time_delta;
578 
579         time_delta = timekeeping_max_deferment();
580 
581         /* Read jiffies and the time when jiffies were updated last */
582         do {
583                 seq = read_seqbegin(&jiffies_lock);
584                 last_update = last_jiffies_update;
585                 last_jiffies = jiffies;
586         } while (read_seqretry(&jiffies_lock, seq));
587 
588         if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) ||
589             arch_needs_cpu() || irq_work_needs_cpu()) {
590                 next_jiffies = last_jiffies + 1;
591                 delta_jiffies = 1;
592         } else {
593                 /* Get the next timer wheel timer */
594                 next_jiffies = get_next_timer_interrupt(last_jiffies);
595                 delta_jiffies = next_jiffies - last_jiffies;
596                 if (rcu_delta_jiffies < delta_jiffies) {
597                         next_jiffies = last_jiffies + rcu_delta_jiffies;
598                         delta_jiffies = rcu_delta_jiffies;
599                 }
600         }
601 
602         /*
603          * Do not stop the tick, if we are only one off (or less)
604          * or if the cpu is required for RCU:
605          */
606         if (!ts->tick_stopped && delta_jiffies <= 1)
607                 goto out;
608 
609         /* Schedule the tick, if we are at least one jiffie off */
610         if ((long)delta_jiffies >= 1) {
611 
612                 /*
613                  * If this cpu is the one which updates jiffies, then
614                  * give up the assignment and let it be taken by the
615                  * cpu which runs the tick timer next, which might be
616                  * this cpu as well. If we don't drop this here the
617                  * jiffies might be stale and do_timer() never
618                  * invoked. Keep track of the fact that it was the one
619                  * which had the do_timer() duty last. If this cpu is
620                  * the one which had the do_timer() duty last, we
621                  * limit the sleep time to the timekeeping
622                  * max_deferement value which we retrieved
623                  * above. Otherwise we can sleep as long as we want.
624                  */
625                 if (cpu == tick_do_timer_cpu) {
626                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
627                         ts->do_timer_last = 1;
628                 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
629                         time_delta = KTIME_MAX;
630                         ts->do_timer_last = 0;
631                 } else if (!ts->do_timer_last) {
632                         time_delta = KTIME_MAX;
633                 }
634 
635 #ifdef CONFIG_NO_HZ_FULL
636                 if (!ts->inidle) {
637                         time_delta = min(time_delta,
638                                          scheduler_tick_max_deferment());
639                 }
640 #endif
641 
642                 /*
643                  * calculate the expiry time for the next timer wheel
644                  * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals
645                  * that there is no timer pending or at least extremely
646                  * far into the future (12 days for HZ=1000). In this
647                  * case we set the expiry to the end of time.
648                  */
649                 if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) {
650                         /*
651                          * Calculate the time delta for the next timer event.
652                          * If the time delta exceeds the maximum time delta
653                          * permitted by the current clocksource then adjust
654                          * the time delta accordingly to ensure the
655                          * clocksource does not wrap.
656                          */
657                         time_delta = min_t(u64, time_delta,
658                                            tick_period.tv64 * delta_jiffies);
659                 }
660 
661                 if (time_delta < KTIME_MAX)
662                         expires = ktime_add_ns(last_update, time_delta);
663                 else
664                         expires.tv64 = KTIME_MAX;
665 
666                 /* Skip reprogram of event if its not changed */
667                 if (ts->tick_stopped && ktime_equal(expires, dev->next_event))
668                         goto out;
669 
670                 ret = expires;
671 
672                 /*
673                  * nohz_stop_sched_tick can be called several times before
674                  * the nohz_restart_sched_tick is called. This happens when
675                  * interrupts arrive which do not cause a reschedule. In the
676                  * first call we save the current tick time, so we can restart
677                  * the scheduler tick in nohz_restart_sched_tick.
678                  */
679                 if (!ts->tick_stopped) {
680                         nohz_balance_enter_idle(cpu);
681                         calc_load_enter_idle();
682 
683                         ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
684                         ts->tick_stopped = 1;
685                         trace_tick_stop(1, " ");
686                 }
687 
688                 /*
689                  * If the expiration time == KTIME_MAX, then
690                  * in this case we simply stop the tick timer.
691                  */
692                  if (unlikely(expires.tv64 == KTIME_MAX)) {
693                         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
694                                 hrtimer_cancel(&ts->sched_timer);
695                         goto out;
696                 }
697 
698                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
699                         hrtimer_start(&ts->sched_timer, expires,
700                                       HRTIMER_MODE_ABS_PINNED);
701                         /* Check, if the timer was already in the past */
702                         if (hrtimer_active(&ts->sched_timer))
703                                 goto out;
704                 } else if (!tick_program_event(expires, 0))
705                                 goto out;
706                 /*
707                  * We are past the event already. So we crossed a
708                  * jiffie boundary. Update jiffies and raise the
709                  * softirq.
710                  */
711                 tick_do_update_jiffies64(ktime_get());
712         }
713         raise_softirq_irqoff(TIMER_SOFTIRQ);
714 out:
715         ts->next_jiffies = next_jiffies;
716         ts->last_jiffies = last_jiffies;
717         ts->sleep_length = ktime_sub(dev->next_event, now);
718 
719         return ret;
720 }
721 
722 static void tick_nohz_full_stop_tick(struct tick_sched *ts)
723 {
724 #ifdef CONFIG_NO_HZ_FULL
725         int cpu = smp_processor_id();
726 
727         if (!tick_nohz_full_cpu(cpu) || is_idle_task(current))
728                 return;
729 
730         if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
731                 return;
732 
733         if (!can_stop_full_tick())
734                 return;
735 
736         tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
737 #endif
738 }
739 
740 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
741 {
742         /*
743          * If this cpu is offline and it is the one which updates
744          * jiffies, then give up the assignment and let it be taken by
745          * the cpu which runs the tick timer next. If we don't drop
746          * this here the jiffies might be stale and do_timer() never
747          * invoked.
748          */
749         if (unlikely(!cpu_online(cpu))) {
750                 if (cpu == tick_do_timer_cpu)
751                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
752                 return false;
753         }
754 
755         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
756                 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
757                 return false;
758         }
759 
760         if (need_resched())
761                 return false;
762 
763         if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
764                 static int ratelimit;
765 
766                 if (ratelimit < 10 &&
767                     (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
768                         pr_warn("NOHZ: local_softirq_pending %02x\n",
769                                 (unsigned int) local_softirq_pending());
770                         ratelimit++;
771                 }
772                 return false;
773         }
774 
775         if (tick_nohz_full_enabled()) {
776                 /*
777                  * Keep the tick alive to guarantee timekeeping progression
778                  * if there are full dynticks CPUs around
779                  */
780                 if (tick_do_timer_cpu == cpu)
781                         return false;
782                 /*
783                  * Boot safety: make sure the timekeeping duty has been
784                  * assigned before entering dyntick-idle mode,
785                  */
786                 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
787                         return false;
788         }
789 
790         return true;
791 }
792 
793 static void __tick_nohz_idle_enter(struct tick_sched *ts)
794 {
795         ktime_t now, expires;
796         int cpu = smp_processor_id();
797 
798         now = tick_nohz_start_idle(ts);
799 
800         if (can_stop_idle_tick(cpu, ts)) {
801                 int was_stopped = ts->tick_stopped;
802 
803                 ts->idle_calls++;
804 
805                 expires = tick_nohz_stop_sched_tick(ts, now, cpu);
806                 if (expires.tv64 > 0LL) {
807                         ts->idle_sleeps++;
808                         ts->idle_expires = expires;
809                 }
810 
811                 if (!was_stopped && ts->tick_stopped)
812                         ts->idle_jiffies = ts->last_jiffies;
813         }
814 }
815 
816 /**
817  * tick_nohz_idle_enter - stop the idle tick from the idle task
818  *
819  * When the next event is more than a tick into the future, stop the idle tick
820  * Called when we start the idle loop.
821  *
822  * The arch is responsible of calling:
823  *
824  * - rcu_idle_enter() after its last use of RCU before the CPU is put
825  *  to sleep.
826  * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
827  */
828 void tick_nohz_idle_enter(void)
829 {
830         struct tick_sched *ts;
831 
832         WARN_ON_ONCE(irqs_disabled());
833 
834         /*
835          * Update the idle state in the scheduler domain hierarchy
836          * when tick_nohz_stop_sched_tick() is called from the idle loop.
837          * State will be updated to busy during the first busy tick after
838          * exiting idle.
839          */
840         set_cpu_sd_state_idle();
841 
842         local_irq_disable();
843 
844         ts = this_cpu_ptr(&tick_cpu_sched);
845         ts->inidle = 1;
846         __tick_nohz_idle_enter(ts);
847 
848         local_irq_enable();
849 }
850 EXPORT_SYMBOL_GPL(tick_nohz_idle_enter);
851 
852 /**
853  * tick_nohz_irq_exit - update next tick event from interrupt exit
854  *
855  * When an interrupt fires while we are idle and it doesn't cause
856  * a reschedule, it may still add, modify or delete a timer, enqueue
857  * an RCU callback, etc...
858  * So we need to re-calculate and reprogram the next tick event.
859  */
860 void tick_nohz_irq_exit(void)
861 {
862         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
863 
864         if (ts->inidle)
865                 __tick_nohz_idle_enter(ts);
866         else
867                 tick_nohz_full_stop_tick(ts);
868 }
869 
870 /**
871  * tick_nohz_get_sleep_length - return the length of the current sleep
872  *
873  * Called from power state control code with interrupts disabled
874  */
875 ktime_t tick_nohz_get_sleep_length(void)
876 {
877         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
878 
879         return ts->sleep_length;
880 }
881 
882 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
883 {
884         hrtimer_cancel(&ts->sched_timer);
885         hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
886 
887         while (1) {
888                 /* Forward the time to expire in the future */
889                 hrtimer_forward(&ts->sched_timer, now, tick_period);
890 
891                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {
892                         hrtimer_start_expires(&ts->sched_timer,
893                                               HRTIMER_MODE_ABS_PINNED);
894                         /* Check, if the timer was already in the past */
895                         if (hrtimer_active(&ts->sched_timer))
896                                 break;
897                 } else {
898                         if (!tick_program_event(
899                                 hrtimer_get_expires(&ts->sched_timer), 0))
900                                 break;
901                 }
902                 /* Reread time and update jiffies */
903                 now = ktime_get();
904                 tick_do_update_jiffies64(now);
905         }
906 }
907 
908 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
909 {
910         /* Update jiffies first */
911         tick_do_update_jiffies64(now);
912         update_cpu_load_nohz();
913 
914         calc_load_exit_idle();
915         touch_softlockup_watchdog();
916         /*
917          * Cancel the scheduled timer and restore the tick
918          */
919         ts->tick_stopped  = 0;
920         ts->idle_exittime = now;
921 
922         tick_nohz_restart(ts, now);
923 }
924 
925 static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
926 {
927 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
928         unsigned long ticks;
929 
930         if (vtime_accounting_enabled())
931                 return;
932         /*
933          * We stopped the tick in idle. Update process times would miss the
934          * time we slept as update_process_times does only a 1 tick
935          * accounting. Enforce that this is accounted to idle !
936          */
937         ticks = jiffies - ts->idle_jiffies;
938         /*
939          * We might be one off. Do not randomly account a huge number of ticks!
940          */
941         if (ticks && ticks < LONG_MAX)
942                 account_idle_ticks(ticks);
943 #endif
944 }
945 
946 /**
947  * tick_nohz_idle_exit - restart the idle tick from the idle task
948  *
949  * Restart the idle tick when the CPU is woken up from idle
950  * This also exit the RCU extended quiescent state. The CPU
951  * can use RCU again after this function is called.
952  */
953 void tick_nohz_idle_exit(void)
954 {
955         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
956         ktime_t now;
957 
958         local_irq_disable();
959 
960         WARN_ON_ONCE(!ts->inidle);
961 
962         ts->inidle = 0;
963 
964         if (ts->idle_active || ts->tick_stopped)
965                 now = ktime_get();
966 
967         if (ts->idle_active)
968                 tick_nohz_stop_idle(ts, now);
969 
970         if (ts->tick_stopped) {
971                 tick_nohz_restart_sched_tick(ts, now);
972                 tick_nohz_account_idle_ticks(ts);
973         }
974 
975         local_irq_enable();
976 }
977 EXPORT_SYMBOL_GPL(tick_nohz_idle_exit);
978 
979 static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now)
980 {
981         hrtimer_forward(&ts->sched_timer, now, tick_period);
982         return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0);
983 }
984 
985 /*
986  * The nohz low res interrupt handler
987  */
988 static void tick_nohz_handler(struct clock_event_device *dev)
989 {
990         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
991         struct pt_regs *regs = get_irq_regs();
992         ktime_t now = ktime_get();
993 
994         dev->next_event.tv64 = KTIME_MAX;
995 
996         tick_sched_do_timer(now);
997         tick_sched_handle(ts, regs);
998 
999         /* No need to reprogram if we are running tickless  */
1000         if (unlikely(ts->tick_stopped))
1001                 return;
1002 
1003         while (tick_nohz_reprogram(ts, now)) {
1004                 now = ktime_get();
1005                 tick_do_update_jiffies64(now);
1006         }
1007 }
1008 
1009 /**
1010  * tick_nohz_switch_to_nohz - switch to nohz mode
1011  */
1012 static void tick_nohz_switch_to_nohz(void)
1013 {
1014         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1015         ktime_t next;
1016 
1017         if (!tick_nohz_enabled)
1018                 return;
1019 
1020         local_irq_disable();
1021         if (tick_switch_to_oneshot(tick_nohz_handler)) {
1022                 local_irq_enable();
1023                 return;
1024         }
1025         tick_nohz_active = 1;
1026         ts->nohz_mode = NOHZ_MODE_LOWRES;
1027 
1028         /*
1029          * Recycle the hrtimer in ts, so we can share the
1030          * hrtimer_forward with the highres code.
1031          */
1032         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1033         /* Get the next period */
1034         next = tick_init_jiffy_update();
1035 
1036         for (;;) {
1037                 hrtimer_set_expires(&ts->sched_timer, next);
1038                 if (!tick_program_event(next, 0))
1039                         break;
1040                 next = ktime_add(next, tick_period);
1041         }
1042         local_irq_enable();
1043 }
1044 
1045 /*
1046  * When NOHZ is enabled and the tick is stopped, we need to kick the
1047  * tick timer from irq_enter() so that the jiffies update is kept
1048  * alive during long running softirqs. That's ugly as hell, but
1049  * correctness is key even if we need to fix the offending softirq in
1050  * the first place.
1051  *
1052  * Note, this is different to tick_nohz_restart. We just kick the
1053  * timer and do not touch the other magic bits which need to be done
1054  * when idle is left.
1055  */
1056 static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now)
1057 {
1058 #if 0
1059         /* Switch back to 2.6.27 behaviour */
1060         ktime_t delta;
1061 
1062         /*
1063          * Do not touch the tick device, when the next expiry is either
1064          * already reached or less/equal than the tick period.
1065          */
1066         delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
1067         if (delta.tv64 <= tick_period.tv64)
1068                 return;
1069 
1070         tick_nohz_restart(ts, now);
1071 #endif
1072 }
1073 
1074 static inline void tick_nohz_irq_enter(void)
1075 {
1076         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1077         ktime_t now;
1078 
1079         if (!ts->idle_active && !ts->tick_stopped)
1080                 return;
1081         now = ktime_get();
1082         if (ts->idle_active)
1083                 tick_nohz_stop_idle(ts, now);
1084         if (ts->tick_stopped) {
1085                 tick_nohz_update_jiffies(now);
1086                 tick_nohz_kick_tick(ts, now);
1087         }
1088 }
1089 
1090 #else
1091 
1092 static inline void tick_nohz_switch_to_nohz(void) { }
1093 static inline void tick_nohz_irq_enter(void) { }
1094 
1095 #endif /* CONFIG_NO_HZ_COMMON */
1096 
1097 /*
1098  * Called from irq_enter to notify about the possible interruption of idle()
1099  */
1100 void tick_irq_enter(void)
1101 {
1102         tick_check_oneshot_broadcast_this_cpu();
1103         tick_nohz_irq_enter();
1104 }
1105 
1106 /*
1107  * High resolution timer specific code
1108  */
1109 #ifdef CONFIG_HIGH_RES_TIMERS
1110 /*
1111  * We rearm the timer until we get disabled by the idle code.
1112  * Called with interrupts disabled.
1113  */
1114 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1115 {
1116         struct tick_sched *ts =
1117                 container_of(timer, struct tick_sched, sched_timer);
1118         struct pt_regs *regs = get_irq_regs();
1119         ktime_t now = ktime_get();
1120 
1121         tick_sched_do_timer(now);
1122 
1123         /*
1124          * Do not call, when we are not in irq context and have
1125          * no valid regs pointer
1126          */
1127         if (regs)
1128                 tick_sched_handle(ts, regs);
1129 
1130         /* No need to reprogram if we are in idle or full dynticks mode */
1131         if (unlikely(ts->tick_stopped))
1132                 return HRTIMER_NORESTART;
1133 
1134         hrtimer_forward(timer, now, tick_period);
1135 
1136         return HRTIMER_RESTART;
1137 }
1138 
1139 static int sched_skew_tick;
1140 
1141 static int __init skew_tick(char *str)
1142 {
1143         get_option(&str, &sched_skew_tick);
1144 
1145         return 0;
1146 }
1147 early_param("skew_tick", skew_tick);
1148 
1149 /**
1150  * tick_setup_sched_timer - setup the tick emulation timer
1151  */
1152 void tick_setup_sched_timer(void)
1153 {
1154         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1155         ktime_t now = ktime_get();
1156 
1157         /*
1158          * Emulate tick processing via per-CPU hrtimers:
1159          */
1160         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1161         ts->sched_timer.function = tick_sched_timer;
1162 
1163         /* Get the next period (per cpu) */
1164         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1165 
1166         /* Offset the tick to avert jiffies_lock contention. */
1167         if (sched_skew_tick) {
1168                 u64 offset = ktime_to_ns(tick_period) >> 1;
1169                 do_div(offset, num_possible_cpus());
1170                 offset *= smp_processor_id();
1171                 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1172         }
1173 
1174         for (;;) {
1175                 hrtimer_forward(&ts->sched_timer, now, tick_period);
1176                 hrtimer_start_expires(&ts->sched_timer,
1177                                       HRTIMER_MODE_ABS_PINNED);
1178                 /* Check, if the timer was already in the past */
1179                 if (hrtimer_active(&ts->sched_timer))
1180                         break;
1181                 now = ktime_get();
1182         }
1183 
1184 #ifdef CONFIG_NO_HZ_COMMON
1185         if (tick_nohz_enabled) {
1186                 ts->nohz_mode = NOHZ_MODE_HIGHRES;
1187                 tick_nohz_active = 1;
1188         }
1189 #endif
1190 }
1191 #endif /* HIGH_RES_TIMERS */
1192 
1193 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1194 void tick_cancel_sched_timer(int cpu)
1195 {
1196         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1197 
1198 # ifdef CONFIG_HIGH_RES_TIMERS
1199         if (ts->sched_timer.base)
1200                 hrtimer_cancel(&ts->sched_timer);
1201 # endif
1202 
1203         memset(ts, 0, sizeof(*ts));
1204 }
1205 #endif
1206 
1207 /**
1208  * Async notification about clocksource changes
1209  */
1210 void tick_clock_notify(void)
1211 {
1212         int cpu;
1213 
1214         for_each_possible_cpu(cpu)
1215                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1216 }
1217 
1218 /*
1219  * Async notification about clock event changes
1220  */
1221 void tick_oneshot_notify(void)
1222 {
1223         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1224 
1225         set_bit(0, &ts->check_clocks);
1226 }
1227 
1228 /**
1229  * Check, if a change happened, which makes oneshot possible.
1230  *
1231  * Called cyclic from the hrtimer softirq (driven by the timer
1232  * softirq) allow_nohz signals, that we can switch into low-res nohz
1233  * mode, because high resolution timers are disabled (either compile
1234  * or runtime).
1235  */
1236 int tick_check_oneshot_change(int allow_nohz)
1237 {
1238         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1239 
1240         if (!test_and_clear_bit(0, &ts->check_clocks))
1241                 return 0;
1242 
1243         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1244                 return 0;
1245 
1246         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1247                 return 0;
1248 
1249         if (!allow_nohz)
1250                 return 1;
1251 
1252         tick_nohz_switch_to_nohz();
1253         return 0;
1254 }
1255 

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