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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/context_tracking.h>
 26 
 27 #include <asm/irq_regs.h>
 28 
 29 #include "tick-internal.h"
 30 
 31 #include <trace/events/timer.h>
 32 
 33 /*
 34  * Per cpu nohz control structure
 35  */
 36 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched);
 37 
 38 struct tick_sched *tick_get_tick_sched(int cpu)
 39 {
 40         return &per_cpu(tick_cpu_sched, cpu);
 41 }
 42 
 43 #if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)
 44 /*
 45  * The time, when the last jiffy update happened. Protected by jiffies_lock.
 46  */
 47 static ktime_t last_jiffies_update;
 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_sched();
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 #endif
155 
156 #ifdef CONFIG_NO_HZ_FULL
157 cpumask_var_t tick_nohz_full_mask;
158 cpumask_var_t housekeeping_mask;
159 bool tick_nohz_full_running;
160 static atomic_t tick_dep_mask;
161 
162 static bool check_tick_dependency(atomic_t *dep)
163 {
164         int val = atomic_read(dep);
165 
166         if (val & TICK_DEP_MASK_POSIX_TIMER) {
167                 trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER);
168                 return true;
169         }
170 
171         if (val & TICK_DEP_MASK_PERF_EVENTS) {
172                 trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS);
173                 return true;
174         }
175 
176         if (val & TICK_DEP_MASK_SCHED) {
177                 trace_tick_stop(0, TICK_DEP_MASK_SCHED);
178                 return true;
179         }
180 
181         if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) {
182                 trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE);
183                 return true;
184         }
185 
186         return false;
187 }
188 
189 static bool can_stop_full_tick(struct tick_sched *ts)
190 {
191         WARN_ON_ONCE(!irqs_disabled());
192 
193         if (check_tick_dependency(&tick_dep_mask))
194                 return false;
195 
196         if (check_tick_dependency(&ts->tick_dep_mask))
197                 return false;
198 
199         if (check_tick_dependency(&current->tick_dep_mask))
200                 return false;
201 
202         if (check_tick_dependency(&current->signal->tick_dep_mask))
203                 return false;
204 
205         return true;
206 }
207 
208 static void nohz_full_kick_func(struct irq_work *work)
209 {
210         /* Empty, the tick restart happens on tick_nohz_irq_exit() */
211 }
212 
213 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
214         .func = nohz_full_kick_func,
215 };
216 
217 /*
218  * Kick this CPU if it's full dynticks in order to force it to
219  * re-evaluate its dependency on the tick and restart it if necessary.
220  * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(),
221  * is NMI safe.
222  */
223 static void tick_nohz_full_kick(void)
224 {
225         if (!tick_nohz_full_cpu(smp_processor_id()))
226                 return;
227 
228         irq_work_queue(this_cpu_ptr(&nohz_full_kick_work));
229 }
230 
231 /*
232  * Kick the CPU if it's full dynticks in order to force it to
233  * re-evaluate its dependency on the tick and restart it if necessary.
234  */
235 void tick_nohz_full_kick_cpu(int cpu)
236 {
237         if (!tick_nohz_full_cpu(cpu))
238                 return;
239 
240         irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu);
241 }
242 
243 /*
244  * Kick all full dynticks CPUs in order to force these to re-evaluate
245  * their dependency on the tick and restart it if necessary.
246  */
247 static void tick_nohz_full_kick_all(void)
248 {
249         int cpu;
250 
251         if (!tick_nohz_full_running)
252                 return;
253 
254         preempt_disable();
255         for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask)
256                 tick_nohz_full_kick_cpu(cpu);
257         preempt_enable();
258 }
259 
260 static void tick_nohz_dep_set_all(atomic_t *dep,
261                                   enum tick_dep_bits bit)
262 {
263         int prev;
264 
265         prev = atomic_fetch_or(dep, BIT(bit));
266         if (!prev)
267                 tick_nohz_full_kick_all();
268 }
269 
270 /*
271  * Set a global tick dependency. Used by perf events that rely on freq and
272  * by unstable clock.
273  */
274 void tick_nohz_dep_set(enum tick_dep_bits bit)
275 {
276         tick_nohz_dep_set_all(&tick_dep_mask, bit);
277 }
278 
279 void tick_nohz_dep_clear(enum tick_dep_bits bit)
280 {
281         atomic_andnot(BIT(bit), &tick_dep_mask);
282 }
283 
284 /*
285  * Set per-CPU tick dependency. Used by scheduler and perf events in order to
286  * manage events throttling.
287  */
288 void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
289 {
290         int prev;
291         struct tick_sched *ts;
292 
293         ts = per_cpu_ptr(&tick_cpu_sched, cpu);
294 
295         prev = atomic_fetch_or(&ts->tick_dep_mask, BIT(bit));
296         if (!prev) {
297                 preempt_disable();
298                 /* Perf needs local kick that is NMI safe */
299                 if (cpu == smp_processor_id()) {
300                         tick_nohz_full_kick();
301                 } else {
302                         /* Remote irq work not NMI-safe */
303                         if (!WARN_ON_ONCE(in_nmi()))
304                                 tick_nohz_full_kick_cpu(cpu);
305                 }
306                 preempt_enable();
307         }
308 }
309 
310 void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
311 {
312         struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu);
313 
314         atomic_andnot(BIT(bit), &ts->tick_dep_mask);
315 }
316 
317 /*
318  * Set a per-task tick dependency. Posix CPU timers need this in order to elapse
319  * per task timers.
320  */
321 void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit)
322 {
323         /*
324          * We could optimize this with just kicking the target running the task
325          * if that noise matters for nohz full users.
326          */
327         tick_nohz_dep_set_all(&tsk->tick_dep_mask, bit);
328 }
329 
330 void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit)
331 {
332         atomic_andnot(BIT(bit), &tsk->tick_dep_mask);
333 }
334 
335 /*
336  * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse
337  * per process timers.
338  */
339 void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits bit)
340 {
341         tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
342 }
343 
344 void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)
345 {
346         atomic_andnot(BIT(bit), &sig->tick_dep_mask);
347 }
348 
349 /*
350  * Re-evaluate the need for the tick as we switch the current task.
351  * It might need the tick due to per task/process properties:
352  * perf events, posix cpu timers, ...
353  */
354 void __tick_nohz_task_switch(void)
355 {
356         unsigned long flags;
357         struct tick_sched *ts;
358 
359         local_irq_save(flags);
360 
361         if (!tick_nohz_full_cpu(smp_processor_id()))
362                 goto out;
363 
364         ts = this_cpu_ptr(&tick_cpu_sched);
365 
366         if (ts->tick_stopped) {
367                 if (atomic_read(&current->tick_dep_mask) ||
368                     atomic_read(&current->signal->tick_dep_mask))
369                         tick_nohz_full_kick();
370         }
371 out:
372         local_irq_restore(flags);
373 }
374 
375 /* Parse the boot-time nohz CPU list from the kernel parameters. */
376 static int __init tick_nohz_full_setup(char *str)
377 {
378         alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
379         if (cpulist_parse(str, tick_nohz_full_mask) < 0) {
380                 pr_warn("NO_HZ: Incorrect nohz_full cpumask\n");
381                 free_bootmem_cpumask_var(tick_nohz_full_mask);
382                 return 1;
383         }
384         tick_nohz_full_running = true;
385 
386         return 1;
387 }
388 __setup("nohz_full=", tick_nohz_full_setup);
389 
390 static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,
391                                        unsigned long action,
392                                        void *hcpu)
393 {
394         unsigned int cpu = (unsigned long)hcpu;
395 
396         switch (action & ~CPU_TASKS_FROZEN) {
397         case CPU_DOWN_PREPARE:
398                 /*
399                  * The boot CPU handles housekeeping duty (unbound timers,
400                  * workqueues, timekeeping, ...) on behalf of full dynticks
401                  * CPUs. It must remain online when nohz full is enabled.
402                  */
403                 if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
404                         return NOTIFY_BAD;
405                 break;
406         }
407         return NOTIFY_OK;
408 }
409 
410 static int tick_nohz_init_all(void)
411 {
412         int err = -1;
413 
414 #ifdef CONFIG_NO_HZ_FULL_ALL
415         if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
416                 WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n");
417                 return err;
418         }
419         err = 0;
420         cpumask_setall(tick_nohz_full_mask);
421         tick_nohz_full_running = true;
422 #endif
423         return err;
424 }
425 
426 void __init tick_nohz_init(void)
427 {
428         int cpu;
429 
430         if (!tick_nohz_full_running) {
431                 if (tick_nohz_init_all() < 0)
432                         return;
433         }
434 
435         if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) {
436                 WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n");
437                 cpumask_clear(tick_nohz_full_mask);
438                 tick_nohz_full_running = false;
439                 return;
440         }
441 
442         /*
443          * Full dynticks uses irq work to drive the tick rescheduling on safe
444          * locking contexts. But then we need irq work to raise its own
445          * interrupts to avoid circular dependency on the tick
446          */
447         if (!arch_irq_work_has_interrupt()) {
448                 pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs\n");
449                 cpumask_clear(tick_nohz_full_mask);
450                 cpumask_copy(housekeeping_mask, cpu_possible_mask);
451                 tick_nohz_full_running = false;
452                 return;
453         }
454 
455         cpu = smp_processor_id();
456 
457         if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) {
458                 pr_warn("NO_HZ: Clearing %d from nohz_full range for timekeeping\n",
459                         cpu);
460                 cpumask_clear_cpu(cpu, tick_nohz_full_mask);
461         }
462 
463         cpumask_andnot(housekeeping_mask,
464                        cpu_possible_mask, tick_nohz_full_mask);
465 
466         for_each_cpu(cpu, tick_nohz_full_mask)
467                 context_tracking_cpu_set(cpu);
468 
469         cpu_notifier(tick_nohz_cpu_down_callback, 0);
470         pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
471                 cpumask_pr_args(tick_nohz_full_mask));
472 
473         /*
474          * We need at least one CPU to handle housekeeping work such
475          * as timekeeping, unbound timers, workqueues, ...
476          */
477         WARN_ON_ONCE(cpumask_empty(housekeeping_mask));
478 }
479 #endif
480 
481 /*
482  * NOHZ - aka dynamic tick functionality
483  */
484 #ifdef CONFIG_NO_HZ_COMMON
485 /*
486  * NO HZ enabled ?
487  */
488 bool tick_nohz_enabled __read_mostly  = true;
489 unsigned long tick_nohz_active  __read_mostly;
490 /*
491  * Enable / Disable tickless mode
492  */
493 static int __init setup_tick_nohz(char *str)
494 {
495         return (kstrtobool(str, &tick_nohz_enabled) == 0);
496 }
497 
498 __setup("nohz=", setup_tick_nohz);
499 
500 int tick_nohz_tick_stopped(void)
501 {
502         return __this_cpu_read(tick_cpu_sched.tick_stopped);
503 }
504 
505 /**
506  * tick_nohz_update_jiffies - update jiffies when idle was interrupted
507  *
508  * Called from interrupt entry when the CPU was idle
509  *
510  * In case the sched_tick was stopped on this CPU, we have to check if jiffies
511  * must be updated. Otherwise an interrupt handler could use a stale jiffy
512  * value. We do this unconditionally on any cpu, as we don't know whether the
513  * cpu, which has the update task assigned is in a long sleep.
514  */
515 static void tick_nohz_update_jiffies(ktime_t now)
516 {
517         unsigned long flags;
518 
519         __this_cpu_write(tick_cpu_sched.idle_waketime, now);
520 
521         local_irq_save(flags);
522         tick_do_update_jiffies64(now);
523         local_irq_restore(flags);
524 
525         touch_softlockup_watchdog_sched();
526 }
527 
528 /*
529  * Updates the per cpu time idle statistics counters
530  */
531 static void
532 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time)
533 {
534         ktime_t delta;
535 
536         if (ts->idle_active) {
537                 delta = ktime_sub(now, ts->idle_entrytime);
538                 if (nr_iowait_cpu(cpu) > 0)
539                         ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta);
540                 else
541                         ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta);
542                 ts->idle_entrytime = now;
543         }
544 
545         if (last_update_time)
546                 *last_update_time = ktime_to_us(now);
547 
548 }
549 
550 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now)
551 {
552         update_ts_time_stats(smp_processor_id(), ts, now, NULL);
553         ts->idle_active = 0;
554 
555         sched_clock_idle_wakeup_event(0);
556 }
557 
558 static ktime_t tick_nohz_start_idle(struct tick_sched *ts)
559 {
560         ktime_t now = ktime_get();
561 
562         ts->idle_entrytime = now;
563         ts->idle_active = 1;
564         sched_clock_idle_sleep_event();
565         return now;
566 }
567 
568 /**
569  * get_cpu_idle_time_us - get the total idle time of a cpu
570  * @cpu: CPU number to query
571  * @last_update_time: variable to store update time in. Do not update
572  * counters if NULL.
573  *
574  * Return the cummulative idle time (since boot) for a given
575  * CPU, in microseconds.
576  *
577  * This time is measured via accounting rather than sampling,
578  * and is as accurate as ktime_get() is.
579  *
580  * This function returns -1 if NOHZ is not enabled.
581  */
582 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time)
583 {
584         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
585         ktime_t now, idle;
586 
587         if (!tick_nohz_active)
588                 return -1;
589 
590         now = ktime_get();
591         if (last_update_time) {
592                 update_ts_time_stats(cpu, ts, now, last_update_time);
593                 idle = ts->idle_sleeptime;
594         } else {
595                 if (ts->idle_active && !nr_iowait_cpu(cpu)) {
596                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
597 
598                         idle = ktime_add(ts->idle_sleeptime, delta);
599                 } else {
600                         idle = ts->idle_sleeptime;
601                 }
602         }
603 
604         return ktime_to_us(idle);
605 
606 }
607 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us);
608 
609 /**
610  * get_cpu_iowait_time_us - get the total iowait time of a cpu
611  * @cpu: CPU number to query
612  * @last_update_time: variable to store update time in. Do not update
613  * counters if NULL.
614  *
615  * Return the cummulative iowait time (since boot) for a given
616  * CPU, in microseconds.
617  *
618  * This time is measured via accounting rather than sampling,
619  * and is as accurate as ktime_get() is.
620  *
621  * This function returns -1 if NOHZ is not enabled.
622  */
623 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
624 {
625         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
626         ktime_t now, iowait;
627 
628         if (!tick_nohz_active)
629                 return -1;
630 
631         now = ktime_get();
632         if (last_update_time) {
633                 update_ts_time_stats(cpu, ts, now, last_update_time);
634                 iowait = ts->iowait_sleeptime;
635         } else {
636                 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) {
637                         ktime_t delta = ktime_sub(now, ts->idle_entrytime);
638 
639                         iowait = ktime_add(ts->iowait_sleeptime, delta);
640                 } else {
641                         iowait = ts->iowait_sleeptime;
642                 }
643         }
644 
645         return ktime_to_us(iowait);
646 }
647 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
648 
649 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
650 {
651         hrtimer_cancel(&ts->sched_timer);
652         hrtimer_set_expires(&ts->sched_timer, ts->last_tick);
653 
654         /* Forward the time to expire in the future */
655         hrtimer_forward(&ts->sched_timer, now, tick_period);
656 
657         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
658                 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
659         else
660                 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
661 }
662 
663 static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
664                                          ktime_t now, int cpu)
665 {
666         struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
667         u64 basemono, next_tick, next_tmr, next_rcu, delta, expires;
668         unsigned long seq, basejiff;
669         ktime_t tick;
670 
671         /* Read jiffies and the time when jiffies were updated last */
672         do {
673                 seq = read_seqbegin(&jiffies_lock);
674                 basemono = last_jiffies_update.tv64;
675                 basejiff = jiffies;
676         } while (read_seqretry(&jiffies_lock, seq));
677         ts->last_jiffies = basejiff;
678 
679         if (rcu_needs_cpu(basemono, &next_rcu) ||
680             arch_needs_cpu() || irq_work_needs_cpu()) {
681                 next_tick = basemono + TICK_NSEC;
682         } else {
683                 /*
684                  * Get the next pending timer. If high resolution
685                  * timers are enabled this only takes the timer wheel
686                  * timers into account. If high resolution timers are
687                  * disabled this also looks at the next expiring
688                  * hrtimer.
689                  */
690                 next_tmr = get_next_timer_interrupt(basejiff, basemono);
691                 ts->next_timer = next_tmr;
692                 /* Take the next rcu event into account */
693                 next_tick = next_rcu < next_tmr ? next_rcu : next_tmr;
694         }
695 
696         /*
697          * If the tick is due in the next period, keep it ticking or
698          * force prod the timer.
699          */
700         delta = next_tick - basemono;
701         if (delta <= (u64)TICK_NSEC) {
702                 tick.tv64 = 0;
703                 /*
704                  * We've not stopped the tick yet, and there's a timer in the
705                  * next period, so no point in stopping it either, bail.
706                  */
707                 if (!ts->tick_stopped)
708                         goto out;
709 
710                 /*
711                  * If, OTOH, we did stop it, but there's a pending (expired)
712                  * timer reprogram the timer hardware to fire now.
713                  *
714                  * We will not restart the tick proper, just prod the timer
715                  * hardware into firing an interrupt to process the pending
716                  * timers. Just like tick_irq_exit() will not restart the tick
717                  * for 'normal' interrupts.
718                  *
719                  * Only once we exit the idle loop will we re-enable the tick,
720                  * see tick_nohz_idle_exit().
721                  */
722                 if (delta == 0) {
723                         tick_nohz_restart(ts, now);
724                         goto out;
725                 }
726         }
727 
728         /*
729          * If this cpu is the one which updates jiffies, then give up
730          * the assignment and let it be taken by the cpu which runs
731          * the tick timer next, which might be this cpu as well. If we
732          * don't drop this here the jiffies might be stale and
733          * do_timer() never invoked. Keep track of the fact that it
734          * was the one which had the do_timer() duty last. If this cpu
735          * is the one which had the do_timer() duty last, we limit the
736          * sleep time to the timekeeping max_deferement value.
737          * Otherwise we can sleep as long as we want.
738          */
739         delta = timekeeping_max_deferment();
740         if (cpu == tick_do_timer_cpu) {
741                 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
742                 ts->do_timer_last = 1;
743         } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
744                 delta = KTIME_MAX;
745                 ts->do_timer_last = 0;
746         } else if (!ts->do_timer_last) {
747                 delta = KTIME_MAX;
748         }
749 
750 #ifdef CONFIG_NO_HZ_FULL
751         /* Limit the tick delta to the maximum scheduler deferment */
752         if (!ts->inidle)
753                 delta = min(delta, scheduler_tick_max_deferment());
754 #endif
755 
756         /* Calculate the next expiry time */
757         if (delta < (KTIME_MAX - basemono))
758                 expires = basemono + delta;
759         else
760                 expires = KTIME_MAX;
761 
762         expires = min_t(u64, expires, next_tick);
763         tick.tv64 = expires;
764 
765         /* Skip reprogram of event if its not changed */
766         if (ts->tick_stopped && (expires == dev->next_event.tv64))
767                 goto out;
768 
769         /*
770          * nohz_stop_sched_tick can be called several times before
771          * the nohz_restart_sched_tick is called. This happens when
772          * interrupts arrive which do not cause a reschedule. In the
773          * first call we save the current tick time, so we can restart
774          * the scheduler tick in nohz_restart_sched_tick.
775          */
776         if (!ts->tick_stopped) {
777                 nohz_balance_enter_idle(cpu);
778                 calc_load_enter_idle();
779 
780                 ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
781                 ts->tick_stopped = 1;
782                 trace_tick_stop(1, TICK_DEP_MASK_NONE);
783         }
784 
785         /*
786          * If the expiration time == KTIME_MAX, then we simply stop
787          * the tick timer.
788          */
789         if (unlikely(expires == KTIME_MAX)) {
790                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
791                         hrtimer_cancel(&ts->sched_timer);
792                 goto out;
793         }
794 
795         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
796                 hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED);
797         else
798                 tick_program_event(tick, 1);
799 out:
800         /* Update the estimated sleep length */
801         ts->sleep_length = ktime_sub(dev->next_event, now);
802         return tick;
803 }
804 
805 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now, int active)
806 {
807         /* Update jiffies first */
808         tick_do_update_jiffies64(now);
809         update_cpu_load_nohz(active);
810 
811         calc_load_exit_idle();
812         touch_softlockup_watchdog_sched();
813         /*
814          * Cancel the scheduled timer and restore the tick
815          */
816         ts->tick_stopped  = 0;
817         ts->idle_exittime = now;
818 
819         tick_nohz_restart(ts, now);
820 }
821 
822 static void tick_nohz_full_update_tick(struct tick_sched *ts)
823 {
824 #ifdef CONFIG_NO_HZ_FULL
825         int cpu = smp_processor_id();
826 
827         if (!tick_nohz_full_cpu(cpu))
828                 return;
829 
830         if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
831                 return;
832 
833         if (can_stop_full_tick(ts))
834                 tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
835         else if (ts->tick_stopped)
836                 tick_nohz_restart_sched_tick(ts, ktime_get(), 1);
837 #endif
838 }
839 
840 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
841 {
842         /*
843          * If this cpu is offline and it is the one which updates
844          * jiffies, then give up the assignment and let it be taken by
845          * the cpu which runs the tick timer next. If we don't drop
846          * this here the jiffies might be stale and do_timer() never
847          * invoked.
848          */
849         if (unlikely(!cpu_online(cpu))) {
850                 if (cpu == tick_do_timer_cpu)
851                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
852                 return false;
853         }
854 
855         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
856                 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
857                 return false;
858         }
859 
860         if (need_resched())
861                 return false;
862 
863         if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
864                 static int ratelimit;
865 
866                 if (ratelimit < 10 &&
867                     (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
868                         pr_warn("NOHZ: local_softirq_pending %02x\n",
869                                 (unsigned int) local_softirq_pending());
870                         ratelimit++;
871                 }
872                 return false;
873         }
874 
875         if (tick_nohz_full_enabled()) {
876                 /*
877                  * Keep the tick alive to guarantee timekeeping progression
878                  * if there are full dynticks CPUs around
879                  */
880                 if (tick_do_timer_cpu == cpu)
881                         return false;
882                 /*
883                  * Boot safety: make sure the timekeeping duty has been
884                  * assigned before entering dyntick-idle mode,
885                  */
886                 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
887                         return false;
888         }
889 
890         return true;
891 }
892 
893 static void __tick_nohz_idle_enter(struct tick_sched *ts)
894 {
895         ktime_t now, expires;
896         int cpu = smp_processor_id();
897 
898         now = tick_nohz_start_idle(ts);
899 
900         if (can_stop_idle_tick(cpu, ts)) {
901                 int was_stopped = ts->tick_stopped;
902 
903                 ts->idle_calls++;
904 
905                 expires = tick_nohz_stop_sched_tick(ts, now, cpu);
906                 if (expires.tv64 > 0LL) {
907                         ts->idle_sleeps++;
908                         ts->idle_expires = expires;
909                 }
910 
911                 if (!was_stopped && ts->tick_stopped)
912                         ts->idle_jiffies = ts->last_jiffies;
913         }
914 }
915 
916 /**
917  * tick_nohz_idle_enter - stop the idle tick from the idle task
918  *
919  * When the next event is more than a tick into the future, stop the idle tick
920  * Called when we start the idle loop.
921  *
922  * The arch is responsible of calling:
923  *
924  * - rcu_idle_enter() after its last use of RCU before the CPU is put
925  *  to sleep.
926  * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
927  */
928 void tick_nohz_idle_enter(void)
929 {
930         struct tick_sched *ts;
931 
932         WARN_ON_ONCE(irqs_disabled());
933 
934         /*
935          * Update the idle state in the scheduler domain hierarchy
936          * when tick_nohz_stop_sched_tick() is called from the idle loop.
937          * State will be updated to busy during the first busy tick after
938          * exiting idle.
939          */
940         set_cpu_sd_state_idle();
941 
942         local_irq_disable();
943 
944         ts = this_cpu_ptr(&tick_cpu_sched);
945         ts->inidle = 1;
946         __tick_nohz_idle_enter(ts);
947 
948         local_irq_enable();
949 }
950 
951 /**
952  * tick_nohz_irq_exit - update next tick event from interrupt exit
953  *
954  * When an interrupt fires while we are idle and it doesn't cause
955  * a reschedule, it may still add, modify or delete a timer, enqueue
956  * an RCU callback, etc...
957  * So we need to re-calculate and reprogram the next tick event.
958  */
959 void tick_nohz_irq_exit(void)
960 {
961         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
962 
963         if (ts->inidle)
964                 __tick_nohz_idle_enter(ts);
965         else
966                 tick_nohz_full_update_tick(ts);
967 }
968 
969 /**
970  * tick_nohz_get_sleep_length - return the length of the current sleep
971  *
972  * Called from power state control code with interrupts disabled
973  */
974 ktime_t tick_nohz_get_sleep_length(void)
975 {
976         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
977 
978         return ts->sleep_length;
979 }
980 
981 static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
982 {
983 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
984         unsigned long ticks;
985 
986         if (vtime_accounting_cpu_enabled())
987                 return;
988         /*
989          * We stopped the tick in idle. Update process times would miss the
990          * time we slept as update_process_times does only a 1 tick
991          * accounting. Enforce that this is accounted to idle !
992          */
993         ticks = jiffies - ts->idle_jiffies;
994         /*
995          * We might be one off. Do not randomly account a huge number of ticks!
996          */
997         if (ticks && ticks < LONG_MAX)
998                 account_idle_ticks(ticks);
999 #endif
1000 }
1001 
1002 /**
1003  * tick_nohz_idle_exit - restart the idle tick from the idle task
1004  *
1005  * Restart the idle tick when the CPU is woken up from idle
1006  * This also exit the RCU extended quiescent state. The CPU
1007  * can use RCU again after this function is called.
1008  */
1009 void tick_nohz_idle_exit(void)
1010 {
1011         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1012         ktime_t now;
1013 
1014         local_irq_disable();
1015 
1016         WARN_ON_ONCE(!ts->inidle);
1017 
1018         ts->inidle = 0;
1019 
1020         if (ts->idle_active || ts->tick_stopped)
1021                 now = ktime_get();
1022 
1023         if (ts->idle_active)
1024                 tick_nohz_stop_idle(ts, now);
1025 
1026         if (ts->tick_stopped) {
1027                 tick_nohz_restart_sched_tick(ts, now, 0);
1028                 tick_nohz_account_idle_ticks(ts);
1029         }
1030 
1031         local_irq_enable();
1032 }
1033 
1034 /*
1035  * The nohz low res interrupt handler
1036  */
1037 static void tick_nohz_handler(struct clock_event_device *dev)
1038 {
1039         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1040         struct pt_regs *regs = get_irq_regs();
1041         ktime_t now = ktime_get();
1042 
1043         dev->next_event.tv64 = KTIME_MAX;
1044 
1045         tick_sched_do_timer(now);
1046         tick_sched_handle(ts, regs);
1047 
1048         /* No need to reprogram if we are running tickless  */
1049         if (unlikely(ts->tick_stopped))
1050                 return;
1051 
1052         hrtimer_forward(&ts->sched_timer, now, tick_period);
1053         tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1054 }
1055 
1056 static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
1057 {
1058         if (!tick_nohz_enabled)
1059                 return;
1060         ts->nohz_mode = mode;
1061         /* One update is enough */
1062         if (!test_and_set_bit(0, &tick_nohz_active))
1063                 timers_update_migration(true);
1064 }
1065 
1066 /**
1067  * tick_nohz_switch_to_nohz - switch to nohz mode
1068  */
1069 static void tick_nohz_switch_to_nohz(void)
1070 {
1071         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1072         ktime_t next;
1073 
1074         if (!tick_nohz_enabled)
1075                 return;
1076 
1077         if (tick_switch_to_oneshot(tick_nohz_handler))
1078                 return;
1079 
1080         /*
1081          * Recycle the hrtimer in ts, so we can share the
1082          * hrtimer_forward with the highres code.
1083          */
1084         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1085         /* Get the next period */
1086         next = tick_init_jiffy_update();
1087 
1088         hrtimer_set_expires(&ts->sched_timer, next);
1089         hrtimer_forward_now(&ts->sched_timer, tick_period);
1090         tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1091         tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
1092 }
1093 
1094 /*
1095  * When NOHZ is enabled and the tick is stopped, we need to kick the
1096  * tick timer from irq_enter() so that the jiffies update is kept
1097  * alive during long running softirqs. That's ugly as hell, but
1098  * correctness is key even if we need to fix the offending softirq in
1099  * the first place.
1100  *
1101  * Note, this is different to tick_nohz_restart. We just kick the
1102  * timer and do not touch the other magic bits which need to be done
1103  * when idle is left.
1104  */
1105 static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now)
1106 {
1107 #if 0
1108         /* Switch back to 2.6.27 behaviour */
1109         ktime_t delta;
1110 
1111         /*
1112          * Do not touch the tick device, when the next expiry is either
1113          * already reached or less/equal than the tick period.
1114          */
1115         delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
1116         if (delta.tv64 <= tick_period.tv64)
1117                 return;
1118 
1119         tick_nohz_restart(ts, now);
1120 #endif
1121 }
1122 
1123 static inline void tick_nohz_irq_enter(void)
1124 {
1125         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1126         ktime_t now;
1127 
1128         if (!ts->idle_active && !ts->tick_stopped)
1129                 return;
1130         now = ktime_get();
1131         if (ts->idle_active)
1132                 tick_nohz_stop_idle(ts, now);
1133         if (ts->tick_stopped) {
1134                 tick_nohz_update_jiffies(now);
1135                 tick_nohz_kick_tick(ts, now);
1136         }
1137 }
1138 
1139 #else
1140 
1141 static inline void tick_nohz_switch_to_nohz(void) { }
1142 static inline void tick_nohz_irq_enter(void) { }
1143 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
1144 
1145 #endif /* CONFIG_NO_HZ_COMMON */
1146 
1147 /*
1148  * Called from irq_enter to notify about the possible interruption of idle()
1149  */
1150 void tick_irq_enter(void)
1151 {
1152         tick_check_oneshot_broadcast_this_cpu();
1153         tick_nohz_irq_enter();
1154 }
1155 
1156 /*
1157  * High resolution timer specific code
1158  */
1159 #ifdef CONFIG_HIGH_RES_TIMERS
1160 /*
1161  * We rearm the timer until we get disabled by the idle code.
1162  * Called with interrupts disabled.
1163  */
1164 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1165 {
1166         struct tick_sched *ts =
1167                 container_of(timer, struct tick_sched, sched_timer);
1168         struct pt_regs *regs = get_irq_regs();
1169         ktime_t now = ktime_get();
1170 
1171         tick_sched_do_timer(now);
1172 
1173         /*
1174          * Do not call, when we are not in irq context and have
1175          * no valid regs pointer
1176          */
1177         if (regs)
1178                 tick_sched_handle(ts, regs);
1179 
1180         /* No need to reprogram if we are in idle or full dynticks mode */
1181         if (unlikely(ts->tick_stopped))
1182                 return HRTIMER_NORESTART;
1183 
1184         hrtimer_forward(timer, now, tick_period);
1185 
1186         return HRTIMER_RESTART;
1187 }
1188 
1189 static int sched_skew_tick;
1190 
1191 static int __init skew_tick(char *str)
1192 {
1193         get_option(&str, &sched_skew_tick);
1194 
1195         return 0;
1196 }
1197 early_param("skew_tick", skew_tick);
1198 
1199 /**
1200  * tick_setup_sched_timer - setup the tick emulation timer
1201  */
1202 void tick_setup_sched_timer(void)
1203 {
1204         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1205         ktime_t now = ktime_get();
1206 
1207         /*
1208          * Emulate tick processing via per-CPU hrtimers:
1209          */
1210         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1211         ts->sched_timer.function = tick_sched_timer;
1212 
1213         /* Get the next period (per cpu) */
1214         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1215 
1216         /* Offset the tick to avert jiffies_lock contention. */
1217         if (sched_skew_tick) {
1218                 u64 offset = ktime_to_ns(tick_period) >> 1;
1219                 do_div(offset, num_possible_cpus());
1220                 offset *= smp_processor_id();
1221                 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1222         }
1223 
1224         hrtimer_forward(&ts->sched_timer, now, tick_period);
1225         hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
1226         tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
1227 }
1228 #endif /* HIGH_RES_TIMERS */
1229 
1230 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1231 void tick_cancel_sched_timer(int cpu)
1232 {
1233         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1234 
1235 # ifdef CONFIG_HIGH_RES_TIMERS
1236         if (ts->sched_timer.base)
1237                 hrtimer_cancel(&ts->sched_timer);
1238 # endif
1239 
1240         memset(ts, 0, sizeof(*ts));
1241 }
1242 #endif
1243 
1244 /**
1245  * Async notification about clocksource changes
1246  */
1247 void tick_clock_notify(void)
1248 {
1249         int cpu;
1250 
1251         for_each_possible_cpu(cpu)
1252                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1253 }
1254 
1255 /*
1256  * Async notification about clock event changes
1257  */
1258 void tick_oneshot_notify(void)
1259 {
1260         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1261 
1262         set_bit(0, &ts->check_clocks);
1263 }
1264 
1265 /**
1266  * Check, if a change happened, which makes oneshot possible.
1267  *
1268  * Called cyclic from the hrtimer softirq (driven by the timer
1269  * softirq) allow_nohz signals, that we can switch into low-res nohz
1270  * mode, because high resolution timers are disabled (either compile
1271  * or runtime). Called with interrupts disabled.
1272  */
1273 int tick_check_oneshot_change(int allow_nohz)
1274 {
1275         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1276 
1277         if (!test_and_clear_bit(0, &ts->check_clocks))
1278                 return 0;
1279 
1280         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1281                 return 0;
1282 
1283         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1284                 return 0;
1285 
1286         if (!allow_nohz)
1287                 return 1;
1288 
1289         tick_nohz_switch_to_nohz();
1290         return 0;
1291 }
1292 

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