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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         /* Reevaluate 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 themselves 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(BIT(bit), dep);
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(BIT(bit), &ts->tick_dep_mask);
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 cumulative 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 cumulative 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                 /*
705                  * Tell the timer code that the base is not idle, i.e. undo
706                  * the effect of get_next_timer_interrupt():
707                  */
708                 timer_clear_idle();
709                 /*
710                  * We've not stopped the tick yet, and there's a timer in the
711                  * next period, so no point in stopping it either, bail.
712                  */
713                 if (!ts->tick_stopped)
714                         goto out;
715 
716                 /*
717                  * If, OTOH, we did stop it, but there's a pending (expired)
718                  * timer reprogram the timer hardware to fire now.
719                  *
720                  * We will not restart the tick proper, just prod the timer
721                  * hardware into firing an interrupt to process the pending
722                  * timers. Just like tick_irq_exit() will not restart the tick
723                  * for 'normal' interrupts.
724                  *
725                  * Only once we exit the idle loop will we re-enable the tick,
726                  * see tick_nohz_idle_exit().
727                  */
728                 if (delta == 0) {
729                         tick_nohz_restart(ts, now);
730                         goto out;
731                 }
732         }
733 
734         /*
735          * If this CPU is the one which updates jiffies, then give up
736          * the assignment and let it be taken by the CPU which runs
737          * the tick timer next, which might be this CPU as well. If we
738          * don't drop this here the jiffies might be stale and
739          * do_timer() never invoked. Keep track of the fact that it
740          * was the one which had the do_timer() duty last. If this CPU
741          * is the one which had the do_timer() duty last, we limit the
742          * sleep time to the timekeeping max_deferment value.
743          * Otherwise we can sleep as long as we want.
744          */
745         delta = timekeeping_max_deferment();
746         if (cpu == tick_do_timer_cpu) {
747                 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
748                 ts->do_timer_last = 1;
749         } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) {
750                 delta = KTIME_MAX;
751                 ts->do_timer_last = 0;
752         } else if (!ts->do_timer_last) {
753                 delta = KTIME_MAX;
754         }
755 
756 #ifdef CONFIG_NO_HZ_FULL
757         /* Limit the tick delta to the maximum scheduler deferment */
758         if (!ts->inidle)
759                 delta = min(delta, scheduler_tick_max_deferment());
760 #endif
761 
762         /* Calculate the next expiry time */
763         if (delta < (KTIME_MAX - basemono))
764                 expires = basemono + delta;
765         else
766                 expires = KTIME_MAX;
767 
768         expires = min_t(u64, expires, next_tick);
769         tick.tv64 = expires;
770 
771         /* Skip reprogram of event if its not changed */
772         if (ts->tick_stopped && (expires == dev->next_event.tv64))
773                 goto out;
774 
775         /*
776          * nohz_stop_sched_tick can be called several times before
777          * the nohz_restart_sched_tick is called. This happens when
778          * interrupts arrive which do not cause a reschedule. In the
779          * first call we save the current tick time, so we can restart
780          * the scheduler tick in nohz_restart_sched_tick.
781          */
782         if (!ts->tick_stopped) {
783                 nohz_balance_enter_idle(cpu);
784                 calc_load_enter_idle();
785                 cpu_load_update_nohz_start();
786 
787                 ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
788                 ts->tick_stopped = 1;
789                 trace_tick_stop(1, TICK_DEP_MASK_NONE);
790         }
791 
792         /*
793          * If the expiration time == KTIME_MAX, then we simply stop
794          * the tick timer.
795          */
796         if (unlikely(expires == KTIME_MAX)) {
797                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
798                         hrtimer_cancel(&ts->sched_timer);
799                 goto out;
800         }
801 
802         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
803                 hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED);
804         else
805                 tick_program_event(tick, 1);
806 out:
807         /* Update the estimated sleep length */
808         ts->sleep_length = ktime_sub(dev->next_event, now);
809         return tick;
810 }
811 
812 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
813 {
814         /* Update jiffies first */
815         tick_do_update_jiffies64(now);
816         cpu_load_update_nohz_stop();
817 
818         /*
819          * Clear the timer idle flag, so we avoid IPIs on remote queueing and
820          * the clock forward checks in the enqueue path:
821          */
822         timer_clear_idle();
823 
824         calc_load_exit_idle();
825         touch_softlockup_watchdog_sched();
826         /*
827          * Cancel the scheduled timer and restore the tick
828          */
829         ts->tick_stopped  = 0;
830         ts->idle_exittime = now;
831 
832         tick_nohz_restart(ts, now);
833 }
834 
835 static void tick_nohz_full_update_tick(struct tick_sched *ts)
836 {
837 #ifdef CONFIG_NO_HZ_FULL
838         int cpu = smp_processor_id();
839 
840         if (!tick_nohz_full_cpu(cpu))
841                 return;
842 
843         if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
844                 return;
845 
846         if (can_stop_full_tick(ts))
847                 tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
848         else if (ts->tick_stopped)
849                 tick_nohz_restart_sched_tick(ts, ktime_get());
850 #endif
851 }
852 
853 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
854 {
855         /*
856          * If this CPU is offline and it is the one which updates
857          * jiffies, then give up the assignment and let it be taken by
858          * the CPU which runs the tick timer next. If we don't drop
859          * this here the jiffies might be stale and do_timer() never
860          * invoked.
861          */
862         if (unlikely(!cpu_online(cpu))) {
863                 if (cpu == tick_do_timer_cpu)
864                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
865                 return false;
866         }
867 
868         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
869                 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
870                 return false;
871         }
872 
873         if (need_resched())
874                 return false;
875 
876         if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
877                 static int ratelimit;
878 
879                 if (ratelimit < 10 &&
880                     (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
881                         pr_warn("NOHZ: local_softirq_pending %02x\n",
882                                 (unsigned int) local_softirq_pending());
883                         ratelimit++;
884                 }
885                 return false;
886         }
887 
888         if (tick_nohz_full_enabled()) {
889                 /*
890                  * Keep the tick alive to guarantee timekeeping progression
891                  * if there are full dynticks CPUs around
892                  */
893                 if (tick_do_timer_cpu == cpu)
894                         return false;
895                 /*
896                  * Boot safety: make sure the timekeeping duty has been
897                  * assigned before entering dyntick-idle mode,
898                  */
899                 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
900                         return false;
901         }
902 
903         return true;
904 }
905 
906 static void __tick_nohz_idle_enter(struct tick_sched *ts)
907 {
908         ktime_t now, expires;
909         int cpu = smp_processor_id();
910 
911         now = tick_nohz_start_idle(ts);
912 
913         if (can_stop_idle_tick(cpu, ts)) {
914                 int was_stopped = ts->tick_stopped;
915 
916                 ts->idle_calls++;
917 
918                 expires = tick_nohz_stop_sched_tick(ts, now, cpu);
919                 if (expires.tv64 > 0LL) {
920                         ts->idle_sleeps++;
921                         ts->idle_expires = expires;
922                 }
923 
924                 if (!was_stopped && ts->tick_stopped)
925                         ts->idle_jiffies = ts->last_jiffies;
926         }
927 }
928 
929 /**
930  * tick_nohz_idle_enter - stop the idle tick from the idle task
931  *
932  * When the next event is more than a tick into the future, stop the idle tick
933  * Called when we start the idle loop.
934  *
935  * The arch is responsible of calling:
936  *
937  * - rcu_idle_enter() after its last use of RCU before the CPU is put
938  *  to sleep.
939  * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
940  */
941 void tick_nohz_idle_enter(void)
942 {
943         struct tick_sched *ts;
944 
945         WARN_ON_ONCE(irqs_disabled());
946 
947         /*
948          * Update the idle state in the scheduler domain hierarchy
949          * when tick_nohz_stop_sched_tick() is called from the idle loop.
950          * State will be updated to busy during the first busy tick after
951          * exiting idle.
952          */
953         set_cpu_sd_state_idle();
954 
955         local_irq_disable();
956 
957         ts = this_cpu_ptr(&tick_cpu_sched);
958         ts->inidle = 1;
959         __tick_nohz_idle_enter(ts);
960 
961         local_irq_enable();
962 }
963 
964 /**
965  * tick_nohz_irq_exit - update next tick event from interrupt exit
966  *
967  * When an interrupt fires while we are idle and it doesn't cause
968  * a reschedule, it may still add, modify or delete a timer, enqueue
969  * an RCU callback, etc...
970  * So we need to re-calculate and reprogram the next tick event.
971  */
972 void tick_nohz_irq_exit(void)
973 {
974         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
975 
976         if (ts->inidle)
977                 __tick_nohz_idle_enter(ts);
978         else
979                 tick_nohz_full_update_tick(ts);
980 }
981 
982 /**
983  * tick_nohz_get_sleep_length - return the length of the current sleep
984  *
985  * Called from power state control code with interrupts disabled
986  */
987 ktime_t tick_nohz_get_sleep_length(void)
988 {
989         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
990 
991         return ts->sleep_length;
992 }
993 
994 static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
995 {
996 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
997         unsigned long ticks;
998 
999         if (vtime_accounting_cpu_enabled())
1000                 return;
1001         /*
1002          * We stopped the tick in idle. Update process times would miss the
1003          * time we slept as update_process_times does only a 1 tick
1004          * accounting. Enforce that this is accounted to idle !
1005          */
1006         ticks = jiffies - ts->idle_jiffies;
1007         /*
1008          * We might be one off. Do not randomly account a huge number of ticks!
1009          */
1010         if (ticks && ticks < LONG_MAX)
1011                 account_idle_ticks(ticks);
1012 #endif
1013 }
1014 
1015 /**
1016  * tick_nohz_idle_exit - restart the idle tick from the idle task
1017  *
1018  * Restart the idle tick when the CPU is woken up from idle
1019  * This also exit the RCU extended quiescent state. The CPU
1020  * can use RCU again after this function is called.
1021  */
1022 void tick_nohz_idle_exit(void)
1023 {
1024         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1025         ktime_t now;
1026 
1027         local_irq_disable();
1028 
1029         WARN_ON_ONCE(!ts->inidle);
1030 
1031         ts->inidle = 0;
1032 
1033         if (ts->idle_active || ts->tick_stopped)
1034                 now = ktime_get();
1035 
1036         if (ts->idle_active)
1037                 tick_nohz_stop_idle(ts, now);
1038 
1039         if (ts->tick_stopped) {
1040                 tick_nohz_restart_sched_tick(ts, now);
1041                 tick_nohz_account_idle_ticks(ts);
1042         }
1043 
1044         local_irq_enable();
1045 }
1046 
1047 /*
1048  * The nohz low res interrupt handler
1049  */
1050 static void tick_nohz_handler(struct clock_event_device *dev)
1051 {
1052         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1053         struct pt_regs *regs = get_irq_regs();
1054         ktime_t now = ktime_get();
1055 
1056         dev->next_event.tv64 = KTIME_MAX;
1057 
1058         tick_sched_do_timer(now);
1059         tick_sched_handle(ts, regs);
1060 
1061         /* No need to reprogram if we are running tickless  */
1062         if (unlikely(ts->tick_stopped))
1063                 return;
1064 
1065         hrtimer_forward(&ts->sched_timer, now, tick_period);
1066         tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1067 }
1068 
1069 static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
1070 {
1071         if (!tick_nohz_enabled)
1072                 return;
1073         ts->nohz_mode = mode;
1074         /* One update is enough */
1075         if (!test_and_set_bit(0, &tick_nohz_active))
1076                 timers_update_migration(true);
1077 }
1078 
1079 /**
1080  * tick_nohz_switch_to_nohz - switch to nohz mode
1081  */
1082 static void tick_nohz_switch_to_nohz(void)
1083 {
1084         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1085         ktime_t next;
1086 
1087         if (!tick_nohz_enabled)
1088                 return;
1089 
1090         if (tick_switch_to_oneshot(tick_nohz_handler))
1091                 return;
1092 
1093         /*
1094          * Recycle the hrtimer in ts, so we can share the
1095          * hrtimer_forward with the highres code.
1096          */
1097         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1098         /* Get the next period */
1099         next = tick_init_jiffy_update();
1100 
1101         hrtimer_set_expires(&ts->sched_timer, next);
1102         hrtimer_forward_now(&ts->sched_timer, tick_period);
1103         tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1104         tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
1105 }
1106 
1107 static inline void tick_nohz_irq_enter(void)
1108 {
1109         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1110         ktime_t now;
1111 
1112         if (!ts->idle_active && !ts->tick_stopped)
1113                 return;
1114         now = ktime_get();
1115         if (ts->idle_active)
1116                 tick_nohz_stop_idle(ts, now);
1117         if (ts->tick_stopped)
1118                 tick_nohz_update_jiffies(now);
1119 }
1120 
1121 #else
1122 
1123 static inline void tick_nohz_switch_to_nohz(void) { }
1124 static inline void tick_nohz_irq_enter(void) { }
1125 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
1126 
1127 #endif /* CONFIG_NO_HZ_COMMON */
1128 
1129 /*
1130  * Called from irq_enter to notify about the possible interruption of idle()
1131  */
1132 void tick_irq_enter(void)
1133 {
1134         tick_check_oneshot_broadcast_this_cpu();
1135         tick_nohz_irq_enter();
1136 }
1137 
1138 /*
1139  * High resolution timer specific code
1140  */
1141 #ifdef CONFIG_HIGH_RES_TIMERS
1142 /*
1143  * We rearm the timer until we get disabled by the idle code.
1144  * Called with interrupts disabled.
1145  */
1146 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1147 {
1148         struct tick_sched *ts =
1149                 container_of(timer, struct tick_sched, sched_timer);
1150         struct pt_regs *regs = get_irq_regs();
1151         ktime_t now = ktime_get();
1152 
1153         tick_sched_do_timer(now);
1154 
1155         /*
1156          * Do not call, when we are not in irq context and have
1157          * no valid regs pointer
1158          */
1159         if (regs)
1160                 tick_sched_handle(ts, regs);
1161 
1162         /* No need to reprogram if we are in idle or full dynticks mode */
1163         if (unlikely(ts->tick_stopped))
1164                 return HRTIMER_NORESTART;
1165 
1166         hrtimer_forward(timer, now, tick_period);
1167 
1168         return HRTIMER_RESTART;
1169 }
1170 
1171 static int sched_skew_tick;
1172 
1173 static int __init skew_tick(char *str)
1174 {
1175         get_option(&str, &sched_skew_tick);
1176 
1177         return 0;
1178 }
1179 early_param("skew_tick", skew_tick);
1180 
1181 /**
1182  * tick_setup_sched_timer - setup the tick emulation timer
1183  */
1184 void tick_setup_sched_timer(void)
1185 {
1186         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1187         ktime_t now = ktime_get();
1188 
1189         /*
1190          * Emulate tick processing via per-CPU hrtimers:
1191          */
1192         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1193         ts->sched_timer.function = tick_sched_timer;
1194 
1195         /* Get the next period (per-CPU) */
1196         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1197 
1198         /* Offset the tick to avert jiffies_lock contention. */
1199         if (sched_skew_tick) {
1200                 u64 offset = ktime_to_ns(tick_period) >> 1;
1201                 do_div(offset, num_possible_cpus());
1202                 offset *= smp_processor_id();
1203                 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1204         }
1205 
1206         hrtimer_forward(&ts->sched_timer, now, tick_period);
1207         hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
1208         tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
1209 }
1210 #endif /* HIGH_RES_TIMERS */
1211 
1212 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1213 void tick_cancel_sched_timer(int cpu)
1214 {
1215         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1216 
1217 # ifdef CONFIG_HIGH_RES_TIMERS
1218         if (ts->sched_timer.base)
1219                 hrtimer_cancel(&ts->sched_timer);
1220 # endif
1221 
1222         memset(ts, 0, sizeof(*ts));
1223 }
1224 #endif
1225 
1226 /**
1227  * Async notification about clocksource changes
1228  */
1229 void tick_clock_notify(void)
1230 {
1231         int cpu;
1232 
1233         for_each_possible_cpu(cpu)
1234                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1235 }
1236 
1237 /*
1238  * Async notification about clock event changes
1239  */
1240 void tick_oneshot_notify(void)
1241 {
1242         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1243 
1244         set_bit(0, &ts->check_clocks);
1245 }
1246 
1247 /**
1248  * Check, if a change happened, which makes oneshot possible.
1249  *
1250  * Called cyclic from the hrtimer softirq (driven by the timer
1251  * softirq) allow_nohz signals, that we can switch into low-res nohz
1252  * mode, because high resolution timers are disabled (either compile
1253  * or runtime). Called with interrupts disabled.
1254  */
1255 int tick_check_oneshot_change(int allow_nohz)
1256 {
1257         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1258 
1259         if (!test_and_clear_bit(0, &ts->check_clocks))
1260                 return 0;
1261 
1262         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1263                 return 0;
1264 
1265         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1266                 return 0;
1267 
1268         if (!allow_nohz)
1269                 return 1;
1270 
1271         tick_nohz_switch_to_nohz();
1272         return 0;
1273 }
1274 

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