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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(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 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                 cpu_load_update_nohz_start();
780 
781                 ts->last_tick = hrtimer_get_expires(&ts->sched_timer);
782                 ts->tick_stopped = 1;
783                 trace_tick_stop(1, TICK_DEP_MASK_NONE);
784         }
785 
786         /*
787          * If the expiration time == KTIME_MAX, then we simply stop
788          * the tick timer.
789          */
790         if (unlikely(expires == KTIME_MAX)) {
791                 if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
792                         hrtimer_cancel(&ts->sched_timer);
793                 goto out;
794         }
795 
796         if (ts->nohz_mode == NOHZ_MODE_HIGHRES)
797                 hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED);
798         else
799                 tick_program_event(tick, 1);
800 out:
801         /* Update the estimated sleep length */
802         ts->sleep_length = ktime_sub(dev->next_event, now);
803         return tick;
804 }
805 
806 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
807 {
808         /* Update jiffies first */
809         tick_do_update_jiffies64(now);
810         cpu_load_update_nohz_stop();
811 
812         calc_load_exit_idle();
813         touch_softlockup_watchdog_sched();
814         /*
815          * Cancel the scheduled timer and restore the tick
816          */
817         ts->tick_stopped  = 0;
818         ts->idle_exittime = now;
819 
820         tick_nohz_restart(ts, now);
821 }
822 
823 static void tick_nohz_full_update_tick(struct tick_sched *ts)
824 {
825 #ifdef CONFIG_NO_HZ_FULL
826         int cpu = smp_processor_id();
827 
828         if (!tick_nohz_full_cpu(cpu))
829                 return;
830 
831         if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
832                 return;
833 
834         if (can_stop_full_tick(ts))
835                 tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
836         else if (ts->tick_stopped)
837                 tick_nohz_restart_sched_tick(ts, ktime_get());
838 #endif
839 }
840 
841 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts)
842 {
843         /*
844          * If this cpu is offline and it is the one which updates
845          * jiffies, then give up the assignment and let it be taken by
846          * the cpu which runs the tick timer next. If we don't drop
847          * this here the jiffies might be stale and do_timer() never
848          * invoked.
849          */
850         if (unlikely(!cpu_online(cpu))) {
851                 if (cpu == tick_do_timer_cpu)
852                         tick_do_timer_cpu = TICK_DO_TIMER_NONE;
853                 return false;
854         }
855 
856         if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) {
857                 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ };
858                 return false;
859         }
860 
861         if (need_resched())
862                 return false;
863 
864         if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
865                 static int ratelimit;
866 
867                 if (ratelimit < 10 &&
868                     (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) {
869                         pr_warn("NOHZ: local_softirq_pending %02x\n",
870                                 (unsigned int) local_softirq_pending());
871                         ratelimit++;
872                 }
873                 return false;
874         }
875 
876         if (tick_nohz_full_enabled()) {
877                 /*
878                  * Keep the tick alive to guarantee timekeeping progression
879                  * if there are full dynticks CPUs around
880                  */
881                 if (tick_do_timer_cpu == cpu)
882                         return false;
883                 /*
884                  * Boot safety: make sure the timekeeping duty has been
885                  * assigned before entering dyntick-idle mode,
886                  */
887                 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE)
888                         return false;
889         }
890 
891         return true;
892 }
893 
894 static void __tick_nohz_idle_enter(struct tick_sched *ts)
895 {
896         ktime_t now, expires;
897         int cpu = smp_processor_id();
898 
899         now = tick_nohz_start_idle(ts);
900 
901         if (can_stop_idle_tick(cpu, ts)) {
902                 int was_stopped = ts->tick_stopped;
903 
904                 ts->idle_calls++;
905 
906                 expires = tick_nohz_stop_sched_tick(ts, now, cpu);
907                 if (expires.tv64 > 0LL) {
908                         ts->idle_sleeps++;
909                         ts->idle_expires = expires;
910                 }
911 
912                 if (!was_stopped && ts->tick_stopped)
913                         ts->idle_jiffies = ts->last_jiffies;
914         }
915 }
916 
917 /**
918  * tick_nohz_idle_enter - stop the idle tick from the idle task
919  *
920  * When the next event is more than a tick into the future, stop the idle tick
921  * Called when we start the idle loop.
922  *
923  * The arch is responsible of calling:
924  *
925  * - rcu_idle_enter() after its last use of RCU before the CPU is put
926  *  to sleep.
927  * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
928  */
929 void tick_nohz_idle_enter(void)
930 {
931         struct tick_sched *ts;
932 
933         WARN_ON_ONCE(irqs_disabled());
934 
935         /*
936          * Update the idle state in the scheduler domain hierarchy
937          * when tick_nohz_stop_sched_tick() is called from the idle loop.
938          * State will be updated to busy during the first busy tick after
939          * exiting idle.
940          */
941         set_cpu_sd_state_idle();
942 
943         local_irq_disable();
944 
945         ts = this_cpu_ptr(&tick_cpu_sched);
946         ts->inidle = 1;
947         __tick_nohz_idle_enter(ts);
948 
949         local_irq_enable();
950 }
951 
952 /**
953  * tick_nohz_irq_exit - update next tick event from interrupt exit
954  *
955  * When an interrupt fires while we are idle and it doesn't cause
956  * a reschedule, it may still add, modify or delete a timer, enqueue
957  * an RCU callback, etc...
958  * So we need to re-calculate and reprogram the next tick event.
959  */
960 void tick_nohz_irq_exit(void)
961 {
962         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
963 
964         if (ts->inidle)
965                 __tick_nohz_idle_enter(ts);
966         else
967                 tick_nohz_full_update_tick(ts);
968 }
969 
970 /**
971  * tick_nohz_get_sleep_length - return the length of the current sleep
972  *
973  * Called from power state control code with interrupts disabled
974  */
975 ktime_t tick_nohz_get_sleep_length(void)
976 {
977         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
978 
979         return ts->sleep_length;
980 }
981 
982 static void tick_nohz_account_idle_ticks(struct tick_sched *ts)
983 {
984 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
985         unsigned long ticks;
986 
987         if (vtime_accounting_cpu_enabled())
988                 return;
989         /*
990          * We stopped the tick in idle. Update process times would miss the
991          * time we slept as update_process_times does only a 1 tick
992          * accounting. Enforce that this is accounted to idle !
993          */
994         ticks = jiffies - ts->idle_jiffies;
995         /*
996          * We might be one off. Do not randomly account a huge number of ticks!
997          */
998         if (ticks && ticks < LONG_MAX)
999                 account_idle_ticks(ticks);
1000 #endif
1001 }
1002 
1003 /**
1004  * tick_nohz_idle_exit - restart the idle tick from the idle task
1005  *
1006  * Restart the idle tick when the CPU is woken up from idle
1007  * This also exit the RCU extended quiescent state. The CPU
1008  * can use RCU again after this function is called.
1009  */
1010 void tick_nohz_idle_exit(void)
1011 {
1012         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1013         ktime_t now;
1014 
1015         local_irq_disable();
1016 
1017         WARN_ON_ONCE(!ts->inidle);
1018 
1019         ts->inidle = 0;
1020 
1021         if (ts->idle_active || ts->tick_stopped)
1022                 now = ktime_get();
1023 
1024         if (ts->idle_active)
1025                 tick_nohz_stop_idle(ts, now);
1026 
1027         if (ts->tick_stopped) {
1028                 tick_nohz_restart_sched_tick(ts, now);
1029                 tick_nohz_account_idle_ticks(ts);
1030         }
1031 
1032         local_irq_enable();
1033 }
1034 
1035 /*
1036  * The nohz low res interrupt handler
1037  */
1038 static void tick_nohz_handler(struct clock_event_device *dev)
1039 {
1040         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1041         struct pt_regs *regs = get_irq_regs();
1042         ktime_t now = ktime_get();
1043 
1044         dev->next_event.tv64 = KTIME_MAX;
1045 
1046         tick_sched_do_timer(now);
1047         tick_sched_handle(ts, regs);
1048 
1049         /* No need to reprogram if we are running tickless  */
1050         if (unlikely(ts->tick_stopped))
1051                 return;
1052 
1053         hrtimer_forward(&ts->sched_timer, now, tick_period);
1054         tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1055 }
1056 
1057 static inline void tick_nohz_activate(struct tick_sched *ts, int mode)
1058 {
1059         if (!tick_nohz_enabled)
1060                 return;
1061         ts->nohz_mode = mode;
1062         /* One update is enough */
1063         if (!test_and_set_bit(0, &tick_nohz_active))
1064                 timers_update_migration(true);
1065 }
1066 
1067 /**
1068  * tick_nohz_switch_to_nohz - switch to nohz mode
1069  */
1070 static void tick_nohz_switch_to_nohz(void)
1071 {
1072         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1073         ktime_t next;
1074 
1075         if (!tick_nohz_enabled)
1076                 return;
1077 
1078         if (tick_switch_to_oneshot(tick_nohz_handler))
1079                 return;
1080 
1081         /*
1082          * Recycle the hrtimer in ts, so we can share the
1083          * hrtimer_forward with the highres code.
1084          */
1085         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1086         /* Get the next period */
1087         next = tick_init_jiffy_update();
1088 
1089         hrtimer_set_expires(&ts->sched_timer, next);
1090         hrtimer_forward_now(&ts->sched_timer, tick_period);
1091         tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
1092         tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
1093 }
1094 
1095 /*
1096  * When NOHZ is enabled and the tick is stopped, we need to kick the
1097  * tick timer from irq_enter() so that the jiffies update is kept
1098  * alive during long running softirqs. That's ugly as hell, but
1099  * correctness is key even if we need to fix the offending softirq in
1100  * the first place.
1101  *
1102  * Note, this is different to tick_nohz_restart. We just kick the
1103  * timer and do not touch the other magic bits which need to be done
1104  * when idle is left.
1105  */
1106 static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now)
1107 {
1108 #if 0
1109         /* Switch back to 2.6.27 behaviour */
1110         ktime_t delta;
1111 
1112         /*
1113          * Do not touch the tick device, when the next expiry is either
1114          * already reached or less/equal than the tick period.
1115          */
1116         delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now);
1117         if (delta.tv64 <= tick_period.tv64)
1118                 return;
1119 
1120         tick_nohz_restart(ts, now);
1121 #endif
1122 }
1123 
1124 static inline void tick_nohz_irq_enter(void)
1125 {
1126         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1127         ktime_t now;
1128 
1129         if (!ts->idle_active && !ts->tick_stopped)
1130                 return;
1131         now = ktime_get();
1132         if (ts->idle_active)
1133                 tick_nohz_stop_idle(ts, now);
1134         if (ts->tick_stopped) {
1135                 tick_nohz_update_jiffies(now);
1136                 tick_nohz_kick_tick(ts, now);
1137         }
1138 }
1139 
1140 #else
1141 
1142 static inline void tick_nohz_switch_to_nohz(void) { }
1143 static inline void tick_nohz_irq_enter(void) { }
1144 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { }
1145 
1146 #endif /* CONFIG_NO_HZ_COMMON */
1147 
1148 /*
1149  * Called from irq_enter to notify about the possible interruption of idle()
1150  */
1151 void tick_irq_enter(void)
1152 {
1153         tick_check_oneshot_broadcast_this_cpu();
1154         tick_nohz_irq_enter();
1155 }
1156 
1157 /*
1158  * High resolution timer specific code
1159  */
1160 #ifdef CONFIG_HIGH_RES_TIMERS
1161 /*
1162  * We rearm the timer until we get disabled by the idle code.
1163  * Called with interrupts disabled.
1164  */
1165 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
1166 {
1167         struct tick_sched *ts =
1168                 container_of(timer, struct tick_sched, sched_timer);
1169         struct pt_regs *regs = get_irq_regs();
1170         ktime_t now = ktime_get();
1171 
1172         tick_sched_do_timer(now);
1173 
1174         /*
1175          * Do not call, when we are not in irq context and have
1176          * no valid regs pointer
1177          */
1178         if (regs)
1179                 tick_sched_handle(ts, regs);
1180 
1181         /* No need to reprogram if we are in idle or full dynticks mode */
1182         if (unlikely(ts->tick_stopped))
1183                 return HRTIMER_NORESTART;
1184 
1185         hrtimer_forward(timer, now, tick_period);
1186 
1187         return HRTIMER_RESTART;
1188 }
1189 
1190 static int sched_skew_tick;
1191 
1192 static int __init skew_tick(char *str)
1193 {
1194         get_option(&str, &sched_skew_tick);
1195 
1196         return 0;
1197 }
1198 early_param("skew_tick", skew_tick);
1199 
1200 /**
1201  * tick_setup_sched_timer - setup the tick emulation timer
1202  */
1203 void tick_setup_sched_timer(void)
1204 {
1205         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1206         ktime_t now = ktime_get();
1207 
1208         /*
1209          * Emulate tick processing via per-CPU hrtimers:
1210          */
1211         hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
1212         ts->sched_timer.function = tick_sched_timer;
1213 
1214         /* Get the next period (per cpu) */
1215         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
1216 
1217         /* Offset the tick to avert jiffies_lock contention. */
1218         if (sched_skew_tick) {
1219                 u64 offset = ktime_to_ns(tick_period) >> 1;
1220                 do_div(offset, num_possible_cpus());
1221                 offset *= smp_processor_id();
1222                 hrtimer_add_expires_ns(&ts->sched_timer, offset);
1223         }
1224 
1225         hrtimer_forward(&ts->sched_timer, now, tick_period);
1226         hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED);
1227         tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);
1228 }
1229 #endif /* HIGH_RES_TIMERS */
1230 
1231 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
1232 void tick_cancel_sched_timer(int cpu)
1233 {
1234         struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
1235 
1236 # ifdef CONFIG_HIGH_RES_TIMERS
1237         if (ts->sched_timer.base)
1238                 hrtimer_cancel(&ts->sched_timer);
1239 # endif
1240 
1241         memset(ts, 0, sizeof(*ts));
1242 }
1243 #endif
1244 
1245 /**
1246  * Async notification about clocksource changes
1247  */
1248 void tick_clock_notify(void)
1249 {
1250         int cpu;
1251 
1252         for_each_possible_cpu(cpu)
1253                 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks);
1254 }
1255 
1256 /*
1257  * Async notification about clock event changes
1258  */
1259 void tick_oneshot_notify(void)
1260 {
1261         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1262 
1263         set_bit(0, &ts->check_clocks);
1264 }
1265 
1266 /**
1267  * Check, if a change happened, which makes oneshot possible.
1268  *
1269  * Called cyclic from the hrtimer softirq (driven by the timer
1270  * softirq) allow_nohz signals, that we can switch into low-res nohz
1271  * mode, because high resolution timers are disabled (either compile
1272  * or runtime). Called with interrupts disabled.
1273  */
1274 int tick_check_oneshot_change(int allow_nohz)
1275 {
1276         struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
1277 
1278         if (!test_and_clear_bit(0, &ts->check_clocks))
1279                 return 0;
1280 
1281         if (ts->nohz_mode != NOHZ_MODE_INACTIVE)
1282                 return 0;
1283 
1284         if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available())
1285                 return 0;
1286 
1287         if (!allow_nohz)
1288                 return 1;
1289 
1290         tick_nohz_switch_to_nohz();
1291         return 0;
1292 }
1293 

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