Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

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

This page was automatically generated by LXR 0.3.1 (source).  •  Linux is a registered trademark of Linus Torvalds  •  Contact us