1/* 2 * linux/kernel/time/tick-sched.c 3 * 4 * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de> 5 * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar 6 * Copyright(C) 2006-2007 Timesys Corp., Thomas Gleixner 7 * 8 * No idle tick implementation for low and high resolution timers 9 * 10 * Started by: Thomas Gleixner and Ingo Molnar 11 * 12 * Distribute under GPLv2. 13 */ 14#include <linux/cpu.h> 15#include <linux/err.h> 16#include <linux/hrtimer.h> 17#include <linux/interrupt.h> 18#include <linux/kernel_stat.h> 19#include <linux/percpu.h> 20#include <linux/profile.h> 21#include <linux/sched.h> 22#include <linux/module.h> 23#include <linux/irq_work.h> 24#include <linux/posix-timers.h> 25#include <linux/perf_event.h> 26#include <linux/context_tracking.h> 27 28#include <asm/irq_regs.h> 29 30#include "tick-internal.h" 31 32#include <trace/events/timer.h> 33 34/* 35 * Per cpu nohz control structure 36 */ 37static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched); 38 39/* 40 * The time, when the last jiffy update happened. Protected by jiffies_lock. 41 */ 42static ktime_t last_jiffies_update; 43 44struct tick_sched *tick_get_tick_sched(int cpu) 45{ 46 return &per_cpu(tick_cpu_sched, cpu); 47} 48 49/* 50 * Must be called with interrupts disabled ! 51 */ 52static 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 */ 98static 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 112static 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 134static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs) 135{ 136#ifdef CONFIG_NO_HZ_COMMON 137 /* 138 * When we are idle and the tick is stopped, we have to touch 139 * the watchdog as we might not schedule for a really long 140 * time. This happens on complete idle SMP systems while 141 * waiting on the login prompt. We also increment the "start of 142 * idle" jiffy stamp so the idle accounting adjustment we do 143 * when we go busy again does not account too much ticks. 144 */ 145 if (ts->tick_stopped) { 146 touch_softlockup_watchdog(); 147 if (is_idle_task(current)) 148 ts->idle_jiffies++; 149 } 150#endif 151 update_process_times(user_mode(regs)); 152 profile_tick(CPU_PROFILING); 153} 154 155#ifdef CONFIG_NO_HZ_FULL 156cpumask_var_t tick_nohz_full_mask; 157cpumask_var_t housekeeping_mask; 158bool tick_nohz_full_running; 159 160static bool can_stop_full_tick(void) 161{ 162 WARN_ON_ONCE(!irqs_disabled()); 163 164 if (!sched_can_stop_tick()) { 165 trace_tick_stop(0, "more than 1 task in runqueue\n"); 166 return false; 167 } 168 169 if (!posix_cpu_timers_can_stop_tick(current)) { 170 trace_tick_stop(0, "posix timers running\n"); 171 return false; 172 } 173 174 if (!perf_event_can_stop_tick()) { 175 trace_tick_stop(0, "perf events running\n"); 176 return false; 177 } 178 179 /* sched_clock_tick() needs us? */ 180#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK 181 /* 182 * TODO: kick full dynticks CPUs when 183 * sched_clock_stable is set. 184 */ 185 if (!sched_clock_stable()) { 186 trace_tick_stop(0, "unstable sched clock\n"); 187 /* 188 * Don't allow the user to think they can get 189 * full NO_HZ with this machine. 190 */ 191 WARN_ONCE(tick_nohz_full_running, 192 "NO_HZ FULL will not work with unstable sched clock"); 193 return false; 194 } 195#endif 196 197 return true; 198} 199 200static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now); 201 202/* 203 * Re-evaluate the need for the tick on the current CPU 204 * and restart it if necessary. 205 */ 206void __tick_nohz_full_check(void) 207{ 208 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 209 210 if (tick_nohz_full_cpu(smp_processor_id())) { 211 if (ts->tick_stopped && !is_idle_task(current)) { 212 if (!can_stop_full_tick()) 213 tick_nohz_restart_sched_tick(ts, ktime_get()); 214 } 215 } 216} 217 218static void nohz_full_kick_work_func(struct irq_work *work) 219{ 220 __tick_nohz_full_check(); 221} 222 223static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = { 224 .func = nohz_full_kick_work_func, 225}; 226 227/* 228 * Kick this CPU if it's full dynticks in order to force it to 229 * re-evaluate its dependency on the tick and restart it if necessary. 230 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(), 231 * is NMI safe. 232 */ 233void tick_nohz_full_kick(void) 234{ 235 if (!tick_nohz_full_cpu(smp_processor_id())) 236 return; 237 238 irq_work_queue(this_cpu_ptr(&nohz_full_kick_work)); 239} 240 241/* 242 * Kick the CPU if it's full dynticks in order to force it to 243 * re-evaluate its dependency on the tick and restart it if necessary. 244 */ 245void tick_nohz_full_kick_cpu(int cpu) 246{ 247 if (!tick_nohz_full_cpu(cpu)) 248 return; 249 250 irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu); 251} 252 253static void nohz_full_kick_ipi(void *info) 254{ 255 __tick_nohz_full_check(); 256} 257 258/* 259 * Kick all full dynticks CPUs in order to force these to re-evaluate 260 * their dependency on the tick and restart it if necessary. 261 */ 262void tick_nohz_full_kick_all(void) 263{ 264 if (!tick_nohz_full_running) 265 return; 266 267 preempt_disable(); 268 smp_call_function_many(tick_nohz_full_mask, 269 nohz_full_kick_ipi, NULL, false); 270 tick_nohz_full_kick(); 271 preempt_enable(); 272} 273 274/* 275 * Re-evaluate the need for the tick as we switch the current task. 276 * It might need the tick due to per task/process properties: 277 * perf events, posix cpu timers, ... 278 */ 279void __tick_nohz_task_switch(struct task_struct *tsk) 280{ 281 unsigned long flags; 282 283 local_irq_save(flags); 284 285 if (!tick_nohz_full_cpu(smp_processor_id())) 286 goto out; 287 288 if (tick_nohz_tick_stopped() && !can_stop_full_tick()) 289 tick_nohz_full_kick(); 290 291out: 292 local_irq_restore(flags); 293} 294 295/* Parse the boot-time nohz CPU list from the kernel parameters. */ 296static int __init tick_nohz_full_setup(char *str) 297{ 298 alloc_bootmem_cpumask_var(&tick_nohz_full_mask); 299 if (cpulist_parse(str, tick_nohz_full_mask) < 0) { 300 pr_warning("NOHZ: Incorrect nohz_full cpumask\n"); 301 free_bootmem_cpumask_var(tick_nohz_full_mask); 302 return 1; 303 } 304 tick_nohz_full_running = true; 305 306 return 1; 307} 308__setup("nohz_full=", tick_nohz_full_setup); 309 310static int tick_nohz_cpu_down_callback(struct notifier_block *nfb, 311 unsigned long action, 312 void *hcpu) 313{ 314 unsigned int cpu = (unsigned long)hcpu; 315 316 switch (action & ~CPU_TASKS_FROZEN) { 317 case CPU_DOWN_PREPARE: 318 /* 319 * If we handle the timekeeping duty for full dynticks CPUs, 320 * we can't safely shutdown that CPU. 321 */ 322 if (tick_nohz_full_running && tick_do_timer_cpu == cpu) 323 return NOTIFY_BAD; 324 break; 325 } 326 return NOTIFY_OK; 327} 328 329static int tick_nohz_init_all(void) 330{ 331 int err = -1; 332 333#ifdef CONFIG_NO_HZ_FULL_ALL 334 if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) { 335 WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n"); 336 return err; 337 } 338 err = 0; 339 cpumask_setall(tick_nohz_full_mask); 340 tick_nohz_full_running = true; 341#endif 342 return err; 343} 344 345void __init tick_nohz_init(void) 346{ 347 int cpu; 348 349 if (!tick_nohz_full_running) { 350 if (tick_nohz_init_all() < 0) 351 return; 352 } 353 354 if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) { 355 WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n"); 356 cpumask_clear(tick_nohz_full_mask); 357 tick_nohz_full_running = false; 358 return; 359 } 360 361 /* 362 * Full dynticks uses irq work to drive the tick rescheduling on safe 363 * locking contexts. But then we need irq work to raise its own 364 * interrupts to avoid circular dependency on the tick 365 */ 366 if (!arch_irq_work_has_interrupt()) { 367 pr_warning("NO_HZ: Can't run full dynticks because arch doesn't " 368 "support irq work self-IPIs\n"); 369 cpumask_clear(tick_nohz_full_mask); 370 cpumask_copy(housekeeping_mask, cpu_possible_mask); 371 tick_nohz_full_running = false; 372 return; 373 } 374 375 cpu = smp_processor_id(); 376 377 if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) { 378 pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu); 379 cpumask_clear_cpu(cpu, tick_nohz_full_mask); 380 } 381 382 cpumask_andnot(housekeeping_mask, 383 cpu_possible_mask, tick_nohz_full_mask); 384 385 for_each_cpu(cpu, tick_nohz_full_mask) 386 context_tracking_cpu_set(cpu); 387 388 cpu_notifier(tick_nohz_cpu_down_callback, 0); 389 pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n", 390 cpumask_pr_args(tick_nohz_full_mask)); 391} 392#endif 393 394/* 395 * NOHZ - aka dynamic tick functionality 396 */ 397#ifdef CONFIG_NO_HZ_COMMON 398/* 399 * NO HZ enabled ? 400 */ 401static int tick_nohz_enabled __read_mostly = 1; 402int tick_nohz_active __read_mostly; 403/* 404 * Enable / Disable tickless mode 405 */ 406static int __init setup_tick_nohz(char *str) 407{ 408 if (!strcmp(str, "off")) 409 tick_nohz_enabled = 0; 410 else if (!strcmp(str, "on")) 411 tick_nohz_enabled = 1; 412 else 413 return 0; 414 return 1; 415} 416 417__setup("nohz=", setup_tick_nohz); 418 419int tick_nohz_tick_stopped(void) 420{ 421 return __this_cpu_read(tick_cpu_sched.tick_stopped); 422} 423 424/** 425 * tick_nohz_update_jiffies - update jiffies when idle was interrupted 426 * 427 * Called from interrupt entry when the CPU was idle 428 * 429 * In case the sched_tick was stopped on this CPU, we have to check if jiffies 430 * must be updated. Otherwise an interrupt handler could use a stale jiffy 431 * value. We do this unconditionally on any cpu, as we don't know whether the 432 * cpu, which has the update task assigned is in a long sleep. 433 */ 434static void tick_nohz_update_jiffies(ktime_t now) 435{ 436 unsigned long flags; 437 438 __this_cpu_write(tick_cpu_sched.idle_waketime, now); 439 440 local_irq_save(flags); 441 tick_do_update_jiffies64(now); 442 local_irq_restore(flags); 443 444 touch_softlockup_watchdog(); 445} 446 447/* 448 * Updates the per cpu time idle statistics counters 449 */ 450static void 451update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time) 452{ 453 ktime_t delta; 454 455 if (ts->idle_active) { 456 delta = ktime_sub(now, ts->idle_entrytime); 457 if (nr_iowait_cpu(cpu) > 0) 458 ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta); 459 else 460 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); 461 ts->idle_entrytime = now; 462 } 463 464 if (last_update_time) 465 *last_update_time = ktime_to_us(now); 466 467} 468 469static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now) 470{ 471 update_ts_time_stats(smp_processor_id(), ts, now, NULL); 472 ts->idle_active = 0; 473 474 sched_clock_idle_wakeup_event(0); 475} 476 477static ktime_t tick_nohz_start_idle(struct tick_sched *ts) 478{ 479 ktime_t now = ktime_get(); 480 481 ts->idle_entrytime = now; 482 ts->idle_active = 1; 483 sched_clock_idle_sleep_event(); 484 return now; 485} 486 487/** 488 * get_cpu_idle_time_us - get the total idle time of a cpu 489 * @cpu: CPU number to query 490 * @last_update_time: variable to store update time in. Do not update 491 * counters if NULL. 492 * 493 * Return the cummulative idle time (since boot) for a given 494 * CPU, in microseconds. 495 * 496 * This time is measured via accounting rather than sampling, 497 * and is as accurate as ktime_get() is. 498 * 499 * This function returns -1 if NOHZ is not enabled. 500 */ 501u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) 502{ 503 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 504 ktime_t now, idle; 505 506 if (!tick_nohz_active) 507 return -1; 508 509 now = ktime_get(); 510 if (last_update_time) { 511 update_ts_time_stats(cpu, ts, now, last_update_time); 512 idle = ts->idle_sleeptime; 513 } else { 514 if (ts->idle_active && !nr_iowait_cpu(cpu)) { 515 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 516 517 idle = ktime_add(ts->idle_sleeptime, delta); 518 } else { 519 idle = ts->idle_sleeptime; 520 } 521 } 522 523 return ktime_to_us(idle); 524 525} 526EXPORT_SYMBOL_GPL(get_cpu_idle_time_us); 527 528/** 529 * get_cpu_iowait_time_us - get the total iowait time of a cpu 530 * @cpu: CPU number to query 531 * @last_update_time: variable to store update time in. Do not update 532 * counters if NULL. 533 * 534 * Return the cummulative iowait time (since boot) for a given 535 * CPU, in microseconds. 536 * 537 * This time is measured via accounting rather than sampling, 538 * and is as accurate as ktime_get() is. 539 * 540 * This function returns -1 if NOHZ is not enabled. 541 */ 542u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time) 543{ 544 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 545 ktime_t now, iowait; 546 547 if (!tick_nohz_active) 548 return -1; 549 550 now = ktime_get(); 551 if (last_update_time) { 552 update_ts_time_stats(cpu, ts, now, last_update_time); 553 iowait = ts->iowait_sleeptime; 554 } else { 555 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) { 556 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 557 558 iowait = ktime_add(ts->iowait_sleeptime, delta); 559 } else { 560 iowait = ts->iowait_sleeptime; 561 } 562 } 563 564 return ktime_to_us(iowait); 565} 566EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us); 567 568static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, 569 ktime_t now, int cpu) 570{ 571 unsigned long seq, last_jiffies, next_jiffies, delta_jiffies; 572 ktime_t last_update, expires, ret = { .tv64 = 0 }; 573 unsigned long rcu_delta_jiffies; 574 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); 575 u64 time_delta; 576 577 time_delta = timekeeping_max_deferment(); 578 579 /* Read jiffies and the time when jiffies were updated last */ 580 do { 581 seq = read_seqbegin(&jiffies_lock); 582 last_update = last_jiffies_update; 583 last_jiffies = jiffies; 584 } while (read_seqretry(&jiffies_lock, seq)); 585 586 if (rcu_needs_cpu(&rcu_delta_jiffies) || 587 arch_needs_cpu() || irq_work_needs_cpu()) { 588 next_jiffies = last_jiffies + 1; 589 delta_jiffies = 1; 590 } else { 591 /* Get the next timer wheel timer */ 592 next_jiffies = get_next_timer_interrupt(last_jiffies); 593 delta_jiffies = next_jiffies - last_jiffies; 594 if (rcu_delta_jiffies < delta_jiffies) { 595 next_jiffies = last_jiffies + rcu_delta_jiffies; 596 delta_jiffies = rcu_delta_jiffies; 597 } 598 } 599 600 /* 601 * Do not stop the tick, if we are only one off (or less) 602 * or if the cpu is required for RCU: 603 */ 604 if (!ts->tick_stopped && delta_jiffies <= 1) 605 goto out; 606 607 /* Schedule the tick, if we are at least one jiffie off */ 608 if ((long)delta_jiffies >= 1) { 609 610 /* 611 * If this cpu is the one which updates jiffies, then 612 * give up the assignment and let it be taken by the 613 * cpu which runs the tick timer next, which might be 614 * this cpu as well. If we don't drop this here the 615 * jiffies might be stale and do_timer() never 616 * invoked. Keep track of the fact that it was the one 617 * which had the do_timer() duty last. If this cpu is 618 * the one which had the do_timer() duty last, we 619 * limit the sleep time to the timekeeping 620 * max_deferement value which we retrieved 621 * above. Otherwise we can sleep as long as we want. 622 */ 623 if (cpu == tick_do_timer_cpu) { 624 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 625 ts->do_timer_last = 1; 626 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) { 627 time_delta = KTIME_MAX; 628 ts->do_timer_last = 0; 629 } else if (!ts->do_timer_last) { 630 time_delta = KTIME_MAX; 631 } 632 633#ifdef CONFIG_NO_HZ_FULL 634 if (!ts->inidle) { 635 time_delta = min(time_delta, 636 scheduler_tick_max_deferment()); 637 } 638#endif 639 640 /* 641 * calculate the expiry time for the next timer wheel 642 * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals 643 * that there is no timer pending or at least extremely 644 * far into the future (12 days for HZ=1000). In this 645 * case we set the expiry to the end of time. 646 */ 647 if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) { 648 /* 649 * Calculate the time delta for the next timer event. 650 * If the time delta exceeds the maximum time delta 651 * permitted by the current clocksource then adjust 652 * the time delta accordingly to ensure the 653 * clocksource does not wrap. 654 */ 655 time_delta = min_t(u64, time_delta, 656 tick_period.tv64 * delta_jiffies); 657 } 658 659 if (time_delta < KTIME_MAX) 660 expires = ktime_add_ns(last_update, time_delta); 661 else 662 expires.tv64 = KTIME_MAX; 663 664 /* Skip reprogram of event if its not changed */ 665 if (ts->tick_stopped && ktime_equal(expires, dev->next_event)) 666 goto out; 667 668 ret = expires; 669 670 /* 671 * nohz_stop_sched_tick can be called several times before 672 * the nohz_restart_sched_tick is called. This happens when 673 * interrupts arrive which do not cause a reschedule. In the 674 * first call we save the current tick time, so we can restart 675 * the scheduler tick in nohz_restart_sched_tick. 676 */ 677 if (!ts->tick_stopped) { 678 nohz_balance_enter_idle(cpu); 679 calc_load_enter_idle(); 680 681 ts->last_tick = hrtimer_get_expires(&ts->sched_timer); 682 ts->tick_stopped = 1; 683 trace_tick_stop(1, " "); 684 } 685 686 /* 687 * If the expiration time == KTIME_MAX, then 688 * in this case we simply stop the tick timer. 689 */ 690 if (unlikely(expires.tv64 == KTIME_MAX)) { 691 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) 692 hrtimer_cancel(&ts->sched_timer); 693 goto out; 694 } 695 696 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { 697 hrtimer_start(&ts->sched_timer, expires, 698 HRTIMER_MODE_ABS_PINNED); 699 /* Check, if the timer was already in the past */ 700 if (hrtimer_active(&ts->sched_timer)) 701 goto out; 702 } else if (!tick_program_event(expires, 0)) 703 goto out; 704 /* 705 * We are past the event already. So we crossed a 706 * jiffie boundary. Update jiffies and raise the 707 * softirq. 708 */ 709 tick_do_update_jiffies64(ktime_get()); 710 } 711 raise_softirq_irqoff(TIMER_SOFTIRQ); 712out: 713 ts->next_jiffies = next_jiffies; 714 ts->last_jiffies = last_jiffies; 715 ts->sleep_length = ktime_sub(dev->next_event, now); 716 717 return ret; 718} 719 720static void tick_nohz_full_stop_tick(struct tick_sched *ts) 721{ 722#ifdef CONFIG_NO_HZ_FULL 723 int cpu = smp_processor_id(); 724 725 if (!tick_nohz_full_cpu(cpu) || is_idle_task(current)) 726 return; 727 728 if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) 729 return; 730 731 if (!can_stop_full_tick()) 732 return; 733 734 tick_nohz_stop_sched_tick(ts, ktime_get(), cpu); 735#endif 736} 737 738static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) 739{ 740 /* 741 * If this cpu is offline and it is the one which updates 742 * jiffies, then give up the assignment and let it be taken by 743 * the cpu which runs the tick timer next. If we don't drop 744 * this here the jiffies might be stale and do_timer() never 745 * invoked. 746 */ 747 if (unlikely(!cpu_online(cpu))) { 748 if (cpu == tick_do_timer_cpu) 749 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 750 return false; 751 } 752 753 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) { 754 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ }; 755 return false; 756 } 757 758 if (need_resched()) 759 return false; 760 761 if (unlikely(local_softirq_pending() && cpu_online(cpu))) { 762 static int ratelimit; 763 764 if (ratelimit < 10 && 765 (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { 766 pr_warn("NOHZ: local_softirq_pending %02x\n", 767 (unsigned int) local_softirq_pending()); 768 ratelimit++; 769 } 770 return false; 771 } 772 773 if (tick_nohz_full_enabled()) { 774 /* 775 * Keep the tick alive to guarantee timekeeping progression 776 * if there are full dynticks CPUs around 777 */ 778 if (tick_do_timer_cpu == cpu) 779 return false; 780 /* 781 * Boot safety: make sure the timekeeping duty has been 782 * assigned before entering dyntick-idle mode, 783 */ 784 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE) 785 return false; 786 } 787 788 return true; 789} 790 791static void __tick_nohz_idle_enter(struct tick_sched *ts) 792{ 793 ktime_t now, expires; 794 int cpu = smp_processor_id(); 795 796 now = tick_nohz_start_idle(ts); 797 798 if (can_stop_idle_tick(cpu, ts)) { 799 int was_stopped = ts->tick_stopped; 800 801 ts->idle_calls++; 802 803 expires = tick_nohz_stop_sched_tick(ts, now, cpu); 804 if (expires.tv64 > 0LL) { 805 ts->idle_sleeps++; 806 ts->idle_expires = expires; 807 } 808 809 if (!was_stopped && ts->tick_stopped) 810 ts->idle_jiffies = ts->last_jiffies; 811 } 812} 813 814/** 815 * tick_nohz_idle_enter - stop the idle tick from the idle task 816 * 817 * When the next event is more than a tick into the future, stop the idle tick 818 * Called when we start the idle loop. 819 * 820 * The arch is responsible of calling: 821 * 822 * - rcu_idle_enter() after its last use of RCU before the CPU is put 823 * to sleep. 824 * - rcu_idle_exit() before the first use of RCU after the CPU is woken up. 825 */ 826void tick_nohz_idle_enter(void) 827{ 828 struct tick_sched *ts; 829 830 WARN_ON_ONCE(irqs_disabled()); 831 832 /* 833 * Update the idle state in the scheduler domain hierarchy 834 * when tick_nohz_stop_sched_tick() is called from the idle loop. 835 * State will be updated to busy during the first busy tick after 836 * exiting idle. 837 */ 838 set_cpu_sd_state_idle(); 839 840 local_irq_disable(); 841 842 ts = this_cpu_ptr(&tick_cpu_sched); 843 ts->inidle = 1; 844 __tick_nohz_idle_enter(ts); 845 846 local_irq_enable(); 847} 848 849/** 850 * tick_nohz_irq_exit - update next tick event from interrupt exit 851 * 852 * When an interrupt fires while we are idle and it doesn't cause 853 * a reschedule, it may still add, modify or delete a timer, enqueue 854 * an RCU callback, etc... 855 * So we need to re-calculate and reprogram the next tick event. 856 */ 857void tick_nohz_irq_exit(void) 858{ 859 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 860 861 if (ts->inidle) 862 __tick_nohz_idle_enter(ts); 863 else 864 tick_nohz_full_stop_tick(ts); 865} 866 867/** 868 * tick_nohz_get_sleep_length - return the length of the current sleep 869 * 870 * Called from power state control code with interrupts disabled 871 */ 872ktime_t tick_nohz_get_sleep_length(void) 873{ 874 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 875 876 return ts->sleep_length; 877} 878 879static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) 880{ 881 hrtimer_cancel(&ts->sched_timer); 882 hrtimer_set_expires(&ts->sched_timer, ts->last_tick); 883 884 while (1) { 885 /* Forward the time to expire in the future */ 886 hrtimer_forward(&ts->sched_timer, now, tick_period); 887 888 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { 889 hrtimer_start_expires(&ts->sched_timer, 890 HRTIMER_MODE_ABS_PINNED); 891 /* Check, if the timer was already in the past */ 892 if (hrtimer_active(&ts->sched_timer)) 893 break; 894 } else { 895 if (!tick_program_event( 896 hrtimer_get_expires(&ts->sched_timer), 0)) 897 break; 898 } 899 /* Reread time and update jiffies */ 900 now = ktime_get(); 901 tick_do_update_jiffies64(now); 902 } 903} 904 905static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) 906{ 907 /* Update jiffies first */ 908 tick_do_update_jiffies64(now); 909 update_cpu_load_nohz(); 910 911 calc_load_exit_idle(); 912 touch_softlockup_watchdog(); 913 /* 914 * Cancel the scheduled timer and restore the tick 915 */ 916 ts->tick_stopped = 0; 917 ts->idle_exittime = now; 918 919 tick_nohz_restart(ts, now); 920} 921 922static void tick_nohz_account_idle_ticks(struct tick_sched *ts) 923{ 924#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE 925 unsigned long ticks; 926 927 if (vtime_accounting_enabled()) 928 return; 929 /* 930 * We stopped the tick in idle. Update process times would miss the 931 * time we slept as update_process_times does only a 1 tick 932 * accounting. Enforce that this is accounted to idle ! 933 */ 934 ticks = jiffies - ts->idle_jiffies; 935 /* 936 * We might be one off. Do not randomly account a huge number of ticks! 937 */ 938 if (ticks && ticks < LONG_MAX) 939 account_idle_ticks(ticks); 940#endif 941} 942 943/** 944 * tick_nohz_idle_exit - restart the idle tick from the idle task 945 * 946 * Restart the idle tick when the CPU is woken up from idle 947 * This also exit the RCU extended quiescent state. The CPU 948 * can use RCU again after this function is called. 949 */ 950void tick_nohz_idle_exit(void) 951{ 952 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 953 ktime_t now; 954 955 local_irq_disable(); 956 957 WARN_ON_ONCE(!ts->inidle); 958 959 ts->inidle = 0; 960 961 if (ts->idle_active || ts->tick_stopped) 962 now = ktime_get(); 963 964 if (ts->idle_active) 965 tick_nohz_stop_idle(ts, now); 966 967 if (ts->tick_stopped) { 968 tick_nohz_restart_sched_tick(ts, now); 969 tick_nohz_account_idle_ticks(ts); 970 } 971 972 local_irq_enable(); 973} 974 975static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now) 976{ 977 hrtimer_forward(&ts->sched_timer, now, tick_period); 978 return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0); 979} 980 981/* 982 * The nohz low res interrupt handler 983 */ 984static void tick_nohz_handler(struct clock_event_device *dev) 985{ 986 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 987 struct pt_regs *regs = get_irq_regs(); 988 ktime_t now = ktime_get(); 989 990 dev->next_event.tv64 = KTIME_MAX; 991 992 tick_sched_do_timer(now); 993 tick_sched_handle(ts, regs); 994 995 /* No need to reprogram if we are running tickless */ 996 if (unlikely(ts->tick_stopped)) 997 return; 998 999 while (tick_nohz_reprogram(ts, now)) { 1000 now = ktime_get(); 1001 tick_do_update_jiffies64(now); 1002 } 1003} 1004 1005/** 1006 * tick_nohz_switch_to_nohz - switch to nohz mode 1007 */ 1008static void tick_nohz_switch_to_nohz(void) 1009{ 1010 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1011 ktime_t next; 1012 1013 if (!tick_nohz_enabled) 1014 return; 1015 1016 local_irq_disable(); 1017 if (tick_switch_to_oneshot(tick_nohz_handler)) { 1018 local_irq_enable(); 1019 return; 1020 } 1021 tick_nohz_active = 1; 1022 ts->nohz_mode = NOHZ_MODE_LOWRES; 1023 1024 /* 1025 * Recycle the hrtimer in ts, so we can share the 1026 * hrtimer_forward with the highres code. 1027 */ 1028 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 1029 /* Get the next period */ 1030 next = tick_init_jiffy_update(); 1031 1032 for (;;) { 1033 hrtimer_set_expires(&ts->sched_timer, next); 1034 if (!tick_program_event(next, 0)) 1035 break; 1036 next = ktime_add(next, tick_period); 1037 } 1038 local_irq_enable(); 1039} 1040 1041/* 1042 * When NOHZ is enabled and the tick is stopped, we need to kick the 1043 * tick timer from irq_enter() so that the jiffies update is kept 1044 * alive during long running softirqs. That's ugly as hell, but 1045 * correctness is key even if we need to fix the offending softirq in 1046 * the first place. 1047 * 1048 * Note, this is different to tick_nohz_restart. We just kick the 1049 * timer and do not touch the other magic bits which need to be done 1050 * when idle is left. 1051 */ 1052static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now) 1053{ 1054#if 0 1055 /* Switch back to 2.6.27 behaviour */ 1056 ktime_t delta; 1057 1058 /* 1059 * Do not touch the tick device, when the next expiry is either 1060 * already reached or less/equal than the tick period. 1061 */ 1062 delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now); 1063 if (delta.tv64 <= tick_period.tv64) 1064 return; 1065 1066 tick_nohz_restart(ts, now); 1067#endif 1068} 1069 1070static inline void tick_nohz_irq_enter(void) 1071{ 1072 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1073 ktime_t now; 1074 1075 if (!ts->idle_active && !ts->tick_stopped) 1076 return; 1077 now = ktime_get(); 1078 if (ts->idle_active) 1079 tick_nohz_stop_idle(ts, now); 1080 if (ts->tick_stopped) { 1081 tick_nohz_update_jiffies(now); 1082 tick_nohz_kick_tick(ts, now); 1083 } 1084} 1085 1086#else 1087 1088static inline void tick_nohz_switch_to_nohz(void) { } 1089static inline void tick_nohz_irq_enter(void) { } 1090 1091#endif /* CONFIG_NO_HZ_COMMON */ 1092 1093/* 1094 * Called from irq_enter to notify about the possible interruption of idle() 1095 */ 1096void tick_irq_enter(void) 1097{ 1098 tick_check_oneshot_broadcast_this_cpu(); 1099 tick_nohz_irq_enter(); 1100} 1101 1102/* 1103 * High resolution timer specific code 1104 */ 1105#ifdef CONFIG_HIGH_RES_TIMERS 1106/* 1107 * We rearm the timer until we get disabled by the idle code. 1108 * Called with interrupts disabled. 1109 */ 1110static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) 1111{ 1112 struct tick_sched *ts = 1113 container_of(timer, struct tick_sched, sched_timer); 1114 struct pt_regs *regs = get_irq_regs(); 1115 ktime_t now = ktime_get(); 1116 1117 tick_sched_do_timer(now); 1118 1119 /* 1120 * Do not call, when we are not in irq context and have 1121 * no valid regs pointer 1122 */ 1123 if (regs) 1124 tick_sched_handle(ts, regs); 1125 1126 /* No need to reprogram if we are in idle or full dynticks mode */ 1127 if (unlikely(ts->tick_stopped)) 1128 return HRTIMER_NORESTART; 1129 1130 hrtimer_forward(timer, now, tick_period); 1131 1132 return HRTIMER_RESTART; 1133} 1134 1135static int sched_skew_tick; 1136 1137static int __init skew_tick(char *str) 1138{ 1139 get_option(&str, &sched_skew_tick); 1140 1141 return 0; 1142} 1143early_param("skew_tick", skew_tick); 1144 1145/** 1146 * tick_setup_sched_timer - setup the tick emulation timer 1147 */ 1148void tick_setup_sched_timer(void) 1149{ 1150 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1151 ktime_t now = ktime_get(); 1152 1153 /* 1154 * Emulate tick processing via per-CPU hrtimers: 1155 */ 1156 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 1157 ts->sched_timer.function = tick_sched_timer; 1158 1159 /* Get the next period (per cpu) */ 1160 hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update()); 1161 1162 /* Offset the tick to avert jiffies_lock contention. */ 1163 if (sched_skew_tick) { 1164 u64 offset = ktime_to_ns(tick_period) >> 1; 1165 do_div(offset, num_possible_cpus()); 1166 offset *= smp_processor_id(); 1167 hrtimer_add_expires_ns(&ts->sched_timer, offset); 1168 } 1169 1170 for (;;) { 1171 hrtimer_forward(&ts->sched_timer, now, tick_period); 1172 hrtimer_start_expires(&ts->sched_timer, 1173 HRTIMER_MODE_ABS_PINNED); 1174 /* Check, if the timer was already in the past */ 1175 if (hrtimer_active(&ts->sched_timer)) 1176 break; 1177 now = ktime_get(); 1178 } 1179 1180#ifdef CONFIG_NO_HZ_COMMON 1181 if (tick_nohz_enabled) { 1182 ts->nohz_mode = NOHZ_MODE_HIGHRES; 1183 tick_nohz_active = 1; 1184 } 1185#endif 1186} 1187#endif /* HIGH_RES_TIMERS */ 1188 1189#if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS 1190void tick_cancel_sched_timer(int cpu) 1191{ 1192 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 1193 1194# ifdef CONFIG_HIGH_RES_TIMERS 1195 if (ts->sched_timer.base) 1196 hrtimer_cancel(&ts->sched_timer); 1197# endif 1198 1199 memset(ts, 0, sizeof(*ts)); 1200} 1201#endif 1202 1203/** 1204 * Async notification about clocksource changes 1205 */ 1206void tick_clock_notify(void) 1207{ 1208 int cpu; 1209 1210 for_each_possible_cpu(cpu) 1211 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks); 1212} 1213 1214/* 1215 * Async notification about clock event changes 1216 */ 1217void tick_oneshot_notify(void) 1218{ 1219 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1220 1221 set_bit(0, &ts->check_clocks); 1222} 1223 1224/** 1225 * Check, if a change happened, which makes oneshot possible. 1226 * 1227 * Called cyclic from the hrtimer softirq (driven by the timer 1228 * softirq) allow_nohz signals, that we can switch into low-res nohz 1229 * mode, because high resolution timers are disabled (either compile 1230 * or runtime). 1231 */ 1232int tick_check_oneshot_change(int allow_nohz) 1233{ 1234 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1235 1236 if (!test_and_clear_bit(0, &ts->check_clocks)) 1237 return 0; 1238 1239 if (ts->nohz_mode != NOHZ_MODE_INACTIVE) 1240 return 0; 1241 1242 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available()) 1243 return 0; 1244 1245 if (!allow_nohz) 1246 return 1; 1247 1248 tick_nohz_switch_to_nohz(); 1249 return 0; 1250} 1251