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 */ 37 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 */ 42 static ktime_t last_jiffies_update; 43 44 struct 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 */ 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(); 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 156 cpumask_var_t tick_nohz_full_mask; 157 cpumask_var_t housekeeping_mask; 158 bool tick_nohz_full_running; 159 160 static 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 } 199 200 static 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 */ 206 void __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 } 217 218 static void nohz_full_kick_work_func(struct irq_work *work) 219 { 220 __tick_nohz_full_check(); 221 } 222 223 static 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 */ 233 void 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 */ 245 void 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 } 252 253 static 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 */ 262 void 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 */ 279 void __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(); 290 291 out: 292 local_irq_restore(flags); 293 } 294 295 /* Parse the boot-time nohz CPU list from the kernel parameters. */ 296 static 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); 309 310 static 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 } 328 329 static 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 } 344 345 void __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 */ 401 static int tick_nohz_enabled __read_mostly = 1; 402 int tick_nohz_active __read_mostly; 403 /* 404 * Enable / Disable tickless mode 405 */ 406 static 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); 418 419 /** 420 * tick_nohz_update_jiffies - update jiffies when idle was interrupted 421 * 422 * Called from interrupt entry when the CPU was idle 423 * 424 * In case the sched_tick was stopped on this CPU, we have to check if jiffies 425 * must be updated. Otherwise an interrupt handler could use a stale jiffy 426 * value. We do this unconditionally on any cpu, as we don't know whether the 427 * cpu, which has the update task assigned is in a long sleep. 428 */ 429 static void tick_nohz_update_jiffies(ktime_t now) 430 { 431 unsigned long flags; 432 433 __this_cpu_write(tick_cpu_sched.idle_waketime, now); 434 435 local_irq_save(flags); 436 tick_do_update_jiffies64(now); 437 local_irq_restore(flags); 438 439 touch_softlockup_watchdog(); 440 } 441 442 /* 443 * Updates the per cpu time idle statistics counters 444 */ 445 static void 446 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time) 447 { 448 ktime_t delta; 449 450 if (ts->idle_active) { 451 delta = ktime_sub(now, ts->idle_entrytime); 452 if (nr_iowait_cpu(cpu) > 0) 453 ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta); 454 else 455 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); 456 ts->idle_entrytime = now; 457 } 458 459 if (last_update_time) 460 *last_update_time = ktime_to_us(now); 461 462 } 463 464 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now) 465 { 466 update_ts_time_stats(smp_processor_id(), ts, now, NULL); 467 ts->idle_active = 0; 468 469 sched_clock_idle_wakeup_event(0); 470 } 471 472 static ktime_t tick_nohz_start_idle(struct tick_sched *ts) 473 { 474 ktime_t now = ktime_get(); 475 476 ts->idle_entrytime = now; 477 ts->idle_active = 1; 478 sched_clock_idle_sleep_event(); 479 return now; 480 } 481 482 /** 483 * get_cpu_idle_time_us - get the total idle time of a cpu 484 * @cpu: CPU number to query 485 * @last_update_time: variable to store update time in. Do not update 486 * counters if NULL. 487 * 488 * Return the cummulative idle time (since boot) for a given 489 * CPU, in microseconds. 490 * 491 * This time is measured via accounting rather than sampling, 492 * and is as accurate as ktime_get() is. 493 * 494 * This function returns -1 if NOHZ is not enabled. 495 */ 496 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) 497 { 498 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 499 ktime_t now, idle; 500 501 if (!tick_nohz_active) 502 return -1; 503 504 now = ktime_get(); 505 if (last_update_time) { 506 update_ts_time_stats(cpu, ts, now, last_update_time); 507 idle = ts->idle_sleeptime; 508 } else { 509 if (ts->idle_active && !nr_iowait_cpu(cpu)) { 510 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 511 512 idle = ktime_add(ts->idle_sleeptime, delta); 513 } else { 514 idle = ts->idle_sleeptime; 515 } 516 } 517 518 return ktime_to_us(idle); 519 520 } 521 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us); 522 523 /** 524 * get_cpu_iowait_time_us - get the total iowait time of a cpu 525 * @cpu: CPU number to query 526 * @last_update_time: variable to store update time in. Do not update 527 * counters if NULL. 528 * 529 * Return the cummulative iowait time (since boot) for a given 530 * CPU, in microseconds. 531 * 532 * This time is measured via accounting rather than sampling, 533 * and is as accurate as ktime_get() is. 534 * 535 * This function returns -1 if NOHZ is not enabled. 536 */ 537 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time) 538 { 539 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 540 ktime_t now, iowait; 541 542 if (!tick_nohz_active) 543 return -1; 544 545 now = ktime_get(); 546 if (last_update_time) { 547 update_ts_time_stats(cpu, ts, now, last_update_time); 548 iowait = ts->iowait_sleeptime; 549 } else { 550 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) { 551 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 552 553 iowait = ktime_add(ts->iowait_sleeptime, delta); 554 } else { 555 iowait = ts->iowait_sleeptime; 556 } 557 } 558 559 return ktime_to_us(iowait); 560 } 561 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us); 562 563 static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, 564 ktime_t now, int cpu) 565 { 566 unsigned long seq, last_jiffies, next_jiffies, delta_jiffies; 567 ktime_t last_update, expires, ret = { .tv64 = 0 }; 568 unsigned long rcu_delta_jiffies; 569 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); 570 u64 time_delta; 571 572 time_delta = timekeeping_max_deferment(); 573 574 /* Read jiffies and the time when jiffies were updated last */ 575 do { 576 seq = read_seqbegin(&jiffies_lock); 577 last_update = last_jiffies_update; 578 last_jiffies = jiffies; 579 } while (read_seqretry(&jiffies_lock, seq)); 580 581 if (rcu_needs_cpu(&rcu_delta_jiffies) || 582 arch_needs_cpu() || irq_work_needs_cpu()) { 583 next_jiffies = last_jiffies + 1; 584 delta_jiffies = 1; 585 } else { 586 /* Get the next timer wheel timer */ 587 next_jiffies = get_next_timer_interrupt(last_jiffies); 588 delta_jiffies = next_jiffies - last_jiffies; 589 if (rcu_delta_jiffies < delta_jiffies) { 590 next_jiffies = last_jiffies + rcu_delta_jiffies; 591 delta_jiffies = rcu_delta_jiffies; 592 } 593 } 594 595 /* 596 * Do not stop the tick, if we are only one off (or less) 597 * or if the cpu is required for RCU: 598 */ 599 if (!ts->tick_stopped && delta_jiffies <= 1) 600 goto out; 601 602 /* Schedule the tick, if we are at least one jiffie off */ 603 if ((long)delta_jiffies >= 1) { 604 605 /* 606 * If this cpu is the one which updates jiffies, then 607 * give up the assignment and let it be taken by the 608 * cpu which runs the tick timer next, which might be 609 * this cpu as well. If we don't drop this here the 610 * jiffies might be stale and do_timer() never 611 * invoked. Keep track of the fact that it was the one 612 * which had the do_timer() duty last. If this cpu is 613 * the one which had the do_timer() duty last, we 614 * limit the sleep time to the timekeeping 615 * max_deferement value which we retrieved 616 * above. Otherwise we can sleep as long as we want. 617 */ 618 if (cpu == tick_do_timer_cpu) { 619 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 620 ts->do_timer_last = 1; 621 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) { 622 time_delta = KTIME_MAX; 623 ts->do_timer_last = 0; 624 } else if (!ts->do_timer_last) { 625 time_delta = KTIME_MAX; 626 } 627 628 #ifdef CONFIG_NO_HZ_FULL 629 if (!ts->inidle) { 630 time_delta = min(time_delta, 631 scheduler_tick_max_deferment()); 632 } 633 #endif 634 635 /* 636 * calculate the expiry time for the next timer wheel 637 * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals 638 * that there is no timer pending or at least extremely 639 * far into the future (12 days for HZ=1000). In this 640 * case we set the expiry to the end of time. 641 */ 642 if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) { 643 /* 644 * Calculate the time delta for the next timer event. 645 * If the time delta exceeds the maximum time delta 646 * permitted by the current clocksource then adjust 647 * the time delta accordingly to ensure the 648 * clocksource does not wrap. 649 */ 650 time_delta = min_t(u64, time_delta, 651 tick_period.tv64 * delta_jiffies); 652 } 653 654 if (time_delta < KTIME_MAX) 655 expires = ktime_add_ns(last_update, time_delta); 656 else 657 expires.tv64 = KTIME_MAX; 658 659 /* Skip reprogram of event if its not changed */ 660 if (ts->tick_stopped && ktime_equal(expires, dev->next_event)) 661 goto out; 662 663 ret = expires; 664 665 /* 666 * nohz_stop_sched_tick can be called several times before 667 * the nohz_restart_sched_tick is called. This happens when 668 * interrupts arrive which do not cause a reschedule. In the 669 * first call we save the current tick time, so we can restart 670 * the scheduler tick in nohz_restart_sched_tick. 671 */ 672 if (!ts->tick_stopped) { 673 nohz_balance_enter_idle(cpu); 674 calc_load_enter_idle(); 675 676 ts->last_tick = hrtimer_get_expires(&ts->sched_timer); 677 ts->tick_stopped = 1; 678 trace_tick_stop(1, " "); 679 } 680 681 /* 682 * If the expiration time == KTIME_MAX, then 683 * in this case we simply stop the tick timer. 684 */ 685 if (unlikely(expires.tv64 == KTIME_MAX)) { 686 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) 687 hrtimer_cancel(&ts->sched_timer); 688 goto out; 689 } 690 691 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { 692 hrtimer_start(&ts->sched_timer, expires, 693 HRTIMER_MODE_ABS_PINNED); 694 /* Check, if the timer was already in the past */ 695 if (hrtimer_active(&ts->sched_timer)) 696 goto out; 697 } else if (!tick_program_event(expires, 0)) 698 goto out; 699 /* 700 * We are past the event already. So we crossed a 701 * jiffie boundary. Update jiffies and raise the 702 * softirq. 703 */ 704 tick_do_update_jiffies64(ktime_get()); 705 } 706 raise_softirq_irqoff(TIMER_SOFTIRQ); 707 out: 708 ts->next_jiffies = next_jiffies; 709 ts->last_jiffies = last_jiffies; 710 ts->sleep_length = ktime_sub(dev->next_event, now); 711 712 return ret; 713 } 714 715 static void tick_nohz_full_stop_tick(struct tick_sched *ts) 716 { 717 #ifdef CONFIG_NO_HZ_FULL 718 int cpu = smp_processor_id(); 719 720 if (!tick_nohz_full_cpu(cpu) || is_idle_task(current)) 721 return; 722 723 if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) 724 return; 725 726 if (!can_stop_full_tick()) 727 return; 728 729 tick_nohz_stop_sched_tick(ts, ktime_get(), cpu); 730 #endif 731 } 732 733 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) 734 { 735 /* 736 * If this cpu is offline and it is the one which updates 737 * jiffies, then give up the assignment and let it be taken by 738 * the cpu which runs the tick timer next. If we don't drop 739 * this here the jiffies might be stale and do_timer() never 740 * invoked. 741 */ 742 if (unlikely(!cpu_online(cpu))) { 743 if (cpu == tick_do_timer_cpu) 744 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 745 return false; 746 } 747 748 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) { 749 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ }; 750 return false; 751 } 752 753 if (need_resched()) 754 return false; 755 756 if (unlikely(local_softirq_pending() && cpu_online(cpu))) { 757 static int ratelimit; 758 759 if (ratelimit < 10 && 760 (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { 761 pr_warn("NOHZ: local_softirq_pending %02x\n", 762 (unsigned int) local_softirq_pending()); 763 ratelimit++; 764 } 765 return false; 766 } 767 768 if (tick_nohz_full_enabled()) { 769 /* 770 * Keep the tick alive to guarantee timekeeping progression 771 * if there are full dynticks CPUs around 772 */ 773 if (tick_do_timer_cpu == cpu) 774 return false; 775 /* 776 * Boot safety: make sure the timekeeping duty has been 777 * assigned before entering dyntick-idle mode, 778 */ 779 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE) 780 return false; 781 } 782 783 return true; 784 } 785 786 static void __tick_nohz_idle_enter(struct tick_sched *ts) 787 { 788 ktime_t now, expires; 789 int cpu = smp_processor_id(); 790 791 now = tick_nohz_start_idle(ts); 792 793 if (can_stop_idle_tick(cpu, ts)) { 794 int was_stopped = ts->tick_stopped; 795 796 ts->idle_calls++; 797 798 expires = tick_nohz_stop_sched_tick(ts, now, cpu); 799 if (expires.tv64 > 0LL) { 800 ts->idle_sleeps++; 801 ts->idle_expires = expires; 802 } 803 804 if (!was_stopped && ts->tick_stopped) 805 ts->idle_jiffies = ts->last_jiffies; 806 } 807 } 808 809 /** 810 * tick_nohz_idle_enter - stop the idle tick from the idle task 811 * 812 * When the next event is more than a tick into the future, stop the idle tick 813 * Called when we start the idle loop. 814 * 815 * The arch is responsible of calling: 816 * 817 * - rcu_idle_enter() after its last use of RCU before the CPU is put 818 * to sleep. 819 * - rcu_idle_exit() before the first use of RCU after the CPU is woken up. 820 */ 821 void tick_nohz_idle_enter(void) 822 { 823 struct tick_sched *ts; 824 825 WARN_ON_ONCE(irqs_disabled()); 826 827 /* 828 * Update the idle state in the scheduler domain hierarchy 829 * when tick_nohz_stop_sched_tick() is called from the idle loop. 830 * State will be updated to busy during the first busy tick after 831 * exiting idle. 832 */ 833 set_cpu_sd_state_idle(); 834 835 local_irq_disable(); 836 837 ts = this_cpu_ptr(&tick_cpu_sched); 838 ts->inidle = 1; 839 __tick_nohz_idle_enter(ts); 840 841 local_irq_enable(); 842 } 843 844 /** 845 * tick_nohz_irq_exit - update next tick event from interrupt exit 846 * 847 * When an interrupt fires while we are idle and it doesn't cause 848 * a reschedule, it may still add, modify or delete a timer, enqueue 849 * an RCU callback, etc... 850 * So we need to re-calculate and reprogram the next tick event. 851 */ 852 void tick_nohz_irq_exit(void) 853 { 854 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 855 856 if (ts->inidle) 857 __tick_nohz_idle_enter(ts); 858 else 859 tick_nohz_full_stop_tick(ts); 860 } 861 862 /** 863 * tick_nohz_get_sleep_length - return the length of the current sleep 864 * 865 * Called from power state control code with interrupts disabled 866 */ 867 ktime_t tick_nohz_get_sleep_length(void) 868 { 869 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 870 871 return ts->sleep_length; 872 } 873 874 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) 875 { 876 hrtimer_cancel(&ts->sched_timer); 877 hrtimer_set_expires(&ts->sched_timer, ts->last_tick); 878 879 while (1) { 880 /* Forward the time to expire in the future */ 881 hrtimer_forward(&ts->sched_timer, now, tick_period); 882 883 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { 884 hrtimer_start_expires(&ts->sched_timer, 885 HRTIMER_MODE_ABS_PINNED); 886 /* Check, if the timer was already in the past */ 887 if (hrtimer_active(&ts->sched_timer)) 888 break; 889 } else { 890 if (!tick_program_event( 891 hrtimer_get_expires(&ts->sched_timer), 0)) 892 break; 893 } 894 /* Reread time and update jiffies */ 895 now = ktime_get(); 896 tick_do_update_jiffies64(now); 897 } 898 } 899 900 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) 901 { 902 /* Update jiffies first */ 903 tick_do_update_jiffies64(now); 904 update_cpu_load_nohz(); 905 906 calc_load_exit_idle(); 907 touch_softlockup_watchdog(); 908 /* 909 * Cancel the scheduled timer and restore the tick 910 */ 911 ts->tick_stopped = 0; 912 ts->idle_exittime = now; 913 914 tick_nohz_restart(ts, now); 915 } 916 917 static void tick_nohz_account_idle_ticks(struct tick_sched *ts) 918 { 919 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE 920 unsigned long ticks; 921 922 if (vtime_accounting_enabled()) 923 return; 924 /* 925 * We stopped the tick in idle. Update process times would miss the 926 * time we slept as update_process_times does only a 1 tick 927 * accounting. Enforce that this is accounted to idle ! 928 */ 929 ticks = jiffies - ts->idle_jiffies; 930 /* 931 * We might be one off. Do not randomly account a huge number of ticks! 932 */ 933 if (ticks && ticks < LONG_MAX) 934 account_idle_ticks(ticks); 935 #endif 936 } 937 938 /** 939 * tick_nohz_idle_exit - restart the idle tick from the idle task 940 * 941 * Restart the idle tick when the CPU is woken up from idle 942 * This also exit the RCU extended quiescent state. The CPU 943 * can use RCU again after this function is called. 944 */ 945 void tick_nohz_idle_exit(void) 946 { 947 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 948 ktime_t now; 949 950 local_irq_disable(); 951 952 WARN_ON_ONCE(!ts->inidle); 953 954 ts->inidle = 0; 955 956 if (ts->idle_active || ts->tick_stopped) 957 now = ktime_get(); 958 959 if (ts->idle_active) 960 tick_nohz_stop_idle(ts, now); 961 962 if (ts->tick_stopped) { 963 tick_nohz_restart_sched_tick(ts, now); 964 tick_nohz_account_idle_ticks(ts); 965 } 966 967 local_irq_enable(); 968 } 969 970 static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now) 971 { 972 hrtimer_forward(&ts->sched_timer, now, tick_period); 973 return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0); 974 } 975 976 /* 977 * The nohz low res interrupt handler 978 */ 979 static void tick_nohz_handler(struct clock_event_device *dev) 980 { 981 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 982 struct pt_regs *regs = get_irq_regs(); 983 ktime_t now = ktime_get(); 984 985 dev->next_event.tv64 = KTIME_MAX; 986 987 tick_sched_do_timer(now); 988 tick_sched_handle(ts, regs); 989 990 /* No need to reprogram if we are running tickless */ 991 if (unlikely(ts->tick_stopped)) 992 return; 993 994 while (tick_nohz_reprogram(ts, now)) { 995 now = ktime_get(); 996 tick_do_update_jiffies64(now); 997 } 998 } 999 1000 /** 1001 * tick_nohz_switch_to_nohz - switch to nohz mode 1002 */ 1003 static void tick_nohz_switch_to_nohz(void) 1004 { 1005 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1006 ktime_t next; 1007 1008 if (!tick_nohz_enabled) 1009 return; 1010 1011 local_irq_disable(); 1012 if (tick_switch_to_oneshot(tick_nohz_handler)) { 1013 local_irq_enable(); 1014 return; 1015 } 1016 tick_nohz_active = 1; 1017 ts->nohz_mode = NOHZ_MODE_LOWRES; 1018 1019 /* 1020 * Recycle the hrtimer in ts, so we can share the 1021 * hrtimer_forward with the highres code. 1022 */ 1023 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 1024 /* Get the next period */ 1025 next = tick_init_jiffy_update(); 1026 1027 for (;;) { 1028 hrtimer_set_expires(&ts->sched_timer, next); 1029 if (!tick_program_event(next, 0)) 1030 break; 1031 next = ktime_add(next, tick_period); 1032 } 1033 local_irq_enable(); 1034 } 1035 1036 /* 1037 * When NOHZ is enabled and the tick is stopped, we need to kick the 1038 * tick timer from irq_enter() so that the jiffies update is kept 1039 * alive during long running softirqs. That's ugly as hell, but 1040 * correctness is key even if we need to fix the offending softirq in 1041 * the first place. 1042 * 1043 * Note, this is different to tick_nohz_restart. We just kick the 1044 * timer and do not touch the other magic bits which need to be done 1045 * when idle is left. 1046 */ 1047 static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now) 1048 { 1049 #if 0 1050 /* Switch back to 2.6.27 behaviour */ 1051 ktime_t delta; 1052 1053 /* 1054 * Do not touch the tick device, when the next expiry is either 1055 * already reached or less/equal than the tick period. 1056 */ 1057 delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now); 1058 if (delta.tv64 <= tick_period.tv64) 1059 return; 1060 1061 tick_nohz_restart(ts, now); 1062 #endif 1063 } 1064 1065 static inline void tick_nohz_irq_enter(void) 1066 { 1067 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1068 ktime_t now; 1069 1070 if (!ts->idle_active && !ts->tick_stopped) 1071 return; 1072 now = ktime_get(); 1073 if (ts->idle_active) 1074 tick_nohz_stop_idle(ts, now); 1075 if (ts->tick_stopped) { 1076 tick_nohz_update_jiffies(now); 1077 tick_nohz_kick_tick(ts, now); 1078 } 1079 } 1080 1081 #else 1082 1083 static inline void tick_nohz_switch_to_nohz(void) { } 1084 static inline void tick_nohz_irq_enter(void) { } 1085 1086 #endif /* CONFIG_NO_HZ_COMMON */ 1087 1088 /* 1089 * Called from irq_enter to notify about the possible interruption of idle() 1090 */ 1091 void tick_irq_enter(void) 1092 { 1093 tick_check_oneshot_broadcast_this_cpu(); 1094 tick_nohz_irq_enter(); 1095 } 1096 1097 /* 1098 * High resolution timer specific code 1099 */ 1100 #ifdef CONFIG_HIGH_RES_TIMERS 1101 /* 1102 * We rearm the timer until we get disabled by the idle code. 1103 * Called with interrupts disabled. 1104 */ 1105 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) 1106 { 1107 struct tick_sched *ts = 1108 container_of(timer, struct tick_sched, sched_timer); 1109 struct pt_regs *regs = get_irq_regs(); 1110 ktime_t now = ktime_get(); 1111 1112 tick_sched_do_timer(now); 1113 1114 /* 1115 * Do not call, when we are not in irq context and have 1116 * no valid regs pointer 1117 */ 1118 if (regs) 1119 tick_sched_handle(ts, regs); 1120 1121 /* No need to reprogram if we are in idle or full dynticks mode */ 1122 if (unlikely(ts->tick_stopped)) 1123 return HRTIMER_NORESTART; 1124 1125 hrtimer_forward(timer, now, tick_period); 1126 1127 return HRTIMER_RESTART; 1128 } 1129 1130 static int sched_skew_tick; 1131 1132 static int __init skew_tick(char *str) 1133 { 1134 get_option(&str, &sched_skew_tick); 1135 1136 return 0; 1137 } 1138 early_param("skew_tick", skew_tick); 1139 1140 /** 1141 * tick_setup_sched_timer - setup the tick emulation timer 1142 */ 1143 void tick_setup_sched_timer(void) 1144 { 1145 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1146 ktime_t now = ktime_get(); 1147 1148 /* 1149 * Emulate tick processing via per-CPU hrtimers: 1150 */ 1151 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 1152 ts->sched_timer.function = tick_sched_timer; 1153 1154 /* Get the next period (per cpu) */ 1155 hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update()); 1156 1157 /* Offset the tick to avert jiffies_lock contention. */ 1158 if (sched_skew_tick) { 1159 u64 offset = ktime_to_ns(tick_period) >> 1; 1160 do_div(offset, num_possible_cpus()); 1161 offset *= smp_processor_id(); 1162 hrtimer_add_expires_ns(&ts->sched_timer, offset); 1163 } 1164 1165 for (;;) { 1166 hrtimer_forward(&ts->sched_timer, now, tick_period); 1167 hrtimer_start_expires(&ts->sched_timer, 1168 HRTIMER_MODE_ABS_PINNED); 1169 /* Check, if the timer was already in the past */ 1170 if (hrtimer_active(&ts->sched_timer)) 1171 break; 1172 now = ktime_get(); 1173 } 1174 1175 #ifdef CONFIG_NO_HZ_COMMON 1176 if (tick_nohz_enabled) { 1177 ts->nohz_mode = NOHZ_MODE_HIGHRES; 1178 tick_nohz_active = 1; 1179 } 1180 #endif 1181 } 1182 #endif /* HIGH_RES_TIMERS */ 1183 1184 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS 1185 void tick_cancel_sched_timer(int cpu) 1186 { 1187 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 1188 1189 # ifdef CONFIG_HIGH_RES_TIMERS 1190 if (ts->sched_timer.base) 1191 hrtimer_cancel(&ts->sched_timer); 1192 # endif 1193 1194 memset(ts, 0, sizeof(*ts)); 1195 } 1196 #endif 1197 1198 /** 1199 * Async notification about clocksource changes 1200 */ 1201 void tick_clock_notify(void) 1202 { 1203 int cpu; 1204 1205 for_each_possible_cpu(cpu) 1206 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks); 1207 } 1208 1209 /* 1210 * Async notification about clock event changes 1211 */ 1212 void tick_oneshot_notify(void) 1213 { 1214 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1215 1216 set_bit(0, &ts->check_clocks); 1217 } 1218 1219 /** 1220 * Check, if a change happened, which makes oneshot possible. 1221 * 1222 * Called cyclic from the hrtimer softirq (driven by the timer 1223 * softirq) allow_nohz signals, that we can switch into low-res nohz 1224 * mode, because high resolution timers are disabled (either compile 1225 * or runtime). 1226 */ 1227 int tick_check_oneshot_change(int allow_nohz) 1228 { 1229 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1230 1231 if (!test_and_clear_bit(0, &ts->check_clocks)) 1232 return 0; 1233 1234 if (ts->nohz_mode != NOHZ_MODE_INACTIVE) 1235 return 0; 1236 1237 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available()) 1238 return 0; 1239 1240 if (!allow_nohz) 1241 return 1; 1242 1243 tick_nohz_switch_to_nohz(); 1244 return 0; 1245 } 1246