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/nmi.h> 21 #include <linux/profile.h> 22 #include <linux/sched/signal.h> 23 #include <linux/sched/clock.h> 24 #include <linux/sched/stat.h> 25 #include <linux/sched/nohz.h> 26 #include <linux/module.h> 27 #include <linux/irq_work.h> 28 #include <linux/posix-timers.h> 29 #include <linux/context_tracking.h> 30 31 #include <asm/irq_regs.h> 32 33 #include "tick-internal.h" 34 35 #include <trace/events/timer.h> 36 37 /* 38 * Per-CPU nohz control structure 39 */ 40 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched); 41 42 struct tick_sched *tick_get_tick_sched(int cpu) 43 { 44 return &per_cpu(tick_cpu_sched, cpu); 45 } 46 47 #if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS) 48 /* 49 * The time, when the last jiffy update happened. Protected by jiffies_lock. 50 */ 51 static ktime_t last_jiffies_update; 52 53 /* 54 * Must be called with interrupts disabled ! 55 */ 56 static void tick_do_update_jiffies64(ktime_t now) 57 { 58 unsigned long ticks = 0; 59 ktime_t delta; 60 61 /* 62 * Do a quick check without holding jiffies_lock: 63 */ 64 delta = ktime_sub(now, last_jiffies_update); 65 if (delta < tick_period) 66 return; 67 68 /* Reevaluate with jiffies_lock held */ 69 write_seqlock(&jiffies_lock); 70 71 delta = ktime_sub(now, last_jiffies_update); 72 if (delta >= tick_period) { 73 74 delta = ktime_sub(delta, tick_period); 75 last_jiffies_update = ktime_add(last_jiffies_update, 76 tick_period); 77 78 /* Slow path for long timeouts */ 79 if (unlikely(delta >= tick_period)) { 80 s64 incr = ktime_to_ns(tick_period); 81 82 ticks = ktime_divns(delta, incr); 83 84 last_jiffies_update = ktime_add_ns(last_jiffies_update, 85 incr * ticks); 86 } 87 do_timer(++ticks); 88 89 /* Keep the tick_next_period variable up to date */ 90 tick_next_period = ktime_add(last_jiffies_update, tick_period); 91 } else { 92 write_sequnlock(&jiffies_lock); 93 return; 94 } 95 write_sequnlock(&jiffies_lock); 96 update_wall_time(); 97 } 98 99 /* 100 * Initialize and return retrieve the jiffies update. 101 */ 102 static ktime_t tick_init_jiffy_update(void) 103 { 104 ktime_t period; 105 106 write_seqlock(&jiffies_lock); 107 /* Did we start the jiffies update yet ? */ 108 if (last_jiffies_update == 0) 109 last_jiffies_update = tick_next_period; 110 period = last_jiffies_update; 111 write_sequnlock(&jiffies_lock); 112 return period; 113 } 114 115 116 static void tick_sched_do_timer(ktime_t now) 117 { 118 int cpu = smp_processor_id(); 119 120 #ifdef CONFIG_NO_HZ_COMMON 121 /* 122 * Check if the do_timer duty was dropped. We don't care about 123 * concurrency: This happens only when the CPU in charge went 124 * into a long sleep. If two CPUs happen to assign themselves to 125 * this duty, then the jiffies update is still serialized by 126 * jiffies_lock. 127 */ 128 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE) 129 && !tick_nohz_full_cpu(cpu)) 130 tick_do_timer_cpu = cpu; 131 #endif 132 133 /* Check, if the jiffies need an update */ 134 if (tick_do_timer_cpu == cpu) 135 tick_do_update_jiffies64(now); 136 } 137 138 static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs) 139 { 140 #ifdef CONFIG_NO_HZ_COMMON 141 /* 142 * When we are idle and the tick is stopped, we have to touch 143 * the watchdog as we might not schedule for a really long 144 * time. This happens on complete idle SMP systems while 145 * waiting on the login prompt. We also increment the "start of 146 * idle" jiffy stamp so the idle accounting adjustment we do 147 * when we go busy again does not account too much ticks. 148 */ 149 if (ts->tick_stopped) { 150 touch_softlockup_watchdog_sched(); 151 if (is_idle_task(current)) 152 ts->idle_jiffies++; 153 /* 154 * In case the current tick fired too early past its expected 155 * expiration, make sure we don't bypass the next clock reprogramming 156 * to the same deadline. 157 */ 158 ts->next_tick = 0; 159 } 160 #endif 161 update_process_times(user_mode(regs)); 162 profile_tick(CPU_PROFILING); 163 } 164 #endif 165 166 #ifdef CONFIG_NO_HZ_FULL 167 cpumask_var_t tick_nohz_full_mask; 168 cpumask_var_t housekeeping_mask; 169 bool tick_nohz_full_running; 170 static atomic_t tick_dep_mask; 171 172 static bool check_tick_dependency(atomic_t *dep) 173 { 174 int val = atomic_read(dep); 175 176 if (val & TICK_DEP_MASK_POSIX_TIMER) { 177 trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER); 178 return true; 179 } 180 181 if (val & TICK_DEP_MASK_PERF_EVENTS) { 182 trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS); 183 return true; 184 } 185 186 if (val & TICK_DEP_MASK_SCHED) { 187 trace_tick_stop(0, TICK_DEP_MASK_SCHED); 188 return true; 189 } 190 191 if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) { 192 trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE); 193 return true; 194 } 195 196 return false; 197 } 198 199 static bool can_stop_full_tick(int cpu, struct tick_sched *ts) 200 { 201 WARN_ON_ONCE(!irqs_disabled()); 202 203 if (unlikely(!cpu_online(cpu))) 204 return false; 205 206 if (check_tick_dependency(&tick_dep_mask)) 207 return false; 208 209 if (check_tick_dependency(&ts->tick_dep_mask)) 210 return false; 211 212 if (check_tick_dependency(¤t->tick_dep_mask)) 213 return false; 214 215 if (check_tick_dependency(¤t->signal->tick_dep_mask)) 216 return false; 217 218 return true; 219 } 220 221 static void nohz_full_kick_func(struct irq_work *work) 222 { 223 /* Empty, the tick restart happens on tick_nohz_irq_exit() */ 224 } 225 226 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = { 227 .func = nohz_full_kick_func, 228 }; 229 230 /* 231 * Kick this CPU if it's full dynticks in order to force it to 232 * re-evaluate its dependency on the tick and restart it if necessary. 233 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(), 234 * is NMI safe. 235 */ 236 static void tick_nohz_full_kick(void) 237 { 238 if (!tick_nohz_full_cpu(smp_processor_id())) 239 return; 240 241 irq_work_queue(this_cpu_ptr(&nohz_full_kick_work)); 242 } 243 244 /* 245 * Kick the CPU if it's full dynticks in order to force it to 246 * re-evaluate its dependency on the tick and restart it if necessary. 247 */ 248 void tick_nohz_full_kick_cpu(int cpu) 249 { 250 if (!tick_nohz_full_cpu(cpu)) 251 return; 252 253 irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu); 254 } 255 256 /* 257 * Kick all full dynticks CPUs in order to force these to re-evaluate 258 * their dependency on the tick and restart it if necessary. 259 */ 260 static void tick_nohz_full_kick_all(void) 261 { 262 int cpu; 263 264 if (!tick_nohz_full_running) 265 return; 266 267 preempt_disable(); 268 for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask) 269 tick_nohz_full_kick_cpu(cpu); 270 preempt_enable(); 271 } 272 273 static void tick_nohz_dep_set_all(atomic_t *dep, 274 enum tick_dep_bits bit) 275 { 276 int prev; 277 278 prev = atomic_fetch_or(BIT(bit), dep); 279 if (!prev) 280 tick_nohz_full_kick_all(); 281 } 282 283 /* 284 * Set a global tick dependency. Used by perf events that rely on freq and 285 * by unstable clock. 286 */ 287 void tick_nohz_dep_set(enum tick_dep_bits bit) 288 { 289 tick_nohz_dep_set_all(&tick_dep_mask, bit); 290 } 291 292 void tick_nohz_dep_clear(enum tick_dep_bits bit) 293 { 294 atomic_andnot(BIT(bit), &tick_dep_mask); 295 } 296 297 /* 298 * Set per-CPU tick dependency. Used by scheduler and perf events in order to 299 * manage events throttling. 300 */ 301 void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit) 302 { 303 int prev; 304 struct tick_sched *ts; 305 306 ts = per_cpu_ptr(&tick_cpu_sched, cpu); 307 308 prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask); 309 if (!prev) { 310 preempt_disable(); 311 /* Perf needs local kick that is NMI safe */ 312 if (cpu == smp_processor_id()) { 313 tick_nohz_full_kick(); 314 } else { 315 /* Remote irq work not NMI-safe */ 316 if (!WARN_ON_ONCE(in_nmi())) 317 tick_nohz_full_kick_cpu(cpu); 318 } 319 preempt_enable(); 320 } 321 } 322 323 void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit) 324 { 325 struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu); 326 327 atomic_andnot(BIT(bit), &ts->tick_dep_mask); 328 } 329 330 /* 331 * Set a per-task tick dependency. Posix CPU timers need this in order to elapse 332 * per task timers. 333 */ 334 void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit) 335 { 336 /* 337 * We could optimize this with just kicking the target running the task 338 * if that noise matters for nohz full users. 339 */ 340 tick_nohz_dep_set_all(&tsk->tick_dep_mask, bit); 341 } 342 343 void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit) 344 { 345 atomic_andnot(BIT(bit), &tsk->tick_dep_mask); 346 } 347 348 /* 349 * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse 350 * per process timers. 351 */ 352 void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits bit) 353 { 354 tick_nohz_dep_set_all(&sig->tick_dep_mask, bit); 355 } 356 357 void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit) 358 { 359 atomic_andnot(BIT(bit), &sig->tick_dep_mask); 360 } 361 362 /* 363 * Re-evaluate the need for the tick as we switch the current task. 364 * It might need the tick due to per task/process properties: 365 * perf events, posix CPU timers, ... 366 */ 367 void __tick_nohz_task_switch(void) 368 { 369 unsigned long flags; 370 struct tick_sched *ts; 371 372 local_irq_save(flags); 373 374 if (!tick_nohz_full_cpu(smp_processor_id())) 375 goto out; 376 377 ts = this_cpu_ptr(&tick_cpu_sched); 378 379 if (ts->tick_stopped) { 380 if (atomic_read(¤t->tick_dep_mask) || 381 atomic_read(¤t->signal->tick_dep_mask)) 382 tick_nohz_full_kick(); 383 } 384 out: 385 local_irq_restore(flags); 386 } 387 388 /* Parse the boot-time nohz CPU list from the kernel parameters. */ 389 static int __init tick_nohz_full_setup(char *str) 390 { 391 alloc_bootmem_cpumask_var(&tick_nohz_full_mask); 392 if (cpulist_parse(str, tick_nohz_full_mask) < 0) { 393 pr_warn("NO_HZ: Incorrect nohz_full cpumask\n"); 394 free_bootmem_cpumask_var(tick_nohz_full_mask); 395 return 1; 396 } 397 tick_nohz_full_running = true; 398 399 return 1; 400 } 401 __setup("nohz_full=", tick_nohz_full_setup); 402 403 static int tick_nohz_cpu_down(unsigned int cpu) 404 { 405 /* 406 * The boot CPU handles housekeeping duty (unbound timers, 407 * workqueues, timekeeping, ...) on behalf of full dynticks 408 * CPUs. It must remain online when nohz full is enabled. 409 */ 410 if (tick_nohz_full_running && tick_do_timer_cpu == cpu) 411 return -EBUSY; 412 return 0; 413 } 414 415 static int tick_nohz_init_all(void) 416 { 417 int err = -1; 418 419 #ifdef CONFIG_NO_HZ_FULL_ALL 420 if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) { 421 WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n"); 422 return err; 423 } 424 err = 0; 425 cpumask_setall(tick_nohz_full_mask); 426 tick_nohz_full_running = true; 427 #endif 428 return err; 429 } 430 431 void __init tick_nohz_init(void) 432 { 433 int cpu, ret; 434 435 if (!tick_nohz_full_running) { 436 if (tick_nohz_init_all() < 0) 437 return; 438 } 439 440 if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) { 441 WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n"); 442 cpumask_clear(tick_nohz_full_mask); 443 tick_nohz_full_running = false; 444 return; 445 } 446 447 /* 448 * Full dynticks uses irq work to drive the tick rescheduling on safe 449 * locking contexts. But then we need irq work to raise its own 450 * interrupts to avoid circular dependency on the tick 451 */ 452 if (!arch_irq_work_has_interrupt()) { 453 pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs\n"); 454 cpumask_clear(tick_nohz_full_mask); 455 cpumask_copy(housekeeping_mask, cpu_possible_mask); 456 tick_nohz_full_running = false; 457 return; 458 } 459 460 cpu = smp_processor_id(); 461 462 if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) { 463 pr_warn("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", 464 cpu); 465 cpumask_clear_cpu(cpu, tick_nohz_full_mask); 466 } 467 468 cpumask_andnot(housekeeping_mask, 469 cpu_possible_mask, tick_nohz_full_mask); 470 471 for_each_cpu(cpu, tick_nohz_full_mask) 472 context_tracking_cpu_set(cpu); 473 474 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, 475 "kernel/nohz:predown", NULL, 476 tick_nohz_cpu_down); 477 WARN_ON(ret < 0); 478 pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n", 479 cpumask_pr_args(tick_nohz_full_mask)); 480 481 /* 482 * We need at least one CPU to handle housekeeping work such 483 * as timekeeping, unbound timers, workqueues, ... 484 */ 485 WARN_ON_ONCE(cpumask_empty(housekeeping_mask)); 486 } 487 #endif 488 489 /* 490 * NOHZ - aka dynamic tick functionality 491 */ 492 #ifdef CONFIG_NO_HZ_COMMON 493 /* 494 * NO HZ enabled ? 495 */ 496 bool tick_nohz_enabled __read_mostly = true; 497 unsigned long tick_nohz_active __read_mostly; 498 /* 499 * Enable / Disable tickless mode 500 */ 501 static int __init setup_tick_nohz(char *str) 502 { 503 return (kstrtobool(str, &tick_nohz_enabled) == 0); 504 } 505 506 __setup("nohz=", setup_tick_nohz); 507 508 int tick_nohz_tick_stopped(void) 509 { 510 return __this_cpu_read(tick_cpu_sched.tick_stopped); 511 } 512 513 /** 514 * tick_nohz_update_jiffies - update jiffies when idle was interrupted 515 * 516 * Called from interrupt entry when the CPU was idle 517 * 518 * In case the sched_tick was stopped on this CPU, we have to check if jiffies 519 * must be updated. Otherwise an interrupt handler could use a stale jiffy 520 * value. We do this unconditionally on any CPU, as we don't know whether the 521 * CPU, which has the update task assigned is in a long sleep. 522 */ 523 static void tick_nohz_update_jiffies(ktime_t now) 524 { 525 unsigned long flags; 526 527 __this_cpu_write(tick_cpu_sched.idle_waketime, now); 528 529 local_irq_save(flags); 530 tick_do_update_jiffies64(now); 531 local_irq_restore(flags); 532 533 touch_softlockup_watchdog_sched(); 534 } 535 536 /* 537 * Updates the per-CPU time idle statistics counters 538 */ 539 static void 540 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time) 541 { 542 ktime_t delta; 543 544 if (ts->idle_active) { 545 delta = ktime_sub(now, ts->idle_entrytime); 546 if (nr_iowait_cpu(cpu) > 0) 547 ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta); 548 else 549 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); 550 ts->idle_entrytime = now; 551 } 552 553 if (last_update_time) 554 *last_update_time = ktime_to_us(now); 555 556 } 557 558 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now) 559 { 560 update_ts_time_stats(smp_processor_id(), ts, now, NULL); 561 ts->idle_active = 0; 562 563 sched_clock_idle_wakeup_event(0); 564 } 565 566 static ktime_t tick_nohz_start_idle(struct tick_sched *ts) 567 { 568 ktime_t now = ktime_get(); 569 570 ts->idle_entrytime = now; 571 ts->idle_active = 1; 572 sched_clock_idle_sleep_event(); 573 return now; 574 } 575 576 /** 577 * get_cpu_idle_time_us - get the total idle time of a CPU 578 * @cpu: CPU number to query 579 * @last_update_time: variable to store update time in. Do not update 580 * counters if NULL. 581 * 582 * Return the cumulative idle time (since boot) for a given 583 * CPU, in microseconds. 584 * 585 * This time is measured via accounting rather than sampling, 586 * and is as accurate as ktime_get() is. 587 * 588 * This function returns -1 if NOHZ is not enabled. 589 */ 590 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) 591 { 592 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 593 ktime_t now, idle; 594 595 if (!tick_nohz_active) 596 return -1; 597 598 now = ktime_get(); 599 if (last_update_time) { 600 update_ts_time_stats(cpu, ts, now, last_update_time); 601 idle = ts->idle_sleeptime; 602 } else { 603 if (ts->idle_active && !nr_iowait_cpu(cpu)) { 604 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 605 606 idle = ktime_add(ts->idle_sleeptime, delta); 607 } else { 608 idle = ts->idle_sleeptime; 609 } 610 } 611 612 return ktime_to_us(idle); 613 614 } 615 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us); 616 617 /** 618 * get_cpu_iowait_time_us - get the total iowait time of a CPU 619 * @cpu: CPU number to query 620 * @last_update_time: variable to store update time in. Do not update 621 * counters if NULL. 622 * 623 * Return the cumulative iowait time (since boot) for a given 624 * CPU, in microseconds. 625 * 626 * This time is measured via accounting rather than sampling, 627 * and is as accurate as ktime_get() is. 628 * 629 * This function returns -1 if NOHZ is not enabled. 630 */ 631 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time) 632 { 633 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 634 ktime_t now, iowait; 635 636 if (!tick_nohz_active) 637 return -1; 638 639 now = ktime_get(); 640 if (last_update_time) { 641 update_ts_time_stats(cpu, ts, now, last_update_time); 642 iowait = ts->iowait_sleeptime; 643 } else { 644 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) { 645 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 646 647 iowait = ktime_add(ts->iowait_sleeptime, delta); 648 } else { 649 iowait = ts->iowait_sleeptime; 650 } 651 } 652 653 return ktime_to_us(iowait); 654 } 655 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us); 656 657 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) 658 { 659 hrtimer_cancel(&ts->sched_timer); 660 hrtimer_set_expires(&ts->sched_timer, ts->last_tick); 661 662 /* Forward the time to expire in the future */ 663 hrtimer_forward(&ts->sched_timer, now, tick_period); 664 665 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) 666 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED); 667 else 668 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); 669 670 /* 671 * Reset to make sure next tick stop doesn't get fooled by past 672 * cached clock deadline. 673 */ 674 ts->next_tick = 0; 675 } 676 677 static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, 678 ktime_t now, int cpu) 679 { 680 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); 681 u64 basemono, next_tick, next_tmr, next_rcu, delta, expires; 682 unsigned long seq, basejiff; 683 ktime_t tick; 684 685 /* Read jiffies and the time when jiffies were updated last */ 686 do { 687 seq = read_seqbegin(&jiffies_lock); 688 basemono = last_jiffies_update; 689 basejiff = jiffies; 690 } while (read_seqretry(&jiffies_lock, seq)); 691 ts->last_jiffies = basejiff; 692 693 if (rcu_needs_cpu(basemono, &next_rcu) || 694 arch_needs_cpu() || irq_work_needs_cpu()) { 695 next_tick = basemono + TICK_NSEC; 696 } else { 697 /* 698 * Get the next pending timer. If high resolution 699 * timers are enabled this only takes the timer wheel 700 * timers into account. If high resolution timers are 701 * disabled this also looks at the next expiring 702 * hrtimer. 703 */ 704 next_tmr = get_next_timer_interrupt(basejiff, basemono); 705 ts->next_timer = next_tmr; 706 /* Take the next rcu event into account */ 707 next_tick = next_rcu < next_tmr ? next_rcu : next_tmr; 708 } 709 710 /* 711 * If the tick is due in the next period, keep it ticking or 712 * force prod the timer. 713 */ 714 delta = next_tick - basemono; 715 if (delta <= (u64)TICK_NSEC) { 716 /* 717 * Tell the timer code that the base is not idle, i.e. undo 718 * the effect of get_next_timer_interrupt(): 719 */ 720 timer_clear_idle(); 721 /* 722 * We've not stopped the tick yet, and there's a timer in the 723 * next period, so no point in stopping it either, bail. 724 */ 725 if (!ts->tick_stopped) { 726 tick = 0; 727 goto out; 728 } 729 } 730 731 /* 732 * If this CPU is the one which updates jiffies, then give up 733 * the assignment and let it be taken by the CPU which runs 734 * the tick timer next, which might be this CPU as well. If we 735 * don't drop this here the jiffies might be stale and 736 * do_timer() never invoked. Keep track of the fact that it 737 * was the one which had the do_timer() duty last. If this CPU 738 * is the one which had the do_timer() duty last, we limit the 739 * sleep time to the timekeeping max_deferment value. 740 * Otherwise we can sleep as long as we want. 741 */ 742 delta = timekeeping_max_deferment(); 743 if (cpu == tick_do_timer_cpu) { 744 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 745 ts->do_timer_last = 1; 746 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) { 747 delta = KTIME_MAX; 748 ts->do_timer_last = 0; 749 } else if (!ts->do_timer_last) { 750 delta = KTIME_MAX; 751 } 752 753 #ifdef CONFIG_NO_HZ_FULL 754 /* Limit the tick delta to the maximum scheduler deferment */ 755 if (!ts->inidle) 756 delta = min(delta, scheduler_tick_max_deferment()); 757 #endif 758 759 /* Calculate the next expiry time */ 760 if (delta < (KTIME_MAX - basemono)) 761 expires = basemono + delta; 762 else 763 expires = KTIME_MAX; 764 765 expires = min_t(u64, expires, next_tick); 766 tick = expires; 767 768 /* Skip reprogram of event if its not changed */ 769 if (ts->tick_stopped && (expires == ts->next_tick)) { 770 /* Sanity check: make sure clockevent is actually programmed */ 771 if (likely(dev->next_event <= ts->next_tick)) 772 goto out; 773 774 WARN_ON_ONCE(1); 775 printk_once("basemono: %llu ts->next_tick: %llu dev->next_event: %llu timer->active: %d timer->expires: %llu\n", 776 basemono, ts->next_tick, dev->next_event, 777 hrtimer_active(&ts->sched_timer), hrtimer_get_expires(&ts->sched_timer)); 778 } 779 780 /* 781 * nohz_stop_sched_tick can be called several times before 782 * the nohz_restart_sched_tick is called. This happens when 783 * interrupts arrive which do not cause a reschedule. In the 784 * first call we save the current tick time, so we can restart 785 * the scheduler tick in nohz_restart_sched_tick. 786 */ 787 if (!ts->tick_stopped) { 788 nohz_balance_enter_idle(cpu); 789 calc_load_enter_idle(); 790 cpu_load_update_nohz_start(); 791 792 ts->last_tick = hrtimer_get_expires(&ts->sched_timer); 793 ts->tick_stopped = 1; 794 trace_tick_stop(1, TICK_DEP_MASK_NONE); 795 } 796 797 ts->next_tick = tick; 798 799 /* 800 * If the expiration time == KTIME_MAX, then we simply stop 801 * the tick timer. 802 */ 803 if (unlikely(expires == KTIME_MAX)) { 804 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) 805 hrtimer_cancel(&ts->sched_timer); 806 goto out; 807 } 808 809 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) 810 hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED); 811 else 812 tick_program_event(tick, 1); 813 out: 814 /* 815 * Update the estimated sleep length until the next timer 816 * (not only the tick). 817 */ 818 ts->sleep_length = ktime_sub(dev->next_event, now); 819 return tick; 820 } 821 822 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) 823 { 824 /* Update jiffies first */ 825 tick_do_update_jiffies64(now); 826 cpu_load_update_nohz_stop(); 827 828 /* 829 * Clear the timer idle flag, so we avoid IPIs on remote queueing and 830 * the clock forward checks in the enqueue path: 831 */ 832 timer_clear_idle(); 833 834 calc_load_exit_idle(); 835 touch_softlockup_watchdog_sched(); 836 /* 837 * Cancel the scheduled timer and restore the tick 838 */ 839 ts->tick_stopped = 0; 840 ts->idle_exittime = now; 841 842 tick_nohz_restart(ts, now); 843 } 844 845 static void tick_nohz_full_update_tick(struct tick_sched *ts) 846 { 847 #ifdef CONFIG_NO_HZ_FULL 848 int cpu = smp_processor_id(); 849 850 if (!tick_nohz_full_cpu(cpu)) 851 return; 852 853 if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) 854 return; 855 856 if (can_stop_full_tick(cpu, ts)) 857 tick_nohz_stop_sched_tick(ts, ktime_get(), cpu); 858 else if (ts->tick_stopped) 859 tick_nohz_restart_sched_tick(ts, ktime_get()); 860 #endif 861 } 862 863 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) 864 { 865 /* 866 * If this CPU is offline and it is the one which updates 867 * jiffies, then give up the assignment and let it be taken by 868 * the CPU which runs the tick timer next. If we don't drop 869 * this here the jiffies might be stale and do_timer() never 870 * invoked. 871 */ 872 if (unlikely(!cpu_online(cpu))) { 873 if (cpu == tick_do_timer_cpu) 874 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 875 /* 876 * Make sure the CPU doesn't get fooled by obsolete tick 877 * deadline if it comes back online later. 878 */ 879 ts->next_tick = 0; 880 return false; 881 } 882 883 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) { 884 ts->sleep_length = NSEC_PER_SEC / HZ; 885 return false; 886 } 887 888 if (need_resched()) 889 return false; 890 891 if (unlikely(local_softirq_pending() && cpu_online(cpu))) { 892 static int ratelimit; 893 894 if (ratelimit < 10 && 895 (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { 896 pr_warn("NOHZ: local_softirq_pending %02x\n", 897 (unsigned int) local_softirq_pending()); 898 ratelimit++; 899 } 900 return false; 901 } 902 903 if (tick_nohz_full_enabled()) { 904 /* 905 * Keep the tick alive to guarantee timekeeping progression 906 * if there are full dynticks CPUs around 907 */ 908 if (tick_do_timer_cpu == cpu) 909 return false; 910 /* 911 * Boot safety: make sure the timekeeping duty has been 912 * assigned before entering dyntick-idle mode, 913 */ 914 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE) 915 return false; 916 } 917 918 return true; 919 } 920 921 static void __tick_nohz_idle_enter(struct tick_sched *ts) 922 { 923 ktime_t now, expires; 924 int cpu = smp_processor_id(); 925 926 now = tick_nohz_start_idle(ts); 927 928 if (can_stop_idle_tick(cpu, ts)) { 929 int was_stopped = ts->tick_stopped; 930 931 ts->idle_calls++; 932 933 expires = tick_nohz_stop_sched_tick(ts, now, cpu); 934 if (expires > 0LL) { 935 ts->idle_sleeps++; 936 ts->idle_expires = expires; 937 } 938 939 if (!was_stopped && ts->tick_stopped) 940 ts->idle_jiffies = ts->last_jiffies; 941 } 942 } 943 944 /** 945 * tick_nohz_idle_enter - stop the idle tick from the idle task 946 * 947 * When the next event is more than a tick into the future, stop the idle tick 948 * Called when we start the idle loop. 949 * 950 * The arch is responsible of calling: 951 * 952 * - rcu_idle_enter() after its last use of RCU before the CPU is put 953 * to sleep. 954 * - rcu_idle_exit() before the first use of RCU after the CPU is woken up. 955 */ 956 void tick_nohz_idle_enter(void) 957 { 958 struct tick_sched *ts; 959 960 WARN_ON_ONCE(irqs_disabled()); 961 962 /* 963 * Update the idle state in the scheduler domain hierarchy 964 * when tick_nohz_stop_sched_tick() is called from the idle loop. 965 * State will be updated to busy during the first busy tick after 966 * exiting idle. 967 */ 968 set_cpu_sd_state_idle(); 969 970 local_irq_disable(); 971 972 ts = this_cpu_ptr(&tick_cpu_sched); 973 ts->inidle = 1; 974 __tick_nohz_idle_enter(ts); 975 976 local_irq_enable(); 977 } 978 979 /** 980 * tick_nohz_irq_exit - update next tick event from interrupt exit 981 * 982 * When an interrupt fires while we are idle and it doesn't cause 983 * a reschedule, it may still add, modify or delete a timer, enqueue 984 * an RCU callback, etc... 985 * So we need to re-calculate and reprogram the next tick event. 986 */ 987 void tick_nohz_irq_exit(void) 988 { 989 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 990 991 if (ts->inidle) 992 __tick_nohz_idle_enter(ts); 993 else 994 tick_nohz_full_update_tick(ts); 995 } 996 997 /** 998 * tick_nohz_get_sleep_length - return the length of the current sleep 999 * 1000 * Called from power state control code with interrupts disabled 1001 */ 1002 ktime_t tick_nohz_get_sleep_length(void) 1003 { 1004 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1005 1006 return ts->sleep_length; 1007 } 1008 1009 /** 1010 * tick_nohz_get_idle_calls - return the current idle calls counter value 1011 * 1012 * Called from the schedutil frequency scaling governor in scheduler context. 1013 */ 1014 unsigned long tick_nohz_get_idle_calls(void) 1015 { 1016 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1017 1018 return ts->idle_calls; 1019 } 1020 1021 static void tick_nohz_account_idle_ticks(struct tick_sched *ts) 1022 { 1023 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE 1024 unsigned long ticks; 1025 1026 if (vtime_accounting_cpu_enabled()) 1027 return; 1028 /* 1029 * We stopped the tick in idle. Update process times would miss the 1030 * time we slept as update_process_times does only a 1 tick 1031 * accounting. Enforce that this is accounted to idle ! 1032 */ 1033 ticks = jiffies - ts->idle_jiffies; 1034 /* 1035 * We might be one off. Do not randomly account a huge number of ticks! 1036 */ 1037 if (ticks && ticks < LONG_MAX) 1038 account_idle_ticks(ticks); 1039 #endif 1040 } 1041 1042 /** 1043 * tick_nohz_idle_exit - restart the idle tick from the idle task 1044 * 1045 * Restart the idle tick when the CPU is woken up from idle 1046 * This also exit the RCU extended quiescent state. The CPU 1047 * can use RCU again after this function is called. 1048 */ 1049 void tick_nohz_idle_exit(void) 1050 { 1051 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1052 ktime_t now; 1053 1054 local_irq_disable(); 1055 1056 WARN_ON_ONCE(!ts->inidle); 1057 1058 ts->inidle = 0; 1059 1060 if (ts->idle_active || ts->tick_stopped) 1061 now = ktime_get(); 1062 1063 if (ts->idle_active) 1064 tick_nohz_stop_idle(ts, now); 1065 1066 if (ts->tick_stopped) { 1067 tick_nohz_restart_sched_tick(ts, now); 1068 tick_nohz_account_idle_ticks(ts); 1069 } 1070 1071 local_irq_enable(); 1072 } 1073 1074 /* 1075 * The nohz low res interrupt handler 1076 */ 1077 static void tick_nohz_handler(struct clock_event_device *dev) 1078 { 1079 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1080 struct pt_regs *regs = get_irq_regs(); 1081 ktime_t now = ktime_get(); 1082 1083 dev->next_event = KTIME_MAX; 1084 1085 tick_sched_do_timer(now); 1086 tick_sched_handle(ts, regs); 1087 1088 /* No need to reprogram if we are running tickless */ 1089 if (unlikely(ts->tick_stopped)) 1090 return; 1091 1092 hrtimer_forward(&ts->sched_timer, now, tick_period); 1093 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); 1094 } 1095 1096 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) 1097 { 1098 if (!tick_nohz_enabled) 1099 return; 1100 ts->nohz_mode = mode; 1101 /* One update is enough */ 1102 if (!test_and_set_bit(0, &tick_nohz_active)) 1103 timers_update_migration(true); 1104 } 1105 1106 /** 1107 * tick_nohz_switch_to_nohz - switch to nohz mode 1108 */ 1109 static void tick_nohz_switch_to_nohz(void) 1110 { 1111 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1112 ktime_t next; 1113 1114 if (!tick_nohz_enabled) 1115 return; 1116 1117 if (tick_switch_to_oneshot(tick_nohz_handler)) 1118 return; 1119 1120 /* 1121 * Recycle the hrtimer in ts, so we can share the 1122 * hrtimer_forward with the highres code. 1123 */ 1124 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 1125 /* Get the next period */ 1126 next = tick_init_jiffy_update(); 1127 1128 hrtimer_set_expires(&ts->sched_timer, next); 1129 hrtimer_forward_now(&ts->sched_timer, tick_period); 1130 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); 1131 tick_nohz_activate(ts, NOHZ_MODE_LOWRES); 1132 } 1133 1134 static inline void tick_nohz_irq_enter(void) 1135 { 1136 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1137 ktime_t now; 1138 1139 if (!ts->idle_active && !ts->tick_stopped) 1140 return; 1141 now = ktime_get(); 1142 if (ts->idle_active) 1143 tick_nohz_stop_idle(ts, now); 1144 if (ts->tick_stopped) 1145 tick_nohz_update_jiffies(now); 1146 } 1147 1148 #else 1149 1150 static inline void tick_nohz_switch_to_nohz(void) { } 1151 static inline void tick_nohz_irq_enter(void) { } 1152 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { } 1153 1154 #endif /* CONFIG_NO_HZ_COMMON */ 1155 1156 /* 1157 * Called from irq_enter to notify about the possible interruption of idle() 1158 */ 1159 void tick_irq_enter(void) 1160 { 1161 tick_check_oneshot_broadcast_this_cpu(); 1162 tick_nohz_irq_enter(); 1163 } 1164 1165 /* 1166 * High resolution timer specific code 1167 */ 1168 #ifdef CONFIG_HIGH_RES_TIMERS 1169 /* 1170 * We rearm the timer until we get disabled by the idle code. 1171 * Called with interrupts disabled. 1172 */ 1173 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) 1174 { 1175 struct tick_sched *ts = 1176 container_of(timer, struct tick_sched, sched_timer); 1177 struct pt_regs *regs = get_irq_regs(); 1178 ktime_t now = ktime_get(); 1179 1180 tick_sched_do_timer(now); 1181 1182 /* 1183 * Do not call, when we are not in irq context and have 1184 * no valid regs pointer 1185 */ 1186 if (regs) 1187 tick_sched_handle(ts, regs); 1188 else 1189 ts->next_tick = 0; 1190 1191 /* No need to reprogram if we are in idle or full dynticks mode */ 1192 if (unlikely(ts->tick_stopped)) 1193 return HRTIMER_NORESTART; 1194 1195 hrtimer_forward(timer, now, tick_period); 1196 1197 return HRTIMER_RESTART; 1198 } 1199 1200 static int sched_skew_tick; 1201 1202 static int __init skew_tick(char *str) 1203 { 1204 get_option(&str, &sched_skew_tick); 1205 1206 return 0; 1207 } 1208 early_param("skew_tick", skew_tick); 1209 1210 /** 1211 * tick_setup_sched_timer - setup the tick emulation timer 1212 */ 1213 void tick_setup_sched_timer(void) 1214 { 1215 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1216 ktime_t now = ktime_get(); 1217 1218 /* 1219 * Emulate tick processing via per-CPU hrtimers: 1220 */ 1221 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 1222 ts->sched_timer.function = tick_sched_timer; 1223 1224 /* Get the next period (per-CPU) */ 1225 hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update()); 1226 1227 /* Offset the tick to avert jiffies_lock contention. */ 1228 if (sched_skew_tick) { 1229 u64 offset = ktime_to_ns(tick_period) >> 1; 1230 do_div(offset, num_possible_cpus()); 1231 offset *= smp_processor_id(); 1232 hrtimer_add_expires_ns(&ts->sched_timer, offset); 1233 } 1234 1235 hrtimer_forward(&ts->sched_timer, now, tick_period); 1236 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED); 1237 tick_nohz_activate(ts, NOHZ_MODE_HIGHRES); 1238 } 1239 #endif /* HIGH_RES_TIMERS */ 1240 1241 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS 1242 void tick_cancel_sched_timer(int cpu) 1243 { 1244 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 1245 1246 # ifdef CONFIG_HIGH_RES_TIMERS 1247 if (ts->sched_timer.base) 1248 hrtimer_cancel(&ts->sched_timer); 1249 # endif 1250 1251 memset(ts, 0, sizeof(*ts)); 1252 } 1253 #endif 1254 1255 /** 1256 * Async notification about clocksource changes 1257 */ 1258 void tick_clock_notify(void) 1259 { 1260 int cpu; 1261 1262 for_each_possible_cpu(cpu) 1263 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks); 1264 } 1265 1266 /* 1267 * Async notification about clock event changes 1268 */ 1269 void tick_oneshot_notify(void) 1270 { 1271 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1272 1273 set_bit(0, &ts->check_clocks); 1274 } 1275 1276 /** 1277 * Check, if a change happened, which makes oneshot possible. 1278 * 1279 * Called cyclic from the hrtimer softirq (driven by the timer 1280 * softirq) allow_nohz signals, that we can switch into low-res nohz 1281 * mode, because high resolution timers are disabled (either compile 1282 * or runtime). Called with interrupts disabled. 1283 */ 1284 int tick_check_oneshot_change(int allow_nohz) 1285 { 1286 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1287 1288 if (!test_and_clear_bit(0, &ts->check_clocks)) 1289 return 0; 1290 1291 if (ts->nohz_mode != NOHZ_MODE_INACTIVE) 1292 return 0; 1293 1294 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available()) 1295 return 0; 1296 1297 if (!allow_nohz) 1298 return 1; 1299 1300 tick_nohz_switch_to_nohz(); 1301 return 0; 1302 } 1303