개념 설명 전체 · v6.6 / kernel/time/tick-sched.c
1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Copyright(C) 2005-2006, Thomas Gleixner <[email protected]> 4 * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar 5 * Copyright(C) 2006-2007 Timesys Corp., Thomas Gleixner 6 * 7 * No idle tick implementation for low and high resolution timers 8 * 9 * Started by: Thomas Gleixner and Ingo Molnar 10 */ 11 #include <linux/cpu.h> 12 #include <linux/err.h> 13 #include <linux/hrtimer.h> 14 #include <linux/interrupt.h> 15 #include <linux/kernel_stat.h> 16 #include <linux/percpu.h> 17 #include <linux/nmi.h> 18 #include <linux/profile.h> 19 #include <linux/sched/signal.h> 20 #include <linux/sched/clock.h> 21 #include <linux/sched/stat.h> 22 #include <linux/sched/nohz.h> 23 #include <linux/sched/loadavg.h> 24 #include <linux/module.h> 25 #include <linux/irq_work.h> 26 #include <linux/posix-timers.h> 27 #include <linux/context_tracking.h> 28 #include <linux/mm.h> 29 30 #include <asm/irq_regs.h> 31 32 #include "tick-internal.h" 33 34 #include <trace/events/timer.h> 35 36 /* 37 * Per-CPU nohz control structure 38 */ 39 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched); 40 41 struct tick_sched *tick_get_tick_sched(int cpu) 42 { 43 return &per_cpu(tick_cpu_sched, cpu); 44 } 45 46 #if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS) 47 /* 48 * The time, when the last jiffy update happened. Write access must hold 49 * jiffies_lock and jiffies_seq. tick_nohz_next_event() needs to get a 50 * consistent view of jiffies and last_jiffies_update. 51 */ 52 static ktime_t last_jiffies_update; 53 54 /* 55 * Must be called with interrupts disabled ! 56 */ 57 static void tick_do_update_jiffies64(ktime_t now) 58 { 59 unsigned long ticks = 1; 60 ktime_t delta, nextp; 61 62 /* 63 * 64bit can do a quick check without holding jiffies lock and 64 * without looking at the sequence count. The smp_load_acquire() 65 * pairs with the update done later in this function. 66 * 67 * 32bit cannot do that because the store of tick_next_period 68 * consists of two 32bit stores and the first store could move it 69 * to a random point in the future. 70 */ 71 if (IS_ENABLED(CONFIG_64BIT)) { 72 if (ktime_before(now, smp_load_acquire(&tick_next_period))) 73 return; 74 } else { 75 unsigned int seq; 76 77 /* 78 * Avoid contention on jiffies_lock and protect the quick 79 * check with the sequence count. 80 */ 81 do { 82 seq = read_seqcount_begin(&jiffies_seq); 83 nextp = tick_next_period; 84 } while (read_seqcount_retry(&jiffies_seq, seq)); 85 86 if (ktime_before(now, nextp)) 87 return; 88 } 89 90 /* Quick check failed, i.e. update is required. */ 91 raw_spin_lock(&jiffies_lock); 92 /* 93 * Reevaluate with the lock held. Another CPU might have done the 94 * update already. 95 */ 96 if (ktime_before(now, tick_next_period)) { 97 raw_spin_unlock(&jiffies_lock); 98 return; 99 } 100 101 write_seqcount_begin(&jiffies_seq); 102 103 delta = ktime_sub(now, tick_next_period); 104 if (unlikely(delta >= TICK_NSEC)) { 105 /* Slow path for long idle sleep times */ 106 s64 incr = TICK_NSEC; 107 108 ticks += ktime_divns(delta, incr); 109 110 last_jiffies_update = ktime_add_ns(last_jiffies_update, 111 incr * ticks); 112 } else { 113 last_jiffies_update = ktime_add_ns(last_jiffies_update, 114 TICK_NSEC); 115 } 116 117 /* Advance jiffies to complete the jiffies_seq protected job */ 118 jiffies_64 += ticks; 119 120 /* 121 * Keep the tick_next_period variable up to date. 122 */ 123 nextp = ktime_add_ns(last_jiffies_update, TICK_NSEC); 124 125 if (IS_ENABLED(CONFIG_64BIT)) { 126 /* 127 * Pairs with smp_load_acquire() in the lockless quick 128 * check above and ensures that the update to jiffies_64 is 129 * not reordered vs. the store to tick_next_period, neither 130 * by the compiler nor by the CPU. 131 */ 132 smp_store_release(&tick_next_period, nextp); 133 } else { 134 /* 135 * A plain store is good enough on 32bit as the quick check 136 * above is protected by the sequence count. 137 */ 138 tick_next_period = nextp; 139 } 140 141 /* 142 * Release the sequence count. calc_global_load() below is not 143 * protected by it, but jiffies_lock needs to be held to prevent 144 * concurrent invocations. 145 */ 146 write_seqcount_end(&jiffies_seq); 147 148 calc_global_load(); 149 150 raw_spin_unlock(&jiffies_lock); 151 update_wall_time(); 152 } 153 154 /* 155 * Initialize and return retrieve the jiffies update. 156 */ 157 static ktime_t tick_init_jiffy_update(void) 158 { 159 ktime_t period; 160 161 raw_spin_lock(&jiffies_lock); 162 write_seqcount_begin(&jiffies_seq); 163 /* Did we start the jiffies update yet ? */ 164 if (last_jiffies_update == 0) { 165 u32 rem; 166 167 /* 168 * Ensure that the tick is aligned to a multiple of 169 * TICK_NSEC. 170 */ 171 div_u64_rem(tick_next_period, TICK_NSEC, &rem); 172 if (rem) 173 tick_next_period += TICK_NSEC - rem; 174 175 last_jiffies_update = tick_next_period; 176 } 177 period = last_jiffies_update; 178 write_seqcount_end(&jiffies_seq); 179 raw_spin_unlock(&jiffies_lock); 180 return period; 181 } 182 183 #define MAX_STALLED_JIFFIES 5 184 185 static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now) 186 { 187 int cpu = smp_processor_id(); 188 189 #ifdef CONFIG_NO_HZ_COMMON 190 /* 191 * Check if the do_timer duty was dropped. We don't care about 192 * concurrency: This happens only when the CPU in charge went 193 * into a long sleep. If two CPUs happen to assign themselves to 194 * this duty, then the jiffies update is still serialized by 195 * jiffies_lock. 196 * 197 * If nohz_full is enabled, this should not happen because the 198 * tick_do_timer_cpu never relinquishes. 199 */ 200 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) { 201 #ifdef CONFIG_NO_HZ_FULL 202 WARN_ON_ONCE(tick_nohz_full_running); 203 #endif 204 tick_do_timer_cpu = cpu; 205 } 206 #endif 207 208 /* Check, if the jiffies need an update */ 209 if (tick_do_timer_cpu == cpu) 210 tick_do_update_jiffies64(now); 211 212 /* 213 * If jiffies update stalled for too long (timekeeper in stop_machine() 214 * or VMEXIT'ed for several msecs), force an update. 215 */ 216 if (ts->last_tick_jiffies != jiffies) { 217 ts->stalled_jiffies = 0; 218 ts->last_tick_jiffies = READ_ONCE(jiffies); 219 } else { 220 if (++ts->stalled_jiffies == MAX_STALLED_JIFFIES) { 221 tick_do_update_jiffies64(now); 222 ts->stalled_jiffies = 0; 223 ts->last_tick_jiffies = READ_ONCE(jiffies); 224 } 225 } 226 227 if (ts->inidle) 228 ts->got_idle_tick = 1; 229 } 230 231 static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs) 232 { 233 #ifdef CONFIG_NO_HZ_COMMON 234 /* 235 * When we are idle and the tick is stopped, we have to touch 236 * the watchdog as we might not schedule for a really long 237 * time. This happens on complete idle SMP systems while 238 * waiting on the login prompt. We also increment the "start of 239 * idle" jiffy stamp so the idle accounting adjustment we do 240 * when we go busy again does not account too much ticks. 241 */ 242 if (ts->tick_stopped) { 243 touch_softlockup_watchdog_sched(); 244 if (is_idle_task(current)) 245 ts->idle_jiffies++; 246 /* 247 * In case the current tick fired too early past its expected 248 * expiration, make sure we don't bypass the next clock reprogramming 249 * to the same deadline. 250 */ 251 ts->next_tick = 0; 252 } 253 #endif 254 update_process_times(user_mode(regs)); 255 profile_tick(CPU_PROFILING); 256 } 257 #endif 258 259 #ifdef CONFIG_NO_HZ_FULL 260 cpumask_var_t tick_nohz_full_mask; 261 EXPORT_SYMBOL_GPL(tick_nohz_full_mask); 262 bool tick_nohz_full_running; 263 EXPORT_SYMBOL_GPL(tick_nohz_full_running); 264 static atomic_t tick_dep_mask; 265 266 static bool check_tick_dependency(atomic_t *dep) 267 { 268 int val = atomic_read(dep); 269 270 if (val & TICK_DEP_MASK_POSIX_TIMER) { 271 trace_tick_stop(0, TICK_DEP_MASK_POSIX_TIMER); 272 return true; 273 } 274 275 if (val & TICK_DEP_MASK_PERF_EVENTS) { 276 trace_tick_stop(0, TICK_DEP_MASK_PERF_EVENTS); 277 return true; 278 } 279 280 if (val & TICK_DEP_MASK_SCHED) { 281 trace_tick_stop(0, TICK_DEP_MASK_SCHED); 282 return true; 283 } 284 285 if (val & TICK_DEP_MASK_CLOCK_UNSTABLE) { 286 trace_tick_stop(0, TICK_DEP_MASK_CLOCK_UNSTABLE); 287 return true; 288 } 289 290 if (val & TICK_DEP_MASK_RCU) { 291 trace_tick_stop(0, TICK_DEP_MASK_RCU); 292 return true; 293 } 294 295 if (val & TICK_DEP_MASK_RCU_EXP) { 296 trace_tick_stop(0, TICK_DEP_MASK_RCU_EXP); 297 return true; 298 } 299 300 return false; 301 } 302 303 static bool can_stop_full_tick(int cpu, struct tick_sched *ts) 304 { 305 lockdep_assert_irqs_disabled(); 306 307 if (unlikely(!cpu_online(cpu))) 308 return false; 309 310 if (check_tick_dependency(&tick_dep_mask)) 311 return false; 312 313 if (check_tick_dependency(&ts->tick_dep_mask)) 314 return false; 315 316 if (check_tick_dependency(¤t->tick_dep_mask)) 317 return false; 318 319 if (check_tick_dependency(¤t->signal->tick_dep_mask)) 320 return false; 321 322 return true; 323 } 324 325 static void nohz_full_kick_func(struct irq_work *work) 326 { 327 /* Empty, the tick restart happens on tick_nohz_irq_exit() */ 328 } 329 330 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = 331 IRQ_WORK_INIT_HARD(nohz_full_kick_func); 332 333 /* 334 * Kick this CPU if it's full dynticks in order to force it to 335 * re-evaluate its dependency on the tick and restart it if necessary. 336 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(), 337 * is NMI safe. 338 */ 339 static void tick_nohz_full_kick(void) 340 { 341 if (!tick_nohz_full_cpu(smp_processor_id())) 342 return; 343 344 irq_work_queue(this_cpu_ptr(&nohz_full_kick_work)); 345 } 346 347 /* 348 * Kick the CPU if it's full dynticks in order to force it to 349 * re-evaluate its dependency on the tick and restart it if necessary. 350 */ 351 void tick_nohz_full_kick_cpu(int cpu) 352 { 353 if (!tick_nohz_full_cpu(cpu)) 354 return; 355 356 irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu); 357 } 358 359 static void tick_nohz_kick_task(struct task_struct *tsk) 360 { 361 int cpu; 362 363 /* 364 * If the task is not running, run_posix_cpu_timers() 365 * has nothing to elapse, IPI can then be spared. 366 * 367 * activate_task() STORE p->tick_dep_mask 368 * STORE p->on_rq 369 * __schedule() (switch to task 'p') smp_mb() (atomic_fetch_or()) 370 * LOCK rq->lock LOAD p->on_rq 371 * smp_mb__after_spin_lock() 372 * tick_nohz_task_switch() 373 * LOAD p->tick_dep_mask 374 */ 375 if (!sched_task_on_rq(tsk)) 376 return; 377 378 /* 379 * If the task concurrently migrates to another CPU, 380 * we guarantee it sees the new tick dependency upon 381 * schedule. 382 * 383 * set_task_cpu(p, cpu); 384 * STORE p->cpu = @cpu 385 * __schedule() (switch to task 'p') 386 * LOCK rq->lock 387 * smp_mb__after_spin_lock() STORE p->tick_dep_mask 388 * tick_nohz_task_switch() smp_mb() (atomic_fetch_or()) 389 * LOAD p->tick_dep_mask LOAD p->cpu 390 */ 391 cpu = task_cpu(tsk); 392 393 preempt_disable(); 394 if (cpu_online(cpu)) 395 tick_nohz_full_kick_cpu(cpu); 396 preempt_enable(); 397 } 398 399 /* 400 * Kick all full dynticks CPUs in order to force these to re-evaluate 401 * their dependency on the tick and restart it if necessary. 402 */ 403 static void tick_nohz_full_kick_all(void) 404 { 405 int cpu; 406 407 if (!tick_nohz_full_running) 408 return; 409 410 preempt_disable(); 411 for_each_cpu_and(cpu, tick_nohz_full_mask, cpu_online_mask) 412 tick_nohz_full_kick_cpu(cpu); 413 preempt_enable(); 414 } 415 416 static void tick_nohz_dep_set_all(atomic_t *dep, 417 enum tick_dep_bits bit) 418 { 419 int prev; 420 421 prev = atomic_fetch_or(BIT(bit), dep); 422 if (!prev) 423 tick_nohz_full_kick_all(); 424 } 425 426 /* 427 * Set a global tick dependency. Used by perf events that rely on freq and 428 * by unstable clock. 429 */ 430 void tick_nohz_dep_set(enum tick_dep_bits bit) 431 { 432 tick_nohz_dep_set_all(&tick_dep_mask, bit); 433 } 434 435 void tick_nohz_dep_clear(enum tick_dep_bits bit) 436 { 437 atomic_andnot(BIT(bit), &tick_dep_mask); 438 } 439 440 /* 441 * Set per-CPU tick dependency. Used by scheduler and perf events in order to 442 * manage events throttling. 443 */ 444 void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit) 445 { 446 int prev; 447 struct tick_sched *ts; 448 449 ts = per_cpu_ptr(&tick_cpu_sched, cpu); 450 451 prev = atomic_fetch_or(BIT(bit), &ts->tick_dep_mask); 452 if (!prev) { 453 preempt_disable(); 454 /* Perf needs local kick that is NMI safe */ 455 if (cpu == smp_processor_id()) { 456 tick_nohz_full_kick(); 457 } else { 458 /* Remote irq work not NMI-safe */ 459 if (!WARN_ON_ONCE(in_nmi())) 460 tick_nohz_full_kick_cpu(cpu); 461 } 462 preempt_enable(); 463 } 464 } 465 EXPORT_SYMBOL_GPL(tick_nohz_dep_set_cpu); 466 467 void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit) 468 { 469 struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu); 470 471 atomic_andnot(BIT(bit), &ts->tick_dep_mask); 472 } 473 EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_cpu); 474 475 /* 476 * Set a per-task tick dependency. RCU need this. Also posix CPU timers 477 * in order to elapse per task timers. 478 */ 479 void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit) 480 { 481 if (!atomic_fetch_or(BIT(bit), &tsk->tick_dep_mask)) 482 tick_nohz_kick_task(tsk); 483 } 484 EXPORT_SYMBOL_GPL(tick_nohz_dep_set_task); 485 486 void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit) 487 { 488 atomic_andnot(BIT(bit), &tsk->tick_dep_mask); 489 } 490 EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_task); 491 492 /* 493 * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse 494 * per process timers. 495 */ 496 void tick_nohz_dep_set_signal(struct task_struct *tsk, 497 enum tick_dep_bits bit) 498 { 499 int prev; 500 struct signal_struct *sig = tsk->signal; 501 502 prev = atomic_fetch_or(BIT(bit), &sig->tick_dep_mask); 503 if (!prev) { 504 struct task_struct *t; 505 506 lockdep_assert_held(&tsk->sighand->siglock); 507 __for_each_thread(sig, t) 508 tick_nohz_kick_task(t); 509 } 510 } 511 512 void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit) 513 { 514 atomic_andnot(BIT(bit), &sig->tick_dep_mask); 515 } 516 517 /* 518 * Re-evaluate the need for the tick as we switch the current task. 519 * It might need the tick due to per task/process properties: 520 * perf events, posix CPU timers, ... 521 */ 522 void __tick_nohz_task_switch(void) 523 { 524 struct tick_sched *ts; 525 526 if (!tick_nohz_full_cpu(smp_processor_id())) 527 return; 528 529 ts = this_cpu_ptr(&tick_cpu_sched); 530 531 if (ts->tick_stopped) { 532 if (atomic_read(¤t->tick_dep_mask) || 533 atomic_read(¤t->signal->tick_dep_mask)) 534 tick_nohz_full_kick(); 535 } 536 } 537 538 /* Get the boot-time nohz CPU list from the kernel parameters. */ 539 void __init tick_nohz_full_setup(cpumask_var_t cpumask) 540 { 541 alloc_bootmem_cpumask_var(&tick_nohz_full_mask); 542 cpumask_copy(tick_nohz_full_mask, cpumask); 543 tick_nohz_full_running = true; 544 } 545 546 bool tick_nohz_cpu_hotpluggable(unsigned int cpu) 547 { 548 /* 549 * The tick_do_timer_cpu CPU handles housekeeping duty (unbound 550 * timers, workqueues, timekeeping, ...) on behalf of full dynticks 551 * CPUs. It must remain online when nohz full is enabled. 552 */ 553 if (tick_nohz_full_running && tick_do_timer_cpu == cpu) 554 return false; 555 return true; 556 } 557 558 static int tick_nohz_cpu_down(unsigned int cpu) 559 { 560 return tick_nohz_cpu_hotpluggable(cpu) ? 0 : -EBUSY; 561 } 562 563 void __init tick_nohz_init(void) 564 { 565 int cpu, ret; 566 567 if (!tick_nohz_full_running) 568 return; 569 570 /* 571 * Full dynticks uses irq work to drive the tick rescheduling on safe 572 * locking contexts. But then we need irq work to raise its own 573 * interrupts to avoid circular dependency on the tick 574 */ 575 if (!arch_irq_work_has_interrupt()) { 576 pr_warn("NO_HZ: Can't run full dynticks because arch doesn't support irq work self-IPIs\n"); 577 cpumask_clear(tick_nohz_full_mask); 578 tick_nohz_full_running = false; 579 return; 580 } 581 582 if (IS_ENABLED(CONFIG_PM_SLEEP_SMP) && 583 !IS_ENABLED(CONFIG_PM_SLEEP_SMP_NONZERO_CPU)) { 584 cpu = smp_processor_id(); 585 586 if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) { 587 pr_warn("NO_HZ: Clearing %d from nohz_full range " 588 "for timekeeping\n", cpu); 589 cpumask_clear_cpu(cpu, tick_nohz_full_mask); 590 } 591 } 592 593 for_each_cpu(cpu, tick_nohz_full_mask) 594 ct_cpu_track_user(cpu); 595 596 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, 597 "kernel/nohz:predown", NULL, 598 tick_nohz_cpu_down); 599 WARN_ON(ret < 0); 600 pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n", 601 cpumask_pr_args(tick_nohz_full_mask)); 602 } 603 #endif 604 605 /* 606 * NOHZ - aka dynamic tick functionality 607 */ 608 #ifdef CONFIG_NO_HZ_COMMON 609 /* 610 * NO HZ enabled ? 611 */ 612 bool tick_nohz_enabled __read_mostly = true; 613 unsigned long tick_nohz_active __read_mostly; 614 /* 615 * Enable / Disable tickless mode 616 */ 617 static int __init setup_tick_nohz(char *str) 618 { 619 return (kstrtobool(str, &tick_nohz_enabled) == 0); 620 } 621 622 __setup("nohz=", setup_tick_nohz); 623 624 bool tick_nohz_tick_stopped(void) 625 { 626 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 627 628 return ts->tick_stopped; 629 } 630 631 bool tick_nohz_tick_stopped_cpu(int cpu) 632 { 633 struct tick_sched *ts = per_cpu_ptr(&tick_cpu_sched, cpu); 634 635 return ts->tick_stopped; 636 } 637 638 /** 639 * tick_nohz_update_jiffies - update jiffies when idle was interrupted 640 * 641 * Called from interrupt entry when the CPU was idle 642 * 643 * In case the sched_tick was stopped on this CPU, we have to check if jiffies 644 * must be updated. Otherwise an interrupt handler could use a stale jiffy 645 * value. We do this unconditionally on any CPU, as we don't know whether the 646 * CPU, which has the update task assigned is in a long sleep. 647 */ 648 static void tick_nohz_update_jiffies(ktime_t now) 649 { 650 unsigned long flags; 651 652 __this_cpu_write(tick_cpu_sched.idle_waketime, now); 653 654 local_irq_save(flags); 655 tick_do_update_jiffies64(now); 656 local_irq_restore(flags); 657 658 touch_softlockup_watchdog_sched(); 659 } 660 661 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now) 662 { 663 ktime_t delta; 664 665 if (WARN_ON_ONCE(!ts->idle_active)) 666 return; 667 668 delta = ktime_sub(now, ts->idle_entrytime); 669 670 write_seqcount_begin(&ts->idle_sleeptime_seq); 671 if (nr_iowait_cpu(smp_processor_id()) > 0) 672 ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta); 673 else 674 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); 675 676 ts->idle_entrytime = now; 677 ts->idle_active = 0; 678 write_seqcount_end(&ts->idle_sleeptime_seq); 679 680 sched_clock_idle_wakeup_event(); 681 } 682 683 static void tick_nohz_start_idle(struct tick_sched *ts) 684 { 685 write_seqcount_begin(&ts->idle_sleeptime_seq); 686 ts->idle_entrytime = ktime_get(); 687 ts->idle_active = 1; 688 write_seqcount_end(&ts->idle_sleeptime_seq); 689 690 sched_clock_idle_sleep_event(); 691 } 692 693 static u64 get_cpu_sleep_time_us(struct tick_sched *ts, ktime_t *sleeptime, 694 bool compute_delta, u64 *last_update_time) 695 { 696 ktime_t now, idle; 697 unsigned int seq; 698 699 if (!tick_nohz_active) 700 return -1; 701 702 now = ktime_get(); 703 if (last_update_time) 704 *last_update_time = ktime_to_us(now); 705 706 do { 707 seq = read_seqcount_begin(&ts->idle_sleeptime_seq); 708 709 if (ts->idle_active && compute_delta) { 710 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 711 712 idle = ktime_add(*sleeptime, delta); 713 } else { 714 idle = *sleeptime; 715 } 716 } while (read_seqcount_retry(&ts->idle_sleeptime_seq, seq)); 717 718 return ktime_to_us(idle); 719 720 } 721 722 /** 723 * get_cpu_idle_time_us - get the total idle time of a CPU 724 * @cpu: CPU number to query 725 * @last_update_time: variable to store update time in. Do not update 726 * counters if NULL. 727 * 728 * Return the cumulative idle time (since boot) for a given 729 * CPU, in microseconds. Note this is partially broken due to 730 * the counter of iowait tasks that can be remotely updated without 731 * any synchronization. Therefore it is possible to observe backward 732 * values within two consecutive reads. 733 * 734 * This time is measured via accounting rather than sampling, 735 * and is as accurate as ktime_get() is. 736 * 737 * This function returns -1 if NOHZ is not enabled. 738 */ 739 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) 740 { 741 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 742 743 return get_cpu_sleep_time_us(ts, &ts->idle_sleeptime, 744 !nr_iowait_cpu(cpu), last_update_time); 745 } 746 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us); 747 748 /** 749 * get_cpu_iowait_time_us - get the total iowait time of a CPU 750 * @cpu: CPU number to query 751 * @last_update_time: variable to store update time in. Do not update 752 * counters if NULL. 753 * 754 * Return the cumulative iowait time (since boot) for a given 755 * CPU, in microseconds. Note this is partially broken due to 756 * the counter of iowait tasks that can be remotely updated without 757 * any synchronization. Therefore it is possible to observe backward 758 * values within two consecutive reads. 759 * 760 * This time is measured via accounting rather than sampling, 761 * and is as accurate as ktime_get() is. 762 * 763 * This function returns -1 if NOHZ is not enabled. 764 */ 765 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time) 766 { 767 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 768 769 return get_cpu_sleep_time_us(ts, &ts->iowait_sleeptime, 770 nr_iowait_cpu(cpu), last_update_time); 771 } 772 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us); 773 774 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) 775 { 776 hrtimer_cancel(&ts->sched_timer); 777 hrtimer_set_expires(&ts->sched_timer, ts->last_tick); 778 779 /* Forward the time to expire in the future */ 780 hrtimer_forward(&ts->sched_timer, now, TICK_NSEC); 781 782 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { 783 hrtimer_start_expires(&ts->sched_timer, 784 HRTIMER_MODE_ABS_PINNED_HARD); 785 } else { 786 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); 787 } 788 789 /* 790 * Reset to make sure next tick stop doesn't get fooled by past 791 * cached clock deadline. 792 */ 793 ts->next_tick = 0; 794 } 795 796 static inline bool local_timer_softirq_pending(void) 797 { 798 return local_softirq_pending() & BIT(TIMER_SOFTIRQ); 799 } 800 801 static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu) 802 { 803 u64 basemono, next_tick, delta, expires; 804 unsigned long basejiff; 805 unsigned int seq; 806 807 /* Read jiffies and the time when jiffies were updated last */ 808 do { 809 seq = read_seqcount_begin(&jiffies_seq); 810 basemono = last_jiffies_update; 811 basejiff = jiffies; 812 } while (read_seqcount_retry(&jiffies_seq, seq)); 813 ts->last_jiffies = basejiff; 814 ts->timer_expires_base = basemono; 815 816 /* 817 * Keep the periodic tick, when RCU, architecture or irq_work 818 * requests it. 819 * Aside of that check whether the local timer softirq is 820 * pending. If so its a bad idea to call get_next_timer_interrupt() 821 * because there is an already expired timer, so it will request 822 * immediate expiry, which rearms the hardware timer with a 823 * minimal delta which brings us back to this place 824 * immediately. Lather, rinse and repeat... 825 */ 826 if (rcu_needs_cpu() || arch_needs_cpu() || 827 irq_work_needs_cpu() || local_timer_softirq_pending()) { 828 next_tick = basemono + TICK_NSEC; 829 } else { 830 /* 831 * Get the next pending timer. If high resolution 832 * timers are enabled this only takes the timer wheel 833 * timers into account. If high resolution timers are 834 * disabled this also looks at the next expiring 835 * hrtimer. 836 */ 837 next_tick = get_next_timer_interrupt(basejiff, basemono); 838 ts->next_timer = next_tick; 839 } 840 841 /* 842 * If the tick is due in the next period, keep it ticking or 843 * force prod the timer. 844 */ 845 delta = next_tick - basemono; 846 if (delta <= (u64)TICK_NSEC) { 847 /* 848 * Tell the timer code that the base is not idle, i.e. undo 849 * the effect of get_next_timer_interrupt(): 850 */ 851 timer_clear_idle(); 852 /* 853 * We've not stopped the tick yet, and there's a timer in the 854 * next period, so no point in stopping it either, bail. 855 */ 856 if (!ts->tick_stopped) { 857 ts->timer_expires = 0; 858 goto out; 859 } 860 } 861 862 /* 863 * If this CPU is the one which had the do_timer() duty last, we limit 864 * the sleep time to the timekeeping max_deferment value. 865 * Otherwise we can sleep as long as we want. 866 */ 867 delta = timekeeping_max_deferment(); 868 if (cpu != tick_do_timer_cpu && 869 (tick_do_timer_cpu != TICK_DO_TIMER_NONE || !ts->do_timer_last)) 870 delta = KTIME_MAX; 871 872 /* Calculate the next expiry time */ 873 if (delta < (KTIME_MAX - basemono)) 874 expires = basemono + delta; 875 else 876 expires = KTIME_MAX; 877 878 ts->timer_expires = min_t(u64, expires, next_tick); 879 880 out: 881 return ts->timer_expires; 882 } 883 884 static void tick_nohz_stop_tick(struct tick_sched *ts, int cpu) 885 { 886 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); 887 u64 basemono = ts->timer_expires_base; 888 u64 expires = ts->timer_expires; 889 ktime_t tick = expires; 890 891 /* Make sure we won't be trying to stop it twice in a row. */ 892 ts->timer_expires_base = 0; 893 894 /* 895 * If this CPU is the one which updates jiffies, then give up 896 * the assignment and let it be taken by the CPU which runs 897 * the tick timer next, which might be this CPU as well. If we 898 * don't drop this here the jiffies might be stale and 899 * do_timer() never invoked. Keep track of the fact that it 900 * was the one which had the do_timer() duty last. 901 */ 902 if (cpu == tick_do_timer_cpu) { 903 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 904 ts->do_timer_last = 1; 905 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) { 906 ts->do_timer_last = 0; 907 } 908 909 /* Skip reprogram of event if its not changed */ 910 if (ts->tick_stopped && (expires == ts->next_tick)) { 911 /* Sanity check: make sure clockevent is actually programmed */ 912 if (tick == KTIME_MAX || ts->next_tick == hrtimer_get_expires(&ts->sched_timer)) 913 return; 914 915 WARN_ON_ONCE(1); 916 printk_once("basemono: %llu ts->next_tick: %llu dev->next_event: %llu timer->active: %d timer->expires: %llu\n", 917 basemono, ts->next_tick, dev->next_event, 918 hrtimer_active(&ts->sched_timer), hrtimer_get_expires(&ts->sched_timer)); 919 } 920 921 /* 922 * nohz_stop_sched_tick can be called several times before 923 * the nohz_restart_sched_tick is called. This happens when 924 * interrupts arrive which do not cause a reschedule. In the 925 * first call we save the current tick time, so we can restart 926 * the scheduler tick in nohz_restart_sched_tick. 927 */ 928 if (!ts->tick_stopped) { 929 calc_load_nohz_start(); 930 quiet_vmstat(); 931 932 ts->last_tick = hrtimer_get_expires(&ts->sched_timer); 933 ts->tick_stopped = 1; 934 trace_tick_stop(1, TICK_DEP_MASK_NONE); 935 } 936 937 ts->next_tick = tick; 938 939 /* 940 * If the expiration time == KTIME_MAX, then we simply stop 941 * the tick timer. 942 */ 943 if (unlikely(expires == KTIME_MAX)) { 944 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) 945 hrtimer_cancel(&ts->sched_timer); 946 else 947 tick_program_event(KTIME_MAX, 1); 948 return; 949 } 950 951 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { 952 hrtimer_start(&ts->sched_timer, tick, 953 HRTIMER_MODE_ABS_PINNED_HARD); 954 } else { 955 hrtimer_set_expires(&ts->sched_timer, tick); 956 tick_program_event(tick, 1); 957 } 958 } 959 960 static void tick_nohz_retain_tick(struct tick_sched *ts) 961 { 962 ts->timer_expires_base = 0; 963 } 964 965 #ifdef CONFIG_NO_HZ_FULL 966 static void tick_nohz_stop_sched_tick(struct tick_sched *ts, int cpu) 967 { 968 if (tick_nohz_next_event(ts, cpu)) 969 tick_nohz_stop_tick(ts, cpu); 970 else 971 tick_nohz_retain_tick(ts); 972 } 973 #endif /* CONFIG_NO_HZ_FULL */ 974 975 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) 976 { 977 /* Update jiffies first */ 978 tick_do_update_jiffies64(now); 979 980 /* 981 * Clear the timer idle flag, so we avoid IPIs on remote queueing and 982 * the clock forward checks in the enqueue path: 983 */ 984 timer_clear_idle(); 985 986 calc_load_nohz_stop(); 987 touch_softlockup_watchdog_sched(); 988 /* 989 * Cancel the scheduled timer and restore the tick 990 */ 991 ts->tick_stopped = 0; 992 tick_nohz_restart(ts, now); 993 } 994 995 static void __tick_nohz_full_update_tick(struct tick_sched *ts, 996 ktime_t now) 997 { 998 #ifdef CONFIG_NO_HZ_FULL 999 int cpu = smp_processor_id(); 1000 1001 if (can_stop_full_tick(cpu, ts)) 1002 tick_nohz_stop_sched_tick(ts, cpu); 1003 else if (ts->tick_stopped) 1004 tick_nohz_restart_sched_tick(ts, now); 1005 #endif 1006 } 1007 1008 static void tick_nohz_full_update_tick(struct tick_sched *ts) 1009 { 1010 if (!tick_nohz_full_cpu(smp_processor_id())) 1011 return; 1012 1013 if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) 1014 return; 1015 1016 __tick_nohz_full_update_tick(ts, ktime_get()); 1017 } 1018 1019 /* 1020 * A pending softirq outside an IRQ (or softirq disabled section) context 1021 * should be waiting for ksoftirqd to handle it. Therefore we shouldn't 1022 * reach here due to the need_resched() early check in can_stop_idle_tick(). 1023 * 1024 * However if we are between CPUHP_AP_SMPBOOT_THREADS and CPU_TEARDOWN_CPU on the 1025 * cpu_down() process, softirqs can still be raised while ksoftirqd is parked, 1026 * triggering the below since wakep_softirqd() is ignored. 1027 * 1028 */ 1029 static bool report_idle_softirq(void) 1030 { 1031 static int ratelimit; 1032 unsigned int pending = local_softirq_pending(); 1033 1034 if (likely(!pending)) 1035 return false; 1036 1037 /* Some softirqs claim to be safe against hotplug and ksoftirqd parking */ 1038 if (!cpu_active(smp_processor_id())) { 1039 pending &= ~SOFTIRQ_HOTPLUG_SAFE_MASK; 1040 if (!pending) 1041 return false; 1042 } 1043 1044 if (ratelimit >= 10) 1045 return false; 1046 1047 /* On RT, softirqs handling may be waiting on some lock */ 1048 if (local_bh_blocked()) 1049 return false; 1050 1051 pr_warn("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n", 1052 pending); 1053 ratelimit++; 1054 1055 return true; 1056 } 1057 1058 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) 1059 { 1060 /* 1061 * If this CPU is offline and it is the one which updates 1062 * jiffies, then give up the assignment and let it be taken by 1063 * the CPU which runs the tick timer next. If we don't drop 1064 * this here the jiffies might be stale and do_timer() never 1065 * invoked. 1066 */ 1067 if (unlikely(!cpu_online(cpu))) { 1068 if (cpu == tick_do_timer_cpu) 1069 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 1070 /* 1071 * Make sure the CPU doesn't get fooled by obsolete tick 1072 * deadline if it comes back online later. 1073 */ 1074 ts->next_tick = 0; 1075 return false; 1076 } 1077 1078 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) 1079 return false; 1080 1081 if (need_resched()) 1082 return false; 1083 1084 if (unlikely(report_idle_softirq())) 1085 return false; 1086 1087 if (tick_nohz_full_enabled()) { 1088 /* 1089 * Keep the tick alive to guarantee timekeeping progression 1090 * if there are full dynticks CPUs around 1091 */ 1092 if (tick_do_timer_cpu == cpu) 1093 return false; 1094 1095 /* Should not happen for nohz-full */ 1096 if (WARN_ON_ONCE(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) 1097 return false; 1098 } 1099 1100 return true; 1101 } 1102 1103 /** 1104 * tick_nohz_idle_stop_tick - stop the idle tick from the idle task 1105 * 1106 * When the next event is more than a tick into the future, stop the idle tick 1107 */ 1108 void tick_nohz_idle_stop_tick(void) 1109 { 1110 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1111 int cpu = smp_processor_id(); 1112 ktime_t expires; 1113 1114 /* 1115 * If tick_nohz_get_sleep_length() ran tick_nohz_next_event(), the 1116 * tick timer expiration time is known already. 1117 */ 1118 if (ts->timer_expires_base) 1119 expires = ts->timer_expires; 1120 else if (can_stop_idle_tick(cpu, ts)) 1121 expires = tick_nohz_next_event(ts, cpu); 1122 else 1123 return; 1124 1125 ts->idle_calls++; 1126 1127 if (expires > 0LL) { 1128 int was_stopped = ts->tick_stopped; 1129 1130 tick_nohz_stop_tick(ts, cpu); 1131 1132 ts->idle_sleeps++; 1133 ts->idle_expires = expires; 1134 1135 if (!was_stopped && ts->tick_stopped) { 1136 ts->idle_jiffies = ts->last_jiffies; 1137 nohz_balance_enter_idle(cpu); 1138 } 1139 } else { 1140 tick_nohz_retain_tick(ts); 1141 } 1142 } 1143 1144 void tick_nohz_idle_retain_tick(void) 1145 { 1146 tick_nohz_retain_tick(this_cpu_ptr(&tick_cpu_sched)); 1147 /* 1148 * Undo the effect of get_next_timer_interrupt() called from 1149 * tick_nohz_next_event(). 1150 */ 1151 timer_clear_idle(); 1152 } 1153 1154 /** 1155 * tick_nohz_idle_enter - prepare for entering idle on the current CPU 1156 * 1157 * Called when we start the idle loop. 1158 */ 1159 void tick_nohz_idle_enter(void) 1160 { 1161 struct tick_sched *ts; 1162 1163 lockdep_assert_irqs_enabled(); 1164 1165 local_irq_disable(); 1166 1167 ts = this_cpu_ptr(&tick_cpu_sched); 1168 1169 WARN_ON_ONCE(ts->timer_expires_base); 1170 1171 ts->inidle = 1; 1172 tick_nohz_start_idle(ts); 1173 1174 local_irq_enable(); 1175 } 1176 1177 /** 1178 * tick_nohz_irq_exit - update next tick event from interrupt exit 1179 * 1180 * When an interrupt fires while we are idle and it doesn't cause 1181 * a reschedule, it may still add, modify or delete a timer, enqueue 1182 * an RCU callback, etc... 1183 * So we need to re-calculate and reprogram the next tick event. 1184 */ 1185 void tick_nohz_irq_exit(void) 1186 { 1187 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1188 1189 if (ts->inidle) 1190 tick_nohz_start_idle(ts); 1191 else 1192 tick_nohz_full_update_tick(ts); 1193 } 1194 1195 /** 1196 * tick_nohz_idle_got_tick - Check whether or not the tick handler has run 1197 */ 1198 bool tick_nohz_idle_got_tick(void) 1199 { 1200 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1201 1202 if (ts->got_idle_tick) { 1203 ts->got_idle_tick = 0; 1204 return true; 1205 } 1206 return false; 1207 } 1208 1209 /** 1210 * tick_nohz_get_next_hrtimer - return the next expiration time for the hrtimer 1211 * or the tick, whatever that expires first. Note that, if the tick has been 1212 * stopped, it returns the next hrtimer. 1213 * 1214 * Called from power state control code with interrupts disabled 1215 */ 1216 ktime_t tick_nohz_get_next_hrtimer(void) 1217 { 1218 return __this_cpu_read(tick_cpu_device.evtdev)->next_event; 1219 } 1220 1221 /** 1222 * tick_nohz_get_sleep_length - return the expected length of the current sleep 1223 * @delta_next: duration until the next event if the tick cannot be stopped 1224 * 1225 * Called from power state control code with interrupts disabled. 1226 * 1227 * The return value of this function and/or the value returned by it through the 1228 * @delta_next pointer can be negative which must be taken into account by its 1229 * callers. 1230 */ 1231 ktime_t tick_nohz_get_sleep_length(ktime_t *delta_next) 1232 { 1233 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); 1234 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1235 int cpu = smp_processor_id(); 1236 /* 1237 * The idle entry time is expected to be a sufficient approximation of 1238 * the current time at this point. 1239 */ 1240 ktime_t now = ts->idle_entrytime; 1241 ktime_t next_event; 1242 1243 WARN_ON_ONCE(!ts->inidle); 1244 1245 *delta_next = ktime_sub(dev->next_event, now); 1246 1247 if (!can_stop_idle_tick(cpu, ts)) 1248 return *delta_next; 1249 1250 next_event = tick_nohz_next_event(ts, cpu); 1251 if (!next_event) 1252 return *delta_next; 1253 1254 /* 1255 * If the next highres timer to expire is earlier than next_event, the 1256 * idle governor needs to know that. 1257 */ 1258 next_event = min_t(u64, next_event, 1259 hrtimer_next_event_without(&ts->sched_timer)); 1260 1261 return ktime_sub(next_event, now); 1262 } 1263 1264 /** 1265 * tick_nohz_get_idle_calls_cpu - return the current idle calls counter value 1266 * for a particular CPU. 1267 * 1268 * Called from the schedutil frequency scaling governor in scheduler context. 1269 */ 1270 unsigned long tick_nohz_get_idle_calls_cpu(int cpu) 1271 { 1272 struct tick_sched *ts = tick_get_tick_sched(cpu); 1273 1274 return ts->idle_calls; 1275 } 1276 1277 /** 1278 * tick_nohz_get_idle_calls - return the current idle calls counter value 1279 * 1280 * Called from the schedutil frequency scaling governor in scheduler context. 1281 */ 1282 unsigned long tick_nohz_get_idle_calls(void) 1283 { 1284 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1285 1286 return ts->idle_calls; 1287 } 1288 1289 static void tick_nohz_account_idle_time(struct tick_sched *ts, 1290 ktime_t now) 1291 { 1292 unsigned long ticks; 1293 1294 ts->idle_exittime = now; 1295 1296 if (vtime_accounting_enabled_this_cpu()) 1297 return; 1298 /* 1299 * We stopped the tick in idle. Update process times would miss the 1300 * time we slept as update_process_times does only a 1 tick 1301 * accounting. Enforce that this is accounted to idle ! 1302 */ 1303 ticks = jiffies - ts->idle_jiffies; 1304 /* 1305 * We might be one off. Do not randomly account a huge number of ticks! 1306 */ 1307 if (ticks && ticks < LONG_MAX) 1308 account_idle_ticks(ticks); 1309 } 1310 1311 void tick_nohz_idle_restart_tick(void) 1312 { 1313 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1314 1315 if (ts->tick_stopped) { 1316 ktime_t now = ktime_get(); 1317 tick_nohz_restart_sched_tick(ts, now); 1318 tick_nohz_account_idle_time(ts, now); 1319 } 1320 } 1321 1322 static void tick_nohz_idle_update_tick(struct tick_sched *ts, ktime_t now) 1323 { 1324 if (tick_nohz_full_cpu(smp_processor_id())) 1325 __tick_nohz_full_update_tick(ts, now); 1326 else 1327 tick_nohz_restart_sched_tick(ts, now); 1328 1329 tick_nohz_account_idle_time(ts, now); 1330 } 1331 1332 /** 1333 * tick_nohz_idle_exit - restart the idle tick from the idle task 1334 * 1335 * Restart the idle tick when the CPU is woken up from idle 1336 * This also exit the RCU extended quiescent state. The CPU 1337 * can use RCU again after this function is called. 1338 */ 1339 void tick_nohz_idle_exit(void) 1340 { 1341 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1342 bool idle_active, tick_stopped; 1343 ktime_t now; 1344 1345 local_irq_disable(); 1346 1347 WARN_ON_ONCE(!ts->inidle); 1348 WARN_ON_ONCE(ts->timer_expires_base); 1349 1350 ts->inidle = 0; 1351 idle_active = ts->idle_active; 1352 tick_stopped = ts->tick_stopped; 1353 1354 if (idle_active || tick_stopped) 1355 now = ktime_get(); 1356 1357 if (idle_active) 1358 tick_nohz_stop_idle(ts, now); 1359 1360 if (tick_stopped) 1361 tick_nohz_idle_update_tick(ts, now); 1362 1363 local_irq_enable(); 1364 } 1365 1366 /* 1367 * The nohz low res interrupt handler 1368 */ 1369 static void tick_nohz_handler(struct clock_event_device *dev) 1370 { 1371 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1372 struct pt_regs *regs = get_irq_regs(); 1373 ktime_t now = ktime_get(); 1374 1375 dev->next_event = KTIME_MAX; 1376 1377 tick_sched_do_timer(ts, now); 1378 tick_sched_handle(ts, regs); 1379 1380 if (unlikely(ts->tick_stopped)) { 1381 /* 1382 * The clockevent device is not reprogrammed, so change the 1383 * clock event device to ONESHOT_STOPPED to avoid spurious 1384 * interrupts on devices which might not be truly one shot. 1385 */ 1386 tick_program_event(KTIME_MAX, 1); 1387 return; 1388 } 1389 1390 hrtimer_forward(&ts->sched_timer, now, TICK_NSEC); 1391 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); 1392 } 1393 1394 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) 1395 { 1396 if (!tick_nohz_enabled) 1397 return; 1398 ts->nohz_mode = mode; 1399 /* One update is enough */ 1400 if (!test_and_set_bit(0, &tick_nohz_active)) 1401 timers_update_nohz(); 1402 } 1403 1404 /** 1405 * tick_nohz_switch_to_nohz - switch to nohz mode 1406 */ 1407 static void tick_nohz_switch_to_nohz(void) 1408 { 1409 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1410 ktime_t next; 1411 1412 if (!tick_nohz_enabled) 1413 return; 1414 1415 if (tick_switch_to_oneshot(tick_nohz_handler)) 1416 return; 1417 1418 /* 1419 * Recycle the hrtimer in ts, so we can share the 1420 * hrtimer_forward with the highres code. 1421 */ 1422 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD); 1423 /* Get the next period */ 1424 next = tick_init_jiffy_update(); 1425 1426 hrtimer_set_expires(&ts->sched_timer, next); 1427 hrtimer_forward_now(&ts->sched_timer, TICK_NSEC); 1428 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); 1429 tick_nohz_activate(ts, NOHZ_MODE_LOWRES); 1430 } 1431 1432 static inline void tick_nohz_irq_enter(void) 1433 { 1434 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1435 ktime_t now; 1436 1437 if (!ts->idle_active && !ts->tick_stopped) 1438 return; 1439 now = ktime_get(); 1440 if (ts->idle_active) 1441 tick_nohz_stop_idle(ts, now); 1442 /* 1443 * If all CPUs are idle. We may need to update a stale jiffies value. 1444 * Note nohz_full is a special case: a timekeeper is guaranteed to stay 1445 * alive but it might be busy looping with interrupts disabled in some 1446 * rare case (typically stop machine). So we must make sure we have a 1447 * last resort. 1448 */ 1449 if (ts->tick_stopped) 1450 tick_nohz_update_jiffies(now); 1451 } 1452 1453 #else 1454 1455 static inline void tick_nohz_switch_to_nohz(void) { } 1456 static inline void tick_nohz_irq_enter(void) { } 1457 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { } 1458 1459 #endif /* CONFIG_NO_HZ_COMMON */ 1460 1461 /* 1462 * Called from irq_enter to notify about the possible interruption of idle() 1463 */ 1464 void tick_irq_enter(void) 1465 { 1466 tick_check_oneshot_broadcast_this_cpu(); 1467 tick_nohz_irq_enter(); 1468 } 1469 1470 /* 1471 * High resolution timer specific code 1472 */ 1473 #ifdef CONFIG_HIGH_RES_TIMERS 1474 /* 1475 * We rearm the timer until we get disabled by the idle code. 1476 * Called with interrupts disabled. 1477 */ 1478 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) 1479 { 1480 struct tick_sched *ts = 1481 container_of(timer, struct tick_sched, sched_timer); 1482 struct pt_regs *regs = get_irq_regs(); 1483 ktime_t now = ktime_get(); 1484 1485 tick_sched_do_timer(ts, now); 1486 1487 /* 1488 * Do not call, when we are not in irq context and have 1489 * no valid regs pointer 1490 */ 1491 if (regs) 1492 tick_sched_handle(ts, regs); 1493 else 1494 ts->next_tick = 0; 1495 1496 /* No need to reprogram if we are in idle or full dynticks mode */ 1497 if (unlikely(ts->tick_stopped)) 1498 return HRTIMER_NORESTART; 1499 1500 hrtimer_forward(timer, now, TICK_NSEC); 1501 1502 return HRTIMER_RESTART; 1503 } 1504 1505 static int sched_skew_tick; 1506 1507 static int __init skew_tick(char *str) 1508 { 1509 get_option(&str, &sched_skew_tick); 1510 1511 return 0; 1512 } 1513 early_param("skew_tick", skew_tick); 1514 1515 /** 1516 * tick_setup_sched_timer - setup the tick emulation timer 1517 */ 1518 void tick_setup_sched_timer(void) 1519 { 1520 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1521 ktime_t now = ktime_get(); 1522 1523 /* 1524 * Emulate tick processing via per-CPU hrtimers: 1525 */ 1526 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD); 1527 ts->sched_timer.function = tick_sched_timer; 1528 1529 /* Get the next period (per-CPU) */ 1530 hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update()); 1531 1532 /* Offset the tick to avert jiffies_lock contention. */ 1533 if (sched_skew_tick) { 1534 u64 offset = TICK_NSEC >> 1; 1535 do_div(offset, num_possible_cpus()); 1536 offset *= smp_processor_id(); 1537 hrtimer_add_expires_ns(&ts->sched_timer, offset); 1538 } 1539 1540 hrtimer_forward(&ts->sched_timer, now, TICK_NSEC); 1541 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD); 1542 tick_nohz_activate(ts, NOHZ_MODE_HIGHRES); 1543 } 1544 #endif /* HIGH_RES_TIMERS */ 1545 1546 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS 1547 void tick_cancel_sched_timer(int cpu) 1548 { 1549 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 1550 1551 # ifdef CONFIG_HIGH_RES_TIMERS 1552 if (ts->sched_timer.base) 1553 hrtimer_cancel(&ts->sched_timer); 1554 # endif 1555 1556 memset(ts, 0, sizeof(*ts)); 1557 } 1558 #endif 1559 1560 /* 1561 * Async notification about clocksource changes 1562 */ 1563 void tick_clock_notify(void) 1564 { 1565 int cpu; 1566 1567 for_each_possible_cpu(cpu) 1568 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks); 1569 } 1570 1571 /* 1572 * Async notification about clock event changes 1573 */ 1574 void tick_oneshot_notify(void) 1575 { 1576 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1577 1578 set_bit(0, &ts->check_clocks); 1579 } 1580 1581 /* 1582 * Check, if a change happened, which makes oneshot possible. 1583 * 1584 * Called cyclic from the hrtimer softirq (driven by the timer 1585 * softirq) allow_nohz signals, that we can switch into low-res nohz 1586 * mode, because high resolution timers are disabled (either compile 1587 * or runtime). Called with interrupts disabled. 1588 */ 1589 int tick_check_oneshot_change(int allow_nohz) 1590 { 1591 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1592 1593 if (!test_and_clear_bit(0, &ts->check_clocks)) 1594 return 0; 1595 1596 if (ts->nohz_mode != NOHZ_MODE_INACTIVE) 1597 return 0; 1598 1599 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available()) 1600 return 0; 1601 1602 if (!allow_nohz) 1603 return 1; 1604 1605 tick_nohz_switch_to_nohz(); 1606 return 0; 1607 }