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