1 /* 2 * linux/kernel/time/tick-sched.c 3 * 4 * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de> 5 * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar 6 * Copyright(C) 2006-2007 Timesys Corp., Thomas Gleixner 7 * 8 * No idle tick implementation for low and high resolution timers 9 * 10 * Started by: Thomas Gleixner and Ingo Molnar 11 * 12 * Distribute under GPLv2. 13 */ 14 #include <linux/cpu.h> 15 #include <linux/err.h> 16 #include <linux/hrtimer.h> 17 #include <linux/interrupt.h> 18 #include <linux/kernel_stat.h> 19 #include <linux/percpu.h> 20 #include <linux/profile.h> 21 #include <linux/sched.h> 22 #include <linux/module.h> 23 #include <linux/irq_work.h> 24 #include <linux/posix-timers.h> 25 #include <linux/perf_event.h> 26 #include <linux/context_tracking.h> 27 28 #include <asm/irq_regs.h> 29 30 #include "tick-internal.h" 31 32 #include <trace/events/timer.h> 33 34 /* 35 * Per cpu nohz control structure 36 */ 37 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched); 38 39 /* 40 * The time, when the last jiffy update happened. Protected by jiffies_lock. 41 */ 42 static ktime_t last_jiffies_update; 43 44 struct tick_sched *tick_get_tick_sched(int cpu) 45 { 46 return &per_cpu(tick_cpu_sched, cpu); 47 } 48 49 /* 50 * Must be called with interrupts disabled ! 51 */ 52 static void tick_do_update_jiffies64(ktime_t now) 53 { 54 unsigned long ticks = 0; 55 ktime_t delta; 56 57 /* 58 * Do a quick check without holding jiffies_lock: 59 */ 60 delta = ktime_sub(now, last_jiffies_update); 61 if (delta.tv64 < tick_period.tv64) 62 return; 63 64 /* Reevalute with jiffies_lock held */ 65 write_seqlock(&jiffies_lock); 66 67 delta = ktime_sub(now, last_jiffies_update); 68 if (delta.tv64 >= tick_period.tv64) { 69 70 delta = ktime_sub(delta, tick_period); 71 last_jiffies_update = ktime_add(last_jiffies_update, 72 tick_period); 73 74 /* Slow path for long timeouts */ 75 if (unlikely(delta.tv64 >= tick_period.tv64)) { 76 s64 incr = ktime_to_ns(tick_period); 77 78 ticks = ktime_divns(delta, incr); 79 80 last_jiffies_update = ktime_add_ns(last_jiffies_update, 81 incr * ticks); 82 } 83 do_timer(++ticks); 84 85 /* Keep the tick_next_period variable up to date */ 86 tick_next_period = ktime_add(last_jiffies_update, tick_period); 87 } else { 88 write_sequnlock(&jiffies_lock); 89 return; 90 } 91 write_sequnlock(&jiffies_lock); 92 update_wall_time(); 93 } 94 95 /* 96 * Initialize and return retrieve the jiffies update. 97 */ 98 static ktime_t tick_init_jiffy_update(void) 99 { 100 ktime_t period; 101 102 write_seqlock(&jiffies_lock); 103 /* Did we start the jiffies update yet ? */ 104 if (last_jiffies_update.tv64 == 0) 105 last_jiffies_update = tick_next_period; 106 period = last_jiffies_update; 107 write_sequnlock(&jiffies_lock); 108 return period; 109 } 110 111 112 static void tick_sched_do_timer(ktime_t now) 113 { 114 int cpu = smp_processor_id(); 115 116 #ifdef CONFIG_NO_HZ_COMMON 117 /* 118 * Check if the do_timer duty was dropped. We don't care about 119 * concurrency: This happens only when the cpu in charge went 120 * into a long sleep. If two cpus happen to assign themself to 121 * this duty, then the jiffies update is still serialized by 122 * jiffies_lock. 123 */ 124 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE) 125 && !tick_nohz_full_cpu(cpu)) 126 tick_do_timer_cpu = cpu; 127 #endif 128 129 /* Check, if the jiffies need an update */ 130 if (tick_do_timer_cpu == cpu) 131 tick_do_update_jiffies64(now); 132 } 133 134 static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs) 135 { 136 #ifdef CONFIG_NO_HZ_COMMON 137 /* 138 * When we are idle and the tick is stopped, we have to touch 139 * the watchdog as we might not schedule for a really long 140 * time. This happens on complete idle SMP systems while 141 * waiting on the login prompt. We also increment the "start of 142 * idle" jiffy stamp so the idle accounting adjustment we do 143 * when we go busy again does not account too much ticks. 144 */ 145 if (ts->tick_stopped) { 146 touch_softlockup_watchdog(); 147 if (is_idle_task(current)) 148 ts->idle_jiffies++; 149 } 150 #endif 151 update_process_times(user_mode(regs)); 152 profile_tick(CPU_PROFILING); 153 } 154 155 #ifdef CONFIG_NO_HZ_FULL 156 cpumask_var_t tick_nohz_full_mask; 157 cpumask_var_t housekeeping_mask; 158 bool tick_nohz_full_running; 159 160 static bool can_stop_full_tick(void) 161 { 162 WARN_ON_ONCE(!irqs_disabled()); 163 164 if (!sched_can_stop_tick()) { 165 trace_tick_stop(0, "more than 1 task in runqueue\n"); 166 return false; 167 } 168 169 if (!posix_cpu_timers_can_stop_tick(current)) { 170 trace_tick_stop(0, "posix timers running\n"); 171 return false; 172 } 173 174 if (!perf_event_can_stop_tick()) { 175 trace_tick_stop(0, "perf events running\n"); 176 return false; 177 } 178 179 /* sched_clock_tick() needs us? */ 180 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK 181 /* 182 * TODO: kick full dynticks CPUs when 183 * sched_clock_stable is set. 184 */ 185 if (!sched_clock_stable()) { 186 trace_tick_stop(0, "unstable sched clock\n"); 187 /* 188 * Don't allow the user to think they can get 189 * full NO_HZ with this machine. 190 */ 191 WARN_ONCE(tick_nohz_full_running, 192 "NO_HZ FULL will not work with unstable sched clock"); 193 return false; 194 } 195 #endif 196 197 return true; 198 } 199 200 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now); 201 202 /* 203 * Re-evaluate the need for the tick on the current CPU 204 * and restart it if necessary. 205 */ 206 void __tick_nohz_full_check(void) 207 { 208 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 209 210 if (tick_nohz_full_cpu(smp_processor_id())) { 211 if (ts->tick_stopped && !is_idle_task(current)) { 212 if (!can_stop_full_tick()) 213 tick_nohz_restart_sched_tick(ts, ktime_get()); 214 } 215 } 216 } 217 218 static void nohz_full_kick_work_func(struct irq_work *work) 219 { 220 __tick_nohz_full_check(); 221 } 222 223 static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = { 224 .func = nohz_full_kick_work_func, 225 }; 226 227 /* 228 * Kick this CPU if it's full dynticks in order to force it to 229 * re-evaluate its dependency on the tick and restart it if necessary. 230 * This kick, unlike tick_nohz_full_kick_cpu() and tick_nohz_full_kick_all(), 231 * is NMI safe. 232 */ 233 void tick_nohz_full_kick(void) 234 { 235 if (!tick_nohz_full_cpu(smp_processor_id())) 236 return; 237 238 irq_work_queue(this_cpu_ptr(&nohz_full_kick_work)); 239 } 240 241 /* 242 * Kick the CPU if it's full dynticks in order to force it to 243 * re-evaluate its dependency on the tick and restart it if necessary. 244 */ 245 void tick_nohz_full_kick_cpu(int cpu) 246 { 247 if (!tick_nohz_full_cpu(cpu)) 248 return; 249 250 irq_work_queue_on(&per_cpu(nohz_full_kick_work, cpu), cpu); 251 } 252 253 static void nohz_full_kick_ipi(void *info) 254 { 255 __tick_nohz_full_check(); 256 } 257 258 /* 259 * Kick all full dynticks CPUs in order to force these to re-evaluate 260 * their dependency on the tick and restart it if necessary. 261 */ 262 void tick_nohz_full_kick_all(void) 263 { 264 if (!tick_nohz_full_running) 265 return; 266 267 preempt_disable(); 268 smp_call_function_many(tick_nohz_full_mask, 269 nohz_full_kick_ipi, NULL, false); 270 tick_nohz_full_kick(); 271 preempt_enable(); 272 } 273 274 /* 275 * Re-evaluate the need for the tick as we switch the current task. 276 * It might need the tick due to per task/process properties: 277 * perf events, posix cpu timers, ... 278 */ 279 void __tick_nohz_task_switch(struct task_struct *tsk) 280 { 281 unsigned long flags; 282 283 local_irq_save(flags); 284 285 if (!tick_nohz_full_cpu(smp_processor_id())) 286 goto out; 287 288 if (tick_nohz_tick_stopped() && !can_stop_full_tick()) 289 tick_nohz_full_kick(); 290 291 out: 292 local_irq_restore(flags); 293 } 294 295 /* Parse the boot-time nohz CPU list from the kernel parameters. */ 296 static int __init tick_nohz_full_setup(char *str) 297 { 298 alloc_bootmem_cpumask_var(&tick_nohz_full_mask); 299 if (cpulist_parse(str, tick_nohz_full_mask) < 0) { 300 pr_warning("NOHZ: Incorrect nohz_full cpumask\n"); 301 free_bootmem_cpumask_var(tick_nohz_full_mask); 302 return 1; 303 } 304 tick_nohz_full_running = true; 305 306 return 1; 307 } 308 __setup("nohz_full=", tick_nohz_full_setup); 309 310 static int tick_nohz_cpu_down_callback(struct notifier_block *nfb, 311 unsigned long action, 312 void *hcpu) 313 { 314 unsigned int cpu = (unsigned long)hcpu; 315 316 switch (action & ~CPU_TASKS_FROZEN) { 317 case CPU_DOWN_PREPARE: 318 /* 319 * If we handle the timekeeping duty for full dynticks CPUs, 320 * we can't safely shutdown that CPU. 321 */ 322 if (tick_nohz_full_running && tick_do_timer_cpu == cpu) 323 return NOTIFY_BAD; 324 break; 325 } 326 return NOTIFY_OK; 327 } 328 329 static int tick_nohz_init_all(void) 330 { 331 int err = -1; 332 333 #ifdef CONFIG_NO_HZ_FULL_ALL 334 if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) { 335 WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n"); 336 return err; 337 } 338 err = 0; 339 cpumask_setall(tick_nohz_full_mask); 340 tick_nohz_full_running = true; 341 #endif 342 return err; 343 } 344 345 void __init tick_nohz_init(void) 346 { 347 int cpu; 348 349 if (!tick_nohz_full_running) { 350 if (tick_nohz_init_all() < 0) 351 return; 352 } 353 354 if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) { 355 WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n"); 356 cpumask_clear(tick_nohz_full_mask); 357 tick_nohz_full_running = false; 358 return; 359 } 360 361 /* 362 * Full dynticks uses irq work to drive the tick rescheduling on safe 363 * locking contexts. But then we need irq work to raise its own 364 * interrupts to avoid circular dependency on the tick 365 */ 366 if (!arch_irq_work_has_interrupt()) { 367 pr_warning("NO_HZ: Can't run full dynticks because arch doesn't " 368 "support irq work self-IPIs\n"); 369 cpumask_clear(tick_nohz_full_mask); 370 cpumask_copy(housekeeping_mask, cpu_possible_mask); 371 tick_nohz_full_running = false; 372 return; 373 } 374 375 cpu = smp_processor_id(); 376 377 if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) { 378 pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu); 379 cpumask_clear_cpu(cpu, tick_nohz_full_mask); 380 } 381 382 cpumask_andnot(housekeeping_mask, 383 cpu_possible_mask, tick_nohz_full_mask); 384 385 for_each_cpu(cpu, tick_nohz_full_mask) 386 context_tracking_cpu_set(cpu); 387 388 cpu_notifier(tick_nohz_cpu_down_callback, 0); 389 pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n", 390 cpumask_pr_args(tick_nohz_full_mask)); 391 } 392 #endif 393 394 /* 395 * NOHZ - aka dynamic tick functionality 396 */ 397 #ifdef CONFIG_NO_HZ_COMMON 398 /* 399 * NO HZ enabled ? 400 */ 401 static int tick_nohz_enabled __read_mostly = 1; 402 unsigned long tick_nohz_active __read_mostly; 403 /* 404 * Enable / Disable tickless mode 405 */ 406 static int __init setup_tick_nohz(char *str) 407 { 408 if (!strcmp(str, "off")) 409 tick_nohz_enabled = 0; 410 else if (!strcmp(str, "on")) 411 tick_nohz_enabled = 1; 412 else 413 return 0; 414 return 1; 415 } 416 417 __setup("nohz=", setup_tick_nohz); 418 419 int tick_nohz_tick_stopped(void) 420 { 421 return __this_cpu_read(tick_cpu_sched.tick_stopped); 422 } 423 424 /** 425 * tick_nohz_update_jiffies - update jiffies when idle was interrupted 426 * 427 * Called from interrupt entry when the CPU was idle 428 * 429 * In case the sched_tick was stopped on this CPU, we have to check if jiffies 430 * must be updated. Otherwise an interrupt handler could use a stale jiffy 431 * value. We do this unconditionally on any cpu, as we don't know whether the 432 * cpu, which has the update task assigned is in a long sleep. 433 */ 434 static void tick_nohz_update_jiffies(ktime_t now) 435 { 436 unsigned long flags; 437 438 __this_cpu_write(tick_cpu_sched.idle_waketime, now); 439 440 local_irq_save(flags); 441 tick_do_update_jiffies64(now); 442 local_irq_restore(flags); 443 444 touch_softlockup_watchdog(); 445 } 446 447 /* 448 * Updates the per cpu time idle statistics counters 449 */ 450 static void 451 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time) 452 { 453 ktime_t delta; 454 455 if (ts->idle_active) { 456 delta = ktime_sub(now, ts->idle_entrytime); 457 if (nr_iowait_cpu(cpu) > 0) 458 ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta); 459 else 460 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); 461 ts->idle_entrytime = now; 462 } 463 464 if (last_update_time) 465 *last_update_time = ktime_to_us(now); 466 467 } 468 469 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now) 470 { 471 update_ts_time_stats(smp_processor_id(), ts, now, NULL); 472 ts->idle_active = 0; 473 474 sched_clock_idle_wakeup_event(0); 475 } 476 477 static ktime_t tick_nohz_start_idle(struct tick_sched *ts) 478 { 479 ktime_t now = ktime_get(); 480 481 ts->idle_entrytime = now; 482 ts->idle_active = 1; 483 sched_clock_idle_sleep_event(); 484 return now; 485 } 486 487 /** 488 * get_cpu_idle_time_us - get the total idle time of a cpu 489 * @cpu: CPU number to query 490 * @last_update_time: variable to store update time in. Do not update 491 * counters if NULL. 492 * 493 * Return the cummulative idle time (since boot) for a given 494 * CPU, in microseconds. 495 * 496 * This time is measured via accounting rather than sampling, 497 * and is as accurate as ktime_get() is. 498 * 499 * This function returns -1 if NOHZ is not enabled. 500 */ 501 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) 502 { 503 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 504 ktime_t now, idle; 505 506 if (!tick_nohz_active) 507 return -1; 508 509 now = ktime_get(); 510 if (last_update_time) { 511 update_ts_time_stats(cpu, ts, now, last_update_time); 512 idle = ts->idle_sleeptime; 513 } else { 514 if (ts->idle_active && !nr_iowait_cpu(cpu)) { 515 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 516 517 idle = ktime_add(ts->idle_sleeptime, delta); 518 } else { 519 idle = ts->idle_sleeptime; 520 } 521 } 522 523 return ktime_to_us(idle); 524 525 } 526 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us); 527 528 /** 529 * get_cpu_iowait_time_us - get the total iowait time of a cpu 530 * @cpu: CPU number to query 531 * @last_update_time: variable to store update time in. Do not update 532 * counters if NULL. 533 * 534 * Return the cummulative iowait time (since boot) for a given 535 * CPU, in microseconds. 536 * 537 * This time is measured via accounting rather than sampling, 538 * and is as accurate as ktime_get() is. 539 * 540 * This function returns -1 if NOHZ is not enabled. 541 */ 542 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time) 543 { 544 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 545 ktime_t now, iowait; 546 547 if (!tick_nohz_active) 548 return -1; 549 550 now = ktime_get(); 551 if (last_update_time) { 552 update_ts_time_stats(cpu, ts, now, last_update_time); 553 iowait = ts->iowait_sleeptime; 554 } else { 555 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) { 556 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 557 558 iowait = ktime_add(ts->iowait_sleeptime, delta); 559 } else { 560 iowait = ts->iowait_sleeptime; 561 } 562 } 563 564 return ktime_to_us(iowait); 565 } 566 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us); 567 568 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) 569 { 570 hrtimer_cancel(&ts->sched_timer); 571 hrtimer_set_expires(&ts->sched_timer, ts->last_tick); 572 573 /* Forward the time to expire in the future */ 574 hrtimer_forward(&ts->sched_timer, now, tick_period); 575 576 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) 577 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED); 578 else 579 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); 580 } 581 582 static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, 583 ktime_t now, int cpu) 584 { 585 struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); 586 u64 basemono, next_tick, next_tmr, next_rcu, delta, expires; 587 unsigned long seq, basejiff; 588 ktime_t tick; 589 590 /* Read jiffies and the time when jiffies were updated last */ 591 do { 592 seq = read_seqbegin(&jiffies_lock); 593 basemono = last_jiffies_update.tv64; 594 basejiff = jiffies; 595 } while (read_seqretry(&jiffies_lock, seq)); 596 ts->last_jiffies = basejiff; 597 598 if (rcu_needs_cpu(basemono, &next_rcu) || 599 arch_needs_cpu() || irq_work_needs_cpu()) { 600 next_tick = basemono + TICK_NSEC; 601 } else { 602 /* 603 * Get the next pending timer. If high resolution 604 * timers are enabled this only takes the timer wheel 605 * timers into account. If high resolution timers are 606 * disabled this also looks at the next expiring 607 * hrtimer. 608 */ 609 next_tmr = get_next_timer_interrupt(basejiff, basemono); 610 ts->next_timer = next_tmr; 611 /* Take the next rcu event into account */ 612 next_tick = next_rcu < next_tmr ? next_rcu : next_tmr; 613 } 614 615 /* 616 * If the tick is due in the next period, keep it ticking or 617 * restart it proper. 618 */ 619 delta = next_tick - basemono; 620 if (delta <= (u64)TICK_NSEC) { 621 tick.tv64 = 0; 622 if (!ts->tick_stopped) 623 goto out; 624 if (delta == 0) { 625 /* Tick is stopped, but required now. Enforce it */ 626 tick_nohz_restart(ts, now); 627 goto out; 628 } 629 } 630 631 /* 632 * If this cpu is the one which updates jiffies, then give up 633 * the assignment and let it be taken by the cpu which runs 634 * the tick timer next, which might be this cpu as well. If we 635 * don't drop this here the jiffies might be stale and 636 * do_timer() never invoked. Keep track of the fact that it 637 * was the one which had the do_timer() duty last. If this cpu 638 * is the one which had the do_timer() duty last, we limit the 639 * sleep time to the timekeeping max_deferement value. 640 * Otherwise we can sleep as long as we want. 641 */ 642 delta = timekeeping_max_deferment(); 643 if (cpu == tick_do_timer_cpu) { 644 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 645 ts->do_timer_last = 1; 646 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) { 647 delta = KTIME_MAX; 648 ts->do_timer_last = 0; 649 } else if (!ts->do_timer_last) { 650 delta = KTIME_MAX; 651 } 652 653 #ifdef CONFIG_NO_HZ_FULL 654 /* Limit the tick delta to the maximum scheduler deferment */ 655 if (!ts->inidle) 656 delta = min(delta, scheduler_tick_max_deferment()); 657 #endif 658 659 /* Calculate the next expiry time */ 660 if (delta < (KTIME_MAX - basemono)) 661 expires = basemono + delta; 662 else 663 expires = KTIME_MAX; 664 665 expires = min_t(u64, expires, next_tick); 666 tick.tv64 = expires; 667 668 /* Skip reprogram of event if its not changed */ 669 if (ts->tick_stopped && (expires == dev->next_event.tv64)) 670 goto out; 671 672 /* 673 * nohz_stop_sched_tick can be called several times before 674 * the nohz_restart_sched_tick is called. This happens when 675 * interrupts arrive which do not cause a reschedule. In the 676 * first call we save the current tick time, so we can restart 677 * the scheduler tick in nohz_restart_sched_tick. 678 */ 679 if (!ts->tick_stopped) { 680 nohz_balance_enter_idle(cpu); 681 calc_load_enter_idle(); 682 683 ts->last_tick = hrtimer_get_expires(&ts->sched_timer); 684 ts->tick_stopped = 1; 685 trace_tick_stop(1, " "); 686 } 687 688 /* 689 * If the expiration time == KTIME_MAX, then we simply stop 690 * the tick timer. 691 */ 692 if (unlikely(expires == KTIME_MAX)) { 693 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) 694 hrtimer_cancel(&ts->sched_timer); 695 goto out; 696 } 697 698 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) 699 hrtimer_start(&ts->sched_timer, tick, HRTIMER_MODE_ABS_PINNED); 700 else 701 tick_program_event(tick, 1); 702 out: 703 /* Update the estimated sleep length */ 704 ts->sleep_length = ktime_sub(dev->next_event, now); 705 return tick; 706 } 707 708 static void tick_nohz_full_stop_tick(struct tick_sched *ts) 709 { 710 #ifdef CONFIG_NO_HZ_FULL 711 int cpu = smp_processor_id(); 712 713 if (!tick_nohz_full_cpu(cpu) || is_idle_task(current)) 714 return; 715 716 if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) 717 return; 718 719 if (!can_stop_full_tick()) 720 return; 721 722 tick_nohz_stop_sched_tick(ts, ktime_get(), cpu); 723 #endif 724 } 725 726 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) 727 { 728 /* 729 * If this cpu is offline and it is the one which updates 730 * jiffies, then give up the assignment and let it be taken by 731 * the cpu which runs the tick timer next. If we don't drop 732 * this here the jiffies might be stale and do_timer() never 733 * invoked. 734 */ 735 if (unlikely(!cpu_online(cpu))) { 736 if (cpu == tick_do_timer_cpu) 737 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 738 return false; 739 } 740 741 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) { 742 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ }; 743 return false; 744 } 745 746 if (need_resched()) 747 return false; 748 749 if (unlikely(local_softirq_pending() && cpu_online(cpu))) { 750 static int ratelimit; 751 752 if (ratelimit < 10 && 753 (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { 754 pr_warn("NOHZ: local_softirq_pending %02x\n", 755 (unsigned int) local_softirq_pending()); 756 ratelimit++; 757 } 758 return false; 759 } 760 761 if (tick_nohz_full_enabled()) { 762 /* 763 * Keep the tick alive to guarantee timekeeping progression 764 * if there are full dynticks CPUs around 765 */ 766 if (tick_do_timer_cpu == cpu) 767 return false; 768 /* 769 * Boot safety: make sure the timekeeping duty has been 770 * assigned before entering dyntick-idle mode, 771 */ 772 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE) 773 return false; 774 } 775 776 return true; 777 } 778 779 static void __tick_nohz_idle_enter(struct tick_sched *ts) 780 { 781 ktime_t now, expires; 782 int cpu = smp_processor_id(); 783 784 now = tick_nohz_start_idle(ts); 785 786 if (can_stop_idle_tick(cpu, ts)) { 787 int was_stopped = ts->tick_stopped; 788 789 ts->idle_calls++; 790 791 expires = tick_nohz_stop_sched_tick(ts, now, cpu); 792 if (expires.tv64 > 0LL) { 793 ts->idle_sleeps++; 794 ts->idle_expires = expires; 795 } 796 797 if (!was_stopped && ts->tick_stopped) 798 ts->idle_jiffies = ts->last_jiffies; 799 } 800 } 801 802 /** 803 * tick_nohz_idle_enter - stop the idle tick from the idle task 804 * 805 * When the next event is more than a tick into the future, stop the idle tick 806 * Called when we start the idle loop. 807 * 808 * The arch is responsible of calling: 809 * 810 * - rcu_idle_enter() after its last use of RCU before the CPU is put 811 * to sleep. 812 * - rcu_idle_exit() before the first use of RCU after the CPU is woken up. 813 */ 814 void tick_nohz_idle_enter(void) 815 { 816 struct tick_sched *ts; 817 818 WARN_ON_ONCE(irqs_disabled()); 819 820 /* 821 * Update the idle state in the scheduler domain hierarchy 822 * when tick_nohz_stop_sched_tick() is called from the idle loop. 823 * State will be updated to busy during the first busy tick after 824 * exiting idle. 825 */ 826 set_cpu_sd_state_idle(); 827 828 local_irq_disable(); 829 830 ts = this_cpu_ptr(&tick_cpu_sched); 831 ts->inidle = 1; 832 __tick_nohz_idle_enter(ts); 833 834 local_irq_enable(); 835 } 836 837 /** 838 * tick_nohz_irq_exit - update next tick event from interrupt exit 839 * 840 * When an interrupt fires while we are idle and it doesn't cause 841 * a reschedule, it may still add, modify or delete a timer, enqueue 842 * an RCU callback, etc... 843 * So we need to re-calculate and reprogram the next tick event. 844 */ 845 void tick_nohz_irq_exit(void) 846 { 847 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 848 849 if (ts->inidle) 850 __tick_nohz_idle_enter(ts); 851 else 852 tick_nohz_full_stop_tick(ts); 853 } 854 855 /** 856 * tick_nohz_get_sleep_length - return the length of the current sleep 857 * 858 * Called from power state control code with interrupts disabled 859 */ 860 ktime_t tick_nohz_get_sleep_length(void) 861 { 862 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 863 864 return ts->sleep_length; 865 } 866 867 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) 868 { 869 /* Update jiffies first */ 870 tick_do_update_jiffies64(now); 871 update_cpu_load_nohz(); 872 873 calc_load_exit_idle(); 874 touch_softlockup_watchdog(); 875 /* 876 * Cancel the scheduled timer and restore the tick 877 */ 878 ts->tick_stopped = 0; 879 ts->idle_exittime = now; 880 881 tick_nohz_restart(ts, now); 882 } 883 884 static void tick_nohz_account_idle_ticks(struct tick_sched *ts) 885 { 886 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE 887 unsigned long ticks; 888 889 if (vtime_accounting_enabled()) 890 return; 891 /* 892 * We stopped the tick in idle. Update process times would miss the 893 * time we slept as update_process_times does only a 1 tick 894 * accounting. Enforce that this is accounted to idle ! 895 */ 896 ticks = jiffies - ts->idle_jiffies; 897 /* 898 * We might be one off. Do not randomly account a huge number of ticks! 899 */ 900 if (ticks && ticks < LONG_MAX) 901 account_idle_ticks(ticks); 902 #endif 903 } 904 905 /** 906 * tick_nohz_idle_exit - restart the idle tick from the idle task 907 * 908 * Restart the idle tick when the CPU is woken up from idle 909 * This also exit the RCU extended quiescent state. The CPU 910 * can use RCU again after this function is called. 911 */ 912 void tick_nohz_idle_exit(void) 913 { 914 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 915 ktime_t now; 916 917 local_irq_disable(); 918 919 WARN_ON_ONCE(!ts->inidle); 920 921 ts->inidle = 0; 922 923 if (ts->idle_active || ts->tick_stopped) 924 now = ktime_get(); 925 926 if (ts->idle_active) 927 tick_nohz_stop_idle(ts, now); 928 929 if (ts->tick_stopped) { 930 tick_nohz_restart_sched_tick(ts, now); 931 tick_nohz_account_idle_ticks(ts); 932 } 933 934 local_irq_enable(); 935 } 936 937 /* 938 * The nohz low res interrupt handler 939 */ 940 static void tick_nohz_handler(struct clock_event_device *dev) 941 { 942 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 943 struct pt_regs *regs = get_irq_regs(); 944 ktime_t now = ktime_get(); 945 946 dev->next_event.tv64 = KTIME_MAX; 947 948 tick_sched_do_timer(now); 949 tick_sched_handle(ts, regs); 950 951 /* No need to reprogram if we are running tickless */ 952 if (unlikely(ts->tick_stopped)) 953 return; 954 955 hrtimer_forward(&ts->sched_timer, now, tick_period); 956 tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); 957 } 958 959 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) 960 { 961 if (!tick_nohz_enabled) 962 return; 963 ts->nohz_mode = mode; 964 /* One update is enough */ 965 if (!test_and_set_bit(0, &tick_nohz_active)) 966 timers_update_migration(true); 967 } 968 969 /** 970 * tick_nohz_switch_to_nohz - switch to nohz mode 971 */ 972 static void tick_nohz_switch_to_nohz(void) 973 { 974 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 975 ktime_t next; 976 977 if (!tick_nohz_enabled) 978 return; 979 980 if (tick_switch_to_oneshot(tick_nohz_handler)) 981 return; 982 983 /* 984 * Recycle the hrtimer in ts, so we can share the 985 * hrtimer_forward with the highres code. 986 */ 987 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 988 /* Get the next period */ 989 next = tick_init_jiffy_update(); 990 991 hrtimer_forward_now(&ts->sched_timer, tick_period); 992 hrtimer_set_expires(&ts->sched_timer, next); 993 tick_program_event(next, 1); 994 tick_nohz_activate(ts, NOHZ_MODE_LOWRES); 995 } 996 997 /* 998 * When NOHZ is enabled and the tick is stopped, we need to kick the 999 * tick timer from irq_enter() so that the jiffies update is kept 1000 * alive during long running softirqs. That's ugly as hell, but 1001 * correctness is key even if we need to fix the offending softirq in 1002 * the first place. 1003 * 1004 * Note, this is different to tick_nohz_restart. We just kick the 1005 * timer and do not touch the other magic bits which need to be done 1006 * when idle is left. 1007 */ 1008 static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now) 1009 { 1010 #if 0 1011 /* Switch back to 2.6.27 behaviour */ 1012 ktime_t delta; 1013 1014 /* 1015 * Do not touch the tick device, when the next expiry is either 1016 * already reached or less/equal than the tick period. 1017 */ 1018 delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now); 1019 if (delta.tv64 <= tick_period.tv64) 1020 return; 1021 1022 tick_nohz_restart(ts, now); 1023 #endif 1024 } 1025 1026 static inline void tick_nohz_irq_enter(void) 1027 { 1028 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1029 ktime_t now; 1030 1031 if (!ts->idle_active && !ts->tick_stopped) 1032 return; 1033 now = ktime_get(); 1034 if (ts->idle_active) 1035 tick_nohz_stop_idle(ts, now); 1036 if (ts->tick_stopped) { 1037 tick_nohz_update_jiffies(now); 1038 tick_nohz_kick_tick(ts, now); 1039 } 1040 } 1041 1042 #else 1043 1044 static inline void tick_nohz_switch_to_nohz(void) { } 1045 static inline void tick_nohz_irq_enter(void) { } 1046 static inline void tick_nohz_activate(struct tick_sched *ts, int mode) { } 1047 1048 #endif /* CONFIG_NO_HZ_COMMON */ 1049 1050 /* 1051 * Called from irq_enter to notify about the possible interruption of idle() 1052 */ 1053 void tick_irq_enter(void) 1054 { 1055 tick_check_oneshot_broadcast_this_cpu(); 1056 tick_nohz_irq_enter(); 1057 } 1058 1059 /* 1060 * High resolution timer specific code 1061 */ 1062 #ifdef CONFIG_HIGH_RES_TIMERS 1063 /* 1064 * We rearm the timer until we get disabled by the idle code. 1065 * Called with interrupts disabled. 1066 */ 1067 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) 1068 { 1069 struct tick_sched *ts = 1070 container_of(timer, struct tick_sched, sched_timer); 1071 struct pt_regs *regs = get_irq_regs(); 1072 ktime_t now = ktime_get(); 1073 1074 tick_sched_do_timer(now); 1075 1076 /* 1077 * Do not call, when we are not in irq context and have 1078 * no valid regs pointer 1079 */ 1080 if (regs) 1081 tick_sched_handle(ts, regs); 1082 1083 /* No need to reprogram if we are in idle or full dynticks mode */ 1084 if (unlikely(ts->tick_stopped)) 1085 return HRTIMER_NORESTART; 1086 1087 hrtimer_forward(timer, now, tick_period); 1088 1089 return HRTIMER_RESTART; 1090 } 1091 1092 static int sched_skew_tick; 1093 1094 static int __init skew_tick(char *str) 1095 { 1096 get_option(&str, &sched_skew_tick); 1097 1098 return 0; 1099 } 1100 early_param("skew_tick", skew_tick); 1101 1102 /** 1103 * tick_setup_sched_timer - setup the tick emulation timer 1104 */ 1105 void tick_setup_sched_timer(void) 1106 { 1107 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1108 ktime_t now = ktime_get(); 1109 1110 /* 1111 * Emulate tick processing via per-CPU hrtimers: 1112 */ 1113 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 1114 ts->sched_timer.function = tick_sched_timer; 1115 1116 /* Get the next period (per cpu) */ 1117 hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update()); 1118 1119 /* Offset the tick to avert jiffies_lock contention. */ 1120 if (sched_skew_tick) { 1121 u64 offset = ktime_to_ns(tick_period) >> 1; 1122 do_div(offset, num_possible_cpus()); 1123 offset *= smp_processor_id(); 1124 hrtimer_add_expires_ns(&ts->sched_timer, offset); 1125 } 1126 1127 hrtimer_forward(&ts->sched_timer, now, tick_period); 1128 hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED); 1129 tick_nohz_activate(ts, NOHZ_MODE_HIGHRES); 1130 } 1131 #endif /* HIGH_RES_TIMERS */ 1132 1133 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS 1134 void tick_cancel_sched_timer(int cpu) 1135 { 1136 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 1137 1138 # ifdef CONFIG_HIGH_RES_TIMERS 1139 if (ts->sched_timer.base) 1140 hrtimer_cancel(&ts->sched_timer); 1141 # endif 1142 1143 memset(ts, 0, sizeof(*ts)); 1144 } 1145 #endif 1146 1147 /** 1148 * Async notification about clocksource changes 1149 */ 1150 void tick_clock_notify(void) 1151 { 1152 int cpu; 1153 1154 for_each_possible_cpu(cpu) 1155 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks); 1156 } 1157 1158 /* 1159 * Async notification about clock event changes 1160 */ 1161 void tick_oneshot_notify(void) 1162 { 1163 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1164 1165 set_bit(0, &ts->check_clocks); 1166 } 1167 1168 /** 1169 * Check, if a change happened, which makes oneshot possible. 1170 * 1171 * Called cyclic from the hrtimer softirq (driven by the timer 1172 * softirq) allow_nohz signals, that we can switch into low-res nohz 1173 * mode, because high resolution timers are disabled (either compile 1174 * or runtime). Called with interrupts disabled. 1175 */ 1176 int tick_check_oneshot_change(int allow_nohz) 1177 { 1178 struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched); 1179 1180 if (!test_and_clear_bit(0, &ts->check_clocks)) 1181 return 0; 1182 1183 if (ts->nohz_mode != NOHZ_MODE_INACTIVE) 1184 return 0; 1185 1186 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available()) 1187 return 0; 1188 1189 if (!allow_nohz) 1190 return 1; 1191 1192 tick_nohz_switch_to_nohz(); 1193 return 0; 1194 } 1195