1 /* 2 * linux/kernel/time/tick-sched.c 3 * 4 * Copyright(C) 2005-2006, Thomas Gleixner <tglx@linutronix.de> 5 * Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar 6 * Copyright(C) 2006-2007 Timesys Corp., Thomas Gleixner 7 * 8 * No idle tick implementation for low and high resolution timers 9 * 10 * Started by: Thomas Gleixner and Ingo Molnar 11 * 12 * Distribute under GPLv2. 13 */ 14 #include <linux/cpu.h> 15 #include <linux/err.h> 16 #include <linux/hrtimer.h> 17 #include <linux/interrupt.h> 18 #include <linux/kernel_stat.h> 19 #include <linux/percpu.h> 20 #include <linux/profile.h> 21 #include <linux/sched.h> 22 #include <linux/module.h> 23 #include <linux/irq_work.h> 24 #include <linux/posix-timers.h> 25 #include <linux/perf_event.h> 26 #include <linux/context_tracking.h> 27 28 #include <asm/irq_regs.h> 29 30 #include "tick-internal.h" 31 32 #include <trace/events/timer.h> 33 34 /* 35 * Per cpu nohz control structure 36 */ 37 DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched); 38 39 /* 40 * The time, when the last jiffy update happened. Protected by jiffies_lock. 41 */ 42 static ktime_t last_jiffies_update; 43 44 struct tick_sched *tick_get_tick_sched(int cpu) 45 { 46 return &per_cpu(tick_cpu_sched, cpu); 47 } 48 49 /* 50 * Must be called with interrupts disabled ! 51 */ 52 static void tick_do_update_jiffies64(ktime_t now) 53 { 54 unsigned long ticks = 0; 55 ktime_t delta; 56 57 /* 58 * Do a quick check without holding jiffies_lock: 59 */ 60 delta = ktime_sub(now, last_jiffies_update); 61 if (delta.tv64 < tick_period.tv64) 62 return; 63 64 /* Reevalute with jiffies_lock held */ 65 write_seqlock(&jiffies_lock); 66 67 delta = ktime_sub(now, last_jiffies_update); 68 if (delta.tv64 >= tick_period.tv64) { 69 70 delta = ktime_sub(delta, tick_period); 71 last_jiffies_update = ktime_add(last_jiffies_update, 72 tick_period); 73 74 /* Slow path for long timeouts */ 75 if (unlikely(delta.tv64 >= tick_period.tv64)) { 76 s64 incr = ktime_to_ns(tick_period); 77 78 ticks = ktime_divns(delta, incr); 79 80 last_jiffies_update = ktime_add_ns(last_jiffies_update, 81 incr * ticks); 82 } 83 do_timer(++ticks); 84 85 /* Keep the tick_next_period variable up to date */ 86 tick_next_period = ktime_add(last_jiffies_update, tick_period); 87 } else { 88 write_sequnlock(&jiffies_lock); 89 return; 90 } 91 write_sequnlock(&jiffies_lock); 92 update_wall_time(); 93 } 94 95 /* 96 * Initialize and return retrieve the jiffies update. 97 */ 98 static ktime_t tick_init_jiffy_update(void) 99 { 100 ktime_t period; 101 102 write_seqlock(&jiffies_lock); 103 /* Did we start the jiffies update yet ? */ 104 if (last_jiffies_update.tv64 == 0) 105 last_jiffies_update = tick_next_period; 106 period = last_jiffies_update; 107 write_sequnlock(&jiffies_lock); 108 return period; 109 } 110 111 112 static void tick_sched_do_timer(ktime_t now) 113 { 114 int cpu = smp_processor_id(); 115 116 #ifdef CONFIG_NO_HZ_COMMON 117 /* 118 * Check if the do_timer duty was dropped. We don't care about 119 * concurrency: This happens only when the cpu in charge went 120 * into a long sleep. If two cpus happen to assign themself to 121 * this duty, then the jiffies update is still serialized by 122 * jiffies_lock. 123 */ 124 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE) 125 && !tick_nohz_full_cpu(cpu)) 126 tick_do_timer_cpu = cpu; 127 #endif 128 129 /* Check, if the jiffies need an update */ 130 if (tick_do_timer_cpu == cpu) 131 tick_do_update_jiffies64(now); 132 } 133 134 static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs) 135 { 136 #ifdef CONFIG_NO_HZ_COMMON 137 /* 138 * When we are idle and the tick is stopped, we have to touch 139 * the watchdog as we might not schedule for a really long 140 * time. This happens on complete idle SMP systems while 141 * waiting on the login prompt. We also increment the "start of 142 * idle" jiffy stamp so the idle accounting adjustment we do 143 * when we go busy again does not account too much ticks. 144 */ 145 if (ts->tick_stopped) { 146 touch_softlockup_watchdog(); 147 if (is_idle_task(current)) 148 ts->idle_jiffies++; 149 } 150 #endif 151 update_process_times(user_mode(regs)); 152 profile_tick(CPU_PROFILING); 153 } 154 155 #ifdef CONFIG_NO_HZ_FULL 156 cpumask_var_t tick_nohz_full_mask; 157 cpumask_var_t housekeeping_mask; 158 bool tick_nohz_full_running; 159 160 static bool can_stop_full_tick(void) 161 { 162 WARN_ON_ONCE(!irqs_disabled()); 163 164 if (!sched_can_stop_tick()) { 165 trace_tick_stop(0, "more than 1 task in runqueue\n"); 166 return false; 167 } 168 169 if (!posix_cpu_timers_can_stop_tick(current)) { 170 trace_tick_stop(0, "posix timers running\n"); 171 return false; 172 } 173 174 if (!perf_event_can_stop_tick()) { 175 trace_tick_stop(0, "perf events running\n"); 176 return false; 177 } 178 179 /* sched_clock_tick() needs us? */ 180 #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK 181 /* 182 * TODO: kick full dynticks CPUs when 183 * sched_clock_stable is set. 184 */ 185 if (!sched_clock_stable()) { 186 trace_tick_stop(0, "unstable sched clock\n"); 187 /* 188 * Don't allow the user to think they can get 189 * full NO_HZ with this machine. 190 */ 191 WARN_ONCE(tick_nohz_full_running, 192 "NO_HZ FULL will not work with unstable sched clock"); 193 return false; 194 } 195 #endif 196 197 return true; 198 } 199 200 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now); 201 202 /* 203 * Re-evaluate the need for the tick on the current CPU 204 * and restart it if necessary. 205 */ 206 void __tick_nohz_full_check(void) 207 { 208 struct tick_sched *ts = &__get_cpu_var(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(&__get_cpu_var(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 /* 330 * Worst case string length in chunks of CPU range seems 2 steps 331 * separations: 0,2,4,6,... 332 * This is NR_CPUS + sizeof('\0') 333 */ 334 static char __initdata nohz_full_buf[NR_CPUS + 1]; 335 336 static int tick_nohz_init_all(void) 337 { 338 int err = -1; 339 340 #ifdef CONFIG_NO_HZ_FULL_ALL 341 if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) { 342 WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n"); 343 return err; 344 } 345 err = 0; 346 cpumask_setall(tick_nohz_full_mask); 347 tick_nohz_full_running = true; 348 #endif 349 return err; 350 } 351 352 void __init tick_nohz_init(void) 353 { 354 int cpu; 355 356 if (!tick_nohz_full_running) { 357 if (tick_nohz_init_all() < 0) 358 return; 359 } 360 361 if (!alloc_cpumask_var(&housekeeping_mask, GFP_KERNEL)) { 362 WARN(1, "NO_HZ: Can't allocate not-full dynticks cpumask\n"); 363 cpumask_clear(tick_nohz_full_mask); 364 tick_nohz_full_running = false; 365 return; 366 } 367 368 /* 369 * Full dynticks uses irq work to drive the tick rescheduling on safe 370 * locking contexts. But then we need irq work to raise its own 371 * interrupts to avoid circular dependency on the tick 372 */ 373 if (!arch_irq_work_has_interrupt()) { 374 pr_warning("NO_HZ: Can't run full dynticks because arch doesn't " 375 "support irq work self-IPIs\n"); 376 cpumask_clear(tick_nohz_full_mask); 377 cpumask_copy(housekeeping_mask, cpu_possible_mask); 378 tick_nohz_full_running = false; 379 return; 380 } 381 382 cpu = smp_processor_id(); 383 384 if (cpumask_test_cpu(cpu, tick_nohz_full_mask)) { 385 pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu); 386 cpumask_clear_cpu(cpu, tick_nohz_full_mask); 387 } 388 389 cpumask_andnot(housekeeping_mask, 390 cpu_possible_mask, tick_nohz_full_mask); 391 392 for_each_cpu(cpu, tick_nohz_full_mask) 393 context_tracking_cpu_set(cpu); 394 395 cpu_notifier(tick_nohz_cpu_down_callback, 0); 396 cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), tick_nohz_full_mask); 397 pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf); 398 } 399 #endif 400 401 /* 402 * NOHZ - aka dynamic tick functionality 403 */ 404 #ifdef CONFIG_NO_HZ_COMMON 405 /* 406 * NO HZ enabled ? 407 */ 408 static int tick_nohz_enabled __read_mostly = 1; 409 int tick_nohz_active __read_mostly; 410 /* 411 * Enable / Disable tickless mode 412 */ 413 static int __init setup_tick_nohz(char *str) 414 { 415 if (!strcmp(str, "off")) 416 tick_nohz_enabled = 0; 417 else if (!strcmp(str, "on")) 418 tick_nohz_enabled = 1; 419 else 420 return 0; 421 return 1; 422 } 423 424 __setup("nohz=", setup_tick_nohz); 425 426 /** 427 * tick_nohz_update_jiffies - update jiffies when idle was interrupted 428 * 429 * Called from interrupt entry when the CPU was idle 430 * 431 * In case the sched_tick was stopped on this CPU, we have to check if jiffies 432 * must be updated. Otherwise an interrupt handler could use a stale jiffy 433 * value. We do this unconditionally on any cpu, as we don't know whether the 434 * cpu, which has the update task assigned is in a long sleep. 435 */ 436 static void tick_nohz_update_jiffies(ktime_t now) 437 { 438 unsigned long flags; 439 440 __this_cpu_write(tick_cpu_sched.idle_waketime, now); 441 442 local_irq_save(flags); 443 tick_do_update_jiffies64(now); 444 local_irq_restore(flags); 445 446 touch_softlockup_watchdog(); 447 } 448 449 /* 450 * Updates the per cpu time idle statistics counters 451 */ 452 static void 453 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time) 454 { 455 ktime_t delta; 456 457 if (ts->idle_active) { 458 delta = ktime_sub(now, ts->idle_entrytime); 459 if (nr_iowait_cpu(cpu) > 0) 460 ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta); 461 else 462 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); 463 ts->idle_entrytime = now; 464 } 465 466 if (last_update_time) 467 *last_update_time = ktime_to_us(now); 468 469 } 470 471 static void tick_nohz_stop_idle(struct tick_sched *ts, ktime_t now) 472 { 473 update_ts_time_stats(smp_processor_id(), ts, now, NULL); 474 ts->idle_active = 0; 475 476 sched_clock_idle_wakeup_event(0); 477 } 478 479 static ktime_t tick_nohz_start_idle(struct tick_sched *ts) 480 { 481 ktime_t now = ktime_get(); 482 483 ts->idle_entrytime = now; 484 ts->idle_active = 1; 485 sched_clock_idle_sleep_event(); 486 return now; 487 } 488 489 /** 490 * get_cpu_idle_time_us - get the total idle time of a cpu 491 * @cpu: CPU number to query 492 * @last_update_time: variable to store update time in. Do not update 493 * counters if NULL. 494 * 495 * Return the cummulative idle time (since boot) for a given 496 * CPU, in microseconds. 497 * 498 * This time is measured via accounting rather than sampling, 499 * and is as accurate as ktime_get() is. 500 * 501 * This function returns -1 if NOHZ is not enabled. 502 */ 503 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) 504 { 505 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 506 ktime_t now, idle; 507 508 if (!tick_nohz_active) 509 return -1; 510 511 now = ktime_get(); 512 if (last_update_time) { 513 update_ts_time_stats(cpu, ts, now, last_update_time); 514 idle = ts->idle_sleeptime; 515 } else { 516 if (ts->idle_active && !nr_iowait_cpu(cpu)) { 517 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 518 519 idle = ktime_add(ts->idle_sleeptime, delta); 520 } else { 521 idle = ts->idle_sleeptime; 522 } 523 } 524 525 return ktime_to_us(idle); 526 527 } 528 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us); 529 530 /** 531 * get_cpu_iowait_time_us - get the total iowait time of a cpu 532 * @cpu: CPU number to query 533 * @last_update_time: variable to store update time in. Do not update 534 * counters if NULL. 535 * 536 * Return the cummulative iowait time (since boot) for a given 537 * CPU, in microseconds. 538 * 539 * This time is measured via accounting rather than sampling, 540 * and is as accurate as ktime_get() is. 541 * 542 * This function returns -1 if NOHZ is not enabled. 543 */ 544 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time) 545 { 546 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 547 ktime_t now, iowait; 548 549 if (!tick_nohz_active) 550 return -1; 551 552 now = ktime_get(); 553 if (last_update_time) { 554 update_ts_time_stats(cpu, ts, now, last_update_time); 555 iowait = ts->iowait_sleeptime; 556 } else { 557 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) { 558 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 559 560 iowait = ktime_add(ts->iowait_sleeptime, delta); 561 } else { 562 iowait = ts->iowait_sleeptime; 563 } 564 } 565 566 return ktime_to_us(iowait); 567 } 568 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us); 569 570 static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, 571 ktime_t now, int cpu) 572 { 573 unsigned long seq, last_jiffies, next_jiffies, delta_jiffies; 574 ktime_t last_update, expires, ret = { .tv64 = 0 }; 575 unsigned long rcu_delta_jiffies; 576 struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev; 577 u64 time_delta; 578 579 time_delta = timekeeping_max_deferment(); 580 581 /* Read jiffies and the time when jiffies were updated last */ 582 do { 583 seq = read_seqbegin(&jiffies_lock); 584 last_update = last_jiffies_update; 585 last_jiffies = jiffies; 586 } while (read_seqretry(&jiffies_lock, seq)); 587 588 if (rcu_needs_cpu(cpu, &rcu_delta_jiffies) || 589 arch_needs_cpu(cpu) || irq_work_needs_cpu()) { 590 next_jiffies = last_jiffies + 1; 591 delta_jiffies = 1; 592 } else { 593 /* Get the next timer wheel timer */ 594 next_jiffies = get_next_timer_interrupt(last_jiffies); 595 delta_jiffies = next_jiffies - last_jiffies; 596 if (rcu_delta_jiffies < delta_jiffies) { 597 next_jiffies = last_jiffies + rcu_delta_jiffies; 598 delta_jiffies = rcu_delta_jiffies; 599 } 600 } 601 602 /* 603 * Do not stop the tick, if we are only one off (or less) 604 * or if the cpu is required for RCU: 605 */ 606 if (!ts->tick_stopped && delta_jiffies <= 1) 607 goto out; 608 609 /* Schedule the tick, if we are at least one jiffie off */ 610 if ((long)delta_jiffies >= 1) { 611 612 /* 613 * If this cpu is the one which updates jiffies, then 614 * give up the assignment and let it be taken by the 615 * cpu which runs the tick timer next, which might be 616 * this cpu as well. If we don't drop this here the 617 * jiffies might be stale and do_timer() never 618 * invoked. Keep track of the fact that it was the one 619 * which had the do_timer() duty last. If this cpu is 620 * the one which had the do_timer() duty last, we 621 * limit the sleep time to the timekeeping 622 * max_deferement value which we retrieved 623 * above. Otherwise we can sleep as long as we want. 624 */ 625 if (cpu == tick_do_timer_cpu) { 626 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 627 ts->do_timer_last = 1; 628 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) { 629 time_delta = KTIME_MAX; 630 ts->do_timer_last = 0; 631 } else if (!ts->do_timer_last) { 632 time_delta = KTIME_MAX; 633 } 634 635 #ifdef CONFIG_NO_HZ_FULL 636 if (!ts->inidle) { 637 time_delta = min(time_delta, 638 scheduler_tick_max_deferment()); 639 } 640 #endif 641 642 /* 643 * calculate the expiry time for the next timer wheel 644 * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals 645 * that there is no timer pending or at least extremely 646 * far into the future (12 days for HZ=1000). In this 647 * case we set the expiry to the end of time. 648 */ 649 if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) { 650 /* 651 * Calculate the time delta for the next timer event. 652 * If the time delta exceeds the maximum time delta 653 * permitted by the current clocksource then adjust 654 * the time delta accordingly to ensure the 655 * clocksource does not wrap. 656 */ 657 time_delta = min_t(u64, time_delta, 658 tick_period.tv64 * delta_jiffies); 659 } 660 661 if (time_delta < KTIME_MAX) 662 expires = ktime_add_ns(last_update, time_delta); 663 else 664 expires.tv64 = KTIME_MAX; 665 666 /* Skip reprogram of event if its not changed */ 667 if (ts->tick_stopped && ktime_equal(expires, dev->next_event)) 668 goto out; 669 670 ret = expires; 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 690 * in this case we simply stop the tick timer. 691 */ 692 if (unlikely(expires.tv64 == 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, expires, 700 HRTIMER_MODE_ABS_PINNED); 701 /* Check, if the timer was already in the past */ 702 if (hrtimer_active(&ts->sched_timer)) 703 goto out; 704 } else if (!tick_program_event(expires, 0)) 705 goto out; 706 /* 707 * We are past the event already. So we crossed a 708 * jiffie boundary. Update jiffies and raise the 709 * softirq. 710 */ 711 tick_do_update_jiffies64(ktime_get()); 712 } 713 raise_softirq_irqoff(TIMER_SOFTIRQ); 714 out: 715 ts->next_jiffies = next_jiffies; 716 ts->last_jiffies = last_jiffies; 717 ts->sleep_length = ktime_sub(dev->next_event, now); 718 719 return ret; 720 } 721 722 static void tick_nohz_full_stop_tick(struct tick_sched *ts) 723 { 724 #ifdef CONFIG_NO_HZ_FULL 725 int cpu = smp_processor_id(); 726 727 if (!tick_nohz_full_cpu(cpu) || is_idle_task(current)) 728 return; 729 730 if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE) 731 return; 732 733 if (!can_stop_full_tick()) 734 return; 735 736 tick_nohz_stop_sched_tick(ts, ktime_get(), cpu); 737 #endif 738 } 739 740 static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) 741 { 742 /* 743 * If this cpu is offline and it is the one which updates 744 * jiffies, then give up the assignment and let it be taken by 745 * the cpu which runs the tick timer next. If we don't drop 746 * this here the jiffies might be stale and do_timer() never 747 * invoked. 748 */ 749 if (unlikely(!cpu_online(cpu))) { 750 if (cpu == tick_do_timer_cpu) 751 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 752 return false; 753 } 754 755 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) { 756 ts->sleep_length = (ktime_t) { .tv64 = NSEC_PER_SEC/HZ }; 757 return false; 758 } 759 760 if (need_resched()) 761 return false; 762 763 if (unlikely(local_softirq_pending() && cpu_online(cpu))) { 764 static int ratelimit; 765 766 if (ratelimit < 10 && 767 (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { 768 pr_warn("NOHZ: local_softirq_pending %02x\n", 769 (unsigned int) local_softirq_pending()); 770 ratelimit++; 771 } 772 return false; 773 } 774 775 if (tick_nohz_full_enabled()) { 776 /* 777 * Keep the tick alive to guarantee timekeeping progression 778 * if there are full dynticks CPUs around 779 */ 780 if (tick_do_timer_cpu == cpu) 781 return false; 782 /* 783 * Boot safety: make sure the timekeeping duty has been 784 * assigned before entering dyntick-idle mode, 785 */ 786 if (tick_do_timer_cpu == TICK_DO_TIMER_NONE) 787 return false; 788 } 789 790 return true; 791 } 792 793 static void __tick_nohz_idle_enter(struct tick_sched *ts) 794 { 795 ktime_t now, expires; 796 int cpu = smp_processor_id(); 797 798 now = tick_nohz_start_idle(ts); 799 800 if (can_stop_idle_tick(cpu, ts)) { 801 int was_stopped = ts->tick_stopped; 802 803 ts->idle_calls++; 804 805 expires = tick_nohz_stop_sched_tick(ts, now, cpu); 806 if (expires.tv64 > 0LL) { 807 ts->idle_sleeps++; 808 ts->idle_expires = expires; 809 } 810 811 if (!was_stopped && ts->tick_stopped) 812 ts->idle_jiffies = ts->last_jiffies; 813 } 814 } 815 816 /** 817 * tick_nohz_idle_enter - stop the idle tick from the idle task 818 * 819 * When the next event is more than a tick into the future, stop the idle tick 820 * Called when we start the idle loop. 821 * 822 * The arch is responsible of calling: 823 * 824 * - rcu_idle_enter() after its last use of RCU before the CPU is put 825 * to sleep. 826 * - rcu_idle_exit() before the first use of RCU after the CPU is woken up. 827 */ 828 void tick_nohz_idle_enter(void) 829 { 830 struct tick_sched *ts; 831 832 WARN_ON_ONCE(irqs_disabled()); 833 834 /* 835 * Update the idle state in the scheduler domain hierarchy 836 * when tick_nohz_stop_sched_tick() is called from the idle loop. 837 * State will be updated to busy during the first busy tick after 838 * exiting idle. 839 */ 840 set_cpu_sd_state_idle(); 841 842 local_irq_disable(); 843 844 ts = &__get_cpu_var(tick_cpu_sched); 845 ts->inidle = 1; 846 __tick_nohz_idle_enter(ts); 847 848 local_irq_enable(); 849 } 850 EXPORT_SYMBOL_GPL(tick_nohz_idle_enter); 851 852 /** 853 * tick_nohz_irq_exit - update next tick event from interrupt exit 854 * 855 * When an interrupt fires while we are idle and it doesn't cause 856 * a reschedule, it may still add, modify or delete a timer, enqueue 857 * an RCU callback, etc... 858 * So we need to re-calculate and reprogram the next tick event. 859 */ 860 void tick_nohz_irq_exit(void) 861 { 862 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 863 864 if (ts->inidle) 865 __tick_nohz_idle_enter(ts); 866 else 867 tick_nohz_full_stop_tick(ts); 868 } 869 870 /** 871 * tick_nohz_get_sleep_length - return the length of the current sleep 872 * 873 * Called from power state control code with interrupts disabled 874 */ 875 ktime_t tick_nohz_get_sleep_length(void) 876 { 877 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 878 879 return ts->sleep_length; 880 } 881 882 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) 883 { 884 hrtimer_cancel(&ts->sched_timer); 885 hrtimer_set_expires(&ts->sched_timer, ts->last_tick); 886 887 while (1) { 888 /* Forward the time to expire in the future */ 889 hrtimer_forward(&ts->sched_timer, now, tick_period); 890 891 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { 892 hrtimer_start_expires(&ts->sched_timer, 893 HRTIMER_MODE_ABS_PINNED); 894 /* Check, if the timer was already in the past */ 895 if (hrtimer_active(&ts->sched_timer)) 896 break; 897 } else { 898 if (!tick_program_event( 899 hrtimer_get_expires(&ts->sched_timer), 0)) 900 break; 901 } 902 /* Reread time and update jiffies */ 903 now = ktime_get(); 904 tick_do_update_jiffies64(now); 905 } 906 } 907 908 static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now) 909 { 910 /* Update jiffies first */ 911 tick_do_update_jiffies64(now); 912 update_cpu_load_nohz(); 913 914 calc_load_exit_idle(); 915 touch_softlockup_watchdog(); 916 /* 917 * Cancel the scheduled timer and restore the tick 918 */ 919 ts->tick_stopped = 0; 920 ts->idle_exittime = now; 921 922 tick_nohz_restart(ts, now); 923 } 924 925 static void tick_nohz_account_idle_ticks(struct tick_sched *ts) 926 { 927 #ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE 928 unsigned long ticks; 929 930 if (vtime_accounting_enabled()) 931 return; 932 /* 933 * We stopped the tick in idle. Update process times would miss the 934 * time we slept as update_process_times does only a 1 tick 935 * accounting. Enforce that this is accounted to idle ! 936 */ 937 ticks = jiffies - ts->idle_jiffies; 938 /* 939 * We might be one off. Do not randomly account a huge number of ticks! 940 */ 941 if (ticks && ticks < LONG_MAX) 942 account_idle_ticks(ticks); 943 #endif 944 } 945 946 /** 947 * tick_nohz_idle_exit - restart the idle tick from the idle task 948 * 949 * Restart the idle tick when the CPU is woken up from idle 950 * This also exit the RCU extended quiescent state. The CPU 951 * can use RCU again after this function is called. 952 */ 953 void tick_nohz_idle_exit(void) 954 { 955 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 956 ktime_t now; 957 958 local_irq_disable(); 959 960 WARN_ON_ONCE(!ts->inidle); 961 962 ts->inidle = 0; 963 964 if (ts->idle_active || ts->tick_stopped) 965 now = ktime_get(); 966 967 if (ts->idle_active) 968 tick_nohz_stop_idle(ts, now); 969 970 if (ts->tick_stopped) { 971 tick_nohz_restart_sched_tick(ts, now); 972 tick_nohz_account_idle_ticks(ts); 973 } 974 975 local_irq_enable(); 976 } 977 EXPORT_SYMBOL_GPL(tick_nohz_idle_exit); 978 979 static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now) 980 { 981 hrtimer_forward(&ts->sched_timer, now, tick_period); 982 return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0); 983 } 984 985 /* 986 * The nohz low res interrupt handler 987 */ 988 static void tick_nohz_handler(struct clock_event_device *dev) 989 { 990 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 991 struct pt_regs *regs = get_irq_regs(); 992 ktime_t now = ktime_get(); 993 994 dev->next_event.tv64 = KTIME_MAX; 995 996 tick_sched_do_timer(now); 997 tick_sched_handle(ts, regs); 998 999 while (tick_nohz_reprogram(ts, now)) { 1000 now = ktime_get(); 1001 tick_do_update_jiffies64(now); 1002 } 1003 } 1004 1005 /** 1006 * tick_nohz_switch_to_nohz - switch to nohz mode 1007 */ 1008 static void tick_nohz_switch_to_nohz(void) 1009 { 1010 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 1011 ktime_t next; 1012 1013 if (!tick_nohz_enabled) 1014 return; 1015 1016 local_irq_disable(); 1017 if (tick_switch_to_oneshot(tick_nohz_handler)) { 1018 local_irq_enable(); 1019 return; 1020 } 1021 tick_nohz_active = 1; 1022 ts->nohz_mode = NOHZ_MODE_LOWRES; 1023 1024 /* 1025 * Recycle the hrtimer in ts, so we can share the 1026 * hrtimer_forward with the highres code. 1027 */ 1028 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 1029 /* Get the next period */ 1030 next = tick_init_jiffy_update(); 1031 1032 for (;;) { 1033 hrtimer_set_expires(&ts->sched_timer, next); 1034 if (!tick_program_event(next, 0)) 1035 break; 1036 next = ktime_add(next, tick_period); 1037 } 1038 local_irq_enable(); 1039 } 1040 1041 /* 1042 * When NOHZ is enabled and the tick is stopped, we need to kick the 1043 * tick timer from irq_enter() so that the jiffies update is kept 1044 * alive during long running softirqs. That's ugly as hell, but 1045 * correctness is key even if we need to fix the offending softirq in 1046 * the first place. 1047 * 1048 * Note, this is different to tick_nohz_restart. We just kick the 1049 * timer and do not touch the other magic bits which need to be done 1050 * when idle is left. 1051 */ 1052 static void tick_nohz_kick_tick(struct tick_sched *ts, ktime_t now) 1053 { 1054 #if 0 1055 /* Switch back to 2.6.27 behaviour */ 1056 ktime_t delta; 1057 1058 /* 1059 * Do not touch the tick device, when the next expiry is either 1060 * already reached or less/equal than the tick period. 1061 */ 1062 delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now); 1063 if (delta.tv64 <= tick_period.tv64) 1064 return; 1065 1066 tick_nohz_restart(ts, now); 1067 #endif 1068 } 1069 1070 static inline void tick_nohz_irq_enter(void) 1071 { 1072 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 1073 ktime_t now; 1074 1075 if (!ts->idle_active && !ts->tick_stopped) 1076 return; 1077 now = ktime_get(); 1078 if (ts->idle_active) 1079 tick_nohz_stop_idle(ts, now); 1080 if (ts->tick_stopped) { 1081 tick_nohz_update_jiffies(now); 1082 tick_nohz_kick_tick(ts, now); 1083 } 1084 } 1085 1086 #else 1087 1088 static inline void tick_nohz_switch_to_nohz(void) { } 1089 static inline void tick_nohz_irq_enter(void) { } 1090 1091 #endif /* CONFIG_NO_HZ_COMMON */ 1092 1093 /* 1094 * Called from irq_enter to notify about the possible interruption of idle() 1095 */ 1096 void tick_irq_enter(void) 1097 { 1098 tick_check_oneshot_broadcast_this_cpu(); 1099 tick_nohz_irq_enter(); 1100 } 1101 1102 /* 1103 * High resolution timer specific code 1104 */ 1105 #ifdef CONFIG_HIGH_RES_TIMERS 1106 /* 1107 * We rearm the timer until we get disabled by the idle code. 1108 * Called with interrupts disabled. 1109 */ 1110 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) 1111 { 1112 struct tick_sched *ts = 1113 container_of(timer, struct tick_sched, sched_timer); 1114 struct pt_regs *regs = get_irq_regs(); 1115 ktime_t now = ktime_get(); 1116 1117 tick_sched_do_timer(now); 1118 1119 /* 1120 * Do not call, when we are not in irq context and have 1121 * no valid regs pointer 1122 */ 1123 if (regs) 1124 tick_sched_handle(ts, regs); 1125 1126 hrtimer_forward(timer, now, tick_period); 1127 1128 return HRTIMER_RESTART; 1129 } 1130 1131 static int sched_skew_tick; 1132 1133 static int __init skew_tick(char *str) 1134 { 1135 get_option(&str, &sched_skew_tick); 1136 1137 return 0; 1138 } 1139 early_param("skew_tick", skew_tick); 1140 1141 /** 1142 * tick_setup_sched_timer - setup the tick emulation timer 1143 */ 1144 void tick_setup_sched_timer(void) 1145 { 1146 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 1147 ktime_t now = ktime_get(); 1148 1149 /* 1150 * Emulate tick processing via per-CPU hrtimers: 1151 */ 1152 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 1153 ts->sched_timer.function = tick_sched_timer; 1154 1155 /* Get the next period (per cpu) */ 1156 hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update()); 1157 1158 /* Offset the tick to avert jiffies_lock contention. */ 1159 if (sched_skew_tick) { 1160 u64 offset = ktime_to_ns(tick_period) >> 1; 1161 do_div(offset, num_possible_cpus()); 1162 offset *= smp_processor_id(); 1163 hrtimer_add_expires_ns(&ts->sched_timer, offset); 1164 } 1165 1166 for (;;) { 1167 hrtimer_forward(&ts->sched_timer, now, tick_period); 1168 hrtimer_start_expires(&ts->sched_timer, 1169 HRTIMER_MODE_ABS_PINNED); 1170 /* Check, if the timer was already in the past */ 1171 if (hrtimer_active(&ts->sched_timer)) 1172 break; 1173 now = ktime_get(); 1174 } 1175 1176 #ifdef CONFIG_NO_HZ_COMMON 1177 if (tick_nohz_enabled) { 1178 ts->nohz_mode = NOHZ_MODE_HIGHRES; 1179 tick_nohz_active = 1; 1180 } 1181 #endif 1182 } 1183 #endif /* HIGH_RES_TIMERS */ 1184 1185 #if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS 1186 void tick_cancel_sched_timer(int cpu) 1187 { 1188 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 1189 1190 # ifdef CONFIG_HIGH_RES_TIMERS 1191 if (ts->sched_timer.base) 1192 hrtimer_cancel(&ts->sched_timer); 1193 # endif 1194 1195 memset(ts, 0, sizeof(*ts)); 1196 } 1197 #endif 1198 1199 /** 1200 * Async notification about clocksource changes 1201 */ 1202 void tick_clock_notify(void) 1203 { 1204 int cpu; 1205 1206 for_each_possible_cpu(cpu) 1207 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks); 1208 } 1209 1210 /* 1211 * Async notification about clock event changes 1212 */ 1213 void tick_oneshot_notify(void) 1214 { 1215 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 1216 1217 set_bit(0, &ts->check_clocks); 1218 } 1219 1220 /** 1221 * Check, if a change happened, which makes oneshot possible. 1222 * 1223 * Called cyclic from the hrtimer softirq (driven by the timer 1224 * softirq) allow_nohz signals, that we can switch into low-res nohz 1225 * mode, because high resolution timers are disabled (either compile 1226 * or runtime). 1227 */ 1228 int tick_check_oneshot_change(int allow_nohz) 1229 { 1230 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 1231 1232 if (!test_and_clear_bit(0, &ts->check_clocks)) 1233 return 0; 1234 1235 if (ts->nohz_mode != NOHZ_MODE_INACTIVE) 1236 return 0; 1237 1238 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available()) 1239 return 0; 1240 1241 if (!allow_nohz) 1242 return 1; 1243 1244 tick_nohz_switch_to_nohz(); 1245 return 0; 1246 } 1247