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 24 #include <asm/irq_regs.h> 25 26 #include "tick-internal.h" 27 28 /* 29 * Per cpu nohz control structure 30 */ 31 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched); 32 33 /* 34 * The time, when the last jiffy update happened. Protected by xtime_lock. 35 */ 36 static ktime_t last_jiffies_update; 37 38 struct tick_sched *tick_get_tick_sched(int cpu) 39 { 40 return &per_cpu(tick_cpu_sched, cpu); 41 } 42 43 /* 44 * Must be called with interrupts disabled ! 45 */ 46 static void tick_do_update_jiffies64(ktime_t now) 47 { 48 unsigned long ticks = 0; 49 ktime_t delta; 50 51 /* 52 * Do a quick check without holding xtime_lock: 53 */ 54 delta = ktime_sub(now, last_jiffies_update); 55 if (delta.tv64 < tick_period.tv64) 56 return; 57 58 /* Reevalute with xtime_lock held */ 59 write_seqlock(&xtime_lock); 60 61 delta = ktime_sub(now, last_jiffies_update); 62 if (delta.tv64 >= tick_period.tv64) { 63 64 delta = ktime_sub(delta, tick_period); 65 last_jiffies_update = ktime_add(last_jiffies_update, 66 tick_period); 67 68 /* Slow path for long timeouts */ 69 if (unlikely(delta.tv64 >= tick_period.tv64)) { 70 s64 incr = ktime_to_ns(tick_period); 71 72 ticks = ktime_divns(delta, incr); 73 74 last_jiffies_update = ktime_add_ns(last_jiffies_update, 75 incr * ticks); 76 } 77 do_timer(++ticks); 78 79 /* Keep the tick_next_period variable up to date */ 80 tick_next_period = ktime_add(last_jiffies_update, tick_period); 81 } 82 write_sequnlock(&xtime_lock); 83 } 84 85 /* 86 * Initialize and return retrieve the jiffies update. 87 */ 88 static ktime_t tick_init_jiffy_update(void) 89 { 90 ktime_t period; 91 92 write_seqlock(&xtime_lock); 93 /* Did we start the jiffies update yet ? */ 94 if (last_jiffies_update.tv64 == 0) 95 last_jiffies_update = tick_next_period; 96 period = last_jiffies_update; 97 write_sequnlock(&xtime_lock); 98 return period; 99 } 100 101 /* 102 * NOHZ - aka dynamic tick functionality 103 */ 104 #ifdef CONFIG_NO_HZ 105 /* 106 * NO HZ enabled ? 107 */ 108 static int tick_nohz_enabled __read_mostly = 1; 109 110 /* 111 * Enable / Disable tickless mode 112 */ 113 static int __init setup_tick_nohz(char *str) 114 { 115 if (!strcmp(str, "off")) 116 tick_nohz_enabled = 0; 117 else if (!strcmp(str, "on")) 118 tick_nohz_enabled = 1; 119 else 120 return 0; 121 return 1; 122 } 123 124 __setup("nohz=", setup_tick_nohz); 125 126 /** 127 * tick_nohz_update_jiffies - update jiffies when idle was interrupted 128 * 129 * Called from interrupt entry when the CPU was idle 130 * 131 * In case the sched_tick was stopped on this CPU, we have to check if jiffies 132 * must be updated. Otherwise an interrupt handler could use a stale jiffy 133 * value. We do this unconditionally on any cpu, as we don't know whether the 134 * cpu, which has the update task assigned is in a long sleep. 135 */ 136 static void tick_nohz_update_jiffies(ktime_t now) 137 { 138 int cpu = smp_processor_id(); 139 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 140 unsigned long flags; 141 142 ts->idle_waketime = now; 143 144 local_irq_save(flags); 145 tick_do_update_jiffies64(now); 146 local_irq_restore(flags); 147 148 touch_softlockup_watchdog(); 149 } 150 151 /* 152 * Updates the per cpu time idle statistics counters 153 */ 154 static void 155 update_ts_time_stats(int cpu, struct tick_sched *ts, ktime_t now, u64 *last_update_time) 156 { 157 ktime_t delta; 158 159 if (ts->idle_active) { 160 delta = ktime_sub(now, ts->idle_entrytime); 161 if (nr_iowait_cpu(cpu) > 0) 162 ts->iowait_sleeptime = ktime_add(ts->iowait_sleeptime, delta); 163 else 164 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); 165 ts->idle_entrytime = now; 166 } 167 168 if (last_update_time) 169 *last_update_time = ktime_to_us(now); 170 171 } 172 173 static void tick_nohz_stop_idle(int cpu, ktime_t now) 174 { 175 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 176 177 update_ts_time_stats(cpu, ts, now, NULL); 178 ts->idle_active = 0; 179 180 sched_clock_idle_wakeup_event(0); 181 } 182 183 static ktime_t tick_nohz_start_idle(int cpu, struct tick_sched *ts) 184 { 185 ktime_t now = ktime_get(); 186 187 ts->idle_entrytime = now; 188 ts->idle_active = 1; 189 sched_clock_idle_sleep_event(); 190 return now; 191 } 192 193 /** 194 * get_cpu_idle_time_us - get the total idle time of a cpu 195 * @cpu: CPU number to query 196 * @last_update_time: variable to store update time in. Do not update 197 * counters if NULL. 198 * 199 * Return the cummulative idle time (since boot) for a given 200 * CPU, in microseconds. 201 * 202 * This time is measured via accounting rather than sampling, 203 * and is as accurate as ktime_get() is. 204 * 205 * This function returns -1 if NOHZ is not enabled. 206 */ 207 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) 208 { 209 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 210 ktime_t now, idle; 211 212 if (!tick_nohz_enabled) 213 return -1; 214 215 now = ktime_get(); 216 if (last_update_time) { 217 update_ts_time_stats(cpu, ts, now, last_update_time); 218 idle = ts->idle_sleeptime; 219 } else { 220 if (ts->idle_active && !nr_iowait_cpu(cpu)) { 221 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 222 223 idle = ktime_add(ts->idle_sleeptime, delta); 224 } else { 225 idle = ts->idle_sleeptime; 226 } 227 } 228 229 return ktime_to_us(idle); 230 231 } 232 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us); 233 234 /** 235 * get_cpu_iowait_time_us - get the total iowait time of a cpu 236 * @cpu: CPU number to query 237 * @last_update_time: variable to store update time in. Do not update 238 * counters if NULL. 239 * 240 * Return the cummulative iowait time (since boot) for a given 241 * CPU, in microseconds. 242 * 243 * This time is measured via accounting rather than sampling, 244 * and is as accurate as ktime_get() is. 245 * 246 * This function returns -1 if NOHZ is not enabled. 247 */ 248 u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time) 249 { 250 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 251 ktime_t now, iowait; 252 253 if (!tick_nohz_enabled) 254 return -1; 255 256 now = ktime_get(); 257 if (last_update_time) { 258 update_ts_time_stats(cpu, ts, now, last_update_time); 259 iowait = ts->iowait_sleeptime; 260 } else { 261 if (ts->idle_active && nr_iowait_cpu(cpu) > 0) { 262 ktime_t delta = ktime_sub(now, ts->idle_entrytime); 263 264 iowait = ktime_add(ts->iowait_sleeptime, delta); 265 } else { 266 iowait = ts->iowait_sleeptime; 267 } 268 } 269 270 return ktime_to_us(iowait); 271 } 272 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us); 273 274 static void tick_nohz_stop_sched_tick(struct tick_sched *ts) 275 { 276 unsigned long seq, last_jiffies, next_jiffies, delta_jiffies; 277 ktime_t last_update, expires, now; 278 struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev; 279 u64 time_delta; 280 int cpu; 281 282 cpu = smp_processor_id(); 283 ts = &per_cpu(tick_cpu_sched, cpu); 284 285 now = tick_nohz_start_idle(cpu, ts); 286 287 /* 288 * If this cpu is offline and it is the one which updates 289 * jiffies, then give up the assignment and let it be taken by 290 * the cpu which runs the tick timer next. If we don't drop 291 * this here the jiffies might be stale and do_timer() never 292 * invoked. 293 */ 294 if (unlikely(!cpu_online(cpu))) { 295 if (cpu == tick_do_timer_cpu) 296 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 297 } 298 299 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) 300 return; 301 302 if (need_resched()) 303 return; 304 305 if (unlikely(local_softirq_pending() && cpu_online(cpu))) { 306 static int ratelimit; 307 308 if (ratelimit < 10) { 309 printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n", 310 (unsigned int) local_softirq_pending()); 311 ratelimit++; 312 } 313 return; 314 } 315 316 ts->idle_calls++; 317 /* Read jiffies and the time when jiffies were updated last */ 318 do { 319 seq = read_seqbegin(&xtime_lock); 320 last_update = last_jiffies_update; 321 last_jiffies = jiffies; 322 time_delta = timekeeping_max_deferment(); 323 } while (read_seqretry(&xtime_lock, seq)); 324 325 if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) || 326 arch_needs_cpu(cpu)) { 327 next_jiffies = last_jiffies + 1; 328 delta_jiffies = 1; 329 } else { 330 /* Get the next timer wheel timer */ 331 next_jiffies = get_next_timer_interrupt(last_jiffies); 332 delta_jiffies = next_jiffies - last_jiffies; 333 } 334 /* 335 * Do not stop the tick, if we are only one off 336 * or if the cpu is required for rcu 337 */ 338 if (!ts->tick_stopped && delta_jiffies == 1) 339 goto out; 340 341 /* Schedule the tick, if we are at least one jiffie off */ 342 if ((long)delta_jiffies >= 1) { 343 344 /* 345 * If this cpu is the one which updates jiffies, then 346 * give up the assignment and let it be taken by the 347 * cpu which runs the tick timer next, which might be 348 * this cpu as well. If we don't drop this here the 349 * jiffies might be stale and do_timer() never 350 * invoked. Keep track of the fact that it was the one 351 * which had the do_timer() duty last. If this cpu is 352 * the one which had the do_timer() duty last, we 353 * limit the sleep time to the timekeeping 354 * max_deferement value which we retrieved 355 * above. Otherwise we can sleep as long as we want. 356 */ 357 if (cpu == tick_do_timer_cpu) { 358 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 359 ts->do_timer_last = 1; 360 } else if (tick_do_timer_cpu != TICK_DO_TIMER_NONE) { 361 time_delta = KTIME_MAX; 362 ts->do_timer_last = 0; 363 } else if (!ts->do_timer_last) { 364 time_delta = KTIME_MAX; 365 } 366 367 /* 368 * calculate the expiry time for the next timer wheel 369 * timer. delta_jiffies >= NEXT_TIMER_MAX_DELTA signals 370 * that there is no timer pending or at least extremely 371 * far into the future (12 days for HZ=1000). In this 372 * case we set the expiry to the end of time. 373 */ 374 if (likely(delta_jiffies < NEXT_TIMER_MAX_DELTA)) { 375 /* 376 * Calculate the time delta for the next timer event. 377 * If the time delta exceeds the maximum time delta 378 * permitted by the current clocksource then adjust 379 * the time delta accordingly to ensure the 380 * clocksource does not wrap. 381 */ 382 time_delta = min_t(u64, time_delta, 383 tick_period.tv64 * delta_jiffies); 384 } 385 386 if (time_delta < KTIME_MAX) 387 expires = ktime_add_ns(last_update, time_delta); 388 else 389 expires.tv64 = KTIME_MAX; 390 391 /* Skip reprogram of event if its not changed */ 392 if (ts->tick_stopped && ktime_equal(expires, dev->next_event)) 393 goto out; 394 395 /* 396 * nohz_stop_sched_tick can be called several times before 397 * the nohz_restart_sched_tick is called. This happens when 398 * interrupts arrive which do not cause a reschedule. In the 399 * first call we save the current tick time, so we can restart 400 * the scheduler tick in nohz_restart_sched_tick. 401 */ 402 if (!ts->tick_stopped) { 403 select_nohz_load_balancer(1); 404 405 ts->idle_tick = hrtimer_get_expires(&ts->sched_timer); 406 ts->tick_stopped = 1; 407 ts->idle_jiffies = last_jiffies; 408 } 409 410 ts->idle_sleeps++; 411 412 /* Mark expires */ 413 ts->idle_expires = expires; 414 415 /* 416 * If the expiration time == KTIME_MAX, then 417 * in this case we simply stop the tick timer. 418 */ 419 if (unlikely(expires.tv64 == KTIME_MAX)) { 420 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) 421 hrtimer_cancel(&ts->sched_timer); 422 goto out; 423 } 424 425 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { 426 hrtimer_start(&ts->sched_timer, expires, 427 HRTIMER_MODE_ABS_PINNED); 428 /* Check, if the timer was already in the past */ 429 if (hrtimer_active(&ts->sched_timer)) 430 goto out; 431 } else if (!tick_program_event(expires, 0)) 432 goto out; 433 /* 434 * We are past the event already. So we crossed a 435 * jiffie boundary. Update jiffies and raise the 436 * softirq. 437 */ 438 tick_do_update_jiffies64(ktime_get()); 439 } 440 raise_softirq_irqoff(TIMER_SOFTIRQ); 441 out: 442 ts->next_jiffies = next_jiffies; 443 ts->last_jiffies = last_jiffies; 444 ts->sleep_length = ktime_sub(dev->next_event, now); 445 } 446 447 /** 448 * tick_nohz_idle_enter - stop the idle tick from the idle task 449 * 450 * When the next event is more than a tick into the future, stop the idle tick 451 * Called when we start the idle loop. 452 * 453 * The arch is responsible of calling: 454 * 455 * - rcu_idle_enter() after its last use of RCU before the CPU is put 456 * to sleep. 457 * - rcu_idle_exit() before the first use of RCU after the CPU is woken up. 458 */ 459 void tick_nohz_idle_enter(void) 460 { 461 struct tick_sched *ts; 462 463 WARN_ON_ONCE(irqs_disabled()); 464 465 /* 466 * Update the idle state in the scheduler domain hierarchy 467 * when tick_nohz_stop_sched_tick() is called from the idle loop. 468 * State will be updated to busy during the first busy tick after 469 * exiting idle. 470 */ 471 set_cpu_sd_state_idle(); 472 473 local_irq_disable(); 474 475 ts = &__get_cpu_var(tick_cpu_sched); 476 /* 477 * set ts->inidle unconditionally. even if the system did not 478 * switch to nohz mode the cpu frequency governers rely on the 479 * update of the idle time accounting in tick_nohz_start_idle(). 480 */ 481 ts->inidle = 1; 482 tick_nohz_stop_sched_tick(ts); 483 484 local_irq_enable(); 485 } 486 487 /** 488 * tick_nohz_irq_exit - update next tick event from interrupt exit 489 * 490 * When an interrupt fires while we are idle and it doesn't cause 491 * a reschedule, it may still add, modify or delete a timer, enqueue 492 * an RCU callback, etc... 493 * So we need to re-calculate and reprogram the next tick event. 494 */ 495 void tick_nohz_irq_exit(void) 496 { 497 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 498 499 if (!ts->inidle) 500 return; 501 502 tick_nohz_stop_sched_tick(ts); 503 } 504 505 /** 506 * tick_nohz_get_sleep_length - return the length of the current sleep 507 * 508 * Called from power state control code with interrupts disabled 509 */ 510 ktime_t tick_nohz_get_sleep_length(void) 511 { 512 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 513 514 return ts->sleep_length; 515 } 516 517 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) 518 { 519 hrtimer_cancel(&ts->sched_timer); 520 hrtimer_set_expires(&ts->sched_timer, ts->idle_tick); 521 522 while (1) { 523 /* Forward the time to expire in the future */ 524 hrtimer_forward(&ts->sched_timer, now, tick_period); 525 526 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { 527 hrtimer_start_expires(&ts->sched_timer, 528 HRTIMER_MODE_ABS_PINNED); 529 /* Check, if the timer was already in the past */ 530 if (hrtimer_active(&ts->sched_timer)) 531 break; 532 } else { 533 if (!tick_program_event( 534 hrtimer_get_expires(&ts->sched_timer), 0)) 535 break; 536 } 537 /* Reread time and update jiffies */ 538 now = ktime_get(); 539 tick_do_update_jiffies64(now); 540 } 541 } 542 543 /** 544 * tick_nohz_idle_exit - restart the idle tick from the idle task 545 * 546 * Restart the idle tick when the CPU is woken up from idle 547 * This also exit the RCU extended quiescent state. The CPU 548 * can use RCU again after this function is called. 549 */ 550 void tick_nohz_idle_exit(void) 551 { 552 int cpu = smp_processor_id(); 553 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 554 #ifndef CONFIG_VIRT_CPU_ACCOUNTING 555 unsigned long ticks; 556 #endif 557 ktime_t now; 558 559 local_irq_disable(); 560 561 WARN_ON_ONCE(!ts->inidle); 562 563 ts->inidle = 0; 564 565 if (ts->idle_active || ts->tick_stopped) 566 now = ktime_get(); 567 568 if (ts->idle_active) 569 tick_nohz_stop_idle(cpu, now); 570 571 if (!ts->tick_stopped) { 572 local_irq_enable(); 573 return; 574 } 575 576 /* Update jiffies first */ 577 select_nohz_load_balancer(0); 578 tick_do_update_jiffies64(now); 579 update_cpu_load_nohz(); 580 581 #ifndef CONFIG_VIRT_CPU_ACCOUNTING 582 /* 583 * We stopped the tick in idle. Update process times would miss the 584 * time we slept as update_process_times does only a 1 tick 585 * accounting. Enforce that this is accounted to idle ! 586 */ 587 ticks = jiffies - ts->idle_jiffies; 588 /* 589 * We might be one off. Do not randomly account a huge number of ticks! 590 */ 591 if (ticks && ticks < LONG_MAX) 592 account_idle_ticks(ticks); 593 #endif 594 595 touch_softlockup_watchdog(); 596 /* 597 * Cancel the scheduled timer and restore the tick 598 */ 599 ts->tick_stopped = 0; 600 ts->idle_exittime = now; 601 602 tick_nohz_restart(ts, now); 603 604 local_irq_enable(); 605 } 606 607 static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now) 608 { 609 hrtimer_forward(&ts->sched_timer, now, tick_period); 610 return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0); 611 } 612 613 /* 614 * The nohz low res interrupt handler 615 */ 616 static void tick_nohz_handler(struct clock_event_device *dev) 617 { 618 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 619 struct pt_regs *regs = get_irq_regs(); 620 int cpu = smp_processor_id(); 621 ktime_t now = ktime_get(); 622 623 dev->next_event.tv64 = KTIME_MAX; 624 625 /* 626 * Check if the do_timer duty was dropped. We don't care about 627 * concurrency: This happens only when the cpu in charge went 628 * into a long sleep. If two cpus happen to assign themself to 629 * this duty, then the jiffies update is still serialized by 630 * xtime_lock. 631 */ 632 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) 633 tick_do_timer_cpu = cpu; 634 635 /* Check, if the jiffies need an update */ 636 if (tick_do_timer_cpu == cpu) 637 tick_do_update_jiffies64(now); 638 639 /* 640 * When we are idle and the tick is stopped, we have to touch 641 * the watchdog as we might not schedule for a really long 642 * time. This happens on complete idle SMP systems while 643 * waiting on the login prompt. We also increment the "start 644 * of idle" jiffy stamp so the idle accounting adjustment we 645 * do when we go busy again does not account too much ticks. 646 */ 647 if (ts->tick_stopped) { 648 touch_softlockup_watchdog(); 649 ts->idle_jiffies++; 650 } 651 652 update_process_times(user_mode(regs)); 653 profile_tick(CPU_PROFILING); 654 655 while (tick_nohz_reprogram(ts, now)) { 656 now = ktime_get(); 657 tick_do_update_jiffies64(now); 658 } 659 } 660 661 /** 662 * tick_nohz_switch_to_nohz - switch to nohz mode 663 */ 664 static void tick_nohz_switch_to_nohz(void) 665 { 666 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 667 ktime_t next; 668 669 if (!tick_nohz_enabled) 670 return; 671 672 local_irq_disable(); 673 if (tick_switch_to_oneshot(tick_nohz_handler)) { 674 local_irq_enable(); 675 return; 676 } 677 678 ts->nohz_mode = NOHZ_MODE_LOWRES; 679 680 /* 681 * Recycle the hrtimer in ts, so we can share the 682 * hrtimer_forward with the highres code. 683 */ 684 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 685 /* Get the next period */ 686 next = tick_init_jiffy_update(); 687 688 for (;;) { 689 hrtimer_set_expires(&ts->sched_timer, next); 690 if (!tick_program_event(next, 0)) 691 break; 692 next = ktime_add(next, tick_period); 693 } 694 local_irq_enable(); 695 } 696 697 /* 698 * When NOHZ is enabled and the tick is stopped, we need to kick the 699 * tick timer from irq_enter() so that the jiffies update is kept 700 * alive during long running softirqs. That's ugly as hell, but 701 * correctness is key even if we need to fix the offending softirq in 702 * the first place. 703 * 704 * Note, this is different to tick_nohz_restart. We just kick the 705 * timer and do not touch the other magic bits which need to be done 706 * when idle is left. 707 */ 708 static void tick_nohz_kick_tick(int cpu, ktime_t now) 709 { 710 #if 0 711 /* Switch back to 2.6.27 behaviour */ 712 713 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 714 ktime_t delta; 715 716 /* 717 * Do not touch the tick device, when the next expiry is either 718 * already reached or less/equal than the tick period. 719 */ 720 delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now); 721 if (delta.tv64 <= tick_period.tv64) 722 return; 723 724 tick_nohz_restart(ts, now); 725 #endif 726 } 727 728 static inline void tick_check_nohz(int cpu) 729 { 730 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 731 ktime_t now; 732 733 if (!ts->idle_active && !ts->tick_stopped) 734 return; 735 now = ktime_get(); 736 if (ts->idle_active) 737 tick_nohz_stop_idle(cpu, now); 738 if (ts->tick_stopped) { 739 tick_nohz_update_jiffies(now); 740 tick_nohz_kick_tick(cpu, now); 741 } 742 } 743 744 #else 745 746 static inline void tick_nohz_switch_to_nohz(void) { } 747 static inline void tick_check_nohz(int cpu) { } 748 749 #endif /* NO_HZ */ 750 751 /* 752 * Called from irq_enter to notify about the possible interruption of idle() 753 */ 754 void tick_check_idle(int cpu) 755 { 756 tick_check_oneshot_broadcast(cpu); 757 tick_check_nohz(cpu); 758 } 759 760 /* 761 * High resolution timer specific code 762 */ 763 #ifdef CONFIG_HIGH_RES_TIMERS 764 /* 765 * We rearm the timer until we get disabled by the idle code. 766 * Called with interrupts disabled and timer->base->cpu_base->lock held. 767 */ 768 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) 769 { 770 struct tick_sched *ts = 771 container_of(timer, struct tick_sched, sched_timer); 772 struct pt_regs *regs = get_irq_regs(); 773 ktime_t now = ktime_get(); 774 int cpu = smp_processor_id(); 775 776 #ifdef CONFIG_NO_HZ 777 /* 778 * Check if the do_timer duty was dropped. We don't care about 779 * concurrency: This happens only when the cpu in charge went 780 * into a long sleep. If two cpus happen to assign themself to 781 * this duty, then the jiffies update is still serialized by 782 * xtime_lock. 783 */ 784 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) 785 tick_do_timer_cpu = cpu; 786 #endif 787 788 /* Check, if the jiffies need an update */ 789 if (tick_do_timer_cpu == cpu) 790 tick_do_update_jiffies64(now); 791 792 /* 793 * Do not call, when we are not in irq context and have 794 * no valid regs pointer 795 */ 796 if (regs) { 797 /* 798 * When we are idle and the tick is stopped, we have to touch 799 * the watchdog as we might not schedule for a really long 800 * time. This happens on complete idle SMP systems while 801 * waiting on the login prompt. We also increment the "start of 802 * idle" jiffy stamp so the idle accounting adjustment we do 803 * when we go busy again does not account too much ticks. 804 */ 805 if (ts->tick_stopped) { 806 touch_softlockup_watchdog(); 807 ts->idle_jiffies++; 808 } 809 update_process_times(user_mode(regs)); 810 profile_tick(CPU_PROFILING); 811 } 812 813 hrtimer_forward(timer, now, tick_period); 814 815 return HRTIMER_RESTART; 816 } 817 818 /** 819 * tick_setup_sched_timer - setup the tick emulation timer 820 */ 821 void tick_setup_sched_timer(void) 822 { 823 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 824 ktime_t now = ktime_get(); 825 826 /* 827 * Emulate tick processing via per-CPU hrtimers: 828 */ 829 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 830 ts->sched_timer.function = tick_sched_timer; 831 832 /* Get the next period (per cpu) */ 833 hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update()); 834 835 for (;;) { 836 hrtimer_forward(&ts->sched_timer, now, tick_period); 837 hrtimer_start_expires(&ts->sched_timer, 838 HRTIMER_MODE_ABS_PINNED); 839 /* Check, if the timer was already in the past */ 840 if (hrtimer_active(&ts->sched_timer)) 841 break; 842 now = ktime_get(); 843 } 844 845 #ifdef CONFIG_NO_HZ 846 if (tick_nohz_enabled) 847 ts->nohz_mode = NOHZ_MODE_HIGHRES; 848 #endif 849 } 850 #endif /* HIGH_RES_TIMERS */ 851 852 #if defined CONFIG_NO_HZ || defined CONFIG_HIGH_RES_TIMERS 853 void tick_cancel_sched_timer(int cpu) 854 { 855 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 856 857 # ifdef CONFIG_HIGH_RES_TIMERS 858 if (ts->sched_timer.base) 859 hrtimer_cancel(&ts->sched_timer); 860 # endif 861 862 ts->nohz_mode = NOHZ_MODE_INACTIVE; 863 } 864 #endif 865 866 /** 867 * Async notification about clocksource changes 868 */ 869 void tick_clock_notify(void) 870 { 871 int cpu; 872 873 for_each_possible_cpu(cpu) 874 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks); 875 } 876 877 /* 878 * Async notification about clock event changes 879 */ 880 void tick_oneshot_notify(void) 881 { 882 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 883 884 set_bit(0, &ts->check_clocks); 885 } 886 887 /** 888 * Check, if a change happened, which makes oneshot possible. 889 * 890 * Called cyclic from the hrtimer softirq (driven by the timer 891 * softirq) allow_nohz signals, that we can switch into low-res nohz 892 * mode, because high resolution timers are disabled (either compile 893 * or runtime). 894 */ 895 int tick_check_oneshot_change(int allow_nohz) 896 { 897 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 898 899 if (!test_and_clear_bit(0, &ts->check_clocks)) 900 return 0; 901 902 if (ts->nohz_mode != NOHZ_MODE_INACTIVE) 903 return 0; 904 905 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available()) 906 return 0; 907 908 if (!allow_nohz) 909 return 1; 910 911 tick_nohz_switch_to_nohz(); 912 return 0; 913 } 914