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/tick.h> 23 #include <linux/module.h> 24 25 #include <asm/irq_regs.h> 26 27 #include "tick-internal.h" 28 29 /* 30 * Per cpu nohz control structure 31 */ 32 static DEFINE_PER_CPU(struct tick_sched, tick_cpu_sched); 33 34 /* 35 * The time, when the last jiffy update happened. Protected by xtime_lock. 36 */ 37 static ktime_t last_jiffies_update; 38 39 struct tick_sched *tick_get_tick_sched(int cpu) 40 { 41 return &per_cpu(tick_cpu_sched, cpu); 42 } 43 44 /* 45 * Must be called with interrupts disabled ! 46 */ 47 static void tick_do_update_jiffies64(ktime_t now) 48 { 49 unsigned long ticks = 0; 50 ktime_t delta; 51 52 /* 53 * Do a quick check without holding xtime_lock: 54 */ 55 delta = ktime_sub(now, last_jiffies_update); 56 if (delta.tv64 < tick_period.tv64) 57 return; 58 59 /* Reevalute with xtime_lock held */ 60 write_seqlock(&xtime_lock); 61 62 delta = ktime_sub(now, last_jiffies_update); 63 if (delta.tv64 >= tick_period.tv64) { 64 65 delta = ktime_sub(delta, tick_period); 66 last_jiffies_update = ktime_add(last_jiffies_update, 67 tick_period); 68 69 /* Slow path for long timeouts */ 70 if (unlikely(delta.tv64 >= tick_period.tv64)) { 71 s64 incr = ktime_to_ns(tick_period); 72 73 ticks = ktime_divns(delta, incr); 74 75 last_jiffies_update = ktime_add_ns(last_jiffies_update, 76 incr * ticks); 77 } 78 do_timer(++ticks); 79 80 /* Keep the tick_next_period variable up to date */ 81 tick_next_period = ktime_add(last_jiffies_update, tick_period); 82 } 83 write_sequnlock(&xtime_lock); 84 } 85 86 /* 87 * Initialize and return retrieve the jiffies update. 88 */ 89 static ktime_t tick_init_jiffy_update(void) 90 { 91 ktime_t period; 92 93 write_seqlock(&xtime_lock); 94 /* Did we start the jiffies update yet ? */ 95 if (last_jiffies_update.tv64 == 0) 96 last_jiffies_update = tick_next_period; 97 period = last_jiffies_update; 98 write_sequnlock(&xtime_lock); 99 return period; 100 } 101 102 /* 103 * NOHZ - aka dynamic tick functionality 104 */ 105 #ifdef CONFIG_NO_HZ 106 /* 107 * NO HZ enabled ? 108 */ 109 static int tick_nohz_enabled __read_mostly = 1; 110 111 /* 112 * Enable / Disable tickless mode 113 */ 114 static int __init setup_tick_nohz(char *str) 115 { 116 if (!strcmp(str, "off")) 117 tick_nohz_enabled = 0; 118 else if (!strcmp(str, "on")) 119 tick_nohz_enabled = 1; 120 else 121 return 0; 122 return 1; 123 } 124 125 __setup("nohz=", setup_tick_nohz); 126 127 /** 128 * tick_nohz_update_jiffies - update jiffies when idle was interrupted 129 * 130 * Called from interrupt entry when the CPU was idle 131 * 132 * In case the sched_tick was stopped on this CPU, we have to check if jiffies 133 * must be updated. Otherwise an interrupt handler could use a stale jiffy 134 * value. We do this unconditionally on any cpu, as we don't know whether the 135 * cpu, which has the update task assigned is in a long sleep. 136 */ 137 static void tick_nohz_update_jiffies(ktime_t now) 138 { 139 int cpu = smp_processor_id(); 140 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 141 unsigned long flags; 142 143 cpumask_clear_cpu(cpu, nohz_cpu_mask); 144 ts->idle_waketime = now; 145 146 local_irq_save(flags); 147 tick_do_update_jiffies64(now); 148 local_irq_restore(flags); 149 150 touch_softlockup_watchdog(); 151 } 152 153 static void tick_nohz_stop_idle(int cpu, ktime_t now) 154 { 155 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 156 ktime_t delta; 157 158 delta = ktime_sub(now, ts->idle_entrytime); 159 ts->idle_lastupdate = now; 160 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); 161 ts->idle_active = 0; 162 163 sched_clock_idle_wakeup_event(0); 164 } 165 166 static ktime_t tick_nohz_start_idle(struct tick_sched *ts) 167 { 168 ktime_t now, delta; 169 170 now = ktime_get(); 171 if (ts->idle_active) { 172 delta = ktime_sub(now, ts->idle_entrytime); 173 ts->idle_lastupdate = now; 174 ts->idle_sleeptime = ktime_add(ts->idle_sleeptime, delta); 175 } 176 ts->idle_entrytime = now; 177 ts->idle_active = 1; 178 sched_clock_idle_sleep_event(); 179 return now; 180 } 181 182 u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time) 183 { 184 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 185 186 if (!tick_nohz_enabled) 187 return -1; 188 189 if (ts->idle_active) 190 *last_update_time = ktime_to_us(ts->idle_lastupdate); 191 else 192 *last_update_time = ktime_to_us(ktime_get()); 193 194 return ktime_to_us(ts->idle_sleeptime); 195 } 196 EXPORT_SYMBOL_GPL(get_cpu_idle_time_us); 197 198 /** 199 * tick_nohz_stop_sched_tick - stop the idle tick from the idle task 200 * 201 * When the next event is more than a tick into the future, stop the idle tick 202 * Called either from the idle loop or from irq_exit() when an idle period was 203 * just interrupted by an interrupt which did not cause a reschedule. 204 */ 205 void tick_nohz_stop_sched_tick(int inidle) 206 { 207 unsigned long seq, last_jiffies, next_jiffies, delta_jiffies, flags; 208 struct tick_sched *ts; 209 ktime_t last_update, expires, now; 210 struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev; 211 int cpu; 212 213 local_irq_save(flags); 214 215 cpu = smp_processor_id(); 216 ts = &per_cpu(tick_cpu_sched, cpu); 217 218 /* 219 * Call to tick_nohz_start_idle stops the last_update_time from being 220 * updated. Thus, it must not be called in the event we are called from 221 * irq_exit() with the prior state different than idle. 222 */ 223 if (!inidle && !ts->inidle) 224 goto end; 225 226 now = tick_nohz_start_idle(ts); 227 228 /* 229 * If this cpu is offline and it is the one which updates 230 * jiffies, then give up the assignment and let it be taken by 231 * the cpu which runs the tick timer next. If we don't drop 232 * this here the jiffies might be stale and do_timer() never 233 * invoked. 234 */ 235 if (unlikely(!cpu_online(cpu))) { 236 if (cpu == tick_do_timer_cpu) 237 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 238 } 239 240 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) 241 goto end; 242 243 ts->inidle = 1; 244 245 if (need_resched()) 246 goto end; 247 248 if (unlikely(local_softirq_pending() && cpu_online(cpu))) { 249 static int ratelimit; 250 251 if (ratelimit < 10) { 252 printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n", 253 local_softirq_pending()); 254 ratelimit++; 255 } 256 goto end; 257 } 258 259 ts->idle_calls++; 260 /* Read jiffies and the time when jiffies were updated last */ 261 do { 262 seq = read_seqbegin(&xtime_lock); 263 last_update = last_jiffies_update; 264 last_jiffies = jiffies; 265 } while (read_seqretry(&xtime_lock, seq)); 266 267 /* Get the next timer wheel timer */ 268 next_jiffies = get_next_timer_interrupt(last_jiffies); 269 delta_jiffies = next_jiffies - last_jiffies; 270 271 if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu)) 272 delta_jiffies = 1; 273 /* 274 * Do not stop the tick, if we are only one off 275 * or if the cpu is required for rcu 276 */ 277 if (!ts->tick_stopped && delta_jiffies == 1) 278 goto out; 279 280 /* Schedule the tick, if we are at least one jiffie off */ 281 if ((long)delta_jiffies >= 1) { 282 283 /* 284 * calculate the expiry time for the next timer wheel 285 * timer 286 */ 287 expires = ktime_add_ns(last_update, tick_period.tv64 * 288 delta_jiffies); 289 290 /* 291 * If this cpu is the one which updates jiffies, then 292 * give up the assignment and let it be taken by the 293 * cpu which runs the tick timer next, which might be 294 * this cpu as well. If we don't drop this here the 295 * jiffies might be stale and do_timer() never 296 * invoked. 297 */ 298 if (cpu == tick_do_timer_cpu) 299 tick_do_timer_cpu = TICK_DO_TIMER_NONE; 300 301 if (delta_jiffies > 1) 302 cpumask_set_cpu(cpu, nohz_cpu_mask); 303 304 /* Skip reprogram of event if its not changed */ 305 if (ts->tick_stopped && ktime_equal(expires, dev->next_event)) 306 goto out; 307 308 /* 309 * nohz_stop_sched_tick can be called several times before 310 * the nohz_restart_sched_tick is called. This happens when 311 * interrupts arrive which do not cause a reschedule. In the 312 * first call we save the current tick time, so we can restart 313 * the scheduler tick in nohz_restart_sched_tick. 314 */ 315 if (!ts->tick_stopped) { 316 if (select_nohz_load_balancer(1)) { 317 /* 318 * sched tick not stopped! 319 */ 320 cpumask_clear_cpu(cpu, nohz_cpu_mask); 321 goto out; 322 } 323 324 ts->idle_tick = hrtimer_get_expires(&ts->sched_timer); 325 ts->tick_stopped = 1; 326 ts->idle_jiffies = last_jiffies; 327 rcu_enter_nohz(); 328 } 329 330 ts->idle_sleeps++; 331 332 /* 333 * delta_jiffies >= NEXT_TIMER_MAX_DELTA signals that 334 * there is no timer pending or at least extremly far 335 * into the future (12 days for HZ=1000). In this case 336 * we simply stop the tick timer: 337 */ 338 if (unlikely(delta_jiffies >= NEXT_TIMER_MAX_DELTA)) { 339 ts->idle_expires.tv64 = KTIME_MAX; 340 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) 341 hrtimer_cancel(&ts->sched_timer); 342 goto out; 343 } 344 345 /* Mark expiries */ 346 ts->idle_expires = expires; 347 348 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { 349 hrtimer_start(&ts->sched_timer, expires, 350 HRTIMER_MODE_ABS_PINNED); 351 /* Check, if the timer was already in the past */ 352 if (hrtimer_active(&ts->sched_timer)) 353 goto out; 354 } else if (!tick_program_event(expires, 0)) 355 goto out; 356 /* 357 * We are past the event already. So we crossed a 358 * jiffie boundary. Update jiffies and raise the 359 * softirq. 360 */ 361 tick_do_update_jiffies64(ktime_get()); 362 cpumask_clear_cpu(cpu, nohz_cpu_mask); 363 } 364 raise_softirq_irqoff(TIMER_SOFTIRQ); 365 out: 366 ts->next_jiffies = next_jiffies; 367 ts->last_jiffies = last_jiffies; 368 ts->sleep_length = ktime_sub(dev->next_event, now); 369 end: 370 local_irq_restore(flags); 371 } 372 373 /** 374 * tick_nohz_get_sleep_length - return the length of the current sleep 375 * 376 * Called from power state control code with interrupts disabled 377 */ 378 ktime_t tick_nohz_get_sleep_length(void) 379 { 380 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 381 382 return ts->sleep_length; 383 } 384 385 static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) 386 { 387 hrtimer_cancel(&ts->sched_timer); 388 hrtimer_set_expires(&ts->sched_timer, ts->idle_tick); 389 390 while (1) { 391 /* Forward the time to expire in the future */ 392 hrtimer_forward(&ts->sched_timer, now, tick_period); 393 394 if (ts->nohz_mode == NOHZ_MODE_HIGHRES) { 395 hrtimer_start_expires(&ts->sched_timer, 396 HRTIMER_MODE_ABS_PINNED); 397 /* Check, if the timer was already in the past */ 398 if (hrtimer_active(&ts->sched_timer)) 399 break; 400 } else { 401 if (!tick_program_event( 402 hrtimer_get_expires(&ts->sched_timer), 0)) 403 break; 404 } 405 /* Update jiffies and reread time */ 406 tick_do_update_jiffies64(now); 407 now = ktime_get(); 408 } 409 } 410 411 /** 412 * tick_nohz_restart_sched_tick - restart the idle tick from the idle task 413 * 414 * Restart the idle tick when the CPU is woken up from idle 415 */ 416 void tick_nohz_restart_sched_tick(void) 417 { 418 int cpu = smp_processor_id(); 419 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 420 #ifndef CONFIG_VIRT_CPU_ACCOUNTING 421 unsigned long ticks; 422 #endif 423 ktime_t now; 424 425 local_irq_disable(); 426 if (ts->idle_active || (ts->inidle && ts->tick_stopped)) 427 now = ktime_get(); 428 429 if (ts->idle_active) 430 tick_nohz_stop_idle(cpu, now); 431 432 if (!ts->inidle || !ts->tick_stopped) { 433 ts->inidle = 0; 434 local_irq_enable(); 435 return; 436 } 437 438 ts->inidle = 0; 439 440 rcu_exit_nohz(); 441 442 /* Update jiffies first */ 443 select_nohz_load_balancer(0); 444 tick_do_update_jiffies64(now); 445 cpumask_clear_cpu(cpu, nohz_cpu_mask); 446 447 #ifndef CONFIG_VIRT_CPU_ACCOUNTING 448 /* 449 * We stopped the tick in idle. Update process times would miss the 450 * time we slept as update_process_times does only a 1 tick 451 * accounting. Enforce that this is accounted to idle ! 452 */ 453 ticks = jiffies - ts->idle_jiffies; 454 /* 455 * We might be one off. Do not randomly account a huge number of ticks! 456 */ 457 if (ticks && ticks < LONG_MAX) 458 account_idle_ticks(ticks); 459 #endif 460 461 touch_softlockup_watchdog(); 462 /* 463 * Cancel the scheduled timer and restore the tick 464 */ 465 ts->tick_stopped = 0; 466 ts->idle_exittime = now; 467 468 tick_nohz_restart(ts, now); 469 470 local_irq_enable(); 471 } 472 473 static int tick_nohz_reprogram(struct tick_sched *ts, ktime_t now) 474 { 475 hrtimer_forward(&ts->sched_timer, now, tick_period); 476 return tick_program_event(hrtimer_get_expires(&ts->sched_timer), 0); 477 } 478 479 /* 480 * The nohz low res interrupt handler 481 */ 482 static void tick_nohz_handler(struct clock_event_device *dev) 483 { 484 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 485 struct pt_regs *regs = get_irq_regs(); 486 int cpu = smp_processor_id(); 487 ktime_t now = ktime_get(); 488 489 dev->next_event.tv64 = KTIME_MAX; 490 491 /* 492 * Check if the do_timer duty was dropped. We don't care about 493 * concurrency: This happens only when the cpu in charge went 494 * into a long sleep. If two cpus happen to assign themself to 495 * this duty, then the jiffies update is still serialized by 496 * xtime_lock. 497 */ 498 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) 499 tick_do_timer_cpu = cpu; 500 501 /* Check, if the jiffies need an update */ 502 if (tick_do_timer_cpu == cpu) 503 tick_do_update_jiffies64(now); 504 505 /* 506 * When we are idle and the tick is stopped, we have to touch 507 * the watchdog as we might not schedule for a really long 508 * time. This happens on complete idle SMP systems while 509 * waiting on the login prompt. We also increment the "start 510 * of idle" jiffy stamp so the idle accounting adjustment we 511 * do when we go busy again does not account too much ticks. 512 */ 513 if (ts->tick_stopped) { 514 touch_softlockup_watchdog(); 515 ts->idle_jiffies++; 516 } 517 518 update_process_times(user_mode(regs)); 519 profile_tick(CPU_PROFILING); 520 521 while (tick_nohz_reprogram(ts, now)) { 522 now = ktime_get(); 523 tick_do_update_jiffies64(now); 524 } 525 } 526 527 /** 528 * tick_nohz_switch_to_nohz - switch to nohz mode 529 */ 530 static void tick_nohz_switch_to_nohz(void) 531 { 532 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 533 ktime_t next; 534 535 if (!tick_nohz_enabled) 536 return; 537 538 local_irq_disable(); 539 if (tick_switch_to_oneshot(tick_nohz_handler)) { 540 local_irq_enable(); 541 return; 542 } 543 544 ts->nohz_mode = NOHZ_MODE_LOWRES; 545 546 /* 547 * Recycle the hrtimer in ts, so we can share the 548 * hrtimer_forward with the highres code. 549 */ 550 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 551 /* Get the next period */ 552 next = tick_init_jiffy_update(); 553 554 for (;;) { 555 hrtimer_set_expires(&ts->sched_timer, next); 556 if (!tick_program_event(next, 0)) 557 break; 558 next = ktime_add(next, tick_period); 559 } 560 local_irq_enable(); 561 562 printk(KERN_INFO "Switched to NOHz mode on CPU #%d\n", 563 smp_processor_id()); 564 } 565 566 /* 567 * When NOHZ is enabled and the tick is stopped, we need to kick the 568 * tick timer from irq_enter() so that the jiffies update is kept 569 * alive during long running softirqs. That's ugly as hell, but 570 * correctness is key even if we need to fix the offending softirq in 571 * the first place. 572 * 573 * Note, this is different to tick_nohz_restart. We just kick the 574 * timer and do not touch the other magic bits which need to be done 575 * when idle is left. 576 */ 577 static void tick_nohz_kick_tick(int cpu, ktime_t now) 578 { 579 #if 0 580 /* Switch back to 2.6.27 behaviour */ 581 582 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 583 ktime_t delta; 584 585 /* 586 * Do not touch the tick device, when the next expiry is either 587 * already reached or less/equal than the tick period. 588 */ 589 delta = ktime_sub(hrtimer_get_expires(&ts->sched_timer), now); 590 if (delta.tv64 <= tick_period.tv64) 591 return; 592 593 tick_nohz_restart(ts, now); 594 #endif 595 } 596 597 static inline void tick_check_nohz(int cpu) 598 { 599 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 600 ktime_t now; 601 602 if (!ts->idle_active && !ts->tick_stopped) 603 return; 604 now = ktime_get(); 605 if (ts->idle_active) 606 tick_nohz_stop_idle(cpu, now); 607 if (ts->tick_stopped) { 608 tick_nohz_update_jiffies(now); 609 tick_nohz_kick_tick(cpu, now); 610 } 611 } 612 613 #else 614 615 static inline void tick_nohz_switch_to_nohz(void) { } 616 static inline void tick_check_nohz(int cpu) { } 617 618 #endif /* NO_HZ */ 619 620 /* 621 * Called from irq_enter to notify about the possible interruption of idle() 622 */ 623 void tick_check_idle(int cpu) 624 { 625 tick_check_oneshot_broadcast(cpu); 626 tick_check_nohz(cpu); 627 } 628 629 /* 630 * High resolution timer specific code 631 */ 632 #ifdef CONFIG_HIGH_RES_TIMERS 633 /* 634 * We rearm the timer until we get disabled by the idle code. 635 * Called with interrupts disabled and timer->base->cpu_base->lock held. 636 */ 637 static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) 638 { 639 struct tick_sched *ts = 640 container_of(timer, struct tick_sched, sched_timer); 641 struct pt_regs *regs = get_irq_regs(); 642 ktime_t now = ktime_get(); 643 int cpu = smp_processor_id(); 644 645 #ifdef CONFIG_NO_HZ 646 /* 647 * Check if the do_timer duty was dropped. We don't care about 648 * concurrency: This happens only when the cpu in charge went 649 * into a long sleep. If two cpus happen to assign themself to 650 * this duty, then the jiffies update is still serialized by 651 * xtime_lock. 652 */ 653 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE)) 654 tick_do_timer_cpu = cpu; 655 #endif 656 657 /* Check, if the jiffies need an update */ 658 if (tick_do_timer_cpu == cpu) 659 tick_do_update_jiffies64(now); 660 661 /* 662 * Do not call, when we are not in irq context and have 663 * no valid regs pointer 664 */ 665 if (regs) { 666 /* 667 * When we are idle and the tick is stopped, we have to touch 668 * the watchdog as we might not schedule for a really long 669 * time. This happens on complete idle SMP systems while 670 * waiting on the login prompt. We also increment the "start of 671 * idle" jiffy stamp so the idle accounting adjustment we do 672 * when we go busy again does not account too much ticks. 673 */ 674 if (ts->tick_stopped) { 675 touch_softlockup_watchdog(); 676 ts->idle_jiffies++; 677 } 678 update_process_times(user_mode(regs)); 679 profile_tick(CPU_PROFILING); 680 } 681 682 hrtimer_forward(timer, now, tick_period); 683 684 return HRTIMER_RESTART; 685 } 686 687 /** 688 * tick_setup_sched_timer - setup the tick emulation timer 689 */ 690 void tick_setup_sched_timer(void) 691 { 692 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 693 ktime_t now = ktime_get(); 694 u64 offset; 695 696 /* 697 * Emulate tick processing via per-CPU hrtimers: 698 */ 699 hrtimer_init(&ts->sched_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 700 ts->sched_timer.function = tick_sched_timer; 701 702 /* Get the next period (per cpu) */ 703 hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update()); 704 offset = ktime_to_ns(tick_period) >> 1; 705 do_div(offset, num_possible_cpus()); 706 offset *= smp_processor_id(); 707 hrtimer_add_expires_ns(&ts->sched_timer, offset); 708 709 for (;;) { 710 hrtimer_forward(&ts->sched_timer, now, tick_period); 711 hrtimer_start_expires(&ts->sched_timer, 712 HRTIMER_MODE_ABS_PINNED); 713 /* Check, if the timer was already in the past */ 714 if (hrtimer_active(&ts->sched_timer)) 715 break; 716 now = ktime_get(); 717 } 718 719 #ifdef CONFIG_NO_HZ 720 if (tick_nohz_enabled) 721 ts->nohz_mode = NOHZ_MODE_HIGHRES; 722 #endif 723 } 724 #endif /* HIGH_RES_TIMERS */ 725 726 #if defined CONFIG_NO_HZ || defined CONFIG_HIGH_RES_TIMERS 727 void tick_cancel_sched_timer(int cpu) 728 { 729 struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu); 730 731 # ifdef CONFIG_HIGH_RES_TIMERS 732 if (ts->sched_timer.base) 733 hrtimer_cancel(&ts->sched_timer); 734 # endif 735 736 ts->nohz_mode = NOHZ_MODE_INACTIVE; 737 } 738 #endif 739 740 /** 741 * Async notification about clocksource changes 742 */ 743 void tick_clock_notify(void) 744 { 745 int cpu; 746 747 for_each_possible_cpu(cpu) 748 set_bit(0, &per_cpu(tick_cpu_sched, cpu).check_clocks); 749 } 750 751 /* 752 * Async notification about clock event changes 753 */ 754 void tick_oneshot_notify(void) 755 { 756 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 757 758 set_bit(0, &ts->check_clocks); 759 } 760 761 /** 762 * Check, if a change happened, which makes oneshot possible. 763 * 764 * Called cyclic from the hrtimer softirq (driven by the timer 765 * softirq) allow_nohz signals, that we can switch into low-res nohz 766 * mode, because high resolution timers are disabled (either compile 767 * or runtime). 768 */ 769 int tick_check_oneshot_change(int allow_nohz) 770 { 771 struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); 772 773 if (!test_and_clear_bit(0, &ts->check_clocks)) 774 return 0; 775 776 if (ts->nohz_mode != NOHZ_MODE_INACTIVE) 777 return 0; 778 779 if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available()) 780 return 0; 781 782 if (!allow_nohz) 783 return 1; 784 785 tick_nohz_switch_to_nohz(); 786 return 0; 787 } 788