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Done either at bootup or dynamically: arch/x86/kernel/process.c: 577 static int __init idle_setup(char *str) 578 { 579 if (!str) 580 return -EINVAL; 581 582 if (!strcmp(str, "poll")) { 583 printk("using polling idle threads.\n"); 584 pm_idle = poll_idle; 585 } else if (!strcmp(str, "mwait")) 586 force_mwait = 1; 587 else if (!strcmp(str, "halt")) { 588 /* 589 * When the boot option of idle=halt is added, halt is 590 * forced to be used for CPU idle. In such case CPU C2/C3 591 * won't be used again. 592 * To continue to load the CPU idle driver, don't touch 593 * the boot_option_idle_override. 594 */ 595 pm_idle = default_idle; 596 idle_halt = 1; 597 return 0; 598 } else if (!strcmp(str, "nomwait")) { 599 /* 600 * If the boot option of "idle=nomwait" is added, 601 * it means that mwait will be disabled for CPU C2/C3 602 * states. In such case it won't touch the variable 603 * of boot_option_idle_override. 604 */ 605 idle_nomwait = 1; 606 return 0; 607 } else 608 return -1; 609 610 boot_option_idle_override = 1; 611 return 0; 612 } 613 early_param("idle", idle_setup); 544 void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c) 545 { 546 #ifdef CONFIG_SMP 547 if (pm_idle == poll_idle && smp_num_siblings > 1) { 548 printk(KERN_WARNING "WARNING: polling idle and HT enabled," 549 " performance may degrade.\n"); 550 } 551 #endif 552 if (pm_idle) 553 return; 554 555 if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) { 556 /* 557 * One CPU supports mwait => All CPUs supports mwait 558 */ 559 printk(KERN_INFO "using mwait in idle threads.\n"); 560 pm_idle = mwait_idle; 561 } else if (check_c1e_idle(c)) { 562 printk(KERN_INFO "using C1E aware idle routine\n"); 563 pm_idle = c1e_idle; 564 } else 565 pm_idle = default_idle; 566 } 567 |
