Format:
<first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
- cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
- CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
- Some features depend on CPU0. Known dependencies are:
- 1. Resume from suspend/hibernate depends on CPU0.
- Suspend/hibernate will fail if CPU0 is offline and you
- need to online CPU0 before suspend/hibernate.
- 2. PIC interrupts also depend on CPU0. CPU0 can't be
- removed if a PIC interrupt is detected.
- It's said poweroff/reboot may depend on CPU0 on some
- machines although I haven't seen such issues so far
- after CPU0 is offline on a few tested machines.
- If the dependencies are under your control, you can
- turn on cpu0_hotplug.
-
cpuidle.off=1 [CPU_IDLE]
disable the cpuidle sub-system
$ echo 1 > /sys/devices/system/cpu/cpu4/online
smpboot: Booting Node 0 Processor 4 APIC 0x1
-The CPU is usable again. This should work on all CPUs. CPU0 is often special
-and excluded from CPU hotplug. On X86 the kernel option
-*CONFIG_BOOTPARAM_HOTPLUG_CPU0* has to be enabled in order to be able to
-shutdown CPU0. Alternatively the kernel command option *cpu0_hotplug* can be
-used. Some known dependencies of CPU0:
-
-* Resume from hibernate/suspend. Hibernate/suspend will fail if CPU0 is offline.
-* PIC interrupts. CPU0 can't be removed if a PIC interrupt is detected.
-
-Please let Fenghua Yu <fenghua.yu@intel.com> know if you find any dependencies
-on CPU0.
+The CPU is usable again. This should work on all CPUs, but CPU0 is often special
+and excluded from CPU hotplug.
The CPU hotplug coordination
============================
def_bool y
depends on SMP
-config BOOTPARAM_HOTPLUG_CPU0
- bool "Set default setting of cpu0_hotpluggable"
- depends on HOTPLUG_CPU
- help
- Set whether default state of cpu0_hotpluggable is on or off.
-
- Say Y here to enable CPU0 hotplug by default. If this switch
- is turned on, there is no need to give cpu0_hotplug kernel
- parameter and the CPU0 hotplug feature is enabled by default.
-
- Please note: there are two known CPU0 dependencies if you want
- to enable the CPU0 hotplug feature either by this switch or by
- cpu0_hotplug kernel parameter.
-
- First, resume from hibernate or suspend always starts from CPU0.
- So hibernate and suspend are prevented if CPU0 is offline.
-
- Second dependency is PIC interrupts always go to CPU0. CPU0 can not
- offline if any interrupt can not migrate out of CPU0. There may
- be other CPU0 dependencies.
-
- Please make sure the dependencies are under your control before
- you enable this feature.
-
- Say N if you don't want to enable CPU0 hotplug feature by default.
- You still can enable the CPU0 hotplug feature at boot by kernel
- parameter cpu0_hotplug.
-
-config DEBUG_HOTPLUG_CPU0
- def_bool n
- prompt "Debug CPU0 hotplug"
- depends on HOTPLUG_CPU
- help
- Enabling this option offlines CPU0 (if CPU0 can be offlined) as
- soon as possible and boots up userspace with CPU0 offlined. User
- can online CPU0 back after boot time.
-
- To debug CPU0 hotplug, you need to enable CPU0 offline/online
- feature by either turning on CONFIG_BOOTPARAM_HOTPLUG_CPU0 during
- compilation or giving cpu0_hotplug kernel parameter at boot.
-
- If unsure, say N.
-
config COMPAT_VDSO
def_bool n
prompt "Disable the 32-bit vDSO (needed for glibc 2.3.3)"
extern int arch_register_cpu(int num);
extern void arch_unregister_cpu(int);
extern void soft_restart_cpu(void);
-#ifdef CONFIG_DEBUG_HOTPLUG_CPU0
-extern int _debug_hotplug_cpu(int cpu, int action);
-#endif
#endif
extern void ap_init_aperfmperf(void);
static DEFINE_PER_CPU(struct x86_cpu, cpu_devices);
#ifdef CONFIG_HOTPLUG_CPU
-
-#ifdef CONFIG_BOOTPARAM_HOTPLUG_CPU0
-static int cpu0_hotpluggable = 1;
-#else
-static int cpu0_hotpluggable;
-static int __init enable_cpu0_hotplug(char *str)
-{
- cpu0_hotpluggable = 1;
- return 1;
-}
-
-__setup("cpu0_hotplug", enable_cpu0_hotplug);
-#endif
-
-#ifdef CONFIG_DEBUG_HOTPLUG_CPU0
-/*
- * This function offlines a CPU as early as possible and allows userspace to
- * boot up without the CPU. The CPU can be onlined back by user after boot.
- *
- * This is only called for debugging CPU offline/online feature.
- */
-int _debug_hotplug_cpu(int cpu, int action)
+int arch_register_cpu(int cpu)
{
- int ret;
-
- if (!cpu_is_hotpluggable(cpu))
- return -EINVAL;
+ struct x86_cpu *xc = per_cpu_ptr(&cpu_devices, cpu);
- switch (action) {
- case 0:
- ret = remove_cpu(cpu);
- if (!ret)
- pr_info("DEBUG_HOTPLUG_CPU0: CPU %u is now offline\n", cpu);
- else
- pr_debug("Can't offline CPU%d.\n", cpu);
- break;
- case 1:
- ret = add_cpu(cpu);
- if (ret)
- pr_debug("Can't online CPU%d.\n", cpu);
-
- break;
- default:
- ret = -EINVAL;
- }
-
- return ret;
-}
-
-static int __init debug_hotplug_cpu(void)
-{
- _debug_hotplug_cpu(0, 0);
- return 0;
-}
-
-late_initcall_sync(debug_hotplug_cpu);
-#endif /* CONFIG_DEBUG_HOTPLUG_CPU0 */
-
-int arch_register_cpu(int num)
-{
- struct cpuinfo_x86 *c = &cpu_data(num);
-
- /*
- * Currently CPU0 is only hotpluggable on Intel platforms. Other
- * vendors can add hotplug support later.
- * Xen PV guests don't support CPU0 hotplug at all.
- */
- if (c->x86_vendor != X86_VENDOR_INTEL ||
- cpu_feature_enabled(X86_FEATURE_XENPV))
- cpu0_hotpluggable = 0;
-
- /*
- * Two known BSP/CPU0 dependencies: Resume from suspend/hibernate
- * depends on BSP. PIC interrupts depend on BSP.
- *
- * If the BSP dependencies are under control, one can tell kernel to
- * enable BSP hotplug. This basically adds a control file and
- * one can attempt to offline BSP.
- */
- if (num == 0 && cpu0_hotpluggable) {
- unsigned int irq;
- /*
- * We won't take down the boot processor on i386 if some
- * interrupts only are able to be serviced by the BSP in PIC.
- */
- for_each_active_irq(irq) {
- if (!IO_APIC_IRQ(irq) && irq_has_action(irq)) {
- cpu0_hotpluggable = 0;
- break;
- }
- }
- }
- if (num || cpu0_hotpluggable)
- per_cpu(cpu_devices, num).cpu.hotpluggable = 1;
-
- return register_cpu(&per_cpu(cpu_devices, num).cpu, num);
+ xc->cpu.hotpluggable = cpu > 0;
+ return register_cpu(&xc->cpu, cpu);
}
EXPORT_SYMBOL(arch_register_cpu);
case PM_HIBERNATION_PREPARE:
ret = bsp_check();
break;
-#ifdef CONFIG_DEBUG_HOTPLUG_CPU0
- case PM_RESTORE_PREPARE:
- /*
- * When system resumes from hibernation, online CPU0 because
- * 1. it's required for resume and
- * 2. the CPU was online before hibernation
- */
- if (!cpu_online(0))
- _debug_hotplug_cpu(0, 1);
- break;
- case PM_POST_RESTORE:
- /*
- * When a resume really happens, this code won't be called.
- *
- * This code is called only when user space hibernation software
- * prepares for snapshot device during boot time. So we just
- * call _debug_hotplug_cpu() to restore to CPU0's state prior to
- * preparing the snapshot device.
- *
- * This works for normal boot case in our CPU0 hotplug debug
- * mode, i.e. CPU0 is offline and user mode hibernation
- * software initializes during boot time.
- *
- * If CPU0 is online and user application accesses snapshot
- * device after boot time, this will offline CPU0 and user may
- * see different CPU0 state before and after accessing
- * the snapshot device. But hopefully this is not a case when
- * user debugging CPU0 hotplug. Even if users hit this case,
- * they can easily online CPU0 back.
- *
- * To simplify this debug code, we only consider normal boot
- * case. Otherwise we need to remember CPU0's state and restore
- * to that state and resolve racy conditions etc.
- */
- _debug_hotplug_cpu(0, 0);
- break;
-#endif
default:
break;
}
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