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Commit 74b84233 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'x86-bsp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull x86 BSP hotplug changes from Ingo Molnar:
 "This tree enables CPU#0 (the boot processor) to be onlined/offlined on
  x86, just like any other CPU.  Enabled on Intel CPUs for now.

  Allowing this required the identification and fixing of latent CPU#0
  assumptions (such as CPU#0 initializations, etc.) in the x86
  architecture code, plus the identification of barriers to
  BSP-offlining, such as active PIC interrupts which can only be
  serviced on the BSP.

  It's behind a default-off option, and there's a debug option that
  allows the automatic testing of this feature.

  The motivation of this feature is to allow and prepare for true
  CPU-hotplug hardware support: recent changes to MCE support enable us
  to detect a deteriorating but not yet hard-failing L1/L2 cache on a
  CPU that could be soft-unplugged - or a failing L3 cache on a
  multi-socket system.

  Note that true hardware hot-plug is not yet fully enabled by this,
  because that requires a special platform wakeup sequence to be sent to
  the freshly powered up CPU#0.  Future patches for this are planned,
  once such a platform exists.  Chicken and egg"

* 'x86-bsp-hotplug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86, topology: Debug CPU0 hotplug
  x86/i387.c: Initialize thread xstate only on CPU0 only once
  x86, hotplug: Handle retrigger irq by the first available CPU
  x86, hotplug: The first online processor saves the MTRR state
  x86, hotplug: During CPU0 online, enable x2apic, set_numa_node.
  x86, hotplug: Wake up CPU0 via NMI instead of INIT, SIPI, SIPI
  x86-32, hotplug: Add start_cpu0() entry point to head_32.S
  x86-64, hotplug: Add start_cpu0() entry point to head_64.S
  kernel/cpu.c: Add comment for priority in cpu_hotplug_pm_callback
  x86, hotplug, suspend: Online CPU0 for suspend or hibernate
  x86, hotplug: Support functions for CPU0 online/offline
  x86, topology: Don't offline CPU0 if any PIC irq can not be migrated out of it
  x86, Kconfig: Add config switch for CPU0 hotplug
  doc: Add x86 CPU0 online/offline feature
parents 50744747 a71c8bc5

Documentation/cpu-hotplug.txt

+24 −0
Original line number Diff line number Diff line
@@ -207,6 +207,30 @@ by making it not-removable. 


In such cases you will also notice that the online file is missing under cpu0.



Q: Is CPU0 removable on X86?

A: Yes. If kernel is compiled with CONFIG_BOOTPARAM_HOTPLUG_CPU0=y, CPU0 is

removable by default. Otherwise, CPU0 is also removable by kernel option

cpu0_hotplug.



But some features depend on CPU0. Two known dependencies are:



1. Resume from hibernate/suspend depends on CPU0. Hibernate/suspend will fail if

CPU0 is offline and you need to online CPU0 before hibernate/suspend can

continue.

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 any poweroff/reboot failure so far after CPU0 is offline on a few tested

machines.



Please let me know if you know or see any other dependencies of CPU0.



If the dependencies are under your control, you can turn on CPU0 hotplug feature

either by CONFIG_BOOTPARAM_HOTPLUG_CPU0 or by kernel parameter cpu0_hotplug.



--Fenghua Yu <fenghua.yu@intel.com>



Q: How do i find out if a particular CPU is not removable?

A: Depending on the implementation, some architectures may show this by the

absence of the "online" file. This is done if it can be determined ahead of

Documentation/kernel-parameters.txt

+14 −0
Original line number Diff line number Diff line
@@ -1984,6 +1984,20 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 


	nox2apic	[X86-64,APIC] Do not enable x2APIC mode.



	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.



	nptcg=		[IA-64] Override max number of concurrent global TLB

			purges which is reported from either PAL_VM_SUMMARY or

			SAL PALO.

arch/x86/Kconfig

+44 −0
Original line number Diff line number Diff line
@@ -1698,6 +1698,50 @@ config HOTPLUG_CPU 
	    automatically on SMP systems. )

	  Say N if you want to disable CPU hotplug.



config BOOTPARAM_HOTPLUG_CPU0

	bool "Set default setting of cpu0_hotpluggable"

	default n

	depends on HOTPLUG_CPU && EXPERIMENTAL

	---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 && EXPERIMENTAL

	---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 y

	prompt "Compat VDSO support"

arch/x86/include/asm/cpu.h

+4 −0
Original line number Diff line number Diff line
@@ -28,6 +28,10 @@ struct x86_cpu { 
#ifdef CONFIG_HOTPLUG_CPU

extern int arch_register_cpu(int num);

extern void arch_unregister_cpu(int);

extern void __cpuinit start_cpu0(void);

#ifdef CONFIG_DEBUG_HOTPLUG_CPU0

extern int _debug_hotplug_cpu(int cpu, int action);

#endif

#endif



DECLARE_PER_CPU(int, cpu_state);

arch/x86/include/asm/smp.h

+1 −0
Original line number Diff line number Diff line
@@ -166,6 +166,7 @@ void native_send_call_func_ipi(const struct cpumask *mask); 
void native_send_call_func_single_ipi(int cpu);

void x86_idle_thread_init(unsigned int cpu, struct task_struct *idle);



void smp_store_boot_cpu_info(void);

void smp_store_cpu_info(int id);

#define cpu_physical_id(cpu)	per_cpu(x86_cpu_to_apicid, cpu)