Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 4d25031a authored by Fenghua Yu's avatar Fenghua Yu Committed by H. Peter Anvin
Browse files

x86, topology: Don't offline CPU0 if any PIC irq can not be migrated out of it 



If CONFIG_BOOTPARAM_HOTPLUG_CPU is turned on, CPU0 hotplug feature is enabled
by default.

If CONFIG_BOOTPARAM_HOTPLUG_CPU is not turned on, CPU0 hotplug feature is not
enabled by default. The kernel parameter cpu0_hotplug can enable CPU0 hotplug
feature at boot.

Currently the feature is supported on Intel platforms only.

Signed-off-by: default avatarFenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1352835171-3958-4-git-send-email-fenghua.yu@intel.com


Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 80aa1dff

arch/x86/kernel/topology.c

+43 −7
Original line number Diff line number Diff line
@@ -30,23 +30,59 @@ 
#include <linux/mmzone.h>

#include <linux/init.h>

#include <linux/smp.h>

#include <linux/irq.h>

#include <asm/cpu.h>



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



int __ref arch_register_cpu(int num)

{

	struct cpuinfo_x86 *c = &cpu_data(num);



	/*

	 * CPU0 cannot be offlined due to several

	 * restrictions and assumptions in kernel. This basically

	 * doesn't add a control file, one cannot attempt to offline

	 * BSP.

	 * Currently CPU0 is only hotpluggable on Intel platforms. Other

	 * vendors can add hotplug support later.

	 */

	if (c->x86_vendor != X86_VENDOR_INTEL)

		cpu0_hotpluggable = 0;



	/*

	 * Two known BSP/CPU0 dependencies: Resume from suspend/hibernate

	 * depends on BSP. PIC interrupts depend on BSP.

	 *

	 * Also certain PCI quirks require not to enable hotplug control

	 * for all CPU's.

	 * If the BSP depencies 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.

		 */

	if (num)

		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);