x86: allow number of additional hotplug CPUs to be set at compile time, V2 (7f2f49a5) · Commits · 戴 / test

x86: allow number of additional hotplug CPUs to be set at compile time, V2 The default number of additional CPU IDs for hotplugging is determined by asking ACPI or mptables how many "disabled" CPUs there are in the system, but many systems get this wrong so that e.g. a uniprocessor machine gets an extra CPU allocated and never switches to single CPU mode. And sometimes CPU hotplugging is enabled only for suspend/hibernate anyway, so the additional CPU IDs are not wanted. Allow the number to be set to zero at compile time. Also, force the number of extra CPUs to zero if hotplugging is disabled which allows removing some conditional code. Tested on uniprocessor x86_64 that ACPI claims has a disabled processor, with CPU hotplugging configured. ("After" has the number of additional CPUs set to 0) Before: NR_CPUS: 512, nr_cpu_ids: 2, nr_node_ids 1 After: NR_CPUS: 512, nr_cpu_ids: 1, nr_node_ids 1 [Changed the name of the option and the prompt according to Ingo's suggestion.] Signed-off-by:

Ingo Molnar <mingo@elte.hu>

arch/x86/Kconfig

+18 −0

Original line number	Diff line number	Diff line
		@@ -1438,6 +1438,24 @@ config HOTPLUG_CPU
		automatically on SMP systems. )
		Say N if you want to disable CPU hotplug.

		config HOTPLUG_RESTRICT_TO_BOOTUP_CPUS
		def_bool n
		prompt "Restrict CPU hotplugging to processors found during boot" if HOTPLUG_CPU
		---help---
		Say no here to use the default, which allows as many CPUs as are marked
		"disabled" by ACPI or MPTABLES to be hotplugged after bootup.

		Say yes if you do not want to allow CPUs to be added after booting, for
		example if you only need CPU hotplugging enabled for suspend/resume.

		If CPU_HOTPLUG is enabled this value may be overridden at boot time
		with the "additional_cpus" kernel parameter.

		config HOTPLUG_ADDITIONAL_CPUS
		int
		default 0 if !HOTPLUG_CPU \|\| HOTPLUG_RESTRICT_TO_BOOTUP_CPUS
		default -1

		config COMPAT_VDSO
		def_bool y
		prompt "Compat VDSO support"

arch/x86/kernel/smpboot.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -1261,7 +1261,7 @@ void __init native_smp_cpus_done(unsigned int max_cpus)
		check_nmi_watchdog();
		}

		static int additional_cpus __initdata = -1;
		static int additional_cpus __initdata = CONFIG_HOTPLUG_ADDITIONAL_CPUS;

		/*
		* cpu_possible_map should be static, it cannot change as cpu's

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