Commit aec6487e authored by Ingo Molnar's avatar Ingo Molnar
Browse files

x86/Kconfig: Further simplify the NR_CPUS config 



Clean up various aspects of the x86 CONFIG_NR_CPUS configuration switches:

- Rename the three CONFIG_NR_CPUS related variables to create a common
  namespace for them:

    RANGE_BEGIN_CPUS => NR_CPUS_RANGE_BEGIN
    RANGE_END_CPUS   => NR_CPUS_RANGE_END
    DEF_CONFIG_CPUS  => NR_CPUS_DEFAULT

- Align them vertically, such as:

    config NR_CPUS_RANGE_END
            int
            depends on X86_64
            default 8192 if  SMP && ( MAXSMP ||  CPUMASK_OFFSTACK)
            default  512 if  SMP && (!MAXSMP && !CPUMASK_OFFSTACK)
            default    1 if !SMP

- Update help text, add more comments.

Test results:

 # i386 allnoconfig:
 CONFIG_NR_CPUS_RANGE_BEGIN=1
 CONFIG_NR_CPUS_RANGE_END=1
 CONFIG_NR_CPUS_DEFAULT=1
 CONFIG_NR_CPUS=1

 # i386 defconfig:
 CONFIG_NR_CPUS_RANGE_BEGIN=2
 CONFIG_NR_CPUS_RANGE_END=8
 CONFIG_NR_CPUS_DEFAULT=8
 CONFIG_NR_CPUS=8

 # i386 allyesconfig:
 CONFIG_NR_CPUS_RANGE_BEGIN=2
 CONFIG_NR_CPUS_RANGE_END=64
 CONFIG_NR_CPUS_DEFAULT=32
 CONFIG_NR_CPUS=32

 # x86_64 allnoconfig:
 CONFIG_NR_CPUS_RANGE_BEGIN=1
 CONFIG_NR_CPUS_RANGE_END=1
 CONFIG_NR_CPUS_DEFAULT=1
 CONFIG_NR_CPUS=1

 # x86_64 defconfig:
 CONFIG_NR_CPUS_RANGE_BEGIN=2
 CONFIG_NR_CPUS_RANGE_END=512
 CONFIG_NR_CPUS_DEFAULT=64
 CONFIG_NR_CPUS=64

 # x86_64 allyesconfig:
 CONFIG_NR_CPUS_RANGE_BEGIN=8192
 CONFIG_NR_CPUS_RANGE_END=8192
 CONFIG_NR_CPUS_DEFAULT=8192
 CONFIG_NR_CPUS=8192

Acked-by: default avatarRandy Dunlap <rdunlap@infradead.org>
Acked-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180210113629.jcv6su3r4suuno63@gmail.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent a0d0bb4d

arch/x86/Kconfig

+40 −26
Original line number Diff line number Diff line
@@ -949,52 +949,66 @@ config MAXSMP 
	  Enable maximum number of CPUS and NUMA Nodes for this architecture.

	  If unsure, say N.



config RANGE_END_CPUS

#

# The maximum number of CPUs supported:

#

# The main config value is NR_CPUS, which defaults to NR_CPUS_DEFAULT,

# and which can be configured interactively in the

# [NR_CPUS_RANGE_BEGIN ... NR_CPUS_RANGE_END] range.

#

# The ranges are different on 32-bit and 64-bit kernels, depending on

# hardware capabilities and scalability features of the kernel.

#

# ( If MAXSMP is enabled we just use the highest possible value and disable

#   interactive configuration. )

#



config NR_CPUS_RANGE_BEGIN

	int

	default NR_CPUS_RANGE_END if MAXSMP

	default    1 if !SMP

	default    2



config NR_CPUS_RANGE_END

	int

	depends on X86_32

	default 8 if SMP && !X86_BIGSMP

	default   64 if  SMP &&  X86_BIGSMP

	default    8 if  SMP && !X86_BIGSMP

	default    1 if !SMP



config RANGE_END_CPUS

config NR_CPUS_RANGE_END

	int

	depends on X86_64

	default 512 if SMP && !MAXSMP && !CPUMASK_OFFSTACK

	default 8192 if  SMP && ( MAXSMP ||  CPUMASK_OFFSTACK)

	default  512 if  SMP && (!MAXSMP && !CPUMASK_OFFSTACK)

	default    1 if !SMP



config RANGE_BEGIN_CPUS

	int

	default 1 if !SMP

	default RANGE_END_CPUS if MAXSMP

	default 2



config DEF_CONFIG_CPUS

config NR_CPUS_DEFAULT

	int

	depends on X86_32

	default 1 if !SMP

	default   32 if  X86_BIGSMP

	default    8 if  SMP

	default    1 if !SMP



config DEF_CONFIG_CPUS

config NR_CPUS_DEFAULT

	int

	depends on X86_64

	default 1 if !SMP

	default 8192 if  MAXSMP

	default   64 if  SMP

	default    1 if !SMP



config NR_CPUS

	int "Maximum number of CPUs" if SMP && !MAXSMP

	range RANGE_BEGIN_CPUS RANGE_END_CPUS

	default DEF_CONFIG_CPUS

	range NR_CPUS_RANGE_BEGIN NR_CPUS_RANGE_END

	default NR_CPUS_DEFAULT

	---help---

	  This allows you to specify the maximum number of CPUs which this

	  kernel will support.  If CPUMASK_OFFSTACK is enabled, the maximum

	  supported value is 8192, otherwise the maximum value is 512.  The

	  minimum value which makes sense is 2.



	  This is purely to save memory - each supported CPU adds

	  approximately eight kilobytes to the kernel image.

	  This is purely to save memory: each supported CPU adds about 8KB

	  to the kernel image.



config SCHED_SMT

	bool "SMT (Hyperthreading) scheduler support"

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