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: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Linus 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: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 9d921b7..a528c14 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -949,52 +949,66 @@ config MAXSMP
          Enable maximum number of CPUS and NUMA Nodes for this architecture.
          If unsure, say N.
 
          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
        int

-       depends on X86_32
-       default 8 if SMP && !X86_BIGSMP
-       default 64 if SMP && X86_BIGSMP
-       default 1 if !SMP
+       default NR_CPUS_RANGE_END if MAXSMP
+       default    1 if !SMP
+       default    2

 
 

-config RANGE_END_CPUS
+config NR_CPUS_RANGE_END

        int
        int

-       depends on X86_64
-       default 512 if SMP && !MAXSMP && !CPUMASK_OFFSTACK
-       default 8192 if SMP && (MAXSMP || CPUMASK_OFFSTACK)
-       default 1 if !SMP
+       depends on X86_32
+       default   64 if  SMP &&  X86_BIGSMP
+       default    8 if  SMP && !X86_BIGSMP
+       default    1 if !SMP

 
 

-config RANGE_BEGIN_CPUS
+config NR_CPUS_RANGE_END

        int
        int

-       default 1 if !SMP
-       default RANGE_END_CPUS if MAXSMP
-       default 2
+       depends on X86_64
+       default 8192 if  SMP && ( MAXSMP ||  CPUMASK_OFFSTACK)
+       default  512 if  SMP && (!MAXSMP && !CPUMASK_OFFSTACK)
+       default    1 if !SMP

 
 

-config DEF_CONFIG_CPUS
+config NR_CPUS_DEFAULT

        int
        depends on X86_32
        int
        depends on X86_32

-       default 1 if !SMP
-       default 32 if X86_BIGSMP
-       default 8 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
        int
        depends on X86_64

-       default 1 if !SMP
-       default 8192 if MAXSMP
-       default 64 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
 
 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.
 
        ---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"
 
 config SCHED_SMT
        bool "SMT (Hyperthreading) scheduler support"