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SubjectRe: [PATCH 2/2] x86: Modify Kconfig to allow up to 4096 cpus
On Tue, Mar 25, 2008 at 06:41:39PM -0700, Mike Travis wrote:
> Increase the limit of NR_CPUS to 4096 and introduce a boolean
> called "MAXSMP" which when set (e.g. "allyesconfig"), will set
> NR_CPUS = 4096 and NODES_SHIFT = 9 (512).


I'm not really getting the point of MAXSMP - people should simply pick
their values, and when they want the maximum "(2-4096)" and "(1-15)"
already provide this information (except that your patch hides the
latter information from the user).

And with your patch, even with MAXSMP=y people could still set
NR_CPUS=7 and NODES_SHIFT=15 or whatever else they want...

More interesting would be why you want it to set NODES_SHIFT to
something less than the maximum value of 15. I'm getting the fact that
2^15 > 4096 and that 15 might be nonsensical high, but this sounds more
like requiring a patch to limit the range to 9?


>...
> --- linux.trees.git.orig/arch/x86/Kconfig
> +++ linux.trees.git/arch/x86/Kconfig
> @@ -522,16 +522,24 @@ config SWIOTLB
> access 32-bits of memory can be used on systems with more than
> 3 GB of memory. If unsure, say Y.
>
> +config MAXSMP
> + bool "Configure Maximum number of SMP Processors"
> + depends on X86_64 && SMP
> + default n
> + help
> + Configure maximum number of CPUS for this architecture.
> + If unsure, say N.
>
> config NR_CPUS
> - int "Maximum number of CPUs (2-255)"
> - range 2 255
> + int "Maximum number of CPUs (2-4096)"
> + range 2 4096
> depends on SMP
> + default "4096" if MAXSMP
> default "32" if X86_NUMAQ || X86_SUMMIT || X86_BIGSMP || X86_ES7000
> default "8"
> help
> This allows you to specify the maximum number of CPUs which this
> - kernel will support. The maximum supported value is 255 and the
> + kernel will support. The maximum supported value is 4096 and the
> minimum value which makes sense is 2.
>
> This is purely to save memory - each supported CPU adds
> @@ -918,12 +926,16 @@ config NUMA_EMU
> number of nodes. This is only useful for debugging.
>
> config NODES_SHIFT
> - int "Max num nodes shift(1-15)"
> + int "Maximum NUMA Nodes (as a power of 2)"
> range 1 15 if X86_64
> + default "9" if MAXSMP
> default "6" if X86_64
> default "4" if X86_NUMAQ
> default "3"
> depends on NEED_MULTIPLE_NODES
> + help
> + Specify the maximum number of NUMA Nodes available on the target
> + system. Increases memory reserved to accomodate various tables.
>
> config HAVE_ARCH_BOOTMEM_NODE
> def_bool y
>

cu
Adrian

--

"Is there not promise of rain?" Ling Tan asked suddenly out
of the darkness. There had been need of rain for many days.
"Only a promise," Lao Er said.
Pearl S. Buck - Dragon Seed



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