Re: [PATCH] x86: Allow NR_CPUS=1024

From: Ingo Molnar
Date: Sun Nov 03 2013 - 05:18:34 EST



* Josh Boyer <jwboyer@xxxxxxxxxx> wrote:

> The current range for SMP configs is 2 - 512, or a full 4096 in the case
> of MAXSMP. There are machines that have 1024 CPUs in them today and
> configuring a kernel for that means you are forced to set MAXSMP. This
> adds additional unnecessary overhead. While that overhead might be
> considered tiny for large machines, it isn't necessarily so if you are
> building a kernel that runs across a wide variety of machines. We
> increase the range to 1024 to help with this.
>
> Signed-off-by: Josh Boyer <jwboyer@xxxxxxxxxxxxxxxxx>
> ---
> arch/x86/Kconfig | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index f67e839..d726b2d 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -825,7 +825,7 @@ config MAXSMP
> config NR_CPUS
> int "Maximum number of CPUs" if SMP && !MAXSMP
> range 2 8 if SMP && X86_32 && !X86_BIGSMP
> - range 2 512 if SMP && !MAXSMP
> + range 2 1024 if SMP && !MAXSMP
> default "1" if !SMP
> default "4096" if MAXSMP
> default "32" if SMP && (X86_NUMAQ || X86_SUMMIT || X86_BIGSMP || X86_ES7000)

Any reason not to allow it to go up to 4096? The original concern was that
CPUS=4096 wasn't working very well and you had to select MAXSMP
deliberately and keep all the pieces.

But today it's all pretty robust so I see no reason why not to allow up to
4096 CPUs.

Thanks,

Ingo
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