Re: [PATCH ARM64]: Introduce CONFIG_MAXSMP to allow up to 512 cpus

[Christoph Lameter (Ampere)]

On Thu, 23 Nov 2023, Catalin Marinas wrote:

> > +config NR_CPUS_RANGE_BEGIN
> > +	int
> > +	default NR_CPUS_RANGE_END if MAXSMP
> > +	default    1 if !SMP
> > +	default    2
>
> We don't support !SMP on arm64.

Ok we can drop that.

> > +	  This is purely to save memory: each supported CPU adds about 8KB
> > +	  to the kernel image.
>
> Is this all needed just to select CPUMASK_OFFSTACK if larger NR_CPUS?
> Would something like this do:
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 7b071a00425d..697d5700bad1 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -119,6 +119,7 @@ config ARM64
> 	select CLONE_BACKWARDS
> 	select COMMON_CLK
> 	select CPU_PM if (SUSPEND || CPU_IDLE)
> +	select CPUMASK_OFFSTACK if NR_CPUS > 512
> 	select CRC32
> 	select DCACHE_WORD_ACCESS
> 	select DYNAMIC_FTRACE if FUNCTION_TRACER
>
> togehther with a larger NR_CPUS in defconfig?

Well that is certainly better because it does not introduce an additional 
kernel config option.