Re: [Xen-devel] [PATCH 1/2] build: introduce CONFIG_NR_CPUS in Kconfig

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 08/01/2016 23:17, Doug Goldstein wrote:
> Introduce an option where the user can modifiy the maximum number of
> supported physical CPUs.
>
> CC: Ian Campbell <ian.campbell@xxxxxxxxxx>
> CC: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
> CC: Keir Fraser <keir@xxxxxxx>
> CC: Jan Beulich <jbeulich@xxxxxxxx>
> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Signed-off-by: Doug Goldstein <cardoe@xxxxxxxxxx>
> ---
> This patch can probably be squashed together with the next one but I
> broke it out with the hope that someone can check the wording on the
> option and also double check the range.
> ---
>  xen/arch/Kconfig     | 8 ++++++++
>  xen/arch/arm/Kconfig | 2 ++
>  xen/arch/x86/Kconfig | 2 ++
>  3 files changed, 12 insertions(+)
>  create mode 100644 xen/arch/Kconfig
>
> diff --git a/xen/arch/Kconfig b/xen/arch/Kconfig
> new file mode 100644
> index 0000000..791d577
> --- /dev/null
> +++ b/xen/arch/Kconfig
> @@ -0,0 +1,8 @@
> +
> +config NR_CPUS
> +     int "Maximum number of CPUs"
> +     range 1 4095

4094

Recursive spinlocks have 12 bit bitfield for cpu, using -1 as a sentinel.

There might be other restrictions, but none currently come to mind.

> +     default "256" if X86
> +     default "128" if ARM
> +     ---help---
> +       Specifies the maximum number of CPUs which Xen will support.

"of physical CPUs"

This will help avoid confusion with virtual cpu limits.

~Andrew

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