Re: [PATCH 1/6] x86/Kconfig: add selection of default x2APIC destination mode

[Jan Beulich <jbeulich@xxxxxxxx>]

On 23.06.2022 10:24, Roger Pau Monne wrote:
> Allow selecting the default x2APIC destination mode from Kconfig.
> Note the default destination mode is still Logical (Cluster) mode.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
>  xen/arch/x86/Kconfig          | 29 +++++++++++++++++++++++++++++
>  xen/arch/x86/genapic/x2apic.c |  6 ++++--
>  2 files changed, 33 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
> index 1e31edc99f..f560dc13f4 100644
> --- a/xen/arch/x86/Kconfig
> +++ b/xen/arch/x86/Kconfig
> @@ -226,6 +226,35 @@ config XEN_ALIGN_2M
>  
>  endchoice
>  
> +choice
> +     prompt "x2APIC default destination mode"

What's the point of using "choice" here, and not a single "bool"?

> +     default X2APIC_LOGICAL
> +     ---help---

Nit: Please don't use ---help--- anymore - we're trying to phase out its
use as Linux has dropped it altogether (and hence once we update our
Kconfig, we'd like to change as few places as possible), leaving just
"help".

One downside of "choice" (iirc) is that the individual sub-options' help
text is inaccessible from at least the command line version of kconfig.

> +       Specify default destination mode for x2APIC.
> +
> +       If unsure, choose "Logical".
> +
> +config X2APIC_LOGICAL
> +     bool "Logical mode"
> +     ---help---
> +       Use Logical Destination mode.
> +
> +       When using this mode APICs are addressed using the Logical
> +       Destination mode, which allows for optimized IPI sending,
> +       but also reduces the amount of vectors available for external
> +       interrupts when compared to physical mode.
> +
> +config X2APIC_PHYS

X2APIC_PHYSICAL (to be in line with X2APIC_LOGICAL)?

Jan