Re: [PATCH 36/37] xen/arm: Provide Kconfig options for Arm to enable NUMA

[Jan Beulich <jbeulich@xxxxxxxx>]

On 24.09.2021 21:39, Stefano Stabellini wrote:
> On Fri, 24 Sep 2021, Wei Chen wrote:
>> On 2021/9/24 11:31, Stefano Stabellini wrote:
>>> On Thu, 23 Sep 2021, Wei Chen wrote:
>>>> --- a/xen/arch/arm/Kconfig
>>>> +++ b/xen/arch/arm/Kconfig
>>>> @@ -34,6 +34,17 @@ config ACPI
>>>>      Advanced Configuration and Power Interface (ACPI) support for Xen is
>>>>      an alternative to device tree on ARM64.
>>>>   + config DEVICE_TREE_NUMA
>>>> +  def_bool n
>>>> +  select NUMA
>>>> +
>>>> +config ARM_NUMA
>>>> +  bool "Arm NUMA (Non-Uniform Memory Access) Support (UNSUPPORTED)" if
>>>> UNSUPPORTED
>>>> +  select DEVICE_TREE_NUMA if HAS_DEVICE_TREE
>>>
>>> Should it be: depends on HAS_DEVICE_TREE ?
>>> (And eventually depends on HAS_DEVICE_TREE || ACPI)
>>>
>>
>> As the discussion in RFC [1]. We want to make ARM_NUMA as a generic
>> option can be selected by users. And depends on has_device_tree
>> or ACPI to select DEVICE_TREE_NUMA or ACPI_NUMA.
>>
>> If we add HAS_DEVICE_TREE || ACPI as dependencies for ARM_NUMA,
>> does it become a loop dependency?
>>
>> https://lists.xenproject.org/archives/html/xen-devel/2021-08/msg00888.html
> 
> OK, I am fine with that. I was just trying to catch the case where a
> user selects "ARM_NUMA" but actually neither ACPI nor HAS_DEVICE_TREE
> are selected so nothing happens. I was trying to make it clear that
> ARM_NUMA depends on having at least one between HAS_DEVICE_TREE or ACPI
> because otherwise it is not going to work.
> 
> That said, I don't think this is important because HAS_DEVICE_TREE
> cannot be unselected. So if we cannot find a way to express the
> dependency, I think it is fine to keep the patch as is.

So how about doing things the other way around: ARM_NUMA has no prompt
and defaults to ACPI_NUMA || DT_NUMA, and DT_NUMA gains a prompt instead
(and, for Arm at least, ACPI_NUMA as well; this might even be worthwhile
to have on x86 down the road).

Jan