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

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.09.2021 10:45, Julien Grall wrote:
> On Mon, 27 Sep 2021, 10:33 Jan Beulich, <jbeulich@xxxxxxxx> wrote:
> 
>> 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).
>>
> 
> As I wrote before, I don't think the user should say "I want to enable NUMA
> with Device-Tree or ACPI". Instead, they say whether they want to use NUMA
> and let Xen decide to enable the DT/ACPI support.
> 
> In other word, the prompt should stay on ARM_NUMA.

Okay. In which case I'm confused by Stefano's question.

Jan