Re: [RFC PATCH v3 01/24] NUMA: Make number of NUMA nodes configurable

[Julien Grall <julien.grall@arm.com>]

On 19/07/17 09:17, Wei Liu wrote:
> On Tue, Jul 18, 2017 at 06:52:11PM +0100, Julien Grall wrote:
>> Hi,
>>
>> On 18/07/17 16:29, Wei Liu wrote:
>>> On Tue, Jul 18, 2017 at 05:11:23PM +0530, vijay.kilari@gmail.com wrote:
>>>> From: Vijaya Kumar K <Vijaya.Kumar@cavium.com>
>>>>
>>>> Introduce NR_NODES config option to specify number
>>>> of NUMA nodes supported. By default value is set at
>>>> 64 for x86 and 8 for arm. Dropped NODES_SHIFT macro.
>>>>
>>>> Also move NR_NODE_MEMBLKS from asm-x86/acpi.h to xen/numa.h
>>>>
>>>> Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@cavium.com>
>>>> ---
>>>>  xen/arch/Kconfig           | 7 +++++++
>>>>  xen/include/asm-x86/acpi.h | 1 -
>>>>  xen/include/asm-x86/numa.h | 2 --
>>>>  xen/include/xen/config.h   | 1 +
>>>>  xen/include/xen/numa.h     | 7 ++-----
>>>>  5 files changed, 10 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/xen/arch/Kconfig b/xen/arch/Kconfig
>>>> index cf0acb7..9c2a4e2 100644
>>>> --- a/xen/arch/Kconfig
>>>> +++ b/xen/arch/Kconfig
>>>> @@ -6,3 +6,10 @@ config NR_CPUS
>>>>  	default "128" if ARM
>>>>  	---help---
>>>>  	  Specifies the maximum number of physical CPUs which Xen will support.
>>>> +
>>>> +config NR_NODES
>>>> +	int "Maximum number of NUMA nodes"
>>>> +	default "64" if X86
>>>> +	default "8" if ARM
>>>> +	---help---
>>>> +	  Specifies the maximum number of NUMA nodes which Xen will support.
>>>
>>> Since this can now be specified by user but the definition of
>>> NUMA_NO_NODE is  not changed, I think you need to sanitise the value
>>> provided somewhere.
>>>
>>> Maybe introduce a build time check? There are some examples in tree. See
>>> cpuid.c:build_assertions.
>>
>> You can do bound-checking in Kconfig:
>>
>> range 1 254
>>
>
> Oh, good to know. Yes this is the way to go.

(Not directed to you Wei :))

Actually looking again at Xen, we are moving away from a power of 2. So 
what is the rationale behind that? Have you looked at why describing the 
number of nodes in term of power of 2 was chosen?

Cheers,

-- 
Julien Grall

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