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Re: [PATCH 02/37] xen: introduce a Kconfig option to configure NUMA nodes number
- To: Wei Chen <Wei.Chen@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 24 Sep 2021 12:47:57 +0200
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- Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "sstabellini@xxxxxxxxxx" <sstabellini@xxxxxxxxxx>, "julien@xxxxxxx" <julien@xxxxxxx>
- Delivery-date: Fri, 24 Sep 2021 10:48:10 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 24.09.2021 12:33, Wei Chen wrote:
>> From: Jan Beulich <jbeulich@xxxxxxxx>
>> Sent: 2021年9月24日 16:56
>>
>> On 23.09.2021 14:02, Wei Chen wrote:
>>> --- a/xen/arch/Kconfig
>>> +++ b/xen/arch/Kconfig
>>> @@ -17,3 +17,14 @@ config NR_CPUS
>>> For CPU cores which support Simultaneous Multi-Threading or
>> similar
>>> technologies, this the number of logical threads which Xen will
>>> support.
>>> +
>>> +config NR_NUMA_NODES
>>> + int "Maximum number of NUMA nodes supported"
>>> + range 1 4095
>>
>> How was this upper bound established? Seeing 4095 is the limit of the
>> number of CPUs, do we really expect a CPU per node on such huge
>> systems? And did you check that whichever involved data types and
>> structures are actually suitable? I'm thinking e.g. of things like ...
>>
>>> --- a/xen/include/asm-x86/numa.h
>>> +++ b/xen/include/asm-x86/numa.h
>>> @@ -3,8 +3,6 @@
>>>
>>> #include <xen/cpumask.h>
>>>
>>> -#define NODES_SHIFT 6
>>> -
>>> typedef u8 nodeid_t;
>>
>> ... this.
>>
>
> you're right, we use u8 as nodeid_t. 4095 for node number in this option
> is not reasonable. Maybe a 255 upper bound is good?
I think it is, yes, but you will want to properly check.
Jan
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