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Re: [XEN RFC PATCH 26/40] xen/arm: Add boot and secondary CPU to NUMA system
- To: Julien Grall <julien@xxxxxxx>, Wei Chen <Wei.Chen@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 26 Aug 2021 11:39:51 +0200
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- Cc: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "sstabellini@xxxxxxxxxx" <sstabellini@xxxxxxxxxx>
- Delivery-date: Thu, 26 Aug 2021 09:40:01 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 26.08.2021 10:49, Julien Grall wrote:
> On 26/08/2021 08:24, Wei Chen wrote:
>>> -----Original Message-----
>>> From: Julien Grall <julien@xxxxxxx>
>>> Sent: 2021年8月26日 0:58
>>> On 11/08/2021 11:24, Wei Chen wrote:
>>>> --- a/xen/arch/arm/smpboot.c
>>>> +++ b/xen/arch/arm/smpboot.c
>>>> @@ -358,6 +358,12 @@ void start_secondary(void)
>>>> */
>>>> smp_wmb();
>>>>
>>>> + /*
>>>> + * If Xen is running on a NUMA off system, there will
>>>> + * be a node#0 at least.
>>>> + */
>>>> + numa_add_cpu(cpuid);
>>>> +
>>>
>>> On x86, numa_add_cpu() will be called before the pCPU is brought up. I
>>> am not quite too sure why we are doing it differently here. Can you
>>> clarify it?
>>
>> Of course we can invoke numa_add_cpu before cpu_up as x86. But in my tests,
>> I found when cpu bring up failed, this cpu still be add to NUMA. Although
>> this does not affect the execution of the code (because CPU is offline),
>> But I don't think adding a offline CPU to NUMA makes sense.
>
> Right, but again, why do you want to solve the problem on Arm and not
> x86? After all, NUMA is not architecture specific (in fact you move most
> of the code in common).
>
> In fact, the risk, is someone may read arch/x86 and doesn't realize the
> CPU is not in the node until late on Arm.
>
> So I think we should call numa_add_cpu() around the same place on all
> the architectures.
FWIW: +1
Jan
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