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Re: [PATCH 1/2] spapr: number of SMP sockets must be equal to NUMA nodes

From: Cédric Le Goater
Subject: Re: [PATCH 1/2] spapr: number of SMP sockets must be equal to NUMA nodes
Date: Wed, 31 Mar 2021 17:22:39 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0

On 3/31/21 6:58 AM, Michael Ellerman wrote:
> David Gibson <david@gibson.dropbear.id.au> writes:
>> On Mon, Mar 29, 2021 at 03:32:37PM -0300, Daniel Henrique Barboza wrote:
> ...
>>> We assign ibm,chip-id=0x0 to CPUs 0-3, but CPUs 2-3 are located in a
>>> different NUMA node than 0-1. This would mean that the same socket
>>> would belong to different NUMA nodes at the same time.
>> Right... and I'm still not seeing why that's a problem.  AFAICT that's
>> a possible, if unexpected, situation under real hardware - though
>> maybe not for POWER9 specifically.
> I think I agree.
>>> I believe this is what Cedric wants to be addressed. Given that the
>>> property is called after the OPAL property ibm,chip-id, the kernel
>>> expects that the property will have the same semantics as in OPAL.
>> Even on powernv, I'm not clear why chip-id is tied into the NUMA
>> configuration, rather than getting all the NUMA info from
>> associativity properties.
> AFAIK we don't use chip-id for anything related to NUMA, if we do I'd
> consider that a bug.

Since PAPR only has NUMA nodes, is the use of chip-id in XIVE PAPR 
considered as a bug ? I would say so.

> We do use it for topology_physical_package_id(), but that's almost
> completely unused.

In that case, I think it should be fine to return -1 like under PowerVM.



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