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

From: Michael Ellerman
Subject: Re: [PATCH 1/2] spapr: number of SMP sockets must be equal to NUMA nodes
Date: Wed, 31 Mar 2021 15:58:03 +1100

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.

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


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