linux-kernel - Re: [PATCH 1/2] x86/CPU/AMD: Present package as die instead of socket

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Date:   Tue, 27 Jun 2017 16:54:50 +0200
From:   Brice Goglin <brice.goglin@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Cc:     Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org, leo.duran@....com,
        yazen.ghannam@....com, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/2] x86/CPU/AMD: Present package as die instead of socket



Le 27/06/2017 16:21, Thomas Gleixner a écrit :
> On Tue, 27 Jun 2017, Suravee Suthikulpanit wrote:
>> On 6/27/17 17:48, Borislav Petkov wrote:
>>> On Tue, Jun 27, 2017 at 01:40:52AM -0500, Suravee Suthikulpanit wrote:
>>>> However, this is not the case on AMD family17h multi-die processor
>>>> platforms, which can have up to 4 dies per socket as shown in the
>>>> following system topology.
>>> So what exactly does that mean? A die is a package on ZN and you can have up
>>> to 4 packages on a physical socket?
>> Yes. 4 packages (or 4 dies, or 4 NUMA nodes) in a socket.
> And why is this relevant at all?
>
> The kernel does not care about sockets. Sockets are electromechanical
> components and completely irrelevant.
>
> The kernel cares about :
>
>     Threads	 - Single scheduling unit
>
>     Cores	 - Contains one or more threads
>
>     Packages	 - Contains one or more cores. The cores share L3.
>     
>     NUMA Node	 - Contains one or more Packages which share a memory
>     	 	   controller.
>
> 		   I'm not aware of x86 systems which have several Packages
> 		   sharing a memory controller, so Package == NUMA Node
> 		   (but I might be wrong here).

You often have multiple NUMA nodes inside a single package. That's what
we see in sysfs on Intel (since haswell, when Cluster-on-Die is enabled)
and on AMD (since magny-cours).

Kernel "packages" contains cores whose "physical_package_id" are the
same. Documentation says:
     physical_package_id: physical package id of cpu#. Typically
     corresponds to a physical socket number, but the actual value
     is architecture and platform dependent.

I don't know if it's possible on x86 to have different
physical_package_ids for different cores on a single socket.

Brice