Messages in this thread | | | Date | Wed, 9 Sep 2020 15:17:55 -0500 | From | Yazen Ghannam <> | Subject | Re: [PATCH v2 1/8] x86/CPU/AMD: Save NodeId on AMD-based systems |
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On Wed, Sep 09, 2020 at 08:06:47PM +0200, Borislav Petkov wrote: > On Thu, Sep 03, 2020 at 08:01:37PM +0000, Yazen Ghannam wrote: > > From: Yazen Ghannam <yazen.ghannam@amd.com> > > > > AMD systems provide a "NodeId" value that represents a global ID > > indicating to which "Node" a logical CPU belongs. The "Node" is a > > physical structure equivalent to a Die, and it should not be confused > > with logical structures like NUMA node. > > So we said in Documentation/x86/topology.rst that: > > "The kernel does not care about the concept of physical sockets because > a socket has no relevance to software. It's an electromechanical > component." >
Yes, I agree with this.
> Now, you're talking, AFAIU, about physical components. Why do you need > them? >
We need to access specific instances of hardware registers in the Northbridge or Data Fabric. The code in arch/x86/kernel/amd_nb.c does this.
> What is then: > > - cpuinfo_x86.phys_proc_id: > > The physical ID of the package. This information is retrieved via CPUID > and deduced from the APIC IDs of the cores in the package. > > supposed to mean? >
Package = Socket, i.e. a field replaceable unit. Socket may not be useful for software, but I think it helps users identify the hardware.
I think the following could be changed in the documentation:
"In the past a socket always contained a single package (see below), but with the advent of Multi Chip Modules (MCM) a socket can hold more than one package."
Replace "package" with "die".
You take multiple dies from the foundry and you "package" them together into a single unit.
> Why isn't phys_proc_id != node_id? >
They could be equal depending on the system. The values are different on MCM systems like Bulldozer and Naples though.
The functions and structures in amd_nb.c are indexed by the node_id. This is done implicitly right now by using amd_get_nb_id()/cpu_llc_id. But the LLC isn't always equal to the Node/Die like in Naples. So the patches in this set save and explicitly use the node_id when needed.
What do you think?
Thanks, Yazen
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