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 18:19:24 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Duran, Leo" <leo.duran@....com>
cc:     "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>,
        Borislav Petkov <bp@...en8.de>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Ghannam, Yazen" <Yazen.Ghannam@....com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: RE: [PATCH 1/2] x86/CPU/AMD: Present package as die instead of
 socket

On Tue, 27 Jun 2017, Duran, Leo wrote:
> > From: Thomas Gleixner [mailto:tglx@...utronix.de]
> > 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).
> > 
> >     Platform	 - Contains one or more Numa Nodes
> [Duran, Leo] 

> That is my understanding of intent as well... However, regarding the L3:

Obviously is that not your understanding.

> The sentence 'The cores share L3.' under 'Packages' may give the
> impression that all cores in a package share an L3.
> In our case, we define a Package a group of cores sharing a memory
> controller, a 'Die' in hardware terms.
>
> Also, it turns out that within a Package we may have separate groups of
> cores each having their own L3 (in hardware terms we refer to those as a
> 'Core Complex').
>
> Basically, in our case a Package may contain more than one L3 (i.e., in
> hardware terms, there may more than one 'Core complex' in a 'Die').
>
> The important point is that all logical processors (threads) that share
> an L3 have a common "cpu_llc_id".

I don't care at all what you call a package. Really. The only relevant view
is what the kernel thinks a package is. And I made that entirely clear.

If you think that's confusing, then feel free to submit patches which
change the names we are using throughout x86 including the documentation.

Thanks,

	tglx