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

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Message-ID: <DM5PR12MB1243BCB120EAE0BEC9114ED4F9DC0@DM5PR12MB1243.namprd12.prod.outlook.com>
Date:   Tue, 27 Jun 2017 16:34:10 +0000
From:   "Duran, Leo" <leo.duran@....com>
To:     'Thomas Gleixner' <tglx@...utronix.de>
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

Thomas,
Please see my comments & question below.
Leo.

> -----Original Message-----
> From: Thomas Gleixner [mailto:tglx@...utronix.de]
> Sent: Tuesday, June 27, 2017 11:19 AM
> To: Duran, Leo <leo.duran@....com>
> Cc: Suthikulpanit, Suravee <Suravee.Suthikulpanit@....com>; Borislav
> Petkov <bp@...en8.de>; x86@...nel.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.
[Duran, Leo] 
Well, our intent is to return what the kernel expects.
So, if we're not doing that properly, we need to fix it.

To be clear,
Are you saying that there can only be a single L3 per 'Package'?


> 
> 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