linux-kernel - Re: [PATCH] x86/topology: Document cpu_llc

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Date:   Mon, 14 Nov 2016 07:29:01 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yazen Ghannam <yazen.ghannam@....com>
Subject: Re: [PATCH] x86/topology: Document cpu_llc_id

On Wed, Sep 07, 2016 at 12:36:41PM +0200, Peter Zijlstra wrote:
> On Wed, Sep 07, 2016 at 11:22:19AM +0200, Borislav Petkov wrote:
> > From: Borislav Petkov <bp@...e.de>
> > 
> > It means different things on Intel and AMD so write it down so that
> > there's no confusion.
> > 
> > Signed-off-by: Borislav Petkov <bp@...e.de>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > ---
> >  Documentation/x86/topology.txt | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/Documentation/x86/topology.txt b/Documentation/x86/topology.txt
> > index 06afac252f5b..7a5485730476 100644
> > --- a/Documentation/x86/topology.txt
> > +++ b/Documentation/x86/topology.txt
> > @@ -63,6 +63,12 @@ The topology of a system is described in the units of:
> >      The maximum possible number of packages in the system. Helpful for per
> >      package facilities to preallocate per package information.
> >  
> > +  - cpu_llc_id:
> > +
> > +    A per-CPU variable containing:
> > +    - On Intel, the first APIC ID of the list of CPUs sharing the Last Level
> > +    Cache
> > +    - On AMD, the Node ID containing the Last Level Cache.
> 
> And there are no AMD parts where there are multiple LLCs on a Node? Like
> where there isn't an L3 and the L2 is only per cluster?

Yes there are (now), see:

http://git.kernel.org/tip/b0b6e86846093c5f8820386bc01515f857dd8faa

But those LLC ID numbers are still increasing IDs of either nodes or
core complexes in Zen's case. So I think the text should say:

"- On AMD, the Node ID or Core Complex ID containing the Last Level Cache. In
   general, numbers identifying an LLC uniquely on the system."

How's that?

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.