linux-kernel - Re: WARNING: at arch/x86/kernel/smpboot.c:310 topology

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Date:	Tue, 29 May 2012 19:25:19 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Borislav Petkov <bp@...64.org>
Cc:	Andreas Herrmann <andreas.herrmann3@....com>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, hpa <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: WARNING: at arch/x86/kernel/smpboot.c:310
 topology_sane.clone.1+0x6e/0x81()

On Tue, 2012-05-29 at 19:13 +0200, Borislav Petkov wrote:
> 
> > As it stands I think we should discuss the definition for the generic
> > topology bits (drivers/base/topology.c), because I think your
> > Magny-Cours thing does the wrong thing here.
> 
> "wrong" is such a strong word :-) Please elaborate and I'll have a look.

Right, so I meant LLC is the useful mask, and in my mind LLC is what
makes a multi-core, without shared cache its just SMP. So core_siblings
to me would mean LLC sharing cores.

But its all very subjective I guess, but using strong words gets the
discussion going better ;-)

> > The core span in a phys_id is all nice and such, but what does it mean?
> 
> AFAICT, this is the physical package id to which the cores belong, i.e.
> physical socket.
> 
> > IOW what would you do with it?
> 
> Shoot empty cans with it... :-) 

Right, I actually came up with proper use-case, physical hotplug :-)

Its not immediately obvious the sysfs topo bits have the llc mask, which
is the more 'useful' one IMO.

Another funny case I don't see represented well is where there's
multiple sockets to a node -- I know this is like ancient tech and
unlikely in these days of multi-node sockets, but still ;-)

I guess what I'm asking is what is the purpose of the sys topo bits?
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