linux-kernel - Re: [PATCH 0/5 v4] x86: Adapt CPU topology detection for AMD Magny-Cours

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Date:	Thu, 6 Aug 2009 12:42:40 +0200
From:	Andreas Herrmann <andreas.herrmann3@....com>
To:	Brice Goglin <Brice.Goglin@...ia.fr>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Borislav Petkov <borislav.petkov@....com>
Subject: Re: [PATCH 0/5 v4] x86: Adapt CPU topology detection for AMD
	Magny-Cours

On Wed, Aug 05, 2009 at 10:23:54PM +0200, Brice Goglin wrote:
> Andreas Herrmann wrote:
> > Changes to previous patch set:
> > - fixed allnoconfig compile error and link error if CONFIG_PCI=n
> > - fixed hotplug issue: cpumask of siblings sharing same L3 were not
> >   properly updated
> > - properly allocate cpu_node_map
> >
> > Current patch set contains 5 patches:
> > - patch 1 adapts common code to show cpu_node_id,
> >   cpu_node_siblings and cpu_node_siblings_list in
> >   /sys/devices/system/cpu/cpu*/topology
> > - patch 2 prepares arch/x86 to provide cpu_node information
> > - patch 3 sets up cpu_node information for AMD Magny-Cours CPU
> > - patch 4 fixes L3 cache information for Magny-Cours
> > - patch 5 fixes mcheck code for Magny-Cours
> >   
> 
> Hello Andreas,
> 
> Reading your first submission I find something disturbing. You say that
> we'll have the following sibling information:
> 
>   Level        | Set of CPUs
>  --------------|---------------
>   phys_package | core_siblings
>   cpu_node     | cpu_node_siblings
>   core         | thread_siblings
>   thread       | one CPU

> This breaks the existing convention/semantics.

Isn't the existing convention that core_siblings denotes all CPUs on
same socket.

> Currently core/thread_siblings contains the cpumask covering *all*
> siblings of current core/thread object. What you're adding only
> shows the cpumask of current "cpu_node" object in
> cpu_node_siblings. I don't have any preference between both
> semantics, but I think "cpu_node" should use the semantics that
> "core" and "thread" do. So the above should be changed into:

>   Level        | Set of CPUs
>  --------------|---------------
>   phys_package | cpu_node_siblings
>   cpu_node     | core_siblings
>   core         | thread_siblings
>   thread       | one CPU

Of course I thought also to implement it this way because it looks
more consistent, but IMHO the patches are less intrusive if this
scheme is _not_ used. Instead I kept core_siblings as is ("for
historic reasons", nobody needs to accustom to new semantics). And use
cpu_node_siblings where it really matters.

But this reminds me that some documentation is required to describe
the new attributes.

What do others think?


Thanks,
Andreas

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