linux-kernel - Re: [PATCH] RFC: Fix AMD Northbridge-ID contiguity assumptions

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Message-ID: <20121003180859.GB15939@aftab.osrc.amd.com>
Date:	Wed, 3 Oct 2012 20:08:59 +0200
From:	Borislav Petkov <bp@...64.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Daniel Blueman <daniel@...ascale-asia.com>,
	Ingo Molnar <mingo@...hat.com>,
	Steffen Persvold <sp@...ascale.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Borislav Petkov <bp@...64.org>,
	x86@...nel.org
Subject: Re: [PATCH] RFC: Fix AMD Northbridge-ID contiguity assumptions

On Wed, Oct 03, 2012 at 08:50:51AM -0700, H. Peter Anvin wrote:
> On 10/03/2012 08:30 AM, Daniel Blueman wrote:
> > >
> > > Is that "on NumaScale systems"?  If so, please say so rather than trying
> > > to make it sound generic; if it is not, can you give some other examples?
> >
> >It is for Numascale (NumaChip) systems for our purposes.
> >
> >Any other systems which interconnect Opterons via address space routing
> >(needed for >8 HT nodes) will get this benefit. I can't put my hand to
> >exactly what is out there, but can find out.
> >
> 
> The reason I'm asking is because it is an important bit of the
> record of the code to know if this is a specific need or a general
> need.  This may be obvious now, but 5-10 years from now someone will
> need to know why or what.
> 
> The two paragraphs above is exactly what is needed, i.e. "NumaChip
> or any other design which shares these specific design features:
> ..."

Absolutely!

And it would be best to put that explanation in the code somewhere
around node_to_amd_index() so that it is there at a first glance.

Btw, I'll review the patch tomorrow since it is a holiday today here.

I have only two nits for now:

* node is u32, do you really have such big systems with 2^32-1 nodes? Or
can the max node number fit into a, say, u16 or u8?

* node_to_amd_index returns 0 in the unsuccessful case but node index 0
seems ok to me, i.e. the first element in the array of northbridges. It
probably should return a negative value rather to signal a failure...

Thanks.

-- 
Regards/Gruss,
Boris.

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