linux-kernel - Re: [PATCH] x86: add /proc/cpuinfo/physical id quirks

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Message-ID: <20090821050240.GA4198@ldl.fc.hp.com>
Date:	Thu, 20 Aug 2009 23:02:40 -0600
From:	Alex Chiang <achiang@...com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: add /proc/cpuinfo/physical id quirks

* Andi Kleen <andi@...stfloor.org>:
> > I agree... if this ID is used for topology detection, we
> > shouldn't replace it arbitrarily with information from BIOS
> > just to hope that it matches the motherboard stencil.
> > *Furthermore*, there is no reason why motherboard stencilAs
> > are purely numeric... consider the rather obvious case of two
> > rows of four CPUs; they may have CPU slots labelled A1, A2,
> > A3, A4, B1, B2, B3, B4.  It might very well be the right
> > thing to support arbitrary strings for platforms we
> > recognize.
> 
> Maintaining a manual mapping to strings in the kernel to such
> strings would be just crazy. You would need a new entry for
> basically every system.
 
Well, ideally we could read it from a standard location, say
evaluating the ACPI _SUN method for the cpu object and then plug
that answer into a standard kernel data structure.

Hardware vendors can stick whatever they want into that method;
the kernel just passes it through to userspace.

It's what we do for PCI slots today, and I wrote a patch for ia64
that does that type of fixup: fe086a7.

> The reason to correct SOCKETID is that it it is output on errors.
> If it is numerical and you know it's wrong you can correct it,
> and then you can identify the right CPU. Otherwise you lose.

I think numerical vs. ascii is the wrong way to think about it,
since ACPI could provide either.

/ac

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