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

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Date:	Thu, 20 Aug 2009 15:20:24 -0600
From:	Alex Chiang <achiang@...com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Suresh Siddha <suresh.b.siddha@...el.com>,
	"hpa@...or.com" <hpa@...or.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 am leaning towards sysfs, and prefer:
> > 
> >  	/sys/devices/system/cpu/$cpu/chassis_id
> > 
> > How does that sound?
> 
> I would prefer to simply use the existing physical id for this
> like in your original patch.  We already have a bewildering zoo
> of different CPU IDs, no need to increase the confusion even
> more.

This was my initial instinct as well, and was why I was trying to
find out the original intent of "physical id". It seemed
unambiguous to me, but I was trying to figure out what history
(if any) there was around its semantics.

Since "physical id" is basically a made-up field (i.e., isn't
represented directly in cpuid instruction), it does seem like the
appropriate place for any quirky platforms to hook into if
necessary.

> Incidentially mcelog already knows how to use physical ID for this,
> would need to be changed for a new sysfs interface

There is probably a lot of userspace stuff that looks at physical
id that would need to be taught about a new interface.

It turns out I need to rework my patch anyway because I need to
think about the case where a user disables some cores in the
BIOS, in which case my (fragile) table selection scheme falls
apart.

But I would like to get some agreement/guidance about how we
end up presenting the information to the user.

Thanks.

/ac

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