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

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Message-ID: <20090820205425.GF13061@ldl.fc.hp.com>
Date:	Thu, 20 Aug 2009 14:54:25 -0600
From:	Alex Chiang <achiang@...com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	"hpa@...or.com" <hpa@...or.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"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

* Suresh Siddha <suresh.b.siddha@...el.com>:
> On Wed, 2009-08-19 at 14:02 -0700, Alex Chiang wrote:
> > I agree with you (although I thought that they should be
> > 0-based) but this quirk addresses a specific platform, where
> > I can assume certain things about the BIOS, etc.
> 
> What happens if for some reason, newer bios/newer cpu
> generations on this platform start having holes in the physical
> id space? We can't rule out these kind of changes and we don't
> want to go behind distros requesting fixes.
> 
> > I agree with you in general, but again, this is a specific
> > platform quirk where I have a good idea of what is a
> > supported configuration.
> 
> I am just nervous about future bios changes etc.

Ok, let's separate the two conversations happening here.

To me, the BIOS concerns are moot. I work closely with the BIOS
engineers for this platform; I have knowledge of future plans for
this BIOS and platform; and I know that they will not make any
changes that break the assumptions in my patch.

If they do, we will catch it during platform testing, file a bug,
and not let them release their BIOS until it's fixed. Does that
satisfy you? :)

So the algorithm for mapping an APIC ID to a physical/chassis ID
for this platform will not ever change.

Now on the other hand, the /interface/ that we present to the
user is the interesting conversation to have.

> > > Easiest route will be to add a new entry in /proc/cpuinfo
> > 
> > Well, if you remain unconvinced that fixing up 'physical id' is
> > the proper thing to do, here are some alternate proposals:
> > 
> > 	/proc/cpuinfo/chassis id
> > 	/sys/devices/system/cpu/$cpu/chassis id
> > 	/sys/devices/system/cpu/$cpu/topology/chassis id
> > 
> 
> I really like this alternate proposal. This is simple and straight
> forward to everyone.

I am leaning towards sysfs, and prefer:

 	/sys/devices/system/cpu/$cpu/chassis_id

How does that sound?

Thanks.

/ac

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