linux-kernel - Re: x86 (Linux Tiny): configure out support for some processors

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Date:	Fri, 2 Jan 2009 10:38:01 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jaswinder Singh Rajput <jaswinderlinux@...il.com>
Cc:	Bryan Donlan <bdonlan@...il.com>,
	Ingo Brueckl <ib@...peronline.de>,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: x86 (Linux Tiny): configure out support for some processors


* Jaswinder Singh Rajput <jaswinderlinux@...il.com> wrote:

> On Fri, Jan 2, 2009 at 10:49 AM, Bryan Donlan <bdonlan@...il.com> wrote:
> > On Thu, Jan 1, 2009 at 3:37 PM, Ingo Brueckl <ib@...peronline.de> wrote:
> >> Is there any reason why CONFIG_PROCESSOR_SELECT is limited to EMBEDDED only?
> >>
> >> In my desktop pc is one specific cpu only, so I do not need support for the
> >> other processors. Unfortunately, I have no chance to disable the other ones.
> >>
> >> As it is already configurable, why not giving this option to everyone?
> >
> > EMBEDDED is just a switch to enable configuration options related to 
> > removing 'core' features of the kernel to save space. Think of it as a 
> > safety to avoid accidentally turning off something important. Feel 
> > free to switch on EMBEDDED if you want to use CONFIG_PROCESSOR_SELECT 
> > - just enabling EMBEDDED doesn't do anything by itself.
> 
> I think EMBEDDED is a misnomer for using CONFIG_PROCESSOR_SELECT and 
> should be used for more specific to Embedded stuff like for Embedded 
> range of CPUs or Embedded Systems.

i think EMBEDDED is justified in this particular case, as enabling 
CONFIG_PROCESSOR_SELECT allows you to create truly CPU-incompatible 
kernels. Kernels that panic on bootup on contemporary CPUs that happen to 
have a different manufacturer.

The normal CPU selection options (like CONFIG_MCORE2) are more like 
performance and preference hints not hard constraints - those kernels will 
generally still boot fine on most other CPUs as well. (with a few 
common-sense exceptions like booting on truly ancient CPUs, i.e. booting 
an CONFIG_MCORE2 kernel on an i486DX CPU will not work)

	Ingo
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