Date: Tue, 15 Jul 2008 11:21:30 +0100
From: Russell King <rmk+lkml@arm.linux.org.uk>
To: Andi Kleen <andi@firstfloor.org>
Cc: Matthew Wilcox <matthew@wil.cx>, Alex Chiang <achiang@hp.com>,
       linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
       linux-acpi@vger.kernel.org
Subject: Re: [PATCH 01/14] Introduce cpu_enabled_map and friends
Message-ID: <20080715102130.GA22866@flint.arm.linux.org.uk>
Mail-Followup-To: Andi Kleen <andi@firstfloor.org>,
	Matthew Wilcox <matthew@wil.cx>, Alex Chiang <achiang@hp.com>,
	linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-acpi@vger.kernel.org
References: <20080715023344.2528.1836.stgit@blender.achiang> <20080715023349.2528.9423.stgit@blender.achiang> <20080715031512.GF14894@parisc-linux.org> <87wsjnxy4w.fsf@basil.nowhere.org>
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On Tue, Jul 15, 2008 at 12:03:27PM +0200, Andi Kleen wrote:
> Matthew Wilcox <matthew@wil.cx> writes:
> >
> > I don't understand why we want to know about these CPUs.  Surely they
> > should be 'possible', but not 'present'?  What useful thing can Linux do
> > with them?
> 
> He explained it in the intro, near the end (I nearly complained about
> this too when I hadn't finished reading it completely :):
> 
> |The big picture implication is that we can allow userspace
> |to interact with disabled CPUs. In this particular example,
> |we provide a knob that lets a sysadmin schedule any present
> |CPU for firmware deconfiguration or enablement.
> 
> The reason sounds pretty exotic, but ok.

I don't see why this needs to be cross architecture then - shouldn't
the generic kernel only be concerning itself with things that are
possible, present and/or online?

If you have an interface which allows you to change the machines
configuration in a machine specific way, shouldn't that be something
for that machine to support and forced upon the entire kernel?

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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