linux-kernel - Re: [PATCH 01/14] Introduce cpu_enabled

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Date:	Tue, 15 Jul 2008 19:48:22 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Matthew Wilcox <matthew@....cx>
Cc:	Alex Chiang <achiang@...com>, Andi Kleen <andi@...stfloor.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH 01/14] Introduce cpu_enabled_map and friends

On Tue, Jul 15, 2008 at 12:16:32PM -0600, Matthew Wilcox wrote:
> On Tue, Jul 15, 2008 at 11:57:40AM -0600, Alex Chiang wrote:
> > My thought was that big SMP systems like ia64, possibly sparc and
> > ppc, and increasingly, x86, might find something like this
> > useful, as systems get larger and larger, and vendors are going
> > to want to do RAS-ish features, like the ability to keep CPUs in
> > firmware across reboots until told otherwise by the sysadmin.
> > 
> > Right now, a 'present' CPU strongly implies 'online' as well,
> > since we're calling cpu_up() for all 'present' CPUs in
> > smp_init(). But this hurts if:
> > 
> > 	- you don't actually want to bring up all 'present' CPUs
> > 	- you still want to interact with these weirdo zombie
> > 	  CPUs that are 'present' but not 'online'
> 
> Have you considered simply failing __cpu_up() for CPUs that are
> deconfigured by firmware?

But what if you want to have a system boot with, say, 4 CPUs and
then decide at run time to bring up another 4 CPUs when required?

How about having smp_init() call into arch code to query whether
it should bring up a not-already-online CPU?  Architectures that
want to do something special can then make the decision there and
everyone else can define the test completely away.

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