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Date: Tue, 22 Dec 2009 11:58:41 +1100
From: Tony Breeds <tony@bakeyournoodle.com>
To: Joel Schopp <jschopp@austin.ibm.com>
Subject: Re: [PATCH] powerpc: update ibm,client-architecture
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Cc: linuxppc-dev@ozlabs.org, Michael Neuling <mikey@neuling.org>
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On Mon, Dec 21, 2009 at 04:14:54PM -0600, Joel Schopp wrote:

> It's a bad interface.  No matter what you choose there will be a
> downside.  1) If you choose NR_CPUS, the best case of how many you
> could boot without SMT, then when you boot with SMT2 or SMT4 you can
> get assigned more cpus than you can boot.  2) If you choose
> NR_CPUS/4, the worst case of how many you could boot, and you get a
> large machine with SMT2 or SMT1 you might have said you support less
> cpus than you actually do and thus not boot all the cpus.  So no
> matter what you choose you could be not booting cpus in some
> theoretical scenario.

We're far enough through boot to determine the threading model, so you /could/
work out what SMT we're in and divide NR_CPUS by that and give that to firmware.

Yours Tony