linux-kernel - Re: [PATCH 2/2] powerpc: implement arch_scale_smt

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Message-ID: <4B5DD9F1.2010002@austin.ibm.com>
Date:	Mon, 25 Jan 2010 11:50:41 -0600
From:	Joel Schopp <jschopp@...tin.ibm.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
CC:	Michael Neuling <mikey@...ling.org>, Ingo Molnar <mingo@...e.hu>,
	ego@...ibm.com, linuxppc-dev@...ts.ozlabs.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] powerpc: implement arch_scale_smt_power for Power7

Benjamin Herrenschmidt wrote:
> On Wed, 2010-01-20 at 16:09 -0600, Joel Schopp wrote:
>   
>> I can turn that into a conditional branch (case statement) with a shift 
>> for the common 1,2,4 cases which should cover all procs available today 
>> falling back to a divide for any theoretical future processors that do 
>> other numbers of threads. 
>>     
>
> Look at the cputhreads.h implementation ... Today we only support
> power-of-two numbers of threads.
>   
I've run 3 threads using cpu hotplug to offline 1 of the 4.  It's 
certainly a stupid idea, but there you go.
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