linux-kernel - Re: [PATCHv3 2/2] powerpc: implement arch_scale_smt

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Message-ID: <4B630C27.1060405@austin.ibm.com>
Date:	Fri, 29 Jan 2010 10:26:15 -0600
From:	Joel Schopp <jschopp@...tin.ibm.com>
To:	Gabriel Paubert <paubert@...m.es>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>, ego@...ibm.com,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCHv3 2/2] powerpc: implement arch_scale_smt_power for	Power7

Gabriel Paubert wrote:
> On Thu, Jan 28, 2010 at 05:20:55PM -0600, Joel Schopp wrote:
>   
>> On Power7 processors running in SMT4 mode with 2, 3, or 4 idle threads 
>> there is performance benefit to idling the higher numbered threads in
>> the core.  
>>
>>     
>
> Really 2, 3, or 4? When you have 4 idle threads out of 4, performance
> becomes a minor concern, no? ;-)
>
> 	Gabriel
>   
Yes, but going from 4 idle to 3 idle you want to keep the slanted 
weights.  If you ignored 4 you'd place wrong and then correct it after 
the fact.
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