Message-ID: <4B577F1A.9060907@austin.ibm.com>
Date: Wed, 20 Jan 2010 16:09:30 -0600
From: Joel Schopp <jschopp@austin.ibm.com>
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To: Michael Neuling <mikey@neuling.org>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>, Ingo Molnar <mingo@elte.hu>,
       linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
       ego@in.ibm.com
Subject: Re: [PATCH 2/2] powerpc: implement arch_scale_smt_power for Power7
References: <1264017638.5717.121.camel@jschopp-laptop> <1264017847.5717.132.camel@jschopp-laptop> <26556.1264021443@neuling.org>
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>> +	if (cpu_has_feature(CPU_FTRS_POWER7) && weight == 4) {
>>     
>
> I think we should avoid using cpu_has_feature like this.  It's better to
> create a new feature and add it to POWER7 in the cputable, then check
> for that here.
>
> The way that it is now, I think any CPU that has superset of the POWER7
> features, will be true here.  This is not what we want.
>   
Any ideas for what to call this feature?  ASYM_SMT4 ?
>
>> +	smt_gain /= weight;
>>     
>
> This results in a PPC div, when most of the time it's going to be a
> power of two divide.  You've optimised the divides a few lines above
> this, but not this one.  Some consistency would be good.
>
>   
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.
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