linux-kernel - Re: [RFC/PATCH 0/3] sched: allow arch override of cpu power

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Message-ID: <20080627142309.GR9594@localdomain>
Date:	Fri, 27 Jun 2008 09:23:09 -0500
From:	Nathan Lynch <ntl@...ox.com>
To:	Breno Leitao <leitao@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Anton Blanchard <anton@...ba.org>
Subject: Re: [RFC/PATCH 0/3] sched: allow arch override of cpu power

Breno Leitao wrote:
> Nathan Lynch wrote:
>> There is an "interesting" quality of POWER6 cores, which each have 2
>> hardware threads: assuming one thread on the core is idle, the primary
>> thread is a little "faster" than the secondary thread.  To illustrate:
>>   
> I found this feature interesting and decided to do some tests.
> After some tests I found that the example you post really runs fast in  
> the first CPU, but a more "elaborated" application runs slower on the  
> first CPU.
> Here is a small example:
>
> # taskset 0x1 time -f "%e,  %U, %S" ./a.out ; taskset 0x2 time -f "%e,  
> %U, %S" ./a.out
> 10.77,  10.72, 0.01
> 10.53, 10.48, 0.01
>
> # taskset 0x2 time -f "%e,  %U, %S" ./a.out ; taskset 0x1 time -f "%e,  
> %U, %S" ./a.out
> 10.55,  10.50, 0.01
> 10.77, 10.72, 0.01

I've been able to duplicate your results, thanks for the testcase.
Guess I'll need to understand what's going on before continuing with
this...
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