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Date: Tue, 18 Mar 2008 12:49:29 -0700
From: Maxim Sobolev <sobomax@FreeBSD.org>
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To: Abdullah Ibn Hamad Al-Marri <wearabnet@yahoo.ca>
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Cc: FreeBSD Current <current@FreeBSD.org>
Subject: Re: Speed Step and powerd for servers status?
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Abdullah Ibn Hamad Al-Marri wrote:
> Hey,
> 
> 
> I would like to use powerd and speed step for my servers, and make sure it will use the MAX CPU if needed then go to idle mode to save the power.
> 
> Any recommendation?

It's questionable whether or not it will have positive effect on the server:

<quote>
The combination of processor-frequency scaling and idle-power states 
provides a somewhat surprising result. On almost all modern hardware, if 
there is code to run, then it is more power efficient to run the 
processor at full speed. This "race to idle" concept stems from the 
power consumption of an idle processor being much lower than an active 
processor, even if running at a lower speed. The overall power 
consumption will be less if the processor spends a short time at full 
speed and then falls back to idle, rather than spending twice as long 
being active at a lower frequency.
</quote>

Full text is here:

http://www.acmqueue.com/modules.php?name=Content&pa=showpage&pid=513

-Maxim