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Date: Fri, 12 Jan 2007 11:41:14 +0100
To: George Hartzell <hartzell@alerce.com>
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From: Bruno Ducrot <ducrot@poupinou.org>
Cc: Peter Jeremy <peterjeremy@optushome.com.au>, freebsd-stable@freebsd.org
Subject: Re: saving power in a Dell Poweredge 750.
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On Thu, Jan 11, 2007 at 09:21:50AM -0800, George Hartzell wrote:
> Bruno Ducrot writes:
>  > [...]
>  > What specific driver(s) were loaded actually?
>  > A devinfo might help.
> 
> It looks like:
> 
>       p4tcc0
>       cpufreq0
> 
> Here's a devinfo and a dmesg:
> 
>  http://shrimp.alerce.com/merlin/merlin.devinfo
>  http://shrimp.alerce.com/merlin/merlin.dmesg
> 
> I'm starting to understand that the box is probably running along as
> quietly as it knows how, unless there's some magic about fans and
> disks that I've missed.
> 

p4tcc0 reduce only frequency (actually it wont reduce the core
frequency), but not core voltage.
You actually wont save a lot of power with it.
It's main usage is to reduce processor temperature if need be.

The cpufreq0 actually is not a real driver.  It's used to merge different
drivers (for example p4tcc0 and est0 if your processor support SpeedStep)
in order to provide an unified interface available via dev.cpu.0.

Cheers,

-- 
Bruno Ducrot

--  Which is worse:  ignorance or apathy?
--  Don't know.  Don't care.