David Rees wrote:
On 7/30/06, bert hubert <[email protected]> wrote:
On Sun, Jul 30, 2006 at 09:46:51PM +0200, Arjan van de Ven wrote:
> as a side note ... you realize that clockmod doesn't actually save you
> any power right? ;)
Indeed, and I've measured that too. But it saves an awful amount of
noise!
If it doesn't save you power, how does it reduce noise? I guess it
keeps you from overheating your processor which causes the fan to spin
up?
The aim of power-saving techniques is to allow the same amount of
computational work to be done while consuming less power. For example,
if a task only uses 20% of the CPU at its maximum speed, the clock speed
can be dropped down to half of the maximum. The main advantage of this
is that it allows reducing the core voltage which I think accounts for
most of the power savings. Essentially the lower performance settings
have higher performance per watt than the higher settings.
Clock modulation doesn't reduce the CPU core voltage, nor does it reduce
the rate at which power is consumed when the CPU is in the active state.
It just causes the CPU to periodically stop its clock for a while,
during which no work is done. This means that the power and heat
produced is reduced but the work that can be done is also reduced by an
proportional amount, so there is little or no improvement in performance
per watt. As well, when the CPU has nothing to do it will be halted
anyway which does pretty much the same as what clockmod is doing.
Essentially clockmod is there as a way to limit the thermal output of
the CPU in thermal emergencies, it's not really very good as a
power-saving feature.
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from [email protected]
Home Page: http://www.roberthancock.com/
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