[Bug 177646] Re: Celeron M530, no frequence scaling

[Andy Whitcroft]

On Fri, Jan 16, 2009 at 10:34:38AM -0000, LeO wrote:
> Pehaps it would not save energy for the CPU. But I assume the CPU does
> not heat that much when running with 500 MHZ  or 1 GHZ instead of 2 GHZ.
> So, perhaps it does not save the CPU-power consumptions, but it saves
> the cooling devices + it saves on the long term the material. Saving the
> cooling devices on a Laptop means in most of the cases to avoid fan-
> activity ==> no power consumption on the fan => power saving.
> 
> I see it more or less the side-effect a reduced CPU-frequ has on the
> overall system. AND therefore I would like to have it enabled.

The problem is that the CPU still has to perform the same number of
cycles at full speed to run any task it is asked to perform, and those
will consume the same amount of energy whether they are done together or
spread out.  There is evidence that the overall energy cost is actually
higher when switching in and out of the sleeping state really often
(which is what occurs when this mode is enabled) and thus more energy is
consumed and heat dissipated.  We also need to consider the temperature
as seen at the heat sink is majorly divorced from the temperature profile
of the chip surface itself.

What I am trying to say here is that it is not at all obvious that enabling
this is a good thing.  There is a lot of "I feel it will be better"
sentiment, mostly as they are running without a power control module and
with one "must be better", but no direct evidence that it is better, and
much comment from those with direct access to the manufacturers saying
the opposite.

To make any progress on this someone would have to take the time to do a
fully measured (power consumption at the wall) comparison on a sensible
workload for the machine and present those results.  Which is what one
commenter seemed to have done but had not explained how the results were
generated to allow verification.

-- 
Celeron M530, no frequence scaling
https://bugs.launchpad.net/bugs/177646
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