[ltp] Regarding cpu TEMPERATURE

[Matthew Garrett]

On Tue, Aug 02, 2005 at 09:30:11PM -0500, Radha Krishna Ganti wrote:

> I think Chris  got it  as low as  50MHz, . This would give a lot
> of power saving.  Does ACPI specs dictate  a minimum of 600 Mhz or 
>  is it dictated by the processor type.  

Speedstep will only drop you to 600MHz. You can then use throttling to
further reduce the speed without reducing the voltage. Assuming an idle
CPU, slowing it to 300MHz (from 600MHz) will drop your power consumption
by a maximum of 2W or so. On an average system, that'll give you, ooh,
about 12% more battery life. And everything will take twice as long as
it did before.

If your system is idle, then the C3 state transition is worth a lot more 
than dropping the CPU frequency (dropping the CPU voltage, on the other 
hand, is very important. Which is why speedstep does that). If your 
system isn't idle, then you generally don't want the processor to be 
running more slowly - certainly not in situations where there's a linear 
relationship between the speed, the power consumption and the time taken 
to do anything. Remember that at low CPU speeds, the power consumption 
of the rest of your system is much more significant than the CPU.
-- 
Matthew Garrett | mjg59@srcf.ucam.org