Re: [PATCHSET] 0/3 Dynamic cpufreq governor and updates to ACPI P-state driver

[Dominik Brodowski <linux@brodo.de>]

On Mon, Nov 03, 2003 at 07:21:34PM -0800, Jan Rychter wrote:
> >>>>> "Len" == Len Brown writes:
>  >> I have done some measurements on a Toshiba S7/290LNKW, which has a
>  >> 900MHz Pentium-M. The results have been posted to this list a while
>  >> ago -- the most surprising one being that the Pentium-M in that
>  >> machine seemed to always consume the same amount of power when idle,
>  >> independent of operating frequency.  The frequency only made a
>  >> difference when the CPU was actually doing something (or when I made
>  >> it not use the C3 state by loading usb-uhci).
> 
>  Len> Probably the cpu is running HLT in the idle loop, so the power
>  Len> consumption there would not vary with MHz.
> 
> Oh -- well, that's exactly what I wanted to check. It seems it does vary
> for speedstepped Pentium-III Mobile, according to my measurements,
> that's why I was surprised.
> 
> This should influence the design of dynamic power management -- if the
> CPU is already idle, there is no point in slowing it down. It only makes
> sense to change the frequency when we're actually doing something.

This assumption is at least partly wrong. Pentium-III Mobile datasheets
clearly show that the power usage when doing nothing varies up to 50%
dependand on the frequency setting. So even if it is no measurable effect on
one processor, this theory isn't true for all processors. And dynamic
power management should work best _for all processors_.

	Dominik