Update on DeviceKit

[Matthew Garrett]

On Thu, May 08, 2008 at 06:02:14PM +0200, Holger Macht wrote:

> I don't expect desktop application to be so intelligent to care about all
> different policy knobs a CPU might export. But they want to tune the
> setting depending on AC or Battery. Then consider the 1-100 scale as just
> two settings, "on AC" and "on battery". It's basically used as that these
> days.

*No*! There is basically nothing you can do in processor power 
management that is sensible on battery but bad on AC (or vice-versa). 
Modern processors (basically anything that can run any current Linux 
distribution) are most efficient when they're doing nothing. The only 
sensible way to use these processors is to ensure that they spend most 
of their time doing nothing, which means that you want them to run as 
fast as possible when they need to do something. Once they've stopped 
running code, it doesn't matter what clock frequency you're running them 
at. The execution units are turned off.

The idea that CPUs have a power/performance tradeoff is basically 
untrue. The best power saving is obtained in a configuration that also 
gives you the best performance. Reducing performance increases overall 
power usage, which means it's certainly not something you want to do 
when you're on battery.

-- 
Matthew Garrett | mjg59 at srcf.ucam.org