a question about energy

[Nikos Chantziaras]

On 03/01/2010 11:06 AM, Zhi Li wrote:
> All,
>
> I'm working in a project which study energy saving on PCs. I saw a
> strange thing which was opposite to my intuition: when PC working on
> graphic mode, it would be more energy saving.
>
> When in graphic mode, on my PC, it is 52w; when I switched to terminal
> mode(on linux alt-ctrl-1), it is 55w.
>
> I also tried to init 3, then startx, the result is same.
>
> Does anyone here know why?

The X11 driver will usually reduce the clocks of your GPU (and possibly 
the voltages; depends on the driver you're using) when it's idle.  When 
you switch to a TTY, the clocks/voltages are increased again since the 
framebuffer driver doesn't do power management.