[ltp] short battery life on t40

[mukesh agrawal]

On Thu, 11 Sep 2003, Neil Weisenfeld wrote:

> One thing to figure out is why, at least with my recent configuration,
> we can't get CPU speeds *below* 600MHz.  That's what Windows does with
> low demand and on battery.

AFAIK, "Enhanced SpeedStep" only supports going down to 600 MHz.

If you want to go lower than that, you have to use CPU throttling (which
turns off the clock pin on the CPU for some amount of time).

There was a discussion about this on the cpufreq mailing list recently. I
think the conclusion was that if the machine really is idle anyway, then
throttling the CPU won't save any more power over calling the CPU halt
instruction anyway.

As to whether or not Linux is calling CPU halt, I don't know.

(I looked into it once on a 2.4-series kernel, and it seemed like the
system would make the CPU halt call once, decide that the call didn't
actually do anything, and then stop making those calls.)