[ltp] Question on APM vs ACPI

[Nathan Kurz]

On Tue, Dec 07, 2004 at 07:50:59AM +0100, Bob Alexander wrote:
> From the help I have received from this list and reading around I have 
> understood that:
> 
> 1) APM is much better when suspending in low battery drainage

I've read that many times too, and while I'm certain it was true at
some point for some hardware, I don't know that it is now.  I just did
a little measuring on my X30 running 2.6.9 and ACPI S3 suspend-to-ram,
and it seems to use abou 550 mW while sleeping.  This is about 1.25 %
of battery capacity per hour, and about what I've seen people claim
for APM sleep. So I'm not sure that ACPI is necessarily worse here.

> 2) ACPI is much better on CPU throttling (ala SpeedStep) when running on 
> battery

I'm trying to understand this myself.  It seems that throttling is
only possible under ACPI, but that frequency scaling is independent of
APM/ACPI.  It also seems that scaling has a much larger effect than
throttling on power consumption.  My impression is that SpeedStep is
the combination of these two.  Is this accurate?

> Is it possible to have the two different options working toghether to 
> get the best of both worlds ?

My current impression is that ACPI offers the better performance in
all the worlds, at the cost of greater complexity.  I also haven't
found anyone who has fully working APM suspend support.  

--nate