Avian’s Blog

Last time I've read on Eee User forums some measurements that suggested that lowering CPU frequency (via the cpufreq kernel module) to conserve battery power isn't useful because the current Eee draws from the battery is the same regardless of the frequency (sorry, can't find that post now). I find that odd, but I would happily get rid of the ondemand CPU frequency governor that's making things sluggish if it really doesn't help a bit.

After some searching around the internet I found some alternative theories why lowering your CPU clock when on battery isn't good. They say that modern CPUs have the ratio of power consumption between idle and full power so high that it is better to always have the CPU at the highest clock so that it spends as little time out of idle as possible.

So today I wanted to solve this out once and for all with some measurements of my own. Unfortunately it wasn't as simple as I thought it will be. It turns out that my particular laptop will not run with an ampermeter in series with the power supply. Without the battery it starts, but is very unstable and most times resets before Debian stops booting. With the battery it doesn't even do that. Weird. I'm guessing the added inducance and resistance is causing some undervoltage protection to trigger.

Well, I'm not going to give up that easily, but this will have to wait until I can set up a more serious experiment.