apm is working fine. In dmesg, I can see that my E-450 APU have 3 speed detected:
cpu0: 1646 MHz: speeds: 1650 1320 825 MHz
So I vim /etc/rc.conf.local and add:
Basically this is to tell apm to use Automatic performance adjustment mode. So with power adapter connected, the processor will be in full force (1650Mhz) and will lower down to (825Mhz) when in battery mode and scale up/down according to load. Nice.
I will still need to find something about the LCD's brightness though because that's one of the major power-sucker. Will update on this later.