[SATLUG] APM in Linux/Ubuntu

Bryan Beicker bryan at beicker.com
Thu Oct 6 21:45:23 CDT 2011

> After my recent $400+ power bill in CA, I was wondering if anyone knew
> how to set up APM/ACPI and deal with (troubleshoot) the issues that
> come up.

Early attempts at lowering the power of the CPU involved frequency 
scaling, such as lowering a multi-gigahertz chip to only a few hundred 
megahertz.  Linux has several governors to do this: "ondemand", 
"performance", and "userspace" being the most popular.  You can read up 
on them if you like, but for the most part power-reduction is now done 
automatically in hardware.

Both Intel and AMD chips now have "turbo" modes that constantly change 
the frequency of the CPU independently of the OS.  Newer designs even 
have "power gating" that can turn off large portions of the chip while 
idle.  The 32nm chips take a small fraction of the power that 45nm chips 
needed, and the newer 22nm process promises even more savings.

Desktop systems from just a year or two ago can easily idle above 100 
watts.  My current desktop (i5 2500K, WD Green 2TB, Seasonic 80+) idles 
in the mid 20's.

Buy yourself one of those in-expensive "Kill-A-Watt" devices and start 
measuring your components yourself.  You may have a lot of low-hanging 
fruit to prune.

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