Just What is Saved?
Though it isn't really apparent from the data, there is a significant amount of power saved at idle. In the case of my CPU, taking a little step down from 1.5V to 1.4V and dropping the clock frequency by 10% from 2GHz to 1.8GHz, the power dissipation drops from 89W to 69W. Thats 20 Watts of power savings from a step down that would be hard to notice even if you were playing a game during the step. The cut from 1.5V@2.0GHZ to 1.1V@1.0GHz drops the power from 89W to 22W, for a whopping 75% savings. Thats about the same as turning off an incandescent light bulb in your computer's case. That is certainly good news for cooling and component life.
Conclusions
The Cool'n'Quiet (PowerNow!) feature is definitely something worth looking into. It's always a comfort to know that you are keeping your power waste to a minimum, and possibly extending the life of your CPU at the same time. When you can do this without a noticeable loss of performance, the choice becomes a no-brainer. I just don't see a downside yet.
The biggest downer so far is the lack of a real-time power monitor/controller for Linux. Without something to give me real-time feedback, I can't even verify that the Linux system is following my instructions to cut back on the settings. I have been keeping it dialed down to minimum power settings, since I don't usually stress the CPU using Linux anyway. I just can't prove that it is saving anything at all.
After lots of poking around, I found that support for Cool n' Quiet is pretty sparse in Linux. I've found a few monitors that claim to work well, but they would either require me to rebuild my kernel after adding some dubious code, or they are geared toward slowing down a server based on some fairly long term load calculations. After seeing how the Windows support works, I'm spoiled for anything else. Any response that isn't instant is too slow for me.
-- C O Jones
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