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Power Management on Linux, Part 2
Five Degrees of Laptop Off
April 17, 2008
In part 1 of this series we learned how to measure how much power our systems are using, both hardware and software, and some tricks for reducing power usage without degrading performance. Today we're going to dive into the world of power management on laptops: ACPI, APM, hard disk spindowns, and spinups.
Power management on laptops is all about squeezing out more battery time. It's a losing battle as laptops get more powerful and use bigger displays. For example, my old Thinkpad R32 runs for three hours on a charge, even on wireless. My shiny new dual-core T61 lasts a bit under two hours. The new machine is brighter and faster, and it has a magnesium roll cage. (Oo la la, like a race car.) Modern laptops with wide glossy screens are lucky to get ninety minutes.
You can get more battery time by dimming the screen, and mobile CPUs can be configured to run slower on battery. So sticking with an old slow dim machine might be a good option, because you get the same effect with no work.
Managing interruptions is a common problem for laptop users. Shutting down and starting up again takes time and eats power. And so we have a confusing array of not-really-off options: