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I installed PowerTOP 1.97 and i got many Bad in Tunables, I know i can press enter to toggle but does it really change anything? and if it does will it still be changed when i reboot? If i get everything to show Good will it make a big difference on the battery life?

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up vote 8 down vote accepted

The Good/Bad settings may or may not help, it really depends on the hardware. Some settings are marginal, others save a fraction of a Watt, others may actually not help at all. Here is some analysis I did a while back. I used a high precision digital multi-meter and a few machines to sanity check all the power top settings for the candidate machines.

http://kernel.ubuntu.com/~cking/power-benchmarking/powertop-good-bad-recommendations/results.txt

and raw sample data: http://kernel.ubuntu.com//~cking/power-benchmarking/powertop-good-bad-recommendations/powertop-good-bad-recommendations.ods

Note that power top tries to figure out the power consumed from the battery ACPI status, but some batteries are not that accurate since they sometimes re-calibrate their capacity settings so one can get some wild fluctuations in battery readings. With the kind of settings you are looking at powertop may not be able to measure the savings because we could be talking about a few mW in savings on each setting.

For big savings, see https://wiki.ubuntu.com/Kernel/PowerManagement

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