Comment 5 for bug 855348

A patch was proposed at:
http://comments.gmane.org/gmane.linux.power-management.powertop/2170
It says that if the file exists then it will write to it.

It seems that a powertop --calibrate may be required after an empty file is created to get benifit from it. E.g. "sudo touch /var/cache/powertop/saved_parameters.powertop" as suggested. Note, you want to make sure of the permissions of this file, especially on multi-user systems.

powertop --calibrate turns things on and off to test power usage. One suggestion said to let it run for an hour or so after and it will show estimates in a new column.