If you read the patch documentation, it only creates the new policy and sets it as the default.
Choosing <which> policy to use as an alternative to the new default is left for something else to do,
And I can only assume that would mean when your system is under load, it will automatically switch to the original Max policy and later return to the Med policy when load has been removed.
I’d guess that is what you should test…
What happens if you put your system (particularly the drive sub-system) under extreme load, and then take your sensor readings (in particular wattage draw). Unfortunately, the patch author doesn’t describe exactly how he set up his sensor readings or used an external device to measure power draw, so you may have to figure this out on your own.
Unless I’m misreading, that’s what the code does.
Since the two biggest draws on power are the display and the disk subsystem, the potential benefit can be very significant.
Would be interesting if the patch indirectly affects CPU stepping, but I don’t see anything that would do so.
I also came to a personal conclusion that acpid won’t likely do what you want properly (maybe someone else will have a different opinion)
The main topic in this thread is described a few sections from the end in the first link.
The benefit is mainly for rotating disks (unlikely to benefit SSD)
Management of SATA power policy is not automatic.
Through a combination of both Wikis,
Laptop Tools describes only completely powering down the disk to save energy, but can result in latencies when powering up and severely shortening the life of the drive. This new option to lower the power draw but not power down the drive completely is potentially the best of all options with power savings without shortening the life of the drive.
So, the remaining question is how to manage your SATA power policy according to whether you’re plugged into external power or not, and the first Wiki link provides a couple suggestions but perhaps the systemd recommendation is best
Although the first reference on Power Management should be read completely for a full picture managing power states with systemd,