A Useful Intel Power Management Feature Has Landed For Linux 4.15

The libata subsystem changes these days tend to not be too interesting, but for Linux 4.15 there is a noteworthy power management change.

Two years ago was a blog post by kernel contributor Matthew Garrett about lowering power use for Haswell and newer laptops. The work he was doing back then for SATA power management didn't end up getting merged and had some issues, but now Red Hat's Hans de Goede has followed the work through and got it merged.

The power management change in question is adding a med_power_with_dipm link_power_management_policy setting. this new "medium" policy should behave nicely with more hardware. The default max performance LPM policy doesn't allow for the CPU to reach the lowest power states while the minimum policy saves more power but can cause issues with some disks/SSDs and lead to crashes or disk corruption.

As Hans explained in the patch, this new medium policy that will be the default matches the behavior of the Intel IRST Windows driver that most laptops use and thus shouldn't cause problems. Hans testing found that this new "med_power_with_dipm" policy on his ThinkPad T440s laptop dropped power use by 1.2 Watts, the same as using the min_power policy.

A one Watt savings with newer power-efficient Intel laptops should be quite noticeable with this feature for Haswell and newer CPUs. This change along with other ATA work was merged via yesterday's libata pull request.