Comment 11 for bug 1686448

r8168-dkms have not made it hit a higher package C state. On page 70 of the document I posted the link on comment 7, it shows the maximum package C state the Skylake U/Y would be able to reach, depending of screen resolution. As this notebook has a 1366x768 screen, I suppose that it would reach up to Package C8 without PSR (Panel Self-Refresh) disabled, but I have it enabled:

[ 0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.16.0-041600rc6-generic root=UUID=6b4ae5c0-c78c-49a6-a1ba-029192618a7a ro i915.enable_psr=1
[ 0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.16.0-041600rc6-generic root=UUID=6b4ae5c0-c78c-49a6-a1ba-029192618a7a ro i915.enable_psr=1
[ 1.450734] Setting dangerous option enable_psr - tainting kernel

It may be on the maximum power save state already this particular notebook model can have. The remaining thing to test would be the powertop proposed changes.

Today is the first time I've seen that the notebook is using less than 5 W of power while in use. If its battery was as when it was new, I would be able to get more than 6 hours of battery.