Comment # 74 on bug 954783 from Sebastian Parschauer

Thanks for confirming! Please check for latest BIOS and if BIOS has an option
to reduce the maximum package C-State. The OS can only prevent the CPU from
entering PC6 by disabling the core C-State C6 which of cause consumes more
power.

You can see in the "powertop" "Idle stats" tab which package and which core
C-States are entered.

Please check with your laptop vendor if BIOS can be adjusted, in case latest
BIOS doesn't help and package C-States can't be configured in BIOS. Until then
I think you would have to favor stability over power consumption.