ubuntu 15.04 much worsen power consumption compared with 14.10

[Nir Yeffet]

After upgrade to 15.04, battery is draining withing 3 hours compared to 15 hours with 14.10, and obviously, the laptop case is very hot. On top of that, performance is worsen (choppy video). I've already found several causes and wanted to document here and get the community help in improving.

Hardware: Macbook air 6,2, core i7, 8GB ram, 128GB SSD.

Current solution: (~15 hours of battery life)
1. use kernel from 14.10 (3.16.0-37-generic #49)
2. x86_energy_perf_policy powersave
3. echo disable > /sys/firmware/acpi/interrupts/gpe66 (otherwise 1 cpu @100%, some weird hw behavior, started after upgrade from 14.04)
4. use upstart instead of systemd (helps with less power consumption and with adding simple scripts to pm-utils - sorry, systemd is new for me)

Status with the new kernel (3.19.0-16-generic):
Out of the box, I get 3 hours of battery life and choppy video after few minutes. Here are the step to improve to ~8 hours and no choppy video:
1. disable (blacklist) intel_powerclamp module. this solves the choppy video.
2. append "acpi_osi=" to the kernel command line (this is *the* major improvement, see below kernel bug)
3. steps 2-4 from the above solution.
Still way to go to get 15 hours.

Here is the related kernel bug, where more interesting information can be found, including turbostat output from the 3 scenarios above: https://bugzilla.kernel.org/show_bug.cgi?id=92111

I'll be happy to provide any information, run any tests and bisect the kernel to help with this.

[Nir Yeffet (nir-launchpad-net-8ff8)]

This is still a problem with the latest 3.19.0-18 push.