1. Computers
  2. Display Drivers
  3. Graphics Cards
  4. Memory
  5. Motherboards
  6. Processors
  7. Software
  8. Storage
  9. Operating Systems


Facebook RSS Twitter Twitter Google Plus


Phoronix Test Suite

OpenBenchmarking Benchmarking Platform
Phoromatic Test Orchestration

Testing For The Latest Linux Kernel Power Regression

Michael Larabel

Published on 29 August 2014
Written by Michael Larabel
Page 1 of 5 - 11 Comments

As I wrote about yesterday, there appears to be a new Linux kernel power regression that's yet to be solved by the latest Linux 3.17 code. The issue was originally tracked down to being a regression introduced during the Linux 3.15 stable cycle that disabled frame-buffer compression support by default for the Intel DRM graphics driver, but the impact it's had on the system power draw is much greater than what was anticipated by the Intel developers. A separate Intel employee is also reporting increased power draw, so I decided to run some tests on a few local systems to see what I'm encountering in the power consumption primarily between Linux 3.15 and 3.16.

Frame-buffer compression (FBC) support was disabled by default in the Linux 3.15 stable series for Haswell hardware and newer since the support wasn't mature and there were Intel HD Graphics users reporting issues with this feature being turned on, so it was disabled by default and hidden behind a kernel module parameter. After an Arch Linux user experienced a 4+ Watt increase in power draw for his Apple laptop, he bisected it to this FBC feature, but Intel Linux developers weren't expecting FBC to make such a huge difference in power draw. The matter is still being investigated but FBC simply can't be flipped back on by default since the code is incomplete and there's still some unmerged patches under review that won't make it until at least the Linux 3.18 kernel.

For seeing how recent kernels have been burning through power on a few of my local systems, first I decided to run some basic tests on an ASUS Zenbook ultrabook with Core i7 3517U processor and HD Graphics 4000 (and NVIDIA Optimus graphics that weren't in use). This system was running Ubuntu GNOME 14.04 where I tested the mainline/vanilla Linux 3.13, 3.14, 3.15, 3.16, and 3.17 Git kernels. All benchmarking was done via the Phoronix Test Suite and with the MONITOR=sys.power environment variable set so it would monitor the laptop's battery usage during testing.

From this Ivy Bridge ultrabook I first ran Xonotic where the reported power difference on battery between the tested kernels wasn't much... Between Linux 3.13 and 3.17 Git, the power consumption only differed by two Watts at most.

While the Xonotic data from the Ivy Bridge laptop wasn't interesting, when running LAME MP3 and watching the battery usage there is a clear difference... When running the MP3 encoding process on this Core i7 ultrabook, the power consumption with Linux 3.13~3.15 was 19~20 Watts, but when turning to the Linux 3.16 stable kernel and Linux 3.17 Git, the power consumption rose to 23 Watts on average. The peak power consumption was also much greater at 26~27 Watts whereas Linux 3.15 peaked at just 20 Watts.

Latest Linux News
  1. Linux 4.2 Bringing Support For ARCv2, HS38 CPU Cores
  2. Libdrm 2.4.62 Is An Important Update For Open-Source GPU Drivers
  3. The State of Unity 3D Game Engine, Editor On Linux
  4. ZFS On Linux 0.6.4.2 Brings Linux 4.1 Support, Fixes
  5. Old Net Burst Tests, Ubuntu Phone & Assembly x86 Were Popular Topics Last Month
  6. Qt 5.5 Officially Released
  7. Global Shortcuts In KDE Plasma Under Wayland
  8. LLVMpipe FP64 Support Knocks Off Some GL4 Extensions
  9. Dell Gets An Airplane Mode Switch Driver In Linux 4.2
  10. I Gave Up Waiting On The Water-Cooled Radeon R9 Fury X
Latest Articles & Reviews
  1. How KDE VDG Is Trying To Make Open-Source Software Beautiful
  2. Attempting To Try Out BCache On The Linux 4.1 Kernel
  3. CompuLab's Fitlet Is A Very Tiny, Fanless, Linux PC With AMD A10 Micro
  4. AMD A10-7870K Godavari: RadeonSI Gallium3D vs. Catalyst Linux Drivers
Most Viewed News This Week
  1. Kubuntu 15.10 Could Be The End Of The Road
  2. NVIDIA Starts Supplying Open-Source Hardware Reference Headers
  3. KDBUS Won't Be Pushed Until The Linux 4.3 Kernel
  4. The Staging Pull For Linux 4.2: "Big, Really Big"
  5. The State & Complications Of Porting The Unity Editor To Linux
  6. Latest Rumor Pegs Microsoft Wanting To Buy AMD
  7. SteamOS "Brewmaster" Is Valve's New Debian 8.1 Based Version
  8. Jonathan Riddell Steps Down From The Kubuntu Council