Ubuntu Wiki

RC6

RC6 is a technology which allows the GPU to go into a very low power consumption state when the GPU is idle (down to 0V). It results in considerable power savings when this stage is activated. When comparing under idle loads with machine state where rc6 is disabled, improved power usage of around 40-60% has been witnessed.

As a bonus, when those states are reached, there are additional thermal and power space for both CPU and GPU to go into a more aggressive turbo mode. This can also improve the performance of intensive workloads by around 10%, and a bit more in some cases.

The above was taken from an indepth summary regarding RC6 posted by Eugeni Dodonov.

Ubuntu RC6 Status

Up until recently, RC6 was disabled by default for Sandy Bridge systems due to reports of hangs and graphics corruption issues when RC6 was enabled. Intel has now asserted that RC6p (deep RC6) is responsible for the RC6 related issues on Sandy Bridge. A patch was therefore submitted upstream to disable RC6p on Sandy Bridge.

In an effort provide more exposure and testing for this proposed patch, the Ubuntu kernel team has applied it to 3.2.0-17.26 and newer Ubuntu 12.04 Precise Pangolin kernels. We have additionally enabled RC6 by default on Sandy Bridge so that users can benefit from the improved power savings by default.

How to Test

We would like to capture any feedback regarding improved power savings Sandy Bridge users witness while running a 3.2.0-17.26 or newer kernel. More importantly, we want to know of any issues which arise as a result of having RC6 enabled. To test, please follow the instructions below:

1. Boot into 3.2.0-17.26 or newer Ubuntu 12.04 Precise Pangolin kernel
2. Gather System Info (BIOS info, kernel version, VGA info)
   • sudo dmidecode -t 0 | grep "Version:"
   • uname -a
   • lspci -nn | grep "VGA"
3. Install power measuring tools
   • sudo add-apt-repository ppa:colin-king/powermanagement
   • sudo apt-get update
   • sudo apt-get install powerstat
4. Unplug the power from your laptop/netbook and run the following command:
   • sudo powerstat
5. Note the average power consumption and standard deviation which are shown at the end of the powerstat run
6. If you experience any issues due to RC6 being enabled, please file a bug:
   • ubuntu-bug linux
7. Reboot into the same kernel but disable RC6. To disable RC6, do the following:
   • Hold down Left-Shift key to enter the Grub menu on boot
   • Hit 'e' to edit the kernel command line
   • Append i915.i915_enable_rc6=0 as a kernel boot parameter

     • For example: linux /boot/vmlinuz-3.2.0-17-generic <...> quiet splash vt.handoff=7 i915.i915_enable_rc6=0

   • Press Ctrl-x to boot
8. Unplug the power from your laptop/netbook and run powerstat again to capture comparative test results with RC6 disabled
   • sudo powerstat
9. Note the average power consumption and standard deviation which as shown at the end of the powerstat run
10. Add test results to the Crowd Sourcing Test Results section below

Extended Testing

We would appreciate and exteneded testing with RC6 enabled. For example, exercising graphics doing normal day to day activities. We are keen to hear about any issues such as hangs or graphics corruptions which are triggered with RC6 enabled. If you experience such issues, please file and bug by running 'ubuntu-bug linux' from a command line.

Crowd Sourcing Test Results