[CFT] RC6 Enabled by Default on Sandy Bridge

Leann Ogasawara leann.ogasawara at canonical.com
Sat Feb 18 21:07:47 UTC 2012

Hi All,

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 [1].

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. As a result, a patch has
recently been submitted upstream to disable RC6p for Sandy Bridge [2].

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

We have decided to post a widespread call for testing from Sandy Bridge
owners running Ubuntu 12.04.  We hope to capture data which supports the
the claims of power saving improvements and therefore justify keeping
these patches in the Ubuntu 12.04 kernel.  We also want to ensure we do
not trigger any issues due to plain RC6 being enabled by default for
Sandy Bridge.

If you are running Ubuntu 12.04 (Precise Pangolin) and willing to test
and provide feedback, please refer to our PowerManagementRC6 wiki for
detailed instructions [3].  Additionally, instructions for reporting any
issues with RC6 enabled are also noted on the wiki.  We would really
appreciate any testing and feedback users are able to provide.

Thanks in advance,
The Ubuntu Kernel Team

[1] http://phoronix.com/forums/showthread.php?68199-Intel-Wants-YOUR-Linux-Questions-Feedback&p=246785#post246785
[2] http://lists.freedesktop.org/archives/intel-gfx/2012-February/015131.html
[3] https://wiki.ubuntu.com/Kernel/PowerManagementRC6

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