It looks like the debacle concerning RC6 power-savings support for Intel Sandy Bridge hardware is finally behind us. Intel thinks everything is worked out and ready to be enabled upstream (again) with the next Linux 3.4 kernel cycle and Canonical has enabled RC6 by default in Ubuntu 12.04 LTS. Here are some tests showing the performance benefits and power-saving abilities of using the RC6 hardware feature on Sandy Bridge processors.
Phoronix tests have shown for months how Intel RC6 power-savings can yield a significant reduction in power while at the same time it's able to boost the graphics core performance. Supporting RC6 has been a mess for the Intel OTC developers since for a small number of Sandy Bridge systems there have been stability issues and other problems when having the feature enabled. RC6 is a new feature to Sandy Bridge, but is looking to be more reliable with the next-generation Ivy Bridge processors. The latest belief is that Intel SNB RC6 should be sane when only enabling the standard RC6 power-savings level but not the deep or deepest levels.
In this article are benchmarks from an Intel Sandy Bridge notebook when running Intel's DRM next kernel tree and having applied the RC6 patches as described in this article. This allowed for testing the Intel Core i5 2520M CPU with RC6 disabled, standard RC6, RC6 + deep RC6, RC6 + deepest RC6, and RC6 + deep RC6 + deepest RC6 levels. This testing looked at the battery consumption while idling then running a range of OpenGL tests. The OpenGL performance was also monitored at each of the RC6 levels. All benchmarking and power monitoring was done by the Phoronix Test Suite.