Intel Flip-Flops Again: RC6 Disabled For Linux 3.2
Ouch, Intel at the last minute has -- once again -- had to disable RC6 power savings support from their open-source Linux graphics driver for Sandy Bridge hardware.
Earlier this month I wrote that Intel would be attempting to enable RC6-by-default for Sandy Bridge and Ivy Bridge graphics processors in the forthcoming Linux 3.2 kernel. RC6 is capable of saving power for mobile (and desktop) systems by allowing the integrated graphics processor to rest in a lower power-state, while at the same time is capable of boosting OpenGL performance.
Earlier this month I questioned whether Linus Torvalds would allow Intel RC6 to be enabled by default outside of the merge window considering this feature has been problematic in the past -- causing stability issues and hangs for some systems -- and he was already mad at one 3.2 DRM pull, but it ended up getting accepted.
Along with that merge this month was enabling of semaphores by default, which was then reverted last week over regressions. Now this week Keith Packard sent over a patch to Linus Torvalds to revert the RC6 by default.
So the Linux 3.2 kernel will not have RC6 by default for Sandy Bridge since it's still causing problems for some systems with this Linux driver, one year after the hardware first shipped. This commit is what does the flip-flop, again (it's been a similar story before).
Those wanting to take advantage of this feature and aren't hit by system freezes, you can pass i915.i916_enable_rc6=1 as a kernel command-line parameter to enable this power conservation feature.
Maybe with the Linux 3.3 kernel Intel will finally get lucky?
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