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04 April 2012, 13:00

Linux 3.4 will use Intel's power saving RC6 GPU technology

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Kernel graphics icon Linus Torvalds has applied a patch for inclusion in Linux 3.4 which will mean this kernel version will, by default, use the RC6 power-saving technology of Sandy Bridge processors and their GPUs. Since RC6 typically reduces the idle power consumption by around 3 to 5 watts, the change will extend the battery life of notebook PCs significantly and reduce noise levels as the fans will have to remove less heat.

Processors with cores from Intel's Sandy Bridge generation are inside many recent notebook and desktop systems. Using the kernel parameter i915.i915_enable_rc6=1, users can enable the power-saving technology on older versions of Linux, but in some systems it can lead to crashes or display errors. This is why the technology has not been enabled by default for the last few versions. Now, though, the problems should be avoided by Linux not using the deepest sleep state of RC6. According to the Intel developers the power consumption in this mode is not much less than the shallower mode Linux now stops at. Users who still want to use the deepest sleep state can enable it through kernel parameters explained in comments on another patch.

If more problems are discovered with the shallower RC6 mode, the kernel developers could still stop the switch to default use of RC6, but that would be twice in the last twelve months that this would have happened in connection with RC6. However, this time, that scenario is likely to be rather unlikely, since the Intel developers seem quite sure that the current approach will avoid any problems.

The two changes are some of the several commits that Torvalds has, despite potential stability problems, applied to the main development branch of Linux even though the merge window for Linux 3.4 closed at the weekend with the release of RC1. Other latecomers included "PRIME", a basic drm dma-buf interface layer for exchanging information about graphics cores without much overhead. This is one of several components which will allow Linux distributions, in the medium term, to switch graphics cores on and off without the user having to restart the X server or make other interventions. This is interesting, not just for DisplayLink monitors, but also for notebooks, where systems like NVIDIA's Optimus technology can activate a more powerful graphics chip at run time. So far, however, no drivers are using the new infrastructure. Corresponding enhancements for the Nouveau, i915, udl and Exynos OMAP will follow in Linux 3.5.


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