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Linux kernel patch slashes power hunger

Energy consumption reduced with smart coding

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Linux users working on laptops and other portable devices may soon have cause to rejoice thanks to a new kernel patch that finally promises to fix power regression problems associated with recent versions of the software.

Affecting Linux systems using version 2.6.38 or later of the Linux kernel, the problems have dramatically increased the amount of power consumed by Linux, resulting in far fewer hours of use per each battery charge.

Power consumption on an Intel Sandy Bridge notebook running Ubuntu Linux with kernel 3.1, for example, has increased by 76 percent since earlier this year due to Linux kernel regressions, according to a report this summer on Phoronix.

Earlier this month, however, a new patch was proposed that appears to be a fix, once and for all. The patch reportedly isn't likely to appear in the mainline Linux kernel until version 3.3, but it could still make it into the Linux 3.2 kernel package for use in Ubuntu 12.04 LTS and other distributions.

The switch from Linux 2.6.37 to version 2.6.38 caused a jump of 9 watts in average power consumption, representing an increase of 36 percent, Phoronix notes, and subsequent versions have increased their demands from there.

At the heart of the problems is the disabling in many systems of PCI Express Active State Power Management, a feature that was designed to save system power. Starting with Linux 2.6.38, ASPM frequently gets disabled when it shouldn't be, resulting in the power usage jumps that have been observed on both mobile and desktop systems.

With the new, roughly 60 line patch created by Red Hat engineer Matthew Garrett, however, power use reverts to what it was in versions of the kernel before Linux 2.6.38, Phoronix reported last week.

Applying the patch on a Core i7 notebook that had been using 14 percent more power because of the problem, for instance, "the power is back to the levels experienced on Linux 2.6.37," Phoronix's Michael Larabel wrote. "Hell yes!"

So, if you've been using a recent version of Linux, chances are your hardware has been hogging more power than it used to, whether you realised it or not. Now, at last, relief is in sight.



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