Lack Of Broadwell RC6 Has Us Looking Toward Linux 3.15
While Intel's upcoming Broadwell processors will have proper graphics driver support with the Linux 3.14 kernel (and updated user-space components), for those concerned about power usage, there's still some very important bits that do not look like they will land until at least the Linux 3.15 kernel.
Ben Widawsky of Intel sent out a patch series on Tuesday evening for implementing RC6 and RPS on Broadwell to increase power-savings. Broadwell should be in good shape for Linux 3.14, but it won't have the RC6 power savings mode to lower the integrated graphics processor's power use even more when under idle. RC6 has been present for several generations of Intel hardware and has caused big power wins when properly implemented within Intel's DRM driver.
Ben wrote, "This patch series implements RC6 and RPS for Broadwell. Most of the work had already been done with the initial merge of Broadwell support, however, there were a couple of missed things, and enough stuff had moved around. The big change is the addition of the interrupt handlers. I am mostly interested in getting RC6 working. RC6 enabling is critical to getting other teams up and running. I decided to table RPS as well because the code isn't quite as isolated as I would like, and the work didn't seem that difficult."
In Ben's final mailing list patch he noted, "It is tested and looking fairly stable now, so turn it on." There's a fair amount of changes and code refactoring that went on to make RC6 work for Broadwell. While the Linux 3.14 kernel merge window is still open, these patches haven't even been queued up for the intel-drm-next branch and are unlikely to be merged until the Linux 3.15 kernel.
Intel Broadwell processors should be out within a few months time and I'm incredibly excited to test them on Linux. Broadwell is the 14nm shrink of Haswell and its graphics abilities should be amazing along with many improvements on the general CPU front as well.
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