Now that we have run the Nouveau open-source NVIDIA tests on the Linux 3.15 kernel and discovered there were no real performance changes for this latest Linux kernel, after finding some Radeon regressions in Linux 3.15, now our attention is on Intel and their Haswell-based HD Graphics. Fortunately, the Intel numbers are slightly more interesting than the Nouveau data.
An Intel Core i7 4770K Haswell processor with HD Graphics 4600 was benchmarked on Ubuntu 14.04 LTS when using the Linux 3.14 and 3.15 Git kernels. The testing is very straightforward and similar to our other Direct Rendering Manager graphics driver benchmarks when comparing kernel releases. All benchmarking was handled via the Phoronix Test Suite.
With the Linux 3.15 kernel the Intel DRM graphics changes are plentiful. There's per-process address space support, improvements to power management, 5.4GHz DisplayPort support, large cursor support for HiDPI displays, many Broadwell support improvements, some continued Bay Trail / Valley View work, and a variety of bug-fixes and other work done by Intel's large open-source Linux graphics team.