Following this week's 3.15-rc1 release, I ran some early tests of the Linux 3.15 kernel compared to the earlier kernel releases. In particular, the early Linux 3.15 Intel results were compared against the stable Linux 3.14 and 3.13 kernels. Testing was done from an Intel Core i7 4770K "Haswell" system with HD Graphics 4600.
The results aren't really interesting when comparing the recent Linux kernel releases, but I'm sharing them for those curious and to prevent those from emailing in asking about any Linux 3.15 Haswell graphics performance changes and why there haven't been any benchmarks published... The results can be found via 1404162-KH-LINUX315I72. For more details on the Intel Haswell changes for the Linux 3.15 kernel that are more functional than performance oriented, see the Linux 3.15 DRM coverage.
More interesting on the recent kernels (given the shift of focus by upstream Intel Open-Source Technology Center developers) will be the performance of Bay Trail and Broadwell hardware. Emerging now is also the start of Intel Cherryview support under Linux.