The Sandy Bridge performance gains found in Linux 3.17 Git over Linux 3.16 came as a bit of a surprise since the i915 DRM driver improvements for this merge window didn't indicate any "SNB" optimizations. After having the time to conduct further testing in non-GPU workloads, there's a few performance improvements to note with the Core i5 "Sandy Bridge" processor with Linux 3.17. This likely indicates that the improved SNB performance with Linux 3.17 isn't due to DRM optimizations but perhaps optimizations to the P-State scaling driver, the kernel scheduler, or other areas that affect the entire processor performance.
The MP3 encoding test saw one of the biggest improvements in performance with Linux 3.17 for the Core i5 CPU found in the Sandy Bridge Apple Mac Mini.
However, not all tests benefit from the Linux 3.17 kernel.
You can dig through all of this Core i5 Sandy Bridge performance data between the Linux 3.16 and 3.17 Git kernels via this OpenBenchmarking.org result file. I'm currently in the process of testing Ivy Bridge and Haswell hardware too in looking for similar changes in performance, followed by AMD APUs/CPUs. If you appreciate all of this Linux hardware testing that's single-handedly done every day, please subscribe to Phoronix Premium or consider a PayPal tip.