New Patches Will Have Cherryview & Broadwell Owners Looking Toward New Kernel

While Intel's Open-Source Technology Center has publicly had Broadwell Linux GPU driver code to post public since the end of 2013 and they've already started on Skylake enablement, there's still yet-to-be-mainlined patches for the Linux kernel to benefit Broadwell graphics performance.

Broadwell laptops/ultrabooks are beginning to ship now, but it looks like more performance optimizations are coming for Linux 3.20 (or later) to better the Haswell successor's open-source experience. Kenneth Graunke posted a new patch this week for enabling a HiZ RAW stall optimization on Broadwell. "This is an important optimization for avoiding read-after-write (RAW) stalls in the HiZ buffer. Certain workloads would run very slowly with HiZ enabled, but run much faster with the hiz=false driconf option. With this patch, they run at full speed even with HiZ. Improves performance in OglVSInstancing by 3.2x on Broadwell GT3e (Iris Pro 6200)."

Besides this HiZ optimization for Broadwell hardware, there's also the Cherryview optimization and another patch for improving Cherryview's HiZ throughput. For the HiZ throughput patch according to Kenneth, "Improves performance in a HiZ microbenchmark by around 50%. Improves performance in OglZBuffer by around 18%."

HiZ optimizations are common among graphics drivers for improving 3D graphics performance. As the Linux 3.19 kernel merge window is over, the earliest these patches will be merged to the mainline kernel is Linux 3.20. I'll test DRM-Next (among other kernel options) when starting my Broadwell Linux benchmarks soon using the ThinkPad X1 Carbon ultrabook with Core i7-5600U sporting HD Graphics 5500. These benchmarks will begin on Phoronix at the end of the month and will also include Broadwell Windows vs. Linux numbers.