While public details on Broadwell have been scarce beyond its 14nm fab process and new instruction set extensions, with the initial kernel driver code we have a feeling for Broadwell from the graphics side... Intel Broadwell graphics should be a terrific upgrade. Ben Widawsky in publishing the initial Broadwell support said, "Broadwell represents the next generation (GEN8) in Intel graphics processing hardware. Broadwell graphics bring some of the biggest changes we've seen on the execution and memory management side of the GPU. There are equally large and exciting changes for the userspace drivers."
Ben additionally said that the eigth-generation Broadwell graphics "dwarf any other silicon iteration during my tenure, and certainly can compete with the likes of the gen3->gen4 changes."
At a technical level, some of the architectural changes going from Haswell to Broadwell graphics include the silicon no longer supporting a force-wake write FIFO but most writes need to explicitly wake the GPU, interrupt registers have been completely reorganized, PTEs format and cachability settings have been changed to more closely resemble x86 PTEs/PAT, the address space has increased, and page table structures have changed for the per-process GTT. Intel developers have been working on this Broadwell Linux graphics driver code for one year, going back to November 2012. A special event with the Broadwell Linux enablement is in writing the initial code they managed to get a simulation environment for Linux graphics development. The developers were able to simulate and run their complete software stack and model most of the Broadwell hardware. Since December of last year they were able to run the well-known glxgears demo on the Broadwell simulator.
While Ivy Bridge and Haswell brought some mighty performance improvements for Intel graphics, it's very exciting to see that Broadwell will be another huge leap forward. With Ben comparing the Broadwell "Gen8" graphics to the changes in going from Gen3 to Gen4 and yielding some of the biggest changes, I'm really excited and growing anxious for the debut of Broadwell. The performance should be a leap forward, power efficiency is going to be even better, and other new features emerge.
When it comes to the Linux vs. Windows support, tests I did just days ago on Haswell showed the Intel Linux vs. Windows GL performance is mixed but hopefully we can see more optimizations land on the Linux side of the Broadwell launch. Besides the OpenGL performance, other areas where the Linux driver is still trailing the binary Windows driver is in GL compliance and OpenGL. Mesa 10.0 is the first release where Ivy Bridge and Haswell finally supports OpenGL 3.3. On the intel OpenCL side, they aren't using the Clover Gallium3D implementation but rather have their own project known as Beignet and its future and direction remain unclear. Patch review for the Broadwell Linux GPU enablement is happening on dri-devel as always. Stay tuned for more coverage on Phoronix as the Linux 3.13 kernel officially enters development in the coming days and as we monitor the repositories with the help of Anzwix to watch Broadwell mature and await the arrival of the Mesa DRI driver support.