When starting with Doom 3 at 1920 x 1080 and low quality settings, the relative results are similar to expectations set by past Phoronix articles:
- The latest Git code tends to usually be faster than the older code found in Ubuntu 12.04 that's months old and with the open-source graphics drivers in a continued game of catch-up compared to the proprietary drivers and Windows counterparts, the latest development code always tends to be faster. However, with Doom 3 for some of the hardware there is not much change in this particular test.
- When tweaking the driver stack with enabling 2D color tiling and PCI-E 2.0 support. The open-source OpenGL performance tends to dramatically go up... PCI Express 2.0 still is not enabled by default even though PCI-E 2.0 graphics cards and motherboards have been around for years and we are now up to PCI Express 3.0... PCI-E 2.0 is not on by default since reportedly for some GPU/motherboard combinations there are some issues. Rather than working to figure out the root cause of the problem and take care of that, the AMD developers just disable the support. This is similar to their approach of disabling HDMI audio now on recent kernels too just because of reported issues for a small minority of users. I hope that sometime they will work to get PCI-E 2.0 enabled by default since it works for the vast majority of users and provides significantly better results. For now enabling it you need to set radeon.pcie_gen2=1 from the kernel command-line / GRUB when booting.
- The proprietary Catalyst driver continues to be several times faster than any open-source Radeon driver configuration on Ubuntu 12.04 for Doom 3 across the multiple generations of ATI/AMD GPUs.