Trying R600g On Mesa 11.3, Cayman GPU On Linux 4.7 Radeon DRM Yields Problems
As I've been delivering many RadeonSI tests already for newer GCN GPUs on Mesa Git, I decided to run some fresh tests when using R600g for pre-GCN (Radeon HD 6000 series and older support) on Mesa Git. Like the other comparisons, I compared Mesa 11.3-devel from the Padoka PPA to Mesa 11.2 offered by Ubuntu 16.04 LTS out-of-the-box. I also then ran more Mesa 11.3 tests when upgrading from Xenial's stock Linux 4.4 kernel to Linux 4.7 drm-next code for the Radeon kernel driver.
For the testing I used a FirePro V7900 "Cayman" graphics processor, similar to the consumer Radeon HD 6900 series. The HD 6900 and HD 5800 series continue to be the lone series supporting OpenGL 4 on the R600g driver. With Mesa 11.3, it's still at OpenGL 4.1 support for these few graphics processors while the other Radeon HD 6000 series (Northern Islands) hardware is left out due to R600g not having floating point emulation support.
There wasn't much change with going from Mesa 11.2 to 11.3-devel for this Cayman GPU on R600g... But there was a heck of a difference in going from Linux 4.4 to the latest DRM-Next code. However, the performance was in the wrong direction. Many of these OpenGL tests regressed.
I don't know immediately if these regressions are from the DRM-Next code or were hitting this old GPU in the Linux 4.5 or 4.6 cycles, but nevertheless they are active on Git.
Xonotic particularly takes a bad tumble with the newer kernel.
But in some synthetic tests, there's actually an improvement with the newer kernel.
Until I have more information, you can view all the results on OpenBenchmarking.org.