With Ubuntu dropping support for the AMD fglrx/Catalyst driver in their upcoming 16.04 LTS "Xenial Xerus" release and manually installing the driver doesn't sound like an option, many have renewed interest in how the open-source Radeon driver stack is performing for Ubuntu 16.04 that's due out next month. In this article are benchmarks comparing the performance of Ubuntu 14.04.4 LTS (on both the open and closed drivers) to that of Ubuntu 16.04 LTS with the sole AMD Linux driver option on a variety of graphics cards.
Canonical had to resort to deprecating the fglrx Catalyst (or now known as Radeon Software) driver support since AMD is no longer actively maintaining that Linux driver and doesn't even have mainline support for the latest Linux kernel and X.Org Server releases, which means it won't work on Ubuntu 16.04 LTS. AMD is replacing the driver later in the year with their AMDGPU kernel based hybrid driver for GCN 1.2+ GPUs and whatever GCN 1.0~1.1 GPUs that end up getting enabled for this newer DRM driver that succeeds the Radeon DRM driver. That new hybrid driver is expected around the middle of the year, likely to be timed with the Polaris launch. AMD's forthcoming Vulkan Linux driver is also contingent upon this AMDGPU driver.
As mentioned in several Phoronix articles already, this long transition is a bit of a pain since in some workloads the open-source Radeon driver still lags behind Catalyst, the OpenCL/compute support still needs a lot of improvements, features like CrossFire aren't yet implemented, the OpenGL 4 support is still several releases behind, there's no rich graphical configuration utility, etc. There is also the uncertainty over what hardware the AMDGPU driver will end up supporting with by default just handling the few select GCN 1.2+ GPUs while there is experimental but disabled-by-default GCN 1.1 support and we haven't seen any GCN 1.0 support in this driver. Both AMD and Ubuntu developers have recommended users needing the high-performance proprietary driver to continue using Ubuntu 14.04 LTS for the time being, at least until the new hybrid driver stack is available later in the year.
For those curious how the Ubuntu 16.04 Radeon performance is stacking up, I ran some benchmarks comparing Ubuntu 16.04 LTS with its open-source AMD driver support to that of Ubuntu 14.04.4 when using the out-of-the-box open-source driver (Linux 4.2 + Mesa 11.0.2) and then again when running Catalyst via their fglrx-updates (15.20.3 / OpenGL 4.3.13399) packages. The Ubuntu 14.04.4 performance should be similar to that of Ubuntu 15.10 given its the hardware enablement stack that was back-ported to this earlier Ubuntu LTS (Long Term Support) release. With the testing on Ubuntu 16.04, its kernel is based on Linux 4.4 but Canonical back-ported the Radeon/AMDGPU changes from Linux 4.5 back to their Xenial kernel. Right now in the Ubuntu 16.04 repository is also Mesa 11.1, but they have a feature freeze exception to land Mesa 11.2. Thus for my testing I enabled the x-staging PPA where there are currently the official Mesa 11.2 packages for Ubuntu 16.04 and used that for my testing. Everything else (aside from also disabling SwapBuffersWait) was tested at their default on both Ubuntu 14.04 and 16.04.
The graphics cards I had available for testing included the Radeon R9 270X, R9 285, R9 290, R7 370, and R9 Fury. But with the Radeon R9 285 Tonga graphics card that's natively supported by AMDGPU, that didn't even end up working on Ubuntu 16.04... Once booting Ubuntu 16.04 with its default kernel, I didn't end up getting a display and when remotely connecting to the system it was quickly noticed that their AMDGPU driver went berserk:
Via the Phoronix Test Suite I ran a variety of OpenGL benchmarks that included BioShock Infinite, DiRT Showdown, OpenArena, Tesseract, Team Fortress 2, Unigine Heaven, Unigine Valley, Xonotic, and GpuTest. The test system was powered by an Intel Xeon E3-1280 v5 processor that is quad-core plus Hyper Threading and has a 3.7GHz base frequency with 4.0GHz turbo.
With all of that said, let's see how the open-source graphics driver performance on Ubuntu 16.04 for Radeon GCN GPUs is comparing to Ubuntu 14.04.4 on the older open and closed drivers.