Yesterday AMD finally posted power management support for the AMDGPU DRM kernel driver when it comes to supported discrete graphics cards like Tonga and Fiji. I've been testing these PowerPlay Linux patches since yesterday to great success. In this article are results from a Radeon R9 285 and Radeon R9 Fury when testing these kernel patches along with the latest Mesa 11.1-devel Git drivers.
These AMDGPU PowerPlay patches are working out well so far in my tests. See the two aforementioned articles for more details on this AMDGPU power management code that lands more than 45000 lines of new code into this Direct Rendering Manager driver for the latest AMD graphics processors. It's just a pity that the code is too late for making it into the Linux 4.4 kernel merge window and thus won't be mainlined for a few months until the Linux 4.5 kernel. Up to now, the newer AMD graphics cards on the open-source AMD Linux driver have been limited to whatever (low) frequencies the core and memory clocks are initialized to at boot time. With PowerPlay, they can finally (and dynamically) ramp up when to their rated specifications.
For this initial testing I was using Alex Deucher's AMDGPU PowerPlay kernel patch and testing it with/with-out the power management support. This PowerPlay support is concealed behind a new Kconfig option (CONFIG_DRM_AMD_POWERPLAY) that must be enabled for the support to turn on by default and for exposing the information via sysfs. So I did one kernel build with CONFIG_DRM_AMD_POWERPLAY enabled and one off in order to compare the performance impact. These tests were done on Ubuntu 15.10 64-bit and was also using Mesa 11.1-devel and LLVM 3.8 SVN via the Padoka PPA. The Intel Core i7 5960X Haswell-E system with Gigabyte X99-UD4 motherboard, 16GB of DDR4 memory, and 240GB OCZ Vertex 3 SSD made up the test system used for this article.
In this testing there isn't DRI3 enabled and such, but with an article this weekend where I compare the revised performance of the R9 285 and R9 Fury to other AMD hardware on the open-source drivers, DRI3 is enabled. All of these AMD OpenGL benchmarks were facilitated in a fully-automated and reproducible manner using the open-source Phoronix Test Suite benchmarking software.