Monday March 04, 2019

Linux 5.0 Release Includes FreeSync Support and Spectre Fixes

The Linux 5.0 kernel has been released, and among other things, it officially adds support for FreeSync displays on AMD GPUs. Phoronix notes that AMD previously supported FreeSync on Linux "via their hybrid driver package with its DKMS module in Radeon Software," but posted a tutorial for enabling it and testing FreeSync support in Ubuntu. They note that Vulkan games (which presumably includes Valve's Proton renderer,) compositors, web browsers, media players and a few other apps aren't currently supported by FreeSync at this time.

Meanwhile, the publication also put the recent Spectre performance mitigation measures to the test, and found that performance on the Core i9 7980XE dropped by about 13% with the Spectre protections enabled. Core i7 8086K performance dropped by about 17%, while Ryzen 7 2700X performance only dropped by 3%. Unfortunately, running the same benchmarks on previous Linux kernels would be like comparing apples to oranges, so its hard to say exactly how much Linux 5.0 mitigates Spectre's performance hit, but it looks like certain workloads are still relatively sensitive to the security countermeasures.

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To utilize FreeSync you need to be using the xf86-video-amdgpu DDX driver. You can verify so looking for "AMDGPU" in the Xorg.0.log. You also need the above-shown Xorg.conf snippet to enable the "VariableRefresh" AMDGPU DDX driver option. Using the xf86-video-modesetting DDX is unsupported at this time. Your xf86-video-amdgpu driver also has to be relatively new, but such supported X.Org driver can be found in the likes of the Padoka PPA... After enabling the VariableRefresh option and restarting the X.Org server, you can verify that the DDX is new enough and option is working by ensuring that VariableRefresh is successfully mentioned in your Xorg log.

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