This is a well known problem acknowledged by Valve. It is particularly bad on AMD hardware:
IVRCompositor::Submit() performance measurement :: SteamVR Developer Hardware General Discussions
Problem using OpenGL to DirectX texture, and submit DirectX texture :: SteamVR Developer Hardware General Discussions
Seems to be a poor implementation of interop2 on AMD hardware?
This is going to make VR on AMD hardware, with applications that run OpenGL, a poor experience. Are you working with Valve to resolve this?
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