RDNA 2 fully supports the latest DXR Tier 1.1 standard, and similar to the Turing RT core, it accelerates the creation of the so-called BVH structures required to accurately map ray traversal and intersections, tested against geometry. In short, in the same way that light 'bounces' in the real world, the hardware acceleration for ray tracing maps traversal and intersection of light at a rate of up to 380 billion intersections per second.
"Without hardware acceleration, this work could have been done in the shaders, but would have consumed over 13 TFLOPs alone," says Andrew Goossen. "For the Series X, this work is offloaded onto dedicated hardware and the shader can continue to run in parallel with full performance. In other words, Series X can effectively tap the equivalent of well over 25 TFLOPs of performance while ray tracing."
It is important to put this into context, however. While workloads can operate at the same time, calculating the BVH structure is only one component of the ray tracing procedure. The standard shaders in the GPU also need to pull their weight, so elements like the lighting calculations are still run on the standard shaders, with the DXR API adding new stages to the GPU pipeline to carry out this task efficiently. So yes, RT is typically associated with a drop in performance and that carries across to the console implementation, but with the benefits of a fixed console design, we should expect to see developers optimise more aggressively and also to innovate. The good news is that Microsoft allows low-level access to the RT acceleration hardware.