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NGG (Next Generation Geometry) is the technology that is responsible for any vertex and geometry processing in AMD RDNA GPUs. I decided to do a write-up about my experience implementing it in RADV, which is the Vulkan driver used by many Linux systems, including the Steam Deck. I will also talk about shader culling on RDNA GPUs.
Previously, I gave you an introduction to mesh/task shaders and wrote up some details about how mesh shaders are implemented in the driver. But I left out the important details of how task shaders (aka. amplification shaders) work in the driver. In this post, I aim to give you some details about how task shaders work under the hood. Like before, this is based on my experience implementing task shaders in RADV and all details are already public information.
In part 1 I gave a brief introduction on what mesh and task shaders are from the perspective of application developers. Now it’s time to dive deeper and talk about how mesh shaders are implemented in a Vulkan driver on AMD HW. Note that everything I discuss here is based on my experience and understanding as I was working on mesh shader support in RADV and is already available as public information in open source driver code. The goal of this blog post is to elaborate on how mesh shaders are implemented on the NGG hardware in AMD RDNA2 GPUs, and to show how these details affect shader performance. Hopefully, this helps the reader better understand how the concepts in the API are translated to the HW and what pitfalls to avoid to get good perf.
Mesh and task shaders (amplification shaders in D3D jargon) are a new way to produce geometry in 3D applications. First proposed by NVidia in 2018 and initially available in the “Turing” series of GPUs, they are now supported on RDNA2 GPUs and on the API are part of the D3D12 API and also as vendor-specific extensions to Vulkan and OpenGL. In this post I’m going to talk about what mesh shaders are and in part 2 I’m going to talk about how they are implemented on the driver side.
I’ve wanted to do this for a long time, but somehow never got around to it. The main inspiration for this blog are the blogs of my colleagues Mike, Bas and Martin who are all writing exciting stuff about their work.
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