what is the meaning that AMD RDNA support wave32?

Question

From AMD RDNA white paper, it is said

The RDNA architecture is natively designed for a new narrower wavefront with 32 work-items, intuitively called wave32, that is optimized for efficient compute. Wave32 offers several critical advantages for compute and complements the existing graphics-focused wave64 mode.

As we know, the size of wavefront is 64. Does wave32 mean that we can config the wavefront from 64 to 32?

Is there any coding example about wave32?

Answer 1

While the RDNA architecture is optimized for wave32, the existing wave64 mode can be more effective for some applications. To handle wave64 instructions, the wave controller issues and executes two wave32 instructions, each operating on half of the work-items of the wave64 instruction. The default way to handle a wave64 instruction is simply to issue and execute the upper and lower halves of each instruction back-to-back – conceptually slicing every instruction horizontally.

https://www.amd.com/system/files/documents/rdna-whitepaper.pdf

An example of application, CAS

AMD’s FidelityFX suite includes a new approach known as Contrast Adaptive Sharpening (CAS) that uses post-processing compute shaders to enhance image quality. CAS enhances details at the interior of an object, while maintaining the smooth gradients created by the antialiasing as illustrated in Figure 12. It is a full-screen compute shader and therefore can work with any type of anti-aliasing and is particularly effective when paired with temporal antialiasing.

CAS is extremely fast, taking just 0.15 milliseconds for a 2560x1440 frame, and benefits from a variety of features in the RDNA architecture such as packed integer math for address calculations, packed fp16 math for compute, faster image loads, and wave32.