CDNA executes 64-threads per compute unit per clock tick. RDNA only executes 32-threads. CDNA is smaller, more efficient, more parallel and much higher compute than RDNA.
Furthermore, all ROCm code from GCN (and older) was on Wave64, because historically AMD's architecture from 2010 through 2020 was Wave64. RDNA changed to Wave32 so that they can match NVidia and have slightly better latency characteristics (at the cost of bandwidth).
CDNA has more compute bandwidth and parallelism. RDNA is narrower, faster latency and less parallelism.
If you actually were using both, you'd know that CDNA was the only supported platform on ROCm for what felt like an eternity. That's because CDNA was designed to be as similar to GCN so that ROCm could support it easier.
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What I'm saying is that today, now that ROCm works on RDNA and CDNA, the two architectures can finally be unified into UDNA. And everyone should be happy with the state of code moving forward.
Not really.
Wave64 on CDNA is provably more throughput. But with most video game code written for NVidia's Wave32, RDNA being reworked to be more NVidia-like and Wave32 is how you reach better practical video game performance.
HPC will prefer the wider execute, 64-bit execution, and other benefits.
Video Gamers will prefer massive amounts of 32MB+ of "Infinity cache", which is used in practice for all kinds of screen-space calculations. But this would NEVER be used for fluid dynamics.