[paulmd]

Navi improves delta compression for memory, which improves effective memory bandwidth for a given "raw" bandwidth. So switching to Navi would have alleviated the memory bandwidth bottleneck to some degree and improved performance.

It is a puzzling decision and perhaps the "wasn't ready when they taped out" explanation is the correct one. Cezanne seems to have been ready for a while now and just waiting for fab capacity - meaning it would have had to have been taped out in parallel with the RDNA2 architecture chips. So a design flaw in RDNA2 might have blown the Cezanne launch.

They could have used RDNA1 though and it still would have improved compression over GCN/Vega. Or ported over just the delta compression. I guess maybe they just wanted to port Zen3 over straight, use the memory controller they'd already proven with Renoir, and not take any risks?

It's definitely puzzling and I haven't heard an explanation I would consider 100% satisfactory.