From 429 GB/s to the DRAM wall: writing an FP8 quantizer on an RTX 5080

This is the story of one CUDA kernel pair in cublade, my personal kernel library. The kernels do per-tensor symmetric FP8 (E4M3) quantization and dequantization. They started at 429 GB/s on a v1 build, then NCU shoved them to roughly 880 GB/s at the kernel level - about 98.5% of the RTX 5080's real DRAM peak. Plus a dequantizer that landed DRAM-bound on its first compile. I'm going to walk through…