Exploring FlashAttention-3/4 optimizations on RTX GPUs

I was curious whether any of the FA-3/4 optimizations transfer to RTX GPUs. vLLM/SGLang attention falls back to FA-2 on consumer cards (FA-3 and FA-4 are datacenter-only), so I wanted to know if there's any performance left on the table, and I rebuilt the attention kernels from scratch. The kernel reaches parity with FA-2 (206us on RTX5090 with batch=1, heads=8, seq_len=4096, head_dim=64), but unfortunately, FA-3/4 optimizations are either not applicable or not helpful on consumer cards. It looks like FA-2