3cc97c1d4e
Key findings from reading dispatch_scan.cuh: 1. Lookahead scan requires PTX ISA >= 860 (NVIDIA SM100+), completely unavailable on BI-V100. Our lookback-only strategy is correct. 2. Lookback scan passes 0 dynamic SMEM — SMEM is all static via __shared__. Different from lookahead which uses dynamic stages. 3. Scan launches exactly num_tiles blocks (not sm_count * subscription), one CTA per tile. For 100K tokens: ~12 tiles all fit in one wave on 16 SMs, explaining why no_delay (dcid=0) is optimal. 4. Lookahead's num_stages auto-tuning is irrelevant for BI-V100 but reveals NVIDIA's pipeline depth selection strategy.