Optimised DSv4-Flash for 2x GH200: 10,000 tok/s PP, >300 tok/s TG on SGLang

There are some PRs to use and a nice trick to speed up PP on really longs contexts in my write up. Hope it helps!

TL;DR:
On this dual GH200 box, you build vLLM v0.26.0 from source, add the merged DSV4 cache-layout patch (PR #48993), disable async scheduling, and run DSpark at 6 predicted tokens to give: ~276 decode tok/s and a 1M context in 192 GB of HBM. SGLang, once it built on ARM64 and it’s DSpark loader bug fixed, is faster on every decode workload and hits ~317.0 tok/s.