This one is not a contest. It is a kernel in a serving path that somebody is paying for by the hour, which is a harder test in one specific way: there is no track to win, only a regression to avoid.
Prefill
The MSA prefill indexer was severely underutilizing the hardware during long-context serving on B300. KDA found it and rewrote around it:
- 6.5× geometric mean speedup across the workloads tested;
- up to 14× on the end-of-prefill chunk tails, which is where the underutilization was worst and where the shape is least convenient;
- no regression anywhere in the set.
The tails are the interesting part. A profile averaged over a run hides them, and a human optimizing by eye tends to spend the week on the shape in the middle of the histogram. An agent reading ncu output as evidence has no such preference.
Decode
The MSA decode indexer, used in speculative verification, went 2.9× faster at the TP4 promotion shape — past the 2.78× theoretical bandwidth band, which means the win is not bandwidth alone — and up to 3.3× on longer contexts.
Accuracy was bitwise identical across every tested workload. That is the gate, not a footnote: a kernel that is faster because it has quietly become incorrect will report a speedup just as happily as one that is faster because it is better.