flashinfer.comm.decide_ulysses_backend

flashinfer.comm.decide_ulysses_backend(requested: str, topologies: List[UlyssesRankTopology], supported_world_sizes: Sequence[int] = (2, 4, 6, 8)) → UlyssesBackendDecision

Pure decision function: gathered per-rank probes -> (backend, reason).

Deterministic in its inputs, so every rank that gathers the same topology list computes the same decision. Conservative: anything unknown, inconsistent, or unverifiable selects NCCL. Raises UlyssesBackendError only when requested == "nvlink" and the NVLink path cannot be used.