Microbenchmark at 64 ranks, [1, 5120] fp32 in a compiled graph: world
all-reduce 3.37 ms, 8 consecutive ranks 0.41 ms, 4-core device group then a
16-device group (one core each) 2.01 ms; a strided 8-device group is rejected
by the runtime. The replicated-token MoE all-reduce (one a layer) now takes
the two-level form (DEEPINFER_NEURON_HIER_ALLREDUCE=0 restores one world
all-reduce). Host tiny cp=8 matches golden.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>