trunk/4078ac41bdf75d5da306a8214384bfa54c85c4b6: [c10d] Make nccl2 the default NCCL backend (#192281)
- PyTorch: 2311 events in the last 90 days
- PyTorch: 2281th Release in the last 90 days
- Previous: earlier the same day · viable/strict/1787985328: Revert "Drop unused includes in c10 (#194959)"
What happened
The standard nccl backend still selected legacy ProcessGroupNCCL unless users opted into nccl2 through an environment variable, even though the explicit nccl2 and nccl-legacy names make backend selection reversible. Invert the registration so an unset variable or TORCH_DIST_USE_NCCL2=1 selects nccl2, while TORCH_DIST_USE_NCCL2=0 and the explicit nccl-legacy name remain rollback paths. Defaulting also exposed three n…
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