This document describes the key features, software enhancements and improvements, and known issues for NCCL 2.5.6. The NVIDIA Collective Communications Library (NCCL) (pronounced “Nickel”) is a library of multi-GPU collective communication primitives that are topology-aware and can be easily integrated into applications. Collective communication algorithms employ many processors working in concert to aggregate data. NCCL is not a full-blown parallel programming framework; rather, it is a library focused on accelerating collective communication primitives.

For previously released NCCL documentation, see NCCL Archives.