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# What is RCCL?

The ROCm Communication Collectives Library (RCCL) includes multi-GPU and multi-node collective communication primitives optimized for AMD GPUs. It implements routines such as `all-reduce`, `all-gather`, `reduce`, `broadcast`, `reduce-scatter`, `gather`, `scatter`, `all-to-allv`, and `all-to-all`, as well as direct point-to-point (GPU-to-GPU) send and receive operations. It is optimized to achieve high bandwidth on platforms using PCIe and xGMI and networking using InfiniBand Verbs or TCP/IP sockets. RCCL supports an arbitrary number of GPUs installed in a single node or multiple nodes and can be used in either single- or multi-process (for example, MPI) applications.

The collective operations are implemented using ring and tree algorithms and have been optimized for throughput and latency by leveraging topology awareness, high-speed interconnects, and RDMA-based collectives. For best performance, small operations can be either batched into larger operations or aggregated through the API.

RCCL uses PCIe and xGMI high-speed interconnects for intra-node communication as well as InfiniBand, RoCE, and TCP/IP for inter-node communication. It supports an arbitrary number of GPUs installed in a single-node or multi-node platform and can easily integrate into single- or multi-process (for example, MPI) applications.