Introduction to HCCL

HCCL (Huawei Collective Communication Library) is a high-performance collective communication library based on Ascend hardware, providing high-performance and high-reliability communication solutions for computing clusters.

Core Features

• Provides high-performance collective communication and point-to-point communication in single-node and multi-node environments.

• Supports collective communication primitives such as AllReduce, Broadcast, AllGather, ReduceScatter, AlltoAll, Send, and Receive.

• Supports communication algorithms such as Ring, Mesh, and Recursive Halving-Doubling (RHD).

• Supports high-speed communication links such as HCCS, RoCE, PCIe, and UB (Unified Bus).

• Supports two execution modes: single-operator mode and graph mode.

• Supports custom development of communication operators.

Software Architecture

HCCL is a core component of CANN, providing high-performance and high-reliability communication solutions for NPU clusters. HCCL supports multiple AI frameworks on the upper layer and enables efficient interconnection among various Ascend AI processors on the lower layer. Its architecture is shown in the following figure.

Figure 1 Collective communication library software architecture

HCCL consists of the HCCL collective communication library and the HCOMM (Huawei Communication) communication basics library:

• HCCL collective communication library: Includes built-in communication operators and extended communication operators, and provides external communication operator interfaces.

  • Built-in communication operators: Basic communication operators provided by HCCL, including collective communication operators and point-to-point communication operators.

  • Extended communication operators: Users can customize extended communication operators using the interfaces provided by the HCOMM communication basics library.

• HCOMM communication basics library: Adopts a layered decoupling design approach, dividing communication capabilities into a control plane and a data plane.

  • Control plane: provides topology information query and communication resource management functions.

  • Data plane: provides data movement and computation functions such as local operations, inter-operator synchronization, and communication operations.

The control plane provides communication resources, while the data plane provides operation resources. The interfaces provided by this approach allow communication operator developers to focus on service innovation without concerning themselves with the complex implementation details at the underlying chip level.

Supported Products

• Ascend 950PR/Ascend 950DT

• Atlas A3 training products/Atlas A3 inference products

• Atlas A2 training products/Atlas A2 inference products

• Atlas training products

• Atlas inference products