oneAPI Collective Communications Library (oneCCL)

Note

In oneCCL version 2021.17 included with the 2025.3 oneAPI release, oneCCL has added support for a new C API that closely follows the NVIDIA Collective Communications Libary (NCCL)* API standard. Details about the new API, instructions on how to build, and run an example can be found here.

The existing C++ API will remain the default API for the 2021.17 release.

About

• Release Notes
• Introduction

Get Started

• Install oneCCL from Source
  • System Requirements
  • Installation using CLI
  • Learn More
• Build a Sample Application
  • Build the Library
  • Run the Sample
• Use oneCCL package from CMake
  • oneCCLConfig files generation

Developer Guide

• Programming Model
  • Host Communication
  • Device Communication
• General Configuration
  • Execution of Communication Operations
  • Transport Selection
• Advanced Configuration
  • Selection of Collective Algorithms
  • Low-precision Datatypes
  • Caching of Communication Operations
  • Prioritization of Communication Operations
  • Fusion of Communication Operations
  • Enabling OFI/verbs/dmabuf Support

Developer Reference

• oneCCL API
  • Initialization
  • oneCCL Concepts
  • Communication Operations
  • Generic workflow
  • Error Handling
• Environment Variables
  • Collective Algorithms Selection
  • Workers
  • KVS
  • ATL
  • PROCESS LAUNCHER
  • Multi-NIC
  • Inter Process Communication (IPC)
  • Low-precision Data Types
  • CCL_LOG_LEVEL
  • Profiling
  • Fusion
  • CCL_PRIORITY
  • CCL_MAX_SHORT_SIZE
  • CCL_SYCL_OUTPUT_EVENT
  • CCL_ZE_LIBRARY_PATH
  • Point-To-Point Operations
  • CCL_ZE_TMP_BUF_SIZE

Benchmark User Guide

• oneCCL Benchmark Collective User Guide
  • Build oneCCL Benchmark
  • Run oneCCL Benchmark
  • Example
• oneCCL Benchmark Point-to-Point User Guide
  • Build oneCCL Benchmark
  • Run oneCCL Point-to-Point Benchmark
  • Examples