Fusion of Communication Operations

In some cases, it may be beneficial to postpone execution of communication operations and execute them all together as a single operation in a batch mode. This can reduce operation setup overhead and improve interconnect saturation.

oneCCL provides several knobs to enable and control such optimization:

• The fusion is enabled by CCL_FUSION.

• The advanced configuration is controlled by:

  • CCL_FUSION_BYTES_THRESHOLD

  • CCL_FUSION_COUNT_THRESHOLD

  • CCL_FUSION_CYCLE_MS

Note

For now, this functionality is supported for allreduce operations only.