How would you know GPUDirect RDMA is not being used, given that nothing reports an error when it is disabled?

Distinguish GPU-memory capability, registration and selected transport. Compare direct and staged paths without relying on a half-speed rule or one log substring.

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Distinguish GPU-memory capability, registration and selected transport. Compare direct and staged paths without relying on a half-speed rule or one log substring.

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The concepts behind this question

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GPUDirect RDMA and GPUDirect StorageGPUDirect enables supported devices to transfer data to or from GPU memory without a host staging buffer. Its benefit depends on topology, software support and the transfer path.

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Ring vs Tree All-ReduceTrace one chunk through a ring, separate byte balance from startup rounds, and compare tree depth without assuming identical bandwidth. Use measured message sizes and topology to choose.

Foundational

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Debugging a Slow All-ReduceInterpret NCCL algbw and busbw, then isolate a slow collective with controlled tests. Distinguish rank delays, GPU-memory paths and shared-fabric limits without guessing from bandwidth ratios.

Core

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RDMA, InfiniBand and RoCEv2RDMA lets network adapters transfer data directly between registered memory regions. InfiniBand and RoCE provide different network and operating environments for those transfers.

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FEDITOR'S NOTE

Verify the supported registration path and actual connections. Use matched GPU-buffer tests to establish impact; neither missing nvidia-peermem nor half bandwidth proves fallback.

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