InfiniBand vs. Ethernet: Latency Characteristics for AI and HPC Workloads
InfiniBand Architecture
InfiniBand is designed specifically for cluster interconnects, prioritizing ultra-low and deterministic latency.
Protocol Stack: Features a lean, purpose-built protocol that bypasses the complex TCP/IP layers.
RDMA: Implemented natively in hardware, enabling direct memory-to-memory data transfer between nodes without CPU/OS involvement.
Lossless Transport: Achieved inherently through credit-based flow control, preventing packet drops and minimizing inconsistent latency caused by retransmissions.
Typical Latency: Achieves sub-microsecond latency, making it ideal for tightly coupled, latency-sensitive AI training and simulation workloads.
Ethernet with RoCE (RDMA over Converged Ethernet)
RoCE v2 layers InfiniBand’s RDMA capability over standard Ethernet, closing the latency gap but introducing network dependencies.
RDMA Implementation: Layered over standard Ethernet (MAC/IP).
Lossless Transport: Requires careful configuration of Converged Enhanced Ethernet (CEE) features like Priority Flow Control (PFC) and Explicit Congestion Notification (ECN) to maintain low, consistent latency.
Typical Latency: Achieves few-microsecond latency in well-tuned networks, offering a strong balance between performance and the flexibility of the Ethernet ecosystem.
For the most critical, latency-bound applications, InfiniBand retains a measurable advantage in consistency and absolute minimal delay. Ethernet with RoCE provides a compelling, flexible alternative for many large-scale AI tasks.
Further Reading & Resources
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