NVIDIA ConnectX网卡精确调度与硬件时间戳的实验评估
An Experimental Evaluation of Accurate Scheduling and Hardware Timestamping on NVIDIA ConnectX NICs
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中文总结 AI 辅助
研究NVIDIA ConnectX - 7网卡精确调度和硬件时间戳功能，通过基于FPGA的测量平台实验，评估其定时精度和性能，结果显示该功能适用于5G前传等延迟要求几十微秒量级的应用，不适用于高确定性TSN应用。
中文摘要 AI 辅助
高精度数据包传输在确定性网络应用（如5G前传和时间敏感网络（TSN））中日益重要。NVIDIA ConnectX网卡提供精确调度和硬件时间戳功能，但相关定时精度和性能特征的公开信息较少。本文对NVIDIA ConnectX - 7网卡的精确调度和硬件时间戳功能进行实验表征。利用基于FPGA的测量平台，评估了接收和发送硬件时间戳的精度以及精确调度的传输定时精度。实验结果表明，独立时钟以太网实体间接收和发送硬件时间戳的测量变化约为±7 - 8 ns，精确调度约99%的帧在指定传输时间的±900 ns内发送，偶尔有高达约5 μs的异常值。这些结果表明精确调度适用于5G前传等延迟要求在几十微秒量级的应用，但其定时精度不足以满足通常要求传输定时精度在几到几十纳秒量级的高度确定性TSN应用。
英文摘要
High-precision packet transmission is becoming increasingly important in deterministic networking applications, including 5G fronthaul and Time-Sensitive Networking (TSN). Recent NVIDIA ConnectX network interface cards (NICs) provide Accurate Scheduling, a hardware-assisted mechanism for transmitting Ethernet frames at designated times, as part of their 5T for 5G feature set. They also provide hardware timestamping for received and transmitted frames. Although these functions are expected to satisfy the stringent timing requirements of 5G fronthaul, little public information is available regarding their timing accuracy and performance characteristics. This paper presents an experimental characterization of the Accurate Scheduling and hardware timestamping capabilities of the NVIDIA ConnectX-7 NIC. Using an FPGA-based measurement platform with deterministic frame generation and nanosecond-resolution timestamping, we first evaluate the precision of the receive and transmit hardware timestamps and then evaluate the transmission timing accuracy of Accurate Scheduling. The experimental results show that the receive and transmit hardware timestamps exhibit a measured variation of approximately $\pm$7-8 ns when compared across independently clocked Ethernet entities. Furthermore, Accurate Scheduling transmits approximately 99% of frames within $\pm$900 ns of the specified transmission time, while occasional outliers of up to approximately 5 us are observed. These results indicate that Accurate Scheduling is well suited for applications with latency requirements on the order of several tens of microseconds, such as 5G fronthaul, whereas its timing accuracy is insufficient for highly deterministic TSN applications, which typically require transmission timing accuracy on the order of several to several tens of nanoseconds.
