Network-Connected Device Prefetching for Timing Precision
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Solution Overview
Problem
Existing network adapters face challenges in achieving accurate and low-latency packet transmission due to unpredictable PCIe latency, which degrades the precision of packet transmission timing in time-sensitive applications like TDM, optical switching networks, and HPC environments.
Innovation Solution
The implementation of a Network-Connected Device (NCD) with a network interface, host interface, and processor that buffers and prefetches packet information ahead of time, decoupling processing and transmission from buffering, and using Queue-Pairs to manage prefetching and synchronization, thereby reducing reliance on PCIe transactions for packet data and WQEs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If packet information is buffered and processed in the host before transmission, then transmission timing precision is improved, but PCIe latency variability degrades the overall timing accuracy
Solution Approach 1:
The system segments packet information into two separate buffers: packet data buffer and WQE buffer. This segmentation allows independent optimization of each buffer's timing characteristics and reduces the impact of PCIe latency variability on overall transmission timing precision.
Solution Approach 2:
The system performs preliminary actions by prefetching packet information to the NCD memory before the specified transmission time. The processor schedules prefetching operations to complete before transmission deadlines, ensuring data readiness without relying on unpredictable PCIe latency at the critical transmission moment.
2Loss of time
If packet information is prefetched to NCD memory before transmission, then transmission latency is reduced, but memory bandwidth and buffer management complexity increase
Solution Approach 1:
The memory system is segmented into distinct buffers: packet data buffer for storing packet payloads and WQE buffer for storing work queue elements. This segmentation simplifies buffer management by allowing independent addressing and timing for each buffer type, reducing the complexity of coordinated memory operations.
Solution Approach 2:
The NCD memory acts as an intermediary buffer between the host and network interface. By decoupling the host processing timeline from the network transmission timeline through this intermediate buffer, the system reduces transmission latency without requiring complex real-time coordination between host and network operations.
3Measurement precision
If processing and transmission are decoupled from buffering, then transmission timing precision is improved, but device architecture complexity increases
Solution Approach 1:
The architecture is segmented into distinct functional modules: host interface for receiving packet information, NCD memory for buffering with separate packet data and WQE regions, and network interface for transmission. This modular segmentation improves timing precision by isolating processing stages while maintaining manageable architectural complexity through standardized interfaces between modules.
Data Source
AI summary
A Network-Connected Device (NCD) includes a network interface, a host interface, an NCD memory and an NCD processor. The network interface is configured for communicating over a network. The host interface is configured for communicating with a host. The NCD memory is configured to buffer packet information that originates from the host and pertains to a packet to be transmitted to the network at a specified transmission time. The NCD processor is configured to process the buffered packet information before the specified transmission time, and to transmit the packet to the network at the specified time. Processing of the packet information and transmission of the packet are decoupled from buffering of the packet information.