RDMA Cache-Aligned Write Operations for Latency Reduction
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Solution Overview
Problem
RDMA operations often suffer from latency issues due to unaligned write operations, leading to network congestion and packet loss, as the transmitting host is unaware of the cache line size of the remote peer host, resulting in inefficient data transfer.
Innovation Solution
The system exchanges RDMA credentials, including cache line size information, between computing devices to enable cache-aligned RDMA write operations, reducing the number of partial store operations and minimizing latency by aligning data transfers with cache line boundaries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If RDMA write operations are performed without cache line alignment, then the transmitting host can initiate data transfer immediately, but the remote peer experiences increased latency and network congestion due to multiple partial store operations
Solution Approach 1:
The transmitting host performs preliminary actions by exchanging RDMA credentials including cache line size information with the remote peer before initiating data transfer. This allows the transmitting host to calculate appropriate padding requirements and alignment offsets in advance, ensuring that write operations are properly aligned with the remote peer's cache line boundaries, thereby reducing latency and avoiding network congestion
2Device complexity
If the transmitting host is unaware of the remote peer's cache line size, then the system maintains simplicity in communication setup, but performance degrades due to unaligned write operations requiring multiple partial store operations
Solution Approach 1:
The RDMA credential exchange mechanism serves multiple functions: it establishes communication parameters, conveys cache line size information, enables alignment calculations, and optimizes transfer performance - all within a single integrated setup process. This multi-functional approach maintains simplicity while enabling high-performance aligned operations
3Quantity of substance
If unaligned large write operations are performed, then the transmitting host can send large payloads efficiently, but the remote peer's memory sub-system experiences severe latency due to hundreds of unaligned DMA write operations
Solution Approach 1:
Before transmitting large payloads, the transmitting host performs preliminary calculations using the remote peer's cache line size information to determine the optimal alignment offset and required padding. This ensures that even large write operations are properly aligned with cache line boundaries, reducing the number of DMA operations needed and minimizing latency in the remote peer's memory sub-system
Data Source
AI summary
A system for optimizing remote direct memory accesses (RDMA) is provided. The system includes a first computing device and a second computing device disposed in signal communication with the first computing device. The first and second computing devices are respectively configured to exchange RDMA credentials during a setup of a communication link between the first and second computing devices. The exchanged RDMA credentials include cache line size information of the first computing device by which a cache aligned RDMA write operation is executable on a cache of the first computing device in accordance with the cache line size information by the second computing device.