RDMA Capable iWARP over Datagrams

iWARP is a state of the art high-speed connection-based RDMA networking technology for Ethernet networks to provide InfiniBand-like zero-copy and one-sided communication capabilities over Ethernet. Despite the benefits offered by iWARP, many data center and web-based applications, such as stock-market trading and media-streaming applications, that rely on data gram-based semantics (mostly through UDP/IP) cannot take advantage of it because the iWARP standard is only defined over reliable, connection-oriented transports. This paper presents an RDMA model that functions over reliable and unreliable data grams. The ability to use data grams significantly expands the application space serviced by iWARP and can bring the scalability advantages of a connectionless transport to iWARP. In our previous work, we had developed an iWARP data gram solution using send/receive semantics showing excellent memory scalability and performance benefits over the current TCP-based iWARP. In this paper, we demonstrate an improved iWARP design that provides true RDMA semantics over data grams. Specifically, because traditional RDMA semantics do not map well to unreliable communication, we propose RDMA Write-Record, the first and the only method capable of supporting RDMA Write over both unreliable and reliable data grams. We demonstrate through a proof-of-concept software implementation that data gram-iWARP is feasible for real-world applications. Our proposed RDMA Write-Record method has been designed with data loss in mind and can provide superior performance under conditions of packet loss. It is shown through micro-benchmarks that by using RDMA capable data gram-iWARP a maximum of 256% increase in large message bandwidth and a maximum of 24.4\% improvement in small message latency can be achieved over traditional iWARP. For application results we focus on streaming applications, showing a 24% improvement in memory usage and up to a 74% improvement in performance, although the proposed approach is also applicable to the HPC domain.