Scalable connectionless RDMA over unreliable datagrams

• We demonstrate non-connection-based RDMA methods for iWARP Ethernet networks.
• RDMA Write-Record is the first RDMA operation for unreliable transports.
• The new methods show improved performance and scalability.
• The methods are proven for both commercial and scientific applications.
• The basic design is applicable to other high speed networks.

The overhead imposed by connection-based protocols for high-performance computing (HPC) systems can be detrimental to system resource usage and performance. This paper demonstrates for the first time a unified send/recv and Remote Direct Memory Access (RDMA) Write over datagrams design for RDMA-capable network adapters. We previously designed the first and only unreliable datagram RDMA model, RDMA Write-Record, and demonstrated its superior performance over connection-based RDMA. RDMA Write-Record can be applied to several RDMA capable networks, such as iWARP and InfiniBand (which does not support unreliable RDMA Writes). iWARP is a state-of-the-art, high-speed, connection-based RDMA networking technology for both local and wide-area Ethernet networks. iWARP is used as the platform to demonstrate our unreliable RDMA operation design for both channel and memory semantics. We previously outlined the requirements for extending iWARP to operate over datagrams. Here we extend our work on commercial datacenter applications by providing broadcast support for send/recv. In order to study the scalability of datagram-iWARP, we added Message Passing Interface support for RDMA Write-Record to investigate the scalability of HPC-based scientific applications for both send/recv and RDMA Write-Record. The results show that both models outperform their connection-based alternatives, providing superior performance and scalability in a software prototype.