Userspace RDMA Verbs on Commodity Hardware Using DPDK

RDMA (Remote Direct Memory Access) is a technology that enables user applications to perform direct data transfer between the virtual memory of processes on remote endpoints, without operating system involvement or intermediate data copies. Achieving zero intermediate data copies using RDMA requires specialized network interface hardware. Software RDMA drivers emulate RDMA semantics in software to allow the use of RDMA without investing in such hardware, although they cannot perform zero-copy transfers. Nonetheless, software RDMA drivers are useful for research, application development, testing, debugging, or as a less expensive desktop client for a centralized RDMA server application running on RDMA-capable hardware. Existing software RDMA drivers perform data transfer in the kernel. Data Plane Development Kit (DPDK) provides a framework for mapping Ethernet interface cards into userspace and performing bulk packet transfers. This in turn allows a software RDMA driver to perform data transfer in userspace. We present our software RDMA driver, urdma, that performs data transfer in userspace, discuss its design and implementation, and demonstrate that it can achieve lower small message latency than existing kernel-based implementations while maintaining high bandwidth utilization for large messages.