Notified Access: Extending Remote Memory Access Programming Models for Producer-Consumer Synchronization

Abstract—Remote Memory Access (RMA) programming enables direct access to low-level hardware features to achieve high performance for distributed-memory programs. However, the design of RMA programming schemes focuses on the memory access and less on process synchronization. For exam-ple, in contemporary RMA programming systems, the widely used producer-consumer pattern can only be implemented inefficiently, incurring the overhead of an additional round-trip message. We propose Notified Access, a scheme where the target process of an access can receive a completion notification. This scheme enables direct and efficient synchronization with a minimum number of messages. We implement our scheme in an open source MPI-3 RMA library and demonstrate lower overheads (two cache misses) than other point-to-point syn-chronization mechanisms. We also evaluate our implementation on three real-world benchmarks: a stencil computation, a tree computation, and a Cholesky factorization implemented with tasks. Our scheme always performs better than traditional message passing and other existing RMA synchronization schemes, providing up to 50 % speedup on small messages. Our analysis shows that Notified Access is a valuable primitive for any RMA system. Furthermore, we provide guidance for the design of low-level network interfaces to support Notified Access efficiently. Keywords-RMA; synchronization; notification; MP