Enabling Near-Data Accelerators Adoption by Through Investigation of Datapath Solutions

Abstract

Processing-in-Memory (PIM) or Near-Data Accelerator (NDA) has been recently revisited to mitigate the issues of memory and power wall, mainly supported by the maturity of 3D-staking manufacturing technology, and the increasing demand for bandwidth and parallel data access in emerging processing-hungry applications. However, as these designs are naturally decoupled from main processors, at least three open issues must be tackled to allow the adoption of PIM: how to offload instructions from the host to NDAs, since many can be placed along memory; how to keep cache coherence between host and NDAs, and how to deal with the internal communication between different NDA units considering that NDAs can communicate to each other to better exploit their adoptions. In this work, we present an efficient design to solve these challenges. Based on the hybrid Host-Accelerator code, to provide fine-grain control, our design allows transparent offloading of NDA instructions directly from a host processor. Moreover, our design proposes a data coherence protocol, which includes an inclusion-policy agnostic cache coherence mechanism to share data between the host processor and the NDA units, transparently, and a protocol to allow communication between different NDA units. The proposed mechanism allows full exploitation of the experimented state-of-the-art design, achieving a speedup of up to 14.6× compared to a AVX architecture on PolyBench Suite, using, on average, 82% of the total time for processing and only 18% for the cache coherence and communication protocols.