Task Parallelism-Aware Deep Neural Network Scheduling on Multiple Hybrid Memory Cube-Based Processing-in-Memory

Processing-in-memory (PIM) comprises computational logic in the memory domain. It is the most promising solution to alleviate the memory bandwidth problem in deep neural network (DNN) processing. The hybrid memory cube (HMC), a 3D stacked memory structure, can efficiently implement the PIM architecture by maximizing the existing legacy hardware. To accelerate DNN inference, multiple HMCs can be connected, and data-independent tasks can be assigned to processing elements (PEs) within each HMC. However, owing to the packet-switched network structure, inter-HMC interconnects exhibit variable and unpredictable latencies depending on the data transmission path and link contention. A well-designed task schedule using context switching can effectively hide communication latency and improve PE utilization. Nevertheless, as the number of HMC increases, the variability of a wide range of inter-HMC communication latencies causes frequent context switching, degrading overall performance. This paper proposes a DNN task scheduling that can effectively utilize task parallelism by reducing the communication latency variance owing to HMC interconnect characteristics. Task partitions are generated to exploit parallelism while providing inter-HMC traffic within the sustainable link bandwidth. Task-to-HMC mapping is performed to hide the average communication latency of intermediate DNN processing results. A task schedule is generated using retiming to accelerate DNN inference while maximizing resource utilization. The effectiveness of the proposed method was verified through simulations using various realistic DNN applications performed on a ZSim x86-64 simulator. The simulations revealed that DNN processing with the proposed scheduling improved the DNN processing speed by reducing the processing time by 18.19% over conventional methods where each HMC operated independently.