Architecting Compatible PIM Protocol for CPU-PIM Collaboration

Processing in Memory (PIM) technology is gaining traction with the introduction of several prototype products. However, the interfaces of existing PIM devices hinder CPU performance excessively by delaying normal memory requests for long periods during PIM operations. In this paper, we propose a new PIM command and protocol designed for compatibility across various PIM devices and host processors, focusing on DRAM standards with limited command space. Our proposed command, PIM-ACT, activates multiple banks simultaneously with assigning the specific PIM operation. It closely follows the functionality of the ACT command for straightforward control by the memory controller. We also explore memory scheduling policies that balance the latency of conventional memory requests with the throughput of PIM workloads. Our evaluation demonstrates the effectiveness of our approach in optimizing both PIM and conventional workload performance.