A Comprehensive Study of DRAM Controllers in Real-Time Systems

Abstract

The DRAM main memory is a critical component and a performance bottleneck of almost all computing systems. Since the DRAM is a shared memory resource on multi-core plat- forms, all cores contend for the memory bandwidth. Therefore, there is a keen interest in the real-time community to design predictable DRAM controllers to provide a low memory access latency bound to meet the strict timing requirement of real-time applications. Due to the lack of generalization of publicly available DRAM controller models in full-system and DRAM device simulators, researchers often design in-house simulator to validate their designs. An extensible cycle-accurate DRAM controller simulation frame- work is developed to simplify the process of validating new DRAM controller designs. To prove the extensibility and reusability of the framework, ten state-of-the-art predictable DRAM controllers are implemented in the framework with less than 200 lines of new code. With the help of the framework, a comprehensive evaluation of state-of-the-art pre- dictable DRAM controllers is performed analytically and experimentally to show the im- pact of different system parameters. This extensive evaluation allows researchers to assess the contribution of state-of-the-art DRAM controller approaches. At last, a novel DRAM controller with request reordering technique is proposed to provide a configurable trade-off between latency bound and bandwidth in mixed-critical systems. Compared to the state-of-the-art DRAM controller, there is a balance point between the two designs which depends on the locality of the task under analysis and the DRAM device used in the system.