A memory system design framework: creating smart memories

As CPU cores become building blocks, we see a great expansion in the types of on-chip memory systems proposed for CMPs. Unfortunately, designing the cache and protocol controllers to support these memory systems is complex, and their concurrency and latency characteristics significantly affect the performance of any CMP. To address this problem, this paper presents a microarchitecture framework for cache and protocol controllers, which can aid in generating the RTL for new memory systems. The framework consists of three pipelined engines' request-tracking, state-manipulation, and data movement' which are programmed to implement a higher-level memory model. This approach simplifies the design and verification of CMP systems by decomposing the memory model into sequences of state and data manipulations. Moreover, implementing the framework itself produces a polymorphic memory system. To validate the approach, we implemented a scalable, flexible CMP in silicon. The memory system was then programmed to support three disparate memory models' cache coherent shared memory, streams and transactional memory. Measured overheads of this approach seem promising. Our system generates controllers with performance overheads of less than 20% compared to an ideal controller with zero internal latency. Even the overhead of directly implementing a fully programmable controller was modest. While it did double the controller's area, the amortized effective area in the system grew by roughly 7%.