A Novel Approach to Reduce L2 Miss Latency in Shared-Memory Multiprocessors

Recent technology improvements allow multiprocessor designers to put some key components inside the processor chip, such as the memory controller, the coherence hardware and the network interface/router. In this work we exploit such integration scale, presenting a novel node architecture aimed at reducing the long L2 miss latencies and the memory overhead of using directories that characterize cc-NUMA machines and limit their scalability. Our proposal replaces the traditional directory with a novel threelevel directory architecture and adds a small shared data cache to each of the nodes of a multiprocessor system. Due to their small size, the first-level directory and the shared data cache are integrated into the processor chip in every node. A taxonomy of the L2 misses, according to the actions performed by the directory to satisfy them is also presented. Using execution-driven simulations, we show significant L2 miss latency reductions (more than 60% in some cases). These important improvements translate into reductions of more than 30% in the application execution time in some cases.