FASA-DRAM: Reducing DRAM Latency with Destructive Activation and Delayed Restoration

Abstract

DRAM memory is a performance bottleneck for many applications, due to its high access latency. Previous work has mainly focused on data locality, introducing small but fast regions to cache frequently accessed data, thereby reducing the average latency. However, these locality-based designs have three challenges in modern multi-core systems: (1) inter-application interference leads to random memory access traffic, (2) fairness issues prevent the memory controller from over-prioritizing data locality, and (3) write-intensive applications have much lower locality and evict substantial dirty entries. With frequent data movement between the fast in-DRAM cache and slow regular arrays, the overhead induced by moving data may even offset the performance and energy benefits of in-DRAM caching.

In this article, we decouple the data movement process into two distinct phases. The first phase is Load-Reduced Destructive Activation (LRDA), which destructively promotes data into the in-DRAM cache. The second phase is Delayed Cycle-Stealing Restoration (DCSR), which restores the original data when the DRAM bank is idle. LRDA decouples the most time-consuming restoration phase from activation, and DCSR hides the restoration latency through prevalent bank-level parallelism. We propose FASA-DRAM, incorporating destructive activation and delayed restoration techniques to enable both in-DRAM caching and proactive latency-hiding mechanisms. Our evaluation shows that FASA-DRAM improves the average performance by 19.9% and reduces average DRAM energy consumption by 18.1% over DDR4 DRAM for four-core workloads, with less than 3.4% extra area overhead. Furthermore, FASA-DRAM outperforms state-of-the-art designs in both performance and energy efficiency.