MiCache: An MSHR-inclusive Non-blocking Cache Design for FPGAs
Shaoxian Xu, S.-L. Lu, Zhiyuan Shao, Xiaofei Liao, Hai Jin · 2024
On FPGAs, customizing data parallelism can significantly improve performances of applications. However, a large number of applications, such as sparse matrix multiplication, exhibit irregular memory access patterns, for which further improvements are limited by their low memory access efficiency. It is challenging to solve using traditional caches due to the massive cache misses. To address this, prior research efforts are dedicated to developing non-blocking caches withMiss Status Holding Registers (MSHRs) to manage the cache misses and mitigate stalls caused by the misses. However, exsiting approaches allocate dedicatedBlock RAMs (BRAMs) for implementing MSHRs. It introduces complexities in MSHR configurations and potential resource inefficiencies, as MSHR demand is highly dynamic when solving real-world problems. In this paper, we present MiCache, an MSHR-inclusive non-blocking cache design where cache entries and MSHR entries share the same storage spaces to support the dynamic demand for MSHRs during the executions of applications. We design a consistent storage structure for cache and MSHR entries, ensuring a unified and efficient mechanism for cache/MSHR lookup and data access. To further improve the performance, we design a parallel dual pipeline, one of which processes the requests from processing elements, and the other processes the responses from off-chip memory. We implement and evaluate our proposal on a Xilinx Alveo U280 board. Evaluation results show that, compared to the state-of-the-art non-blocking cache design on FPGAs, with equivalent cache configurations, MiCache reduces the BRAM consumption by up to 17%. When using the same amount of BRAM resources, MiCache achieves up to 1.56x performance improvement.