Cache partitioning for sparse matrix–vector multiplication on the A64FX

Abstract

One of the novel features of the Fujitsu A64FX CPU is the sector cache. This feature enables hardware-supported partitioning of the L1 and L2 caches and allows the programmer control of which partition is used to place data in. This paper performs an in-depth study of applying the sector cache to sparse matrix-vector multiplication (SpMV) in the Compressed Sparse Row (CSR) format using a collection of 490 sparse matrices. A performance model based on reuse analysis is used to better understand situations in which and how the sector cache leads to improved cache reuse and to predict cache behavior. The model predicts the number of L2 cache misses within an error of 2% without cache partitioning. With sector cache enabled, depending on the configuration, the model predicts the number of L2 cache missed within 2–3% and 4–18% for sequential and parallel SpMV with 48 threads, respectively. Further experiments show the effect of various sector cache configurations on performance. A median speedup of about 1.05$\times$ is achieved, whereas the maximum speedup is about 1.6$\times$.