CPpf: a prefetch aware LLC partitioning approach

Abstract

Hardware cache prefetching is deployed in modern multicore processors to reduce memory latencies, addressing the memory wall problem. However, it tends to increase the Last Level Cache (LLC) contention among applications in multiprogrammed workloads, leading to a performance degradation for the overall system. To study the interaction between hardware prefetching and LLC cache management, we first analyze the variation of application performance when varying the effective LLC space in the presence and absence of hardware prefetching. We observe that hardware prefetching can compensate the application performance loss due to the reduced effective cache space. Motivated by this observation, we classify applications into two categories, prefetching sensitive (PS) and non prefetching sensitive (NPS) applications, by the degree of performance benefit they experience from hardware prefetchers. To address the cache contention and also to mitigate the potential prefetch-related cache interference, we propose CPpf, a cache partitioning approach for improving the shared cache management in the presence of hardware prefetching. CPpf consists of a method using Precise Event-Based Sampling techniques for the online classification of PS and NPS applications and a cache partitioning scheme using Cache Allocation technology to distribute the cache space among PS and NPS applications. We implemented CPpf as a user-level runtime system on Linux. Compared with a non-partitioning approach, CPpf achieves speedups of up to 1.20, 1.08 and 1.06 for workloads with 2, 4 and 8 single-threaded applications, respectively. Moreover, it achieves speedups of up to 1.22 and 1.11 for workloads composed of two applications with 4 threads and 8 threads, respectively.