The Gradient-Based Cache Partitioning Algorithm

This paper addresses the problem of partitioning a cache between multiple concurrent threads and in the presence of hardware prefetching. Cache replacement designed to preserve temporal locality (e.g., LRU) will allocate cache resources proportional to the miss-rate of each competing thread irrespective of whether the cache space will be utilized [Qureshi and Patt 2006]. This is clearly suboptimal as applications vary dramatically in their use of recently accessed data. We address this problem by partitioning a shared cache such that a global goodness metric is optimized This paper introduces the Gradient-based Cache Partitioning Algorithm (GPA), whose variants optimize either hitrate, total instructions per cycle (IPC) or a weighted IPC metric designed to enforce Quality of Service (QoS) [Iyer 2004]. In the context of QoS, GPA enables us to obtain the maximum throughput of low-priority threads, while ensuring high performance on high-priority threads. The GPA mechanism is robust, low-cost, integrates easily with existing cache designs and improves the throughput of an in-order 8-core system sharing an 8MB L3 cache by similar to 14%.