Symmetry-agnostic coordinated management of the memory hierarchy in multicore systems

Abstract

In a multicore system, many applications share the last-level cache (LLC) and memory bandwidth. These resources need to be carefully managed in a coordinated way to maximize performance. DRAM is still the technology of choice in most systems. However, as traditional DRAM technology faces energy, reliability, and scalability challenges, nonvolatile memory (NVM) technologies are gaining traction. While DRAM is read/write symmetric (a read operation has comparable latency and energy consumption as a write operation), many NVM technologies (such as Phase-Change Memory, PCM) experience read/write asymmetry: write operations are typically much slower and more power hungry than read operations. Whether the memory's characteristics are symmetric or asymmetric influences the way shared resources are managed. We propose two symmetry-agnostic schemes to manage a shared LLC through way partitioning and memory through bandwidth allocation. The proposals work well for both symmetric and asymmetric memory. First, an exhaustive search is proposed to find the best combination of a cache way partition and bandwidth allocation. Second, an approximate scheme, derived from a theoretical model, is proposed without the overhead of exhaustive search. Simulation results show that the approximate scheme improves weighted speedup by at least 14% on average (regardless of the memory symmetry) over a state-of-the-art way partitioning and memory bandwidth allocation. Simulation results also show that the approximate scheme achieves comparable weighted speedup as a state-of-the-art multiple resource management scheme, XChange, for symmetric memory, and outperforms it by an average of 10% for asymmetric memory.