SWAP: Effective Fine-Grain Management of Shared Last-Level Caches with Minimum Hardware Support

Performance isolation is an important goal in server-class environments. Partitioning the last-level cache of a chip multiprocessor (CMP) across co-running applications has proven useful in this regard. Two popular approaches are (a) hardware support for way partitioning, or (b) operating system support for set partitioning through page coloring. Unfortunately, neither approach by itself is scalable beyond a handful of cores without incurring in significant performance overheads. We propose SWAP, a scalable and fine-grained cache management technique that seamlessly combines set and way partitioning. By cooperatively managing cache ways and sets, SWAP (“Set and WAy Partitioning”) can successfully provide hundreds of fine-grained cache partitions for the manycore era. SWAP requires no additional hardware beyond way partitioning. In fact, SWAP can be readily implemented in existing commercial servers whose processors do support hardware way partitioning. In this paper, we prototype SWAP on a 48-core Cavium ThunderX platform running Linux, and we show average speedups over no cache partitioning that are twice as large as those attained with ThunderX's hardware way partitioning alone.