Symbiotic job scheduling on the IBM POWER8

Abstract

Simultaneous multithreading (SMT) processors share most of the microarchitectural core components among the co-running applications. The competition for shared resources causes performance interference between applications. Therefore, the performance benefits of SMT processors heavily depend on the complementarity of the co-running applications. Symbiotic job scheduling, i.e., scheduling applications that co-run well together on a core, can have a considerable impact on the performance of a processor with SMT cores. Prior work uses sampling or novel hardware support to perform symbiotic job scheduling, which has either a non-negligible overhead or is impossible to use on existing hardware. This paper proposes a symbiotic job scheduler for the IBM POWER8 processor. We leverage the existing cycle accounting mechanism to predict symbiosis between applications, and use that information at run-time to decide which applications should run on the same core or on separate cores. We implement the scheduler in the Linux operating system and evaluate it on an IBM POWER8 server running multiprogrammed workloads. The symbiotic job scheduler significantly improves performance compared to both an agnostic random scheduler and the default Linux scheduler. With respect to Linux, it achieves an average speedup by 8.8% for workloads comprising 12 applications, and by 4.7% on average across all evaluated workloads.