Reducing Migration-induced Cache Misses

Abstract

In a large multiprocessor server platform, using multicore chips, the scheduler often migrates a scheduling entity, i.e. a thread or process or virtual machine, in order to achieve better load balancing or ensure fairness. The migration impact is likely to be more severe in virtualized environments, where high over-subscription of logical CPUs is very common for server consolidation workloads or virtual desktop infrastructure deployment. We demonstrate the performance benefit of saving and restoring cached data during migration. In particular, we measure the efficiency (benefit per cache block) of saving various subsets of the cached data, in order to balance implementation cost and complexity with improvements in cycle time. We also describe an implementation that moves cached data when a thread migrates, and we show the benefits in terms of reduced misses and reduced processor cycles.