Hybrid Co-scheduling Optimizations for Concurrent Applications in Virtualized Environments

Concurrent applications in virtualized environments (VE) encounter synchronization problems such as Lock Holder Preemption (LHP). Hybrid co-scheduling is an effective approach to address such problems. However, the contention and exclusiveness between multiple concurrent domains in hybrid co-scheduling cause a serious performance degradation and unfairness. To keep the benefits brought by hybrid co-scheduling for multiple concurrent domains in VE, we propose two optimization schemes named Partial Co-Scheduling (PCS) and Boost Co-Scheduling (BCS) using finer space granularity. Instead of raising co-scheduling signals for all online CPUs, PCS scheme raises the co-scheduling signals only for the indispensable CPUs, while the rest CPUs are untouched. BCS scheme boosts the priorities for co-scheduled virtual CPUs (VCPUs) to induce the scheduler to pick the appropriate VCPUs. We implement both PCS and BCS into Credit Scheduler in Xen 4.0.1 and evaluate their performance compared with original hybrid co-scheduling and co-descheduling under different scenarios. The experimental results show that our proposals effectively alleviate the CPU run-time contention and achieve better performance and fairness compared to traditional hybrid co-scheduling.