CoINT: Proactive Coordinator for Avoiding Interruptability Holder Preemption Problem in VSMP Environment

In a Virtual Symmetric Multiprocessing (VSMP) environment, the behavior of hypervisor scheduler can significantly influence a guest's I/O responsiveness. The interrupt remapping mechanism, which can leverage multiple virtual CPUs in the VSMP guest to process I/O events, is known to be an efficient and prevalent solution to improve the I/O performance. However, in this paper we identified a novel challenge called the “Interruptability Holder Preemption” (IHP) problem in interrupt remapping mechanism. The IHP issue presents that a virtual CPU (vCPU) disabling the interruptability of guest's network device is descheduled by the hypervisor scheduler, which can easily invalidate the efficiency of the interrupt remapping mechanism. To solve this problem, we propose CoINT, a gasket coordinator residing in the hypervisor, to substantially enhance the network I/O performance by empowering the hypervisor to be proactively aware of the interruptability information of the guest's network device. ColNT completely eliminates the “Interruptability Holder Preemption” problem and largely reduces I/Ointerrupt processing delay caused by hypervisor scheduler. We implement ColNT in KVM hypervisor and evaluate its efficiency and responsiveness using both macro and microlevel benchmarks. The results show that ColNT can improve the netperf throughput up to 3x compared with native KVM, and up to 1.3x compared with traditional interrupt remapping of hypervisor-Ievel solution, in sacrifice of an negligible and reasonable overhead in the hypervisor.