CoINT: Proactive Coordinator For Avoiding The Interruptability Holder Preemption Problem In VSMP Environment

Wang Zhang Shanghai Jiao Tong University, P.R. China
Xiaokang Hu Shanghai Jiao Tong University, P.R. China
Jian Li Shanghai Jiao Tong University, P.R. China
Haibing Guan Shanghai Jiao Tong University, P.R. China


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. CoINT completely eliminates the "In-terruptability Holder Preemption" problem and largely reduces I/O interrupt processing delay caused by hypervisor scheduler. We implement CoINT in KVM hypervisor and evaluate its efficiency and responsiveness using both macro and micro-level benchmarks. The results show that CoINT can improve the netperf throughput up to 3x compared with native KVM, and up to 1.3x compared with traditional interrupt remapping of hypervisor-level solution, in sacrifice of an negligible and reasonable overhead in the hypervisor.

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