Mitigating excessive vCPU spinning in VM-Agnostic KVM

Kenta Ishiguro, Naoki Yasuno, Pierre Louis Aublin, Kenji Kono

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

In virtualized environments, oversubscribing virtual CPUs (vCPUs) on physical CPUs (pCPUs) is common to utilize CPU resources efficiently. Unfortunately, excessive vCPU spinning, which occurs when a vCPU is waiting in a spin loop for an event from a descheduled vCPU, causes serious performance degradation. Usually, the VM-Agnostic hypervisor tries to prevent excessive vCPU spinning by rescheduling vCPUs when an excessive spin is detected by hardware support for virtualization. This paper investigates the effectiveness of KVM vCPU scheduler and shows it fails to avoid excessive vCPU spinning in many opportunities. Our in-depth analysis reveals simple modifications to KVM (41 LOC) improve the mitigation of excessive vCPU spinning. We have identified three problems: 1) scheduler mismatch, 2) lost opportunity, and 3) overboost. The first problem comes from the mismatch between the KVM vCPU scheduler and the Linux scheduler. The second and third problems come from an inefficient algorithm for choosing the next candidate vCPU to be scheduled. Our simple modifications gracefully resolves the problems and the performance improves by up to 80 %. Our results imply the VM-Agnostic hypervisor can resolve excessive vCPU spinning more gracefully than previously believed.

Original languageEnglish
Title of host publicationVEE 2021 - Proceedings of the 17th ACM SIGPLAN/SIGOPS International Conference on Virtual Execution Environments
EditorsBen L. Titzer, Harry Xu, Irene Zhang
PublisherAssociation for Computing Machinery, Inc
Pages139-152
Number of pages14
ISBN (Electronic)9781450383943
DOIs
Publication statusPublished - 2021 Apr 16
Event17th ACM SIGPLAN/SIGOPS International Conference on Virtual Execution Environments, VEE 2021 - Virtual, Online, United States
Duration: 2021 Apr 162021 Apr 16

Publication series

NameVEE 2021 - Proceedings of the 17th ACM SIGPLAN/SIGOPS International Conference on Virtual Execution Environments

Conference

Conference17th ACM SIGPLAN/SIGOPS International Conference on Virtual Execution Environments, VEE 2021
CountryUnited States
CityVirtual, Online
Period21/4/1621/4/16

Keywords

  • Hypervisor
  • Virtualization

ASJC Scopus subject areas

  • Artificial Intelligence
  • Software

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