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Wednesday, September 15 • 11:00 - 11:25
Mitigating Excessive Pause-Loop-Exiting in VM-Agnostic KVM - Kenta Ishiguro, Keio University

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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. VM-agnostic KVM tries to prevent excessive vCPU spinning by rescheduling vCPUs when an excessive spin is detected by pause-loop-exiting. This talk explains how the KVM vCPU scheduler fails to avoid excessive vCPU spinning in many opportunities. Three problems have been identified: 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. Simple modifications gracefully resolve the problems and the performance improves by up to 80 %. Results imply the VM-agnostic hypervisor can resolve excessive vCPU spinning more gracefully than previously believed.


Kenta Ishiguro

Ph.D student, Keio University
Kenta Ishiguro is a Ph.d student in the department of information and computer science at Keio university, advised by Kenji Kono. He is working on KVM performance analysis related to Pause-loop-exiting. He has made two academic contributions to KVM: "Mitigating Excessive vCPU Spinning... Read More →

Wednesday September 15, 2021 11:00 - 11:25 UTC
  KVM Track 1
  • Presentation Slides Attached Yes