Date of Award
5-10-2026
Date Published
June 2026
Degree Type
Thesis
Degree Name
Master of Science (MS)
Department
Electrical Engineering and Computer Science
Advisor(s)
Bryan Kim
Second Advisor
Jae Oh
Keywords
CPU Oversubscription;Hypervisors;Inter-VM Contention;Lock Holder Preemption;Virtualization;Virtualization Overhead
Subject Categories
Computer Sciences | Physical Sciences and Mathematics
Abstract
To address the severe multi-threaded performance degradation caused by lock contention in oversubscribed cloud environments, this thesis examines and improves on the Pause Loop Exit (PLE) mechanism used by hypervisors to deschedule unproductive virtual CPUs (vCPUs). These oversubscribed environments introduce contention which frequently leads to Lock Holder Preemption (LHP), where a hypervisor preempts a vCPU holding a critical spinlock, causing waiting vCPUs to waste cycles spinning. To mitigate LHP, hardware mechanisms trigger PLE events to inform hypervisors of spinning vCPUs, relying on a PLE_gap parameter to differentiate spinlock instances. The PLE_gap dictates spinlock detection sensitivity—a component of the virtualization stack that remains significantly under-studied, as previous works rely on static values. Incorrect PLE sensitivity incurs unnecessary vCPU scheduling during low contention and fails to prevent excessive spinning during high contention, rendering existing LHP mitigations suboptimal. This thesis makes two primary contributions: 1) examining the effectiveness of adjusting PLE sensitivity and its relationship with contention, 2) proposing and implementing Sensitivity Adjusted Gap Exiting (SAGE), a dynamic PLE sensitivity adjustment method for contention-aware preemption. Evaluations show that SAGE achieves up to a 110% speedup on PLE-sensitive workloads and an average 6.3% speedup in contended environments, while maintaining negligible overhead in uncontended scenarios.
Access
Open Access
Recommended Citation
Stowers, Sam Thomas, "SAGE: Contention-Aware Sensitivity Adjustment for Spin Lock Exiting in VMs" (2026). Theses - ALL. 1023.
https://surface.syr.edu/thesis/1023
