You Can Always Get What You Want: CPU Virtualization Made Fast and Free

Dedicated VMs provide near bare-metal performance through CPU pinning, interrupt passthrough, and idle passthrough. In conventional deployments, however, these optimizations lock physical cores to individual VMs and prevent CPU sharing. In one of the world's largest cloud platforms, 74% of Dedicated VMs average below 10% CPU utilization, yet they occupy 95% of the physical infrastructure. This paper describes more than three years of deployment experience with Dynamic-Dedicated VMs (DDVMs) to safely reclaim this spare capacity. DDVMs combine workload-signature profiling, mediated posted interrupts, and occupancy-aware idle reclamation to dynamically share CPU cores while preserving Dedicated-VM-level SLOs. The challenge lies not in any single mechanism, but in making conservative, production-safe sharing decisions: identifying when sharing is safe, bounding interrupt latency when vCPUs are preempted, and recovering quickly when conditions change. Deployed across 37 regions and 92,000 servers, DDVMs improve CPU utilization by 10.5% at a 1.1× oversubscription ratio, while keeping SLO scores within the 20% latency-tolerance threshold and the mature-deployment performance-related ticket rate at 0.00035%.