Kakao Details CPU-Centric VM Density Testing for VMware Infrastructure

Kakao engineers (author) published a study on determining optimal VM density from a CPU perspective for VMware infrastructure. The testing methodology involved progressively increasing the number of VMs on a single Physical Machine (PM) and measuring CPU performance using the CoreMark benchmark. The tests varied VM flavors (2, 4, and 8 vCPUs) and simulated CPU usage levels from 10% to 100% in 10% increments. A separate analysis using stress-ng examined internal CPU performance counters. Key findings indicate that performance degradation becomes significant once the total vCPUs exceed the PM's physical cores, even if Hyper-Threading is enabled. The study provides a reference table for maximum VM counts based on tolerable performance degradation levels (0-10%, 10-20%, 20-30%). For example, on a PM with Intel Xeon Silver 4214 CPUs running 4 vCPU VMs at 40% average CPU usage, 21 VMs are suggested if a 20% performance degradation is tolerated. The author notes that these results are CPU-centric and assume sufficient memory and disk resources.