Guest CPU saturation happens when the application and operating system running in a VM use all of the CPU resources that the ESXi host is providing for that VM. However, this guest CPU saturation does not necessarily indicate that a performance problem exists.

Compute-intensive applications commonly use all of the available CPU resources, but this is expected and might be acceptable (as long as the end user thinks that the job is completing quickly enough). Even less-intensive applications might experience periods of high CPU demand without experiencing performance problems. However, if a performance problem exists when guest CPU saturation is occurring, steps should be taken to eliminate the condition.

When a VM is configured with more than one vCPU but actively uses only one of the vCPUs, resources that could be used to perform useful work are being wasted. At this time, you may at least see a potential performance problem from the most active vCPU perspective.