VMware vSphere: The CPU Scheduler in VMware ESX 4.1

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July 12, 2010

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The CPU scheduler in VMware vSphere 4.x (ESX 4.x) is crucial to providing good performance in a consolidated environment. Because most modern processors are equipped with multiple cores per processor, or chip multiprocessor (CMP) architecture, it is easy to build a system with tens of cores running hundreds of virtual machines. In such a large system, allocating CPU resources efficiently and fairly is critical.In ESX 4, there are some significant changes to the CPU scheduler”for better performance and scalability. This paper describes these changes and their impacts on performance. It also provides certain details of the CPU scheduling algorithms. This paper is updated to reflect the changes in the ESX 4.1 CPU scheduler.