Date Added: Jul 2010
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.