Cloud Computing is a new paradigm where resources are used as on-demand utility. Infrastructure as a Service(IaaS) cloud uses virtual machine(VM) based implementation for numerous advantages like elasticity, fault isolation, efficient hardware utilization, security and ease of management. Virtual machine monitor(VMM) like Xen is a popular virtualization software to manage virtual machines by scheduling them to use resources such as CPU, memory and network. Performance isolation is desirable in virtual machine based infrastructures to meet Service Level Agreements(SLAs). In performance isolation, no virtual machine should affect performance of other co hosted virtual machine, which shares the same hardware. The thesis aims to evaluate the performance isolation achieved by Xen in different scheduler configurations. This thesis also investigates requirements of global balancing of load across all the available physical processors in a physical machine and discusses algorithmic design and implementation of a developed user space load balancing program.