1. A method for managing skew between a plurality of virtual CPUs assigned to a virtual machine to execute threads of the virtual machine, the virtual machine being supported by a computer system having multiple physical processors (PCPUs), the method comprising: for each thread of the virtual machine, reducing a virtual time of the thread by a corun bonus, the virtual time being an accumulation of real time of executing the thread as modified by a weight assigned to the thread and the corun bonus being a measure of a number of virtual CPUs assigned to the virtual machine that are running on different PCPUs; and granting execution priority to one of the threads that has the lowest virtual time.