Virtual machine CPU usage spikes and remains abnormally high
Starting with ESX Server 3.5 and VirtualCenter 2.5, VMware DRS applies a cap to the memory overhead of virtual machines to control the growth rate of this memory. VMware DRS raises this cap at a controlled rate (1MB per minute, by default) to grant the required memory until the virtual machine overhead memory reaches a steady-state and as long as there are sufficient resources available on the host.
However, for VirtualCenter 2.5, this cap is not increased to satisfy the virtual machine's steady-state demand as expected. Thus, the virtual machine operates with an overhead memory that is less than its desired size, which in turn may lead to higher observed virtual machine CPU usage and lower virtual machine performance in a VMware DRS-enabled cluster.
VMWARE Knowledge Base KB # 1003638