Category Archives: CPU

ESXi and VM CPU Performance Issues

The following is a description of some common ESXi and VM CPU Performance Issues:

High Ready Time

Ready Time above 10% could indicate CPU contention and might impact the Performance of CPU intensive application. However, some less CPU sensitive application and virtual machines can have much higher values of ready time and still perform satisfactorily.

High CoStop (CSTP) Time

CoStop time indicates that there are more vCPUs than necessary, and that the excess vCPUs make overhead that drags down the performance of the VM. The VM will likely run better with fewer vCPUs. The vCPU(s) with high CoStop is being kept from running while the other, more-idle vCPUs are catching up to the busy one.

Continue reading

vCPU States

vCPUs are always in one of four states (vCPU States):


WAIT – This can occur when the virtual machine’s guest OS is idle (Waiting for Work), or the virtual machine could be waiting on vSphere tasks. ┬áSome examples of vSphere tasks that a vCPU may be waiting on are either waiting for I/O to complete or waiting for ESX level swapping to complete. These non-idle vSphere system waits are called VMWAIT.

Continue reading