Use the esxtop command-line utility to periodically monitor the CPU and memory usage of individual hosts and their VMs. The esxtop utility provides a detailed look at how ESX uses resources in real time.

Here are some examples and guidelines for interpreting host-related esxtop data:

  • If the load average on the first line of the esxtop CPU panel is equal to the number of physical processors in the system, the host is overloaded.

  • If the usage percentage for the physical CPUs on the PCPU line (PCPU USED(%)) is 90% or greater, the CPUs are approaching an overloaded condition.

    Here are some examples and guidelines for interpreting VM-related esxtop data:

  • High values for ready wait (%RDY) and %CSTP indicate contention for CPU. %RDY should be less than 10%-15% per vCPU. %CSTP should be less than 5% per vCPU.

  • VMs with a high %CSTP might indicate that they have more vCPUs than required. For an IP Availability ManagerVM with four vCPUs and a high %CSTP, consider reducing the vCPUs to two.

    Also, check the esxtop data for memory ballooning and swapping. (In the CPU panel, check the swap wait %SWPWT value; in the Memory panel, check the MCTLTGT (MB) value, the SWCUR (MB) value, and other balloon- and swap-related lines.) Swapping can be avoided in a VM by reserving memory for the VM that is at least equal in size to the VM’s active working set.