The CPU (%) chart displays virtual machine CPU usage and ready values.

This chart is located in the Home view of the virtual machine Performance tab.

Table 1. Data Counters
Chart Label Description
Usage Amount of actively used virtual CPU as a percentage of total available CPU.

CPU usage is the average CPU utilization over all available virtual CPUs in the virtual machine.

For example, if a virtual machine with one virtual CPU is running on a host that has four physical CPUs and the CPU usage is 100%, the virtual machine is using one physical CPU completely.

virtual CPU usage = usagemhz ÷ (number of virtual CPUs × core frequency)

Note: This is the host's view of the CPU usage, not the guest operating system view.
  • Counter: usage
  • Stats Type: Rate
  • Unit: Percentage (%). Precision is to 1/100%. A value between 0 and 100.
  • Rollup Type: Average (Minimum/Maximum)
  • Collection Level: 1 (4)
Ready Percentage of time that the virtual machine was ready, but could not get scheduled to run on the physical CPU.
CPU ready time is dependent on the number of virtual machines on the host and their CPU loads. At collection level 1, the average CPU ready time of all virtual CPUs on the virtual machine is displayed. At collection level 3, the average CPU ready time of each virtual CPU is also displayed.
  • Counter: ready
  • Stats Type: Rate
  • Unit: Percentage (%)
  • Rollup Type: Summation
  • Collection Level: 1

Chart Analysis

A short spike in CPU usage or CPU ready indicates that you are making the best use of the virtual machine resources. However, if the CPU usage value for a virtual machine is above 90% and the CPU ready value is above 20%, performance is being impacted.

If performance is impacted, consider taking the following actions.

Table 2. CPU Performance Enhancement Advice
# Resolution
1 Verify that VMware Tools is installed on every virtual machine on the host.
2 Set the CPU reservations for all high-priority virtual machines to guarantee that they receive the CPU cycles required.
3 Compare the CPU usage value of a virtual machine with the CPU usage of other virtual machines on the host or in the resource pool. The stacked line chart on the host's Virtual Machine view shows the CPU usage for virtual machines on the host.
4 Determine whether the high ready time for the virtual machine resulted from its CPU usage time reaching the CPU limit setting. If so, increase the CPU limit on the virtual machine.
5 Increase the CPU shares to give the virtual machine more opportunities to run. The total ready time on the host might remain at the same level if the host system is constrained by CPU. If the host ready time doesn't decrease, set the CPU reservations for high-priority virtual machines to guarantee that they receive the required CPU cycles.
6 Increase the amount of memory allocated to the virtual machine. This decreases disk and or network activity for applications that cache. This might lower disk I/O and reduce the need for the host to virtualize the hardware. Virtual machines with smaller resource allocations generally accumulate more CPU ready time.
7 Reduce the number of virtual CPUs on a virtual machine to only the number required to execute the workload. For example, a single-threaded application on a four-way virtual machine only benefits from a single vCPU. But the hypervisor's maintenance of the three idle vCPUs takes CPU cycles that could be used for other work.
8 If the host is not already in a DRS cluster, add it to one. If the host is in a DRS cluster, increase the number of hosts and migrate one or more virtual machines onto the new host.
9 Upgrade the physical CPUs or cores on the host if necessary.
10 Use the newest version of hypervisor software, and enable CPU-saving features such as TCP Segmentation Offload, large memory pages, and jumbo frames.