Temporary spikes in CPU usage are not necessarily a concern, but consistently high CPU usage might indicate a problem. You can use the CPU performance charts to monitor CPU usage for hosts, clusters, resource pools, virtual machines, and vApps.
- Host CPU usage constantly is high. A high CPU usage value can lead to increased ready time and processor queuing of the virtual machines on the host.
- Virtual machine CPU usage is above 90% and the CPU ready value is above 20%. Application performance is impacted.
- The host probably is lacking the CPU resources required to meet the demand.
- There might be too many virtual CPUs relative to the number of physical processor cores.
- There might be an IO storage or networking operation that places the CPU in a wait state.
- The Guest OS generates too much load for the CPU.
- Verify that VMware Tools is installed on every virtual machine on the host.
- 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 bar chart on the host's Virtual Machine view shows the CPU usage for all virtual machines on the host.
- 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.
- 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 does not decrease, set the CPU reservations for high-priority virtual machines to guarantee that they receive the required CPU cycles.
- Increase the amount of memory allocated to the virtual machine. This can potentially decrease disk and/or network activity for applications that cache. This might lower disk I/O and/or network traffic, which could in turn reduce CPU utilization. Virtual machines with smaller resource allocations generally accumulate more CPU ready time.
- 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 ESXi's maintenance of the three idle vCPUs takes CPU cycles that could be used for other work.
- 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.
- Upgrade the physical CPUs on the host if necessary.
- Use the newest version of hypervisor software, and enable CPU-saving features such as TCP Segmentation Offload, large memory pages, and jumbo frames.