Yesterday I have noticed that one of my home lab ESXi hosts has unusual high CPU usage. One CPU core was running at 100% constantly for a week or so. My first reaction was to look for which virtual machine went crazy and started consuming all its alocated CPU resources. To my surprise all VMs running on the host were almost idle. Obviously the CPU usage of VMs did not add up to the CPU usage of the host. For further investigation I run esxtop on the tech support console with the following result:
The process dcui.345917 had unusual high CPU usage. DCUI is the Direct Console User Interface on ESXi hosts (the yellow BIOS like page). The host has been rebooted 3 days before and that did not fix the problem. Google and VMware KB search did not return anything. Something funny had to be going on directly on the DCUI console. So I went directly to the host attached monitor and immediately noticed the screen was flashing. Why? The two keyboards of my ESXi hosts were stacked on top of each other and one was pushing a key on the other. And that was it. The pressed key (probably Enter) generated so much interupts to keep one CPU core busy.