vmR3HaltGlobal1Halt hogs host CPU

[Mihai Hanor]

Running a single CPU VM Windows 10 1803/1809/1903 64 bit or 32 bit (default VirtualBox VM settings for Windows 10 32 or 64 bit guest), the VM host process hogs the CPU, while the guest idles. If I start a 2nd VM (no OS, no boot medium, single CPU), it's enough to lower the CPU usage of the Windows 10 VM. On Windows, the CPU usage is lower if I start the VM while the PC is playing a video

To reproduce, just start the Windows 10 VM (no other VMs running or suspended), booting the Windows 10 1803/1809/1903 installation ISO, until it has completely loaded the setup and you are shown the first window. To check the CPU load in the guest, press Shift+F10 and type in Command Prompt: wmic cpu get loadpercentage
Booting Windows 10 1709 installation ISO is a very different experience. The host CPU is idling while the guest is idling

I am able to build VirtualBox OSE on Windows and I have observed that it spends a most of time in vmR3HaltGlobal1Halt. I can also record an ETL log with the official VirtualBox release build, if needed.
I can reproduce this issue on Windows 10 1803/1903 64 bit host OS and Debian 64 bit host OS. I first mentioned about this issue on #12851
There's also a forum thread, where some of the users reported similar issues ​link

[Mihai Hanor]

On Windows, the CPU usage is lower if I start the VM while the PC is playing a video in a video player (not in the browser)