VirtualBox 4.2.16 with Multi-CPU Guest does not use multiple host CPU.

[KeepTriin]

I'm using VirtualBox 4.2.16 on Fedora 19 (kernel 3.9.9-302.fc19.x86_64) with a 64 bit Windows 7 2xCPU guest.

On Fedora 17 with 4.2.16 this configuration works successfully, but on Fedora 19, only a single CPU is loaded even though a dual CPU guest is specified.

The issue looks similar to an old issue, here: https://www.virtualbox.org/ticket/6936

If I revert to a single CPU (1xCPU, capped @95%) VirtualBox 4.2.16 works as expected. However, with a dual-CPU specification (2xCPU, capped 75%), a single CPU occupies 100% utilisation and the guest machine is noticeably slower than when configured with a single CPU.

The host reports no problems in any logs.

[KeepTriin]

VBox.log using single CPU - works ok.

[KeepTriin]

VBox.log for 2CPU guest. - Terminated by guest machine poweroff.

[Frank Mehnert]

So what you actually report is that with 2 configured guest CPUs, the guest runs notably slower than with one guest CPU. Of course this shouldn't happen but keep in mind that there is always some virtualization overhead involved.

Do I understand you correctly that with Fedora 17 your 2-CPU guest runs without any problem and with a normal CPU load? Did you already try to disable 3D for this guest?

[KeepTriin]

Replying to frank:

So what you actually report is that with 2 configured guest CPUs, the guest runs notably slower than with one guest CPU. Of course this shouldn't happen but keep in mind that there is always some virtualization overhead involved.

Agreed. There is some virtualization overhead, but this is a significant (Guest running with 2 CPUs is unusable)

Do I understand you correctly that with Fedora 17 your 2-CPU guest runs without any problem and with a normal CPU load? Did you already try to disable 3D for this guest?

That is correct. The same VM ran perfectly well on Fedora 17. Following an upgrade to F19, the guest became unusable and necessitated the change to a single CPU for a working VM. I have tried with and without 3D for the guest. But there is no noticeable difference.

[KeepTriin]

After a yum upgrade and reinstall of VirtualBox, this issue has now gone away.

[Frank Mehnert]

So in fact you upgraded the host Linux kernel and this fixed your problem? That's quite interesting. Do you have the output of 'dmesg' available for the old kernel and the new kernel? If so, could you attach it to this ticket?

[Frank Mehnert]

No response, closing.