Virtualbox.exe use 100% CPU when debug VM with WinDBG. -> fixed in SVN

[AaronWang]

I have a kernel debug on Guest OS with WinDBG. When debugger has been connected. Process VirtualBox.exe in Host OS use 100% CPU.When I break Guest OS by debugger. It still use 100% CPU.

[Sander van Leeuwen]

That's to be expected due to the polling nature with which the serial port is controlled. Once you've booted up and there's no more communication (new executables/modules being loaded) cpu usage should go down.

[AaronWang]

But, my debugger can't work. I resovle this by set priority of virtualbox.exe that running the Guest OS to "Below normal". Everything is working fine.

[Sander van Leeuwen]

That works or if you have more than one core/cpu. I'll close the defect then.

[Nick Dowell]

VMware has a nice option (on by default) which prevents 100% CPU usage when the guest is polling the serial port. It would be great it VirtualBox could implement similar functionality.
​http://www.vmware.com/support/ws5/doc/ws_devices_serial_advanced.html

As it stands, VirtualBox is not very useful for doing kernel mode debugging with WinDBG because of this problem. There's been some discussion of this over on the forum:
​http://forums.virtualbox.org/viewtopic.php?p=59612

[Sander van Leeuwen]

That's already fixed in SVN: vboxmanage setextradata VMNAME "VBoxInternal/Devices/serial/0/Config/YieldOnLSRRead" 1

And again this is not an issue if you have more than one core/cpu. It's been working well with such hardware for years.

[Nick Dowell]

Great to know it's been addressed in SVN :-)

I take it that this change isn't in the 2.1.4 release?

FWIW, my machine is a dual-core, but I couldn't get kernel debugging working. Maybe I was doing something wrong, but had no trouble doing so with VMware.

[sunlover]

Right, this change was not included in 2.1.4. It will be available in the 2.2.x version of VBox.

And you are right, the problem can be noticed on a dual core too (that is why I've implemented the workaround :) ).

[Nick Dowell]

I look forward to trying it out in the 2.2.x series :-)

Not sure if we should close this case for now...? I can always re-open if things are still iffy ;)

[sunlover]

We close tickets when the VirtualBox version, that fixes the problem, is actually released. So this ticket should stay open for now.

[AaronWang]

Terrible thing!!!!!! In Virutalbox 2.1.4 When debug VM with WinDBG. When I press 'CTRL+Break' In WinDBG, Process 'Virtualbox.exe'( guest vm ) deadlock. The VM I'm debugging doesn't response. WinDBG doesn't show any infomation. After five minutes. I kill 'virtualbox.exe'. It's seem I can't debug VM with WinDBG now.

I have two pc. AMD Althlon 3500+, 1GB DDR Intel Dual Core E2200 2.20GHz, 4GB DDR2 The same thing happenes. I hope this problem will be fixed soon.

[Nick Dowell]

I've re-tested this with 2.0.0 r45846

After enabling YieldOnLSRRead with VBoxManage, WinDBG debugging is working nicely :-)

May I suggest exposing this option in the configuration GUI?