VirtualBox using 100% CPU on host

[drgrog]

VirtualBox is using 100% of one cpu on the host when the guest is idle, with 0-1% cpu usage.

Both host and guest are on ubuntu 14.04, and have run fine for years using previous ubuntu and virtualbox versions. It's not clear what triggered this as I don't really monitor this box often, and nor can I seem to figure it out.

The most recent update was the distro upgrade on the guest, however I'm certain it had been running fine after that upgrade. Another recent change is that I removed the secondary spinning disk on the host, one that the vm was stored on, moved the vm onto the primary SSD, and replaced the old mount point with a symbolic link so that virtualbox still sees everything in the same place. I believe it was working well after that, but cannot be certain.

I have since tried upgrading virtualbox from 4.2 to 5.0.6, yet the problem remains.

This seems like a "virtualisation not enabled in the BIOS" problem, however I have checked and confirmed it is still enabled. Another issue on the forums (viewtopic.php?f=8&t=68525) suggested a problem with handling of NAT on the host, however I am running bridged network. Another post online suggested that running a second dummy vm worked for an older virtualbox version, however that did not fix it for me.

Any ideas? Bug? Log attached.

[Perryg]

Not sure yet, but updating the guest additions might help.

VirtualBox VM 5.0.6 r103037 linux.x86 (Oct 2 2015 13:02:11) release log
00:00:19.942848 VMMDev: Guest Additions information report: Version 4.2.26 r95022 '4.2.26'

Also from the looks of the log you are in fact using hardware virtualization.

[drgrog]

Thanks Perryg, I did update the guest additions, but I still have the problem.

Attached is the latest log running headless like it normally does, yet still hogging one cpu core, with around 80% sys and 20% usr if that helps.

[Perryg]

What is the guest exactly and what are you using it for? What services are actually running?

[drgrog]

The guest is a multi-purpose server: web, ssh, mail, etc.; dns & dhcp for the subnet; snmp & data capture/logging from external sensors on serial port; proxy;

Looking at the threads from top -H shows the SerRecv thread as the culprit. Looks like SerRecv is something to do with serial data, which is required here. The guest needs access to a data capture device connected to serial/rs232 on the host.

Using 'VBoxManage modifyvm guest-name --uart1 off' to temporarily disable the serial port fixes the issue, and the cpu usage drops - but unfortunately it is not a permanent solution, as access to the serial port is required.

[drgrog]

Think this may be a regression/bug, and have raised ticket https://www.virtualbox.org/ticket/14721