[Qemu-discuss] guest slowing down host and other guests

[Raphael Bauduin]

Hi,

yesterday I've had a problem on a server hosting 5 KVM domains managed with libvirt.
The first symptoms were connectivity problems, and it appeared there were 2 domains showing problems:
1) a domain had a disk image configured as IDE and not virtio, and had these logs: http://pastie.org/8881997
2) a second domain was overloaded and out of memory, and I suspect it was swapping heavily.

The total memory assigned to the domains was less than half the memory on the host. The host CPU is a quad core.

The host CPU usage and memory usage was low, but its load was 15+.
Operations on the host were slow. For example copying a qcow image paused seconds and even tens of seconds a took a long time to complete. When the copy paused, I looked at the vmstat output, and the bo was 0!

I'm trying to understand what happened to prevent it from happening again. Anyone having suggestions?

I'm using qemu-1.7.0 and libvirt 1.2.1, but on an old kernel 2.6.32.


Thanks

Raph