[ovirt-users] high load on hosts

I'm wondering how I can best limit the ability of VMs to overrun the load on hosts. I have a fairly stock 4.2 HCI setup with three well spec'ed servers, 10Gbe/SSDs, plenty of ram and CPU with only a hand full of light use VMs. I notice when the occasional demanding job is run on a VM I'm seeing load average on host node shoot up in to the 20-30s, how can a single "medium" vm cause host load to rise so high?