I've been running vSphere 6.0 and ran into an issue with my hosts. Basically I have a VM that is using 100% CPU and is assigned 2 vCPUs. My hosts have 12 cores. When the VM hits 100% CPU, the host becomes unresponsive. If I use reservations I'm able to control this but I really shouldn't have to. This is a brand new install, but I have tested the same configuration on vSphere 5.5 which didn't have this issue.
I've done some Googling, but haven't found anyone else who has run into this problem. So it's either a fluke, a misconfiguration on my end, or not enough people are on vSphere 6.0 yet that no one else is seeing the issue. I will update as I patch and try to find the problem.