I found many similar questions in the forum. However, they doesn't resolve my issue.
I have two Windows Server 2012 R2 installed with Hyper-V and cluster enabled. They are managed by a SCVMM 2012 R2(the RTM version). I have "Automatically migrate virtual machines to balance load" and have CPU and Memory threshold specified. However, nothing happened. I tried to execute "OPtimize Hosts" and got the following information.