This issue is resolved please read post: http://datacenter-flo.de/?p=2050
Some customers reported me about performance issue with virtual machines running on Hyper-V V3 (Windows Server 2012) after creating a switch.
Together with colleagues we found out that the issue only appears with Broadcom network interface cards.
We saw that the issue is related by “Virtual Machine Queues” enabled on the networkadapter.
If you are facing this issue, please try to disable “Virtual Machine Queues” first on the virtual NIC in your VM. If this doesn’t resolve your issue, please disable “Virtual Machine Queues” also on the physical NIC of your server.
The issue should be fixed with a Broadcom firmware and driver update for the NIC.
You can do this in the Adapter Properties of the Network Interface Card.