While working on a Hyper-V project I was noticing that the virtual machines had very sluggish network performance. This was a brand new enviroment with a good bandwidth so therefore I was a bit stumped on why the Network was acting so sluggish.
After doing some testing we saw that the hyper-v host had about 100mbit access to the internet and low latency on the link. The virtual machine that was running on it with a shared network card has about 1/3 of the speed and was getting quite high latency when accessing the internet.
After playing around with the Network driver I tried disabling VMQ on the card and voila! everything worked perfectly. When I saw it was a Broadcom driver and did a quick google search I found that there is a known issue with Broadcom network adapter drivers and VMQ
You can read more about it here –> http://support.microsoft.com/kb/2902166
So if you are having trouble with virtual machines and sluggish network performance with Broadcom drivers, try disabling VMQ
NOTE: I had added the latest Broadcom drivers to the hyper-v host but they did not fix the issue, I contacted Broadcom which gave me a hotfix which I used in this instance.