I'm running 64 bit Windows 8.. decent specs.. SSD/16GB of ram/AMD  6 Core 1055T and an AMD 7950 3GB video card.  I tried playing Crysis 3.. noticed it did not matter what settings I used.. even at the lowest settings my frame rate would be quite low.. switched to an older video card.. same thing..What was strange though is if I opened up Resource Monitor or an utility which monitored the GPU they were not being pushed at all.. CPU was 50%.. GPU was 20%..

Hyper V was installed.. and there was 6 VM's in a saved state.. but they were not being started when Windows started.  I removed Hyper-V and now everything is normal, and well Crysis 3 is a thing of beauty..

But I'm not sure why Hyper-V would stop other apps from getting the full use of my hardware?

We already have a topic here:

http://social.technet.microsoft.com/Forums/en-US/w8itprovirt/thread/afe0c6cf-fbf4-4e07-8ccc-78de5e481bd3

And it is known to reduce game performance. This is caused because Hyper-V is a type1 hypervisor.

Thanks checked the thread.. I guess there is no known solution.. Like can I disable certain services or settings and only enable them when I need to use Hyper-V.

no. The hyperviso is loaded all the time. Use a type2 solution like VMware worksattion/player and stop the VMware services if you don't need them ( I wrote a .cmd with does this for me)

But there is probably a configuration setting that windows reads at boot time that tells the machine to be a hyper visor or not right? IE can I toggle a reg key and disable some services.. and when I need to use hyper v I re-enable? Uninstalling is quite straight forward if I didn't have to re import my machines and recreate switches.. so its extra work I'd prefer to avoid.

yes, with BCDedit you can remove the hypervisor launchtype entry and this stops hyper-v. But you have to reboot each time after changing the value.

Thanks..

This is what I do now.. when I'm not going to use hyper-v on Windows 8:

#1) Stop all my Virtual Machines and close Hyper-V

#2)  Set the "Hyper-V Virtual Machine Management" service to disabled

#3) Open an elevated cmd prompt and type: "bcdedit /set hypervisorlaunchtype off"

#4) Restart

#5) Open up AMD Overdrive, check your GPU utilization.. Launch Crysis 3.. now Im using 88% of my GPU again

If you need to use Hyper-V again just turn the hypervisor launch type back and restart.. better than uninstalling.

ok, thanks for the feedback.

In case it helps anyone, here are a couple batch files which (when run as administrator) will perform the above steps:

Hyper-V Off:

sc config vmms start= disabled
bcdedit /set hypervisorlaunchtype off
shutdown /r /t 0

Hyper-V On:

sc config vmms start= automatic
bcdedit /set hypervisorlaunchtype on
shutdown /r /t 0