This fix only works with Windows 7 x64 and x32 and only in systems using more than 2 physical CPUs or more than 2 logical cores.
Windows 7 has a feature called “Core Parking” which turns off CPU cores when not being utilized. For many gaming applications, this can be unhelpful. There is no switch to turn off this Core Parking, so you need to edit a few registry values to force Core Parking off. For me, this boosted my performance from 30 fps in Low settings to 45 on Ultra (i7 2600k CPU, GTX 570 GPU). These registry changes are reversible and there are no deletion of anything in the registry. It is all outlined in the forum link below. Please read the whole forum page to understand what is changing and if it applies to your setup, and edit the registry with caution.
This utility will allow you to easily enable or disable core parking for your CPU. The first thing that you should do is to go to a resource manager to check if you have parked cores. The reason of doing so is that core parking is not enabled for all the multicore CPU’s. For example, if you have Intel Q9550 Quad Core CPU you may not see any parked cores at all.
Once you have started “Manage Parked CPU Utility,” you have to press “Check status button” to allow program to search registry for the keys and values that are responsible for the “core parking”.