For Ivy Bridge system, CPU power management is controlled by X86PlatformPlugin.kext, it’s in IOPlatformPluginFamily.kext. MacPro 5,1 doesn’t support Ivy Bridge by Apple, only Sandy Bridge. To fix this you need to copy MacMini6,2.plist to a new plist with MacPro 5,1 board type. Goto /Extra folder SMBios.plist look for SMboardproduct key
Run these command:
$ cd /System/Library/Extensions/IOPlatformPluginFamily.kext/Contents/PlugIns/X86PlatformPlugin.kext/Contents/Resources
$ sudo kextcache -system-prelinked-kernel
$ sudo kextcache -system-caches
Goto /System/Library/Coreservices/PlatformSupport.plist. Open with PlisEditor Pro, check if you have Mac-F221BEC8 in SupportedBoardIds, if not manual add it.