CPU frequency below BIOS setting at 100% load - Windows 10 issue?

lodders

Admirable
I have a 4690k on a Gigabyte motherboard which I overclocked to 4.2Ghz.
I have just upgraded to Windows 10
I recently noticed that my CPU was running at only 1.8Ghz when at 100% load.
No, it is not overheating, and there is nothing wrong with my power supply.
I did lots of messing about with windows power management and BIOS, but I can no longer get the computer to overclock, or even to run in turbo mode.
The best I can do is get it to run a constant 3.5GHz (windows performance mode, all the C states disabled in BIOS).
With C states enabled, the more load you put on the CPU, the slower it goes.
It was fine in Windows 7
Has anyone else seen this problem?
 
Solution
"i5 4690k at 4.2Ghz with stock cooler on Gigabyte H81"

H-Boards of usually for non-K CPUs so not made for overclocking that might be the reason.
You use Z-Boards for unlocked CPUs. Any Z97 board will do the job.


It ran OK on windows 7