I'm having some CPU overclocking troubles. My CPU is an i7 6850k running in an Asrock X99 Taichi motherboard and I'm using the intel_pstate driver (Arch Linux on the 4.10.1 kernel). I've set the max Turbo multiplier to 42x for all cores in EFI and the most I can ever get out of this overclock is 4GHz on core 0 and 3.8GHz on all of the other cores. Here's a screenshot of the output of i7z while I'm running mprime in the background. Of particular note is that it says the max turbo multiplier with 1/2/3/4/5/6 cores enabled is 40x/40x/42x/42x/42x/42x. I also set the max multiplier to 40 and 44 in EFI and the single and dual core boost never changed. Moreover, this is a stable overclock and all cores run at 4.2GHz under load in Windows.
I do not think its throttling since I get the same speeds even if my CPU is at 60c. I also cannot figure out how to lock the clock multiplier. I've also tried many combinations of C-States off/on, Turbo Boost 3 off/on, and SpeedStep off/on. If I disable turbo boost, I lose all control of the multiplier.
Does anyone have an idea about what could cause this issue? I've emailed Asrock and their support blamed a lack of drivers for Linux (I didn't see that coming at all /s). I also would like to know if other have had success overclocking their Broadwell-E CPUs on other motherboards, cause it might be a problem with my motherboard.