I'm experiencing a very strange cpu/power issue in Windows 10. Before I go into a necessarily long-winded explanation, here's the tl;dr: using the Windows 10 Preview, my system appears to be ignoring Turbo mode. The Intel Xtreme Tuning Utility reports that the cpu IS Turbo enabled, is NOT throttling, and IS set to receive additional voltage in Turbo mode. Under heavy workload, the core clock increases per my multiplier, but the system does NOT give it extra Turbo voltage. Making absolutely NO changes to the bios settings, I can dual boot into Windows 7 and all clocks and voltage are reported to be working as expected. In other words, something in Windows 10 is telling my hardware not to give my cpu the right amount of power.
Now, in greater detail....
CPU: Intel i7 4930K @ 4.6ghz (multiplier = x46)
Mobo: Asus Rampage IV Black Edition
vcore: +offset = .025
This all started in Windows 8.1 a few weeks ago when kb3000850 ("November 2014 update rollup for Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2") was released. This 8.1 update had the same effect. After installing it, my system was unstable and reported lower voltage than it should have been receiving in Turbo mode. I have my system set to use efficient power settings so the voltage increases and decreases as necessary with the cpu load (called "Additional Turbo Voltage" in the asus bios & Intel XTU software interface). Once the update was applied, the system would apply vcore (vid + offset), but it would NOT apply any "Additional Turbo Voltage". In order to achieve stability again, I had to set the base +offset vcore to compensate for the Turbo voltage that was not being applied because the system no longer recognized Turbo mode.
before the update, under heavy load: VID 1.27 + Offset .025 + Additional Turbo Voltage .05 = ~1.34v
since the update, under heavy load: VID 1.27 + Offset .025 (Additional Turbo Voltage .05) = ~1.29v
for stability since, under heavy load: VID 1.27 + Offset .07 + Additionaly Turbo Voltage .00 = ~1.34v
I corrected the problem by rolling back the update and hiding it so it would not reinstall. Once the update was removed from my system, the clock, voltage, and stability of my system returned to normal. Since then, I decided to ditch Windows 8.1 for now and set up a dual boot with Windows 7 & Windows 10 Preview instead.
In Windows 7, using the exact same bios settings, the system reports the expected clock & voltage, just as Windows 8.1 did before kb3000850. With EIST & cstates enabled, the cpu downclocks to x12 when it's idle, and ramps up to 4600mhz (x46) with vcore= ~1.344v. This is with offset +.025v & "Additional Turbo Voltage" +.055v. (as shown above).
In Windows 10, however, again with no change to the bios settings and using identical Power Options in Windows, the system behaves exactly as it did after kb3000850 in 8.1. Which is to say, again under Windows 10 the system seems to not recognize Turbo mode even when the cpu thinks it is in Turbo mode. Intel XTU reports that the cpu is NOT throttling, IS Turbo enabled, and IS set to .055v Additional Turbo Voltage.
After a LOT of troubleshooting, the only thing I've concluded that while at first glance this may seem like a hardware problem, it actually MUST be related to the OS environment, because the hardware, with the exact same settings, is acting exactly as expected in Windows 7 (and Windows 8.1 without the kb). I'm perplexed how Windows could block voltage set up in the bios, or how Intel software used within the Windows 10 environment can "see" the Turbo settings and report Turbo success when every sensor in the system, MS or otherwise, says it is not. Also, I don't think this is just a sensor malfunction, as the system actually crashes under a stress test load which it easily passes at the same settings in the other OS.
Anyway, I've shared this problem on several tech hardware forums, but nobody else seems to be seeing anything like this. I don't know if that means there something unique to my setup that is causing a conflict, or if my settings are just so specific and so finely tuned that I've found a problem nobody else has noticed yet. Either way, I figured it was worth sharing here since it seems to be something tied to the most recent Windows 8.1 and Windows 10 updates.
If anybody has any ideas or suggestions they would be most appreciated. :)