I have DP67DE MB with a i5-2500K uP (dating myself) and am exploring overclocking via the turboboost settings. Nothing extreme, say a ratio of 45.
Running stressors such as Prime95 or Linpack result in the uP changing from 16 ratios to 45 as expected, but then after a minute or two the uP "throttles" back to a ratio of 33 and stays there. There is not much in the forums about this for this board, but what there is confirms the result, and noone knows why.
It does not appear to be thermal throttling. I have a waterblock on the CPU and the 4 core temps never go above 52 degC. All the other temps (from Intel Desktop Utilities and CPUID/HW Monitoring) are below 40 degC.
I have been up and down the MSRs (using CrystalCPUID and BITS from biobits.org) and can't see what is triggering it. I've peeked and even poked a few times. The target is a ratio of 45. On demand Clock modulation is not active. For the cores, Thermal Stautus Log is 0, PROCHOT# or FORCEPR# log is 0, TM1 and TM2 logs are 0, and Power Limitation log is 0. Same for the Pkg Therm Status flags. The C-state counters are holding steady. The BIOs power settings (increased to move them out of the way) appear where they should in the RAPLs.
The bios has a max current setting, but I can't find it in the MSRs. The only potential location for it gives a GPF when read.
So I'm stumped as to why to it is throttling. The only thing I notice is the when you start the run, CPUID/HWMonitor show power ramping up to between 90 and 92 watts, as if it is reading and averaging over several seconds. When it reaches about 90 watts, the CPU throttles down to 33 ratios.
My best guess is the MB Voltage Regulator is limiting power and/or current independently of the CPU and the BIOS settings. If so, I don't see how it is telling the CPU to throttle. Stealing clock cycles perhaps? The VR temperatures are low, less than 30 degC.
Is the VR current power/current likely the limiting factor?
I see a design change notice for this board to upgrade it from a 3-phase to 4-phase VR. I happen to have a B2 stepping board, can I swap for one of these down the road?