Saturday, August 31, 2013

[Article] Not AVX Stable @ 4.4GHz, are we now? Shame!

I was able to run Intel XTU at 4.4GHz for 12Hrs+ and I thought it was stable. How wrong I was! It crashed in Handbrake after encoding videos for many hours. Once after 10hrs! After that I figured that there was something that I must have overlooked. When I asked around, I came to understand that XTU doesn’t use AVX in its stress test. Handbrake does, but still it doesn’t bombard it with AVX instructions like Prime95 does. BTW, Prime 95 27.9 (which is the latest version out with AVX support) crashes easily with the settings that XTU ran for hours and hours without failing.

Then I figured that it could be stable everywhere but AVX. One way to check it was to run Prime95 without AVX. That’s version 26.6. I ran it for hours and it didn’t fail. Now I was sure that it was the AVX instructions that caused the issue. 1.285V just isn’t enough when the components that makes AVX instructions work also become alive inside the CPU. I’m sure I would probably be able to escape by using Adaptive Vcore which automatically increases the Vcore by 0.1V when AVX instructions are heavily used. I tried 1.285V Adaptive, but it still failed in Handbrake. Probably the voltage fluctuation is also not a good thing.

Since then I’ve come to accept that you cannot have everything you want in life and 100MHz isn’t worth that increase in Vcore and temps (and increase in fan speed). So, now I’m going to settle with my 4.3GHz OC and tweak it a little bit to get every bit of power I can get with it. I’ve successfully managed to up the Uncore to 39x at just 1.08V and Memory to 1600MHz @ XMP. I’m also in the process of tweaking the Digi+ power delivery settings (image below) to lower the power consumption and the temps as much as possible without crippling stability. The following screenshot was taken while running Handbrake. Look at the fan RPM – bottom right hand side. It’s completely silent. That’s just great. I won’t be able to achieve that with close to 1.3V. The temps it shows is not very accurate though. Those are not the core temps. Core temps hover between 60C and 70C.

Digi+ settings: M6H

I haven’t done a lot of testing, but after dropping the LLC to level 6, enabling Active Frequency Mode and setting CPU Power Phase Control to optimized, at least it is stable in Intel Burn Test, Handbrake and Crysis 3. If it passes 6hrs of Prime95, I say I’m stable enough.

Intel Burn Test stable @ 4.3


  1. Same for me on 4.4 Was stable under Aida6 and IBT. Then I play BF3 for 3 hours and i get BSOD.

    Clocked down to 4.3 and am planning to tweak the voltage.

  2. Haswell is a real pain in the arse if you didn't get a above average CPU. :(

    even the 4.3GHz settings i've given in this post were not really stable. last night i managed to run OCCT for 6hrs and i would call that stable enough. what i found out was that the Core was fine at 1.24V, but Cache ratio at 39x needed 1.175V and when i increased the cache voltage from 1.15V to 1.175V, i got reboots without any BSODs. had to up the Input Voltage to 1.90V (LLC level 6) to make it stable. i only tried 1.75V, 1.85V and 1.90V. i'm sure i can tweak it later. but for now, that is fine.

    time to see if i can do 4.4 :)


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