[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.

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.

My 4.5GHz overclock on 2600K has become unstable!

It's been a while since I tested for stability of my CPU's 4.5GHz overclock. I ran the blend test of Prime95 of more than 6hrs back then and I felt that was sufficient. However, PC has been giving random lockups in the past couple of months and I didn't want to accept that the reason for this instability was because my overclock wasn't stable enough. For some reason, it was so hard to find the settings that made my PC stable, and I didn’t want to go through all that again. It could be because I wanted to both overclock and save power at the same time. That's not something that's easy to achieve, obviously. Or it could be because the motherboard is not the best when it comes to overclocking. Or it can even be that this CPU is a bad clocker. Or I could have been doing something wrong in the first place.

Anyways, the reason for the recent instability could be due to many reasons. The first one could be because the last time I checked for stability, I didn't use a version of Prime95 that supported AVX instructions. Then, I did a couple of UEFI updates and maybe I needed to change “some values” to make the CPU stable under the firmware that I'm using currently. Or it could well be a problem with the power supply or motherboard or memory.

 

Want to overclock your CPU? Here are some tips to make it stable.

Remember those days when overclocking the CPU was considered dangerous and only a few people would even attempt it, and those people were treated like gods? Not anymore. Anyone can overclock their CPU if the CPU is overclockable and necessary hardware is available. Getting a modest overclock is easy, but if you are trying to squeeze all that extra juice from your CPU, you might need more than just luck.

Overclocking is not dangerous if properly done. Know your limits and obey by those limits. For example, don't insert a lot of volts to the CPU because it will damage the CPU. Keep it within the manufacturer recommended/commonly accepted volts for your particular CPU. Also be wary of the temps of the CPU as well as other components like VRM heat sinks of the motherboard.

Here are some tips.

1) Prepare a separate environment for overclocking if possible. If you have a spare drive lying around, install a free copy of Windows in it and don't install anything else - not even Windows updates or driver updates. Why this is important is because when your OS crashes while stress testing because your overclock is not stable, it can corrupt the files and settings and that alone can give a BSOD when you stress test with different settings the net time. You might think the CPU is unstable, but in reality it could be a corrupted driver or corrupted software that is running in the background.

2) Stress test for a couple of hours at stock settings. This will rule out any issues that might be present in the original hardware. No point trying to overclocking broken hardware. You'll only waste your "precious" time. Running Prime95's blend test should do the trick.

3) Don't overclock your RAM at the same time. Overclock only one component at a time, otherwise you won't know the culprit of the instability if you discover any. Overclocking RAM doesn't give any tangible benefits anyways. You will get better performance by overclocking the CPU. So, if you have high speed RAM (i.e. faster than 1600MHz), I would suggest that you drop the speed to 1600MHz CL9 timings. That would rule out the memory being the culprit of a crash. This is not needed, but just to be sure

4) Make a target. The target should not be in terms of clock speed, but in terms of max CPU temperature or max Vcore, whichever is reached first. For example, max Vcore = 1.4V and max CPU Temp = 85C. First, try Vcore = 1.4V at stock clock speed and run a stress test while monitoring CPU temperature. If you are below 85C, then you can simply try increasing the CPU clock speed. If you hit 85C, then stop stress testing and lower the CPU Vcore until your max temps are below 85C.

However, please note that when you increase the clock speed, the temps would increase a bit more even without increasing the Vcore. So try to stop about 5C below your suggested max CPU temps (i.e. 80C) to give some room for the temps to increase due to clock increase. Now that you have found your max voltage, it is time to increase the clock speed.

5) Be patient. Don't try to rush out thing. If you know that the CPU model you have usually overclocks to, say, 4GHz undoubtedly (all the current generation CPUs do), that would be a good place to start. You don't have to start from the stock speeds. That's not necessary. However, only increase clock speeds one step at a time.

For example, when it comes to Intel, the only way to effectively increase the clock speed is by raising the multiplier. Increase the multiplier one step at a time. That means, if you were starting from 4GHz, which means the multiplier was at 40x, increase to 41x, then 42x and likewise. At each step, stress test for like 30 minutes of Prime95's blend test. That should be enough for the intermediate stress tests. Once you find the maximum overclock, stress test for 24hrs (at least 12hrs) to make sure that is completely stable. If the stress test fails while doing the extensive stress tests, you'll have to drop the multiplier by one level. Then it is 24hrs of stress testing again. (Overclocking takes times. Don't rush it.)

6) Now that you (hopefully) found out your max CPU clock, you can revert to the original RAM settings or even try to overclock it. Remember that when you overclock your RAM, you might have to increase the VTT (memory controller voltage) to make it stable.

7) If you want to overclock further and you were limited by temperature, it is time to invest in a better cooler.

8) If you are having some particular issues, such as crashes at idle, take a look at this thread.

Those were some common guidelines and all that they do is make your life easier, even though at first it might seem like time wasters (preparing a separate environment just for overclocking, for example).

There are more extensive instructions on the forums such as Overclock.net, Techpowerup.com and XtremeSystems.org so read the guides posted there, ask questions and participate. You will learn a lot by doing that.