Monday, September 9, 2013

[Article] The ultimate stress test for Haswell CPUs - Prime 95 with AVX2/FMA3 support

Overclocking Haswell CPUs is a lot of work. Checking whether the overclock is stable or not is very time consuming. Some people go for a couple of hours of stress testing because most of the times that is enough to ensure that the CPU will run stably in every real world situation. But there are some people who cannot sleep if they know that one of their favorite stress testing apps didn't pass.

When it comes to stress testing applications, we are hearing a whole new story with Haswell. "This stress testing application is not certified for Haswell." Basically, that's what people say when they hear that you are using Prime 95 or LinX or OCCT. If by that they mean is that these applications don't  test every part of the CPU, the fine. But ironically, these apps can crash the CPU way quicker than those Certified applications. It makes one wonder, if Intel's CPUs don't work as they should. I mean, why cannot you simply run anything? Applications don't have to be certified for a CPU.

If it was the former, that is the application doesn't stress all the parts of the CPU, then the developers of Prime95 is finally fixing that. The current stable version, 27.9, supports up to AVX instructions. But no AVX 2 or FMA3 instructions. The developers have released an evaluation version of the upcoming version 28 which supports all these new instructions in Haswell. You can download it from THIS LINK.

Result?

Simply don't run the Small FFT test! On most setups, if you are above 1.20V, you'll be at instant throttling state. With 4.3GHz/1.24V, it would go to 97C within a couple of seconds. Well, I have my CPU fans at 1000RPM instead of the max 2400RPM, so it takes a couple of seconds to ramp up the fan speed. Maybe if I started at full fan speed, it might not hit that high. But still it will definitely be in the 90's,

But I don't stress test using Small FFT. I've found that almost always it is the in-place large FFT test that fails with my CPU. I ran it for a couple of hours, with each test running for only 3 minutes. The temps weren't that bad, however yesterday's weather was a tad cooler. 


Note: The Vcore written in the notepad is wrong. It should read 1.250V (1.264V in CPU-Z).

If you are running this, just be aware of the temps. There is no other stress test that can heat up the Haswell CPUs this much.
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