Skylake-X AVX offset fun

porina · July 22, 2017

Been tinkering with a 7800X build all day. So far I've established that I can run Prime95 stable at 4.3 GHz stock voltage with both CPU and VRM temps reported below 80C. 4.5 reboot crashed and 4.4 BSOD.

Now I'm looking at the AVX offset feature. I want to explore what clock I can achieve when not running Prime95. Thing is, a lot of software is activating the AVX offset. Aida64, Realbench, OCCT default all do it. Are there OC test tools that specifically don't have AVX? I could turn it off on Prime95, or use the non-AVX linpack provided in OCCT, but I'm curious if there are other options I might be overlooking. I'd ideally like software that will report calculation errors before requiring a hard crash or similar to show up.

DrMikeNZ · July 22, 2017

Some applications use AVX for a small number of the calculations. With this you might find every hundred or so cycles an AVX cycle might creep in when it is efficient to do so. Applications like AIDA64. Realbench etc may be switching between AVX and non-AVX workloads stressing all of the CPU instructions triggering the clock reduction. This clock reduction tends to linger for a while after the AVX cycle hindering performance overall for other instructions as well. The occasional AVX cycle shouldn't cause huge issues.

I recommend just leaving the AVX offset feature off, and validating your overclock for your workloads with the programs you use. If you need to use AVX2 etc, then just run at 4.3GHz or lower, if not then feel free to push further.

porina · July 23, 2017

8 hours ago, DrMikeNZ said:

I recommend just leaving the AVX offset feature off, and validating your overclock for your workloads with the programs you use. If you need to use AVX2 etc, then just run at 4.3GHz or lower, if not then feel free to push further.

Upon further research it seems Realbench, specifically the Handbrake component of it, does use AVX: https://rog.asus.com/articles/overclocking/realbench-benchmarking-stress-test-insights/

It is a common argument if you need to be Prime95 stable or not. For one major use, the answer is yes. That limits my overall overclock with previous generations since there was no way to separate out AVX and non-AVX loads. I've kinda looked on at others who don't need P95 stability reach upper 4.x GHz and beyond. Now I do have that freedom to set it separately, why let it go to waste. I do want to see how far I can push it in other use cases, but I still prefer OC stability testing tools as something that can alert instability faster than waiting for a normal application to crash. As a new area to explore, I don't have existing experience in it hence starting this thread.

Schoolofmonkey · July 23, 2017

Realistically using a 4Ghz AVX/AVX512 offset is fine even if you're OC is higher.

Even 4Ghz gives you better benchmark numbers than the previous generations.

Not setting an offset on a moderately high overclock can cause the dreaded phantom vrm throttling or kick in over current protection.

On my 7820x I have them set to 4Ghz though 4.3Ghz AVX is fine but why generate extra heat and power draw.

This was my power draw with everything on Auto, no AVX offsets and the XMP profile set.

(7820x/GTX1080ti in Realbench, 500w full system load)

porina · July 23, 2017

22 minutes ago, Schoolofmonkey said:

Realistically using a 4Ghz AVX/AVX512 offset is fine even if you're OC is higher.

Even 4Ghz gives you better benchmark numbers than the previous generations.

Not setting an offset on a moderately high overclock can cause the dreaded phantom vrm throttling or kick in over current protection.

On my 7820x I have them set to 4Ghz though 4.3Ghz AVX is fine but why generate extra heat and power draw.

One of my uses does hit AVX2 heavily, so I like to run that as fast as possible without touching voltage. I'm happy enough to have proven 4.3 GHz Prime95 stable at stock voltage, and now also at 3000 cache giving another 3 to 6% improvement in early testing.

However as this was to be my next gaming system, I also need to look at non-AVX loads and see if I can push further at stock voltage. I tend not to like increasing voltage, as that has a disproportionate hit on power draw.