5900x / 5950x OC’ing for a8 performance

[Slash_2CPU]

Has anyone done a deep dive into OC vs PPD settings for these chips? With the new CCX layout in Zen 3, comparisons to 3000-series Zen 2 may not apply well here.

I’m wondering if there’s any real improvement in PPD with all-core 4650MHz vs all-core 4650MHz then pushing the one fastest core in each of the two CCX’s to 4900-ish. It would be interesting to see if a8 benefits from having a couple faster cores, if perfect symmetry performs better, or if it’s a simple linear change and all threads appear to benefit equally where the extra ~350MHz on two cores gives about the same as 25-50MHz extra on all.

I’m hoping for a positive nonlinear improvement. Possible that it will be a disappointing linear improvement.

Also possible the extra heat/power draw on those two cores will slow down the other 14 for a net loss.

[JimboPalmer]

"I’m hoping for a positive nonlinear improvement. Possible that it will be a disappointing linear improvement."

I am expecting sublinear improvement with crashes, but that is just me.

AVX2-256 SIMD is going to run hot.

https://news.ycombinator.com/item?id=13925039
This is an older discussion, Zen and Zen+ emulated AVX2-256
Zen2 runs it natively.

How fast a given CCX is at 'normal' code is not going to be representative of how fast it is at AVX2-256.

[Slash_2CPU]

Cool. Thanks for your opinion and reminding me why it’s been years since my last posting here. I’ll go figure it out myself.

AVX-256 is hot and the sun is bright when you stare at it.

It’s returned a couple months of a8’s at 4650MHz at 1.25v running 61-63°C under a custom water loop, and has run stable at 4900MHz on 2 cores with the others at 4650MHz as my “workstation” profile also for 2 months handling massive point-cloud scans, which make F@H work units look like idle.

[JimboPalmer]

As the discussion I pointed you to states, Intel down clocks their CPUs any time you use AVX, while AMD is driven by heat.

The 'best' core on some other test will be no guide to the coolest core running AVX. So yes, your test with F@H will be the true guide. ( My guess is that your core farthest upstream will be coolest and farthest downstream will run hot. My guess is worth what you are paying for it. Past experiences have shown that overclocking equals errors in calculation, but you may be special)