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3900x and AVX workloads - instability

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post #1 of 4 (permalink) Old 07-20-2019, 01:28 AM - Thread Starter
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3900x and AVX workloads - instability

A curious one, this, but I am running my 3900x completely stock (in an X370 Taich), with Micron E-die at 3600C16 currently at 1.48v to try to exclude its part in the 'problems' I'm experiencing.

Basically, it fails Prime95 Small FFT with AVX enabled. Curiously, it will only run 3.8-3.9GHz all-core during this test, and the CPU doesn't go much above 70C. However, CPU voltages are also a measly 1.1v on each core. Small FFT AVX will fail within 10-20 minutes, usually on Worker 13. When I downclocked the RAM all the way to 2400c16, it would run longer, but I hadn't tested that longer than half an hour. There seems to be *some* dependency on the memory speed, but the curiosity here is that 9 out of 10 times, it's Worker 13 that fails first (so the 7th core).

When I disable AVX, the CPU boosts to 4.2GHz all-core at 1.2x-1.3x volts, and it runs an hour of Small FFT and just now ran an entire night of non-AVX blend, no problems.

Could this have something to do with too low a voltage at 3.9GHz? It seems that specifically for AVX workloads the CPU runs this frequency. And are there tables I can adjust to fix this?
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post #2 of 4 (permalink) Old 07-20-2019, 03:58 AM
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Prime95 29.8b5 version?

Try 29.8b3 instead.

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post #3 of 4 (permalink) Old 07-20-2019, 05:51 AM - Thread Starter
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I was indeed on Prime 29.8b5. I just tried 29.8b3 on settings that failed yesterday, Small FFT with AVX, and it took 18 minutes this time, and this time it happened in Worker 14. So still core 7... 3.8GHz 132W power consumption.

If it was a memory issue, it shouldn't happen on the same core over and over, should it? I think I've seen this core fail 5-7 times now, so statistically this seems very unlikely to be random (as one'd expect if RAM was at fault). Or does it get allocated the exact same block of memory as well each time?
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post #4 of 4 (permalink) Old 07-20-2019, 11:46 AM
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Did you try using "Dram calculator for Ryzen", and setting the parameters manually in the BIOS? (Even thought in my case it didn't work, you should probably give it a try)

I personally gave up on pairing the 3900x with my Taichi x370, I had what seems to be memory stability issues since day 1 (almost 2 weeks now), and I think I tried every possible solution out there, if you want, I can share with you several optional solutions that were provided by ASrock's tech team and public forums.

I just think that the 3900x is relatively too power/voltage demanding, that its causing stability issues with the first generation boards, and I don't want to be in the same place I was with the 1st generation Ryzen, where I had to wait 3 firmware updates until I got my 1700 stabilized. (not sure if you have noticed, but the 3900x was added only later to the supported CPU list of the x370 taichi, I'm assuming there was a reason for that ;-)

Please share if the above, or any other solution worked out
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