SkylakeX teasers (aka prime95 29.5)

[chalsall]

Originally Posted by simon389

More than happy to

Sweet. Please understand that just about everyone here uses the Scientific Method.

It's never personal. We're just trying to find the truth....

[Mysticial]

Originally Posted by simon389

More than happy to

Perfect.

Here's what we know:

1. Stock + XMP fails on AIDA64 and P95 PRP AVX512. Everything is stable on AVX.
2. Downclocking the CPU doesn't fix anything.
3. Repros on all 4 systems with identical symptoms.
4. All the errors are soft errors. It never crashes or BSODs.

Known issues that are not the cause:

1. BIOS not doing the AVX(512) offsets correctly.
2. The CPU's AVX and AVX512 are the sole cause.

Unanswered questions:

1. Is the error CPU only? Or memory related?
2. If memory related: What's the cause? Mobo/incompatibility? XMP?
3. If CPU related: ???
4. Or cache?

-----

My initial debug suggestions:

1) Turn off XMP, set the offsets to -3 or lower and repeat AIDA64 P95 tests with AVX512. Is the system stable now? If yes, that's the cause. Get rid of the XMP. If not, keep going...

2) Determine if the error is CPU or memory related.

Attempt to reproduce the issue with other workloads. Most obviously Prime95 stress-tests with small FFTs and then large FFTs. My y-cruncher benchmark also has different tests that hit different components of the hardware. If you want to try this, I can go into further detail.

From here on, it depends on what the results of #2 are. If it looks like a memory issue, then try:

• Downclocking the memory from stock 2133 -> 1600 MT/s. Repeat tests.
• If you have any other memory. (non-G.Skill, or G.Skill that's no better than 3000cl16)
• Try fewer than 4 channels. (I'd try 2 channels, each side individually)

For all these tests, let's keep the AVX and AVX512 at offsets of -3 or lower. Because I mentioned before that the 4.1 they were running at before is way out of spec. And even though we (think) we've ruled that out, we're not 100% certain so let's keep that separate.

If everything fails and we're still nowhere closer, I'd considering trying a different motherboard model.

[chalsall]

Originally Posted by Mysticial

If everything fails and we're still nowhere closer, I'd considering trying a different motherboard model.

I understand and appreciate what you're trying to do here, but changing the MB would be a bit expensive.

Also, there are already four different MBs in play in this test, and they all perform equally (badly).

Perhaps you missed it, but there is a single class of CPU which has demonstratively failed across all four different MBs.

Perhaps drill down on that?

[Mysticial]

Originally Posted by chalsall

I understand and appreciate what you're trying to do here, but changing the MB would be a bit expensive.

Also, there are already four different MBs in play in this test, and they all perform equally (badly).

Perhaps you missed it, but there is a single class of CPU which has demonstratively failed across all four different MBs.

Perhaps drill down on that?

The mobos are all the same as well. A minor revision difference is unlikely to change anything. Likewise, the ram is all the same, but with a different heatspreader design.

One thing I didn't recommend is to swap the memory around between the different boards. The reason I didn't recommend this is that we're seeing this on all 4 machines - which are basically the same hardware (minus minor differences). So one-off defects or incompatibilities is less likely. IOW, there has to be either a design flaw or part incompatibility that's making them consistent.

But once you've exhausted all possibilities, you have to spend money at some point to try completely different hardware.

[chalsall]

Originally Posted by Mysticial

The mobos are all the same as well.

I respectfully disagree.

Have you ever examined under a microscope the "drill-through holes" of a PCB? I have.

Originally Posted by Mysticial

A minor revision difference is unlikely to change anything.

Respectfully, I disagree.

[Mysticial]

Originally Posted by chalsall

I respectfully disagree.

Have you ever examined under a microscope the "drill-through holes" of a PCB? I have.



Respectfully, I disagree.

And I respectfully disagree with you as well. Ever heard of bugs that last multiple versions before they are finally caught and fixed? It applies equally to hardware as it does to software.

I see 4 machines with virtually identical hardware showing the exact same issues. Here is what's guiding my plan of testing:

1. It is unlikely to be a one-off defect. Because otherwise it wouldn't affect all 4 systems identically. And if was "fixed" in one mobo version, we'd see it in 2 of 4.
2. It is more likely to be something in the design of a component or combination of components. Because that's what's common across all 4 systems.

If you have a better proposal let's hear it then.

[simon389]

I’m game. I’ll begin tonight. If we want to move to a different thread that may be a good idea.

[chalsall]

Originally Posted by Mysticial

If you have a better proposal let's hear it then.

LOL...

I once was on a plane, flying to Toronto. During the flight I studied the schematic my business partner had laided out, and something didn't seem quite correct.

Turns out my partner had made an error in the traces, but he had envisioned this possibly which could be corrected by simply cutting a trace on the copper foil.

All the boards manufactured were cut as needed, and everything manufactured made it into product.

We produced.

[Prime95]

Build 10 for Simon and Ken.

1) Fixed some possible bugs in Gerbicz PRP running on flaky hardware.
2) Fixed (I hope) the hang during benchmarking.

Windows 64-bit: ftp://mersenne.org/gimps/p95v295b10.win64.zip

[Prime95]

Originally Posted by ATH

This has happened a few times in 29.5b9, but only to my 2 PRP CF DC instances:

[Comm thread Feb 5 09:54:40] 
[Comm thread Feb 5 09:54:40] PrimeNet error 9: Access denied
[Comm thread Feb 5 09:54:40] Invalid security signature

Can you send prime.log? Please add Debug=2 to the [Primenet] section of prime.txt in case it happens again.

Thanks.

[kriesel]

Originally Posted by Prime95

Build 10 for Simon and Ken.

1) Fixed some possible bugs in Gerbicz PRP running on flaky hardware.
2) Fixed (I hope) the hang during benchmarking.

Windows 64-bit: ftp://mersenne.org/gimps/p95v295b10.win64.zip

Benchmark, 1-3,6 workers, with and without hyperthreading, try all, 1024k to 31768k, still running after 10.3 hours, has advanced from 1024k to 3456k, on the "reliable" i7-8750H Win 10 system. Previously it would stall in minutes.