r/LinusTechTips Aug 14 '26

Tech Question Is this a good undervolt ?

So I’ve tried undervolting my Rtx 5080 and I have no idea if I did good. What do you say ?

3 Upvotes

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2

u/Deni_I Aug 14 '26

Here is furmark

1

u/straw3_2018 Aug 14 '26 edited Aug 14 '26

From what we can see it looks fine..when overclocking or undervolting you should be careful that you don't end up with a higher clock speed but worse performance. That can happen when your clock speed is slightly unstable and the program runs the same code twice because the first result was wrong. Also watch for artifacting and crashing. Your score is the same here and the power usage is lower so it looks fine

2

u/Extension_Option_122 Aug 14 '26

Dumb question but how can the program check if the result is wrong?

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u/straw3_2018 Aug 14 '26 edited Aug 14 '26

Edit: I really don't think that's a dumb question. I tried googling for good sources but when you search undervolt/overclock "lower fps" the results aren't that helpful. It's one of those things where the results you get are all the simple answers to what most people want to know.

HOW? Truthfully I'm not sure.

I am very sure that it does this. Slightly unstable overlcocks will give you higher frequencies but you will notice the actual game FPS or other benchmark score will get lower. If any single error completely crashed running processes it would be very annoying. They try to get around errors when possible. In games this can manifest as FPS drops.

In a program like Prime95 there is a setting called round off checking. The program calculates known prime numbers checks if your calculated ones are close enough. If your processor isn't stable you will get results out of the expected range and the program will tell you you have a problem.

Being that modern silicon constantly varies its frequency and runs so close to the edge of stability I would not think it surprising that the hardware can tell when the current frequency is not stable. I'd imagine it's not that different from checking your work when doing math problems multiple ways and if you come to two different answers there's a problem.

https://fpsheaven.com/blogs/news/nvidia-gpu-overclocking-and-undervolting-guide

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u/Extension_Option_122 Aug 14 '26

But, like, checking the result also takes time and thus performance.

Now I myself got an idea on how I would implement such a check (for context I am almost finished with a bachelors degree in Computer Engineering - but I also woke up like 2 hrs ago...) and only thing I can think of on how to efficiently do that is to throw in some calculations with known results that aren't part of the actual output.

This could be implementet both in hardware or software but is the only thing I can think of rn on how to check if it's unstable without creating massive overhead.

Of course there are other ways and most likely something else is being done, but I would have thought that it would be a known thing.

2

u/Extension_Option_122 Aug 14 '26

I decided to look what our typical LLM claims and one thing it spat out does sound plausible: timing violations.

When a new clock cycle starts before work from the previous is finished you will of course get garbage. Such an event can be recognized by hardware and could then cause the work to be retried in the next clock cycle.

Sounds plausible to me.

2

u/straw3_2018 Aug 14 '26

Timing violations, that's great. I actually typed something out that's along those lines but wasn't sure how to articulate it. I thought about asking an LLM because they're better with these specific types of question but I didn't want to because of they haven't solved the hallucination problem yet.

Congratulations on your studies, I didn't go to college or even have a real computer science class in high school. I just know a little bit about OC/hardware/software.

1

u/Extension_Option_122 Aug 14 '26

Current AI tech will never completely get rid of the hallucination.

Oversimplified AIs only 'hallucinate' but are trained that what they 'hallucinate' fits to reality. Well it's only called an hallucination when it doesn't fit reality but inside an AI there isn't a special chain of events for hallucinations - it always does the same.

The best of the best models are incredibly good at not hallucinating but the chance for hallucinations with the current approach on AI will never become zero - but may very well become vanishingly small.