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by sunrunner 220 days ago
Ignoring floating point errors, assuming a perfectly spherical cow, and taking air resistance as zero.
1 comments

Imagine you are predicting the next token, you have two tokens very close in probability in the distribution, kernel execution is not deterministic because of floating point non-associativity - the token that gets predicted impacts the tokens later in the prediction stream - so it's very consequential which one gets picked.

This isn't some hypothetical - it happens all the time with LLM's - it isn't some freak accident that isn't probable

Okay yes, but would you really say that the main part of non-determinism in LLM-usage stems from this ? No its obviously the topk sampling.

I don't think my tech-lead was trying to suggest the floating-point error/non-associativity was the real source.

> Would you really say that the main part of non-determinism in LLM-usage stems from this

Yes I would because it causes exponential divergence (P(correct) = (1-e)^n) and doesn't have a widely adopted solution. The major labs have very expensive researchers focused on this specific problem.

There is a paper from Thinking Machines from September around Batch Invariant kernels you should read, it's a good primer on this issue of non-determinism in LLM's, you might learn something from it!

Unfortunately the method has quite a lot of overhead, but promising research all the same.

Alright fair enough.

I dont think this is relevant to the main-point, but it's definitely something I wasn't aware of. I would've thought it might have an impact on like O(100)th token in some negligible way, but glad to learn.