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Attention Is Off By One

evanmiller.org

141–150 of 347 posts

Re: Attention Is Off By One

#141

This trick “they found” is part of the standard torch implementation of multi head attention, namely it is called, add_zero_attention. They add a zero to the logits, resulting in a one in the denominator as e^0=1 https://pytorch.org/docs/stable/generated/torch.nn.Multihead...

It's an option which is set to false by default. Does that mean people have tried it and it's not usually helpful...?

Yes.

Re: Attention Is Off By One

#142
It’s interesting. It looks like if you’re trying to improve the accuracy/perplexity of the model and using fp32 it doesn’t make a difference , but if you want to quantize it/make it compressible a modified soft max makes a huge difference ( this is what I understand from the Qualcomm paper). Different goals, different findings ?

Re: Attention Is Off By One

#143

I might be missing something obvious, but I am not sure why everyone in the comments think it's a big deal. I've seen this trick in practice multiple times. For example, see this snippet from an old Google repo: https://github.com/google/flaxformer/blob/ee62754ebe5a5eeb11...

The argument / reasoning is a bit dubious. Technically softmax is not implemented as presented but through exp(x_i-max(x)), and summing over it in the denom. But maybe I am missing something. Furthermore, the residuals are used exactly because the networks cant learn the identity function; but they can learn zero; at which point the residual is `f(x): x+g(x)` with being `g:x ~> 0` (ie approximately 0). It is also the…

Implementations usually replace replace the 1 in the denominator with exp(-max(x)) for this reason.

Re: Attention Is Off By One

#144

I might be missing something obvious, but I am not sure why everyone in the comments think it's a big deal. I've seen this trick in practice multiple times. For example, see this snippet from an old Google repo: https://github.com/google/flaxformer/blob/ee62754ebe5a5eeb11...

Yeah we used to use this in our older models years ago... I don't recall the details exactly, but I don't think it ever did very much. I certainly don't think it will help at all with stability. Things like Q/K layernorm are better tricks for softmax stability when scaling: https://arxiv.org/pdf/2302.05442.pdf

> I don't recall the details exactly, but I don't think it ever did very much.

How would you have known if the trick actually reduces the outliers in the weights? Even if the transformer quality does not improve overall, having less outliers as a result is very beneficial for more accurate quantization of the data

Re: Attention Is Off By One

#145
post #8

I don't really understand the subject matter enough, so I apologize in advance for the meta-comment... The author mentions that he would maybe have written this as a scientific paper: > I tried writing a serious-looking research paper about the bug and my proposed fix, but I lost a series of pitched battles against Pytorch and biblatex, so I figured I’d just write a blog post instead. (History is written by the winne…

Nah, scientific papers are supposed to be precise and technical. This reads like those quite frequent suggestions here of switching all equations in papers to plain English or code: it honestly comes from a place of ignorance, and I say that as basically a layman myself. What should be encouraged is for academics to blog about their research as well. It would even help when recruiting and onboarding new members. Righ…

>Nah, scientific papers are supposed to be precise and technical.

They're also, more often than not, tedious, badly explained, error prone, oft-skipped, and hardly ever read carefully, even during peer review for the paper that contains them. That's how mistakes stay unnoticed for decades in influential papers with tons of citations.

In essense, a paper's tone and languge is often more formality, academic tradition, ritual, and padding for publication purposes, than serving a real purpose.

Re: Attention Is Off By One

#146

Earlier quoted context omitted.

You seem to really disregard the positions of this author. They seem to have invested substantial efforts in that specific area of research. To validate the idea the author has, it would be required to train a LLM from zero. If the author is right, you would get similar results to the current generation of LLMs, but with (a lot) less space required for the intermediate layers. The time to achieve that is still measur…

You don't need to train a ChatGPT-sized LLM, a toy nanoGPT would have been enough. You can train those on a consumer GPU in an afternoon. And yes I do disregard his research effort. There are hundreds of well-justified and well-researched "clever tricks" for improving Transformers, and almost all of them don't work. I'll believe it when I see the results.

Do you know of handy testing steps? I suppose I could ask ChatGPT, but if someone has a validated "here, this is how you do it" I have a 3090 that I can do it on, but I'm not keen to debug anything here.

Re: Attention Is Off By One

#147

Earlier quoted context omitted.

See figure 1: https://arxiv.org/pdf/2208.07339.pdf Outliers appear at model size 6.7B and are not present at 2.7B

Sure, emergent properties can arise as parameters increase. Everyone knows that. That’s a much less specific claim than to say that the benefit of modifying softmax can only arise as an emergent property after N parameters, and therefore the benefit can only be evaluated on models above a certain size. To my understanding the author of TFA isn’t suggesting the same issue as the one in your linked paper.

The second heading in the TFA is "It’s All About Outliers"

Re: Attention Is Off By One

#148
post #132

Earlier quoted context omitted.

There was this sociologist who had written a paper for us all to read ahead of time. I started to read the damn thing, and my eyes were coming out: I couldn’t make head nor tail of it! I figured it was because I hadn’t read any of the books on the list. I had this uneasy feeling of “I’m not adequate,” until finally I said to myself “I’m gonna stop, and read one sentence slowly so I can figure out what the hell it mea…

I hadn't seen that Feynman quote before, but I discovered then when reading Donna Harraway's books (Cyborg Manifesto, Modest_Witness@Second_Millennium.FemaleMan©Meets_OncoMouse, Primate Visions). The criticism was """Haraway's work has been criticized for being "methodologically vague"[39] and using noticeably opaque language that is "sometimes concealing in an apparently deliberate way""""

>Haraway's work has been criticized for being "methodologically vague"[39] and using noticeably opaque language that is "sometimes concealing in an apparently deliberate way

So you're saying that "Her work is basically handwaving and bullshitting".

Re: Attention Is Off By One

#149

Earlier quoted context omitted.

There was this sociologist who had written a paper for us all to read ahead of time. I started to read the damn thing, and my eyes were coming out: I couldn’t make head nor tail of it! I figured it was because I hadn’t read any of the books on the list. I had this uneasy feeling of “I’m not adequate,” until finally I said to myself “I’m gonna stop, and read one sentence slowly so I can figure out what the hell it mea…

> It seems like, when you have something of substance to say, you say it. And this blog post probably could be condensed into 1/4 of its size or less with a less conversational/bloggy tone.

There are words that are added to drive the point in multiple ways, ease into it, and make the text more engaging.

And there are words that are added to add empty padding, keep up academic pretenses, and appear smart.

The post could have been condensed, but it would lose the former, not the latter.

Re: Attention Is Off By One

#150

Earlier quoted context omitted.

Yeah we used to use this in our older models years ago... I don't recall the details exactly, but I don't think it ever did very much. I certainly don't think it will help at all with stability. Things like Q/K layernorm are better tricks for softmax stability when scaling: https://arxiv.org/pdf/2302.05442.pdf

> I don't recall the details exactly, but I don't think it ever did very much. How would you have known if the trick actually reduces the outliers in the weights? Even if the transformer quality does not improve overall, having less outliers as a result is very beneficial for more accurate quantization of the data

Are you asking "why would you have bothered to look at"?

The "how" is pretty straightforward.

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