gptq VS OmniQuant

I think it's not that LLMs have redundant layers in general - it's a specific problem with OPT-66B, not anything else.

An 2022 paper "Scaling Language Models: Methods, Analysis & Insights from Training Gopher" (http://arxiv.org/abs/2112.11446) has captured it well on page 103, Appendix G:

> The general finding is that whilst compressing models for a particular application has seen success, it is difficult to compress them for the objective of language modelling over a diverse corpus.

The appendix G explores various techniques like pruning and distillation but found that neither method was an efficient way to obtain better loss at lower number of parameters.

So why does pruning work for OPT-66B in particular? I'm not sure but there are evidence that OPT-66B is an outlier: one evidence is in the GPTQ paper ("GPTQ: Accurate Post-Training Quantization for Generative Pre-trained Transformers", https://arxiv.org/abs/2210.17323) that mentions in its footnote on its 7th page:

> [2] Upon closer inspection of the OPT-66B model, it appears that this is correlated with the fact that this trained

Can anyone provide any additional details on the EXL2[0]/GPTQ[1] quantisation, which seems to be the main reason for a speedup in this model?

I had a quick look at the paper which is _reasonably_ clear, but if anyone else has any other sources that are easy to understand, or a quick explanation to give more insight into it, I'd appreciate it.

[0] https://github.com/turboderp/exllamav2#exl2-quantization

[1] https://arxiv.org/abs/2210.17323

GPTQ is better than GGML quantization, because it reoptimizes the weights to compensate for the lost accuracy. With 4 bit and groupsize 128 it can approximate, the FP16 performance pretty good. GGML just does round to nearest (RTN) without reoptimizing the weights against some dataset (generally the C4 dataset, as per default GPTQ-for-LLaMA configuration). But llama.cpp could probably implement such a method themselves, the paper is freely available: https://arxiv.org/abs/2210.17323

When you click on the strip link to preorder the tinybox, it is advertised as a box running LLaMA 65B FP16 for $15000.

I can run LLaMA 65B GPTQ4b on my $2300 PC (used parts, Dual RTX 3090), and according to the GPTQ paper(§) the quality of the model will not suffer much at all by the quantization.

(§) https://arxiv.org/abs/2210.17323

GPTQ is another quantization method, that works only for transformer model architectures. It quantizes the stored model weights in a non-linear fashion, and ends up having better quality compared to just linear quantization into a smaller data type. GPTQ has a triton and a cuda branch, which was tricky initially, as it lead to a lot of confusion and non-compatibility especially on windows.

Training uses gradient descent, so you want to have good precision during that process. But once you have the overall structure of the network, https://arxiv.org/abs/2210.17323 (GPTQ) showed that you can cut down the precision quite a bit without losing a lot of accuracy. It seems you can cut down further for larger models. For the 13B Llama-based ones, going below 5 bit per parameter is noticeably worse, but for 30B models you can do 4 bits.

The same group did another paper https://arxiv.org/abs/2301.00774 which shows that in addition to reducing the precision of each parameter, you can also prune out a bunch of parameters entirely. It's harder to apply this optimization because models are usually loaded into RAM densely, but I hope someone figures out how to do it for popular models.

This is the one everybody's using to quantize language models. It includes a link to the paper explaining their algorithm.

Not on iOS. On macOS, I personally think WizardLM 13B v1.2 is a very strong model and keep hearing good things about it from users on our discord and in support emails. Now that there's OmniQuant support for Mixtral models[1], I'm plan to add support for Mixtral-8x7B-Instruct-v0.1 in the next version of the macOS app, which in my tests, looks like a very good all purpose model that's also pretty good at coding. It's pretty memory hungry (~41GB of RAM), but that's the price to pay for an uncompromising implementation. Existing quantized implementations quantize the MoE gates, leading to a significant drop in perplexity when compared with results from fp16 inference.

[1]: https://github.com/OpenGVLab/OmniQuant/commit/798467

I think OmniQuant is notable because it shifts the bend of the curve to 3-bit. While < 3-bit still ramps up, it's notable in that it's usable and doesn't go asymptotic: https://github.com/OpenGVLab/OmniQuant/blob/main/imgs/weight...

What EXL2 seems to bring to the table is that you can target an arbitrary quantize bit-weight (eg, if you're a bit short on VRAM, you don't need to go from 4->3 or 3->2, but can specify say 3.75bwp). You have some control w/ other schemes by setting group size, or with k-quants, but EXL2 is definitely allows you to be finer grained. I haven't gotten a chance to sit down with EXL2 yet, but if no one else does it, it's on my todo-list to be able to do 1:1 perplexity and standard benchmark evals on all the various new quantization methods, just as a matter of curiosity.