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Mixtral

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Mixtral

Overview

Mixtral-8x7B was introduced in the Mixtral of Experts blogpost by Albert Jiang, Alexandre Sablayrolles, Arthur Mensch, Chris Bamford, Devendra Singh Chaplot, Diego de las Casas, Florian Bressand, Gianna Lengyel, Guillaume Lample, Lélio Renard Lavaud, Lucile Saulnier, Marie-Anne Lachaux, Pierre Stock, Teven Le Scao, Thibaut Lavril, Thomas Wang, Timothée Lacroix, William El Sayed.

The introduction of the blog post says:

Today, the team is proud to release Mixtral 8x7B, a high-quality sparse mixture of experts models (SMoE) with open weights. Licensed under Apache 2.0. Mixtral outperforms Llama 2 70B on most benchmarks with 6x faster inference. It is the strongest open-weight model with a permissive license and the best model overall regarding cost/performance trade-offs. In particular, it matches or outperforms GPT3.5 on most standard benchmarks.

Mixtral-8x7B is the second large language model (LLM) released by mistral.ai, after Mistral-7B.

Architectural details

Mixtral-8x7B is a decoder-only Transformer with the following architectural choices:

Mixtral is a Mixture of Experts (MoE) model with 8 experts per MLP, with a total of 45 billion parameters. To learn more about mixture-of-experts, refer to the blog post.
Despite the model having 45 billion parameters, the compute required for a single forward pass is the same as that of a 14 billion parameter model. This is because even though each of the experts have to be loaded in RAM (70B like ram requirement) each token from the hidden states are dispatched twice (top 2 routing) and thus the compute (the operation required at each forward computation) is just 2 X sequence_length.

The following implementation details are shared with Mistral AI’s first model Mistral-7B:

Sliding Window Attention - Trained with 8k context length and fixed cache size, with a theoretical attention span of 128K tokens
GQA (Grouped Query Attention) - allowing faster inference and lower cache size.
Byte-fallback BPE tokenizer - ensures that characters are never mapped to out of vocabulary tokens.

For more details refer to the release blog post.

License

Mixtral-8x7B is released under the Apache 2.0 license.

Usage tips

The Mistral team has released 2 checkpoints:

a base model, Mixtral-8x7B-v0.1, which has been pre-trained to predict the next token on internet-scale data.
an instruction tuned model, Mixtral-8x7B-Instruct-v0.1, which is the base model optimized for chat purposes using supervised fine-tuning (SFT) and direct preference optimization (DPO).

The base model can be used as follows:

>>> from transformers import AutoModelForCausalLM, AutoTokenizer

>>> model = AutoModelForCausalLM.from_pretrained("mistralai/Mixtral-8x7B-v0.1", device_map="auto")
>>> tokenizer = AutoTokenizer.from_pretrained("mistralai/Mixtral-8x7B-v0.1")

>>> prompt = "My favourite condiment is"

>>> model_inputs = tokenizer([prompt], return_tensors="pt").to("cuda")
>>> model.to(device)

>>> generated_ids = model.generate(**model_inputs, max_new_tokens=100, do_sample=True)
>>> tokenizer.batch_decode(generated_ids)[0]
"My favourite condiment is to ..."

The instruction tuned model can be used as follows:

>>> from transformers import AutoModelForCausalLM, AutoTokenizer

>>> model = AutoModelForCausalLM.from_pretrained("mistralai/Mixtral-8x7B-Instruct-v0.1", device_map="auto")
>>> tokenizer = AutoTokenizer.from_pretrained("mistralai/Mixtral-8x7B-Instruct-v0.1")

>>> messages = [
...     {"role": "user", "content": "What is your favourite condiment?"},
...     {"role": "assistant", "content": "Well, I'm quite partial to a good squeeze of fresh lemon juice. It adds just the right amount of zesty flavour to whatever I'm cooking up in the kitchen!"},
...     {"role": "user", "content": "Do you have mayonnaise recipes?"}
... ]

>>> model_inputs = tokenizer.apply_chat_template(messages, return_tensors="pt").to("cuda")

>>> generated_ids = model.generate(model_inputs, max_new_tokens=100, do_sample=True)
>>> tokenizer.batch_decode(generated_ids)[0]
"Mayonnaise can be made as follows: (...)"

As can be seen, the instruction-tuned model requires a chat template to be applied to make sure the inputs are prepared in the right format.

Speeding up Mixtral by using Flash Attention

The code snippets above showcase inference without any optimization tricks. However, one can drastically speed up the model by leveraging Flash Attention, which is a faster implementation of the attention mechanism used inside the model.

First, make sure to install the latest version of Flash Attention 2 to include the sliding window attention feature.

pip install -U flash-attn --no-build-isolation

Make also sure that you have a hardware that is compatible with Flash-Attention 2. Read more about it in the official documentation of the flash attention repository. Make also sure to load your model in half-precision (e.g. torch.float16)

To load and run a model using Flash Attention-2, refer to the snippet below:

>>> import torch
>>> from transformers import AutoModelForCausalLM, AutoTokenizer

>>> model = AutoModelForCausalLM.from_pretrained("mistralai/Mixtral-8x7B-v0.1", torch_dtype=torch.float16, attn_implementation="flash_attention_2", device_map="auto")
>>> tokenizer = AutoTokenizer.from_pretrained("mistralai/Mixtral-8x7B-v0.1")

>>> prompt = "My favourite condiment is"

>>> model_inputs = tokenizer([prompt], return_tensors="pt").to("cuda")
>>> model.to(device)

>>> generated_ids = model.generate(**model_inputs, max_new_tokens=100, do_sample=True)
>>> tokenizer.batch_decode(generated_ids)[0]
"The expected output"

Expected speedups

Below is a expected speedup diagram that compares pure inference time between the native implementation in transformers using mistralai/Mixtral-8x7B-v0.1 checkpoint and the Flash Attention 2 version of the model.

Sliding window Attention

The current implementation supports the sliding window attention mechanism and memory efficient cache management. To enable sliding window attention, just make sure to have a flash-attn version that is compatible with sliding window attention (>=2.3.0).

The Flash Attention-2 model uses also a more memory efficient cache slicing mechanism - as recommended per the official implementation of Mistral model that use rolling cache mechanism we keep the cache size fixed (self.config.sliding_window), support batched generation only for padding_side="left" and use the absolute position of the current token to compute the positional embedding.

Shrinking down Mixtral using quantization

As the Mixtral model has 45 billion parameters, that would require about 90GB of GPU RAM in half precision (float16), since each parameter is stored in 2 bytes. However, one can shrink down the size of the model using quantization. If the model is quantized to 4 bits (or half a byte per parameter), a single A100 with 40GB of RAM is enough to fit the entire model, as in that case only about 27 GB of RAM is required.

Quantizing a model is as simple as passing a quantization_config to the model. Below, we’ll leverage the bitsandbytes quantization library (but refer to this page for alternative quantization methods):

>>> import torch
>>> from transformers import AutoModelForCausalLM, AutoTokenizer, BitsAndBytesConfig

>>> # specify how to quantize the model
>>> quantization_config = BitsAndBytesConfig(
...         load_in_4bit=True,
...         bnb_4bit_quant_type="nf4",
...         bnb_4bit_compute_dtype="torch.float16",
... )

>>> model = AutoModelForCausalLM.from_pretrained("mistralai/Mixtral-8x7B-Instruct-v0.1", quantization_config=True, device_map="auto")
>>> tokenizer = AutoTokenizer.from_pretrained("mistralai/Mixtral-8x7B-Instruct-v0.1")

>>> prompt = "My favourite condiment is"

>>> messages = [
...     {"role": "user", "content": "What is your favourite condiment?"},
...     {"role": "assistant", "content": "Well, I'm quite partial to a good squeeze of fresh lemon juice. It adds just the right amount of zesty flavour to whatever I'm cooking up in the kitchen!"},
...     {"role": "user", "content": "Do you have mayonnaise recipes?"}
... ]

>>> model_inputs = tokenizer.apply_chat_template(messages, return_tensors="pt").to("cuda")

>>> generated_ids = model.generate(model_inputs, max_new_tokens=100, do_sample=True)
>>> tokenizer.batch_decode(generated_ids)[0]
"The expected output"

This model was contributed by Younes Belkada and Arthur Zucker . The original code can be found here.

Resources

A list of official Hugging Face and community (indicated by 🌎) resources to help you get started with Mixtral. If you’re interested in submitting a resource to be included here, please feel free to open a Pull Request and we’ll review it! The resource should ideally demonstrate something new instead of duplicating an existing resource.

Text Generation

A demo notebook to perform supervised fine-tuning (SFT) of Mixtral-8x7B can be found here. 🌎
A blog post on fine-tuning Mixtral-8x7B using PEFT. 🌎
The Alignment Handbook by Hugging Face includes scripts and recipes to perform supervised fine-tuning (SFT) and direct preference optimization with Mistral-7B. This includes scripts for full fine-tuning, QLoRa on a single GPU as well as multi-GPU fine-tuning.
Causal language modeling task guide

Transformers

Mixtral

Overview

Architectural details

License

Usage tips

Speeding up Mixtral by using Flash Attention

Expected speedups

Sliding window Attention

Shrinking down Mixtral using quantization

Resources

MixtralConfig

class transformers.MixtralConfig

MistralCommonTokenizer

class transformers.MistralCommonTokenizer

apply_chat_template

batch_decode

convert_ids_to_tokens

convert_tokens_to_ids

decode

encode

from_pretrained

get_special_tokens_mask

get_vocab

pad

prepare_for_model

save_pretrained

tokenize

truncate_sequences

MixtralModel

class transformers.MixtralModel

forward

MixtralForCausalLM

class transformers.MixtralForCausalLM

forward

MixtralForSequenceClassification

class transformers.MixtralForSequenceClassification

forward

MixtralForTokenClassification

class transformers.MixtralForTokenClassification

forward

MixtralForQuestionAnswering

class transformers.MixtralForQuestionAnswering

forward