docs : how to add a model (ggml-org#6565)

* docs: how to add a model

* docs: model: typo and docs

* docs: model: add prevision on RoPE

* docs: model: rephrasing README.md

* docs: model: rephrasing README.md

* docs: model: README.md fix trailing spaces

* docs : some fixes

* Update README.md

---------

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

Author: phymbert

README.md

@@ -122,6 +122,8 @@ Typically finetunes of the base models below are supported as well.
 - [x] [SEA-LION](https://huggingface.co/models?search=sea-lion)
 - [x] [GritLM-7B](https://huggingface.co/GritLM/GritLM-7B) + [GritLM-8x7B](https://huggingface.co/GritLM/GritLM-8x7B)
 
+(instructions for supporting more models: [HOWTO-add-model.md](./docs/HOWTO-add-model.md))
+
 **Multimodal models:**
 
 - [x] [LLaVA 1.5 models](https://huggingface.co/collections/liuhaotian/llava-15-653aac15d994e992e2677a7e), [LLaVA 1.6 models](https://huggingface.co/collections/liuhaotian/llava-16-65b9e40155f60fd046a5ccf2)

docs/HOWTO-add-model.md

@@ -0,0 +1,117 @@
+## Add a new model architecture to `llama.cpp`
+
+Adding a model requires few steps:
+
+1. Convert the model to GGUF
+2. Define the model architecture in `llama.cpp`
+3. Build the GGML graph implementation
+
+After following these steps, you can open PR.
+
+Also, it is important to check that the examples and main ggml backends (CUDA, METAL, CPU) are working with the new architecture, especially:
+- [main](../examples/main)
+- [imatrix](../examples/imatrix)
+- [quantize](../examples/quantize)
+- [server](../examples/server)
+
+### 1. Convert the model to GGUF
+
+This step is done in python with a `convert` script using the [gguf](https://pypi.org/project/gguf/) library.
+Depending on the model architecture, you can use either [convert.py](../convert.py) or [convert-hf-to-gguf.py](../convert-hf-to-gguf.py).
+
+The convert script reads the model configuration, tokenizer, tensor names+data and converts them to GGUF metadata and tensors.
+
+The required steps to implement for an HF model are:
+
+1. Define the model `Model.register` annotation in a new `Model` subclass, example:
+
+```python
+@Model.register("MyModelForCausalLM")
+class MyModel(Model):
+    model_arch = gguf.MODEL_ARCH.GROK
+```
+
+2. Define the layout of the GGUF tensors in [constants.py](../gguf-py/gguf/constants.py)
+
+Add an enum entry in `MODEL_ARCH`, the model human friendly name in `MODEL_ARCH_NAMES` and the GGUF tensor names in `MODEL_TENSORS`.
+
+Example for `falcon` model:
+```python
+    MODEL_ARCH.FALCON: [
+        MODEL_TENSOR.TOKEN_EMBD,
+        MODEL_TENSOR.OUTPUT_NORM,
+        MODEL_TENSOR.OUTPUT,
+        MODEL_TENSOR.ATTN_NORM,
+        MODEL_TENSOR.ATTN_NORM_2,
+        MODEL_TENSOR.ATTN_QKV,
+        MODEL_TENSOR.ATTN_OUT,
+        MODEL_TENSOR.FFN_DOWN,
+        MODEL_TENSOR.FFN_UP,
+    ]
+```
+
+3. Map the original tensor names to the standardize equivalent in GGUF
+
+As a general rule, before adding a new tensor name to GGUF, be sure the equivalent naming does not already exist.
+
+Once you have found the GGUF tensor name equivalent, add it to the [tensor_mapping.py](../gguf-py/gguf/tensor_mapping.py) file.
+
+If the tensor name is part of a repetitive layer/block, the key word `bid` substitutes it.
+
+Example for the normalization tensor in attention layers:
+
+```python
+block_mappings_cfg: dict[MODEL_TENSOR, tuple[str, ...]] = {
+        # Attention norm
+        MODEL_TENSOR.ATTN_NORM: (
+            "gpt_neox.layers.{bid}.input_layernorm",                # gptneox
+            "transformer.h.{bid}.ln_1",                             # gpt2 gpt-j refact qwen
+            "transformer.blocks.{bid}.norm_1",                      # mpt
+            ...
+        )
+}
+```
+
+`transformer.blocks.{bid}.norm_1` will be mapped to `blk.{bid}.attn_norm` in GGUF.
+
+Depending on the model configuration, tokenizer, code and tensors layout, you will have to override:
+- `Model#set_gguf_parameters`
+- `Model#set_vocab`
+- `Model#write_tensors`
+
+NOTE: Tensor names must end with `.weight` suffix, that is the convention and several tools like `quantize` expect this to proceed the weights.
+
+### 2. Define the model architecture in `llama.cpp`
+
+The model params and tensors layout must be defined in `llama.cpp`:
+1. Define a new `llm_arch`
+2. Define the tensors layout in `LLM_TENSOR_NAMES`
+3. Add any non standard metadata in `llm_load_hparams`
+4. Create the tensors for inference in `llm_load_tensors`
+5. If the model has a RoPE operation, add the rope type in `llama_rope_type`
+
+NOTE: The dimensions in `ggml` are typically in the reverse order of the `pytorch` dimensions.
+
+### 3. Build the GGML graph implementation
+
+This is the funniest part, you have to provide the inference graph implementation of the new model architecture in `llama_build_graph`.
+
+Have a look to existing implementation like `build_llama`, `build_dbrx` or `build_bert`.
+
+When implementing a new graph, please note that the underlying `ggml` backends might not support them all, support of missing backend operations can be added in another PR.
+
+## GGUF specification
+
+https://github.com/ggerganov/ggml/blob/master/docs/gguf.md
+
+## Resources
+
+- YaRN RoPE scaling https://github.com/ggerganov/llama.cpp/pull/2268
+- support Baichuan serial models https://github.com/ggerganov/llama.cpp/pull/3009
+- support attention bias https://github.com/ggerganov/llama.cpp/pull/4283
+- Mixtral support https://github.com/ggerganov/llama.cpp/pull/4406
+- BERT embeddings https://github.com/ggerganov/llama.cpp/pull/5423
+- Grok-1 support https://github.com/ggerganov/llama.cpp/pull/6204
+- Command R Plus support https://github.com/ggerganov/llama.cpp/pull/6491
+- support arch DBRX https://github.com/ggerganov/llama.cpp/pull/6515
+- How to convert HuggingFace model to GGUF format https://github.com/ggerganov/llama.cpp/discussions/2948