# TensorRT LLM Checkpoint

## Overview

The earlier versions (pre-0.8 version) of TensorRT LLM were developed with a very aggressive timeline. For those versions, emphasis was not put on defining a unified workflow. Now that TensorRT LLM has reached some level of feature richness, the development team has decided to put more effort into unifying the APIs and workflow of TensorRT LLM. This file documents the workflow around TensorRT LLM checkpoint and the set of CLI tools to generate checkpoint, build engines, and evaluate engines.

There are three steps in the workflow:

1. Convert weights from different source frameworks into TensorRT LLM checkpoint.
2. Build the TensorRT LLM checkpoint into TensorRT engines with a unified build command.
3. Load the engines to TensorRT LLM model runner and evaluate with different evaluation tasks.

```
NeMo -------------
                  |
HuggingFace ------
                  |   convert                             build                    load
Modelopt ---------  ----------> TensorRT LLM Checkpoint --------> TensorRT Engine ------> TensorRT LLM ModelRunner
                  |
JAX --------------
                  |
DeepSpeed --------
```

## Prepare the TensorRT LLM Checkpoint

TensorRT LLM aims at supporting different sources:

1. Trained models from NVIDIA NeMo, Microsoft DeepSpeed, and JAX
2. Quantized models from NVIDIA Modelopt
3. Popular models from HuggingFace

TensorRT LLM defines its own checkpoint format. A checkpoint directory includes:

1. One config `json` file, which contains several model hyper-parameters.
2. One or several rank weights files, each file contains a dictionary of tensors (weights).
The different files are loaded by different ranks in a multi-GPU (multi-process) scenario.

### Config

| Field                                  | Type       | Default Value       |
| :------------------------------------- | :--------- | :------------------ |
| architecture                           | string     | mandatory           |
| dtype                                  | string     | mandatory           |
| logits_dtype                           | string     | 'float32'           |
| vocab_size                             | int        | mandatory           |
| max_position_embeddings                | int        | null                |
| hidden_size                            | int        | mandatory           |
| num_hidden_layers                      | int        | mandatory           |
| num_attention_heads                    | int        | mandatory           |
| num_key_value_heads                    | int        | num_attention_heads |
| hidden_act                             | string     | mandatory           |
| intermediate_size                      | int        | null                |
| norm_epsilon                           | float      | 1e-5                |
| position_embedding_type                | string     | 'learned_absolute'  |
| mapping.world_size                     | int        | 1                   |
| mapping.tp_size                        | int        | 1                   |
| mapping.pp_size                        | int        | 1                   |
| quantization.quant_algo                | str        | null                |
| quantization.kv_cache_quant_algo       | str        | null                |
| quantization.group_size                | int        | 64                  |
| quantization.has_zero_point            | bool       | False               |
| quantization.pre_quant_scale           | bool       | False               |
| quantization.exclude_modules           | list       | null                |

`mapping.world_size` means `mapping` is a dictionary containing the `world_size` sub field.

```json
{
    "architecture": "OPTForCausalLM",
    "mapping": {
        "world_size": 1
    }
}
```

Supported quantization algorithm list:

- W8A16
- W4A16
- W4A16_AWQ
- W4A8_AWQ
- W4A16_GPTQ
- FP8
- W8A8_SQ_PER_CHANNEL

Supported KV cache quantization algorithm list:

- FP8
- INT8

The config field is extensible, a model could add its own specific config fields.
For example, OPT model has a `do_layer_norm_before` field.

Here is the model specific config list:

| Field                                  | Type       | Default Value       |
| :------------------------------------- | :--------- | :------------------ |
| OPT                                    |            |                     |
| do_layer_norm_before                   | bool       | False               |
|                                        |            |                     |
| Falcon                                 |            |                     |
| bias                                   | bool       | True                |
| new_decoder_architecture               | bool       | False               |
| parallel_attention                     | bool       | False               |

### Rank Weights

Like PyTorch, the tensor (weight) name is a string containing hierarchical information,
which is uniquely mapped to a certain parameter of a TensorRT LLM model.

For example, each transformer layer of the OPT model contains an `Attention` layer, an `MLP` layer. and two `LayerNorm` layers.

#### Attention Weights

The `Attention` layer contains two `Linear` layers, qkv and dense; each `Linear` layer contains one weight and one bias.
There are four tensors (weights) in total, whose names are:

- `transformer.layers.0.attention.qkv.weight`
- `transformer.layers.0.attention.qkv.bias`
- `transformer.layers.0.attention.dense.weight`
- `transformer.layers.0.attention.dense.bias`

where `transformer.layers.0.attention` is the prefix name, indicating that the weights/biases are in the Attention module of the 0-th transformer layer.

#### MLP Weights

The `MLP` layer also contains two `Linear` layers, fc and proj; each `Linear` layer contains one weight and one bias.
There are four tensors (weights) in total, whose names are:

- `transformer.layers.0.mlp.fc.weight`
- `transformer.layers.0.mlp.fc.bias`
- `transformer.layers.0.mlp.proj.weight`
- `transformer.layers.0.mlp.proj.bias`

where `transformer.layers.0.mlp` is the prefix name, indicating that the weights/biases are in the MLP module of the 0-th transformer layer.

#### LayerNorm Weights

Each of the two `LayerNorm` layers, namely `input_layernorm` and `post_layernorm`, contains one weight and one bias.
There are four tensors (weights) in total, whose names are:

- `transformer.layers.0.input_layernorm.weight`
- `transformer.layers.0.input_layernorm.bias`
- `transformer.layers.0.post_layernorm.weight`
- `transformer.layers.0.post_layernorm.bias`

where `transformer.layers.0.input_layernorm` and `transformer.layers.0.post_layernorm` are prefix names for the two `layernorm` modules.

#### KV Cache Quantization Scaling Factors

If we quantize the model, there will be different tensors (depending on the quantization method applied).
For example, if we quantize the KV cache, the `Attention` layer will have this extra scaling factor:

- `transformer.layers.0.attention.kv_cache_scaling_factor`

#### FP8 Quantization Scaling Factors

Here is the FP8 scaling factors of `attention.qkv` linear layer:

- `transformer.layers.0.attention.qkv.activation_scaling_factor`
- `transformer.layers.0.attention.qkv.weights_scaling_factor`

#### AWQ Quantization Scaling Factors

Here is the AWQ scaling factors of `mlp.fc` linear layer:

- `transformer.layers.0.mlp.fc.weights_scaling_factor`
- `transformer.layers.0.mlp.fc.prequant_scaling_factor`

    ```{note}
    The linear weights in TensorRT LLM checkpoint always follows (`out_feature`, `in_feature`) shape, whereas some quantized linear in TensorRT LLM implemented by plugin may use (`in_feature`, `out_feature`) shape. The `trtllm-build` command adds a transpose operation to post-process it.

### Example

Let's take OPT as an example and deploy the model with tensor parallelism 2:

```bash
cd examples/opt
python3 convert_checkpoint.py --model_dir ./opt-125m \
                --dtype float16 \
                --tp_size 2 \
                --output_dir ./opt/125M/trt_ckpt/fp16/2-gpu/
```

Here is the checkpoint directory:

```
./opt/125M/trt_ckpt/fp16/1-gpu/
    config.json
    rank0.safetensors
    rank1.safetensors
```

Here is the `config.json`:

```json
{
    "architecture": "OPTForCausalLM",
    "dtype": "float16",
    "logits_dtype": "float32",
    "num_hidden_layers": 12,
    "num_attention_heads": 12,
    "hidden_size": 768,
    "vocab_size": 50272,
    "position_embedding_type": "learned_absolute",
    "max_position_embeddings": 2048,
    "hidden_act": "relu",
    "mapping": {
        "world_size": 2,
        "tp_size": 2
    },
    "use_parallel_embedding": false,
    "embedding_sharding_dim": 0,
    "do_layer_norm_before": true,
}
```

## Build Checkpoint into TensorRT Engine

TensorRT LLM provides a unified build command: `trtllm-build`. Before using it,
you may need to add it to the `PATH`.

```bash
export PATH=/usr/local/bin:$PATH

trtllm-build --checkpoint_dir ./opt/125M/trt_ckpt/fp16/2-gpu/ \
                --gemm_plugin float16 \
                --max_batch_size 8 \
                --max_input_len 924 \
                --max_seq_len 1024 \
                --output_dir ./opt/125M/trt_engines/fp16/2-gpu/
```

## Make Evaluation

```bash
mpirun -n 2 --allow-run-as-root \
    python3 ../summarize.py --engine_dir ./opt/125M/trt_engines/fp16/2-gpu/ \
                        --batch_size 1 \
                        --test_trt_llm \
                        --hf_model_dir opt-125m \
                        --data_type fp16 \
                        --check_accuracy \
                        --tensorrt_llm_rouge1_threshold=14
```